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Diels -Alder reactions between fullerene[60] andvarious pentacenesJames Mack II.University of New Hampshire, Durham

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DIELS-ALDER REACTIONS BETW EEN FULLERENE[60]

AND

VARIOUS PENTACENES

BY

James Mack II

B.A. M iddlebury College. 1995

DISSERTATION

Submitted to the University o f New Hampshire

in Partial Fulfillment o f

the Requirements for the Degree of

Doctor o f Philosophy

In

Chemistry

December. 2000


UMI Number 9991558

_ ___

UMIUMI Microform9991558

Copyright 2001 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition is protected against

unauthorized copying under Title 17, United States Code.

Bell & Howell Information and Learning Company 300 North Zeeb Road

P.O. Box 1346 Ann Arbor, Ml 48106-1346


This dissertation has been exam ined and approved.

9CZ. P -.Dissertation Director. Glen P. M iller. A ssistant Professor o f Chemistry

Richard P. Johnson. Pro(es^or o f Chem istry

R o y ^ P ^ ^ ^ ia lp ^ A s ^ ^ ^ e 1P r^ ss 'o T o fC h em is try

■ G JL j<JLa ( a _ - c ( ^Charles K. Zercher.Associate Professor o f Chemistry

O lof EKht. Professor o f Physics

J^) I ^ > 2-<ZfgS ^

Date


DEDICATION

This dissertation is dedicated to my parents, especially my mother for her undying

support in everything I do. Her words o f encouragement and love have given me the

strength necessary to achieve this honor.

iii


ACKNOWLEDGEMENTS

First and forem ost I would like to thank God for giving me the strength to endure

life as a Ph.D chem istry student. I would like to thank my parents James M ack and Lena

F. Mack and my brother V incent E. Mack for giving me support, love and encouragem ent

throughout my tenure as a graduate student. I am in great debt to my fiancee Carol for

her understanding, love and her growing patience. I am proud to be able to have shared

this experience with her. I would like to thank Allison for giving me the motivation to be

successful. I would like to thank my "brother from another mother" M ike, we had this

plan since high school.

I would like to thank my advisor Glen P. M iller for giving me the guidance and

discipline to realize my full potential. I would like to thank the rest of the University o f

New Hampshire Chem istry Department faculty for providing a wonderful education as

well as an excellent w ork environment. I would like to thank the chemistry departm ent

staff especially Cindi and Peggy for bailing me out on many an occasion. I would like to

thank members o f the M iller group past and present Bill, Gabrielle, Steve, Ingyu, M ark,

Julie, Drew and Jon for making all the long and sometimes frustrating hours as enjoyable

as can be. I would like to thank past and present University o f New Ham pshire chem istry

graduate students for teaching me the things that are not taught inside the classroom . I

would like to thank the Buckyballs; I hope we can win it all one day. I would like to

thank the University Instrum entation Center, especially Kathy not only for her N M R

advice but also for being a good listener in my most frustrating moments.

iv


I would like to thank the Graduate School for supporting me and providing a

com fortable environm ent outside o f the chemistry department. I w ould like to thank the

New England Board o f H igher Education for providing me with financial, moral and

em otional support. This is truly one o f the best program s with which I ’ve been

associated. I am proud to have been a NEBHE doctoral scholar. I w ould like to thank

the NEBHE doctoral Scholars especially John and Karielle for enduring New Ham pshire

with me, providing me with much needed support. I would like to thank non-chem istry

graduate students for giv ing me support and giving me knowledge o f m aterial outside o f

chemistry.

I would to thank the B lack Student Union for supporting me and keeping m e in

tune with what was going on outside o f Parsons Hall.

v


TABLE OF CONTENTS

D EDICATION........................................................................................................................... iii

ACKN O W LED GEM EN TS....................................................................................................iv

LIST OF FIG U RES...................................................................................................................ix

LIST OF SC H EM ES................................................................................................................ xii

LIST OF T A B L E S .................................................................................................................... xvi

A BSTRACT................................................................................................................................xvii

INTRODUCTION..................................................................................................................... 1

A. Fullerene[60] discovery and synthesis............................................................. 1

1. Physical properties o f fullerene[60] ................................................... 4

2. Chemical properties o f fullerene[60].................................................. 9

B. Reactivity o f fullerene[60] in cvcloaddition reactions .................................11

1. 1.3-DipoIar additions to fu llerene[60]................................................ 11

2. Diels-Alder cyclizations involving fullerene[60].............................19

C. Bisadducts o f fullerene[60]..................................................................................24

1. Hirsch nom enclature................................................................................24

2. Regioselectivity o f b isadducts.............................................................. 25

D. Bisfullerene[60] adducts .......................................................................................32

RESULTS AND D ISCU SSIO N ............................................................................................ 37

A. D iels-A lder reactions between fullerene[60] and pentacene......................37

1. Formation o f a C^v m onoadduct........................................................... 37

vi


2. Azabridged pentacenes as precursors to bisfullerene[60] adducts o f pentacene.................................................................................. 44

3. The formation o f bispentacene adducts o f fullerene[60].............61

B. D iels-A lder chemistry between fullerene[60] and6.13- disubstituted pentacenes................................................................... 68

1. Calculations and literature p recedence............................................. 68

2. Bisfullerene[60] adducts o f 6.13-disubstituted pentacenes..........71

a. Synthesis, isolation, and spectroscopic characterizationo f various 6.13- disubstituted pentacenes.............. 71

b. Regioselective reactions o f fullerene[60] and 6.13-disubstituted pentacenes: synthesis, isolation, and spectroscopic characterization........................................................... 81

c. c7.y-StereoseIectivitv in the formation of bisfullerene[60]adductsof 6.13-disubstituted pentacenes............................. 107

d. Anions o f cis- bisfullerene[60] adductsof 6.13- disubstituted pentacenes............................ 116

CONCLUSIONS AND FUTURE DIRECTIONS............................................................124

EXPERIM ENTAL SE C T IO N ..............................................................................................126

1. General M ethods........................................................................................... 126

2. Solvents............................................................................................................126

3. Column Chromatography.............................................................................127

4. R eagents...........................................................................................................127

5. Syntheses......................................................................................................... 129

vii


Appendix A: NM R Spectra....................................................................................................... 156

Appendix B: X-rav structure o f 24 ..........................................................................................223

Appendix C: UV/Vis spec tra ................................................................................................... 226

Appendix D: mass sp ec tra ........................................................................................................231

Appendix E: electrochem istry..................................................................................................237

R E FE R E N C E S ........................................................................................................................... 242

viii


LIST OF FIGURES

Number PAGE

1 Schem atic o f laser ablation apparatus used to generatecarbon c lu s te rs ......................................................................................................... 1

2 Carbon cluster distribution observed by Rohling and co-w orkers...............2

3 Carbon cluster distribution observed by Kroto and co -w orkers................3

4 Structure o f fullerene[60]....................................................................................... 4

5 Scheme for separating and purify ing various fullerenes.................................7

6 Carbon nanotubes..................................................................................................... 8

7 Mass spectroscopy data for the first endohedral m etallofullereneL a .......................................................................................................................9

8 Chem istry o f fullerene[60].................................................................................... 10

9 Generic exam ple o f a 1.3- dipolar addition....................................................... 11

10 Isomerization o f 6 .6-m ethanofullerenes............................................................13

11 Isomerization o f 6 .5-m ethanofullerenes............................................................14

12 Generic structure o f an azom ethine v'lide...........................................................16

13 Hirsch nom enclature for bisadducts o f fu llerene[60].................................... 25

14 Sym m euy and degeneracy o f bisadducts o f fullerene[60]............................ 27

15 Multiple diene moieties o f various linear acenes............................................ 37

16 cv.v-1 and trans- 2 Bisfullerene[60] adducts o f pentacene............................. 40

17 'FI NM R spectrum o f fullerene[60]-pentacene m onoadduct 3 .................... 42

ix


18 1H N M R spectrum o f fullerene[60]-5.14-dihydropentacen-5.14-im ineaddition product. 1 7 ..............................................................................................54

19 ljC NM R spectrum o f fulIerene[60]-5.14-dihvdropentacen-5.14-imineaddition product. 1 7 ...............................................................................................55

20 tra m - 2 Bispentacene adduct o f fullerene[60]. 18...........................................62

21 ‘H N M R spectrum o f 1 8 .........................................................................................63

22 ljC NM R spectrum o f 1 8 ..................................................................................... 63

23 PM3 calculated heats o f formation for bispentaceneadducts o f fullerene[60].......................................................................................64

24 'H N M R spectrum o f the c/.v- bisfullerene[60] adduct o f6.13-diphenvlpentacene. 2 4 ................................................................................. 82

25 Comparison o f hindered 6.13-diphenvl rotation in 24 with similarly hindered phenyl rotation in 2.6-disubstituted biphenyl................................. 84

26 .vy/7-9-Phenvl-2.1 l-dithia[3.3]m etacvclophane................................................ 84

27 trans- Bisfullerene[60] adduct o f 6.13- diphenylpentacene. 25 ................. 85

28 ljC NM R o f the aromatic m ethine region o f 2 4 ............................................ 86

29 Possible trisfullerene[60] adduct structures.................................................... 88

30 ‘H NM R spectra o f oligomers generated in the reaction betweenfullerene[60] and 6.13-diphenvlpentacene. 22 .............................................. 89

31 'H NM R spectrum o f the c7.v-bisfullerene[60] adduct o f 6.13-di-(4"-hydroxymethvlphenyl) pentacene. 4 4 .............................................................91

32 The aromatic methine region o f a Dept 135 spectrum for the cis- bisfullerene[60] adduct o f6.13-di-(4'-hydroxymethylphenyl)pentacene. 4 4 ...........................................92

33 [H NM R spectrum o f the Cs sym m etric fullerene[60]m onoadduct o f 6.13-phenethynylpentacene. 45 ...........................................95

34 'id NM R spectrum o f the cis- bisfullerene[60] adduct o f 6.13-diphenethynylpentacene. 4 6 ..............................................................................96

x


35 'H NM R spectrum o f the Cs symmetric fullerene[60]monoadduct o f 6.13-di(trimethylsilylethynyl)pentacene. 47 ..................98

36 'H NM R spectrum o f cis- and tram - bisfullerene[60]adducts o f 6.13-di(trimethylsilylethynyl)pentacene 48 and 4 9 ................99

37 l3C NM R spectrum o f 48 and 4 9 ......................................................................... 100

38 'H NM R spectrum o f the C s symmetric fullerene[60] m onoadduct o f 6.13-diethynvlpentacene. 50 .......................................................................................103

39 'H NM R spectrum o f the cis- bisfullerene[60] adduct o f6.13-diethvnylpentacene. 51 ............................................................................... 104

40 Two different approaches by which a second fullerene[60]may add to a Cs symmetric m onoadduct......................................................... 109

41 MM2 calculated ground state o f a cis- bisfullerene[60] adduct and PM3-MM2 calculated syn- transition state preceding formation o fcis- bisfullerene[60] adduct o f pentacene....................................................... 115

42 CV and DPP o f 24 ....................................................................................................117

43 CV and DPP o f 44 ....................................................................................................119

44 UV/Vis spectrum o f 242" prepared by reducing 24with Zn dust in THF so lven t.............................................................................. 122

45 UV/Vis spectrum o f 244’ prepared by reducing 24with Zn dust in DMSO so lv en t..........................................................................122

xi


LIST OF SCHEMES

Number PAGE

1 Reaction o f fullerene[60] with diphenyidiazom ethane.......................... 12

2 Reaction o f azide with fiillerene[60]........................................................... 15

3 Preparation o f N-methylpyrrolidine-fullerene[60] m onoadduct 16

4 Use o f pyrrolidine product in subsequent chemistry'.............................. 17

5 Reaction o f fu!lerene[60] with azirid ine .................................................... 18

6 Reaction o f fullerene[60] with propionitrile o x id e ................................. 18

7 Formation o f a donor-acceptor m olecu le ...................................................19

8 Reaction o f fullerene[60] with cvclopentadiene......................................20

9 Reaction o f fullerene[60] with anthracene.................................................21

10 Reaction o f fullerene[60] with o-quinodim ethane.................................. 22

1 1 Reaction o f fullerene[60] with benzocyclobutene followedDIBAL-H reduction ....................................................................................... 23

12 Reaction o f fullerene[60] with th ioacrylam ide........................................ 23

13 Solid state synthesis o f ircms-l bisanthracene adduct............................ 28

14 The Bingel reaction ......................................................................................... 28

15 Formation o f hexaadduct via consecutive equatorial attacks................30

16 D iederich 's tether directed syn thesis.......................................................... 31

xii


17 Synthesis o f C 120 via reaction with KCN underhigh-speed vibration m illing conditions.................................................. 33

18 Formation o f C 122 via dimerization o f m ethanofullerene carbene 34

19 Formation o f C 121 and C 122 via thermolysis o f dibrom o andmonoethylcarboxylated m ethanofullerenes..............................................34

20 Bisfullerene[60] adduct formation via bis-o-quinodim ethane.............35

21 Formation o f a bisfullerene[60] adduct using abisazomethine ylide........................................................................................36

22 Reaction o f fullerene[60] with tetracene................................................... 39

23 Reaction o f fullerene[60] with pentacene in refluxing toluene............41

24 Pathway for the formation o fcis- and irons- bisfullerene[60] adducts................................................... 43

25 Synthetic scheme for formation o fcis- and tram - bisfullerene[60] adducts o f pen tacene ..........................45

26 Conversion o f am inobridged aromatics totheir corresponding acenes..........................................................................46

27 Synthetic scheme for the formation o fcis- and trans- bisfullerene[60] adducts.................................................. 47

28 Formation o f N -m ethyl-1.4-dihydronapthalen-1.4-imine. 1 2 ..............48

29 Formation o f N-methylisoindole. 7. from3.6-di-2 '-pyridvl-1,2.4 .5-tetrazine 49

30 Formation o f N-methyl-isoindole. 7. viaN-methyl-isoindoleum salt...........................................................................50

31 Dimerization and regeneration o f N-m ethyl-isoindole w ith light 51

32 Synthesis o f 2.3-dibrom o-9.10-dihvdroanthracen-9.10-imine. 15.....51

33 Synthesis o f 2.3-dibromoanthracene. 16 ...................................................52

34 Synthesis o f 5 .14-dihvdropentacen-5.14-imine. 5 ................................ 53

xiii


35 Formation o f unique animation product o f fullerene[60]with 5 .14-dihvdropentacen-5.14-imine. 5 ................................................ 56

36 Probable amination mechanism for the addition o fprimary and secondary aliphatic amines to fullerene[60].................... 57

37 Analogous am ination mechanism with tertiary am in es.........................58

38 Proposed mechanism for the formation o f the fullerene[60]-5.14-dihydropentacen-5.14-imine product. 17 ................................................. 59

39 Formation o f rran.s-bisfullerene[60] adduct o f pentacene. 2 .................60

40 Formation o f diphenyl methanofullerene. 21. via initialaddition to a collection o f trans- bispentacene adducts ........................67

41 Formation o f 6.13-pentacenequinone. 2 6 ................................................. 71

42 Formation o f the 6.13-diphenylpentacene. 22 .......................................... 73

43 Oxidation o f 6.13-diphenylpentacene........................................................73

44 Formation o f 6.13-diphenethynylpentacene. 3 1 .......................................74

45 Formation o f 6.13-di(trimethylsilvlethynyl)pentacene. 3 2 ...................76

46 Formation o f 6.13-diethynyIpentacene. 3 4 ...............................................76

47 Formation o f THP-protected propargvl pentacene. 37 ...........................78

48 Formation o f 6.13-di-4'-hydroxymethylphenylpentacene. 3 8 .............79

49 Dimerization o f parent pentacene in thepresence o f visible lig h t............................................................................... 80

50 Formation o f c7x-bisfullerene[60] adduct o f6.13-diphenylpentacene. 2 4 ........................................................................ 81

51 Formation o f c7.v-bisfullerene[60] adduct o f 6.13-di-(4*-hydroxymethylphenyl)pentacene. 4 4 ........................................................90

52 Formation o f Cs symmetric 45 and bisfullerene[60]adduct 4 6 .........................................................................................................94

53 Formation o f cis- and trans- bisfullerene[60] adducts.48 and 49. in addition to Cs monoadduct 4 7 ............................................97

xiv


54 Formation o f the Cs symmetric 50 and bisfiillerene[60] adduct 5 1 ... 102

55 Formation o f Cs symmetric monoadduct 52 andbisfullerene[60] adduct 53 .......................................................................... 105

56 Form ation o f 44 under thermodynamic conditions................................. 108

57 cis- and trans- BisDM AD adducts o f 6.13- diphenylpentacene. 22 .. 110

58 Chem ical reduction o f fullerene[60] using zinc dust to givefullerene[60]*' and fullerene[60]2' ...............................................................120

xv


LIST OF TABLES

Number Page

1 Enhanced solubilities o f bispentacene adducts o f fiillerene[60].......... 65

2 PM3 calculated Diels-Alder reactivity o f 6.13- diphenyl pentacene ...70

3 PM3 calculated transition states....................................................................114

4 Half-wave potentials for 2 2 ......................................................................... 118

XVI


ABSTRACT

DIELS-ALDER REACTIONS BETW EEN FULLERENE[60]

AND VARIOUS PENTACENES

By

Jam es M ack II University o f New Ham pshire. December. 2000

The reaction o f fullerene[60] with pentacene and various 6.13- disubstituted

pentacenes has been studied and the formation o f cis- bisfiillerene[60] adducts has been

achieved. The reaction o f fullerene[60] with pentacene was studied with the goal o f

preparing cis- 1 and trans-2 bisfuilerene[60] adducts.

1 2

xvii


Instead, the solution phase Diels-Alder reaction between fullerene[60] and pentacene

yields a Cz\ symmetric monoadduct. 3. in 59% yield.

3

Semi-empirical PM3 calculations suggest that fiillerene[60] should react

favorably with 6.13- disubstituted pentacenes such that molecules sim ilar to 1 and 2

would form. Several 6.13- disubstituted pentacenes were synthesized and subsequently-

reacted with fullerene[60] resulting in the formation o f various cis- bisfullerene[60]

adducts in high yield. The reactions are completely regioselective. cvcloadditions

occurring exclusively across the 5.14- and 7.12- positions o f the pentacene backbone, and

highly- cis- stereoselective as well. The corresponding trans- bisfullerene[60] adducts are

not detected above trace levels. The reactions proceed through the formation o f Cs

symmetric m onoadducts. some o f which form in high yield and are easily isolated. 6.13-

Diethvnyl substituted pentacenes are especially prone to Cs monoadduct formation in

good yield. N M R spectroscopy in conjunction with mass spectrometry and X-ra\r

structure analysis has enabled a thorough characterization o f the products

xviii


24

A combination o f experim ental data, model compound studies, and com putational

results suggest that favorable ^-stacking interactions between fullerene[60] moieties in

the ground state and in transition states are responsible for the high cis- stereoselectivities

observed in these reactions w hether they be run under kineticallv controlled or

therm odynam ically controlled conditions. Electrochem istry o f two bisfullerene[60]

adducts has been studied. Separate 1 electron reductions for each fullerene[60] m oiety on

one o f the bisfullerene[60] adducts are resolved at low negative potential.

Bisfullerene[60] adducts are also susceptible to chemical reductions and reactions with

Zn dust in 2 different solvents have been studied.

xix


INTRODUCTION

A. Fullerene[60| discovery and synthesis

In 1984. Rohlfing. Cox. and Kaldor studied the mass spectrum o f synthetically

prepared carbon c lu sters .1 These clusters were generated by a laser ablation procedure,

sim ilar to procedures utilized earlier by the same group to prepare metal clusters (Figure

1).

VAPORIZATIONLASER

10 ATM

ROTATING GRAPHITE ^ OISC —

Figure 1. Schem atic o fla se r ablation apparatus used to generate carbon clusters

(Reprinted with perm ission from Nature. 1985. 318. 162: copyright (©) M acM illian

Magazines Limited.)

1


The carbon clusters are generated using a high-powered laser to vaporize a spot

on a graphite disc: helium is used as a carrier gas to push the carbon vapors into the

integration cup. The hot carbon plasm a is then allowed to cluster in the integration cup

where the helium gas cools it. Once the hot carbon plasma cools, clustering ceases. The

gas mixture is opened into a vacuum chamber whereby the clusters are studied by mass

spectrometry.

Rohlfing and co-workers observed an intriguing result in the mass spectrometry

data (Figure 2).

Q m t t r I k ( A d m i)

Figure 2. Carbon cluster distribution observ ed by Rohling and co-workers

(Reprinted with permission from J.Chem. Phys.. 1984. 81. 3322. Copyright (©)

Am erican Institute o f Physics.)


The distribution o f carbon clusters was such that at masses below twenty-carbon atoms,

they saw odd and even num bered all-carbon clusters. When looking at clusters whose

mass was above forty atom s, they only observ ed even numbered clusters. The result w as

puzzling to them and they could not fully explain the clustering phenomenon.

In 1985. FCroto. Sm alley and Curl began studying carbon clusters using a sim ilar

apparatus but they increased the time allowed for the clustering process to occur.2 They

observ ed a significant increase in the amount o f a sixty-atom carbon cluster compared to

all other clusters (Figure 3).

52 60 68 76 8444N o. of c a rb o n a t o m s p e r c lu s te r

Figure 3. Carbon cluster distribution observ ed by ICroto and co-workers

(Reprinted with perm ission from Nature. 1985. 3 IS . 162: copyright (© ) MacM illian

Magazines Limited.)

After much thought. Kroto and co-workers believed the sixty-atom carbon cluster

was an all-carbon m olecule in the shape o f a truncated icosahedron. The structure o f the

regular truncated icosahedron has been an interest to mankind since the days o f Leonardo

->


Da Vinci in the 1500V (Figure 4). Since the sixtv-atom all carbon m olecule resembled

R. Buckminster Fuller's geodesic domes. Kroto and co-vvorkers decided to name the

molecule “Buckm insterfullerene."

V C O C tD R O N ARJCISW VACVVS.

Figure 4. (a) Leonardo Da V inci's regular truncated icosahedron, which is drawn

out by mathematician Luca Pacioli: (b) Structure o f fullerene[60]

1. Physical properties o f fullerene[60]

Fullerene[60] has a cage structure and is com prised o f sixty .y/?2-like hybridized

carbon atoms. These carbon atoms are located at the vertices o f a truncated icosahedron

rendering all carbon atom s equivalent. The l3C N M R spectrum o f fullerene[60] gives

rises to one resonance at 142.7 ppm (benzene-d6). confirm ing its Ih sym m etry.4 Although

the carbon atoms on fullerene[60] are equivalent, the bond lengths are not.

4


Fullerene[60] contains two types o f bonds- bonds bordering two hexagonal rings (i.e..

6.6-junctions) and bonds bordering one pentagonal and one hexagonal ring (i.e.. 6.5-

junctions). The bond lengths at a 6.6-junction are 1.40A. while the bond lengths at a 6.5-

junction are 1.46 A .' 6.5- Junctions exhibit less double bond character then 6.6-

junctions. Putting a double bond at a 6 .5 -junction significantly increases the strain on the

whole molecule.6 Thus, all the double bonds on fullerene[60] are exo to the pentagons.

No two pentagonal faces on the fullerene[60] structure share an edge and this structural

feature is known as the "isolated pentagon rule.” ' Having the pentagons surrounded by

hexagons provides the least amount o f curvature which gives the resulting fullerene[60]

structure the greatest am ount o f stabilization.

The term fullerenes represents the whole class o f closed caged molecules

consisting only o f carbon atoms. Although the sixty-atom carbon molecule was shown to

be most prevalent in the mass spectrometer, higher fullerenes are also generated and have

a similar structure.

The laser ablation method only produces microscopic quantities o f fullerenes in

the gas phase. Since only microscopic quantities are produced, few scientists around the

world were able to study this molecule upon initial discovery. In 1990. Kratschmer and

Huffman discovered a method to produce macroscopic quantities o f fullerenes.8 Under a

helium atmosphere, they took two spring loaded carbon rods and put a 100 A ac current

across them. This arc discharge method easily generates several grams o f soot w'hich

contains - 7-10% fullerenes.g Unlike the laser ablation procedure, multiple gram

quantities o f fullerenes can be generated and isolated using the arc discharge method.

5


The arc discharge method not only gives isolabie amounts o f fullerene[60]. but

also isolabie amounts o f higher fullerenes. Fullerenes greater than C 70 were observed in

the original Rohlfmg and co-workers experim ent, but were present only in trace

quantities under the laser ablation technique employed by Kroto and co-w'orkers. Using

the arc discharge approach, higher fullerenes are routinely formed and observed.

Isolation methods were developed to purify several o f the fullerenes generated.10

Typically, the arc discharge soot is placed in a soxhlet extractor. Fullerenes below 100

atoms are extracted w ith toluene, while the higher fullerenes are extracted with 1.2.4-

trichlorobenzene. Fullerenes below 100 atoms are further purified via a neutral alumina

column, which is useful for isolating C60 and C 7 0 - Fullerenes between C 70 and C 100 are

purified via HPLC separations (Figure 5).

Kratschmer and H uffm an's macroscopic synthesis provided fullerenes to

scientists worldwide. The arc discharge approach also led to the synthesis o f other

fullerene like structures. In 1991. lijima discovered carbon nanotubes, another carbon

cage like structure.11 There are two general types o f nanotubes: the single walled

nanotube (S\VNT) and the multi-walled nanotube (MWNT). SW N T 's have a wall

thickness o f one atom, while the M W NT's consist o f multiple SW NTs nested within each

other like a Russian doll. Nanotubes are sim ilar to fullerenes. in that each is an all-carbon

cage like molecule, but they differ in terms o f specific structure. The structure o f a

SW NT is achieved by cutting fullerene[60] in h a lf and using each h a lf to cap the open

ends o f a graphene tube. There are several different ways to dissect fullerene[60]. It can

be dissected such that each hemispherical m oiety maintains a five-fold symmetry axis.

6


Using each o f these m oieties to cap a graphene tube would give rise to the "arm chair"

nanotube.

1.2.4-Trichiarabanz«fw extractionhaxanartofuane

(95:5)

Alumina.haxanafoiuana(95 S )

soot

Extract with

Toiuena insoluble

fultorena soot

Toluene extract with C aoto- C100

2-3H PLC runs on C18 reversed phase CHgCNDoluene (1:1)

Cts pure| P z ^ r a pure| P j-Ct* pure| C |4. mixture of at

toast 2 isomers

Figure 5. Schem e for separating and purifying various fullerenes.

(Reprinted with permission from John W iley & Sons. Inc. Billups. W .E.; C iufolini. M.A.

Buckminsterfullerene. 1993.60)

Dissecting fullerene[60] such that each piece m aintains a three-fold sym m etry axis is

another option. Using these moieties to cap a graphene tube gives a so-called "zigzag”

nanotube. The third form o f nanotube is the chiral nanotube. Unlike the arm chair or

zigzag nanotubes, the hexagons along the chiral nanotube tube are angled. This causes

7


the hexagons to spiral along the long axis o f the nanotube giving the appearance that the

tube is tw isted (Figure 6).

(a)

Figure 6. Three different types o f carbon nanotubes (a) arm -chair; (b) Zigzag; (c)

one o f several chiral nanotubes. (Reprinted with permission from Science o f Fullerenes

and Carbon Nanotubes. 1996. 758; Copyright (©) 1996 by Academ ic Press)

These tube-like fullerenes have different overall properties and scientists are currently

studying them. Unlike fullerenes. nanotubes are not soluble in com m on organic solvents.

Consequently their chem istries have been difficult to study.

Shortly after Kroto and co-workers synthesized fullerenes. it was thought that

atoms, specifically metals, could be placed inside o f the fullerene cages in order to

produce endohedral metallofullerenes. To test this theory. Kroto and co-workers soaked

the carbon disc in L a d j . 1' Upon vaporizing a soaked carbon disc, they discovered a La

atom trapped inside the fullerene cage (Figure 7). Since Kroto and Sm alley 's initial

discovery, many other endohedral metallofullerenes have been prepared .Ij

8


Figure 7. M ass spectrometry data for the first endohedral metallofullerene.

Cm'Ti La. (Reprinted with permission from J Am. Chem. Soc. 1985. 107. 7779.:

Copyright (@) 1985 by American Chemical Society'.)

2. Chemical properties o f fiillerene[60]

Unlike diam ond and graphite. fullerene[60] is chemically reactive and can be

chemically altered. Fullerene[60] is soluble in several organic solvents forming a

magenta colored solution. Due to its solubility and chemical reactivity, scientists all over

the world have been able to study this m olecule's reactivity for the last ten years.

Fullerene[60] has been shown to be a strong electron acceptor. It has three low-

lying degenerate LU M O s.14 and has shown the ability to reversibly accept up to six

electrons.1' Although fullerene[60] is comprised o f thirty conjugated double bonds in the

forms o f fused benzene rings, it does not react as an aromatic molecule. Fullerene[60]

behaves chemically as an electron deficient polvalkene with most o f its reactivity

occurring across 6 .6 -junctions, site o f the m ost 7t-electron density. A lthough Kroto and

9


co-workers demonstrated the possibility o f placing atoms on the inside o f the fullerene

cage, its chem ical reactivity is alm ost exclusively on the outside (i.e.. exohedral).

Throughout the last decade, scientists have explored the chem ical reactivity o f

fullerene[60] and to a lesser extent higher fullerenes. Fullerenes have been

hydrogenated.16 halogenated.17 and they readily undergo nucleophilic addition18 (Figure

8). Scientists have also discovered that many o f the chemistries o f fullerene[60] are

reversible. Like fiillerene[60]. many o f its derivatives show limited solubility in common

organic solvents. Solubility problem s coupled with the reversible addition o f addends

causes m ost reactions o f fullerenes to proceed in yields less than 50% . often far less. Still,

the ability o f fullerene[60] to react with many different types o f addends has enabled the

formation o f a vast number o f new fullerene derivatives in the last decade.

Figure 8. Chemistry o f fullerene[60]

(Reprinted with permission from Science o f Fullerenes arid Carbon N anotubes . 1996.

297: Copyright ( ©) 1996 by Academ ic Press)

10


B. Reactivity of fullerene[60| in cycloaddition reactions

Cycloadditions are amongst the most im portant class o f reactions for derivatizing

fullerene[60], Fullerenes has been shown to undergo [4+2]. [3+2], [2+ 2].19 [2+1 ].20 and

[8+2]21 cycloadditions. O f the various cycloadditions. the two most studied

cycloadditions are o f the 1.3- dipolar and the D iels-A lder variety.

1. 1,3- Dipolar additions to fiillerene[60]

A 1.3- dipolar addition is the cyclization o f a 1.3- dipolar m olecule (a. b. c) with a

dipolarophile (d. e) to g ive a five-membered ring product (Figure 9).22 This reaction is

analogous to the D iels-A lder reaction in that it is a [4^+2;t] .yy«-cycloaddition.2'’

Fullerene[60] has shown the ability to react as a dipolarophile with 1.3- dipolar molecules

such as azides. nitrile oxides, diazomethane. and azom ethine ylides. These reactions

have led to a variety o f new fullerene derivatives.

\ / d e

Figure 9. Generic exam ple o f a 1.3- dipolar addition

1 1

+


Wudl demonstrated that fullerene[60] undergoes a 1.3- dipolar addition with

diphenyldiazom ethane.24 Diphenvldiazomethane reacts readily with fullerene[60] in

toluene at room temperature (Scheme 1). The 1.3- dipolar addition occurs first to give a

pyrazoline intermediate. The pyrazoline intermediate rapidly losses a molecule o f

nitrogen leaving behind a diphenyl carbon radical and a fullerene radical that couple to

form a cyclopropane. The fullerene radical is delocalized such that closure can occur

across an adjacent 6 .6 -junction or across an adjacent 6.5- junction.

PY ”

PhP h

-N-

P h Ph

A

P h P h

Scheme 1. Reaction o f fullerene[60] with diphenyldiazomethane.

Closure across a 6 .6-junction gives cyclopropanated structures known as

methanofullerenes. Methanofullerenes could in principal isom erize to an open bridged

structure in order to relieve ring strain. Opening the 6.6- closed methanofullerene to a

6.6- open methanofullerene would relieve some o f the strain o f the cyclopropane ring but

in doing so would create new strain on the fullerene skeleton by placing twro double

12


bonds at the bridgehead (anti-Bredt) positions (Figure 10). These two 6.5-tc- bonds

destabilize the structure. Therefore, in 6.6-m ethanofullerenes. the cyclopropane is

normally in closed form.

\

Closed 6.6-methanofuIlerene Open 6.6-methanofullerene with bridgehead alkene functions

Figure 10. Isomerization o f 6.6-methanofullerenes.

Closure across a 6 .5 -junction also results in the formation o f a cyclopropanated

structure. This structure is destabilized by two 6.5- 7c-bonds located on the hexagon

bearing the cyclopropane addend (Figure 11). In order to relieve the strain associated

with two 6.5- 7r-bonds. closed 6.5-methanofullerenes can isomerize to an open bridged

structure. The 6.5-open methanofullerenes are called fulleroids. and they bear no 6.5-71-

13


bonds. Fulleroid structures do. however, contain two bridgehead (anti-Bredt) alkene

functions that destabilize them relative to closed 6.6-m ethanofullerenes

Closed 6.5- m ethanofullerene Open 6.5- m ethanofullerenewith two 6.5- k - bonds with no 6.5- 7t- bonds-

a fulleriod

Figure 11. Isom erization o f 6.5- m ethanofullerenes

W udl discovered that upon heating a mixture o f the closed 6.6- diphenyl

m ethanofullerene and the open 6.5- diphenyl fulleriod a t elevated temperature for 2

hours, the therm odynam ically favored closed 6.6- diphenylm ethanofullerene is formed

exclusively.2'"' The interesting structural properties o f m ethanofullerenes and fulleriods

have been review ed26 and continue to be studied.2'

Fullerene[60] also undergoes facile 1.3- dipolar additions with a number o f other

1.3- dipoles including azides. Sim ilar to the reaction w ith diazo compounds, reaction

with azides first goes through a triazoline intermediate followed by loss o f nitrogen to

14


give both open and closed aza-bridged products (Schem e 2). In this reaction the open

6.5- aza-bridged product is the major isomer.28

CH=N

N.

-N.

Minor Major

Scheme 2. Reaction o f azide with fullerene[60]

Fullerene[60] readily undergoes 1.3- dipolar additions with azomethine vlides

(Figure 12). The use o f a variety o f azomethine vlides can lead to a variety' o f different

fullerene[60] products. Prato and co-workers first observed a 1.3- dipolar addition

between fullerene[60] and an azomethine ylide.2g N-methyl glycine and

paraformaldehyde react in refluxing toluene to give the resulting imine. Upon

decarboxylation, the N-methyl substituted azom ethine vlide is formed. The azom ethine

ylide readily adds across a 6.6-junction on the fullerene to give rise to a N-

methylpyrrolidine adduct in 41% yield (Schem e 3).

15


N

Figure 12. Generic structure o f an azom ethine vlide

2 CHjNUCHjCOOH 5 p ara fo rm ald eh y d e

Tol 2hrs N ;

Scheme 3. Preparation o f N-methylpyTroIidine-fullerene[60] monoadduct

Prato also demonstrated the use o f 3-triphenvlmethyl-5-oxazolidinone in refluxing

toluene to give the corresponding N-triphenylmethyl substituted azomethine ylide. The

N-tritvl azomethine ylide adds to fullerene[60] to provide the N-trityl pyrrolidine adduct.

The triphenylmethyl group can be removed by acid to give the parent pyrrolidine. The

parent pyrrolidine was subsequently reacted with dansyl chloride to give the N-dansyl

pyrrolidine fullerene[60] monoadduct (Scheme 4 ) . '9 This method shows the utility o f

azom ethine ylide chemistry in building new fullerene[60] molecules with moderately

complex structures.

16


N

,so2

2hrs N

2. Pvridine

. DnsCI

Scheme 4. Use o f pyrrolidine product in subsequent chem istry

A nother method to produce an azomethine ylide is by means o f thermal ring

opening o f an aziridine. Heating N- benzyl-2-methvlcarboxylate aziridine in the

presence o f fullerene[60] gives a 40% yield o f a pyrrolidine product (Scheme 5).26a

Nitrile oxides also undergo 1.3- dipolar addition with fullerene[60].J° M eier

demonstrated that reaction o f propionitrile oxide with fullerene[60] gives the isoxazoline

derivative product in 29% yield (Scheme 6).

17


Scheme 5. Reaction o f fiillerene[60] w ith aziridine

O—N^^=-

Scheme 6. Reaction o f fullerene[60] with propionitrile oxide

Fullerene[60] has strong electron accepting properties and tetrathiafulvalenes

have strong electron donating properties. M etzger and co-workers used a 1.3- dipolar

addition to attach the strongly electron donating tetrathiafulvalene to the fullerene[60]

c o r e /1 They then studied the donor-acceptor properties o f the unique product (Schem e

7). Metzger observed the fullerene[60] radical anion at 77K by EPR spectroscopy.

18


OHC

M e SS M e

S M e

Toluene j[

2 C H 3NHCH2COOH

M e SS M e

C H 2 s-S M e

Scheme 7. Formation o f a donor-acceptor molecule.

2. Diels-Alder cyclizations involving fullerene[60]

The Diels-Alder reaction has been one o f the most studied and influential

reactions in fullerene[60] chemistry. The broad scope and ease o f reaction has made

Diels-Alder chemistry a workhorse for fullerene[60] functionalization. Unfortunately,

some Diels-Alder products are thermally unstable. Hosts o f dienes have been added to

fullerene[60] via the D iels-Alder reaction. Fullerene[60] undergoes Diels-Alder reaction

with traditional 1.3- dienes. dienes prepared in situ, heterodienes. dienes with additional

functionality, and dienes em bedded in linear acenes. Rotello and co-workers

demonstrated that cyclopentadiene and fullerene[60] react at room temperature in

benzene to give a m onoaddition product in 74% yieldj2 (Scheme 8 ) . The cyclopentadiene

19


was shown to react across a 6.6-junction. D iels-Alder reaction products are not known to

undergo rearrangements as in the case o f 1.3- dipolar cyclizations.

Scheme 8. Reaction o f fullerene[60] with cyclopentadiene

Nogami and others have demonstrated the reaction o f fullerene[60] with anthracene

(Scheme 9).JJ This reaction is not as facile as the Diels-Alder reaction w ith

cyclopentadiene. Lower yields o f anthracene m onoadduct are obtained under all

conditions studied. Fullerene[60] reacts with anthracene to give a 24% yield o f

anthracene m onoaddition product in toluene at 50 °C. Nogami observed that the product

thermally degrades (i.e.. retro-Diels-Alder) at tem peratures higher than 60 °C to give

fullerene[60] and an th racen e /la Nogami studied the effect o f temperature on this

reaction and showed that higher temperatures are accompanied by lower yields o f

monoaddition product. When the reaction was run in toluene at 50 °C. a 24% yield o f

monoadduct was obtained. When the reaction was run in toluene at 80 °C. a 17% yield

was observ ed. W hen the reaction was run in toluene at 110 °C. an 8.5% yield was

T o l u e n e

20


observed. The reaction is clearly reversible at elevated tem peratures, the equilibrium

increasingly favoring reactants (greater entropy) at higher tem peratures.

Toluene

Scheme 9. Reaction o f fullerene[60] with anthracene

To combat this problem, scientists have run reactions with highly reactive dienes

that can be generated in situ and which giv e high yields o f therm ally stable products.

Mullen has shown o-quinodim ethanes. for example, undergo reaction with fullerene[60]

in 88% yield in refluxing toluene (Schem e 10).j4 The product is therm ally stable due to

the aromatization o f the o-quinodim ethane portion. In order for a retro-D iels-A lder

reaction to occur, the product must be converted from a very stable arom atic to the less

stable o-quinodimethane.

21


Scheme 10. Reaction o f fullerene[60] with o-quinodim ethane

The Diels-Alder reaction can also be used to prepare fullerene[60] derivatives

containing additional functional groups. Tom ioka demonstrated the reaction of

benzocyclobutenone with fullerene[60] in 1.2- dichlorobenzene to give a monoaddition

product in 49% yield. Benzocyclobutenone ring opens to an interesting o-

quinodim ethane structure containing a ketene function in refluxing 1.2-

dichlororobenzene (b.p. 180 °C). The resulting monoadduct with ketone function was

shown to undergo a facile Dibal-H reduction to give the corresponding alcohoE' (Scheme

11).

Eguchi has shown the ability o f fullerene[60] to undergo a hetero-Diels-Alder

reaction. Using thioacrvlamide in the presence o f fullerene[60], Eguchi obtained the

dihydrothiopyran-fused fullerene heterocycle in 57% yieldj6(Schem e 12). The use o f a

heterodiene is an attractive route by which to incorporate heterocycles onto the fullerene

core.

22


T o l u e n e

O i

DIBAL-HO H

Scheme 11. Reaction o f fullerene[60] with benzocyclobutenone followed by

Dibal-H reduction

NCOPh

T o l u e n e

NCOPh

Schem e 12. Reaction o f fullerene[60] with thioacrylamide

23


B. Bisadducts of fullerene[60]

1. Hirsch nomenclature

The chem istry o f fullerene[60] gives rise to m onoaddition products, but is often

complicated by formation o f multiple addition products. Fullerene[60] consist o f 30

equivalent double bonds, each capable o f reacting independently. Reactivity at one site

leaves 29 additional double bonds that can undergo subsequent chemistry. Early

nomenclature was devised in order to name fullerene products o f multiple additions. In

this system, each carbon atom was systematically num bered. Addition products were

named in reference to the carbon atom s by which addends were attached. Using this

nomenclature, it is very difficult to picture the product strictly by name alone. Hirsch

devised an alternative scheme by which one can to easily name and visualize

fullerene[60] m ultiple addition products. J/

With respect to the first addition, the second addition can occur either on the same

hemisphere (i.e.. cis-). the opposite hemisphere (i.e.. trans-) or at the equator (i.e.

equatorial). On the cis- hemisphere, a second reactant can add to three unique sites. The

double bond closest to the first addend (c/'.v-/). the double bond next removed (cis -2 ). or

the double bond (cis-3) third removed from the initial addend. The second addition can

also occur directly across the middle o f the fullerene[60] core giving rise to an equatorial

bisadduct. Lastly, the second addition can occur on the f/*<ms-hemisphere. There are four

unique sites on the trans- hemisphere. The addition can occur at a double bond closest to

an equatorial site (trans-4). a double bond next rem oved (trans -3 ) . a double bond thrice

24


removed (trans-2). o r the double bond completely opposite (i.e.. transannular) from the

original addend (trans-1) (Figure 13).

tnns-2

Figure 13. Hirsch nom enclature for bisadducts o f fullerene[60]

2. Regioselectivity o f bisadducts

O f the 29 total sites that can undergo a second addition, there are only eight

unique sites. In m ost cvcloaddition reactions with fullerene[60]. only seven o f the eight

potential bisadducts are formed. The c7.v-l bisadduct is often not observed in the crude

reaction m ixture due to the van der W aals strain associated with this product. The seven

remaining bisadduct products are all thermodynamically similar and all seven have been

seen in crude product slates.

25


Most fullerene products are purified by chromatographic methods. These

m ethods are sufficient for separating unreacted fullerene[60] from a monoaddition

product and for separating m onoaddition products from the slate o f bisadditon products.

In m any cases, separation o f different types o f bisadducts from one another can be

achieved (e.g.. c/.v-bisadducts can often be separated from equatorial and equatorial from

/ram -b isadducts). In rare cases, isolation o f several individual bisadducts has been

reported. However, given the strong structural similarities between the bisadduct

isomers, isolation o f all 7 can only be achieved via HPLC methods.

To further complicate bisadduct characterization, many o f the bisadducts possess

the sam e symmetry and give rise to similar NMR spectra. For example, cis-1, cis-2.

trans-4 and equatorial bisadducts generally possess Cs symmetry while cis-3. trans-3 and

trans-2 bisadducts generally posses CN symmetry (Figure 14). The tram-1 bisadduct

generally possess a Dih symmetry. Since the trans-l bisadduct is the only bisadduct with

unique symmetry, it may be the only bisadduct that can be identified on the basis o f

NMR. Although the tram -l bisadduct can be identified by spectroscopic means, there is

only one tra m - 1 site compared to 4 equivalent sites for each o f the other bisadducts.

Consequently, trans- 1 products are usually produced in the lowest yield.

The lack o f regioselectivity which accompanies the formation o f most

fullerene[60] bisadducts is disturbing. In few cases, however, chemists have developed

m ethods to synthesize specific bisadducts with high regioselectivity. The Krautler group

discovered a 100% regioselective solid-state synthesis o f the trans-l bisadduct o f

an th racen e /8

26


Bisadduct Symmetry’ = O f Equivalent sites

Cis-1 cs 4

Cis-2 Cs 4

Cis-3 c2 4

Equatorial Cs 4

T rans-4 Cs 4

Trans-3 C2 4

Trans-2 C2 4

Trans-l D2h I

Total 29

Figure 14. Symmetry and degeneracy o f bisadducts o f fullerene[60]

Heating an X-ray quality crystal o f anthracene monoadduct to 180 °C in the solid state for

10 minutes gave C<,0 and the trans-l bisadduct o f anthracene. The crystal structure o f the

anthracene monoadduct places the structure in a head to tail stacked arrangement. At

elevated temperature, a retro Diels-Alder followed by a Diels-Alder can selectively

produce the trans-1 bisadduct product in decent yield (Scheme 13).

Although seven o f the eight bisadducts are typically formed under thermodynamic

conditions, certain sites have shown to be more reactive under kinetic conditions. The

cyclopropanation reaction o f fullerene[60] using bromodiethylmalonate in the presence

o f a strong base (i.e.. "the Bingel reaction'09) has been used to the study bisadduct

formation under kinetically controlled conditions (Scheme 14).

27


A 10 Min

Scheme 13. Solid state svnthesis o f trans-l bisanthracene adduct

Toluene 12 H ours

R.T.

Scheme 14. The Bingel reaction

Hirsch observed the Bingel reaction produced the trans-3 and equatorial

bisadducts in preference to other bisadduct products. He used sem i-em pirical AMI

molecular orbital calculations to help explain the result. Hirsch found the highest LUMO

28


coefficient for the monoaddition product was found at the equatorial position, with the

next highest LUM O coefficient being at the trans-3 site.40 Further calculations revealed

that as the num ber o f additions increased, the psuedo- equatorial positions were

increasingly m ore reactive. Thus. Hirsch observed that the equatorial bisadduct reacted

regioselectively to give equatorial, equatorial, equatorial (i.e.. e.e.e-) trisadduct. He also

observed that the trans-3 bisadduct produced the trans-3. trans- 3. trans-3 trisadduct

exclusively. Taking the e.e.e- trisadduct and allowing it to react further under Bingel

conditions gave a Th symmetric hexaadduct. Hirsch also observed and isolated the Cs

symmetric tetraadduct and the symmetric pentaadduct as precursors along the way to

Th hexaadduct (Schem e 15).

Select other reactions also show regioselectivitv. Diederich demonstrated

completely regioselective reactions using a tether directed synthesis.41 First, an anchor

group was attached to the fullerene core via a Bingel type reaction. To the anchor group

was tethered a diene. Depending upon the length o f the tether, the diene added

selectively across one site. Thus. Diederich used a Bingel reaction to anchor the /7-xylvl

tethered 1.3- m ethylbutadiene onto the fullerene core. Computational analysis on the

product indicated that the tethered diene was too short to add to any o f the trans-sites on

the fullerene core.

29


e.e.e- trisadduct

Th hexadducl

Schem e 15. Formation o f hexaadduct via consecutive equatorial attacks.

R = C O O E T

Calculations also suggested that the product resulting from addition to the cis-3 site was

6.5 kcal/mol higher in energy than the product resulting from addition to the equatorial

site. When the product was heated to 80°C in toluene. Diels-Alder addition occurred in a

completely regioselective fashion at the equatorial sites in 48% yield (Scheme 16).

30


o o

DBU. Tol

Tol 80°C

Scheme 16. D iederich 's tether directed synthesis

Eschogoven and Diederich observed regioselective rearrangements under

electrochemical conditions.42 While studying bisadducts derived from the Bingel

reaction, they discov ered the reaction to be reversible under electrochemical conditions.

Presumably, a thermodynamic distribution o f isomers is form ed upon subjecting the

bisadducts to electrochemical conditions. Thus, when pure cis-2 bisadduct was subject to

reversible electrochemical conditions, a mixture o f frcins-2 bisadduct (52% yield).

31


equatorial bisadduct (23% yield). trans-l( 12% yield), trans-3 bisadduct (8% yield), and

trans-4 bisadduct (4% yield) is formed. No cis- isom ers were observ ed. W hen pure

samples o f the o ther isolated isom ers were subjected to the same conditions, the same

presumably therm odynam ic m ixtures was obtained.

Krautler and co-workers also demonstrated formation o f a D iels-A lder hexadduct

in 26% yield upon reacting fiillerene[60] with an excess o f 2.3-dim ethyl-1.3- butadiene

for several days in re fluxing 1.2-dichlorobenzene.4j

D. Bisfullerene[60] adducts

Since the discovery o f fullerene[60]. num erous scientists have pondered the

possibility o f form ing bisfullerene[60] adducts.44 Fullerene[60] displays very interesting

electrochemical properties. Stringing two or m ore fullerene[60] moieties together on one

molecule would create a very interesting structure with exciting electronic properties.

The sim plest bisfullerene[60] molecule is C 120. the fullerene[60] dim er. The

fullerene[60] dim er was first thought be found in fullerene[60] films.4' Since it is

difficult to study m olecular structures in films, the fullerene[60] dim er could not be

completely characterized. Komatsu and co-workers developed a different m ethod by

w hich to produce the C 120 fullerene[60] dimer. This method allows the fullerene dim er to

be isolated and com pletely characterized. Using a high-speed vibrational m illing

procedure {vide infra). fullerene[60] was reacted with potassium cyanide to give the

fullerene[60] dim er in 18% yield (Scheme 17).46

32


K.CN (cat.)

HighSpeed Vibration M illing

Scheme 17. Synthesis o f C 120 via reaction with K.CN under high-speed vibration

milling conditions.

Chem ists have also developed methods to synthesize C 121 and C 122

bisfullerene[60] products. C 121 and C 122 bisfullerene[60] molecules are formed via a

methanofullerene carbene intermediate. Strongin and co-workers first reported the

isolation and characterization o f C 122- They reacted fullerene[60] with an atomic carbon

precursor, diazotetrazole. in order to form the methanofullerene carbene. The

methanofullerene carbene presumably dim erized to give the C 122 bisfullerene[60] product

(Scheme 18). 4'

Dragoe and co-workers used a different method to produce the methanofullerene

carbene. Heating dibromomethanofullerene and fullerene[60] to 450 °C in an argon

atmosphere afforded both C 121 and C 122 bisfullerene[60] products. Dragoe found the

same products were obtained when a m ixture o f the monoethylcarboxylated

methanofullerene and fullerene[60] were heated at 550 °C (Scheme 19).

33


Scheme 18. Formation o f C 122 via dimerization o f methanofullerene carbene

Scheme 19. Formation o f C 121 and C 122 via thermolysis o f dibromo and

monoethylcarboxylated methanofullerenes.

34


Other groups have used well-knovvn fullerene chem istries in order to make

bisfullerene[60] products. Instead o f using monofunctionilized reactants, bi-directional

approaches have been used. Mullen first described the D iels-A lder reaction o f o-

quinodimethane with fullerene[60].j4 U sing a bis-o-quinodim ethane allowed production

o f a bisfullerene[60] product. The bis o-quinodim ethane was generated from a reaction

o f tetrakis(bromomethyI)benzene and potassium iodide. The two resulting dienes capture

two fullerene[60] m olecules in sequence to give the corresponding bisfullerene[60]

adduct (Scheme 20 ) . '4

Kl, [18]Crown-6 Toluene, A

Scheme 20. Bisfullerene[60] adduct formation via bis-o-quinodim ethane

The method o f using bifunctional reactants has also been applied to 1.3 dipolar

additions. Martin synthesized a bisfullerene[60] adduct using a bisazom ethine ylide.

Using a dialdehyde and reacting it with N-m ethyl glycine gives a bisazom ethine ylide.

35


The bisazom ethine ylide reacts w ith two equivalents o f fullerene[60] to give the novel

bisfullerene[60] product (Scheme 21 ).48

Scheme 21. Formation o f a bisfullerene[60] adduct using a bisazomethine ylide.

Although the form ation o f bisfullerene[60] adducts has been accom plished, the products

often show poor solubilities in organic solvents making them difficult to isolate and

completely characterize. Poor solubility' and lack o f thorough characterizations impedes

progress tow ards the synthesis o f higher fullerene[60] adducts such as tris- and

tetrakisfullerene[60] adducts.

C H ;N H C H : COOI I

36


RESULTS AND DISCUSSION

A. Diels-Alder reactions between fullerene[60] and pentacene

1. Formation o f a C2v monoadduct

Numerous Diels-Alder reactions o f fullerene[60] with various dienes have been

studied. One o f the more intriguing sets o f dienes that undergo a D iels-Alder reaction

with fullerene[60] is linear acenes. Linear acenes contain m ultiple diene moieties and

multiple sites for Diels-Alder cyclization. Looking at a molecule o f benzene, there exists

one ring across which a cyclization can occur. Naphthalene contains two rings, either

one o f which is a potential Diels-Alder reaction site. Anthracene has three rings for

potential reaction and so on (Figure 15).

Benzene Napthalene Anthracene

Figure 15. M ultiple diene moieties o f various linear acenes.

37


Although m ultiple diene moieties exist in each linear acene. Diels-Alder

reactions are not always thermodynamically favorable. Fullerene[60] does not undergo a

Diels-Alder reaction with benzene or naphthalene. Diels-Alder reactions with benzene

and naphthalene would result in the form ation o f less stable products, the consequence o f

sacrificing part o r all o f the aromatic ^-system . Anthracene is the sm allest linear acene

that undergoes D iels-A lder reaction w ith fullerene[60].

The D iels-A lder reaction between anthracene and fullerene[60] has been

demonstrated by Nogami and o th e rs /0 The reaction is 100% regioselective occurring

across a 6 .6 -junction o f the fullerene and the 9.10- positions o f anthracene. Addition is

preferred across the 9.10- positions o f anthracene because two fully aromatic benzenoid

rings are retained in the process. Addition across the 1.4- positions o f anthracene would

result in the form ation o f one naphthalene ring, which is not as therm odynam ically stable.

Anthracene is the sm allest linear acene that undergoes a D iels-A lder reaction with

fullerene[60], but it is not the only one.

Komatsu demonstrated that fullerene[60] undergoes a D iels-A lder reaction with

tetracene to give a fullerene[60] m onoaddition product in 61% yield.49 The fullerene[60]

adds across the 5.12- positions o f the tetracene with 100% regioselectivity (Scheme 22).

38


H i g h s p e e d v i b r a t i o n a l

M i l l i n g t e c h n i q u e

Scheme 22. Reaction o f fullerene[60] with tetracene

Extending fullerene[60] D iels-A lder reactions to pentacene provides very

intriguing chem istry. Pentacene has three positions across w hich a Diels-Alder reaction

can occur. In principal, reaction can occur across the 1.4- carbons o f the pentacene

backbone resulting in the form ation o f a tetracene moiety. Looking at the reactions with

anthracene and tetracene and noting the non-reactivity o f benzene and naphthalene.

Diels-Alder additions across the 1.4- positions o f pentacene seem unlikely and have

never been observed. Alternatively, reaction can occur across the 6.13- positions which

results in the formation o f two naphthalene rings. Thirdly, reaction can occur across the

5.14- positions o f pentacene resulting in the formation o f one benzene and one anthracene

moiety. With an anthracene m oiety left behind, a subsequent Diels-Alder reaction with a

second equivalent o f fullerene[60j can occur to give new bisfullerene[60] adducts (Figure

16).

39


1 2

Figure 16. cis- 1 and (runs- 2 Bisfullerene[60] adducts o f pentacene

The bisfullerene[60] adduct can be formed in either a cis- or trans- fashion.

According to MM2 calculations, the calculated difference in energy betw een the two

stereoisom ers is about 1.4 kcal/mol, the cis- isomer preferred.

The bisfullerene[60] adducts o f pentacene are both chemically and physically

intriguing. O f the two isomers, the cis- isomer is expected to posses unique

electrochemical properties. The c-/.y-bisfullerene[60] adduct has both o f its fullerene

moieties in close proxim ity to one another, and held somewhat rigidly along a pentacene

backbone. Because o f these structural features. c7A-bisfullerene[60] adducts o f pentacene

would lend them selves well to the study' o f intermolecular as well as intramolecular

electron transfers.

As the first step in the synthesis o f the cis- and trans- bisfullerene[60] adducts.

Ch() was reacted with pentacene in refluxing toluene for 64 hours. C6o cycloadds across

the 6.13- positions o f pentacene with 100% regioselectivity to provide a symmetric

m onoadduct 3 in 59% yield (Scheme 23).'° Using a 5-fold excess o f C6o pushes the yield

o f 3 to 86% based on pentacene consumed.

40


T o l u e n e

+

3

59% isolated yield

Scheme 23. Reaction o f fullerene[60] with pentacene in refluxing toluene

'H NMR spectroscopy alone can be used to determine the products o f the reaction

with pentacene. Since C6o does not have any protons, it is not detected by 'H NM R

spectroscopy. The *H NM R spectrum o f the C^v monoadduct 3 reveals an X X ' aromatic

singlet at 8.3 ppm which integrates for 4 protons. A A ' M M ' aromatic multiplets at 8.0

and 7.6 ppm. respectively, each integrating for 4 protons, and a singlet m ethine at 6.2

ppm integrating for 2 protons (Figure 17).

41


Figure 17. ‘H NMR spectrum o f fullerene[60]-pentacene m onoadduct 3.

The number o f signals, m ultiplicity, and chemical shifts are all consistent with a

Cz\ structure. Mass spectra are also was consistent with a m onoaddition adduct (LDMS.

tn z. 999 (M~)) and |JC NMR spectra show the appropriate num ber o f signals consistent

with a C :v structure. The ‘H N M R spectrum for Cs symmetric m onoadduct 4 (i.e.. the

product o f addition across the 5.14- positions o f pentacene) would show seven *H NMR

signals, each integrating for two protons. The 'H NMR spectrum for either

bisfullerene[60] adduct would consist o f four 'H signals, but the integration would be

such that the m ethine protons at o r near 6.2 ppm would integrate for 4 protons, while the

X X ’ arom atic singlet would only integrate for 2 protons. There is no sign o f either the

cis- 1 or Ira m - 2 bisfullerene[60] adducts upon heating C60 and pentacene in toluene. Nor

is there sign o f the Cs symmetric m onoadduct 4 in the crude product. 4 is a necessary

interm ediate along the path leading to bisfullerene[60] adducts (Schem e 24).

42


1 2

Scheme 24. Pathway for the formation o f cis- and iram - bisfullerene[60] adducts.

Semi-empirical calculations were performed in order to understand why addition

o f fullerene[60] only occurs across the 6.13- positions o f pentacene. PM3 semi-empirical

calculations were performed on both Cs symmetric 4 and sym m etric 3. According to

these calculations. 3 is 4 kcal/mol lower in energy than 4. This suggests that under

thermodynamic conditions the symmetric 3 should be formed to the near exclusion of

the Cs symmetric 4.

43


PM3 calculations were also performed on transition state structures preceding

formation o f 3 and 4. Because transition states with C6o are too large to be studied by

semi-empirical methods, bicyclopentylidene was used as the dieneophile. The energies

for the transition states accompanying addition o f bicyclopentylidene across the 6.13- and

5.14- positions o f pentacene were calculated. According to PM3 calculations, the

addition o f bicyclopentylidene across the 5.14- position o f pentacene is about 1.4

kcal/mol higher in energy than addition across the 6.13- position o f pentacene. Thus, it

appears that C<-,o cycloaddition with pentacene favors formation o f 3 under both kinetic

and thermodynamic conditions. Consequently, an alternative route to prepare

bisfullerene[60] adducts o f pentacene was deemed necessary.

2. Azabrided pentacenes as precursors to bisfullerene[60] adducts o f pentacene.

Since the Diels-Alder reaction between C6o and pentacene occurs exclusively

across the 6.13- positions in retluxing toluene, an alternative approach using a protected

pentacene was devised (Scheme 25).

44


1. H-.NNHCH-J2.KOH ,N-CH3

mCPBAN—CH3

'• Qo 2. m C PB A

2

Scheme 25. Synthetic scheme for formation o f cis- and trans- bisfullerene[60]

adducts o f pentacene.

The scheme utilizes a convenient reaction developed by Gribble whereby an

aminobridged aromatic is converted quantitatively to the corresponding aromatic

molecule (Scheme 26).?l

45


RN

F

m-CPBACHCL3

F

R= Me

Scheme 26. Conversion o f aminobridged aromatics to their corresponding acenes

(See reference 46).

The 5.14-dihydropentacen-5.14-im ine. 5. can be viewed as a derivative o f anthracene. It

has been dem onstrated that C’6o adds across the 9.10- positions o f anthracene to provide a

monoadduct. It was felt that the Diels-Alder reaction betw een C6o and 5 would follow a

similar path to afford Cs symmetric monoadduct 6. U tilizing G ribbles rearomatization

procedure, the elusive Cs symmetric 4 could then be synthesized. With 4 in hand, a

subsequent reaction with CAo would then provide the c is-1 and trans- 2 bisfullerene[60]

adducts o f pentacene (Schem e 27).

46


m CPBA

Fullerene[60]

Scheme 27. Synthetic scheme for the form ation o f cis- and trans-

bisfullerene[60] adducts

One o f the key intermediates in the overall synthesis o f 5 is the formation o f N-

methvlisoindole. 7. Two methods were employed to synthesize N-methvlisoindole. 7: (1)

synthesis via a fragmentation o f a 1.4-dihydronapthalen-1.4-imines with 3.6-di-2-pyridyl-

47


1,2.4.5-tetrazine. 8 (Scheme 29). and (2) synthesis via basification o f the N-

methylisoindoleum salt. 9 (Schem e 30).

Benzyne undergoes a Diels-Alder reaction with the N-methylcarboxylate o f

pyrrole. 10, in 21% yield to give the N-methylcarboxylate-1.4-dihydronapthalen-1.4-

imine. 11 (Scheme 28).' 2 10 is generated from the addition o f methylchloroformate to

the pyrrole lithium salt.^ To 11 is added Dibal-H in order to form the N-methyl-1.4-

dihvdronapthalen-1.4-imine. 12. in 89% yield (Scheme 28).

C O O M e

1 0 R = C O O M e21%

D i b a l - H

8 9 %

R = M e

1 9 % i s o l a t e d y i e l d

Scheme 28. Formation o f N-methyl-1.4-dihydronapthalen-1.4-imine. 12.

48


The N-methyl-1.4-dihydronapthalen-1.4-imine. 12. is then reacted with 3.6-di-2*-pyridyl-

1.2.4.5-tetrazine. 8. to give N-methvlisoindole. 7. in quantitative yield (Scheme 29).54

R= M e 12

Py

N ^'NII INL

Py

8

100% con version

NMe

Py

Py

Scheme 29. Formation o f N-m ethylisoindole from 3 .6-d i-2 '-pvridyl-l.2.4.5-

tetrazine

The reaction allows for the synthesis o f small am ounts o f pure N-methylisoindole. 7.

Due to the low yield and difficult isolation o f product formed in the benzvne reaction, the

synthesis o f N -m ethylisoindole via this route is problematic. An alternative route which

could produce N-methylisoindole. 7. in multiple gram quantities was needed and found.

Reacting a.a 'd ibrom o-o-xylene. 13." itself prepared via the brom ination o f o-xylene.

reaction with N-methvlhydrazine gives the N-methylisoindoleum salt. 9. In the solid

state. 9 is basified with excess potassium hydroxide producing 7 in addition to ammonia

49


gas and water. 7 is cleanlv sublimed at 0.1 torr and 100°C and isolated in 70% overall

yield (Scheme 30).?6 Isolating 7 as a solid via sublimation is advantageous since 7

degrades photolyticallv in solution. Solid 7 can be stored for m onths in a dark vial

without significant decomposition.

13

Br

Br

H2N N

Ether

NH2

KOH

2H B r

NMe + H20 + NH3

70 % isolated v ie ld

Scheme 30. Formation o f N -m ethylisoindole via N-methylisoindoleum salt

*H N M R spectra show the N-methyl protons o f 7 at 4.00 ppm and they integrate

for 3 protons. A A ' M M - aromatic m ultiplets at 6.94 and 7.53 ppm are also observed and

each integrates for 2 protons. Finally, an arom atic singlet is seen at 7.06 ppm and

integrates for 2 protons. ljC NMR spectra show five resonances at 49.0. 111.7. 119.4.

120.6. and 130.7 ppm.

50


Although 7 can be cleanly isolated, it is photolyticallv unstable in solution. In the

presence o f ambient light. 7 dimerizes rapidly in solution to give the dim er product 14

(Scheme 31).''

Visible liaht

NMeL V Liaht

14

Scheme 31. Dim erization and regeneration o f N-methylisoindole with light

14 is observed to revert back to 7 in the presence o f ultraviolet light. Placing solid 7 in

the dark at cold tem peratures significantly decreases the rate o f dimerization.

7 was reacted in a Diels-Alder fashion with 1.2- dibromobenzvne. itself generated

from 1.2.4.5 tetrabrom obenzene and phenyl lithium. The corresponding 2.3-dibrom o-

9. lO-dihvdroanthracen-9.10-imine. 15. was isolated in 27% yield (Schem e 32) via flash

silica column chromatography.

Br 1) N M e

2 ) 1 . 3 e q P h L i T o l 0 ° - 2 0 ° C

Br-

N M e

15


Scheme 32. Svnthesis o f 2.3-dibromo-9.10-dihvdroanthracen-9.10-imine. 15.

51


Characterization by !H NM R spectroscopy indicates the expected broad N-methyl singlet

at 2.25 ppm integrating for 3 protons, the bridgehead methines at 4.89 ppm integrating

for 2 protons, and three broad arom atic m ultiplets centered at 7.04. 7.32. and 7.57 ppm.

each integrating for 2 protons. Broadening o f the 'H N M R signals is due to pyramidal

inversion o f the N-methyl group. IjC NM R spectra o f 15 displays the N-methyl at 36.6

ppm. the bridgehead methines at 72.3 ppm. and the remaining six aromatic carbons are

overlapped at 121.0. 123.5. 126.1. and 128.7 ppm.

With 15 isolated, it could be converted to the corresponding 2.3-

dibrom oanthracene. 16. via the Gribble oxidation procedure. Thus. 15 was reacted with

excess /w-chloroperoxvbenzoic acid to give a 95% isolated yield of 16 (Scheme 33).

O

CH,C125° C

95 % isolated yield

Scheme 33. Synthesis o f 2.3-dibrom oanthracene. 16.

The yellow solids were filtered from the crude reaction mixture to provide pure 16. *H

NM R spectra show 2 aromatic singlets at 7.92 and 7.70 ppm. each integrating for 2

protons. A A 'M M ' aromatic m ultiplets are seen at 7.63 and 7.19 ppm. each integrating 2

protons. 16 was then reacted with an equivalent o f phenvllithium to generate the

corresponding 2.3- anthryne which reacts in a D iels-Alder fashion with N-

52


methylisoindole. 7. to generate the desired 5.14-dihvdropentacen-5.14-im ine. 5. in 21%

isolated yield (Scheme 34).

2 1 % iso la ted yie ld

Scheme 34. Synthesis o f 5.14-dihydropentacen-5.14-im ine. 5.

Flash silica column chromatography allow ed for the com plete isolation o f 5. 'H N M R

spectra show the expected N-methyl signal at 2.30 ppm integrating for 3 protons, the

bridgehead methine at 5.06 ppm integrating for 2 protons and six aromatic resonances at

7.07. 7.39. 7.44. 7.80. 7.95. and 8.24 ppm . each integrating for 2 protons.

A 5-fold excess o f Cfto was reacted with 5 in 1.2- dichlorobenzene for 36 hours.

Flash silica column chromatography w as utilized to remove unreacted C6oand to isolate

the fullerene[60]-5.14-dihydropentacen-5.14-im ine adduct. 17. in 83% yield based on

5.14-dihydropentacen-5.14-imine. 5. consum ed. 'H and ljC N M R spectroscopy reveal,

however, that the expected Diels-Alder reaction did not occur. Instead, an unexpected

am ination product was formed. D iels-A lder addition across the 7.12- positions o f 5

would have given a Cs symmetric m onoadduct. The Cs sym m etric m onoadduct w ould

give rise to a 'H NM R spectrum sim ilar to that o f 5 itself. Instead. 'H NM R spectra show

the N-methyl proton as a singlet at 3.20 ppm integrating for 3 protons. There are two

unique methine protons observed in the 'H NM R spectrum, one adjacent to the nitrogen

53


and the other apparently adjacent to the fuilerene[60] skeleton at 5.98 and 6.39 ppm.

respectively, each integrating for 1 proton. The rest o f the arom atic protons are

overlapped m ultiplets centered at 7.56. 7.98. 8.16 and 8.22 ppm (Figure 18).

*c h c i3

S .4 S 0 * 6 * 2 6 .S 6 .4 6 .0 5 .6 5 .2 4 .* 4 .4 4 .0 J .6 J .2

(ppm)

Figure 18. 1H NMR spectrum o f fullerene[60]-5.14-dihvdropentacen-5.14-imine

addition product. 17.

Likewise the ljC N M R spectrum reveals an N-methyl signal at 38.1 ppm and two

different spJ fullerene carbons at 71.51 and 71.53 ppm. There are also two unique spJ

carbon signals corresponding to the pentacene backbone at 53.0 and 58.5 ppm. The sp2

region indicates 42 carbon signals including several especially intense peaks signifying

54


coincidental overlap (Figure 19). The large number o f ljC signals observed indicates a

lack o f symmetry in the product.

I** in in i# it» m ** «• «• a

‘FP»*

Figure 19. |JC NM R spectrum o f fullerene[60]-5.14-dihydropentacen-5.14-imine

addition product. 17.

These spectra are consistent with a product o f fullerene insertion into the bridgehead C-N

bond o f the 5.14-dih\rdropentacen-5.14-imine. as shown in Scheme 35.

55


1.2 Dichlorobenzene

5

17

83% isolated yield

Scheme 35. Form ation o f unique am ination product o f fullerene[60] with 5.14-

dihydropentacen-5.14-im ine. 5.

Fullerene[60] is know n to aminate upon reacting with primary and secondary

aliphatic amines. However, tertiary amines are not known to produce fullerene[60]

am ination products. Primary and secondary aliphatic amines are believed to add to C6o

via a mechanism where the first step is an electron transfer (Scheme 36) from the am ine

^ oto Cw, to give a fullerene[60] radical anion and an am ine radical cation.'

56


C H

C H

C H

C H

Scheme 36. Probable am ination mechanism for the addition o f primary and

secondary aliphatic am ines to fullerene[60].

The amine radical cation can protonate the fullerene[60] radical anion to give a pair o f

radicals which can then couple to give the stable am ination product. Using an analogous

mechanism with tertiary amines, electron transfer followed by radical recombination can

occur, but there is no proton to transfer. Thus, the zw itterion. if formed, fragments back

to the starting m aterial resulting in no net reaction (Schem e 37).

57


N(CH3)3

Scheme 37. Analogous amination m echanism with tertian,' amines

In the case o f the 5.14-dihvdropentacen-5.14-imine. 5. a different reactivity is observed.

Electron transfer to Cf,o from 5 results in a fullerene[60] radical anion and a strained

amine radical cation (Scheme 38).

58


CH

X HX H

• •

17

Scheme 38. Proposed m echanism for the formation o f the fullerene[60]-5.l4-

dihydropentacen-5.l4-im ine product. 17.

Recombination o f the radicals provides a zwitterion. Due to the strain o f the azabridge.

and the stability' afforded benzylic cations, ring opening may be favorable. After ring

opening, the positive charge is transferred from an ammonium ion to a highly stabilized

dibenzvlic cation. The resulting dibenzyl cation can then be captured by the fullerene

anion giving rise to a unique fullerene[60] am ination product. The reaction between

59


strained tertiary amines and C60 needs to be studied further in order to determine if it is a

general reaction class.

Following our synthesis o f the 5.14-dihydropentacen-5.14-im ine. 5. Komatsu and

co-workers reported the synthesis o f the rra/7s-bisfullerene[60] adduct o f pentacene. 2. in

11% yield using the solid state technique termed high speed vibrational milling (Scheme

39).44

+

i/H i g h s p e e d

v i b r a t i o n a l M i l l i n g *•y y

- /

i /

Scheme 39. Formation o f m m s-bisfullerene[60] adduct o f pentacene. 2.

High speed vibrational milling (H SV M ) is a technique in which the reactants are placed

in a canister containing a ball-bearing. The canister is sealed and allowed to shake at

speeds o f 3600 cvcles/min. The rapid m ovem ent o f the canister allows the ball-bearing

to impact the reactants in a mechanochemical fashion inducing reactivity. Due to the

rapid m ovem ent o f the canister and the ball bearing, heat is produced to the extent that

many D iels-A lder reactions are reversible. As discussed earlier, the C^v symmetric

monoadduct. 3. is both thermodynamically and kineticallv favored to the Cs symmetric

60


monoadduct. 4. Under C6o rich HVSM conditions. 4 is apparently formed and rapidly

trapped by C6o to give the rram -bisfullerene adduct. 2 .

3. The formation o f bispentacene adducts o f fiillerene[60]

During our studies o f the reaction between C6o and pentacene. w e not only noted

formation o f 3. but also bispentacene adducts (i.e.. two pentacenes adding to one

fullerene[60] molecule) o f C6o- The bispentacene adducts posses interesting structures

and properties. As with most bisadditions involving C6o- regioselectivity in the second

addition is low. Seven o f the eight possible bisadducts are formed in the reaction between

C6() and pentacene. the cis-\ most likely absent. Bisadducts o f pentacene are formed in an

overall 61% yield (8 : 1 (trans- + e-) : cis- ratio) when using a 2 : 1 excess o f pentacene to

Cfto- Flash silica column chromatography allows for the separation o f the trans- and e-

bispentacene adducts from the cis- bispentacene adducts. Six o f the eight bispentacene

adducts give rise to 'H NM R spectra containing two singlet methine protons and a double

set o f A A 'M M 'X X ' aromatic signals. The Dih symmetric trans- 1 bispentacene adduct

gives rise to only one methine signal and one set o f aromatic signals. The e- bispentacene

adduct exhibits three methine resonances (2:1:1) and three sets o f arom atic protons. In

the |JC N M R spectra, the fullerenic cage carbons o f the various bispentacene adducts are

jum bled between 135-156 ppm. while the spJ carbons on the fullerene as well as the sp'

carbons on the pentacene backbone are well resolved at approximately 70-80 ppm and

55-65 ppm . respectively.

61


Flash silica column chromatography allows for purification o f the irans-2

bispentacene adduct. 18. (Figure 20).

Figure 20. trcms- 2 Bispentacene adduct o f fullerene[60]. 18.

The 'H NM R spectrum o f 18 shows two unique methines. one at 5.93 ppm and another at

6.14 ppm. each integrating for 2 protons. Two sets o f AA‘ MM" aromatic protons

centered at 7.44. 7.58. 7.85. and 8.06 ppm (Figure 21). Two separate sets o f XX'

singlets are observed at 8.04. 8 .10. 8.31. and 8.42 ppm. each integrating for 2 protons

(Figure 22). ljC NMR spectra o f 18 show two spJ fullerene carbons, one at 70.9 ppm and

the other at 71.1 ppm. The two spJ pentacene carbons are observed at 58.9 and 58.4 ppm.

The sp 2 carbons are observed between 130-155 ppm (Figure 22). The molecule was

assigned a trans-2 structure based upon elution order o ff o f a flash silica column as well

as the NMR data.

62


Figure 21. 'H N M R spectrum o f 18

Figure 22. l jC NM R spectrum o f 18

63


PM3 semi-empirical calculations were run to determ ine the therm odynam ic

relationship between each o f the various bispentacene adducts. The results indicate that 7

o f the 8 bispentacene adducts differ in AHt-° by only 1. 8 kcal/mol (Figure 23). The cA-1

adduct was the exception, higher by about 50 kcal/mol than the others. This is clearly

due to intense van der W aals repulsion between adjacent pentacene addends on the cis- 1

isomer.

§ 1000I 990 o 980 *3 970S 960Ql? 950| 940J 930 o 920

Bispentacene Adduct

Figure 23. PM3 calculated heats o f form ation for bispentacene adducts o f

fullerene[60]

As with most Diels-Alder reactions involving fiillerene[60]. the reaction with

pentacene is reversible. When the collection o f bispentacene adducts is refluxed in 1.2-

dichlorobenzene (b.p. 180) in the presence o f excess dim ethylacetylenedicarboxylate. 19.

64


(i.e.. DM AD. 19). bare fullerene[60] is completely recovered along with the

dimethylacetylenedicarboxylate-pentacene m onoadduct. 20. 'H NM R spectra indicate

that the only product formed in the DMAD reaction involves addition o f DMAD across

the 6.13- carbons o f pentacene (i.e.. a C2v m onoadduct).

Fullerene[60] and many of its derivatives show poor solubility in common

organic solvents. However, bispentacene adducts o f fullerene[60] show excellent

solubility in a host o f organic solvents where fullerene[60] itself is only minimally

soluble or insoluble (Table 1).

Table 1. Enhanced solubilities o f bispentacene adducts o f fullerene[60]

Solvent

Solubilities (mg/mL) in select solvents

FullerenefbO]'^ M ixture o f Bispentacene

adductsCH Ch 0.16 >332

CH 2C12 0.26 > 1 0

CC14 0.32 > 1 0

THF 0 . 0 0 > 1 0

(CH 3)2CO 0 . 0 0 1 ~ 1

(CH3)20 ---- ' 1

The limited solubility o f Cho in organic solvents is believed to play a role in the low

yields o f many fullerene[60] reactions. Using soluble bispentacene adducts. several

fullerene[60] reactions were studied in order to increase the yield o f fullerene addition

products. Since fullerene[60] has 30 ;r- bonds which react somewhat independent o f one

65


another, the reactivity o f fullerene[60] adducts is observed to mimic that o f fullerene[60]

itself. Likewise, a bispentacene adduct o f fullerene[60] should react as fullerene[60]

does, provided the pentacene addends do not block all reactive sites. Once the

subsequent chem istry has been performed, the pentacene addends can be rem oved

leaving the new fullerene[60] derivative.

To determ ine if bispentacene adducts can act as soluble fullerene[60] mimics,

/ram -bispentacene adducts were used in a reaction with diphenyldiazomethane. The

fram -bispentacene adducts were used rather than the c/.v-bispentacene adducts because

they are formed in greater yield from fullerene[60] and pentacene. The reaction between

the tram - bispentacene adducts o f fullerene[60] and diphenyldiazomethane was run in

the dark for 2 hours in CHCI3 and the resulting fullerene[60] trisadducts w ere studied by

!H NMR. Given the large number o f new isomers formed in the addition o f

diphenyldiazomethane to the various tram - bispentacene adducts. the 'H NM R spectrum

o f the crude reaction mixture is very complex. The previously resolved methine proton

signals o f the bispentacene adducts are no longer resolved and the arom atic region is

complex.

Upon allow ing the crude product mixture to react with DMAD in refluxing 1.2-

dichlorobenzene. the pentacene addends are affectively removed from the fullerene[60]

skeleton. Refluxing the diphenyldiazomethane products at elevated tem perature allows

for the conversion o f any 6.5- open fulleriods to 6 .6 - closed m ethanofullerenes . 2 6 A fter

removing 1 ,2-dichlorobenzene and the DMAD-pentacene product. 20. the diphenyl

methanofullerene. 21. is obtained in 44% isolated yield (Scheme 40).

66


18 DMAD,1,2- dichlorobenzene

21

44% isolated vield

Scheme 40. Formation o f diphenyl m ethanofullerene. 21. via initial addition to a

collection o f trans- bispentacene adducts.

Wudl reported an approximate yield o f 40% in his original paper describing the

reaction between fullerene[60] and diphenyldiazom ethane.2j U sing the trans-

bispentacene adducts as a soluble fullerene[60] mimic only slightly increased the yield o f

67


product. One possible reason for the relatively low yield o f 21 is that the steric bulkiness

o f the pentacene addends may have slow ed diphenyldiazomethane addition. In trans-

bispentacene adducts. the pentacene addends are attached to both spheres o f the C6o

moiety. With both spheres containing stericallv bulky pentacene addends, there are a

limited number o f sites for the diphenyldiazom ethane to add in an energetically favorable

manner, thus decreasing the overall reactivity. Using the c/s-bispentacene adducts should

reduce the steric bulkiness since both pentacene addends are on the sam e sphere o f the

C6o moiety. This leaves the other sphere uncongested, providing energetically favorable

sites for a subsequent addition o f diphenyldiazom ethane. Further w ork needs to be done

in order to ascertain the utility o f em ploying bispentacene adducts o f C6oas highly

soluble fullerene[60] mimics. Since this approach requires such a large investment (i.e..

the initial synthesis o f bispentacene adducts as well as the subsequent removal o f

pentacenes addends), it is valuable only if yields o f reaction are dram atically improved

compared to the fullerene[60] base case

B. Diels-Alder chemistry between fullerene[60| and 6,13-disubstituted pentacenes

1. Calculations and literature precedence

Semi-empirical calculations played an important role in understanding the

reaction between fullerene[60] and pentacene. PM3 semi-empirical calculations suggest

that the reaction between fullerene[60] and pentacene occurs preferentially across the

68


6.13- positions under both kinetically and thermodynamically controlled conditions. The

calculations give very different results when applied to 6.13-disubstituted pentacenes.

PM3 semi-em pirical calculations were performed using ethylene as the dienophile

with 6.13-diphenvlpentacene. 22. The calculated heats o f formation for addition o f

ethylene across the 5.14- positions and the 6.13- positions were compared. PM3

calculated heats o f formation suggest ethylene addition across the 5.14- positions o f 22 to

be 9.1 kcal/mol lower in energy than addition across the 6.13- positions o f 22. Using

bicyclopentvlidene as the dieneophile. calculated heats o f formation suggest addition

across the 5.14- positions o f 22 to be 28.8 kcal/mol lower in energy- than addition across

the 6.13- positions o f 22. From the PM3 semi-empirical heat o f formation data, we

conclude that cycloaddition across the 5.14- positions o f 6.13- disubstituted pentacenes

becomes progressively more favorable as the size o f the dienophile increases. We further

postulate that cycloaddition with fullerene[60] as dienophile should be com pletely

regioselective. occurring exclusively across the 5.14- positions o f 6.13-disubstituted

pentacenes.

PM3 semi-em pirical transition state calculations were also performed. PM3 semi-

empirical transition state calculations suggest that addition o f ethylene across the 5.14-

positions o f 22 is kinetically favored by 4 kcal/mol over addition across the 6.13-

positions o f 22. M oreover. PM3 semi-empirical transition state calculations suggest that

addition o f bicyclopentvlidene across the 5.14- positions o f 22 is favored by a whopping

19.8 kcal/mol over addition across the 6.13- positions o f 22 (Table 2).

69


Table 2. PM3 calculated Diels-Alder reactivity of 6,13-diphenylpentacene

AHVAHVvs (kcal/mol) AH * (kcal/mol)

Dienophile 6,13-product

5,14-product

6,13-Transition

State

5,14- T ransition

State

C2H4 147.8/-32.4 138.6/-41.5 211.4 207.4

L K J 151.5/+12.3 122.6/-16.5 201.1 181.3

Thus. PM3 semi-empirical calculations suggest that the D iels-A lder reaction between

dienophiles and 22 should be both kinetically and thermodynamically driven to the 5.14-

positions. Diels-Alder reaction between fullerene[60] and 22 should also favor addition

across the 5.14- positions. Fullerene[60] addition across the 5.14- positions o f 22 would

result in the formation o f the elusive Cs sym m etric monoadduct. 23. The Cs symmetric

monoadduct would then be free to undergo a second Diels-Alder reaction with a second

equivalent o f fullerene[60] to provide the cis- and trans- bisfullerene[60] adducts. 24 and

25. respectively

A careful review o f the literature supports the com putational findings. In 1943.

Alan and Bell reported the reaction between maleic anhydride and 6.13-

diphenylpentacene. They reported m onoaddition o f maleic anhydride across the 6.13-

positions o f the 6.13- diphenylpentacene as well as a diaddition product where two

70


maleic anhydride molecules added across the 5.14- and 7.12- positions, respectively, to

give a bisadduct.60 With favorable computational data and the work o f Alan and Bell in

hand, we sought to react fullerene[60] with 22 in order to form bisfullerene[60] adducts.

24 and 25.

2. Bisfullerene[60] adducts o f 6,13- disubstituted pentacenes

a. Synthesis, isolation, and spectroscopic characterization o f various 6.13- disubstituted pentacenes

Before studying the reactions between fullerene[60] and 6.13-diphenvlpentacene.

the 6.13-diphenylpentacene needed to be prepared. The key intermediate in the

preparation o f 6.13-diphenylpentacene is 6.13-pentacenequinone. 26. a .a .a 'a '-

Tetrabromo-o-xylene. 27.61 was reacted with benzoquinone and sodium iodide in DMF at

120°C to give 6.13- pentacenequinone. 26. in 94% yield (Schem e 41 ).62 26 was vacuum

filtered from the crude reaction mixture, washed with saturated sodium bisulfite, and

dried.

Nal

DMF

27

94% isolated yield

Schem e 41. Formation o f 6.13-pentacenequinone. 26.

71


The 'H NM R spectrum for 26 shows the expected XX' aromatic singlet at 8.97 ppm

integrating for 4 protons, and A A ' M M ‘ aromatic multiplets centered at 7.73 and 8.14

ppm. each integrating for 4 protons. To 26 was added an excess o f phenylithium . 26

undergoes nucleophilic attack at the carbonyls to give 6.13-diphenylpentacene-6.13-diol.

28. in 65 % crude yield. The phenyl lithium also adds in a Michael addition fashion to

give undesired M ichael addition products. Crude 28 was reductively arom atized by

refluxing in acetic acid in the presence o f potassium iodide to give 6.13-

diphenylpentacene. 22. Gravity filtration o f the blue solids allowed for isolation o f 22 in

92% yield (Scheme 42).'° !H NM R spectra for 22 show the expected X X ’ aromatic

singlet at 8.6 ppm integrating for 4 protons. A A ' M M ' aromatic m ultiplets centered at

6.90 and 7.37 ppm and integrating for 4 protons each, and aromatic protons for the 6.13-

diphenyl groups centered at 7.43 and 7.58 ppm. integrating for 6 and 4 protons

t ^

respectively. The "C NM R spectrum for 22 shows nine resonances at 125.5. 126.2.

128.8. 129.1. 129.4. 131.8. 132.2. 137.6. and 140.4 ppm (one resonance appears to be

buried under the solvent).

Although 22 can be formed and cleanly isolated, it is photolvtically unstable. In

solution with am bient light, oxygen adds across the 6.13- positions o f 22 to generate a

peroxide. 29 (Schem e 43).'° It was discovered that keeping 22 dry and in the dark allows

for its safe storage for extended periods o f tim e without decom position (vide infra).

72


26 28, mixture o f cis and trans-

KI. AcOH

P h

P h

22

44 % isolated yield

Scheme 42. Formation o f the 6 .13-diphenylpentacene. 22

P h P h O

P hLight

P h

22 29

Scheme 43. Oxidation o f 6.13-diphenylpentacene

73


In addition to 22. other 6.13- disubstituted pentacenes were also synthesized.

6 .13-Pentacenequinone. 26. was added to lithium phenylacetylenide generated from the

reaction between ethynvlbenzene and n-butylithium at 0 °C under a N 2 atm osphere.

Addition into the carbonyls provided 6 .13-diphenethvnylpentacene-6.13-diol. 30. in 50%

crude yield. Crude 30 was reductivelv aromatized by adding it to a filtered solution o f

Sn(II) chloride in 50% acetic acid . The blue suspension was stirred for 10 hours in the

dark then vacuum filtered to give the 6.13-diphenethynvlpentacene. 31. in 71% isolated

yield (Scheme 44). 63

Ph- iS Li

TOL, 0°C, N2

Ph

OH

HO

Ph

30

50%, mixture of c /sand trans-

SnCI2, AcOH Ph Ph

31

71%

Scheme 44. Formation o f 6.13-diphenethvnylpentacene. 31.

74


'H NM R spectra o f 31 displayed the expected X X ' aromatic singlet at 9.34 ppm

integrating for 4 protons, and A A ' MM* arom atic m ultiplets centered at 7.47 and 8.14

ppm. each integrating for 4 protons. The arom atic multiplets for the phenyl rings o f the

phenethynyl substituent are centered at 7.55 and 7.97 ppm and integrate for 6 protons and

4 protons respectively.

In a sim ilar manner. 6 .13-di(trim ethylsilylethynyl)pentacene. 32, was prepared.

Thus 6.13-pentacenequinone. 26, w as added to lithium irimethylsilylacetylenide

generated from the reaction o f n-butyllithium writh trimethvlsilylacetylene in toluene

solution under NN at 0°C. Addition into the carbonyls gives the 6.13-

di(trim ethylsilylethynyl)pentacene-6.13-diol. 33 in 50% crude yield. 33 was reductively

aromatized by addition to a filtered solution o f Sn(II) chloride to give a blue suspension.

The 6.13-di(trim ethylsilylethynyl)pentacene. 32. was then vacuum filtered and collected

in 36% isolated yield (Scheme 45). 'H N M R spectra o f 32 show the expected XX '

aromatic singlet at 9.17 ppm integrating for 4 protons, and AA' M M ' arom atic multiplets

centered at 7.42 and 8.02 ppm. each integrating for 4 protons. The trimethvlsilyl group is

observed at 0.58 ppm and integrates for 18 protons.

To 32 was added tetrabutylam m onium fluoride (TBAF) providing the 6.13-

diethvnylpentacene. 34. The crude reaction m ixture was passed through a short silica

plug to isolate 34 (Scheme 46).64 'H N M R spectra o f 34 show the expected XX'

aromatic singlet at 9.25 ppm integrating for 4 protons. AA* MM' arom atic multiplets

centered at 7.43 and 8.04 ppm. each integrating for 4 protons, and the ethynyl protons at

4.42 ppm integrating for 2 protons.

75


TOL. 0°C, N2 Si.\

33

50%, mixture of c/sand trans-

SnCI2, AcOH Si

32

36%

Schem e 45. Formation o f 6 .13-di(trimethylsiiylethynyl)pentacene. 32.

— S i -

— S i - - - - - -

TBA F

100% conversion

32 34

Scheme 46. Formation o f 6 .13-diethynvlpentacene. 34.

76


Two pentacenes containing polar functional groups at the 6.13- positions were

also synthesized. 2-Propvn-l-ol was protected with a tetrahydropyran (THP) group. The

THP protected 2-propvn-l-ol. 35. was reacted with n-butvllithium in toluene at 0°C under

nitrogen to give the corresponding lithium acetvlenide. To the THP protected acetylenide

was added 6.13-pentacenequinone. 26. Addition into the carbonyls provides the 6.13-di-

(THP protected 2-propyn-l-ol )pentacene-6.13-diol. 36.6' 'H NM R spectra o f the crude

reaction m ixture are complicated due to the different diastereomers generated by the

addition o f 2 chiral THP protecting groups. Crude 36 was allowed to reductively

aromatize via reaction with a filtered Sn(II) chloride solution to give crude 6.13-di(THP

protected 2-propvn-l-ol)pentacene. 37 (Scheme 47). Again. ’H NMR spectra for 37 are

complex due to the different diastereom ers present.

6.13-di-4'-hvdroxymethylphenylpentacene. 38. was also prepared. To avoid the

diastereomeric mixture observed in the THP protected pentacene. a /e/v-butvl

dimethylsilyl (TBDM S) group was used to protect /7-bromobenzvlalcohol. 39. itself

prepared via a reduction of/7-bromobenzoic acid.66 The TBDM S protected p-

bromobenzyl alcohol. 40. was subject to lithium halogen exchange with /-butyl lithium to

give the corresponding lithium salt. Nucleophilic addition o f the lithium salt into the

carbonyls o f 6.13- pentacenequinone. 26 provided the TBDM S protected 6.13-di-4‘-

hydroxymethylphenvlpentacene-6.13-diol. 41. 41 wras deprotected with TBAF to give

6.13-di-4'-hydroxym ethvlphenylpentacene-6.13-diol. 42. Aromatization under

conditions o f Sn(II) chloride and 10M hydrochloric acid provided the 6.13-di-4‘-

hydroxymethylphenylpentacene. 38 (Scheme 48). The 'H N M R spectrum for 38 displays

the expected X X ' aromatic singlet at 7.67 ppm integrating for 4 protons, and AA" M M '

77


aromatic m ultiplets centered at 7.44 and 7.72 ppm. each integrating for 4 protons. Two

6.13-/7-hydroxymethylphenyl 'H resonances are observ ed at 7.75 and 7.88 ppm . each

integrating for 4 protons. The benzyl protons are observed as a singlet at 4.97 ppm and

integrate for 4 protons.

O T H P

T H P O\ =S Li

T O L . 0 ° C . N 2

O T H P

S n C I 2 , A c O H O T H P

T H P O

37

Scheme 47. Formation o f THP-protected propargvl pentacene. 37.

78


TBDMS

Br

O26

40 TOL, 0°C, N2

OTBDMS

,OH

HO

OTBDMS41

mixture of cis- and trans-

TBAF

OH

OH

HO

OH42

Sn(ll)CI2

HCI

OHmixture of cis- and trans-

38

19% isolated yield

Scheme 48. Formation o f 6 .13-di-4'-hydroxymethylphenylpentacene. 38.

Although 6 .13- disubstituted pentacenes can be synthesized, their isolation is not

always trivial. Parent pentacene was observed to dimerize in solution that is not

protected from light. D imerization was shown to occur at the 6.13- positions to give a

C’2\ symmetric dim er product. 43 (Schem e 49).

79


CHCI;

43

Scheme 49. Dimerization o f parent pentacene in the presence o f visible light.

The 6.13- diarvl substituted pentacenes are less prone to dimerization than

pentacene itself. Dimerization o f the 6.13- diaryl substituted pentacenes across the 6.13-

carbons would cause significant van der Waals repulsion between the and substituents.

The sam e rationale can be used for the trimethylsilylethynvl and the phenethynyl

substituted pentacenes. Since the inflexible ethynyl group is attached to a large

substituent in these cases, dimerization would lead to significant van der Waal repulsion

making it an energetically costly path. However, when sm aller groups and/or flexible

groups are attached to the pentacene at the 6.13- positions, dim erization occurs rapidly.

In the case o f the 6.13-di-(THP protected 2-propyn-l-ol)pentacene. 37. and 6.13-

diethynylpentacene. 34. dimerization occurs rapidly because there is little van der Waals

repulsion in the dimer product. Since aromatization o f these pentacenes occurs in

solution, it can be difficult to cleanly isolate the desired pentacene products free o f dimer

and/or peroxide side products. Keeping the pentacene solutions in the dark and under Nt

significantly decreases the rate o f dimerization and oxidative degradation.

80


b. Regioselective reactions o f fullerene[60] and 6.13- disubstituted pentacenes : synthesis, isolation, and spectroscopic characterization

W ith several 6.13- disubstituted pentacenes prepared, the corresponding reactions

with fullerene[60] were studied. A 5-fold excess o f C6o vvas reacted with 6.13-

diphenylpentacene. 22. in re fluxing carbon disulfide (b.p. 46 °C) to give an 85% isolated

yield o f the c7.v-bisfullerene[60] adduct o f 6.13- diphenylpentacene. 24. (Schem e 50).

22

24

85% isolated yield

Scheme 50. Formation o f c7.v-bisfullerene[60] adduct o f 6.13-diphenylpentacene.

24.

Flash silica column chrom atography was used to purify 24. 'H NMR. i3C N M R . and an

X-ray structure analysis6' have been used to thoroughly characterize the product

structure.

81


As with the C 2v m onoadduct prepared from C6o and pentacene. *H N M R spectra

provide definitive structural evidence fo ra C^v cis- bisfullerene[60] structure. In the 'H

NMR spectrum, the methine proton is seen at 5.7 ppm and integrates for 4 total protons.

The A A ' M M ' multiplets for the arom atic rings on the pentacene backbone are centered

at 7.45 and 7.60 ppm. each integrating for 4 total protons (Figure 24). The *H N M R

spectrum is neither consistent with a C iv nor a Cs symmetric monoadduct. T he !H NMR

spectrum o f a symmetric m onoadduct would show A A ' M M ' and XX* signals for the

aromatic protons o f the pentacene backbone. Moreover the C^v m onoadduct structure

would show no methine 'H signal at 5.7 ppm due to the 6.13- substitution pattern on the

pentacene backbone.

*.* '« * ’ .4 ' . 2 "« l fa.* fc.* fc.4 fc.2 fc.f» 5 .* 5.fc 5.4

t p p m y

Figure 24. !H NM R spectrum o f the cis- bisfullerene[60] adduct o f 6.13-

diphenvlpentacene. 24.

82


While the presence o f a methine proton signal at 5.7 ppm and the absence o f an

X X ' aromatic singlet rules out the C^v sym m etric monoadduct. the Cs sym m etric

monoadduct. 23. still needs to be considered. The !H NMR spectrum o f 23 with

cycloaddition across the 5.14- carbons o f the pentacene backbone would include five

pentacene resonances: one X X ' and two different sets o f A A ' M M ' m ultiplets. The

absence o f the X X ' aromatic singlet and two unique sets o f A A 'M M ' arom atic multiplets

rules out the possibility that the product formed is 23. Having ruled out a C 2v and a Cs

symmetric monoadduct. the 1H NM R spectrum is only consistent with a bisfiillerene[60]

adduct.

The resonances o f the 6.13- diphenyl rings in 24 indicate a cis- stereochem istry in

the bisfullerene[60] adduct. Thus, because 5 unique 6.13- diphenyl 'H resonances are

observed, the 6.13- diphenyl substituents m ust be rotating slowly on the N M R timescale

and the stereochemistry o f the isolated product must be cis-. The 6.13- diphenyl

substituents show hindered rotation due to van der Waals repulsion between the o-

hydrogens o f the phenyl substituents and the bridgehead methines o f the pentacene

backbone. This is sim ilar to the hindered rotation seen with 2.6- disubstituted biphenyl

molecules where one phenyl group has been substituted with tertiary alkyl groups (Figure

25).

83


Figure 25. Comparison o f hindered 6.13- diphenyl rotation in 24 with similarly

hindered phenyl rotation in 2.6-disubstituted biphenyl.

There are several cases is the literature where hindered phenyl rotation is seen.

The most relevant to the c7's-bisfullerene[60] adduct case is the .vv«-9-phenyl-2.11-

dithia[3.3]metacvclophane (Figure 26).68

)

Figure 26. .sr«-9-Phenyl-2.1 l-dithia[3.3]m etacvclophane

84


Mitchell and co-w orkers dem onstrated that the o-protons o f the 9-phenyl ring in

.s\77-9-phenyl-2.1 l-dithia[3.3]m etacvclophane were well resolved at room temperature

with coalescence occurring at approxim ately 60 °C. 24 was heated to 85 °C and only

m inor changes were observed in its 'H NM R spectrum. Noting the rigidity o f the

bisfullerene[60] adduct com pared to .vy/7-9-phenyl-2.1 l-dithia[3.3]m etacyclophane. a

higher coalescence tem perature is to be expected. Notably, the bisfullerene[60] adduct

did not undergo a retro-D iels-A lder reaction at 85 °C verify ing the kinetically controlled

nature o f the reaction run in refluxing C S 2 (b.p. 46 °C). The five unique aromatic

resonances for the 6.13- diphenyl rings, each integrating for 2 protons, point squarely to a

C'2 , cis- stereochemistry rather than a C^h trcins- stereoisomer. The CNh trans-

bisfullerene[60] adduct. 25 (Figure 27). would only have three unique 6.13- diphenyl

resonances, regardless o f phenyl rotation.

25

Figure 27. trans- Bisfullerene[60] adduct o f 6.13-diphenylpentacene. 25.

85


The ljC N M R spectrum for 24 further confirm s a cis- stereochemistry. The cis-

bisfullerene[60] adduct consists o f 30 fullerene cage carbons which show up in the

crowded sp2 region between 135 and 157 ppm . The aromatic methine protons o f the

pentacene backbone as well as the carbons bearing hydrogen on the 6.13- diphenyl rings

are well resolved in the region between 125 and 130 ppm. In this region, seven distinct

signals are observed. The seven include five sm aller signals for the arom atic methines o f

the 6.13- diphenyl rings as well as two larger signals for the aromatic methines on the

pentacene backbone (Figure 28).

IJO.-I IJn .o tM.fc 121.2 t2X.lt t2».4 12*.n I2 "6 12" 2 I24W.M 124.4 126.0 125.6 1 25.2<PP«>

Figure 28. ljC NMR o f the aromatic m ethine region o f 24.

While the spectrum is entirely consistent with a Civ cis- bisfullerene[60] adduct. it

is inconsistent with a Cih trans- bisfullerene[60] adduct. The latter would show a total o f

86


5 aromatic methines between 125 and 130 ppm. only 3 o f which would arise from the

6.13- diphenyl substituents. The remaining 2 o f double intensity would arise from the

equivalent sets o f methine carbons on the pentacene backbone. A fter completely

characterizing the cxs-stereochemistry by 'H and ljC NM R spectra, an X-ray structural

analysis62 verified the c/.v-stereochemistry. The rm«5-bisfullerene[60] adduct o f 6.13-

diphenylpentacene. 25, is also believed to be formed, but only in very small quantity. A

'H NMR spectrum o f an isolated by-product formed in low yield is consistent with 25 but

is noise ridden. Complete characterization is not possible without m ore sample. The

reaction o f fullerene[60] with 6.13- diphenylpentacene. 22. also gives rise to small

quantities o f oligermeric products. Since the reaction is run with an excess o f

fullerene[60] and Cs symmetric monoadduct 23 is an intermediate along the path leading

to the 24. it is reasonable that 23 can add to 24 in order to give one or more o f the

numerous possible trisfullerene[60] adducts (Figure 29). Although each fullerene[60]

moiety has multiple reactive 7t-bonds at which a Cs monoadduct could add. only the

rra/?.y-alkene functions are suitably positioned to avoid serious van der Waals repulsions

in the resulting trisadduct structures. At each unique alkene function, the Cs symmetric 23

can add to the c7.v-bisfullerene[60] adduct in either an exo- or endo- fashion. Figure 29

illustrates the 2 unique structures formed upon adding 23 to the trans- 1 position o f 24.

Due to the complexity o f the structures formed. ‘H NM R spectroscopy alone may not be

sufficient to thoroughly characterize to products (Figure 30). It is anticipated that X-ray

structure analysis will be required to firmly establish each trisfullerene[60] adduct

structure. Work continues along these lines.

87


Figure 29. Possible trisfullerene[60] adduct structures: a C :v trisadduct generated

upon adding 23 to the trans-1 position o f 24 in an endo- fashion (top): the corresponding

C:h trisadduct generated upon adding 23 to the trans- 1 position o f 24 in an exo-fashion

(bottom).

88


Figure 30. 'H NMR spectra o f oligom ers generated in the reaction between

fuilerene[60] and 6 .1 3 -diphenylpentacene. 22.

Fullerene[60] was allowed to react with 6.13-di-(4*-hydroxymethylphenvl)

pentacene. 38. A 5-fold excess o f fullerene[60] was used and the c7.y-bisfullerene[60]

89


adduct o f the 6.13-di(4'-hydroxym ethylphenyl) pentacene. 44. was formed in 75%

isolated yield (Scheme 51).


Scheme 51. Formation o f c7.v-bisfullerene[60] adduct o f 6 .13-di-(4 -

hydroxymethy[phenyl)pentacene. 44.

Flash silica column chrom atography allowed for clean isolation o f 44 and

oligomeric products. Hindered rotation o f the phenyl group is again seen in the product.

The ‘H NM R spectrum for 44 shows a methine singlet at 5.7 ppm integrating for 4

protons, and A A ' MM' arom atic m ultiplets centered at 7.43 and 7.56 ppm. each

90


integrating for 4 protons. The methylene protons o f the /?-hydroxymethvl groups

resonate at 4.85 ppm and integrate for 4 protons (Figure 31).

* CHCI3

Figure 31. 1H NM R spectrum o f the C7.s-bisfullerene[60] adduct o f 6 .13-di-(4'-

hydroxymethylphenvl )pentacene. 44.

Positive ion electrosprav mass spectra o f 44 shows a strong [M»Na~] signal at m /r = 1954

confirm ing bisadduct formation. The absence o f an XX' arom atic singlet in the ’H NM R

spectrum further confirm s the bisfullerene[60] adduct product. D ue to the hindered

rotation o f the phenyl rings in 44. 4 unique aromatic doublets corresponding to the 6.13-

diaryl rings are observ ed, each integrating for 2 protons. This pattern is only consistent

with a C 2v c/.v-stereochemistry in 44 as the corresponding C 2h //vms-structure would give

rise to only 2 6.13- diarvl *H signals, irrespective o f slow phenyl rotation. ljC NMR

91


spectra are also consistent with a cis- stereochemistry' in 44. A Dept 135 experiment

confirms that the I3C resonances between 125 ppm and 130 ppm consist entirely o f

aromatic m ethine signals from the 6.13- diaryl rings and the pentacene backbone. The

Dept 135 spectrum displays 6 resonances including 4 w eaker signals for the aromatic

methines o f the 6.13- diarvl rings and 2 stronger signals for the 2 unique aromatic

methines o f the pentacene backbone (Figure 32).

I3P .0 I2L5 127.5 127.1

( p p « )

Figure 32. The arom atic methine region o f a Dept 135 spectrum for the cis-

bisfullerene[60] adduct o f 6.13-di-(4'-hydroxym ethyiphenyl) pentacene. 44.

As with the previous reaction involving 6.13-diphenylpentacene. reaction with 6.13-di-

(4 '-hvdroxym ethylphenyl) pentacene. 38. gives rise to small quantities o f oligomeric

structures that require further effort in order to be fully characterized.

92


Fullerene[60] was reacted with 6.13-diphenethynylpentacene. 31. Once again,

cycloaddition occurred exclusively across the 5.14- positions o f the 6.13-disubstituted.

35. H owever, reaction was sluggish in this case and the corresponding bisfullerene[60]

adduct was not the m ajor product. After 16 hours o f refluxing in CS2 . Cs symmetric

m onoadduct 45 is formed in 83% yield with the corresponding bisfullerene[60] adduct.

46. formed in only 14% yield (Scheme 52). Reaction with 31 is likely sluggish because

o f an electronic effect. Thus, the alkynvl substituents (sp hybridized) at the 6.13-

positions o f 31 render the pentacene ring less electron rich and consequently less reactive

with dienophiles in Diels-Alder chemistry.

Flash silica column chromatography was used to isolate each product. 'H NM R

spectroscopy can be used to distinguish between the products. The 1H NM R spectrum

for Cs sym m etric 45 has a methine singlet at 6.62 ppm which integrates for 2 protons and

two sets o f A A ‘ M M ' aromatic multiplets from the pentacene backbone centered at 7.73

(4 total *H's). 7.93 (2 total ’H 's). and 8.17 ppm (2 total ’H 's). An X X ' singlet is

observed at 9.15 ppm and integrates for 2 protons. Two aromatic multiplets due to the

6.13-diphenethvnyl substituents are centered at 7.46 and 7.58 ppm integrating for 6 and 4

protons respectively (Figure 33). |JC NMR spectra are also consistent with a Cs

symmetric structure.

93


cs. 031

R= \ /45


+

46


Scheme 52. Formation o f Cs symmetric 45 and bisfullerene[60] adduct 46.

94


i

‘» 6 *1.4 'i .Z *1.0 U * .6 * .4 X.D " J l " .6 " .4 ' I I 6.A 6 .6 6.4

(ppm I

Figure 33. 'H NM R spectrum o f the Cs symmetric fullerene[60] monoadduct o f

6.13-diphenethynylpentacene. 45.

Bisfullerene[60] adduct 46 can also be thoroughly characterized by ‘H NMR

spectroscopy. The ‘H NM R spectrum o f 46 shows a m ethine singlet at 6.54 ppm which

integrate for 4 total protons. The A A ‘ MM* aromatic m ultiplets o f the pentacene

backbone are centered at 7.88 and 7.54 ppm . each integrating for 4 protons. The phenyl

protons o f the 6.13- diphenethynyl groups overlap at 7.38 and 7.58 ppm integrating for 6

and 4 protons respectively (Figure 34).

95


* Spinning side bands

CHCI3

Figure 34. ‘H NMR spectrum o f the cis- bisfullerene[60] adduct o f 6.13-

diphenethynvlpentacene. 46.

Unfortunately, there was not enough 46 isolated in order to obtain a ljC NM R spectrum .

Although ljC NM R and mass spectroscopy data is absent, the 'H NM R data alone

prov ide reasonably strong evidence for a bisfullerene[60] adduct structure. How ever, the

stereochemistry o f 46 cannot be determ ined on the basis o f NM R spectroscopy because

there is no hindered rotation o f the phenyl ring in the phenethvnyl substituent. Thus, the

cis- and trans- bisfullerene[60] adducts will possess qualitatively similar 'H and ljC

NMR spectra.

96


Fullerene[60] reaction with 6.13-di(trimethylsilylethvnyl)pentacene. 32. also

gives rise to a C s symmetric m onoadduct. 47. as well as both cis- . 48, and trans- . 49

bisfullerene[60] adducts. 47 was isolated in 8% yield w hile 48 and 49 were isolated in a

combined yield o f 5.6% (Scheme 53).

R= -TMS

48

49

47

Scheme 53. Formation o f cis- and trans- bisfullerene[60] adducts. 48 and 49. in

addition to C\ monoadduct 47.

97


Flash silica column and preparative thin layer chromatographies were utilized to purify

each o f the products. Since the 47. 48. and 49 have similar retention times on the flash

silica column, several additional separations (preparative TLC) were needed in order to

cleanly separate m onoadduct 47 from 48 and 49. The low isolated yields o f products is

not attributed to the reaction itself but more to the difficult isolation o f products. The 'H

NM R spectrum o f 47 shows a methine singlet at 6.53 ppm integrating for 2 protons and

two sets o f AA* M M ' arom atic multiplets from the pentacene backbone centered at 7.57

(4 protons). 7.90 (2 protons) and 8.14 ppm (2 protons). An XX* singlet is seen at 9.03

ppm integrating for 2 protons. The trimethylsilyl group is observed at 0.39 ppm and

integrates for 18 protons (Figure 35). ljC NMR spectra display the appropriate num ber

o f carbon signals and are consistent with a Cs symmetric 47.

impurities in CDCI3

C H C I 3 T M S

Figure 35. 'H NMR spectrum o f the Cs symmetric fullerene[60] monoadduct o f 6.13-

di(trimethvlsilylethynyl)pentacene. 47.

98


The m ixture o f bisfullerene[60] adducts 48 and 49 have also been characterized

by NMR spectroscopy. In the ’H N M R spectrum, the expected methine singlet is seen at

6.44 ppm and integrates for 4 protons. The A A ' M M ' arom atic multiplets from the

pentacene backbone are centered at 7.52 and 7.86 ppm. each integrating for 4 protons.

The trimethylsilyl group is seen at 0.21 ppm and integrates for 18 protons (Figure 36).

Although the *H N M R spectrum shows only one set o f proton signals, the ljC N M R

spectrum (Figure 37) displays two sets o f carbon signals. The appearance o f two sets o f

carbon signals suggests that the reaction between fullerene[60] and 6.13-

di(trimethylsilylethynyl)pentacene. 32. gives rise to both cis- 48 and trans- 49

bisfullerene[60] adducts.

*

* I m p u r i t i e s i n C D C I 3

C H C I 3

*

( 1

Figure 36. 'H N M R spectrum o f cis- and rram -bisfullerene[60] adducts o f 6.13-

di(trimethylsilylethynyl)pentacene. 48 and 49.

99


Looking closely at the l3C N M R spectrum. 4 spJ carbon signals are observed at 56.3.

56.8. 71.9. and 72.5 ppm. The signals centered around 56 ppm are those corresponding

to the bridehead m ethine carbons o f 48 and 49 while the other carbon signals at

approximately 72 ppm correspond to the sp* fullerenic cage carbons. In the region

between 118 ppm and 156 ppm. a total o f 58 sp2 carbons signals are observed

corresponding to the sp2 fullerenic carbons and the sp2 carbons o f the pentacene

backbone. Several especially large signals are seen in this region, the result o f

coincidental overlap. Each cis- and trans- bisfullerene[60] adduct should give rise to 34

sp2 carbon signals for a total o f 6 8 unique sp 2 carbons. In the sp region there are only two

signals seen, one at 101.0 ppm and the other at 106.7 ppm. indicating coincidental

overlap o f the cis- and trans- alkynyl carbons.

140 I <0 140 t JO 120 110 100 40 0 0 ~9 4 0 «0 40 JO 2 0 SO 0

Figure 37. 1jC NM R spectrum o f 48 and 49.

100


A lthough one o f the isomers is present in a roughly 2.5:1 excess. NMR spectroscopy

cannot distinguish between the cis- and trans- diastereom ers in this case. Thus, it is not

known which diasteromer dominates. Either way. the use o f a 6.13- disubstituted

pentacene with sterically dem anding substituents results in a loss o f cis- stereoselectivity.

Fullerene[60] was also reacted with 6.13-diethynvlpentacene. 34. in refluxing

carbon disulfide for 24 hours. The products generated were again a Cs symmetric

monoadduct. 50 along with a bisfullerene[60] adduct o f 6.13-diethynylpentacene. 51. Cs

sym m etric 50 is formed in 2.2% yield while a bisfullerene[60] adduct. 51. is formed in

8 % yield (Scheme 54). Flash silica column chromatography was again used to isolate the

products, and similar to the case with the products o f 6.13-

di(trimethylsilylethynyl)pentacene. chromatographic separations were difficult. The

difficult separation is apparently responsible for the low isolated yields since no

unreacted pentacene is observed at the reaction's conclusion.

'H NM R spectra completely distinguish the 2 products. For the Cs symmetric

m onoadduct. ‘H NMR spectra show a methine singlet at 6.55 ppm integrating for 2

protons and the two sets o f A A ' M M ' aromatic protons centered at 7.58 (4 protons). 7.92

(2 protons) and 8.15 ppm (2 protons). The XX' aromatic proton is seen at 9.09 ppm and

integrates for 2 protons. The acetylinic proton resonates at 3.99 ppm and integrates for 2

protons (Figure 38).

101


50

Scheme 54. Formation o f Cs symmetric 50 and bisfullerene[60] adduct 51.

1 0 2


* c h c i 3[II

Ethyl A cetate

it

. . j \ *i , i j . .

V * * * Vl«*»»4 «*, / < * * * * * * « << m »«Nw «mhm ■

* 2 %.* * .4 « .n *.fc * 2 O l fc.4 fc.o 5 .* 5 .2 4JI 4.4 4.0

t p p m i

Figure 38. lH NM R o f Cs sym m etric fullerene[60] m onoadduct o f 6.13-

diethvnylpentacene. 50.

Due to the small am ount o f product isolated. IjC N M R spectra could not be obtained for

50. The bisfullerene[60] adduct. 51. w as also characterized by 'H NM R spectroscopy.

The !H NM R spectrum for 51 shows a m ethine singlet at 6.44 ppm integrating for 4

protons, and A A 'M M ' aromatic m ultiplets centered at 7.52 and 7.81 ppm. each

integrating for 4 protons. The acetylene protons resonate at 3.80 ppm and integrate for 2

protons (Figure 39). Once again, lack o f sufficient sam ple prohibited the acquisition o f

ljC NMR spectra.

103


b e n z e n e . CHCI3

I

'

1 g | | I*.0 ~A ~.b 7 .4 "-I *.0 6JI 6.b 6 .4 6.2 6 .0 5JI 5 .6 5.4 5.2 5 .0 4JI 4 .6 4 .4 4.2 4 .0 J J

(p p m )

Figure 39. !H NMR spectrum o f bisfullerene[60] adduct o f

6.13-diethvnylpentacene. 51.

Fullerene[60] was also reacted with 6.13-di(THP protected l-propyn-2-

ol)pentacene. 37 to give a Cs symmetric m onoadduct. 52, and a bisfullerene[60] adduct.

53 (Scheme 55).

104


R

R

OTHP

Scheme 55. Formation o f Cs symmetric m onoadduct 52 and bisfullerene[60]

adduct 53.

Because 37 readily degrades, a crude sample o f the pentacene was used for the reaction.

The incorporation o f the tetrahydropvran protecting group introduces 2 stereogenic

centers in 52 and 53. Thus. 52 exists in 2 diastereomeric forms (1 meso. 1 pair o f

enantiomers) for a total o f 3 different stereoisomers. Likewise. bisfullerene[60] adduct

53 could exist in as many as 6 different stereoisomeric forms assuming formation o f both

105


c7.v- and trans- bisfullerene[60] adducts. The existence o f sev eral different stereoisom ers

makes characterization o f 52 and 53 by 'H N M R spectroscopy more difficult. Flash

silica column chrom atography was sufficient to isolate the 3 stereoisomeric C s symmetric

monoadducts from bisfullerene adducts but no t sufficient to separate the individual

diastereomers from one another.

'H NMR spectra o f the stereoisomeric Cs m onoadducts 52 reveal tw o unique

methine signals at 6 .50 and 6.51 ppm. each integrating for 2 protons. Tw o different sets

o f A A 'M M ' m ultiplets are overlapped at 7.57 ppm ( 8 protons) with resolved A A 'M M '

multiplets at 7.90 (4 total protons) and 8.13 ppm (4 protons). The XX ’ arom atic protons

are observed at 9.03 and 9.05 ppm. each integrating for 2 protons. The m ethylene

protons adjacent to the alkvne and the various protons o f the terahydropyran ring are

observed at 5.07 (4 protons). 4.84 ( 8 protons). 3.94 (4 protons). 3.59 (4 protons), and

2.04-1.55 ppm (24 protons). Positive ion electrosprav m ass spectra o f 52 show a strong

[M*Na]~ signal at m /z = 1297.1 which is consistent with the monoaddition product.

'H NMR spectra for the stereoisomeric forms o f 53 reveal a methine singlet at

6.43 ppm integrating for 8 protons and A A ' M M ‘ arom atic multiplets centered at 7.52

and 7.83 ppm. each integrating for 8 protons. The methylene adjacent to the alkvne and

the remaining o f the tetrahydropvran moiety resonate at 4.95 (4 protons). 4 .70 ( 8

protons). 3.83 (4 protons). 3.49 (4 protons) and 2.03-1.4 ppm (24 protons). Positive ion

electrosprav mass spectra o f 53 show a strong [M*Na]~ signal at m/z = 1297.1 which

matches for the m olecular ion o f monoadduct 52. Since the *H NMR spectra are not

consistent with 52. it appears that a retro-Diels-A lder reaction occurs in the mass

spectrom eter releasing an equivalent o f fullerene[60].

106


Since crude 37 was used in the reaction, an accurate isolated yield could not be

obtained. A lthough isolated yields were not obtained. 52 was isolated in greater quantity

than 53. Thus, it is reasoned that in the D iels-A lder reaction between fullerene[60] and

37, 52 is formed higher yield than 53. consistent with the results for other 6.13- diethynyl

substituted pentacenes. Given the lack o f slowly rotating functions at the 6.13- positions

o f 37. cis- and trans- stereochemistry' could not be assigned to any o f the stereoisomers

o f 53.

c. c/x-Stereoselectivity in the formation o fbisfullerene[60] adducts o f 6.13-disubstituted pentacenes

W hen fullerene[60] is added to bare pentacene. cycloaddition occurs

preferentially across the 6.13- positions o f pentacene to give symmetric monoadduct

3. W hen the 6.13- positions o f pentacene are substituted with a group as small as the

ethynyl function, regioselectivity switches to the 5.14- positions. W hen employing 6.13-

diaryl substituted pentacenes. reaction with fullerene[60] is facile and bisfullerene[60]

adducts form in high yield. W hen em ploying 6.13- diethynyl substituted pentacenes.

reaction with fullerene[60] is slow and the interm ediate Cs symmetric monoadduct is seen

as the m ajor product. Regioselectivity' and rate o f cycloaddition aside, the most

surprising aspect o f the reaction between C ao and 6.13- disubstituted pentacenes is the

rem arkably high c7.s-stereoselectivity associated with these reactions.

The reaction conditions discussed thus far have been kinetically controlled ones

(i.e.. refluxing CSi. bp 46 °C). However, the D iels-A lder reaction between fullerene[60]

and 6.13- diaryl substituted pentacene also exhibits high cis- stereoselectivity under

107


therm odynam ically controlled conditions. Thus, upon reacting a 5-fold excess o f

fullerene[60] with 6.13-di(4'-hydroxymethylphenyl)pentacene. 38, in refluxing 1.2

dichlorobenzene (b.p 180 °C) for 24 hours, none o f the corresponding trans-

bisfullerene[60] adduct is formed. Isolated c/.y-bisfullerene[60] adducts rapidly undergo

retro-D iels-A lder reaction in refluxing 1.2-dichlorobenzene demonstrating the

therm odynam ic nature o f the reaction. Purification via flash silica column

chrom atography gives 44 in 55% yield, along with oligermeric products in 43 % yield

(Scheme 56).

1 .2 -d ich lo ro b cn /cn c

55°o iso la ted yield

Schem e 56. Formation o f 44 under thermodynamic conditions.

The lack o f formation of trans-bisfu 11 erene[60] adduct under both kinetically and

therm odynam ically controlled conditions is striking. To help further understand these

108


reactions, a model reaction was investigated and sem i-em pirical and m olecular mechanic

calculations were performed.

Bisfullerene[60] adducts are believed to proceed through C s symmetric

monoadduct. At the intermediate Cs symmetric m onoadduct stage, the second

fullerene[60] molecule can approach in either a syn o r an anti fashion leading to either a

cis- or trans- bisfullerene[60] adduct respectively (Figure 40). The least stericallv

dem anding approach would seem to be the anti approach, however lack o f sufficient

trans- product suggests that more than steric hindrance is influencing the stereochemistry

o f the reaction.

Figure 40. Two different approaches by which a second fuilerene[60] may add to

a Cs symmetric monoadduct.

Addition of Fullerene[60] via anti-approach resulting in frans-bisfullerene[60] adduct.

Addition of Fullerene[60] via syn-approach resulting in c/s-bisfullerene[60] adduct.

109


A Diels-Alder reaction between DM AD. 19. and 6.13-diphenylpentacene. 22.

was run to determine w hether DMAD bisadducts would show similar stereoselectivity for

the cis- isomer. Upon heating 19 and 22 under N : in the absence o f light in refluxing

toluene for 60 hours, a --95% yield o f cis- and trans- bisDMAD addition products 54 and

55 were observed to form (Schem e 57).

Ph

r = c o 2c h 3

22 54 55

43 57

-95% combined yield

Scheme 57. cis- and trans- BisDM AD adducts o f 6.13- diphenylpentacene. 22.

Flash silica column chrom atography allowed for the isolation o f the cis- and trans-

bisD M A D addition products, the c/'.v-bisDMAD adduct eluting last. From 'H NM R

integration, cis- 54 and trans- 55 were observed in a 43:57 ratio. Heating the isolated

products in refluxing toluene, for 3 days resulted in no retro-Diels-Alder reaction

dem onstrating the kinetically controlled nature o f the forward reaction. ‘H NMR. I3C

N M R and DEPT 135 spectroscopy were utilized for the complete characterization o f both

cis- 54 and trans- 55 isomers. Analogous to 24 and 44. hindered rotation o f the 6.13-

1 1 0


diphenyl rings is observ ed which allows for the positive identification o f the cis-

bisDM AD isomer. DEPT 135 spectra best distinguish between the two isomers. The

DEPT 135 spectrum for cis-54 displays seven total aromatic methine carbons. Two

resonances correspond to the aromatic methine carbons on the pentacene backbone, while

the remaining 5 correspond to the unique aromatic methines o f the 6.13- diphenyl

substituents. The observation o f 5 unique signals for the 6.13- diphenyl rings is only

consistent with a Ci\ c7 .v-structure. The DEPT 135 spectrum for trcins-55 consists o f 5

aromatic signals. Once again. 2 signals correspond to the arom atic methine carbons on

the pentacene backbone, with the remaining 3 corresponding to the 3 unique aromatic

methine carbons o f the 6.13- diphenyl substituents. The observation o f 3 aromatic

methine carbons for the 6.13- diphenyl rings is consistent with a C^h /ra/?.v-structure.

The presence o f both stereoisomers in the DMAD reaction demonstrates the

uniqueness o f the reaction with fullerene[60]. That means that the fullerene[60] m oieties

themselves are causing heightened cri-stereoselectivity. Fullerene[60] has exhibited a

strong preference for syn addition under both kinetically and thermodynamically

controlled conditions. Therefore, there must exist an interaction at both the syn transition

state and cis- ground state which significantly stabilizes these structures. It is proposed

that favorable fullerene[60] k- stacking interactions at both the transition state as well as

the ground state lead to the high cis- stereoselectivities observed in the reactions between

6.13- disubstituted pentacenes and fullerene[60].

Non-bonding interactions between aromatic systems play an important role in the

stabilization o f a variety o f m olecules including nucleic acids69 and proteins . 70 Favorable

7r-stacking interactions can occur in three different ways. Favorable 7t-stacking

1 1 1


interactions have been observed face to face (i.e.. where the two aromatic systems face

one another), edge to face. (i.e.. where one ^-system is perpendicular to the other k-

system) or face to face offset, (i.e.. where the ^-systems are parallel-displaced). These

three conformations are known to exist as energy minima on the benzene dim er potential

energy surface. Both molecular mechanics and ab intio71 calculations suggest that

optimal spacing between ^-stacking centroids o f the benzene rings is 3.7- 4.1 A with

binding energies on the order o f 1-1.3 kcal/mol. Calculations predict the optimal spacing

between n- stacking centroids o f the toluene dim er to be 3.5-3.6 A with binding energies

o f 2.5-2 . 6 kcal/m ol.'6a Given the strength o f these ^-stacking interactions, it is

conceivable that similar interactions between fullerene[60] functions in bisfullerene[60]

adducts may alter the cis-/trans- ratio o f bisfullerene[60] adducts. Since there are

structural differences between benzene and fullerene[60], the optimal spacing between

fullerene[60] moieties in a cis- bisfullerene[60] adduct would differ. Nonetheless, the

notion o f the strong influence o f ̂ -stacking interactions in bisfullerene[60] adduct

formation seems reasonable provided the fullerene[60] functions are separated by

distances close to 3.5-4.1 A.

MM2 calculations suggest that, the nearest carbon atoms on adjacent

fullerene[60] moieties in 24 reside on C 5. not Cf, rings. When separate planes defined by

the atoms o f each C 5 ring are dropped an equal distance to a horizontal plane, the

corresponding base angle is 8 6 °. Thus, the 2 C 5 rings are nearly parallel to one another

(parallel at 90°). Since the fullerene[60] surface is curved, the carbon atoms are

pvramidalized. The pyramidalization angle for fullerene[60] is 1 1 .6 ° . 72 The consequence

o f this pyramidal ization angle is that the p-orbitals o f the carbons atoms on nearest

112


neighbor C> rings in 24 are not radiating directly toward one another. Consequently, the

optimal centroid to centroid spacing between nearest adjacent C 5 rings in 24 should be

sm aller than the centroid to centroid spacings calculated for the dim ers o f benzene and

toluene. MM2 calculations place the centroids o f nearest neighbor C 5 rings in 24 3 .3 A

apart. An X-ray structural analysis confirm s that the centroids o f the nearest neighbor C 5

rings are indeed 3 .3 A ( 3 .2 8 4 A ) apart. This separation between nearest neighbor C$ rings

in 24 is consistent and perhaps optim al for it- stacking between adjacent fullerene[60]

m oieties in 24 and related structures.

At the transition state leading to cis- bisfullerene[60] adduct. the two fullerene[60]

moieties should be slightly closer than 3.3 A apart, due to the flattened nature o f the

pentacene backbone at the transition state. The large number o f a tom s involved in these

systems precludes locating semi-em pirical transition state structures. However, a crude

syn transition state structure was m odeled using a combination o f semi-empirical and

m olecular mechanics calculations. First, the transition state leading to the cis-bisethylene

adduct o f pentacene was located by PM3 semi-empirical m ethods. W hile constraining all

other atoms, the hydrogens o f each ethylene subunit were rem oved and replaced with 116

carbon atoms in the form o f 2 fullerene[60] moieties. Next, the fullerene[60]-pentacene

bond lengths were assigned a value o f 2.26 A. a reasonable value for the bond length at a

transition state involving fullerene[60] (Table 3). The fullerene[60] moieties were then

allowed to minimize via an iterative MM2 routine in which all a tom s and bonds along the

pentacene backbone were constrained. 0 The resulting transition state structure should be

considered a crude estim ate only, but still deserving o f a close look. Thus, the centroid to

centroid distance between nearest neighbor C 5 rings is calculated to be 3 .2 A . slightly

113


sm aller than the ground state calculations and in accordance with expectations (Figure

41).

Table 3. PM3 calculated transition states

Dienophile Diene T.S. 5.14-Bond

Lengths (A )A

C 2 H4

pentacene 2 . 2 0 1

6.13- diphenvlpentacene. 2 2 2 . 2 0 1

6.13-di(trimethylsilylethvnyl) pentacene. 32

2.206

o - o

pentacene 2.258

6.13-diphenylpentacene. 2 2 2.265

6.13-di(trimethylsilylethynvI) pentacene. 32

2.259

114


Figure 41. MM2 calculated ground state o f a cis- bisfullerene[60] adduct (top)

and PM 3-M M2 calculated sy«-transition state (bottom ) preceding formation o f cis-

bisfullerene[60] adduct.

Computational studies have demonstrated that the centroids o f nearest neighbor

C> rings on the fullerene moieties are separated an appropriate distance for favorable n-

stacking interactions. These interactions may greatly influence the cis!tram

stereoselectivity seen in the product. Although the reaction with 6.13- diaryl substituted

pentacenes have generally shown high c/.s-stereoseIectivities. reaction with the 6.13-

di(trimethvlsilylethynyl)pentacene. 32. did not exhibit the same stereoselectivity. Small

changes in the ^-stacking geometries and/or distances between fullerene[60] functions

can have significant impact on jr-stacking binding energies. Computational studies done

115


on the reaction with 6.13-di(trimethylsilylethynyl)pentacene. 32, suggest that the bulky

trimethylsilyl group m ay aiter the ^-stacking interactions seen at the syn-transition state.

Experimental results show the formation o f both stereoisom ers suggesting that indeed the

trimethylsilyl group altered the ^-stacking interaction at the .n>7-transition state. The anti

transition state must also be altered but to a different extent.

d. Anions o f c/.y-bisfullerene[60] adducts o f 6.13- disubstituted pentacenes

One o f the goals in the synthesis o f m -bisfullerene[60] adducts was to study their

electrochemical properties. Electrochemical experiments were preform ed on 24 and 44.

Both cyclic voltammetry (CV) and differential pulse polarography (D PP) techniques

were employed using 1 .2 - dichlorobenzene as solvent, tetrabutylam m onium

tetraflouroborate (TBA BF4) and tetrabutylammonium hexaflourophospate (TBAPF6 ) as

supporting electrolytes, and a glassy working carbon electrode.

Fullerene[60] has the ability to reversibly accept up to six electrons . 74 Since the

two fullerene[60] m oieties in c7.v-bisfullerene[60] adducts are in close proximity to one

another, electron reduction o f one o f the fullerene[60] moieties likely influences the

reduction potential o f the other. CV and DPP traces o f 24 (Figure 42) reveal that the first

2 reductions occur at very nearly the same potential (—0.5 V) giving an overall 242'

species. As 24 is further reduced, there is greater dispersion between successive 1

electron steps due to a build up o f charge repulsion between the fullerene[60] moieties.

Thus, the third 1 electron reduction occurs at a potential o f -0.90 V while the fourth does

not occur until a potential o f -1 .02 V is reached. The separation o f half-wave potentials

116


is even more evident upon exam ining the fifth and sixth 1 electron reductions which

occur at -1.32 and -1.62V respectively. As expected, the results suggest that the

reduction o f one fullerene[60] moiety influences the reduction o f the other (Table 4).

+ 1 2

* 8 -

<3c£3o

o-

- 1 .o- 0.6 - 1.4 - 1 . B

Potential.V

c£w3o

*16

Potential.V

Figure 42. CV (Top) and DPP (Bottom) o f 24.

117


Table 4. Half-wave potentials for 24

Ph * ° f electrons

A B

Number o f electrons Half-wave potential for

FuIIerene[60] A

Half-wave potential

for Fullerene[60] B

A E | / 2

1 -0.52 V

2 -0.52 V 0

j -0.90 V

4 -1.02 V 0.12 V

5 -1.32 V

6 -1.62 V 0.30 V

Interestingly, cis- bisfullerene[60] adduct 44 does not display the same electrochemical

results as 24. Unlike 24. 44 exhibits what appears to be simultaneous electron reductions

o f both fullerene[60] moieties with little or no resolution observed between successive

odd and even numbered reductions (Figure 43).

118


+ 1 6

* 12 -

♦ 8 -

O-

_ r _.

- 1.0- 0.2+ 0.2 -0 8 - 1.8- 1.4

Potential.V

+120

+105

<c'Bl=

o

+ 15-

- 0.4 - 0.6 - 1.2 - 1 .6 - 2.0

Potential.V

Figure 43. CV (Top) and DPP (Bottom ) o f 44

119


The large qualitative disparity betw een the electrochemical results obtained for 24 and 44

are not understood at this time. Further electrochemical w ork needs to be done to

determine the electrochemical differences between 24 and 44.

Xu developed a method by which fullerene[60] can be chem ically reduced to

fuIlerenefbO]1* or fullerene[60]2' depending upon choice o f so lvent . 0 Thus, treating

fullerene[60] with zinc dust under nitrogen in caustic w ater and tetrahydrofuran gives a

stable solution o f fullerene[60]‘\ However, treating the sam e fullerene[60] w ith zinc dust

under nitrogen in caustic water and dimethylsulfoxide produced a stable solution o f the

fullerene[60]2'(S chem e 58).

- i 2 -

Scheme 58. Chemical reduction o f fullerene[60] using zinc dust to give

fullerenelhO]1' and fullerene[60]2'.

Separate solutions o f both anions were studied by UV-VIS spectrophotom etry.

Fullerene[60]''has characteristic absorbances at 1075 and 994 nm. while the

1 2 0


fullerene[60]2' has characteristic absorbances at 945 and 836 nm. Using X u 's technique.

24 was separately reduced with zinc in both tetrahvdrofuran and dimethyl sulfoxide. The

corresponding anions w ere analyzed by UV-VIS spectrophotometry. Since the reduction

o f fullerene[60] goes exclusively to fullerene[60]‘' in THF. we expect that 24 and 44 will

be converted to 242' and 442' under sim ilar conditions. Recall that CV and DPP traces

reveal that the first and second reductions for 24 and 44 are observed at similar reduction

potentials (Figures 42 and 43). A c/.y-bisfullerene[60] adduct having an overall charge o f

2- could have a 1- charge on each fullerene[60] moiety. I f so. then the UV-VIS spectrum

should resemble the U V -V IS spectrum for fu llerene[60]'\ However, if an intramolecular

electron transfer occurs to give one fullerene[60]2' and one neutral fulierene[60] moiety,

then the UV-VIS spectrum should resemble that observed for fiillerene[60]2\ 24 was

chem ically reduced w ith zinc dust under nitrogen in a tetrahvdrofuran and caustic water

m ixture. A UV-VIS spectrum was recorded and shown to resem ble the fullerene[60]N

spectrum. Thus. 24 reduced in this fashion has strong UV/VIS absorbances at 999 and

1074 nm (Figure 44). very sim ilar to the 994 and 1075 nm absorbances reported for

fullerene[60]‘'. A lthough electron transfer between the 2 fullerene[60] moieties in 242'

cannot be ruled out. it appears that the dom inant species present in solution has a 1 -

charge on each fullerene[60] moiety. 24 was also reduced by zinc dust under nitrogen in

caustic water and dim ethyl sulfoxide to give presumably a

244' species. UV-VIS spectrophotom etry shows a different spectrum than that reported

for fullerene[60]2'. Thus. 244' had strong absorbances at 713 and 876 nm. substantially

different from the characteristic absorbances for fullerene[60]2' at 945 and 836 nm.

(Figure 45).

121


1.0 -

I 0.8

MO •00 1000 1060MO 1100Wavatongth (nm)

Figure 44. UV/VIS spectrum o f 242' prepared by reducing 24 with Zn dust in

THF solvent

0.7

0.3 -

•00700 1000MOWamtength (nm)

Figure 45. UV/VIS spectrum o f 244' prepared by reducing 24 with Zn dust in

DM SO solvent

1 2 2


The qualitative differences between the UV-VIS spectra o f fullerene[60]2' and 244’ may

be the result o f a unique electron distribution in 244' w hich m inim izes charge repulsion.

Further w ork is needed to study this and other possibilities.

123


CONCLUSIONS AND FUTURE DIRECTIONS

Diels-Alder reactions between fullerene[60] and 6.13- disubstituted pentacenes

produce novel t7.s-bisfullerene[60] adducts. Fullerene[60] cvcloadds across the 6.13-

positions o f pentacene under both kinetically and thermodynamically controlled

conditions. However. D iels-A lder reaction between fullerene[60] and 6.13- disubstituted

pentacene enables the regioselective formation o f Cs sym m etric monoadducts in which

cycloaddition occurs across the 5.14- positions. A ddition o f a second equivalent o f

fullerene[60] gives cis- bisfullerene[60] adducts in high yield and with exceptional cis-

stereoselectivitv. A com bination o f experimental data, m odel compound studies, and

com putational data suggests that n- stacking interactions at both the syn transition state as

well as the cis- ground state are responsible for the high cis- stereoselectivity observed.

W ith the form ation o f c7s-bisfullerene[60] adducts achieved, the future focus o f

the research can be sw itched to the synthesis o f more elaborate structures. Diels-Alder

reactions between fullerene[60] and 6.13- diaryl substituted pentacenes are already

know n to produce oligom eric structures containing more than two fullerene[60] moieties.

G iven the bulky nature o f the 6.13- diaryl substituted pentacenes as well as the preference

for n- stacking transition states and ground states, there ex ist few low energy isomers for

trisadduct formation (i.e.. three fullerene[60] moieties on one molecule). Presumably.

D iels-A lder reaction betw een 23 and 24 should give interesting trisadducts. N oting the

124


interesting electrochem istry o f 24. trisadducts should show even m ore intriguing CV and

DPP results.

Isolation o f 23 would also lead to prom ising reactions. In particular. 23 could be

reacted with other fullerenes (e.g.. C~o) in order to determine if heightened cis-

stereoselectivity is also observed in a mixed bisfullerene adduct.

125


EXPERIMENTAL SECTION

1. General Methods.

Melting points (mp) were recorded on a Thomas Hoover capillary melting point

apparatus and are uncorrected.

'H NM R spectra (*H NMR) were obtained on a Bruker AM360 FT-NMR spectrometer

operating at 360.134 MHz. All chemical shift (5tI) values are reported in parts per

million (ppm) relative to Me4Si (TMS) unless otherw ise noted.

ljC NM R spectra ( ljC NMR) were obtained on a Bruker AM360 FT-NMR spectrometer

operating at 90.556 MHz. All chemical shift (5c) values are reported in parts per million

(ppm) relative to Me4Si (TMS) unless otherwise noted.

Low resolution mass spectra (M S) were obtained on a Hewlett-Packard model 5988A

GC/MS quadropolar spectrometer equipped with a 25-m eter methyl silicone (O V -1)

capillary column and was performed by the University o f New Hampshire

Instrumentation Center.

Ultraviolet-Visible-Near Infrared Spectrophotometers (UV/Vis/NIR) wrere obtained on a

Cary 500 and absorptions are reported in wavelengths (nm).

Electrosprav Mass Spectroscopy was performed by the University o f New Hampshire

Mass Spectroscopy Labs on a Finnigan MAT model LCQ IT-MS spectrometer equipped

with a Paul Ion Trap.

126


2. Solvents

A 'ole: A ll solvents were used without further purification unless otherwise noted.

A cetic Acid (CH 3CO 2 H) was obtained from J.T. Baker.

Acetone (reagent grade) was obtained from Fisher Chemical Co.

Carbon Disulfide (CS->) was obtained from EM Science.

Chloroform (CHCI3 ) was obtained from EM Science.

Deuterated NM R solvents were obtained from Cambridge Isotope Laboratories.

1.2-Dichlorobenzene (C^LLCM was obtained from Acros Organics Co.

1 ,4-D ioxane ((CLLCFLhCh) was obtained from Aldrich Chemical Co.

Ethvlether ((C FE C IThO ) was obtained from VW R Chemical Co.

Ethvl Acetate ( CH 3C O 2CH 2CH 3 ) was obtained from Pharmco.

Tetrahvdrofuran (THF) was obtained from Acros Organics Co. It was distilled over Na°

from a solution containing benzophenone ((C 6 H 5 )2CO) as indicator.

Toluene (PhCFL) was obtained from EM Science. It was distilled over Na° prior to use.

3. Colum n Chromatography

Sea sand was obtained from Fisher Chemical Co.

Silica gel: Silica gel (40jim Flash Chromatography Packing) was obtained from J.T.

Baker and Silica gel (38-75pm Flash Chromatography Packing) was obtained from

Natland International Co.. Research Triangle Park. N.C.

127


4. Reagents

Note: A ll reagents were used without fu r th er purification unless otherwise noted.

Ammonium Chloride ( NH4 CI) was obtained from Aldrich Chem ical Co.

Benzoauinone (C 6 H4 0 2 ) was obtained from Aldrich Chemical Co.

Bromine (Br3) was obtained from Acros Organics Co.

4-Brom obenzoic acid (BrC 6H4 C 0 2 H) was obtained from A ldrich Chemical Co.

1 -Brom o-2-fluorobenzene (C 6 H4 BrF) was obtained from A ldrich Chemical Co.

/•e/y-Butvldimethvlsilvlchloride (CftHi^SiCl) was obtained from Aldrich Chemical Co.

n-Butvllithium (C 4 HqLi) was obtained from Acros Organics Co.

/•-Butvilithium (CiHqLi) was obtained from Aldrich Chemical Co.

3-Chloroperoxvbenzioc acid (C1C6 H4 C 0 3 H) was obtained from Aldrich Chem ical Co.

3.4-dihvdro-2 H -pvran (C 5H8O) was obtained from Aldrich Chem ical Co.

Diisobutvlaluminum hvdride [(C F^hC H C FFbA LH was obtained from Aldrich

Chemical Co.

Dimethvlacetvlene dicarboxvlate (C H 3 0 2 CCC C 0 2 CH3) was obtained from Aldrich

Chemical Co.

Fullerener601 (C()0) was obtained from M ER Chemical Co.

Iodine (F) was obtained from M allinckrodt Chemical Co.

M ethvlhvdrazine (CH 3N 2 fF ) was obtained from Acros Organics Co.

M ethvlchloroformate (CH 3C0 2 C 1) was obtained from Acros O rganics Co.

Pentacene (C 2 2 H 1.1) was obtained from A ldrich Chemical Co.

Phenvlacetvlene (C«H6) was obtained from Aldrich Chemical Co.

Phenvllithium (C 6H 5Li) was obtained from Aldrich Chemical Co.

128


Potassium Hvdroxide (K.OH) was obtained from J.T.Baker Chemical Co.

Potassium Iodide (K.I) was obtained from M allinckrodt Chemical Co.

Propargvl alcohol (C 3 H 3O) was obtained from Aldrich Chemical Co.

Pvrrole (C4H5N) was obtained from Aldrich Chemical Co.

Sodium Borohvdride (NaBH4) was obtained from Aldrich Chemical Co.

Sodium Hvdroxide (NaOH) was obtained from J.T.Baker Chemical Co.

Sodium Iodide (N al) was obtained from M allinckrodt Chemical Co.

1.2.4.5 Tetrabrom obenzene (CftfFBra) was obtained from Aldrich Chem ical Co.

Tetrabutvlammonium fluoride ((CH?(CH->h).iNF) was obtained from Fluka Chemical Co.

Tin(Il) Chloride (SnCl->) was obtained from Fisher Chemical Co.

(Trimethvlsilvl)acetvlene ((C fhbS iC C H ) was obtained from GFS Chem ical Co.

(j-xvlene (CftH-i(CHri->) was obtained from Aldrich Chemical Co.

5. Syntheses

A 'ole: All routine solvent evaporations were carried out on a standard rotary evaporator using aspirator pressure unless otherwise noted.

Fullerene[60|-pentacene monoaddition product (3). To a round-bottomed

flask with a reflux condenser. fullerene[60] (0.647 grams. 0.9 mmol) was dissolved in

toluene (150mL). Pentacene (0.05 grams. 0.18 mmol) was then added and the purple

solution was allow ed to reflux for a period 64 hours. The resulting brown solution was

concentrated in vacou. The crude product w'as then separated via column

chromatography using 1:1 (v:v) carbon disulfide:hexanes as eluent. The first band was

unreacted fullerene[60]. followed by a m ixture o f fullerene[60] and m onoaddition

129


product. A second colum n was run using 1:1 (v/v) carbon disulfiderhexanes eluent to

further separate unreacted fullerene[60] and product. The brow n second band was

collected as the fullerene[60]-pentacene mono adduct (R r= 0.76. 0.158 grams.

0 .158mmol) in 8 8 % overall isolated yield. 3: 'H N M R (360 M Hz. CS2-CDCI3 ) 6 6 .1 4

(s. 2H). 7.54 (m. 4H). 7.98 (m. 4H). 8.27 (s. 4H): 13C N M R (90.56 M Hz. CS2-acetone-

d 6 ) 6 58.5. 72.6. 125.1. 126.9. 128.7. 133.6. 137.6. 139.4. 140.5. 142.5. 142.9. 143.0.

143.4. 145.5. 146.2. 146.3. 147.0. 147.2. 155.9.

N-methyl-5,14-dihydropentacen-S,14>imine (5). To a flame dried three-necked

flask under nitrogen. N-m ethylisoindole. 7. (1 gram. 7.6 mmol), and 2.3-

dibrom oanthracene. 16 (0.426 grams. 1.2 mmol), w ere suspended in dry toluene (200

mL) and cooled to 0 °C. To the yellow suspension w as added phenyllithium (4mmol)

over a period o f 1 hour via syringe pump. After com plete addition o f the phenyllithium.

the resulting brown solution was allowed to stir and w arm ed to room temperature

overnight. To the brown solution was added maleic anhydride (5 grams. 50 mmol)

predissolved in methanol (100 ml). After stirring for ten minutes, the solution was

washed with a 6 M sodium hydroxide solution (3 X 100 mL). The organic layer was

dried and concentrated in vacou. Flash silica gel colum n chrom atography was done

using 95:5 (v:v) chloroform:ethyl acetate eluent. 5 (R r= 0.08. 0.083 grams. 0.27mmol)

was isolated in 21% yield. 5: 'H NM R (360 MHz. C D C I3 : Note: broadening o f signals

is due to pyramidal inversion o f the methyl group) 6 2 .30 (s. 3H). 5.06 (s. 2H). 7.07 (s.

2H). 7.39 (s. 2H). 7.44 (m. 2H). 7.80 (s. 2H). 7.95 (m. 2H). 8.24 (s. 2H): l3C NMR

(90.56 MHz. CDCI3 )- 6 36.4. 72.0. 125.2. 126.1. 126.2. 128.0. 131.0. 131.8.

130


N-mcthyl isoindole (7). 7 w as prepared by a published method . ' 4 a a '-

dibromo-o-.xyiene. 13 (13.2 grams. 0.05m ol). was predissolved in diethyl ether (350 ml)

in a 500 mL beaker. To the clear solution was added dropw ise methylhydrazine (5.1

grams. 0.11 mol) predissolved in diethyl ether (10 mL). The solution immediately

became hot and cloudy. The suspension was allowed to stir overnight with a watchglass

cov ering the beaker. The ether was decanted leaving behind white-green solids w hich

were caked to the sides o f the beaker. The solids along with powered potassium

hydroxide (35 grams. 0.625 mol) w ere grinded together w ith a mortar and pestle. The

solids becom e yellowish, extremely hot. and em itted w ater and ammonia. The crude N-

m ethviisoindole was sublimed at 0.01 torr at 100°C. 7 (4.5 grams. 0.035mol) was

isolated in 70% yield. (Note: 7 dim erizes in the presence o f ambient light. For long

term storage, solid 7 should be remov ed from am bient light and placed in a cool

environm ent. For further discussion, see Results and Discussion.) 7: !H NM R (360

MHz. CDCL ) 6 4.00. (s. 3H). 6.94 (m . 2H). 7.06 (s. 2H). 7.53 (m. 2H): l3C NM R

(90.56 M Hz. CDCI3 ) 6 49.0. 111.7. 119.4. 120.6. 124.6.

Pyrrole-1 -carboxylate, methyl ester (10). To a flame dried round-bottom ed

flask w ith a reflux condenser, freshly distilled pyrrole (9.67grams. 0.144 mol) was

dissolved in dry ether (200 mL). The reaction flask was placed under nitrogen and

cooled to 0 °C. 17-Butyllithium (0.04 mol) was added and the reaction mixture was

allowed to retlux for 1 hour. To the suspension, methylchloroformate ( 6 grams. 0.06

mol) was added dropwise at a rate such that the reaction was under control. The ether

131


was concentrated in vacou and the sweet smelling oil was vacuum distilled at 24 mm.

collecting the fraction between 73-77°C. 10 (2.7 grams. 0.22mol) was isolated in 54%

yield. 10: 'H N M R (360 MHz. CDC13) 6 3.89 (s. 3H). 6.23 (m. 2H). 7.28 (m. 2H):

l3C NM R (90.56 MHz. CDC13 ) 6 54.0. 108.1. 112.5. 120.1.

N-methylcarboxylate-l,4-dihydronapthalen-l,4-imine (11). To a flame dried

round-bottom ed flask fitted with a reflux condenser and a dropping funnel, magnesium

turnings (0.4 grams. 0.016 mol) were added. l-Brom o-2-fluorobenzene (2.8 grams.

0.016 mol) was dissolved in dry' tetrahydrofuran (15 mL) and added to the addition

funnel. 1 -Bromo-2-fluorobenzene (2 mL) was added dropwise to the round-bottomed

flask with stirring. Once the suspension became cloudy. 10 (2 grams. 0.016 mol) was

added. The remaining 1 -bromo-2-fluorobenzene solution was added dropwise over a 1-

hour period. The reaction was allowed to reflux overnight. The crude reaction was

quenched with a saturated ammonium chloride solution and the organic layer was dried

over magnesium sulfate. The crude solution was concentrated in vacou to a black oil.

The black oil was dissolved in chloroform and filtered through activated charcoal to give

a yellow solution, which was concentrated in vacou. 11 (0.667 grams. 0.003 mol) was

isolated in 21 % yield. 11: 'H NMR (360 MHz. CDC13: Note: broadening o f signals is

due to pyramidal inversion o f the methyl group) 5 3.60 (s. 3H). 5.56 (broad s. 2H). 6.95

(m .4 H ). 7.23 (b roads. 2H): 13C NMR (90.56 MHz. CDC13 ) 5 5 3 .0 .66 .4 .121 .1 .125 .3 .

143.3. 148.3. 156.0.

132


N-methyl-l,4-dihydronapthalen-l,4-imine (12). To an oven dried round-

bottomed flask flushed with nitrogen. 11 (2.25 grams. 11 mmol) was dissolved in dry

toluene (50 mL). DIBAL-H (22 mmol) was added to the solution. A fter fours hours

another portion o f DIBAL-H (22 mmol) was added. The reaction was allowed to stir

overnight. The reaction flask was quenched with methanol, and the precipitate was

washed with chloroform (3 X 100 mL). The filtered solution and the chloroform

washings were added to toluenesulfonic acid m onohvdrate (3.5 grams. 16 mmol). The

organic layer was extracted with water until the washings became clear. The acidic

aqueous layer was basified with sodium hydroxide pellets in an ice bath. The alkaline

aqueous layer was cooled and extracted with chloroform . 12(1 .54 gram s. 9.8 mmol) was

isolated in 89% yield. 12: !H NMR (360 M Hz. CDCI3 : Note: broadening o f signals is

due to pyramidal inversion o f the methyl group) 5 2.08 (3H. s). 2.34 (3H. s). 4.45 (1H. s)

4.60 ( 1H. s). 6 . 6 8 (4H. s). 6.92 (4H. m). 7.18 (4H. m): 13C NMR (90.56 M Hz. CDC13 ) 5

36.0. 36.9. 71.9. 72.7. 120.3. 123.6. 124.4. 125.0. 138.6. 143.9. 147.7. 150.2.

a a ’-Dibromo-a-xylene (13). 13 was prepared by a published m e t h o d .T o a

three-necked round-bottomed flask was fitted a reflux condenser with a gas trap,

thermometer, and dropping funnel. To the three-necked flask was added o-xylene (53.35

grams. 0.5 mol) which was stirred and heated to 120°C. Bromine (191.78 grams. 1.2

mol) was added to the addition funnel and then added dropwise to the hot o-xylene. The

bromine was added at a rate such that the evolution o f hydrogen bromide was not

excessive. As the bromine was added to the o-xylene. the color o f the bromine

immediately disappeared. Bromine was allowed to drip slowly overnight, being careful

1 ->j


bromine was continually being added to the hot solution. After com plete addition o f

bromine, the crude brown oil was poured directly into a 600 ml beaker. The hot oil was

allowed to cool and solidify. The solid product was filtered and w ashed with cold

chloroform in the hood. A fter the solids w ere washed with cold chloroform . 13 (89.2

grams. 0.34 mol ) was allowed to dry and isolated in 6 8 % yield. (N ote: a-brom o-o-

xylene is a by-product o f the reaction and is a potent lachrymator. T hus, the crude

reaction m ixture m ust be handled in the hood at all times.) NMR spectra were consistent

with published spectra.

2,3-Dibromoanthracen-9,10-imine (15). To a flame dried three-necked round-

bottomed flask flushed with nitrogen was added dry toluene (400 m L). 1.2.4.5-

Tetrabrom obenzene (15.3 grams. 39 m m ol) and N-methylisoindole (4.5 grams. 35 mmol)

were added and the suspension was cooled to 0 °C. Phenyllithium (42 mmol) was added

dropwise via syringe pum p ov er a 1-hour period. The reaction flask w as allowed to

warm to room tem perature overnight. M aleic anhydride (5 grams. 50 mmol) was

predissolved in methanol (50 mL) and added to the crude reaction flask. After stirring for

ten minutes, the solution was washed with a 6 M sodium hydroxide solution (3 X 100

mL). The organic layer was dried over m agnesium sulfate and concentrated in vacou.

Flash silica gel colum n chromatography was run using 95:5 (v.v) chloroform :ethyl

acetate eluent. 15 ( R t- = 0 .2 2 . 3.83 grams. 0 . 1 0 mmol) was isolated in 27% yield. 15: 'H

NMR (360 M Hz. CDCL: Note: broadening o f signals is due to pyram idal inversion o f the

methyl group ) 5 2.26 (s. 3H). 4.89 (s. 2H) 7.04 (s. 2H) 7.32 (s. 2H ). 7.57 (s. 2H): l3C

NMR (90.56 MHz. CDCI3 ) 6 36.6. 72.3. 121.0. 123.5. 126.1. 128.7.

134


23-Dibromoanthracene (16). 15 (3.7 grams. 9.4 m m ol) was dissolved in the

m inim um amount o f chloroform. To the brown solution was added 70-95% m-

chloroperbenzoic acid (5.0 grams. 0.029 mol) predissolved in 95% ethanol (30 mL). The

brown solution im m ediately turned into a yellow suspension. The yellow suspension was

stirred for 2 hours. The yellow solids were then filtered via vacuum filtration and washed

with cold 95% ethanol. 16 (3.25 grams. 8.9 mmol) was collected in 95% yield. 16: *H

N M R (360 MHz. benzene-dh ) 5 7.19 (m. 2H). 7.63 (m. 2H). 7.70 (s. 2H). 7.92 (s. 2H)

Fullercne[60] N-methyl-5,14-dihydropentacen-5,14-imine adduct (17).

Fullerene[60] (0.5 grams. 0.69 mmol) and 5 (0.05 gram s. 0.16 mmol) were dissolved in

(9 -dichIorobenzene (50 mL) in a round-bottomed flask. The purple solution was refluxed

for 36 hours. The resulting purple-brown solution was concentrated in vacou. The crude

product was suspended in chloroform and the excess fullerene[60] was filtered off. Flash

silica gel colum n chromatography using carbon disulfide as eluent allowed for removal o f

the remaining unreacted fullerene[60]. Switching to a 7:3 (v:v) chloroform:carbon

disulfide eluent allowed for isolation o f 17 (0.133 gram s. 0.13 mmol) in 83 % yield.

17: ‘H NM R (360 M Hz. CDC13 ) 5 3.20 (s. 3H). 5.98 (s. 1H). 6.39 (s. 1H). 7.56 (m.

4H). 7.98 (m .4H ). 8.17 (m .2H ). 8.22 (s. 2H): 13C N M R (90.56 MHz. CDC13) 5 38.07.

53.02. 58.48. 71.50. 71.53. 119.64. 122.56. 123.89. 124.29. 125.62. 125.98. 126.07.

126.09. 127.87. 127.95. 127.99. 128.62. 129.36. 129.39. 132.68. 132.70. 133.54. 136.58.

136.72. 136.74. 136.76. 138.54. 138.55. 138.70. 138.73. 138.94. 138.96. 139.70. 139.73.

139.75. 141.29. 141.31. 141.67. 141.80. 141.94. 142.18. 142.53. 142.55. 142.70. 142.73.

135


144.25. 144.97. 145.01. 145.05. 145.08. 145.10. 145.77. 145.80. 146.01. 147.14. 147.16.

154.72. 154.75. 154.77. 154.88.

Bispentacene adducts o f fullerene[60| including 18. To a round-bottomed flask

was added fullerene[60] (0.129 grams. 0.18 mm ol), toluene (75 mL). and pentacene

(0.100 grams. 0.36 m m ol). The purple solution was allowed to reflux for a period o f 64

hours. The resulting brow n solution was concentrated in vacou. The crude product was

washed with chloroform and filtered until the washings became practically colorless.

The brown solution was concentrated in vacou and separated by flash silica gel column

chromatography using 9:1 carbon disulfide h exanes (v:v) as eluent. The first band

eluented was unreacted fullerene[60]. while the second band was 3. The third band

collected was trans- 2 bispentacene adduct 18 followed by a collection o f trans- and e-

bispentacene adducts (R r= 0.46. 0.200 grams. 0.157 mmol) recovered in 49% combined

yield. The fifth band contained a collection o f cis- bispentacene adducts (Rf= 0.38.

0.049. 0.038 mmol) recovered in 12 % combined yield. 18: *H NM R (360 MHz. C S 2-

CDCL 6 5.95 (s. 2H). 6.14 (s. 2H). 7.45 (m. 4H). 7.58 (m. 4H). 7.85 (m. 4H). 8.07 (m.

8 H). 8.31 (s. 2H). 8.42 (s. 2H): l3C NMR (90.56 MHz. CS 2-CDC13). 5 58.40. 58.88.

70.87. 71.08. 124.90. 124. 96. 125.30. 125.40. 126.76. 126.94. 126.97. 128.64. 128.83.

128.87. 133.36. 133.39. 133.67. 134.92. 135.89. 139.19. 139.27. 139.29. 139.64. 140.94.

141.89. 142.51. 142.68. 142.94. 143.00. 143.20. 143.99. 144.35. 144.58. 145.48. 145.50.

145.63. 146.01. 146.38. 146.59. 146.71. 146.97. 147. 52. 147.64. 148.38. 153.05. 153.52.

153.72.

136


Pentacene-dimethvl acetvlenedicarboxvlate adduct (20). To a round-bottomed

flask \\Tapped in aluminum foil, o-dichlorobenzene (50 ml) was added along with a

collection o f bispentacene adducts o f ftillerene[60] (0.040 grams. 0.03 mmol) and

dimethyl acetvlenedicarboxvlate (0.313 grams. 2.2 mmol). The brow-n solution was

refluxed for 4 hours. The o-dichlorobenzene was removed by vacuum distillation along

with excess dimethyl acetvlenedicarboxvlate. The crude solids were w ashed with

chloroform (5 mL) to rem ove 20. The remaining solids were dissolved in carbon

disulfide and concentrated in vacou to give fullerene[60] (0.017 grams. 0.024 mmol). 20

(0.031 grams. 0.074 m m ol) was isolated from the chloroform wash. 20: 'H NM R (360

M Hz. CDCL ) 5 3.81 (s. 6 H). 5.68 (s. 2H). 7.40 (m. 4H). 7.73 (m. 4H). 7.84 (s. 4H): 13C

N M R (90.56 MHz. C D Cb ) 6 30.11. 122.5. 126.2. 127.7. 127.8. 130.6. 131.9. 139.3.

143.1.

Diphenylmethanofullerene (21). To a round-bottom ed flask was added a

collection o f trans- and e- bispentacene adducts o f fullerene[60] (0.45 gram s. 0.035

mmol) were dissolved in chloroform (20 mL). The flask w'as wrapped in aluminum foil

and fitted with a septum cap. Diphenyidiazomethane (0 . 0 2 0 grams. 0 . 1 0 2 mmol) was

dissolved in chloroform (5 mL) and added via syringe into the flask. The reaction was

allowed to stir for 5 hours. The brown solution was concentrated in vacou. Flash silica

gel column chromatography using carbon disulfide as eluent was used to separate

unreacted bispentacene adducts o f fullerene[60] (0 . 0 2 0 grams. 0.016 m m ol) from

diphenyidiazomethane addition products (0.022 grams). (Note: ‘H and ljC NM R spectra

are complicated due to the various isomers formed in the reaction.) In a round-bottom ed

137


flask wrapped in alum inum foil, diphenyidiazom ethane addition adducts (0 . 0 2 2 grams)

and dimethyl acetvlenedicarboxvlate (0.313 grams. 2.2 m m ol) were dissolved in o-

dichlorobenzene (50 mL). The brow n solution was refluxed for 4 hours. The o-

dichlorobenzene was removed by vacuum distillation along w ith excess dimethyl

acetvlenedicarboxvlate. The crude solids were washed with ethanol (5 mL) to remove

20. The remaining solids were dissolved in carbon disulfide and concentrated in vacou.

21 (0.013 grams. 0.015 mmol) was isolated in 44% yield. N M R spectra were consistent

with the reported spectra for 2 1 . 24

6,13-diphenylpentacene (22). 22 was prepared by the published m ethod . 58 28

(0.336 grams. 0.73 mmol) was added to a round-bottomed flask along with potassium

iodide (0.5 gram. 3 mmol) and glacial acetic acid (20 mL). The brown solution was

refluxed for 2 hours. The brow nish-red solution was allowed to cool to room temperature

and the purple solids were gravity filtered and washed with w ater to give 2 2 (0.28 grams.

0.66 mmol) 92% isolated yield. (Note: 22 oxidizes in the presence o f ambient light

while in solution. For long-term storage. 22 should be kept dry and removed from

am bient light.) 22: 'H NMR (360 M Hz. benzene-d6 ) 6 6.90 (m. 4H). 7.37 (m. 4H). 7.43

(m. 6 H) 7.58 (m. 4H). 8.60 (m. 4H): ljC N M R (90.56 M Hz. benzene-d6 ) 5 125.5. 126.2.

128.8. 129.1. 129.4. 131.8. 132.1. 137.6. 140.4.

ci5-Bisfullerene(60| adduct o f 6,13-diphenylpentacene (24). To a round-

bottom ed flask fitted with a reflux condenser was added fullerene[60] (0.108 grams. 0.15

m mol) in carbon disulfide (100 mL). The reflux condenser w as fitted with a septum cap

138


and nitrogen w as flushed through the reaction vessel. 22 was added (0.014 grams. .03

mmol) and the flask and condenser were wrapped in alum inum foil. The purple solution

was refluxed o v e rn ig h t. The resulting purple-brown solution was concentrated in vacou.

Repeated flash silica gel column chromatography was done using 9:1 carbon

disulfiderhexanes (v:v) as eluent. 24 (Rf = 0.85. 0.048 gram s. 0.026 mmol) was isolated

in 85% yield. 24: 'H NM R (360 M Hz. CDC13 ) 6 5.76 (s. 4H). 7.13 (m. 2H). 7.33 (m.

2H). 7.44 (m. 4H). 7.51 (m. 2H). 7.60 (m. 4H). 7.66 (2H). 7.73 (m. 2H): 13C NMR

(90.56 MHz. CDCI3 ) 5 55.37. 72.52. 125.79. 127.43. 128.14. 128.85. 129.01. 129.82.

130.01. 136.33. 136.86. 137.65. 139.02. 139.71. 140.03. 141.59. 141.66. 141.91. 141.96.

142.03. 142.26. 142.45. 142.55. 142.60. 142.93. 144.60. 144.70. 145.22. 145.30. 145.39.

145.51. 145.83. 146.15. 146.22. 146.40. 146.53. 147.55. 155.39. 155.98.

6,13 pentacenequinone (26). 26 was prepared by the published method .60 To a

three-necked flask fitted with a reflux condenser. 27 (122 grams. 0.29 mol) was dissolved

in dimethylformam ide (400 mL). To the clear solution was added benzoquinone (12.5

grams. 0.12 m ol) and sodium iodide (109 grams. 0.73 mol). The resulting brown

suspension was heated and stirred at 120 °C overnight. The flask was allowed to cool to

room temperature and the yellow solids were filtered via vacuum filtration. The yellow

solids were washed with water, saturated sodium bisulfite solution, and allowed to oven

dry at 180 °C. 26 (31.08 grams. 0.11 mol) was isolated in 92% yield. (Note: After

w ashing with w ater and saturated sodium bisulfite solution, if the solids remain brow™,

then they were washed with cold chloroform.) 26: !H N M R (360 MHz. CDCI3 ) 6 7.73

(m. 4H). 8.14 (m. 4H). 8.97 (s. 4H).

139


а , a , a ’, a ’ Tetrabromo-o-xylcne (27). 27 was prepared by the published

m ethod . ' 9 To a three-necked round-bottomed flask was fitted a reflux condenser with a

gas trap, thermometer, and dropping funnel. To the three-necked flask was added o-

xylene (106 grams. 1 mol) which was stirred and heated to 120 °C in an oil bath.

Bromine (700 grams. 4.37 mol) was added to the addition funnel and then dropwise to

the hot o-xylene. The bromine was added at a rate such that the evolution o f hydrogen

bromide was manageable. As the bromine was added to the o-xylene. the color o f the

bromine immediately disappeared. Bromine was allowed to drip slowly into the reaction

mixture for several hours overnight. The resulting crude brown oil was poured directly

into a 600 mL beaker. The hot oil was allowed to cool and solidify. 27 was filtered and

washed with cold chloroform. 27 (278 grams. 0.66 m ol) was dried and isolated in 6 6 %

yield. (Note: The crude reaction mixture must be handled in the hood at all times.)

27: 'H NMR (360 M Hz. CDCfy Note: The 'H NM R spectrum is broadened due to slow

bond rotation about the methylene carbons: 'H integrations are not reported.) 6 4.60 (s).

7.16 (broad m). 7.36 (broad m). 7.67 (broad m): ljC N M R (90.56 MHz. C D Cb: Note:

The ijC NM R spectrum is broadened due to slow bond rotation about the methylene

carbons) 6 36.8. 129.4. 130.5. 137.7.

б,13- diphenylpentacene-6,13-diol (28). 28 was prepared by the published

m ethod.-' To a flame dried three-necked flask flushed with nitrogen was added dry

toluene (200mL). To the dry toluene was added 26 (1 gram. 3 mmol). 26 was stirred at -

78 °C for ten minutes and then phenyllithium (8.5 m m ol) was added dropwise over a

140


fifteen-m inute period. The reaction was allowed to warm to room temperature over a

period o f two hours and stirred at room temperature for an additional hour. The green

solution was quenched with a saturated ammonium chloride solution. The resulting

orange-brown solution was dried with magnesium sulfate and concentrated in vacou.

The orange solids were first dissolved in dioxane then chloroform was added to

precipitate out one o f the diastereom ers. 28 (0.336 gram s. 0.73 mmol) was isolated as a

diastereom eric mixture (cis- and trans-) in 24% com bined yield. (Note: If crude 28 is

acceptable, then the precipitation step can be omitted. C rude 28 (0.91 grams. 2 m m ol)

was collected in 65% yield.) 28: 'H NM R (360 MHz. DMSO-d6: Note: The 'H N M R

spectrum reported is for one diastereom er which selectively precipitates from

chloroform -dioxane: it is not known which one) 5 6.67 (s. 2H). 7.18. (m. 2H). 7.29 (m .

4H). 7.42 (m. 4H). 7 .7 l(m . 4H). 7.80(m. 4H). 7.97(s. 4H): 13C NM R (90.56 MHz.

DM SO -d6: Note: The ljC N M R spectrum reported is for one diastereomer) 8 74.7. 126.3.

126.4. 127.2. 127.8. 127.9. 128.5. 132.9. 141.4. 151.7.

6,13'diphenethynylpentacene-6,13-diol (30). 30 was prepared by the published

m ethod . 61 To a flame dried three-necked flask flushed w ith nitrogen was added

phenylacetvlene (2.75 grams. 27 mmol) and dry toluene (200m l) cooled to -78 °C. n-

Butvllithium (12 mmol) was added dropwise over a 1 -hour period via a syringe pump.

After addition o f the butyllithium. the flask was kept at -7 8 °C and allowed to stir for an

additional hour. 26 (1 gram .3 m m ol) was added and the reaction flask was stirred for 4

hours at room temperature. The green solution was quenched with a saturated

am m onium chloride solution and the organic layer was w ashed with water and dried o ver

141


m agnesium sulfate. The brow n solution was concentrated in vacou. Crude 30 (.740

grams. 1.5 mmol) was collected as a diastereomeric m ixture (cis- and trans-) in 50 %

crude com bined yield. 30: 'H NM R (360 MHz. C D C b ) 8 7.33 (m. 6 H). 7.54 (m. 8 H).

7.95 (m .4 H ). 8.71 (m. 4H).

6.13-diphenethynylpentacene (31). 31 was prepared by the published m ethod . 61

30 (0.640 grams. 1.3 mmol) was predissolved in dioxane (100 ml). Tin (II) chloride

(0.750. 3.9 mmol) was predissolved in 50% acetic acid solution (200 ml) and the excess

solids were filtered. The two clear solutions were com bined. The resulting blue

suspension was allowed to stir overnight in the absence o f am bient light. The blue solids

were filtered via a vacuum filtration to give 31 (0.453 gram s. 1 mmol) in 71% isolated

yield. (Note: 31 oxidizes in solution in the presence o f am bient light. For long-term

storage. 31 should be kept dry and removed from am bient light.) 31: ’H NMR (360

MHz. C D C b ) 8 7.47 (m. 4H). 7.55 (m. 6 H). 7.97 (m . 4H). 8.14 (m. 4H). 9.34 (s. 4H).

6.13-Di(trimethylsilylethynyl)pcntacenc (32). 33 (1.28 grams. 2.5 mmol) was

dissolved in dioxane (150 mL). Tin (II) chloride (3.6 gram s. 20 mmol) was predissolved

in 50% acetic acid solution (260 mL) and the excess solids were filtered. The two clear

solutions were combined and the resulting blue suspension was allowed to stir at room

tem perature for 0.5 hours in the absence o f ambient light. The blue solids were collected

via vacuum filtration, washed with cold methanol and allow ed to dry. 32 (0.424

gram s.0.9m m ol) was isolated in 36% yield. (Note: 32 oxidizes in solution in the

presence o f ambient light. For long-term storage. 32 should be kept dry and removed

142


from ambient light.) 32: 'H NMR (360 M Hz. CDCI3 . no TM S ) 5 0.58 (s. 18H) 7.42 (m.

4H). 8.02 (m. 4H). 9.17(s. 4H).

6.13-Di(trimethyisilvlethynyl)pentacene-6,13-diol (33). To a flame dried three-

neck flask under a nitrogen environment containing dry toluene(200 mL) was injected

trimethylsilylacetylene (4.1 grams. 41.7 mmol). The flask was cooled to 0 °C and to it

was added /7-butyllithium (32.5 mmol) dropwise over a period o f fifteen minutes. The

resulting yellow solution was allowed to stir at 0 °C for one hour. To the yellow solution

was added 26 (1 gram . 3 mmol). The suspension was allowed to warm to room

temperature and stirred overnight. The reaction was quenched with water, the toluene

layer was dried with magnesium sulfate and concentrated in vacou to give 33 (0.76

grams) in 50 % crude yield. 33: !H NMR (360 MHz. CDCI3 : Note: 'H NMR shifts are

referenced to protio CDCI3 at 7.27 ppm) 6 0.26 (s. 18H). 3.89 (s. 2H). 7.54 (m. 4H).

7.91 (m. 4H). 8.62 (s. 4H): l3C NM R (90.56 M Hz. CDC13: Note: 13C NMR shifts are

referenced to the CDCI3 triplet centered at 77.0 ppm) 6 -0 .2 . 69.8. 93.5. 107.0. 125.8.

126.9. 128.2. 133.1. 136.1.

6.13-Diethynylpentacene (34). 32 (0.04 grams. 0.08 mmol) was dissolved in

chloroform (< lm l). Tetrabutylammoniumfluoride trihydrate (0.06 grams. 0.23 mmol)

was dissolved in chloroform (<1 ml). The two solutions were mixed together and

agitated for two minutes. The blue solution was passed through a silica gel cartridge

using carbon disulfide as eluent. 32 was completely converted to 34 as judged by ’H

NMR spectroscopy. (Note: 34 rapidly oxidizes and dimerizes in solution in the presence

143


o f ambient light. Thus. 34 was immediately reacted w ith fullerene[60] w ithout isolation.

Isolated yields are not reported.) 34: 'H NMR (360 M Hz. CDCI3 : !H NM R shifts are

referenced to protio CDCI3 at 7.27 ppm) 6 4.42 (s. 2H). 7.43 (m. 4H). 8.04 (m . 4H). 9.25

(s. 4H).

Tetrahydropyran protected propargyl alcohol (35). In an Erlenmeyer flask,

propargvl alcohol (15 grams. 0.27 mol) was dissolved in chloroform (100 mL). To the

clear solution was added 3.4-dihydro-2 //-pyran (24 gram s. 0.28 mol). The solution was

cooled to 0 °C. To the cold solution was added with stirring toluenesulfonic acid

monohydrate (1 gram. 5 mmol). The reaction was stirred for 2 hours. Diethyl ether was

added and the solution was washed with water and brine. The organic layer w as dried

with magnesium sulfate and concentrated to an oil. 35 (15.4 grams. .11 mol) was

v acuum distilled at 24 mm at 89 °C and isolated in 41% yield. 35: ‘H NM R (360 MHz.

CDCI3 ) 6 1.40-1.68 (m .6 H). 2.32 (m. lH ).3 .3 8 (m . lH ).3 .6 7 (m . 1H). 4.08 (m. 2H).

4.66 (m. 1 H): l3C NMR (90.56 MHz. CDC15 ) 6 1 8 .8 .2 5 .2 .3 0 .0 .5 3 .7 .6 1 .6 .7 4 .0 .7 9 .6 .

96.4.

6,13-di(THP protected Z-propyn-l-oO pentacene^O -diol (36). To a flame

dried three-neck tlask under a nitrogen environment was added 35 (5.4 grams. 38 mmol)

dissolved in dry toluene (200 ml). The flask was cooled to 0 °C and to it was added n-

butyllithium (34 mmol) dropwise over a period o f fifteen minutes. To the yellow

solution was added 26 (1 gram. 3 mmol) and the suspension was stirred for 72 hours.

The resulting orange solution was quenched with saturated ammonium chloride solution.

144


The toluene layer w as dried with magnesium sulfate and concentrated to an orange oil

(1.9 grams) (Note: M ass reported is for the m ixture o f crude 36 and unreacted 35; *H

and ljC NM R spectra are complex due to the six stereoisomers produced in the reaction

four which give rise to unique NMR spectra. NM R shifts are not reported. For further

discussions, see Results and Discussion.)

6.13-di(THP protected 2-propyn-l-ol)pentacenc (37). Crude 37 (1.9 grams)

was predissolved in dioxane (100 ml) and added to a filtered solution o f tin(II) chloride

(2.0 grams. 10.4 m m ol) dissolved in 50% acetic acid (200 mL). The reaction

immediately turned blue. A fter stirring for 1 hour, the reaction turned to a green

suspension. The dioxane solution was extracted with chloroform to give a green solution

which was concentrated in vacou to give crude product (0.078 grams). (Note: 37 rapidly

oxidizes and dim erizes in solution in the presence o f ambient light. Thus. 37 was

immediately reacted with fullerene[60] w ithout isolation. Isolated yields are not

reported. Due to the rapid degradation o f 37. N M R spectra are not reported. For further

discussions, see Results and Discussion.)

6.13-di-(4’-hydroxymethylphenyl) pentacene (38). To a round-bottom ed flask

was added 6.13-di-(4'-hvdroxymethyIphenyl) pentacene-6.13-diol. 42 ( 0.307 grams.

0.56mmol). predissolved in dioxane (10 m l) along with tin (II) chloride (0.750 grams. 4

mmol). To the golden solution was added 10M HCL (2 ml). The solution immediately

turned pink and stirred for fifteen minutes. The reaction flask was cooled and water w as

145


added to precipitate out the product (0.103 grams. 0.22 mmol). ( Note: If crude 38 is

green in color, wash with cold carbon disulfide which removes the yellow impurities.)

38: 'H NM R (360 MHz. CDCI3 ) 5 4.97 (s. 4H). 7.44 ( m. 4H). 7.67 (s. 4H). 7.72 (m.

4H).7.75 (m . 4H). 7.88 (m. 4H).

4-bromobenzylalcohol (39). 39 was prepared by the published method .64 To a

flame dried three-necked flask, sodium borohydride (3.4 grams. 0.09 mol) was suspended

in dry tetrahvdrofuran (125 mL). To the flask was slowly added 4-bromobenzoic acid

(15 grams. 0.075 mol) over 30 minutes. Iodine (9.5 grams. 0.375 mol) was dissolved in

dry tetrahvdrofuran (20mL) and added dropwise over a 1 hour period. The reaction was

stirred overnight and quenched with methanol. Ether (100 mL) was added and the

organic layer w as washed w ith brine (4 x lOOmL). The organic layer was dried with

magnesium sulfate and concentrated to an oil. Flash silica gel colum n chromatography-

using 7:3 chloroform .hexanes as eluent gave 39 (8.4 grams. 0.045 mol) in 50% isolated

yield. NM R spectra were consistent with the literature NM R spectra . 64

terS-Butyldimethylsilyl protected p-bromo benzyl alcohol (40). To an

Erlenmeyer flask was added. 39 (2.5grams. 0.013 mol) dissolved in chloroform (50 mL).

To this solution was added /erf-butyldimethylsilylchloride (2.2 grams. 0.015 mol)

predissolved in chloroform (10 ml). Imidazole ( l . lg . 0.016 mol) was added and

immediately solid precipitate formed. The reaction was stirred for an additional hour.

The solids were filtered and the solution was concentrated in vacou. The crude material

was purified via flash silica gel column chromatography using 9:1 chloroform/hexanes

146


(r:v) as eluent. The first band isolated was 40 (3.56 grams. 0.011 mol) recovered in 87%

yield. 40: 'H NMR (360 MHz. CDC13 ) 6 0.25 (s. 6 H). 1.10 (s. 9FI). 4.80 (s. 2H). 7.29

(d. 2H). 7.54(d. 2H): l3C NMR (90.56 MHz. C D C b ) 626.1. 64.4. 120.7. 127.7. 131.4.

140.5.

6,13-di-(4,-hydroxymethylphenyl) pentacene-6,13-diol (42). To a flame dried

three-necked flask flushed with nitrogen was added 40 (3.56 grams. 12 mmol) dissolved

in dry toluene (200 mL). The mixture was cooled to -78 °C. re/V-Butyllithium (26

mmol) was added dropwise over a 1-hour period via syringe pump. After addition o f the

re/7-butyllithium. the flask was stirred for an additional hour at -7 8 °C. 26 (1 gram. 0.3

mmol) was added and the reaction flask was allowed to warm to room temperature and

stirred overnight. Tetrabutylammonium fluoride (3.0 grams. 0.011 mol) was predissolved

in methanol and added to the crude reaction mixture. The reaction mixture was stirred

for 1 hour at room temperature. Flash silica gel column chromatography using

chloroform as eluent effectively removed fast eluting impurities. Switching to a 9:1 (v;v)

chloroformrethyl acetate mixture enabled the isolation o f 42 (Rt = 0.06. 0.307 grams. 0.56

mmol) in 19 % yield. 42: ‘H NMR (360 MHz. CDCI3 ) 6 4.39 (s. 2H). 4.7 (s. 2H). 6 . 6 (s.

2H). 7.33 (s. 2H). 7.46 (m. 4H). 7.59 (m. 2H). 7.79 (s. 2H). 8.00 (s. 2H). 8.02 (s. 2H).

8.60 (s. 2H).

Pentacene Dimer (43). Pentacene was added with CDCI3 to an NMR tube. The

NMR tube was allowed to sit in ambient light for a period o f 16 hours. 43: 'H NMR

(360 M Hz. CDCL3) 6 6.36 (s. 2H). 7.49 (m. 4H). 7.86 (m. 4H). 7.94 (s. 2H).

147


c/s-Bisfullerene adduct o f 38 (44). To a round-bottom ed flask fitted with a

reflux condenser was added fullerene[60] (1.7 grams. 2.3 m m ol) predissolved in carbon

disulfide (100 ml). The reflux condenser was fitted with a septum cap and nitrogen was

flushed through the reaction vessel. To this solution was added 38 (0.07 grams. 0.14

mmol). The flask and condenser were wrapped in aluminum foil and the solution was

refluxed o v e rn ig h t. Unreacted fullerene[60] was recovered on a flash silica gel column

with carbon disulfide as eluent. Switching to a 75:25 chloroform rethvl acetate (v:v)

eluent gives 44 (0.210 grams. 0.11 m m ol) in 75% isolated yield. 44: *H NM R (360

MHz. C D C h ) 6 4.85 (s. 4H). 5.75 (s. 4H). 7.07 (d. 2H). 7.43 (d. 2H). 7.43 (m. 4H). 7.57

(m. 4H). 7.61 (d. 2H). 7.74 (d. 2H): l3C N M R (90.56 MHz. CDC13 ) 5 55.09. 64.94.

72.25. 125.54. 127.09. 127.32. 129.64. 130.05. 135.87. 136.67. 136.75. 138.81. 139.58.

139.87. 140.63. 141.39. 141.52. 141.64. 141.83. 141.84. 142.01. 142.36. 142.41. 142.45.

142.61. 142.77. 144.43. 144.51. 145.13. 145.16. 145.21. 145.22. 145.25. 145.52. 145.96.

146.02. 146.24. 146.32. 147.34. 155.01. 155.61.: l3C N M R(D ept 135. CDC13) 5 55.3

(u). 65.16 (d). 125.8 (u). 127.3 (u). 127.5 (u). 129.9 (u). 130.3 (u):

Electrospray M.S. m /z = 1954.

Cs symmetric fullerene(60| monoadduct o f 31 (45). To a round-bottom ed flask

fitted with a reflux condenser. fullerene[60] (0.430 grams. 0.6 m m ol) was dissolved in

carbon disulfide (100 mL). The reflux condenser was fitted with a septum cap and

nitrogen was flushed through the reaction vessel. To it was added 31 (0.057 grams. 0.1


148


refluxed overnight. The resulting purple- brown solution was concentrated in vacou.

Repeated column chrom atography perform ed using 9:1 carbon disulfide:hexanes v:v to

give 45. 45 (Rr = 0.85. 0.118 grams. 0.083 m m ol) was isolated in 83% yield. 45: lH

NM R (360 MHz. CD CI3 ) 5 6.62 (s. 2H). 7.46 (m. 6 H). 7.58 (m. 4H). 7.73 (m .4H ). 7.93

(m. 2H). 8.17 (m. 2H). 9.15 (s. 2H): 13C N M R (90.56 MHz. CDC13 ) 5 56 .96 .71 .99 .

85.99. 100.79. 117.91. 123.26. 126.48. 126.52. 126.58. 128.09. 128.60. 128.72. 128.96.

129.93. 131.98. 132.49. 136.91. 137.11. 140.14. 140.19. 140.53. 141.23. 141.72. 141.79.

142.06. 142.12. 142.28. 142.34. 142.58. 142.94. 143.00. 143.14. 144.65. 144.66. 145.36.

145.46. 145.48. 146.20. 146.24. 146.44. 146.47. 147.60. 154.75. 154.99.

Bisfullerene[60| adduct of 31 (46). To a round-bottomed flask fitted w ith a

reflux condenser was added fullerene[60] (0.430 grams. 0.6 mmol) dissolved in carbon

disulfide (100 ml). The reflux condenser was fitted with a septum cap and nitrogen was

flushed through the reaction vessel. To this solution was added 31 (0.057 grams. 0.1


refluxed overnight. The resulting purple-brown solution was concentrated in vacou.

Repeated flash silica gel column chrom atography was performed using 9:1 carbon

disulfide:hexanes (v;v) to give 46. 46 (R r= 0.73. 0.027 grams. 0.014m m ol) w as isolated

in 14% yield. 46: 'H NM R (360 MHz. CDC13 ) 6 6.54 (s. 4H). 7.38 (m. 6 H). 7.54 (m.

4H). 7.58 (m. 4H) 7.88 (m. 4H).

Cs symmetric fullerene[60| monoadduct of 32 (47). To a round-bottom ed flask

with a fitted reflux condenser was added fullerene[60] (0.564 grams. 0.78 m m ol) was

149


dissolved in carbon disulfide (200 ml). The reflux condenser was covered with a fitted

septum cap and nitrogen was flushed into the top. To this solution was added 32 (0.075

grams. 0.16 mmol). The flask and condenser were wrapped in alum inum foil and the

solution was refluxed overn igh t. The resulting purple-brown solution was concentrated

in vacou. 47 was isolated utilizing both flash silica gel column chrom atography and

preparatory' thin layer chromatography with carbon disulfide as eluent. 47 (0.015 grams.

0.013 mmol) was isolated in 8 % yield. 47: *H NMR (360 MHz. CDCb: Note: !H NM R

shifts are referenced to protio CDCb at 7.27 ppm) 6 0.39 (s. 18H). 6.53 (s. 2H). 7.57 (m .

4H). 7.90 (m. 2H) 8.14 (m. 2H). 9.03 (s. 2H): l3C NM R (90.56 M Hz. CDCb: Note: I3C

NMR shifts are referenced to the CDCb triplet centered at 77.0 ppm ) 5 1 .0 0 . 56.74.

71.90. 100.97. 106.69. 117.82. 126.26. 126.29. 126.50. 127.96. 128.44. 129.59. 132.32.

136.64. 136.90. 139.86. 140.08. 140.53. 141.60. 141.69. 141.88. 141.96. 142.04. 142.27.

142.38. 142.50. 142.53. 142.90. 142.93. 143.08. 144.59. 144.61. 145.20. 145.25. 145.28.

145.32. 145.39. 145.44. 145.59. 146.13. 146.18. 146.36. 146.39.147.57. 154.85. 154.92.

Bisfullerene[60| adducts of 32 (48 and 49). To a round-bottom ed flask fitted

with a reflux condenser was added fullerene[60] (0.564 grams. 0.78 mmol) dissolved in

carbon disulfide (200 mL). The reflux condenser was covered with a septum cap and

nitrogen was flushed into the top. To this solution was added 32 (0.075 grams. 0.16


refluxed overnight. The resulting purple-brown solution was concentrated in vacou. 48

and 49 were isolated together utilizing both column chromatography and preparatory thin

layer chromatography with carbon disulfide as eleunt. 48 and 49 (0.017 grams. 0.009

150


m mol) were collected in a 5.6 % com bined yield. 48. 49: *H NM R (360 MHz. CDCI3 :

Note: 'H NM R shifts are referenced to C H C ^ a t 7.27 ppm ) 5 0.21 (s.18H). 6.44 (s. 4H).

7.52 (m. 4H). 7.86 (m.4H): 13C N M R (90.56 MHz. CDCI3 : l3C N M R shifts are

referenced to the CDCI3 triplet centered at 77.0 ppm) 6 0.17. 56.76. 71.90. 72.45. 100.97.

106.70. 117.82. 126.27. 126.29. 126.51. 127.63. 127.71. 127.87. 127.96. 128.45. 12959.

132.32. 136.65. 136.89. 136.90. 136.97. 139.86. 139.92. 139.99. 140.09. 140.53. 141.06.

141.58. 141.60. 141.70. 141.89. 141.98. 142.01. 142.05. 142. 23.. 142.27. 142.30. 142.39.

142.50. 142.53. 143.09. 144.59. 144.62. 144.69. 145.02. 145.25. 145.29. 145.33. 145.35.

145.39. 145.44. 145.60. 146.14. 146.18. 146.36. 146.39. 146.45. 147.56. 147.58. 147.60.

154.85. 154.92. 155.19.

Cs symmetric fullerene[60| monoadduct o f34 (50). To a round-bottomed flask

with a fitted reflux condenser was added fullerene[60] (0.240 grams. 0.33 mmol)

dissolved in carbon disulfide (200 ml). The reflux condenser was fitted with a septum

cap and nitrogen was flushed into the top. 34 was prepared as stated in the above

procedure. Freshly prepared 34 (0.04 grams. 0.08 mmol) was immediately placed into

the reaction flask. The flask and condenser were wrapped in alum inum foil and the

solution was refluxed overnight. The resulting purple-brown solution was concentrated

in vacou. 50 was isolated utilizing both flash silica gel colum n chromatography and

preparatory thin layer chromatography with carbon disulfide as eleunt. 50 (0.002 grams.

0.00016 mmol) was isolated in 2.2 % yield. (Note: Due to instability. 34 was not

isolated. The mass o f 34 and the calculated % yield for 50 assum e complete conversion

151


o f 32 to 34.) 50: *H N M R (360 M Hz. CDCI3) 5 3.99 (s. 2H). 6.55 (s. 2H ). 7.58 (m. 4H).

7.92 (m. 2H). 8.15 (m. 2H). 9.09 (s. 2H).

Bisfullerene[60| adduct o f 34 (51). To a round-bottom ed flask w ith a fitted

reflux condenser. fullerene[60] (0.240 grams. 0.33 m m ol) was added dissolved in carbon

disulfide (200 mL). The reflux condenser was fitted w ith a septum cap and nitrogen was

flushed into the top. Freshly prepared 34 (0.04 gram s. 0.08 mmol) was im m ediately

placed into the reaction flask. The flask and condenser were wrapped in alum inum foil

and the solution was refluxed overnight. The resulting purple-brown solution was

concentrated in vacou. 51 was isolated utilizing both flash silica gel colum n

chromatography and preparatory thin layer chrom atography with carbon disulfide as

eleunt. 51 (0.011 grams. 0 .0064 mmol) was isolated in 8 % yield. (Note: D ue to

instability. 34 was not isolated. The mass o f 34 and calculated % yield o f 51 assume

com plete conversion o f 32 to 34.) 51: lH NMR (360 M Hz. CDC13) 5 3.80 (s. 2H). 6.44

(s. 4H). 7.52 (m. 4H). 7.81 (m . 4H).

Cs symmetric fullerene[60| monoadduct o f 37 (52). To a round-bottom ed flask

fitted with a reflux condenser was added fullerene[60] (0.240 grams. 0.33 m m ol)

dissolved in carbon disulfide (100 mL). The reflux condenser was fitted w ith a septum

cap and nitrogen was flushed through the reaction vessel. To the purple solution was

added crude 37 (0.078 gram s). The flask and condenser was wxapped in alum inum foil

and the solution was refluxed overnight. The resulting purple-brown solution wras

concentrated in vacou. U nreacted fullerene[60] was rem oved via flash silica gel column

152


chromatography using carbon disulfide as eluent. Sw itching to a 75:25 chloroformrethyl

acetate (v:v) eluent allowed for collection o f the crude product. The crude product was

washed with 95% ethanol to remove any residual 35 leaving both m ono- and bisaddition

products. Preparatory thin layer chromatography using 75:25 carbon

disulfidexhloroform eluent (v;v) was sufficient to isolate 52 (Rf = 0.037 grams. 0.03

mm ol). (Note: Due to instability. 37 was not isolated. Thus a % yield could not be

calculated. The *H NM R and ljC NM R spectra o f 52 are com plex due to the three

possible stereoisomers produced in the reaction.) 52: 'H N M R (CDCI3 )- 8 2.04-1.55

(m. 24H). 3.59 (m. 4H). 3.94 (m. 4H). 4.84 (s. 8 H). 5.07 (m . 4H). 6.50 (s. 2H). 6.51 (s.

2H). 7.57 (m. 8 H). 7.9 (m. 4H). 8.13 (m. 4H). 9.03 (s. 2H). 9.04 (s. 2H). Electrospray

M.S. m z = 1297.K M~). 961.7.

Bisfullerene[60)adduct of 37 (53). To a round-bottom ed flask fitted with a

reflux condenser was added fullerene[60] (0.240 grams. 0.33 mmol) dissolved in carbon

disulfide (100 mL). The reflux condenser was fitted with a septum cap and nitrogen was

flushed through the reaction vessel. To the purple solution was added crude 37 (0.078

grams). The flask and condenser were \\Tapped in alum inum foil and the solution was

refluxed overnight. The resulting purple-brown solution was concentrated in vacou.

Unreacted fullerene[60] was removed via flash silica gel colum n chromatography using

carbon disulfide as eluent. Switching to a 75:25 chloroform :ethyl acetate (v:v) eluent

allowed for collection o f the crude product. The crude product was washed with 95%

ethanol to remove any residual 35 leaving both mono- and bisaddition products.

Preparatory thin layer chromatography with 75:25 carbon disulfidexhloroform (v. v) as

153


eluent was used to isolate 53 (0.020 grams.0.01 mmol) (Note: Due to instability. 37 was

not isolated. Thus, a % yield for 53 was not calculated.) 53: 'H N M R fC D C h ) 5 1.4-

2.03 (m. 24H). 3.49 (m. 4H ). 3.83 (m. 4H). 4.70 (s. 8 H). 4.95 (m . 4H). 6.43 (s. 8 H). 7.52

(m. 8 H). 7.83 (m. 8 H).: ,3C NMR (CDC13 ) 5 19 .09 .22 .68 .25 .33 .26 .49 .29 .35 .30 .34 .

54.71.56.17. 56.20. 62.17. 70.61.72.40. 80.80. 95.20. 96.60. 117.97. 126.21. 126.22.

127.67. 136.89. 136.98. 139.79. 139.81. 140.19. 140.22. 140.25. 141.06. 141.49. 141.51.

141.60. 142.03. 142.26. 142.29. 142.30. 142.32. 142.34. 142.36. 142.53. 142.57. 142.94.

142.98. 144.63. 145.13. 145.36. 145.38. 145.44. 145.47. 146.16. 146.20. 146.21. 146.47.

146.50. 147.56. 154.85. 154.88. 155.05.

Cis a nd trans dimethyl acctylcnedicarboxylate bisadduct o f 22 (54 and 55)-

To a round-bottomed flask fitted with a reflux condenser was added 22 (0.500 grams.

1.16 mmol). The reflux condenser was fitted with a septum cap and nitrogen was flushed

through the reaction vessel. To this solution was added dimethyl acetvlenedicarboxvlate

(1 . 8 8 grams. 13.24 mmol) predissolved in toluene (30 ml) and the solution was refluxed

for 60 hours. The resulting yellow solution was concentrated in vacou. Flash silica gel

colum n chromatography using 95:5 chloroform:ethvl acetate (v:v) was sufficient to

isolate cis- 54 and trans- 55 bisaddition products. (Note: 54 and 55 were synthesized to

their compare NMR spectra with those o f 24 and 25. Small pure samples of 54 and 55

were isolated in order to obtain their respective NM R spectra.) 54: 'H NMR (360 MHz.

CD C b ) 6 3.73 (s. 12H). 5.31 (s. 4H). 6.93 (m. 4H). 7.13 (m. 6 H). 7.57 (m. 8 H): l3C

NM R (90.56 MHz. C D C b) 6 49.93.52.24. 123.63.125.36. 127.87. 128.44. 128.62

129.45. 130.43. 133.66. 136.96. 139.63. 144.03. 147.51. 165.71; l3C NMR (Dept 135.

154


CDC13) 5 50.00 (u). 52.23 (u). 123.63 (u). 125.36 (u). 127.87 (u). 128.44 (u). 128.62 (u).

129.45 (u). 130.43 (u): 55: *H NM R (360 M Hz. C D C b ) 5 3.63 (s. 1 2 H). 5.26 (s. 4H).

6.92 (m. 4H). 7.10 (m. 4H). 7.31 (m. 4H )7.61 (6 H): 13C N M R (90.56 M Hz. C D C b ) 5

49.92. 52.22. 123.69.125.35. 127.85. 128.50. 130.01. 133.61. 136.92. 139.64. 144.07.

147.45. 165.71.: I3C NM R (Dept 135. C D C b) 6 49.92 (u). 52.23 (u). 123.69 (u). 125.35

(u). 127.85 (u). 128.50. 130.01 (u).

155


A P P E N D IX A:

N M R spectra


M.S

8.4 8.„»

H.2

H.l

H.O

7.9 7.8

7.7 7

7.5 7.4

8.0034

2.0300

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157


140

97058532794699968541

310910584208010564425270138750144830420754535672

128.7612126.9370125.1348

• 72.6139

■ 58.51 1 1

158


8.5 8.0

7.5 7.0

6.5 6.0

5.5 5.0

4.5 4.0

3.5 3.0

(pp

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1.0302

1-0724

1.0085

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2.3051

159

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission

(ppm)

160

131.7703131.0084127.8534120.1051126.0706125.1766

72.0255

36.4497


(ppm)

a | Integralo 1

b- 1 . 0 0 0 0 f

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A 1.0000^7.06246.9361

o» >• —•*

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140 130

120 110

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49.0361

162


6.5 6.0

5.5 5.0

4.5 4.0

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JLOflQO7.2793

0.9996- 6.2345

8

3.8880

163


(ppm)

hi(II

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M(II

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112.5172

108.1059

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a i

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7.2318

6.9513

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143.8732

138.6423

124.9643 124.3709 123.3724

120.2610

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•72.7875■71.9083

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168


8.0 7.9

7.0 6.9

6.0 9.9

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1.5741

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7.5706

7.3259

7.0412

4.8905

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(ppm)

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72.3186

36.6036

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7.80 7.70

7.60 7.50

7.40 7.30

7.20 7.10

7.00 6.9

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e o

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ff»c(

1.0482

1.0438

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2.4760

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7.9227

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7.1880


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8.0 7.6

7.2 6.8

6.4 6.0

5.6 5.2

4.8 4.4

4.0 3.6

3.2 2.8

(ppm)

Integral

-TDSUk - 8.2275TOME ~ — 8.1733

4.0042- >— 7.9784

. 3.9842, 7.5572

3.1076- ---------------------- 3.1965

172


(ppm)

141.7991141.6691141.3113141.2936139.7603139.7326139.7060136.9610138.9432138.7304138.7036138.6830138.5362136.7614136.7436136.7170136.6751

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58.4809

53.0174

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173


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2.2152

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0.9881

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■8.3093

■8.1009 ■8.0695 '8.0373

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7.4458

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145 140

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130 125

120 115

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105 IO

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95 90

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75 70

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(pp

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128.871 1 128.8272 128.63C7 126.9603

' 126.9446 ■ 26.7612 125.3986 I 25.2887 1 24.9590 124.9004

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165 160

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■44.6987 144.601 1 142.9339 142.S969 142.SS2S 142.4SSO 142.2399 142.0293 141.9583 141.9051 141.6568 141.5947

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136.8501u 136.3268- 130.0124 -129.8173- 129.0103- 1 28.8S07- 128.1412

127.4317 125.7910

■72.5179

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181


9.2 9.1

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8.8 8.7

8.6 8.5

8.4 8.3

8.2 8.1

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1.0440

1.0355

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8.1394

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187


(pp

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188


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7.5 7.0

6.5 6.0

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2.5 2.0

1.5 1.0

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Integral

9.1724

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1 .0 0 3 ^ 1 *

8.0165

7.4174

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4.6863, r=------------------------------------- 0.5772

189


7.5 7.0

6.5 6.0

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3.5 3.0

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1.5 1.0

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190


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126.9058 —125.8142

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197


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5.5 5.0

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1.5 1.0

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120.7078

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199


8.4 8.0

7.6 7.2

6.8 6.4

6.0 5.6

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l)

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t .OOOO

2.9998

2.0914

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1.0091-4

X

x 2.0108

■Am

H

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• 7.7403

'7.61 15 ' 7.5683

■7.4327

■7.3104

• 7.0700

■S.74SS

■ 4.8349

202


(lIM

ltl)

146.3225 146.2427 146.0209 145.9677 145.5243 145.2493 ■45.2227 145.2050 ■45.1606 145.1251 144.5132 1 4 4 . 4 3 3 3 142.7748 142.6063 142.4466 1423579 142.0120■ 41.S43S 141.8238

u 141.6395■ 41.3242

-1413912- 140.6284- 139.8743- 139.3818 ~ 138.8102- 136.7323

136.6727u 133.8636- 130.0473- 1 29.6393- 127.3136

127.0830 123.3417

72.2549

64.9377

35.0928

203


31

e

e

HI

130.2575 129.8382 127.5175 127.3124 125.7888

HIe

71

204


( pp

m)

ki‘

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x

x_

Xm'

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/ "1.1 182

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■7.5810

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205


155 150

145 140

135 130

125 120

115 MO

105 IO

O

OS 90

H5 NO

75 70

05 60

■ >45.4849 ' 145.4554 ' 145.3404 ■144.4444• 144.6497 ■>43.1405 ■143.0013■ 142.9354• 142.5837■ 142.3420 •142.2741■ 142.1222• 142.0543 ■141.7852■ 141.7193 ■141.2284 ■140.5324 ■140.1881■ 140.1441 •137.1111■ 134.9040

1 1 7.9093

1 00.7880

■85.9892

■71.9889

■54.9554

206


8.0 7.0

7.H

7.7 7.6

7.5 7.4

7.3 7.2

7.1

7.0

6.9 O.H

6.7 6.6

0.5 6

.4(p

pn

t)

1 . 0 0 0 0

■ 7 . 8 7 6 7

• 7 . 8 7 7 6

■ 7.S3S2

■7.3810

■ 6.8888

207


9.0 8.0

7.0 6.0

5.0 4.0

3.0 2.0

(ppm)

Integral

1 .OOOO- 9.0342

2.1692>

8.14797.9004

7.S742

1 .0 0 QB- 6.5276

n<*>K>Inan

JOii

to

JO

JO

7.5434= 0.3917

208


(ppm)

CMo

uo

Mo

COO

142.9345142^990142.52551 4 2 ^ 9 9 9142.3845142.2593142.0385141.9585141.8790141.8927141.5982140.5309140.0785139.8588138.9033138.6372132.3179129.5861128^420127.9831126.4996126.2888126.2601117.8188106.6945100.9737

71.9002

55.7425

CMO

o

w - o -

Mo

0.9989

209


7.5 7.0

6.5 6.0

5.5 5.0

4.5 4.0

3.5 3.0

2.5 2.0

1.5 1.0

(ppm)

e j-

In tefr il

i***-JL89C6 iI.OOOflL r ^

L .r

0.9660- r~ii

7.8646

7.S191

'6.4396

30II

sco

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4.4467- -T ---------------------------------------------- 0.2146

210


(uid

d)

Me

OBo

8 »O

*e

wo

142J0471420993142033414101711410120141.97941410979141.7014

'1410041141.5774

' 141.0430

' 1404)474 ' 130.4410 ' 130.0104

i :134.0441132.3170129.50411240809127.9031127.8744127.7000127.0200120.50401 2 0 .2 0 0 0120.2090117.0100100.7033100.973772.450171.900250.7002

ah

zc/>

0.1741

211


(ppm)

«M

9.09020.9078

OBB

01B

8.1821OiBO 7.9140

7.S793

BM

0 )aOB

6.5463

0 )Bo

MBa

CflM

OB

S j .O O O Ch 3.9948

212


(ppm)

213


»0 8.0

7.0 6.0

5.0 4.0

3.0 2.0

1.0

(ppm)

1.0000

1.0473

2.2628

: 1.0436- jp4.9673- r 0.5943- r

_______ t-1.9878 P

t

14.148

9.04619.0342

8.13437.9047

7.5699

6.51666.5014

5.10325.04984.84054.6981

3.9473

3.65583.5914

2.03651.83141.74161.70341.66701.62211.5526

214


(uid

d)

— 7.8352

7.5208

~ 6.4353 6.43191.9906

- ~ 4.9498"4.7032

4.6964

O 1.0005

-1.3116

u

2.033918.474

— 1.6272 “1.5551 -1.4933

215


siU d

s ie :

M

—. <D ■H O

(IIe

uo

NO

t

142.3402142.3229142.3047142.2970142^604142.0209141.9992141.9194141.4989141.0930140.2470140.2204140.1938139.8129139.7947138.9831136.8948127.6704126.2247126.2069117.9673

96.601295.1998

80.7961

72.396870.6052

62.1705

56.201556.174954.7114

30.338629.345226.489325.336322.675519.0923

216


(pp

m)

2.0853

1.5627

1 .OOOO

0.9865

■ 7.6479 -7.5708 7.5250

-7.1293

-6.9310

-5.3125

3.7312

217


165.7051

147.5143

144.0343

139.6313 136.9646

- T 133.6605 r 130.4297

129.4480 128.6201 128.4443 127.8728125.3600 123.6383

3 *3

e

2 8 2

*O

vlo

*c

VIo-52.2376-49.9299

6O'

218


145 140

135 130

125 120

115 HO

105 100

95 90

85 80

75 70

65 60

55 SO

45 40

(pp

m)

S -

130.4297 129.4480 128.6201 128.4443 127.8728

125.3600 123.6310

■52.230349.9518

219


(pp

m)

90 In leg ri IO'

1.5429

1.0176

1 . 0 0 0 0

3.0057

-7.6077

-7.3170

-7.0594

-6.9188

- 5.2553

-3.6377

220


(pp

m)

221

165.7051

147.4483144.0710

139.6460136.9206133.6165 130.0121 128.5029 127.8509 125.3526 123.6896

52.222949.9225


(pp

m)

*-e

u-VI

w-e

K»-'Jl

130.0121 128.5029 127.8509

125.3526 123.6896

M-O

VI

e-VI

o-o

VI

o

06VI

06O

V I '

'Jo

aVI

ao

*nxn

VIVI

VI©

-52.230349.9225

*VI

o

222


APPENDIX B:

X-ray structure o f 24


X -ray structure provided by professor Alan Balch and Pam ela Lord at UC D avis

224


X-ray structure provided by professor Alan Balch and Pamela Lord at UC Davis

225


APPENDIX C:

UV/Vis spectra


Wavelength

(nm)

w»

oo

K>

*ooI

I

Ol

2 2 7


Wavelength

(nm)

228


1000 1500

Wavelength

(nm)

A bsM (4

OO

N

229


106003:21 .xj* M

Pag

*lo

ll

1000 1500

Wavelength

(nm)

230


10500 3

2543 PM

Pagalofl

APPENDIX D:

mass spectra


Poaitlvc Ion Klectronpray MS- 1000-2000 mlz

LCQ I n s t r u m e n t C o n t ro l 12 J u l 2000 03:46 PMI

S I : BS6 IT: 14.20 8T: 1.11 «A: 30

100

«P

50

2 . 1 3e *004

1951.9

R = 4'-liydroxymethylplienyl1447.6

1307.1

1113.9 1197.91269.0 15 ;n. o

1053.01792.3

1703.7 17 7 7 9

1804.5

1415.1 1522 . 1

01000 1100 1200 1300 1400 1500 1500 1700 1000 1900 2000

<Nro<N

Rep

rodu

ced

with

pe

rmis

sion

of

the

copy

right

ow

ner.

Furth

er

repr

oduc

tion

proh

ibite

d w

ithou

t pe

rmis

sion

.

1900 1950

2000 2050

2100 2150

2200 2250

2300 2350

2400 2450

2500


Puattlve Ion

l;lccl rospr.iy HS-

1900 2500

mIt.

03

i3

3 &7 aIT

^ *

? 2.Mm

SJ©QO

z

Aft

234


Poaltiva Ion

Elactroaprny

NS- Olow

up of

1954 ieftl<m

33

235


236


A P P E N D IX E:

electrochem istry


Potential,V

Current, uA

238


+12

Potential ,V

Current, nA

iO .N>

iO J

o_CD

i

0

1

Kj

i■

*

i

0 1i

4W1 0

4*©

_L-s

+s-4-

\>rtr

L

239


Potential,V

Current,uA

S

240


91

+

Potential.V

Current,nA+

241


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244


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245


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246


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Diels -Alder reactions between fullerene[60] and various pentacenes · 2020. 2. 27. · Diels -Alder reactions between fullerene[60] and various pentacenes James Mack II. ... I would