The Research of Alan H. Cowley (Abridged) by Keith T. Quisenberry February 20, 2006 Chisholm Group Presentation

The Research of Alan H. Cowley (Abridged)

by Keith T. Quisenberry

February 20, 2006

Chisholm Group Presentation

Alan H. Cowley: a Major Player in Main Group Chemistry

Alan Herbert CowleyUniversity of Manchester B.Sc. (1955), M.S. (1956), Ph.D. (1958)

University of FloridaPostdoctoral Fellow/Instructor (1958–60)

Exploratory Group of Imperial Chemical Industries Technical Officer(Billingham Div.) (1961)

University of Texas at AustinAssistant Prof. (1962–67), Associate Prof. (1967–70), Prof. (1970–84), George W. Watt Cent. Prof. (1984–88)

Imperial College, London, England Sir Edward Frankland Prof. (1988–89)

University of Texas at AustinRobert A. Welch Chair of Chemistry (1989–current)

Alan Herbert Cowley

Royal Society of Chemistry for Main Group Element Chemistry (1980)

Centenary Medal and Lectureship, Royal Society ofChemistry (1986)

American Chemical Society Southwest RegionalAward (1986)

Fellow of the Royal Society (1988)

Chemical Pioneer Award of the American Institute of Chemists (1994)

von Humboldt Prize (1996)

Mexican Academy of Sciences (2004)

Early Research

Trimethylsiloxyaluminum dihalides are stable! (cf. Me3SiOBF2)

Me3SiOAlCl2∆

Me3SiCl + AlOCl

well-defined crystalscan be distilled under vacuum at 145 ˚C decompose upon heating at 1 atm

Electron donor activity of hexamethyldisiloxane?

(Me3Si)2O + 1/2 Al2Cl6

Me3SiCl + Me3SiOAlCl2

(Me3Si)2O: AlCl3X. .

Cowley, A. H.; Fairbrother, F.; Scott, N. J. Chem. Soc., 1959, 717.

BN

BN

B

N

R1

R2

R1

R2

R1

R2 -

--+ +

+

BN

BN

B

N

R1

R2

R1

R2

R1

R2 -

--+ +

+

Early Research

Cowley, A. H.; Sisler, H. H.; Ryschkewitsch, G.E. J. Am. Chem. Soc., 1960, 501.

First preparation of compound containing B–Si bond

borazine

N

BN

B

NB

R1

R2

R1

R2

R1

R2

Early Research


First preparation of compound containing B–Si bond

Ph3SiSiPh3 + NaK Ph3SiKN

BN

B

NB

R1

R2

R1

R2

R1

R2

+

R1 = ClR2 = Ph (or Me)

N

BN

B

NB

SiPh3

R2

Ph3Si

R2

SiPh3

R2

80–90% yield

waxy solid (mp = 55–58 ˚C)

soluble in Et2O, C6H6, CCl4

moisture sensitive

Over the years…

Studies of unusual main group compoundsGroups 13 and 15 complexes of low oxidation and

coordination numbers

synthetic chemistry

structural assays

bonding descriptions

reactivity studies

Thin Filmsdeposition studies (e.g.; MOCVD, molecular beam epitaxy)single source precursors (e.g., nitrides, carbides, nobel metals)

New Catalysts

Over the years…

Studies of unusual main group compoundsGroups 13 and 15 complexes of low oxidation and

coordination numbers

synthetic chemistry

structural assays

bonding descriptions

reactivity studies

Use of appropriate ligands that confer thermodynamic or kinetic stabilization

bulky substituentsmoieties that impart electronic influence

Low Oxidation/Low Coordination Number Main Group Complexes

In search of stable analogs of alkenes and diimines

Group 13 Group 14 Group 15 R2B– R2C RN R2Al– R2Si RP R2Ga– R2Ge RAs R2In– R2Sn RSb R2Tl– R2Pb RBi

carbenoid analogs2 R2C: C2R4

Early reports of monomeric (RP=PR), (RAs=AsR) and (R2Si=SiR2) were oligomers

Use bulky substituents (R) to inhibit oligomerization!

Realization of Alkenes Analogs Via Use of Bulky Ligands

1976, Lappert

{Sn[CH(SiMe3)2]2}2

1981, West

(mesityl)4Si2

ditin derivative disilene derivative

Cowley, A. H. J. Organomet. Chem., 2004, 3866.

Cowley Contributions: RAs=AsR, RP=AsR and RP=SbR

Li + AsCl3 AsCl2 RAs=AsRred.

As

Cl

CH2

Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am. Chem. Soc., 1983, 5506.


RAs=AsRred.AsF2Li + AsF3

mp 119–121 ˚C

AsH2

LiAlH4

+ (Me3Si)2CHAsCl2 + N

N

1,5-diazabicyclo[5.4.0]undec-5-ene




72% yield

orange crystals

mp 110–113 ˚C

trans geometry of ligands

As–As bond length: 2.224(2)Å

First compound with As–As double bond!


Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. Whittlesey, B. J. Chem. Soc., Chem. Commun., 1983, 881.

AsH2+ (Me3Si)2CHPCl2 + N

N

As P CSiMe3

SiMe3H

P As CSiMe3

SiMe3H

Four Valence Electron Species: RB, RAl, RGa, RIn

typically tetramers or hexamers

useful sources of monomers

bulky ligands can stablize monomer

Al4(C5Me5)4

[{HC(CMeNAr)2}Al]; Ar = 2,4,6-i-Pr2C6H2

See refs. 21, 27 in Cowley, A. H. J. Organomet. Chem., 2004, 3866.

Terminal Borylene Complex

(C5Me5)BCl2 + K2[Fe(CO)4]

30% yield

Completes C5Me5M series (M =

B–In)

11B NMR chemical shift: –35.3 ppm (cf. >100 ppm in bridged borylenes)

FeCO4 is C3v ( CO = 2018,

1938, 1908, 1884 cm–1)

NMR equivalence of C5Me5 to –

78 ˚C

B

OC FeCO

CO

CO

(C5Me5)BFe(CO)4

Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401.

Terminal Borylene Complex

(C5Me5)BCl2 + K2[Fe(CO)4]

mp: 155 ˚C (dec)

no intermolecular contacts

axial (C5Me5)B unit

B–Fe bond length: 2.010(3) Å (cf. 1.95–2.03 Å)

B–C(Cp) bond length: 1.814(4) Å (cf. 1.683 Å in [BBr (C5Me5)]+)

Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401.

Nature of the Four Electron Monomer (RM)

ground state is a singletsinglet-triplet gap increases with atomic numberpronounced lone pair character

No backbonding seen in RM (R = C5H5)

DFT studies on singlet and lowest-lying triplet state…

RM M´Ln RM M´LnRM M´Ln RM M´Ln

Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc., 1999, 12113.

Group 13–Group 13 Donor–Acceptor Bonds Lewis acid adduct of allanediyl

40% yield, mp 126–129 ˚C (dec)

mass spectral data confirms proposed formula

11B NMR chemical shift indicative of tetracoordinate

center

19F NMR values were similar to other Lewis base complexes of B(C6H5)3

NMR equivalence of C5Me5 indicates 5-attachmentGorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950.

[Al(C5Me5)]4 + B(C6F5)3 (C5Me5)Al B(C6F5)3

Group 13–Group 13 Donor–Acceptor Bonds

40% yield

Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950.

(C5Me5)Al B(C6F5)3

No intermolecular contacts

(B–Al–Cpcent) = 172.9(1)˚

Al–B bond length: 2.169(3) Å

Short Al–C bond legth: 2.171(3) Å av (cf. 2.344 Å for [(C5Me5)Al ]4)

Sum of B–C bond angles: 339.8(2)˚ (cf. (C6H5)3P B(C6F5)3)


Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950.

[Al(C5Me5)]4 + In(C6F5)3 (C5Me5)Al In(C6F5)3

mp 158 ˚C

(3-C5Me5)Al(C6F5)2

C6F5 transfer from (C5Me5)Al

In(C6F5)3 ?

(3-coordination seen in

[(3-C5Me5)(Me)AlCl]2

Valence Isomer of Dialane (R2AlAlR2)

Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Cowley, A. H. Chem. Commun., 2001, 75.

DFT studies show…

HAl AlH3 less stable than H2AlAlH2 by 9.17 kcal/mol

(C5H5)Al AlH3 more stable than H2AlAlH2 by 10.79 kcal/mol

[(C5Me5)Al]4 + Al(C6F5)3 ·PhCH3

27Al NMR data: –115.7 ppm (s), 106.9 ppm (s)

(cf. –150 ppm ((C5Me5)Al) and 52 ppm (Al(C6F5)3 ·PhCH3))


(C5Me5)M M’(C6F5)3

2005, Cowley Al Ga2005, Cowley Ga Al

2002, Power In B

[Ar(dipp)2]In B(C6F5)3

2001, Jutzi Ga Ga

[Tp’]Ga GaI3

[nacnac’]Ga B(C6F5)3

(C5Me5)M M’(C6F5)3

2000, Jutzi B B2001, Cowley Ga B

1996, Piggott In In

[Tp’]In InI3

See refs in Cowley, A. H. Chem. Commun., 2004, 2369.

C

N

N

R

R

C

N

N

R

R

R'

R'

N-heterocyclic Carbenes

1962, Wanzlick 1991, Arduengo

R = adamantyl; R’ = H

Electronic behavior like that of electron-rich phosphines

N-heterocyclic Carbenes

PMe3 + (PCF3)4 Me3P: PCF3

+ (ER’3)n

N

C

N

R

R

ER’N

C

N

R

RR = Mes; E = P; R’ = Ph; n = 5R = Mes; E = As; R’ = C6F5; n = 4R = Mes; E = P; R’ = CF3; n = 4R = Mes; E = As; R’ = Ph; n = 6

Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105.

Nature of the Carbene Bond

E:

R’N

C

N

R

R

..

N

C

N

R

R

ER’

..

Fischer-like Schrock-like

P–Ccarbene and As–Ccarbene bonds are ca. 4% shorter than typical

single bonds

31P NMR shifts ( –23.0 and –23.6 ppm) outside of

phosphaalkene range

Reaction with Lewis Acid?


Nature of the Carbene Bond

E:

R’N

C

N

R

R

..

N

C

N

R

R

ER’

..


BH3 E

R’N

C

N

R

R

BH3

BH3

References

Cowley, A. H.; Fairbrother, F.; Scott, N. J. Chem. Soc., 1959, 717.




Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. Whittlesey, B. J. Chem. Soc., Chem. Commun., 1983, 881.

Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401.Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc., 1999, 12113.Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.;

Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950.

Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Cowley, A. H. Chem. Commun., 2001, 75.


Cowley, A. H. Chem. Commun., 2004, 2369.


Documents

The Research of Alan H. Cowley (Abridged) by Keith T. Quisenberry February 20, 2006 Chisholm Group Presentation