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Chemical ReviewsVolume 83 , Number 3 June 1983

Alkyne-Substituted Homo- and Heterometallic Carbonyl Clusters of the Iron,Cobalt, and Nickel TriadsENRICO SAPPA

Istituto di Chimlca Gsneraie ed Inorganic& Universiti di Torino, 10 125 Torlno, ItalyANTONIO TIRIPICCHIO

Istituto dl Chimica Oeneraie ed Inorg anica , UniversitB di Parma, Centro di Studio per la Strutturfstka Diffrattometrica del C.N.R.,43100 Parma, ItalyPIERRE BRAUNSTEIN

Laboratoire de Chimie de Coordination, Associci au C.N.R. S., UniversitS Louis Pasteur, 67070 Strasbourg C a e x , FranceReceived July 12, 1982 (Revlsed Manuscript Recelved December 29, 1982)

Conf entsI. ntroduction

11. Synthesis of the Complexes1. Thermal Substitutlon2. Photochemical or Assisted

B. Rearrangements and Reactionsof the Coordinated Alkynes

C. Reactions of Tetrahedral Clusters withAlkynes and Condensationof MetalFragments Induced by Alkynes

D. Ligand Exchange between Metals andMetal Exchange on Clusters

E. Oxidative Additionof C-H and H2 to MetalClusters and M-H Addition to UnsaturatedLigands

A. Substitution of the CO Groups

Substitutions

F. Protonation Reactions0 . Reactions of Carbonyl AnionsH. Other ReactionsI. urification Techniques

111. Structural Data in the Solid StateA. Interactionof a Single Alkyne (orAlkyne-Derived Ligand) with Clusters.Structures and Trlple Bond Activation1. Complexes in Which the Alkyne (orAcetyllde) Interacts with One MetalAtom2. Complexes in Which the Alkyne (orAlkyne-Derived Ligand) Interacts withTwo Metal Atoms

Three Metal Atoms4. Complexes in Which the Alkyne (or203 Alkyne-Derived Ligand) Interacts with20 520 520 520 520 9209 Oligomers

Four Metal AtomsB. Activation of the Alkyne uponCoordlnatlon to the Metals

C. Complexes Containing Organic Rings orChains Formed upon Interaction ofAlkynes Held in Proximity

D. Complexes Containing Open ChainI V . Spectroscopic Data in SolutionA. Infrared Studies

B. H NMR StudiesC. 13C NMR Studies

21 121 1 V. Mass SpectraVI . ReactivityA. Reactivity of HC2R, RC2R, and RC2R

B. Reactivity of the Alkyne-SubstitutedAlkynes toward the Same Metal Cluster1 1

21 1212 Clusters212212213

1. Reactivity of the Clusters2. Reactivity of the Coordinated Alkynesor Acetylides3. Other Reactlonsof Single AlkyneMolecules with Clusters

4. CO Insertion Reactions13 V I I . ApplicationsV II .ReferencesI . Introduction

213

219

22022 1

22222222222322322 622 722 7229229229232232233234

3. Complexes in Which the Alkyne (or 215 This review deals with the alkyne-substituted car-bony1 cluster complexes of the iron, cobalt, and nickellkyne-Derived Ligand) Interacts with0009-2865/83/0783-0203$0~,50/0 0 1983 American ChemicalSociety


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204 Chemical Revlews, 1983. Vci. 83. No. 3 Sappa. Tirlpicchb. and Braunstelnavailable to attem pt system atic discussion.Several review articles, and books dealing with relatedasp&$ of this che mistry have recently been published;some of these take into account alkyne derivatives.Th us, metal-metal bonding, m etal-cluster prep ara-tion? growth, and stoichiometry,3and chemist$ havebeen recently reviewed, as well as the alkynecobaltchemistry?Th e interest in the alk yne clus ter chemistry is dueto two m ain reasons, which will certainly influence thegeneral setting of this w ork.T he f i t one is th e wish of gaining a better knowledgeof the interactions of small molecules with metalclusters-the alkyne complexes (and in particular themonoalkyne derivatives) being considered as usefulmodels for th e chem isorption of sma ll molecules onmetal surfaces6-and for the carb on- xrb on triple-bondactivationand reduction.? Also considerableanalogiescan be found between t he coo rdination modes of alk-ynes and of carbon monoxide to several metal centers;in particular, t he alky nes show a grea ter variety of in-teractions resulting from t he possibility of varying thesubstituents, and hence the polarity of th e triple bond.

The other main reason for interest in the alkynecluster chemistry is the importance of acetylene asfeedstock for industrial organic chemistry. Indeed, aftera period of predominant importance followed by a sha rpdecline of in tere st due to the availability of cheaper,mo re readily accessible an d workable olefins,acetyleneis slowly becoming again an at trac tive sourc e of chem -icals in view of the present shortage in oil supplies.New interest in coal is presently shown by manycountries; thus the CO/H2 mixture from coal gasifica-tions and the acetylene obtained either by conventionalor by new methodsO are at present of great importance.In this light, the activation and reactions of CO andof alkyn es on meta l clusters is already considered ofgreat importance for a better understan ding of catalyticprocesses and for the development of new catalysts. Inparticular, the pre-World War Two acetylene chem istrywas based mainly on heterogen eous or on homogeneousmonom etallic catalysts and only a few studies on t hereactivity of acety lene coordinated to clusters had beenmade until recently.A t present a considerable number of alkyne-suhsti-tut ed clusters is known; those reported, un til the en d1981are given in Table I together with some chemicallyor structurally related complexes.Often clusters containing a different number ofmetals or a d ifferent number of alkyne (or alkyne-de-rived) ligands are structurally related. Th is makes itdifficult to order th e complexes on th e basis of stru c-tural analogies.For this reason we preferred an orde ring based onincreasing cluster nuclearity; in each triad the metalsare disposed in order of increasing weight. Th e ho-mom etallic complexes precede th e heterometallic ones;in the formula of the la tter th e metals are ordered onth e basis of increasing weight. Finally, the num ber ofalkyne substitue nts has been considered.Non cluster, polymetallic alkyne derivatives are alsoknown; some of these contain acetylides or alkynesbonded to several metallic centers in the sam e way asfound for th e cluster complexes, and in some instancesthese will be considered in the following discussion.

Enrko SappaObtaWMwee h c lml lwy h m e niversityof Talno h 1964. After a posMoaoralappointment atme IsHModl Chlmlca Generale of the same University. he started his aca-demic career and is now Associate hof ess or at the University ofTorino. His present res ear ch interests include the chemistry ofheterometallic clusters and the reactivity of muitisfie-bound hy-drocarbyls on clusters.

Antonlo Tirlplcchb received his -rea In Chemistry from theUniversity of Parma in 1959 He is now Professor of GeneralChemistry at the Facuity of Sclence of the same University. Hismain research interests are in the field of structural chemistry oforganometallic and coordination compounds.

plene Bramstein received his degree of IngenleurChlmlste fromthe Ecole Sup6rieure de Chimie de Mulhouse in 1969. He thenwent to the University of Strasbourg and obtained his Dr.-Ing.Thesis with Prof. J. Dehand in 197 1. This was followed by apostdoctoral year at University College London wfih Prof. R. S.Nyholm. After returning to Strasbourg. he rece ived his DoctoratdEtat in 1974 and then spent a year at Technische UniversititMunich wtth Prof. E. 0. Fischer as an 6. von Humboldt Fellow.Since 1979. he has held a position of Maie de Reche rche in ttmC.N.R.S. at tw Univenit6 Lovis Pasteur of Strasbourg. His pesentresearch Interests include cluster chemism and the use of func-tional llgands In transition-metal chemistry.triads, and w ith some related clusters obtained by re-action s of alkenes, dienes, and isonitriles. Also someclusters containing alkyne-deriued ligands, such asacetylide-, alkenylidene-, and alkylidyne-substitutedcomplexes, will be considered. The se can be formed,indeed, upon reaction of th e alkynes coordinated to th eclusters.The chemistry of these derivatives has been devel-oped in recent years and considerable material is now


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Alkyne-Substltuted Carbonyl ClustersExamples of these complexes are given in refer-ences.160J61As a preliminary comment, Table I shows that th egreater part of the alkyne clusters are trinuclear ortetranuc lear; few examp les are kno wn of 5- and 6-atomclusters, and only one 7-atom derivative is known. A tthe present state of the a rt a considerable number ofstru ctur al stud ies is available, which allows a discussionbased on well-established parameters for th e solid state.On the o ther han d, a considerable lack of fluxionalityand mass spectrometric studies is still observed.Som e isonitrile (or isonitrile-derived) complexes tha tshow comparable bonding characteristics are listed inTable 11.

Chemical Revlews, 1983, Vol. 83,No. 3 205

I I . Synthesis of the ComplexesThe preparative methods are the usual ones forsu bst itute d carbo nyl clusters, e.g.: CO sub stitutio n(thermal or photochemical, assisted by Me3N O), rear-rangement or reaction s of the coordinated ligands, re-action of closo tetrah edr al clusters with alkynes, andmetal fragment condensation induced by alkynes,ligand or m etal exchange between complexes, oxidativeaddition- reduc tive elimina tion of C-H an d H2 , M-Haddit ion to unsaturated molecules, protonation ofneutra l comp lexes, reaction of carbon yl anions towardsorganic substrates , pyrolysis, meta l vapor sy ntheses, etc.

A. Substltution of the CO Groups1. Thermal Substitution

For t he trimetallic carbonyls of th e iron triad this isusually the first reaction ste p (in hydrocarbons: re-fluxing penta ne to octane temperatu re). Complexes ofgeneral formula M3(CO)loLor HM3(CO)lo(L-H) andM3(CO)& or HM,(CO),(L-H) are usually obtained; thealkyne acta as a 4-o 6-electron donor, depending u ponits substitution.W hen considering the CO-su bstitution reactions fourbasic types of alkynes should be con sidered, namely:Symm etrical alkynes, with arom atic substituentssuch asC2Ph2 , re coordinated w ithout rearrangement.Alkyl-substituted intern al alkynes, such as C2 Et2orC2M eEt, which in some instances a re coordinatedwithout dra stic change (on iron), bu t usually isomerizeto allenyl and allylic ligands, with tran sfer of on ehydrogen on the cluster.Term inal alkynes, HC 2R, which usually sp lit intobridging hydride and m ultisite bound ac etylides. Sim -ilar behavior has also been observed for C1C2Ph.176Phosphinoalkynes, Ph2PC2R,which split into bridg-ing phosphido ligands, and m ultisite bou nd acetylides.Functionalized alkynes also give oxidative additionto Ru3(CO),,; in particular MeC=CCH2NMe2 giveshigh yields of the allenic HRu,(CO),(MeC=C=CH NM e2) and of the allylic HRu,(CO),(MeCi-C H - C N M e 2 ) ~ 1 u s t e r s . l ~ ~T he behavior of the hydroxyalkynes is discussed inthe section on th e reactivity.CO substitution also occurs on phosphine-subs titutedruthenium clusters. Thus, u,(CO),(PMe,), reacts withHC2CBu-t to give HRU~(CO)~(PM~~)~(C~BU-~).~~Whereas on the unsubstituted carbonyl cluster threeCOs were displaced, in the s ubstituted cluster only twoare removed.

1v

HOs3(C0)9(C2H4)(SMe) ( r e f . 79)

2N

Figure 1. Complexes in which acetylide or alkene interact withone metal atom (bonding modes A an d B).Usually, the interaction of t he alkyne occurs withmore tha n one metal atom: no example of a linearacetylide on a cluster is known, and one only has beenrepo rted for a bim etallic complex179 Figure 1 , l ) . Onthe contrary, the isonitriles apparently show a greatertendency to coordinate linearly. For both th e alkynesand the isonitriles, it is difficult to s top th e reactions

a t the stage of simp le subs titution: with aUrynes usuallyoligomerization occurs; few examples of complexescontaining two indep endently coordinated alkynes areknown. Among these are Fe3(C0)8 (C2P h2)2violet iso-mer), lg P t3(PEt3)4(C2Ph2)2Figure 2, 6),lo5 nd Fed-(CO),,(HC2 Et)2 (Figure 9, 28).125Th e isonitriles rear-range, especially in the presence of hydrogen , to morecomplex ligands (T able 11).2. Photochemical or Assisted Substitutions

Until now, very few photochem ical experimen ts havebeen p erformed; there is, however, an increasing interesttoward the photochemical syntheses of clusters, henceit is predictable th at this m ethod will soon be used to


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20 6 Chemical Reviews, 1983, Vol. 83, No. 3 Sappa, Tiripicchio, and BraunsteinTABLE I. AlkynpSubstituted Carbonyl Clusters of the Iron, Cobalt, and Nickel Triads

referencesX-rayprepn , I R c mass ( o r n e u t r o n )en t ry complex 'H NMR NMRa s pec t ruma s t ruc tu re

A . Trinuclear Complexes12345678910111 21 31 41 51 61 7181 92 0

2 1222 32425262728293 03 13 23 33 43 53 637383 94 04 14 24 34 44 54 6474 84 95 05 15 2535 45 55 657585 96 0616 26 36 46 56 66 76 86 97 07 1

I ron

H Fe,C;( C0 ,C R( C p ) F e C o N i ( C O ) , ( P h C , C O O R )( C p ) ( C ,H , ) F e R h W ( C O ) 6 ( C R ) C % d(Cp ) , FeN N o (CO ),( PhC ,COOR )

( C p ) , F e N i , ( C O ) , ( R C , R ' )(Cp) , FeNi , (CO) , (RC, COOR)(Cp)Fe , Ni (CO) , (CCH, R)( C p ) (P E t , )F e P t W ( C O ) ,( C R ) C ~ d(Cp)Fe,W(CO),(CC,H,Me-4)(Me,SiC

(Cp)Fe2Ni(C0)6(C7,R)[(Cp)Fe2Ni(C0)6(C2R2)1-

('P) ZF eW 2(") 6 [ 2 g H qMe) 2 1R u then iumeR u 3 ( C 0 ) l , ( P P h 2 C 2 R )Ru3(C0)10(C2Ph?)Ru3(C0)9(C2Ph2)R u , ( C O ) , ( R C , R ' )HRu, (CO) , C , -Bu- tHRu, (CO),C,RH Ru , (CO ) , (C6 H ~o ) (C2 Bu - t )(PPh2)Ru3(C0)9(C2R)Ru, (CO) , (PPh , ) (C , Bu- t )HRu, ( CO ) , ( RCHCCR' )H R u , ( C O ) , ( R C C H C R ' )HRu,(CO)9(CrlHm)CHRu,(CO),(C5H,)CH R u , ( C O ) , ( P h C ~ C 6 H , ) cHRu,(CO), (CsH5)CHRu, (CO) ,[ HCCHCC(=O)OH]HRu, (CO) ,[ HCCHCCH, OH]HRu, ( CO) , [C , RR ' (OH)]HRu, ( CO) , [C,C( =C H,)P h]HRu3(CO),-,(RCCHCR')(PR,),HRu3(C0)9_, (C2R)(PR3X1H2Ru3(C0)9(C2H2)H Ru, (CO), ( HC,Bu-t)H2Ru3(C0 ) 9 ( C f l H , Z ) CH,Ru, (CO),CMeRu ,( CO), ( C,Ph, ), , violet isomerRu, (CO), (C,Ph, ) ,, orang e isomerH,Ru, (CO),CCH,Bu-t( C p ) R u 3 ( C 0 ) 8 C C H > R

3( 8 (L2 -H 2Ru3(C0)8(C5H6)2Ru, (CO) , [ (CF, )Ph , PC=CPPh, ] ,Ru3(C0)Y(C2Ph2)3R u 3 ( C 0 ) 8 ( H C 2 B u - t ) 3Ru3(C0)8(C10H15)R u 3 ( C 0 ) 8 ( H C 2 B u ~ t ) ( C 5 H 6 ~ ~Ru,(CO)6(C,Bu-t),(PPh2)2(Ph2PC2B~Ru, ( CO) , (C,Bu-t) [PhC,( H)P h ( C 2 P hR u 3 ( C 0 ) 6 ( C ~ 2 H 2 0 ) ( C ~ 3 H 2 0 0 )Ru (C O1 (C 2H 0 1 C YH )o0 )

,Sin

- t )2 )

1 21 3 , 1 41 6171 31 32 1 , 2 22 324252 22 6281 0 81 1 01111 1 21 1 31 1 41 1 41151 1 61 1 562 . 1181 1 91 2 01 1 56 2 , 1 2 01 1 63 32327295 23031 , 323 33 32 3 5292 93 9374 1424 34 3444 444456 7 & 87 04 64741, 84 94 7623 03 0245 35 43 0 , 315 75 6555 859606 1

1 51 61 71 8 1 918 2 0 1 92 02522 20 2226 27 2628

1 1 01 1 3

1 1 51 1 61 1 5 1 1 51 1 7 1181 1 91 2 01 1 63 32327

34

3 9374 34 34 44 44 4677 0 b

35 , 362 3 52 9294 03 84 142

444 567

485 0 5 147 47

5 35 75 6555 85 96061


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Alkyne-Substituted Carbonyl ClustersTABLE I ( C o n t i n u e d )

Chemlcal Reviews, 1983, Vol. 83, No. 3 207

references

e n t r y c o m p l e x~-X-rayp r e p n , IR mass ( o r n e u t r o n )'H N M R NMRa s pec t ruma s t ruc tu re

7 27374757 67778798 08 18 283848586878 8899 09 19 29 394959 69798991001011 0 21 0 31 0 41051 0 610 71 0 81 0 9

1101111 1 21 1 31 1 41 1 51 1 61171 1 81 1 91 2 01 2 11 2 21 2 31 2 41251 2 61 271 2 81 2 91 3 01 3 11 3 21 3 31 3 41 3 51 3 613 71 3 81 3 914 0

[ ( R u 3 ( C o ) 9 ( C 2 B u - t ) ( H g B r ) 1 2O s m i u m0s3(C0)10(HC2Ph)0s3(C0)10(C2Ph2)0s3(C0)10(C4H6)0s3(C0)10(RC2R' )HOs , (CO) , , (RC=CHR)H0s3(C0)10(C2Ph)H2s3(C0)10(C2Ph)HOs3(CO), ,RcHOs,(CO), ,( C H = C H 2 ) CHOs,( CO) , (CH=CHE t )HOs, ( C O ) , (CCF,=CHCF,)(PEtHOs,( C O ) C P h = C H P h )H O s , ( C O ) C H C H = N E t 2 ) CH O s , ( C O ) l o ( C H C H 2 P M e ~ P h )H0s3(C0)10(CF3C2HCF3)H0s3(C0)9(C3H20R)H0s3(C0)9(C6H7)H0s3(C0)9(C2R)HOs,(CO), (C.CH,Ph)HOs, (CO), (C=CH,)H O S , ( C O ) , ( R C H = C H R ) ~HOs, (CO), (C,H, )H0s3(C0)9(AsMe2)(C,H,)HOs3(CO)9(C6H3Me)CH0s3(C0)9(C9H13)CH0s3(C0)9(C2H,)(SMe)CH, Os , (CO) , (C=CHPh)H,Os, (CO), (HC=CMe)H 2 0 s 3 ( O ) , ( R C = C R )H2s3(C0)9(CCH2)CH2s3(C0)9(C?7HVl)CH2s3(c0)9(c5H4)cH 2 0 s 3 ( C O ) 9 ( C 2 R R ' ) CH,Os,(CO),CMe0 s 3 (C 0 )9 (R C 2 R ' )Os,(CO), ( HC,Bu-t)Os , (CO)9(C,Ph, )(CH,)~ ~ 3 ~ ~ ~ ~ 9 ~ C ~ ~ 2 ~ ~ 2 ~ ~ ~ ~ 1Os,(CO), [(RC,R' ) , (CO)l0s3(C0)9(C2Ph2)2

) 9 ( RC Z R ' )ZH0s3(C0)8(C2Ph2)(PhC2c6H~)HOs,(CO),L0s3 (C 0)7 (C 2P h2)30s3(C0)7(RC2R' )32('O S ( p p h 3 ) Z(ZMe2(cP ) ,w20s(co ) , [C2(C6H,Me)2 1,Coba l t fC o3(C O) ,C R bC03(CO g - n ( L n ) (C R )Co,(CO),C.CHR+

3 )

two isomers

M o , W

1 2 16 36 4656 669, 74, 757 47 4696831 77232621 87 13 3 17 632, 63, 75637 4 , 7 57 47 432 577787969, 7569, 7569, 758 080438 18 232, 63323 30637 4 , 8 4856 3 , 7 4878 9856 3 , 8 5329327, 3289 191, 95, 969497981019 99 91001 2 21011 0 61 0 6 , 1 0 71 2 41 0 21 0 3 , 1 0 41 0 91 2 01 2 01 2 01 2 3

70,a 7332 6

325

1 2 1

64

683177 23262187 0 , 7 37 13 3 1

325787 9

8 0

5 0 6 33 30

838 688

9 2

1011 0 0101

1 0 9

93

9 0329327, 328

9 1 , 2 2 19 1 , 9 59798

99991 2 21 0 61 0 61 2 4

1 0 91 2 01 2 3


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208 Chemical Reviews, 1983, Vol. 83, No. 3T AB L E I ( C o n t i n u e d )

Sappa , Tiripicchio, and Braunstein

1 2 1

1 4 21/431 4 41 4 51 4 61 1 71 4 81 4 91 6 01511 5 21531541551 5 61 5 71 5 81 5 91 6 01 6 11 6 21 6 31 6 41 6 51 6 61 6 71 6 81 6 91 7 01 7 11 7 21731 7 11 7 51 7 61 7 71781 7 91 8 01811 8 2

references -X-raymas s (o r neu t ron)3Cprepn , IRentry complex 'H NMR NMR" spectrum " s t ructure____.I__ -l a t inum' 10 51 2 51 2 7

1 2 9 2 7 4298 2981311 3 3 , 1 3 41 3 51 3 61 3 71 3 91 4 01'401 4 21 4 31 4 4145

1 4 61 4 71481 0 91 4 9 , 1 5 01 4 9151. 1 5 21 6 31 5 41551 5 61 3 415 71 5 79 11 5 81 5 9

Refere nces are reported only f or the papers part icularly concerning I3C NMR or mass spectra l studies of the complexes ,* Series of complexes wi th d i f fe ren t R g roups , on ly in pa r t ob ta ined f ro m a lkynes . " Complexes conta ining l igands differen tfrom the a lkynes , or obta ined from othe r s tar t ing l igands , but showing c lose s t ructura l propert ie s with the a lk yne c lusters.

See alsoObta ined f rom me ta l ca rbynes .See a ls o en t r i e s 21 and 23-28 . ' ee also e n t r ie s 1 4 , 15, a n d 1 3 7 - 1 4 0 . f S e e also en t r i e s 16-21 .See also entries 29 an d 118. I See a ls o ent r ie s 14 3-14 4 , 1 6 3 and 171-174 .See also en t ry 22 .e n t r ie s 1 4 5 a n d 1 4 7 . ' S e e a l so e n t r y 1 4 6 .a greater extent w ith the alkyne derivatives.CO substitution und er m ild conditions, in the pres-ence of anhydrou s M e3N 0,has been shown to occur byC a r t y a n d c o - w ~ r k e r s , ~ ~ho obtained R u ~ ( C O ) ~ ~ -(PPh,C,R) mo nosu bstitute d derivatives, in which thealkyne acts as a formal 2-electron donor; this complexis one of few examples of such behavior. The mono-substituted derivative, upon thermal rearrangement,gives an interes ting series of trim etallic clusters char-acterized by different modes of coordination of the

alkyn e, a nd a pentan uclear c ~ m p l e x . ~ ~ J ~ ~hen hy-drated (o r moist) Me 3N 0 is used a surprising tetra-metallic cluster with a vinylidene sub stitu tent as wellas a triply bridging OH substitutent is obtained.135This examplifies the great potential of this m ethod,which also allows greater selectivity in the productdistribution with respect to the simple thermal sub-stitutions.Th e reaction scheme for the synthesis of th e aboveproducts is given in Scheme I.


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Alkyne-Substituted Carbonyl ClustersScheme I

Chemical Reviews, 1983,Vol. 83,No. 3 209

TABLE 11. Nitrile and Isonitrile (or Derived ther efr om )Complexes Structurally Related to the Alkyne-CarbonylDerivativesre f

X-rayprepn, IR, (or neutron)com plex H NMR structureR u , ( C O ) , , ( C N B u - t ) 1 6 2Fe;(CO j,?NCCH,) HF e, ( CO) , ( HNCCH,)H F e , ( C O ) , ~ N C ( H ) C H , )H 2 Fe 3 ( C0 ) 9 ( NCH 2 CH 3 )HRu, ( CO) , ( HC=NB u- t ),OS,(C O ) o( C N B U - t )H,Os, lCO),(CNBu-t)

1 6 31 6 31 6 31 6 31 6 21 6 4 1 6 41 6 4 1 6 4 . 1 6 6H;Os;(COji (HC=NPh) 1 6 4 1 6 4 ; 1 6 6HOs,(CO),(HC=NPh)[P(OMe)3] 1 6 4 1 6 4HOS, ( CO) , ,( C=N( H ) B u- t ) 1 6 5 1 6 5H W C O ,(C NM e,) 167 1671 6 8 1 6 81 7 0 1 7 0HRu3( CO) , , ( CNM e, )F e 3 (CO), , ( CNBu-f ), 1 7 1 1 7 11 7 2 1 7 2r, (CO) ,,( C N B u - t )Ni , (CNBu-t) , 1 7 3 1 7 3Os6(C O ) 6 ( C N B U - f ) , 1 7 4 1 7 40 s 6 ( C 0 ) 1 8 ( C N R ) 2 1 7 5 1 7 5

P t 3 (C N R ) 6

B. Rearrangements and Reactions of theCoordinated AlkynesTwo se parate cases have to be considered, namely,the rearrangement of a single alkyne molecule, after COsubstitution and coordination to the cluster, and thereaction of a coordinated alkyne w ith other alkynes orligands.Ligand tautomerism can be observed w hen C2 Etzis reacted with Ru,(CO),,; the first reaction prod uct isan allenic hydride obtained upon isome rization of th ealkyne.39*40 ode rate warming of this cluster leads toth e allylic isomer (Figu re 6, 18, 17).37938By reac t ion o f HRU,(CO)~C~BU-~ith the cyclo-

pentadiene ligand, ( C ~ ) R U ~ ( C O ) ~ C C H ~ B ~ - ~s obtained,which shows an other alkyne-to-cluster bonding and ,moreover, the alkyne itself has been hydrogenated.62Reaction with excess alkyne usually leads to poly-substitu ted products and finally to com plexes of lowernuclearity. Th e main reactions on clusters are forma-tion of 5- and 6-membered m etallacycles, som etimeswith c luster opening,l3Jg activatio n an d cleavage of aC=C bond,28,98nsertion of an alkyne into a M-C(a)bond already formed57 or nucleophilic addition of analkyne on theAll these processes will be discussed in detail w henconsidering th e reactivity of th e coordinated alkynes.Cluster formation or opening can be favored by thepresence of ligands; an example of form ation of an open

Scheme I1

0 C

cluster in the presence of an organic ligand is found inScheme 11; displa cem ent of a CO molecule an d forma-tion of a new metal-metal bond a re observed.312 On theother han d, phosphine substitution on a closed metalcluster can ind uce a cluster opening , either in case ofhomometallic derivative^^^ or heterom etallic clusters.C. Reactions of Tetrahedral Clusters withAlkynes and Condensation of Meta l FragmentsInduced by Alkynes

Whereas tetrahedral clusters can react with isonitrilesby simply sub stituting CO ligands, and w ith cyclic di-enes in the same way,180*181he common reaction patternin the presence of alky nes is a cluster opening to givebutterfly structures.2Indeed, tetrahedra l alkyne-substituted clusters arenot common and are usually obtained by indirect re-action pathway^.'^^^'^^^'^ Cluster opening to bu tterflystructures was first observed by treating C O ~ ( C O ) ~ ~ithstoichiometric amounts of alkynes; complexes c04-(CO)lo(RC2R)were obtained,14, the yields dependin gupon t he s ubs titue nts R an d R.lE2 Excess of alkyne sresults in the formation of CO ~( C O )~ (C ~R R )omplexes,with cluster demolition.182Rhodium homologues havebeen reported,lE3which can be obtained by carbynecoupling,lM hat is the opposite of th e C r C b ondbreaking

110 o c2M3(C0)6(CD3)arene)-M4(CO)lo[C2(CD3),]+ 2 M + 2CO + 2 areneIsomers F ~ R U ~ ( C O ) ~ ~ ( R C ~ R ) ~ howing eitherhinge-apex m etal isom erism, and alkyne isomerismwith respect to the heterometallic hinge were ob tainedfrom H2FeRu3(C0)13. In contrast, only alkyneisome rism and no hinge-apex isomerism was detecte dfor the ( C ~ ) N ~ R U ~ ( C O ) ~ ( C ~ H ~ )o m p 1 e x e s . l ~ ~heseisomers are depicted in Scheme 111.Sometimes an extreme situation is found, tha t isthe to tal flattening of a tetrahed ral me tal core to give


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210 Chemical Reviews, 1983, Vol. 83 , No. 3 Sa pp a, Tiripicchio, and Braunstein

Fe2(C0)8(C2Ph2) (ref. 209)3c

Ir4(C0)8 [C2(COOMe)2]4 (ref. 148)

B

b

3NFigure 2. Examples of alkyne or alkyne-derived ligands interacting with two metal atom s (bo nding modes C, D, E, and F).S c h e m e I11

?h Ph

a rectangular ensemble of four metals, as in Ir4(CO)8-[Cz(COOMe)z]4 Figure 2, 5).laThe above way of formation of alkyne-substitutedbutterfly clusters was considered the only one available;2more recently, the butterfly Rk(C0)1 z(RC 2R)was ob-tained from R U ~ ( C O ) ~ ~ ~lso, the tetrametallic Fe4-(CO)11(HC2Et)z 28)%was obtained from Fe3(C0Il2.T w o main hypotheses could be formulated for th e

formation of the above complexes, namely, the presencein solution of tetram etallic species formed upon pyro-lysis of the trim etallic carbonyls, or metal fragmentscondensation.Evidence for me tal fragm ent condensation is obtainedin the synthesis of heterometallic clusters; thus, theformation of (Cp)NiRu3(H)(CO),[C2(H)Bu-t]31) fromHRu3(CO),CZBu-t nd [ Cp)Ni(CO )I2 s best explainedin thismanner.151J52 t has been shown for NiR ua mixedme tal clusters th at th e cond ensation of nickel frag-men ts with a trimetallic ruthenium core depends uponthe structure of the starting ruthenium reactants (whichin turn depends upon the n ature of the alkyne); thus,in presence of HC2R-substituted ruthenium clusters,nickel addition is observed,151whereas for RC2R(R ,R = alkyl) substituted ruthenium clusters, nickelinsertion occurs?53and finally, for Ry(C0)12(C2Ph2)nickel subs titution is the m ore probable process.120This behavior is summarized in Scheme IV.Also, several iron-nickel complexes have been o b-ta ined by fragment ~o nd en sa t io n . 6~ J~ ~* ~ ~n particular,it has been shown that the square-planar complex(Cp)2Ni2Fez(CO)B(C2EbJ25)274annot be obtained byreaction of th e tetrahe dra l (Cp),Ni2Fe2(CO ), withEtC2Et; hence, once more th e m etal fragment conden-sation is the m ost probable explanation for the form a-tion of the mixed alkyne derivatives. The condensationis probably favored by the alkynes, which could act in


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Alkyne-Substituted Carbonyl Clusters Chemical Reviews, 1983, Vol. 83, No. 3 211Scheme IV

Phh

the same way as he semibridging COS",^^ by reducingthe differences in electron density between th e differentmetal atom centers.D. Ligand Exchange between Metals and M etalExchange on Clusters

In the synthesis of the above ruthenium-nickel andiron-nickel derivatives, we observed that ligand ex-change (cyclopentadienyl, CO, and a lkyne) also occursbetween metals; although in most instances this be-havior isnot useful as a preparative method, as simplerroutes for the products are available, in some casesproducts are obtained which cannot be synthesizedotherwise.Thus, whereas R u ~ ( C O ) ~ ( H C ~ B U - ~ ) ~ ~Figure 12) anbe obtained by treating Ru3(CO),2or H R U ~ ( C O ) ~ C & U - ~with excess HC2B u-t, bette r yields are obtained fromt he reactio n of R U ~ ( C O ) ~ ~ith (Cp),Ni2(HC2Bu-t).Nickel has been shown to be a good catalyst for alkynecyclotrimerization, and indeed, in th e produ ct th e alk-ynes are linked in th e same way as is usually fou nd innickel-assisted oligomerization. In this reaction obvi-ously alkyne migration occurs.The product (C~)N~(C~)RU~(CO)~(~~-CO)(C~P~,)(16)123 i s o b t a i n e d b y r e a c t i n g R U ~ ( C O ) ~ith(Cp),Ni2(C2Ph2); ince it bears a cyclopentadieny l ligandon one ruthenium, ligand migration mu st have occurred.No alternative pre paration for this complex is knownat present.The synthetic application of metal exchange inclusters has been reported very recently; (Cp)MCo2-(CPh) (M = Cr, Mo, W) (12) complexes have been ob-tained un der mild condit ions from C O ~ Clusters ViaCO~(CO)~CR-A~M~~M(CO)~(C~)ntermediates;lZ somerelated Fe-Co-M clusters are obtained via the sameprocedure.laIn the above discussed synthesis of (Cp)NiRu3-(CO)g(C2Ph2)see Scheme IV) nickel atom su bstitutesfor a ruthenium in a butterly cluster.

Finally, metal extrusion from a heterometalliccluster has been reported to give a lower nuclearitymolecule. Th is process occurs, for example, in th epresence of phosphine, which complexes one of thenickel atoms eliminated from a Fe2Ni2core,11g Pro-to n- in du ced fr ag m en ta tio n of [ C O ~ R U (C O )~ ~ ( C , P ~ ~in to C O ~ R U ( C O ) ~ ~ ( C ~ P ~ ~ )as recently been eviden-~ e d . ~ ~E. Oxldatlve AddRlon of C-H and H2 to MetalClusters and M-H Addltlon to UnsaturatedLlgands

These reactions lead to hydrido clusters and arewidespread in the ruthe nium and osmium alkyne anda l k en e ch em i ~ t ry . ~ he synthes is of HR U ~( C O )~ -(C 2 B ~ - t )9 3n d of th e H R u ~ ( C O ) ~ ( C ~ H ~ )s 0 m e r s ~ ~ 9 ~reexamp les of oxidative add ition of C-H bonds. Inte r-and intramolecular hydrogen s hifts involving the or-ganic moieties are foun d, respectively, in the synthe sisof Fe3(CO)8(HC2M e)4lo),%Cp)N*e2(CO)&2Me, and(Cp)NiFe2(C0)7CCH2Me.62Oxidative addition of hy drogen is usually reversible:a remarkable example is the synthesis of H3Ru3-( CO )g C CH 2 Bu -t ro m H R U ~ ( C O ) & ~ B U - ~nd H2, as apart of a catalytic cycle.47 In other cases, addition ofhydrogen induces th e loss of th e alkyne ligand, as withR U & O ) ~ ~ ( C ~ P ~ Jhat gives high yields of H 4 R ~ (C 0 ) 1 2a n d t r u n s - ~ t i l b e n e . ~ ~ J ~ ~Th e M-H addition to unsaturated ligands is a generalprocess. A very useful starting ma terial is the unsatu-r at ed c lu ste r H 2 0s3(CO )lo h a t re ac ts with a l k y n e ~ ~ ~ Jas well as with cyclic dienes.78Sometimes, however, hydrogen loss is observed asalready discussed for the reactions of H2FeRu 3(C0)13w ith alk yn es an d in th e syn th es is of ( C ~ ) N ~ R U ~ ( C O )(c6 H9 ) somers.s3F. Protonatlon ReactlonsThese reactions afford cationic derivatives; the pro-cedure is not general because often th e strong proton-ating agents used induce cluster dem olition; the fewderivatives obtained with this technique a re listed inTable 111. Cationic cobalt reactants have been shownto be useful intermed iates in the synthesis of neutralcobalt c l ~ s t e r s . ~ ~ ~ - ~ ~ ~e believe th at th e protonationreactions will be used to a larger exte nt, in view of th einterest in the protonation-reduc tion of CO ligands. Acomparative study of the ease of protonation of themetal framework vs. the ligands (alkynesor CO) wouldbe very informative and useful.0. Reactlons of Carbonyl Anlons

Only few examples of such synth eses invo lving alk-ynes have been reported. T he anions are formed inwatel-alcohol solutions in the presence of strong bases;the final products, usually hydrides, are obtained upo nacidification.H2R u3(C O)g (C2P h2) as obtained in this way48 aswere structurally related chalcogen complexes.lWCobalt derivatives HC O,(CO )~ nd Co3(CO)&OH,obtained from cobalt anions, react with alkynes to giveC O ~ ( C O ) ~ C Re r i v a t i v e ~ . ~ ~ J ~ ~An interesting reaction sequence starting from ironcarbonyl anions and CH3CN and leading t o th e re-


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212 Chemical Reviews, 1983, Vol. 83, No. 3 Sappa, Tlrlpicchlo, and BraunsteinTABLE I11

reaction refCo, (CO),CCOOEtCo, (CO), + C F , C O O R , R = HCo, (CO) , C C(0)R + Et,SiH, R = H ,Ru, (CO), , + R C k C R ,CH,, Ph

R = R = P h; R = Ph, R = CH,R u , ( C O ) , , + (CH,),C--C=CHM, (CO) , , + C,H1,, M = R u , O so s , ( c O ) l z + C2H4H,Os,(CO),CCH,Os, (CO), , + R C H = C H R ,R Z= H , R = H, Ph , CM e, ;R R 2 P h

%SO,H,O+% o, (CO),CCOOH- o, (CO),CCOOR (EtCO),O- o, (CO),CC(R)HOSiEt , %SO,

H S 0 3 F- u4( C 0) 12( C 2R R ) so, C F ~ C O O H__f H,Os, (CO), (C=CH,) CF,COOD

+H, Ph,C+BF,-- ,Os,(CO),CMe in so,H +

HZO__f H , O s , ( C O ) , , ( R C = C H R ) ~

H+5 , Os , (CO) , , (RC=CR) , __*R I RZ IPh)duct ion of acetonit ri le has been r e ~ 0 r t e d . I ~ ~Bis(carbyne) apical clusters of general formula(Cp)3C03(p3-CR)(p3-CR) re formed in yields up to27 % in the synthesis of organic molecules via alkynecooligom erization in th e presence of ( C ~ ) C O ( C O ) ~ . ~ ~ ~ * ~ ~ ~H. Other Reactions

Variations to the above methods, or new reaction s ofnongeneral application a t present are:Cluster formation from N i(CO)4and hexafluorobut-2-yne in sealed vessels, periodically displacing theequilibrium in solution by cooling a t -196 OC andpumping off CO. T he product is Ni4(CO)4[Cz(CF3)z]a.1mPyrolysis of a cyclohexadienone-osmium complexobta ined from alkynes, with activation of a C-H bond,followed by insertion of a CO molecule between theorganic moiety and the cluster metals.lg3Reaction of m etal acety lides with m ono- or bimetalliccarbonyls to give heterome tallic acetylide clusters, ofeither open or closed s t r u c t ~ r e . ~ ~ ~ ~ ~ ~ ~ ~ ~ ~T o our knowledge no reaction of metal vapors in thepresence of alkyn e and CO has been reported so far; thiscould be a very promising synthetic m ethod for unusualderivatives.Also, no redox condensations were attem pted in thepresence of alkynes; these reactions would be particu-larly suitable for volatile alkynes. However, there is agreat probability th at instead of cluster formation, bi-metallic derivatives would be obtained as main prod-ucts.I . Purification Techniques

The usual purification procedures, crystallization,sublimation, and solvent extraction can be used whenfew complexes are present in th e reaction mixtures, orwhen the se show volatility or solubility properties verydifferent from each other. This is not th e common case,especially for the iron derivatives.Inde ed, few examples of high-yield synthesis an d verys imple purification p rocedures have been r e p ~ r t e d . ~ * ~ ~ . ~

[Co, (CO),CCO]+ 18 7[ c o , ( c o ) , c c o ] + 187[Co , (CO) , CC(H)R + 187[HRu4(CO)iz (RCzR) 130[ H , R u ~ ( C O ) , ( H C , B U - ~ ) ]+ 60[H,RM,(CO),C,H, , ]+, R = H , D 188[H , ROs , (CO) , (C=CH , ) ]+ , R = H , D 188[H30s3(CO)9(C=CHz) 188[ H , 0 s , ( C O ) , ( R C = C H R 2 ) ] + 142

[H ,Os,( CO ), RC= CR) I+ 1 4 2Chromatographic techniqu es are the most widespreadpurification methods; HPLC has been reported as auseful system for separating mixed-metal clusters.2Column chromatography, either under air or undernitrogen, is used for separating mixtures of relativecomplexity.Preparative th in layer chroma tography has been veryuseful for complex mixtures ( in some reactions of ironcarbonyls with HCzR alkynes, up to 30 products areobtained). Negative aspects of this technique are tha tair-sensitive products (in particular cobalt and nickelderivatives) are lost; high costs and small quantities ofproducts obtainable are other limiting factors. Some-times, also,some side reactions occur on the TLC plates,thus, care is required when discussing the reactionsleading to oxygenated ligands when this purificationtechnique is employed. On the other hand, the sepa-ration of isom eric products th at would cocrystallize isoften easily achieved by TLC.

I I I . Structural Data In the Solld StateSince 1966 considerable structural work has beenperformed on th e alkyne cluster complexes and a greatvariety of structures has been encountered.In t he following discussion , two m ain aspec ts will beseparately considered: the coo rdination and interac tionof a single alkyne molecule (or of a single alkyne-derivedligand) with more than one metal center and th e oli-gomerization of alkynes on clusters.Th is schem e will also be followed when consideringthe structural d ata in solution, and when discussing thereactivity of the coordinated alkynes.Th e first aspect, namely the activation-reduction oftriple bonds upon coordination to several metal c enterseithe r in clusters and on surface s, has been ex tensivelyconsidered by M u e t t e r t i e ~ . ~ ~ ~ ~ ~owever, only a lim itednum ber of exam ples was quo ted, wh ereas, several newcomplexes containing unusually bound alkynes havebeen recently reported.In this model study of th e activation-reduction ofsmall molecules on clusters, isonitriles, C0,l and alk-


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AlkynaSubstituted Carbonyl Clusters Chemical Reviews, 1983,Vol. 83, o. 3 213Scheme V

C2R , RC$' , C 2 R R ' , C 2 H R R 'R R

R R'\ /c=cI' R,C/R C

R-C=,C-R' ! I \1C

iKJ iL ) :MJ IN ) io1RI H-C /R R P

IO) f RI ( S ic o

ynes were considered, together with hydrogen. Th ealkynes show several advantages with respect t o CO,namely th at th e different substi tuents on the alkynetriple bond can modify both the "basicity" and thepolarity of these m olecules to a considerable extent.Th us, term inal (HC2R ), internal (RC2R', R or R' =alkyl), and symm etrical alkynes (RC 2R, R = alkyl,phenyl, func tionalized organic group) often give rise todifferent reaction patterns, and to a great number ofbonding situations. Further more , the alkynes can actas formal donors of different num bers of electrons ina more complex and versatile way than CO.In Scheme V the bonding interactions of alkyne s andalkyne-derived ligands with one or more metal centersare reported. Only eight bonding modes (namely B, E,F, I, L, N, 0, and P) refer to "true" alkyne ligands,whereas all the others refer to acetylides or to otheralkyne-derived ligands. Bonding mode C was foundneither for alkyne nor for alkyne-derived clusters: ithas been include d, neve rtheless, because-at least inprinciple-this feature could be found in th e near futurefor alkyne-derived complexes.By com parison, the interactions of CO with one ormore m etal centers are also shown in the scheme. Onecan observe th at t he alkynes give a greater variety ofbonding interactions; these can be divided in th e fol-lowing way: interaction with a single metal atom(bonding modes A, B); nteraction with two metal atoms(bonding modes C, D, E, F, G); interaction with threemetal atoms (bonding modes I, J, K, L, M ); and in-teraction with four metal atoms (bonding modes N, 0,P, Q , R, S).

For th e bonding discussion we have used the old uan d a notation, when possible, and th e k n y m otation,even if this latte r, in some cases, may gene rate confu-sion."The second main aspect of the discussion of thestructural d ata concerns the alkyne oligomerization onclusters, and is of importance in view of some stoi-chiometric or catalytic applications. The se complexescan be divided into complexes in which the alkynesform organic rings (cyclopentadienyls, cyclo-pentadienones, benzenes, quinones, tropones) w ith orwithout CO insertion in the o rganic moiety, complexescontaining metallacyclic rings (sometimes these areopen clusters), or complexes containing "open chain"ligands interacting with closed or open clusters.A recent systematization of th e structural data for thealkyne-substituted clusters (am ong others ) consideringthe carbon atoms of the triple bond as part of thecluster skeleton has been proposed by Wadelg5 nd isuseful for explaining some structural p articulars and theelectron counting in these molecules.Few studies have been performed on hy dridic clustersin which the hydrogen is located on the b asis of dire ctevidence.l%For cyclopentadienyl-substituted omplexes, it hasbeen hypothesized th at the q5-C5H5 igand has stericrequirements approximately equal to that of 2.5 car-bonyls, which also agrees with the effective atomicnumber (E.A.N.) rule.lg7A. Interaction of a Single Alkyne (orAlkyne-Derived Ligand) with Clusters.Structures and Triple Bond Activation1. Complexes in Which the Alkyne (or Acetylide)Interacts with One Metal Atom

Examples of "pure" acetylides on clusters (bondingmode A ) are not known and there is low probability forobtaining this struc tural fea ture, which is, on the con-trary, very common with CO and CNR ligands. Thisis probably due to the ease with which the C=C bondcan interact with the other metals present in the cluster;thus, in some metal acetylides, mainly those of thecoinage metals,lg8polymeric structures were found inwhich the acetylide is u bonded to one metal and in-teracts in a a manner with another one.An examp le of linear acetylide sub stitutio n on a bi-metal l ic complex has been found in Pt2(C2Ph)2-(SiMe2)(PRJ2(l);179his is probably achieved becauseof the num ber an d steric hindrance of the other sub-stituents in the complex.

The simple a interac tion of one alkyn e molecule withone metal atom (bonding mode B ) ,which is quite com-mon for monometallic platinum complexes,199 nd israre in bimetallic platinum is not foun din clusters; however, in H O S ~ ( C O ) ~ ( C ~ H ~ ) ( S M ~ )2)moneethylene is coordinated to one osmium atom in this way.Th e structures of the complexes 1 an d 2 are depictedin Figure 1.2. Complexes in Which the Alkyne (or Alkyne-DerivedLigand) Interacts with Two Metal Atoms

Two different bonding modes (C nd D) an be foundwith the ligand perpendicular to the M-M bond axis.An example of the first mode (alkenylidene ligand) is


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214 Chemical Reviews, 1983 , Voi. 83, No. 3 Sappa, Tiripicchio, and BraunsteinTABLE IV. Bonding Parameters for Alkynes Interact ing with One or Tw o Metal Atom s

bond lengths , Abondingcompl ex modea c-c M-C (u) M-C(n) M M reffree alkynePt2(C2Ph)~(siMe2)(PPh3)2 ACu6(C6H4NMe2)4(C2C6H4Me)2 DFe,(CO 1E4CZPhZ)

Ir, (CO),[C,(COOMe), 1 4 EPt( PhC,Ph), BPt , (PMe,) , (PhC,Ph) , BFe2(C0)6(Ph2PC2Ph)2 B(Cp)NiFe(CO),(Ph,PC,H) FPt,(PMe,),(PhC,Ph), FNi,( CO),(Ph,PC,Bu-t), BC O , ( C O ) ~ (hC,Ph) F(CP) ,Ni , (PhC,Ph) FF e z (CO),( t -BuC2Bu -t) FC O , ( C O ) ~ ( ~ - B U C , B U - ~ ) FFe,(CO),( t -BuC,Bu-t) , FH0s3(C0)9(C2H4)(SMe) BF e , ( CO) , ( C ,P h) ( P P h, ) GRhAg2(pph3)3(c2c6F5)5 G1rZCu4(PP 3) Z( c2p h ) 8 GHOs,(CO), , (CH=CH,) HHOs,(CO), , (CH=CHEt) HHOs , ( CO) , , ( CP h=CHP h) HHOs , ( CO) , , ( CF 3C=CHCF 3) HR u (co (c Bu-t)~ ( P p h z '

CDU (C O),( C,Bu-t ) ( PPh,) , -($h,PC,Bu.t)

t3 )4(' hCZP h, 2 F

GG(co 5 ( Zp h , (pp Z )( pp 3 )Pt2(C2Ph)2(SiMe2)(PR3)2

FeCo3(CO),(C,Ph,)(CPh=CHPh) HG(Ph,PC,Bu-t)

1 . 2 04 ( 2 )1 . 2 0 ( 2 )1 . 1 81 . 171 . 371 . 19 (1 )1 . 2 7 8 (11)1 . 2 80 ( 6 )1 . 2 6 ( 5 )1 . 2 6 0 (11)'1 . 2 7 3 (ll)c1 . 37 ( 3 )1 . 3 6 ( 5 )1 . 2 6 9 ( 1 5 ) c1 . 2 9 1 ( 1 3 ) '1 . 4 61 . 3 5 ( 3 )1 . 3 1 1 (10)1 . 3 3 5 ( 6 )1 . 2 8 31 . 34 ( 3 )1 . 421 . 2 3 2 ( 1 0 )1 . 2 2 5 ( 6 )1 . 26 (1 )1.19-1 . 22d1.226'1 . 3 9 6 ( 3 )1 . 4 0 ( 3 )1 . 4 0 ( 5 ) '1 . 3 1 ( 5 )1 . 4 1 ( 4 )1 . 4 1 ( 2 )1 . 2 4 ( 3 )

2 . 0 1 (1)2 . 025 , 2 . 0152 . 028 , 2 . 0541 . 9 6 , 1 . 9 72 . 1 8 5 ( 9 )2 . 1 27 ( 9 ) , 2 .0 9 5 ( 7 )2 . 22 (1 )

2 . 10 (3 ) '

1 . 8 9 1 ( 6 )1 . 96 (1 )2.01-2.04d9i2 .0 4 43g2 . 10 7 ( 3 )2 . 1 5 ( 2 )

1 . 8 9 0 ( 4 )

2.11 (4)C2 . 1 8 ( 4 )1 . 9 8 1 ( 1 l ) j2 . 1 6 ( 3 )

2 . 025b2 . 046 (8 ) , c 2 . 076 (8 )2.064 (8),c .068 (8)1 . 9 4 ( 2 ) , 1 .9 8 ( 2 ) ( F e )1 . 9 3 ( 2 ) , 1 .9 3 ( 2 ) ( N i )1 . 8 9 8 ( l o ) , 1 . 9 3 3 (10)1 . 9 1 9 ( l l ) , . 9 1 6 ( 9 )1 . 8 9 , 1 . 9 3

2 . 0 1 ( 3 ) b

2 . 01 , 2 . 021 . 89 ( 2 ) , 1 .9 0 ( 2 )1 . 8 9 ( 2 ) , 1 .8 7 ( 2 )2 . 0 6 0 ( 7 ) , 2 . 1 3 0 ( 7 )2 . 09 4 ( 7 ) , 2 .0 4 4 ( 7 )1 . 9 9 4 ( 4 ) , 2 . 0 0 3 ( 4 )1 . 9 9 2 ( 4 ) , 1 . 9 9 5 ( 4 )2 . 048 , 2 . 1132 . 049 , 2 . 1162 . 07 (2 ) '2 . 2 3 ( 4 )2 . 23 (4)2 . 125 (8 ) , 2 . 3 0 4 ( 7 )2 . 1 1 6 ( 4 ) , 2 . 2 8 4 ( 5 )2.14 (l), 2.47 (1 )2 . 34-3 . 1 3d*e1 . 98 9 , 2 .186b8h2 . 2 7 3 ( 3 ) , 2 . 3 6 2 ( 3 )2 . 2 8 ( 2 ) , 2 .4 6 ( 3 )2 . 3 4 ( 4 ) , 2 . 4 4 ( 4 ) '2 . 2 1 ( 4 ) , 2 .4 5 ( 4 )2 . 2 0 ( 3 ) , 2 .2 4 ( 3 )1 . 9 9 6 ( l o ) , 2 . 127 ( 1 l ) j

1 7 92 . 4 6 6 2 0 82 . 4742.64 2092 . 8 6 3 (1 ) 5 82 . 715 (1 ) 1 4 83 1 33 1 320 62 . 42 0 ( 4 ) 2 1 12 . 89 0 ( 2 ) 3 1 32062 . 47 3142 . 3 2 9 ( 4 ) 3 1 52.316 (1) 2052 . 4 6 3 (1) 2052 . 2 1 5 2 0 52 . 905 (1 ) 1 0 57 92 . 59 7 ( 2 ) 3 1 62 . 648 (1 ) 2 122 . 7 0 3 (1) 1 7 93 . 086-3 . 1025 1241 5 82 .8 4 5 ( 2 ) 6 82 . 834 (1 ) 31 72 . 820 (3 ) ' 3262 . 8 2 1 ( 3 )2 . 84 8 ( 2 ) 7 22 . 36 9 ( 4 ) 2 9 83 . 139 (1) 5 8

a See also Schem e V. Mean values . Values in tw o independen t .molecules . Mini,mum and maxim um values . e Ag-Cdistances. f Rh-Ag distances . g Ir-C distances. Cu-C distances. Rh-C distances. I Co-C distances.Fe2(C0)8(C2Ph2)3),209 evertheless obtained by irra-diating a solution of diphenylketene and iron penta-carbonyl in benzene; examples of th e second mode ( p -bonded acetylide) are Ru~(CO)~(C~BU-~)~(PP~~)~'(Ph2PC2Bu-t) 4),68 directly obtained from th e corre-sponding alkyne an d C U G R ~ ( C ~ R ' ) ~ . ~ ~ ~The bonding with the ligand perpendicular to theM-M axis is quite common for CO, when involved asa bridge between tw o metal atom s either in a symme-trical or in an unsymm etrical way. Also some =CORligandszo2 n d =CNMe2167J68or - C N B u - P may bebonded to metals in th is way.Exa mp les of alkynes disposed parallel to the M-Mbond (ea-bonded alkyne, bond ing mode E) are rela-tively rare; one example is Ir4(C0)8[C2(COOMe)2]4(5). '48Alkynes, bonded only via 2x bonds ( bond ing modeF) re very comm on in bim eta llic complexes of cobalt,314iron,205 nd In cluster complexes, on thecontrary, this bonding is rarely found ; only in t he opencluster Pt3(PEt3),(CzPh2), 6)Io5has such a behaviorbeen found.Some examples of the bonding modes C, D, E, andF are represented in Figure 2.

Both acetylide and alkenyl ligands can form a a bondand a x bond w ith two metal atom s bridging an edgeof the cluster (a,x- or p-v2-bonded ligand, bondingmodes G an d H).Bonding mode G of the acetylideshas been proposed for several osmium complexes andfound in the trinuclear RU~(CO)~(C~BU-~)~((Ph2PC2Bu-t)4, Figure 2),58 n which the two acetylidegroups behave in a different way (bonding modes D andG). Also in some mixed-metal acetylide derivatives,such as RhAg2(PPh3)3(C2C6F5)5 7)lZ4and Ir2Cu4-(PPh3)2(C2Ph)25sll the acetylides interact in this waywith two different metals. Bonding mode H of thealkenyl (vinyl and stilbenyl) ligands, derived from alk-y n e s , h a s b e e n f o u n d i n H O S ~ ( C O ) ~ ~ ( C H = C H ~H O S ~ ( C O ) ~ ~ ( C H = C H E ~ ) , ~ ~ ~O S ~ ( C O ) ~ ~ ( C P ~ = C H P(9, in the solid state both enantiomers are present),326and in the te tr anuclea r mixed c luster F~ C O ~ ( C O ) ~(C2Ph2)(CPh=CHPh) (8).298 Some examples of thebonding modes G and H are shown in Figure 3. Againfor comparison with the CO ligand, few examples havebeen repo rted , in which the C -0 bond is involved in ax interaction w ith m etals.20'In Tab le IV the structu ral parameters for complexeswith alkynes interacting with one or two metal atoms


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Alkyne-Substituted Carbonyl Clusters Chemical Reviews, 1983, Vol. 83 , No. 3 2150-Q

HOsg CO) < C?h=CHPh)

FeCo3(CO)9(C2Ph2)(CPh=CHPh) (ref.298)~

8A

:WO enantiomers) (ref. 326)9w

Figure 3. Examples of acetylide or alkenyl l igands interacting with two metals (bonding modes G an d H).are reported.3. Complexes in Which the Alkyne (or Alkyne-DerivedLigand) Interacts with Three Metal Atoms

A large number of clusters containing a tetrahedralor pseudo tetrahedral M3C core is known, in particularfor cobalt; in these complexes the apical or cappingCR group (R = alkyl, aryl, halogen) can be derived ornot from alky nes (bond ing mode M , p3-alkylidyne lig-and). A large number of cobalt complexes is known atpresent5 and the chem istry of th ese derivatives has beenextensively studied (see the section reactivity and theScheme XII). Complexes in which metals other tha ncobalt occupy the place of th e CR gro up have also beenreported.213Th e above cobalt complexes are obtained by variousreactions; among these is the acidic degradation of theCO2(CO)6(RC2R) com plex es.21 4Carby ne complexes have been shown to be precursorsfor the synthesis of these clusters215

-20 CMEC-R + COZ(CO)~Co3(CO)&R -I- oz(C0)6(C&)-20 O CM=C-R + (Cp),Ni-(Cp)&CR + ( C P ) ~ N ~ ~ ( C ~ R ~ )

Another synthetic p ath for Co3(CO)&R complexesuses bimetallic cobalt carbonyl lactone derivatives.322C 4 ond cleavage alsoafford s M3C derivatives,%Y2l6finally, hydrogenation of HR U ~ (C O )& ~B U -~ither with

molecular H 2 or hydrogen-releasing ligands affordsapical derivative^.^^?^^Nickel derivatives like those above have also beenobtained from (Cp),Ni and (C6H5CH2)MgC1.103Finally the reaction of Fe3(C 0)12with H C2R alkynesaffords complexes Fe3(C0)8(H C2R)4lo ) ,which, uponinternal hydrogen shift within the alkyne, are charac-terized by CR apical ligands.26 Also, the reactions of(Cp),Ni2(HC2R) with iron carbonyls gave complexeswith apical ligands, upon intermolecular hydrogentransfer.62A comparable situation on a large m etal cluster hasbeen reported157with O S ~ ( C ~ ) ~ ~ ( C M ~ ) ~ ,btained fromethylene.Finally, it is noteworthy t ha t, whereas at th e begin-ning of th e stu dy on th e alkyne complexes, only apicalcobalt derivatives were known, this structura l type isnow widespread also for nickel and the iron triad.Th e struc ture of some significant complexes with CRapical ligands are reported in Figure 4.Thu s, sufficient evidence for the derivation of the seclusters from alkynes in different reactions is obtained(see also the section reactivity).When considering the structures of the complexes,the m ain feature is the tetrahedral core with the ap-ical carbon atom. T he M-C-M angles are close to 80and thus considerably different from th e ones expectedfor sp3 hybridization of th e carbon atom.217This situation is also typical for the triply bridgingCOs, which have been shown in the past years to bea relatively common feature in metal atom clusters.


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216 Chemical Reviews, 1983, Vol. 83, No. 3 Sappa, Tiripicchio, and Braunstein

~e~ (co ) 8 ( H C ~ M ~10

( r e f . 2 6 ) c o g (CO 19 ( me )11

F i g u r e 4. Complexes with CR apical l igands (bond ing mode M).-/rcl

Fig ur e 5. Complexes with alkyne (2u + a) nteracting with threemetal atoms (bond ing mode I).In Table V the bonding param eters for complexeswith apical CR a re reported.Alkyne and alkenylidene ligands can be bonded tothree m etal atoms via two u and one ?r bonds ( 2 u + ?r

or p 3 - q 2 ) . When t he alkyne is bonded, the two u bondsinvolve two different carbon atom s belonging to th ealkyne (bonding modeI).Wh en th e alkenylidene ligandis bonded, the two u bonds interact with the samecarbon atom , whereas the second carbon interacts onlyin a T manner (bonding mode J).Bonding mode I is commonly found in homo- andheterom etallic alkyne clusters and is also common forisonitriles (see Ta ble 11). Som e significant complexesof this type are represented in Figure 5 and their rele-vant structural parameters are reported in Table VI.From th e struc tural da ta, one can see th at th is class ofcomplexes is one of the most common and representsthe one for which the greater number of structuralstudies has been achieved. It is noteworthy th at this

( r e f . 221) Co2Mo(CO)g(Cp)(CPh) (ref . 122)!2

H R L ~ ! L O ) ~ ( C ~ H ~ ~allyl-isorer f r e f . 38

1 -4

Q

F i g u r e 6. Com plexes with allyl and allenyl ligands.bonding brings the alkynic C-C bond nea rly parallel toone edge of the cluster (from which the notation p 3 -( ~ ~ - 1 1 ) s derived for this bonding).Th e bonding mode J is less well encou ntered, at leastfrom the struc tural poin t of view. It has been suggestedmain ly for osmium derivatives, on the basis of N MRevidence4 and found for H2 0s3(C0)9(CC H2).80A bonding situation with a system of carbon atom sacting as a delocalized v-donor ligand and th e term inalcarbon atoms o-bonded to the metals has been alsofound. Th e system of carbon atoms o ften is an allylicligand, obtaine d by isomerization of th e alkyne,38bycondensation of a CR fragment (from C=C bondcleavage) with an other alkyne,28 nd from th e reactionof alkyne s with osmium d erivatives containing ligandswith n itrogen an d oxygen atoms.331 Exam ples of thistype of bonding are shown in Figure 6.


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Alkyne-Substituted Carbonyl Clusters Chemical Reviews, 1983, Vol. 83, No. 3 217T A B L E V . Structural Parameters for Com plexe s Containing "Apical" CR Ligands

c o m p l e xbonding distances, A

M-M M -C c-c M-C-M ang les refCo,(CO),CMeCo,( CO),(PPh,)CMe

(Cp)2C03(C0)~CMe(' SMeS 2c03(c0Co3(CO)s[P(OMe)3 1,CMeCo,(CO),(As,Me,C,F,)CMeCo,(CO ),( C,H,Me,)CPhCo,( CO),CC( =O )Ph(Cp) ,Co,( CSiMe, )(C,SiMe,)Co3(C0)7(C,H8)CEtCo, ( CO) , sC ,H[c03(c0)9c2 1 2

[ ( c P ) , ( c o ) , c l , c oc08(c0)24c6

Co,M o( C O) , ( Cp)CP hFe3(C0)8[CSH2Me2(C2H3) 1H,Ru, ( CO) ,CM eH , R u , ( C O ) , C . C H , B U - ~0s6(C0),6(CMe)2

2.4662 . 4 7 52 . 4 6 22 . 5102 . 4952 . 4902 . 3682.4772 . 4802.4052 . 4842 . 5 0 12 . 4 9 12 . 4 7 52 . 4 8 52 . 4 4 02 . 4792 . 4702 . 4 4 12.4772 . 4762 . 4672.4672 . 3 8 32 . 4 8 32 . 4752 . 4702 . 4622.4702 . 4 8 52 . 4652 . 4 8 52 . 4622 . 46 , ~2.45. :2.46; 2 .452 . 4 4 7 ( 7 )2 . 4 5 3 ( 7 )2 . 4 6 2 ( 7 )2 . 4 9 0 ( 7 )2 . 4 6 6 ( 7 )2 . 4 6 8 ( 7 )2.457 (2)2 . 4 5 6 ( 2 )2 . 457 (1 )2 . 4 67 ( 6 )2 . 4 6 0 ( 6 )2 . 4 7 7 ( 6 )2 . 48 2 ( 6 )2 . 4 71 ( 6 )2 . 47 2 ( 6 )2 . 4 8 3 (1 )2.677 (l)c2 . 52 5 ( 3 )2 . 5 83 ( 2 )2 . 5 15 ( 3 )2 . 8 4 1 ( 6 )2 . 8 4 4 ( 6 )2 . 832 (1 )2 . 836 (1 )2 . 820 (1 )2 . 73 0 ( 6 )2 . 6 7 2 ( 6 )2 . 7 2 2 ( 6 )

a Values in two independent m olecules. Averaged values.Both alkyne and acetylide ligand can be bonded tothree m etal atoms via one u and two 77 bonds (a + 277,

~ ~ - 7 7 ~ ) .his bonding is more common for acetylideligands, in closed and open clusters (bonding mod e K ) .Some of these clusters, such asH R U ~ ( C O ) & ~ B U - ~22),%are considerably stable and have been studied in detail.W ith this type of bonding the m ultiple C-C bond is

1 . 8 6 ( 2 )1 . 9 3 ( 2 )1 . 9 0 ( 2 )1 . 9 0 (1 )1 . 8 9 ( 2 )1 . 9 3 (1)1 . 8 8 ( 2 )1 . 8 2 ( 2 )1 . 8 4 ( 2 )1 . 8 57 ( 6 )1 . 8 6 6 ( 6 )1 . 9 32 ( 6 )1 . 9 2 (1 )1 . 8 9 (1 )1 . 9 0 (1 )1 . 9 0 7 ( 7 )1 . 8 9 5 ( 7 )1 . 9 07 ( 7 )1 . 8 7 ( 2 )1 . 8 9 1 ( 6 )1 . 8 9 3 ( 6 )1 . 9 2 1 ( 6 )1 . 8 73 ( 9 ) b1 . 86 (1 )1 . 88 ( 2 )1 . 9 0 ( 2 )1 . 8 9 (1 )1 . 9 3 (1 )1 . 9 3 ( 2 )1 . 9 1 (1 )1 . 92 (1 )1 . 9 3 (1 )1.93 , 1 .92"1 . 8 7 , 1 . 9 21 . 8 1 , 1 . 9 41 . 9 5 ( 4 )

1 . 90 (1 )

1 . 8 9 ( 3 )1 . 9 1 ( 3 )1 . 9 0 ( 3 )1 . 8 7 ( 3 )1 . 9 5 ( 3 )1 . 9 5 (1 )1 . 97 (1 )1 . 97 (1 )1 . 9 44 ( 2 7 )1 . 9 18 ( 2 7 )1 . 9 1 2 ( 2 8 )1 . 9 0 6 ( 3 2 )1 . 9 3 5 ( 3 2 )1 . 9 70 ( 3 2 )1 . 9 33 ( 5 )2 . 1 0 4 ( 7 ) c1 . 9 74 ( 5 )1 . 9 3 8 ( 4 )2 . 086 (10)2 . 0 7 8 ( 1 2 )2 . 0 91 ( 5 )2 . 0 9 8 ( 5 )2 . 1 1 6 ( 5 )2 . 10 ( 7 )2 . 14 ( 7 )1 . 9 5 ( 7 )

1 . 9 1 0 ( 4 )

1 . 5 3 ( 3 )1 . 5 0 ( 2 )1 . 5 5 ( 3 )1 . 4 9 7 ( 9 )1 . 5 0 ( 2 )1 . 5 0 (1 )1 . 3 7 ( 3 )1 . 4 7 3 ( 8 )1 . 4 1 2 ( 1 4 )1 . 5 2 ( 2 )1 . 4 6 ( 2 )1 . 37 (1)1 . 60 , 1 . 42"1 . 4 4 ( 3 )1 . 3 6 ( 3 )1 . 37 (1 )1 . 3 70 ( 3 9 )1 . 3 6 1 ( 4 4 )

1 . 5 0 9 ( 5 )1 . 5 1 1 ( 2 0 )1 . 5 25 ( 9 )

8 1 . 2 ( 7 )8 0 . 5 ( 7 )8 1 . 7 ( 7 )8 3 . 1 ( 5 )8 1 . 3 ( 5 )8 1 . 3 ( 5 )

8 1 . 9 ( 2 )8 2 . 4 ( 2 )8 0 . 5 ( 2 )8 1 .7 ( 5 )8 0 . 8 ( 5 )8 1 . 8 ( 5 )7 8 . 9 ( 3 )8 1 . 1 ( 3 )8 1 . 0 ( 3 )8 0 . 7 ( 5 )8 1 . 5 ( 6 )8 0 . 6 6 ( 2 2 )8 1 . 7 4 ( 2 3 )8 0 . 5 9 ( 2 1 )8 3 . 0 ( 6 )8 2 . 2 ( 6 )8 1 . 4 ( 6 ) '8 0 . 4 ( 6 )8 0 . 6 ( 6 )8 0 . 2 ( 5 )8 0 . 2 ( 4 )8 0 . 6 ( 3 )8 2 . 4 , 8 1 .0 "83 . 9 , 78 . 981 . 0 , 80 . 27 9 . 5 ( 3 )

7 9 (1)7 9 (1)8 1 (1)8 3 (1)8 0 (1)8 0 (1)7 7 . 6 ( 2 )7 7 . 6 ( 2 )7 7 . 3 ( 2 )79 . 4 (1.1)7 9 . 9 (1.1)79.9 (1.1)8 0 . 5 ( 1 . 2 )79 . 2 (1 . 2 )7 8 . 5 ( 1 . 2 )8 3 . 0 ( 2 ) c8 2 . 0 ( 2 )8 2 . 6 ( 2 )8 0 . 7 ( 2 )8 6 . 0 ( 4 )8 4 . 5 ( 2 )8 4 . 8 ( 2 )8 4 . 6 ( 2 )

7 9 .9 ( 3 )

2 2 12 2 23 2 0

979 5

2 2 32 252 26

9 82272 282 2 92 3 02 3 1

2 3 3234

1 2 22 65 147

1 5 7

Co-Mo and Mo-C distances and Mo-C-Co angles.disposed nearly perpendicular to one side of the metalcluster (so this bonding is indicated by the notation

Examples of this bondin g involving alkynes (bondingm o d e L ) are rather rare; it has been found first inFe3(C0)9(C2Ph2)24).15Also, some tetrahed ral nickelclusters show, on the triangular faces, this alkyne ar-

P 3 - ( V 2 - 1 ) ) .


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218 Chemical Reviews, 1983,Vol. 83,No. 3 Sappa, Tiripicchio, and Braunstein

0Q,

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17/37

AkynaSubstltuted Carbonyl ClustersTABLE VII. St ruc tu ra l Pa rame te rs fo r (u t 2 n ) [ p , - ( q 2 - l ) ]Alkyne Clusters

Chemlcal Revlews, 1983, Vol. 83, No. 3 219

bond dis tances , A com plex M-M M-C(U) M-C(n 1 C-C ref

H R u , ( C O ) , [C,C(= CH,)Ph 1(PPh , )Ru3 CO ),( C Pr-i)(PPh ,)Os, (C O ),( C Pr-i )

(Cp )NiFe, (CO), (C B ud )(PPh, )Ru, (CO), (C,Bu-t)

(cP )Fe3(C0),(C2Ph)H R u 3 ( C 0 ) , ( C , H , , ) ( C 2 B u - t )

H R u 3 ( C O ) , ( C , B ~ - t )HRu,(CO),(Ph,POEt)(C,Bu-t )[Ru3(CO), (CZBu-t)(HgBr) 2

Ni4(CNBu- t ) , (C , Ph2) ,Fe3(C0)Q(C2Ph2)

Bonding Mode K1 . 9 0 4 ( 1 4 ). 7 9 1 ( 2 ) , 2 . 8 1 0 ( 2 )2 . 81 2 ( 2 )2.8392.8792 . 82 5 7 ( 4 ) , 2 . 8 1 5 1 ( 4 )2 . 7084 (42 . 378 (3 ) , c 2 . 564 (3)c 1 . 8 1 32 . 610 13) . . . .2 . 639 (1 2 . 8 6 4 ( 2 ) , 2 . 8 2 6 ( 2 )2 . 8 4 1 ( 2 ) 1 . 9 4 4 ( 2 1 ). .2 . 7 9 8 8 ( 5 ) , 2. 8 2 12 ( 4 )2 . 8407 ( 5 ) 1 . 9 4 6 ( 4 )2 . 9 0 0 ( 3 ) , 2 . 8 1 3 ( 3 ) 1 . 9 6 ( 2 )2 . 80 6 ( 2 )

Bonding Mode L2 . 3 7 7 ( 7 ) , 2 .6 7 0 ( 6 ) 1 . 9 9 ( 3 )2 . 385 (7 ) , 2 .670 (10)2 . 3 7 4 ( 2 ) , 2 . 6 86 ( 6 )2 . 4 8 0 ( l o ) , 2 . 5 0 1 ( 9 )2 . 579 (11)

2 . 0 1 ( 4 )1 . 9 7 2 (8 )1 . 977 ( 8 ) f2 . 0 4 8 ( 1 6 )

(Cp),W,Fe(CO),[C,(C,H.,Me),] 2 . 7 4 5 (l)? 2 . 731 (ly 2 . 264 ( 7 ) h2 . 747 (1 )

2 . 178 (15) , 2 . 188 (14)2 . 1 9 0 ( 1 5 ) , 2 . 27 6 ( 1 4 )

1 . 9 2 9 (10): 2.034 (10)2 . 010 ( l o ) $ 2 . 060 ( l o ?2.040 ( 4 ) , 2 . 0 8 1 ( 5 )2 . 006 (5 ) , 2 . 031 (5 )2 . 165 (13) , 2 . 243 (2 0)2 . 209 (13) , 2 . 252 (14 )2 . 207 (3 ) , 2 . 268 (3 )2 . 214 (3 ) , 2 . 271 ( 3 )2 . 209 (4 ) , 2. 194 (4 )2 . 243 (4 ) , 2. 252 (4 )2 . 19 (2 ) , 2 . 25 (2 )2 . 20 (2 ) , 2 . 26 (2 )2.17 (3 ) , 2 .16 (3)1 . 9 3 ( 3 ) , 1 . 97 ( 3 )2.22 (3),1 . 9 6 ( 3 )2 . 203 (8 )2 . 0 9 8 ( 1 5 ) , 1. 9 47 ( 1 6 )2 . 04 8 ( 1 6 1 . 9 4 5 ( 1 5 )2.052 (5): 2 . 011 (5 )d2 . 04 0 ( 6 ) ,k 2 . 2 8 9 ( 5 ) h

1.2 72 (22)O1 . 2 8 4 (8 )1 . 28 (1 )

1 . 2 8 4 ( 1 4 )1 . 2 99 ( 9 )1 . 3 0 3 ( 2 7 )1 . 3 1 5 ( 3 )1 . 3 2 1 ( 6 )1 . 3 1 ( 3 )

1 . 2 7 ( 4 )1 . 2 9 ( 6 )1 . 3 4 4 (10)1 . 4 09 ( 2 2 )1 . 3 9 9 ( 9 )

T he com plexes a re in o rde r o f increas ing a lkyne ac t iva t ion . Op en c lus ters , mea n value of tw o bond ing d i s tances.He te rome ta l l i c M-M distances. Fe-C distances. e Ni-C distances. Averaged values. 8 W-Fe distances. W-Cdistances.rangement.1wJ4gJMThis particular bonding mode (L)of th e alkyne to the clusters has been discussed by Dahlan d co-workers in detail.15Some examples of th e bonding mode K (complexes21,22, nd 23) nd one example of the bonding modeL (complex 24) are represented in Figure 7. T h estruc tural parameters of the com plexes presenting thesebonding modes are given in Table VII.4. Complexes in Which the Alkyne (or Alkyne-DerivedLigand) Interacts with Four Metal Atoms

This is the maximum number of metal atom s withwhich an alkyne has been found to interact, at thepresent state of the knowledge. This interaction cannotoccur, for obvious reasons, in tetrahedral clusters;whereas it has been found in butterfly, square-pyram-idal, or square-planar clusters and in more complexarrangements.Planar clusters are rare, and within the tetram etallicones one example is Ir4(C0)8[C2(COO Me)2]45, igure2,where th e alkynes behave in two different w ays),l&in which two alkyne units interact with four metalsapparently only via u bonds ( bond ing mode N).Other examples of planar clusters are the hetero-metallic (Cp)2Ni2Fe2(CO)6(RC2R)25) R = R = E t ,Ph;274R = P h , R = COOR)16 in which the alkyneinteracts with all the metals; these are alternativelydisposed, and, as both the iron atoms interact ?r and thenickel atom s interact u with the organic moiety, a u-?r-u-?r bonding situation results ( bond ing mode 0).A square-planar face bearing an acetylide is alsofound in R U ~ ( C O ) ~ ~ ( P P ~ ~ ) ( C ~ P ~ ) ( ~ ~ ) ; ~ ~n this struc-ture, however, two adjacent metal atoms a re interestedin u bonds with th e acetylide, whereas the other two

0

U

4 52 9292 9

1181 7

23 53 667

1 2 1

1 0 91 5 0

15327

HRu~ (CO )~( C~B U~) (ref. 36)

Fe3(CO),(CzPh2) (ref. 1 5 )

24Figure 7. Complexes with alkyne or acetylide ligands (a + 27~)interact ing with three m eta l a toms (bonding modes K and L).adjacent atoms interact ?r ( bond ing mode R ) . Th e re-sulting situation is a two-by-two a-u-7r-a interaction.These three bonding situations on a square-planarmetal arrangement are depicted in Figure 8 and inFigure 2 for the iridium complex.On the other hand, alkyne-substituted butterflyclusters, either homo- or heterometallic, a re relativelycommon; the bonding of the alkyne is usually p4-v2


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220 Chemical Reviews, 1983, Vol. 83, No. 3 Sappa, Tiripicchio, and BraunsteinBu-t] (31),151J52 here the vinylidene interacts u withthree metal atoms and a with the fourth (bonding mode8). A com parable situation in a homom etallic clusteris found in ( H O ) R U ~ ( C O ) ~ ~ ( P P ~ ~ )C,(H)Pr-i] (29).135Finally, the situation with an acetylide interacting u an da with two (wingtip and hinge) metals has been foundin th e h ete ro me tallic com plex N ~ R U ~ ( C O ) ~ ( P P ~(CzPr-i)z 30)156 bond ing mode S) . The structures ofthe complexes 27-31 are represented in Figure 9.A similar coordination for CO and for methyne hasbeen found respectively in HF e4(C0)13-23 6nd HFe4-(CO)lz(CH);237related structu re is tha t of the H Fe4-(C0)12(COM e) luster.318 All thes e have been shown tobe of im porta nce in the general picture of th e homo-geneously catalyzed Fischer-Trop sch reactions. Indeed,from the methyn e carbido clusters can beobtained by reversible hydrogenation-dehydrogenation;on th e other hand , it was shown tha t reactions of co-ordinated CO with acetyl chloride afford carbido clus-tersZMand release C O J . Th is type of carbido clustersis expected to pre sen t carbocation ic r e a c t i ~ i t y . ~ ~Th e stru cture s of these formally analogous complexesare represented in Figure 10.A t present, no similar reactions were a ttemp ted orfound for alkyne derivatives. Further investigations inthis field would be highly desirable.In T able VI11 the main s tructura l features of theabove complexes are reported.

6

22

Ru~(CO),~(PP~,)(C~P~) i e f . 1 5 5 )2

Figure 8. Examples of alkyne or alkyne-derived igands inter-acting with four metal atoms (bonding modes 0 an d R).(u-a-u-a) ( bond ing mode P ) ,e.g., R U ~ ( C O ) ~ ~ ( C ~ P ~ ~ ) -(27).131These structures can be formally considered asderived from u-a--6, p3-q2 complexes upon addition ofa M(CO), fra gm ent on one side of the cluster. Con-versely, this fragm ent can be removed from th e tetra -me t a l l i c c l u s t e r , a s s h o wn wi t h [ C O~ R U( C O) ~ ~ -(CzPhz)]-.33sTh e already discussed substitution ofa R u ( C 0 I 3 with a N i( Cp ) f ra gme nt on R U ~ ( C O ) ~ ~ -(C2Ph2)120ndicates that this interpre tation is probablyc or re ct. T h e iso merism of t h e F ~ R U ~ ( C O ) ~ ~ ( R C ~ R )butterfly com plexes showing this type of s tructur e hasalready been discussed (see Scheme 3) . lZ7Furth er su bstitutio n with alkyne of the above struc-tures leads to flattened butterflies, or nearly square-planar s tructure s with two indepen dent alkynes, e.g.,Ru4 CO) (RC2 R) RCzR). 30 Th e structure of thesecomplexes has been hyp otheszied; whereas an iron ho-mologue, Fe4(CO )ll(HC2Et)228), has been studied byX-ra y diffraction.lZ5 Also in t his complex a p4-q2 (u-7r-u-a) bonding m ode is observed for each alkyne unit.Alkyl-substituted alkynes on ruthenium clustersisomerize to allenic, then to allylic ligand^.^^.^^ Theseallylic ligands ar e also found to coordinate to butterflyclusters. In particular it was found for the (C p)-N ~ R U ~ ( C O ) ~ ( C ~ H ~ )somers153hat there is no significantmo dification of th is organic moiety when passin g fromthe starting trinuclear complex to the tetranuclearproduct (see Scheme 111).Another structural arrangement is found in somebutterfly derivatives, like (Cp)N iRu3(H )CO),[ Cz(H )-

B. Activation of the Alkyne upon Coordinationto the MetalsFollowing a criterion introduced by Muetterties:either for CO , isonitriles, or alkyne triple bonds, theelongation of this bond after co ordination to more thanone metal center is taken as a parameter of activationupon coordination, and used for comparison with thebehavior of these molecules on surfaces. (Wh en dis-cussing the C-C bond activation, and th e bonding pa-rameters in general, in m ixed-metal clusters, the dif-ferent metal radii should be taken into account and thedistances should be corrected in this sense.) This meanstha t the structural parameters in the solid state playa very impo rtant role in discussing th e effects of th ecoordination to several metal centers. It should also benote d th at the concept of activation is obviously re-lated to chemical reactivity and may often involvespecific features of the solution chem istry (such as la-bility, dynamic behavior ...) that are not directly ac-cessible through solid-state structura l data.A gap still exists between metal surfaces and clusters;indeed relatively few very high -nuclearity clusters havebeen obtained, which could be compared to crystallite^.^Th e other clusters still are sm all metal fragme nts, inwhich the ligands play a major role; thus, there is adifference in the M-M distances in the bulk me tals andin small clusters, as pointed out by Mu etterties; themetal-metal distances in clusters are usually longerthan in the bulk metal. On the other hand, the bridgingligands (hydrogen,CO, isonitriles, alkynes) can sho rtenor lengthen the M-M distan ces with respect to non-bridged situations.Th us, a delicate balance of effects determines th ecluster size, and hence, in p art, the activationof smallmolecules on clusters. Th is has been discussed, inparticular, for the 2 0 + K clusters;lZ0 lectronic and


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AkynaSubstlMed Carbonyl Clusters Chemical Revlews, 1983, Vol. 83, No. 3 221

n 0 h

Ru4(C0)12(C2Ph2) ( r e f . 1 3 1 )27Y

V

Fe4(CO) (HC2Et)2 ( r e f . 125)11

(Cp)NiRu,( H)( C 0 ) J C,(H)But] (ref.151)F i g u r e 9. Examples of alkyne or alkyne-derived ligands interacting with four m etal atoms (bonding modes 0,P, Q, an d S).

31

steric fado rs also play a role in de termining the degreeof activation, and some times clusters of com parablesize interact with alkynes in different ways.However, the considerable num ber of structures nowavailable, for ca rbonyl clusters as well as for alkyne-substituted clusters, allows at least some statisticalconsiderations. For th e alkyne clusters, in particular,these agree to a considerable extent with th e hypothesisof Muetterties.Thus, he stronger is the interaction with th e cluster,either for only u-bound or for u-?r-bound alkyne s, th egreater is the probability of finding long C- C distances,sometimes close to the single C- C bond. Perhaps, themain irregularity is found for the 2u + ?r and u + 21rderivatives; in th e forme r a slightly greater activationis found. Thismay be exp lained when considering th erelationships between th e different structures (see re-activity section).

C. Complexes Contalnlng Organlc Rlngs orChalns Formed upon Interaction of Alkynes HeldIn ProximityOften, after th e coordination of one (or two) alkyneson clusters, interaction between the ligands occurs,which leads to st i l l coordinated oligomers. This processis usually accompanied by hydrogen shift; sometim escluster opening is also observed. For the iron clusters,easy dem olition to products of lower nuclearity is alsoobserved in th e presence of excess alkyne.Few exam ples are know n in which the alkynes oli-gomerize to give an organic cyclic ligand coord inatedto the metals; thus in Fe3(C0)8(HC2 Me)4 andFes(CO),(HC,Et), (19)28 ubstituted cyclopentadienylsare forme d from alkynes. Complexes containing me-tallacyclic ringsaremore common. Metallacyclobuteneshave been reported, as well as metallacyclo-


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222 Chemical Reviews, 1983,Vol. 83,No. 3Me

Sa pp a, Tirlpicchio, and B raunstein

\t 0

b 0

HFeL(CO)12(CH) [ ; ?4 ( co ) 1 3 J -F i gure 10. Butt erfly clusters in which CO, CH , COMe, and Cintera ct with four iron atom s (see related 29 a n d 31).

3 a

3 s (CC,q[(HC2Ph)2CO/ ( r e f . 8 3 )Fe ( C C J , ~ H C ~ ~ ~ ) ~r e t . 2 2 )

22 !!F i g u r e 11. Complexes containing metallacycles obtained fromalkynes.pentadienes either on closo osmium clusters86~se~wr onthe central atom of an open ironlg or ruthenium clus-ter.53s55 n some instances one of th e term inal m etalsof an ope n cluster can be incorporated in to a 5-mem-bered ring.57 Isomers of the se derivatives can be ob-tained, depending upon the alkyne substitution. Aunique metallacyclohexatrienic ring has been found inFe3(CO)8(HC2Me)332).22Unusual metallacyclic rings with insertion of one CO,which is probably a former terminal CO of the cluster,have been found fo r Os3(CO)g[(HC2Ph)zCO]3 3 P an dfor the isomers R U ~ ( C O ) ~ ( C ~ ~ H ~ ) ( C ~ ~ H ~ O ) ,hese latteralso containing an open chain alkyne dimer@ see thenext section). T he structu res of the complexes 32 and33 are represented in Figure 11and tho se of th e isomersin Figure 12 .D. Complexes Contalnlng Open ChainOligomers

Alkyne di- and trimerization can result in openchain substituents linked to metal clusters; thus, in theabove R u ~ ( C ~ ) ~ ( C ~ ~ H ~ ~ ) ( C ~ ~ H ~ ~ ) ~ne of the sub stitu-ents is a dimer formed upon insertion or nucleophilic

lJl(CO)g(HC2Bct)3 RL3(C0)g(C1~H12) RJ3(CO), {(C2P~21(c28Yt) PhC2(H)Ph;](re:. 5:) ( r e f . jY )( r e f . 5 1

F i gure 12. Comp lexes contai ning open chain oligomers ob-tained from alkynes.attack to the coordinated acetylide in the startingH R U ~ ( C O ) ~ C ~ B U - ~ ;he same process occurs for Ru3-(C0)7(C2Ph2)[(C2Bu-t)(HC2Ph2)]59nd results in acomparable organic moiety.Also, insertion of two tert-butylacetylene moleculesin the Ru-C u bond of th e above hydride acco unts forthe formation of th e open chain chelating the centralmetal atom of t h e op en tr ia ng le in R U ~ ( C O ) ~ ( H C ~ B Ut)3.57Dimerization of isopropenylacetylene on Ru3 (C-0)12lso affords an open chain inTh e structu res of th e above com plexes, in which thecarbonyl groups are o mitte d for clarity, are schem ati-cally represented in Figure 12.The open chains discussed above always containone carbon atom involved in a complex bonding withth e metals, which is characterized by irregular bond-ing angles, not consistent with th e known hy bridizationsof the carbon atoms. At presen t the reasons for thisrather common behavior are not clearly understood.On the other hand, the dienes simply substitute COligands without affecting the main characteristics of t heclusters, either su bstituted235 r not.242I V. Spectroscoplc Data In SolutlonA. Infra red Studies

At presen t no studies on frequency assignments orforce constant calculations have been perform ed, mainlybecause of the complexity of these molecules. Also,whereas it is very easy to detect t he different types ofcoordinated COs, the detection of th e C-C vibra tionis very difficult.On the other hand, routine use of IR has been shownto be useful for the d etection of some functional groups,as well as for indications on the bonding of t he COsubstituents.In particular, th e observation in solution of one moreabsorption th an expected for the bridging carbonyls of( C P ) ~ N ~ R U ~ ( C O ) ~ ( ~ ~ - C O ) ( C ~ P ~ ~ )as shown thepresence of an isomer with a doub le CO bridge, whereasin the solid state an asym metrical triple bridge has beenfound. A similar isomerism has been found for Fe3-(CO)9(p3-CO)S143n solution, and for rhodium com-


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AkynaSubstltuted Carbonyl ClustersScheme VI

Chemlcal Reviews, 1983, Vol. 83 , No. 3 223

plexes with different a lkynes, in th e solid state.These isomers are represented in Scheme VI.B. H NMR Studies

Th e best known application of this technique is thedetection of the h ydrido ligands, which are freque ntlyfound in th e alkyne-carbonyl cluster chemistry.The hydrido clusters have been recently re ~ ie w e d ,~thus only few commen ts will be ad ded here.Although som e differences can be observed betweenth e chemical shifts in different complexes, these d ataare not sufficient for unequivocal structural assign-ments. Indeed the re are only limited correlations be-tween the sub stituent type and the hydridic signals, alsoit is difficult to find suitable param eters for describingthe influence of th e alkyne ligands on the cluster, andhence on th e hydrido ligand chemical shift.Alkyne fluxionality has been detected by means ofNMR for a + 2 x and 2a + x bond ed ligands;261 hes efindings agree with the stru ctura l relationships foundfor these complexes (see reactivity section).Exam ples of hydride fluxionality, and H /D exchangeprocesses have been o b ~ e r v e d ; ~ ~ ~ ~ ~lso, protonationstudies have been performed.60 These are of interestin order to detect the nucleophilic centers in theseclusters.Two other potentialities of the NM R technique de-serve attention, namely:T he identification of sub stitution isomers either inhomo- or in heterometallic which could bedetected , bu t not fully characterized by IR. However,the knowledge of their molecular struc ture by X -raydiffraction remains fund ame ntal for a complete iden-tification.T he detection of hydrogen atoms bound t o carbonsinteracting e ither u or x with the metals. Th is allowsstructural predictions with remarkable accuracy, as,either in bim etallic derivatives or in clusters it has been

found th at these hydrogens give rise to lowfield s ignalswith respect to their expected normal shifts.These data are collected in Table IX.One can observe tha t these signals fall usually be-tween -1 and +1.5 7 and hence the y constitute a gooddiagnostic mean. T he very deep reason for this be-havior has no t been clearly explained; it is interestingto observe that carbon atoms a-n-bond ed to metals alsogive lowfield signals in the 13C NM R prob ably b ecau seof their pseudocarbenic situation (see Tab le XI).C. lS CNMR Studies

Of the many struc tural studies using this technique,relatively few concern alkyne clusters. Com mon fea-tures in alkyne-carbonyl clusters are multistep pro-c e s ~ e s . ~ ~ hus, in the spectra of Fe3 (C0)8(C2Ph2)2,black an d v iolet isomers,18 and of Fe3 (C0 )8-(HC2Me)332)22 t wa s found th at the COs on the ironatoms a-bonded to th e organic moiety did not partici-pate to the exchange processes. In the spectrum ofFe3(C 0)8(H C2E t)4 a two-step exchange processwas found: equivalence of term inal COs (via axial-equa torial or pairwise bridge-terminal CO exchange ),the n delocalized scrambling involving bridging carbo-nyls.Rigidity up to 100 C has been reported for theH3M3(CO)gCMe M = Ru, Os) species.258 In theHM3(CO)9C2Bu-t M = Ru, Os) hydrides34first ste-reochemical nonrigidity a t M-C( u), then delocalizedscrambling for Ru (for Os only up to 17 3 C) were ob-served. In sev eral HRu3(CO),(RCCHCR) derivativess9only localized scrambling h as been observed and theexchange processes at each m etal have different acti-vation energies depending upon the n ature of the M-Cbonding, the substituen ts of th e organic moiety and th epresence or not of hydrido bridges. Th e nature of theM-C bon ding may also influence the regiospecificsubstitution of phosphines for COs.In these complexes no fluxionality was found for th eorganic moiety with respect to the cluster; in these, aswell as in other examp les, the flwion ality of t he alkynewould require intermediates w ith different metal-car-bon bond s, hence high activation energies.Indeed, Hoffmanns recent work on bimetallic per-pendicular a nd parallel acetylene complexes has shownthat the two alternative geometries have differentelectronic requirements;323 ach mode of acetylene co-ordination requires a different coordination geometryat the metals and the interconversions hence requirea relatively high activation energy.324However, some exam ples of alkyne fluxionality havebeen d iscussed, on similar s tructures.2 44 Also, in th eH O S ~ ( C O ) ~ ~ ( C H = C H R )erivativesm results consistentwith ligand fluxionality were repo rted. One of th e formsof H2M 3(CO)&R R) (M = Ru, Os) show s CO rigidityup to 100 C , the n localized exchange and hydrogenmigration, whereas the other one shows three processes,namely, hydride exchange , the n localized exchange ofCOs at M-C(u), then fluxionality of the organicmoiety.261Rapid intramo lecular rotation of the benzy ne ligandin HOs3(CO)g(AsMe2)(C6H4),ia the formation of CO-bridged interm ediates has been recently proposed.325Also, the differen t orientation of the alkenyl ligandswith respect to th e hydridic clusters in the complexes


22/37

224 Chemical Reviews, 1983, Vol. 83, No. 3 Sappa, Tiripicchio, and Braunstein

0*3

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0

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+ W"." *v! sr+ rl H O S ~ ( C O ) ~ ~ ( R C = C H R ' )n the solid state has beenconsidered; hu s the vinyl groups -HC==CHR (R = H ,Et) behave differently from the stilbenyl ligand -PhC=CH Ph.326 Th e fluxional behavior of this latterhas been reported326 nd th e proposed fluxional mech-anism is shown in the Scheme VII.Th e 'H and 13C NM R techniques have also allowedseveral reactions of t he alkynes on clusters to be easilyfollowed. Th us, therm al decarbonylation of Osg-(CO)11(AsMe2CHCH2)n refluxing hydrocarbo ns givessuccessively OS~(CO)~~(ASM~~)(CHCH~),O S ~ ( C O ) ~ -(A sM e2) (C .C H 2) n d H O S ~ (C O )~ (A S M ~ ~ ) (C H C H ) ;hisis the first known example of isomerization of pug-vinylidene t o p3-acetylene on clusters.256Also, the reactivity of hydroxyalkynes and amino-alkynes has been followed by this technique (see, forexample, ref 45).Also, temperature-depe ndent "flipping" of a n organicmoiety has been found, in the binuclear Fe2(COI6-[(COO )(C2Eh)] omplex, and in related systems.262Asa personal opinion of th e autho rs, we consider th at theseNM R experiments should be m ore often followed bya comp lete and stoichiometric recharacterization of t heproducts after variable temperature runs.Among th e te tran uc lea r derivatives, C O ~ ( C O ) ~ ~ ( C ~has been studied;18 he limiting spe ctrum was not ob-tained because of the poor so lubility of th e com pound.Interchange of bridging and term inal CO's on the fourmetals was reported.From th e above results, and with the expressed res-ervations, one can see tha t CO fluxionality is obviouslydepen dent upon th e structu re of the complexes; andth at alkyne fluxionality is not infreq uent, despite thepredicted high-ac tivation energies. Th e significance ofthese behaviors for the study of the adsorption phe-nomena of small molecules onto surfaces are clearlyunderstandable.From I3C NM R spectroscopy other interesting da tacan be ob tained, such as chemical shifts of the alkynecarbons involved in the bonding with the metals. Thisis of considerable value, either when considering thelack of IR results available on these ligands, or whendiscussing th e electron donor-acceptor prop erties ofthese carbons.Unfortunately, only few attempts of rationalizationof these d ata have been p erformed, one being addressedto the Co,(CO)&R complexes.92 In Ta ble X the datafor these com plexes and for "apical" COS re compared;also, some complexes for which struc tural work has notbeen possible are considered.Also th e chemical shifts of carbons involved in C-T-bonding with the metals can be of inter est, and usu allylow-field chemical shifts are found. Experimen talproblems, as well as several steric an d electronic factorssuperimposed with the p rimary interaction, limit theutility of these data. Nevertheless a rough correlation

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24/37

226 Chemical Reviews, 1983, Vol. 83,No. 3 Sappa, Tiripicchio, and BraunsteinTable IX .( a n d R e l a t e d C o m p o u n d s )Low-Field 'H Chemical Shif ts in Binuclear and Clus ter-Alkyne Complexes Conta ining o-n-Bonded Carbo n Ato ms

complex 'H chem. s h i f t , T ref( C p ) F e ( C O ) , ( R C O C H = C H ) R = Me 1. 23 24 6R = Ph 0.79 24 6( C p ) F e , ( C O ) , ( R C O C H = C H ) R = Me -1.34 24 6R = Ph -1.60 246(Cp)Fe,(CO),(X')(XCH=CH)= X = I 0 . 83 24 7X = Br, X' = I 1 . 0 9 2 4 IX = X' = Br 1 . 35 24IX = X =c1 1 . 7 6 2 4 7

X = F. X' = Br 2.10 24 7Fe , (CO) , (SR)(CH= CH, ) 1 . 85 247F e , ( C O ) 6 [ ( R ' C , R ) ( C O ) ( H C , R ) ]R = Ph , R ' = H 0 . 50 24 8R = R ' = Ph 0.64 24 8R = R ' = Bu-t 1 . 30 24 8R = R ' = Pr-n 1 . 3 5 2 4 8R = R ' = M e 1 . 4 2 2 4 8R = Pr-n , R ' = H 1 . 5 0 2 4 8R = Me, R ' = H 1.54 24 8R = B u - t , R ' = H 1 . 7 6 2 4 8F e , ( C O ) , ( H C , R ) , ( C O ) R = Ph -1.80 24 9R = E t -0 .1 5 250R = B u - t 0.01 249comp lex s o lven t t emp, K chem. s h i f t , T ref

0 s 3 ( C 0 ) , 0 ( H C 2 C 6 H 5 ) (CD, ), CO -0 . 06 6 30s3(C0)10(HC2C6H5)~ cc1, 1 . 2 0 6 3H0s3(C0)9(C6H4 CDC1, 213 1.45, 0 . 9 9 2 5 1H0s3(C0)9(C6H4 CDC1, 223 1 . 35 , 0 . 88 251CDC1, 36 5 1.16 251HOs, (CO), (C,H, ) , form B CDC1, 300 1.9 4 ( d ) 74

H0s3(C0 C DC l; 3 3 3 1 . 3 2 ( m ) 3 0 9H0s3(C0)9(HC2H) (CD,) ,CO 1 53 1.6 4, -0 .14 24 4HOs , (CO) , (HC, Ph) CDCI ,HO s,(CO ),(C,H4 1 CDC1,H 2 s 3 ( C 0 ) 9 ( C 8 H 1 4 ) CDC1,H,Os3(CO), ,(CH) CDC1,HRu, (CO)9(C , H, ) cc1,HRu, (CO) , (C , H, ) cc1,H R u , ( C O ) , ( H C = N B u - t )0s4(C0)12( '4C~H) CD,Cl,0s4(C0)1,(HC,Et) CD,Cl,H,Os , (CO), , (CHCHCHMe)H,Os,( CO) (CHCPhCHMe)H,Os, (CO) , , (HC ,HR ) CDC1,H , O s , ( C O ) , , (H C ? R ) R = H CDC1,R = P h C DCI,R = Bu-t CDCl;

with th e reactivity of t he involved carbons can be evi-d e n ~ e d . ~ ~ ~The chemical shifts for "pseudo-carbenic" carbons,by comparison w ith terminal an d doubly bridging CO'sare in Table XI.Provided tha t the NMR da ta are somew hat indicativeof th e electronic density on th e involved carbons, andtha t m uch more system atic work is made, this couldbecome in the fu ture an even more important m ethodfor predicting the reactivity of the complexes.V. Mass Spectra

Mass spectrometry is a quick and useful tool foridentification-and som e stru ctu ral predictions-onvolatile complexes, which is usually the case for tri-metallic alkyne derivatives of the iron triad.Na ture of the metal cluster (particularly imp ortantin case of hetero meta llic clusters), number of carb onylsand other ligands, molecular weight, a nd hydrogen lossare the m ain information obtainable on small samples.Instrume nts w orking with electron impact ionizationsystems have been rep orted 2 as the m ost useful; otherionization tec hniq ues (chemical ionization, field ioni-

3 0 0 1 . 5 5 7 43 0 8 1 . 0 5 813 1 3 1 . 8 2 810 . 64 (9 ) 2541 . 3 8 3 91 . 4 5 3 90 . 5 5 2 5 5- 0 . 2 8 1 4 0- 1 . 0 1 4 0- 0 .3 7 ( d d d ) 2 5 3- 0 .2 5 ( d d ) 2 5 3308 1 . 32 , 1 . 17 , 0 . 94 2523 0 8 0 . 2 0 2 5 23 0 8 0 . 07 2 5 23 0 8 0.10 252

zation or desorption, negative ionization) have beenapplied in very limited exte nt until now. Field de-sorption and fast atom bombardment (FAB) seemparticularly useful for detecting the parent ions incomplexes that would otherwise fragment.269!270Lim iting factors are essentially:Volatility of the sam ples: it is drastically reduced inthe case of phosph idoalkynes, phosphine derivatives,anionic clusters an d large polymetallic derivatives.Rearrangements in the instrument; this has beenrepo rted in particular for Co-Rh derivatives.*Dependence of the results from the characteristics ofthe instrument271or from the experimental condi-t i o n ~ . ~ ~ ~ ~ ~ ~Finally, in th e working co nditions, especially whenthe tem peratu re increase in the introduction systemsis no t rigorously controlled, deposition of me tal in theinstrum ent can occur, resulting in gradua l loss of sen -sitivity and reduced machine lifetime, and frequentmaintenan ce operations. In particular, instrumentswith sealed-glass connections must be avoided for theseanalyses.For thes e reasons a low number of stu dies has beenperformed on alkyne clusters, whereas it would be


25/37

AlkynaSubstRuted Carbonyl ClustersT AB L E X .TriDlv Bridging COs and AD ical-COR GroupsNMR Chemical Shifts for Apical Carbons,

Chemlcal Reviews, 1983 , Vol. 83,No. 3 227

t e m p , c h e m .co m p lex so lv en t K sh i f tu refA . Trip ly Bridging COsRh,(CO)l , I - e 2 0 4 2 4 5 . 3 , 2 6 32 3 9 . 2 .

Fe,(CO), , (COCH,)- f 1 5 3Fe,(CO), , [ COC(= O)CH, 1- f 1 7 3Fe?,(C0)10(C0CH3)~ f 1 5 3F e , ( C O ) , o [ C O C ( = O ) C H , ] - f 1 7 3HFe3(C0)10(C0CH3) f 1 5 3f 1 7 3

f 1 6 6[ H F e , ( C O ) ~ ~ l - f 1 5 3[ H F e , ( C O ) , , ] - b,d f 1 8 6HRu3(C0)10(C0CH3) f 1 7 3Fe4(C0)12(C0CH3)- e 1 8 3

B. Apical COR

HFe3(C0)10(C0H)[HFe3(C0)11 1-

H,Os , (CO) , (COCH,)

Co,(CO),CH gCo,( CO),CCH, gCo,(CO),CPh gC o 3 (CO) ,CCF , gCo , (CO) ,CCOOCH, gCo,(CO),CX, X = F g

C. Apical CR

x = c1 P

2 3 2 . 92 6 4 2 6 52 8 1 . 6 2 6 53 3 6 . 8 2 6 52 9 2 . 9 2 6 53 5 6 . 5 2 6 53 5 8 . 8 2 6 53 0 1 . 3 2 6 62 8 5 . 7 2 6 63 5 5 . 1 2 6 63 6 6 . 5 2 6 72 0 5 . 2 2 6 43 6 1 . 2 2 6 82 6 3 9 22 9 6 9 22 8 6 9 22 5 5 9 22 6 8 9 23 0 9 9 22 7 6 9 2,X = Br g 2 6 9 9 2x = g 2 3 4 9 2Fe,(CO),(HC,Me)4 g 345 .6c 26Fe,(CO ) , (HC,Et 14 g 3 4 2 . 3 c 2 5 0

6 0H,Ru,(CO),CCH,Bu-t g 2 0 5 . 2 4 7 ,s , downfield posi t ive wi th respect to TMS. Differen tco u n te r io n s . I so m er 1 of k n o w n s t ru c tu re ) . Wi thBF, .Et ,O. e CD,Cl,. f CHFCl, /CD,Cl , . g CDCl,.

highly desirable th at more sy stematic information wasavailable, especially when considering th e accessibilityof this technique.Mass spectro metric irregularities were useful for amo

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B9C1 Alkine Rev