1980 923Organosilicon Chemistry. Part 26.la Silyl Derivatives of SubstitutedCobalt Carbonyls, of the Type [Co(SiR3)(CO),L4-,]By Robert N. Haszeldine, Adrian P. Mather, and I?. V. (Dick) Parish,* Department of Chemistry, TheUniversity of Manchester Institute of Science and Technology, Manchester M60 1 ODThe series of cobalt(i) silyl complexes [Co(SiR,)(CO),L,,] (R = F, n = 1-3; R = Ph or OEt, n = 2 or 3;L = tertiary phosphine or arsine) has been prepared, and the reaction of [Co(SiR,)(CO),] with PPh, has beenstudied. For R = Ph, substitution of CO occurs rapidly to give the unstable cis-[Co(SiPh,)(CO),(PPh,)], whichisomerises slowly to the stable trans form. For R = Et, however, decomposition occurs to give Si,Et, and [{Co-(CO),(PPh,)},]. Three distinct geometric isomers of [Co(SiR,)(CO),L,] have been obtained by different prepar-ative routes.COBALT forms a wide variety of complexes of the type[Co(MR,)(CO),] (M = Si, Ge, Sn, or Pb), but those inwhich the CO groups have been partially replaced byanother neutral ligand are relatively uncommon.Forthe heavier members of Group 4, the reaction of MR,Xwith [Co(CO),]- is a satisfactory and convenient pre-parative method, but with silicon derivatives success ismuch less A better route to cobalt-silyl com-plexes appears to be the oxidative addition of a tertiarysilane, SiR,H, to cobalt carbonyl, which is known to pro-ceed in part by hydrogen elimination between the silaneand [CoH(CO),] ., The hydrogen-elimination route ap-peared to be a promising method of obtaining substitutedderivatives, although we have previously found that[CoH(N,)(PPh,),] and [CoH,(PPh,),] react with silanesto give cobalt(1rr) silyl complexes.lb We now present anexamination of the reaction of tertiary silanes with[(Co(CO),L},] and with [CoH(CO),L,-,] (L = tertiaryphosphine or arsine) and of [Co(SiR,) (CO),] with neutralligands.RESULTSReactions of Tertiary Silanes with Cobalt Carbony1s.--(i)With [{Co(CO),L},].The triphenylphosphine derivative[{Co(CO) ,(PPh,)}d was unreactive towards SiF,H, SiCl,H,SIR,oc-~-co\ / oc ILSiH(OEt),, or SiEt,H in benzene, toluene, tetrahydrofuran(thf), or nitromethane, a t temperatures up to 70 "C. Thecomplex does not dissolve in any of the solvents underthese conditions, which probably explains the lack ofreaction since the anticipated products were obtained byother routes.The complexes [{Co(CO),L},] (L = PMe,Ph, PEt,, PBu",,or AsMe,Ph) were more soluble and more reactive.,411reacted readily with SiF,H to give extremely air-sensitiveoils which were difficult to characterise. For L = PMe,I'h,a solid was obtained the analysis of which was consistentwith the formulation [Co(SiF,) (CO),(PMe,Ph)]. The i.r.spectra of these complexes and of the product of reactionbetween [{Co(CO),(PMePh,)},] and SiH(OEt), (also an oil)showed two C-0 stretching bands a t ca. 1 970 and ca. 1 910cm-l. The spectrum of solid [Co(SiF,) (CO),(PMe,Ph)] alsoshowed a band a t 324 cm-l attributed to Co-Si stretch-ing.lb- 5-7 These complexes are expected to have trigonal-bipyrainidal structures ( l ) , as in the related germyl andstannyl derivatives 'p8 and the isoelectronic [Fe(CO),L,] ;the i.r.spectra are consistent with this structure.'OWhen these reactions were attempted with chlorosilanes,SiClR,H (K = C1 or Me), or in chlorinated solvents, decom-position occurred to give residues of the green [CoCl(PPh,),]or blue [CoCl,(PPh,),].(ii) With [CoH(CO),(PPh,)]. The complex [CoH(CO),-(PPh,)] in pentane (prepared in situ) reacted with SiF,Ha t - 95 "C with evolution of a non-condensable gas and pre-cipitation of a yellow solid. The i.r. spectrum of the solidwas very similar to those of the complexes described above(Table l), and on this basis and the (rather poor) analyticaldata the product is formulated as [Co(SiF,) (CO),(PPh,)].On one occasion a product with an i.r. spectrum identical tothat of [Co(SiF,) (CO),(PPh,),] (see below) was obtained.As explained in the Experimental section, it is difficult toavoid an excess of PPh,.When SiH(OEt), was used a bis-(phosphine) complex was again isolated. Since [CoH(CO),-(PPh,),] was found not to react with SiH(OEt), (see below),this product must arise by attack of PPh, on [Co{Si(OEt),}-(co) 3(PPh3) 1.Triphenylsilane reacted with [CoH(CO),(PPh,)] a t - 78 "Cto give a yellow-orange solid, but no gas evolution wasobserved. The i.r. spectrum of the solid was complex: theC-0 stretching region showed bands a t 1880w, 1922vs,1 95Os, 1 975s, and 2 000s cm-l, indicating that the productwas a mixture of a t least two compounds.The solid wasdissolved in benzene and treated with carbon monoxide forseveral hours, when a white solid was obtained which showedonly a single strong i.r. band in the C-0 stretching region, a t1950 cm-l, which agrees with the reported spectrum of[Co(SiPh,) (CO),(PPh,)] ., It seems likely that the initialorange solid contained this complex together with its pre-sumed precursor, [CoH,(SiPh,) (CO),(PPh,)].No reaction was found between [CoH(CO),(PPh,)] andeither SiEt,H or SiMe,H a t low temperatures ; when warmed,the reaction mixtures rapidly deposited [{ Co(CO),(PPh,) } 2 ] .The disubstituted hydride[CoH(CO),(PPh,),] did not react with SiMe,H, SiEt,H,SiF,MeH, or SiH(OEt),.With SiF,H a yellow solid wasobtxined, the i.r. spectrum of which showed two strong C-0stretching bands (1 920 and 1 965 cm-l) and analysis con-(iii) With [CoH(CO),(PPh,),]924 J.C.S. Daltonfirmed the formulation [Co(SiF,) (CO),(PPh,),]. The spec-trum of the Si(OEt), derivative described above is verysimilar. A product of the same stoicheiometry was obtainedearlier lb by reaction of [C.oH,(SiF,) (PPh,),] with carbonmonoxide, but this showed strong C-0 bands at 1 935 and2 000 cm-l; this reaction was repeated, and the same pro-duct was obtained. These two compounds must be theisomers (2) and (3), since structures like (4), with Ph,P-Co-PPh, bond angles of ca. 90°, would be unfavourable on stericgrounds, while (5), with a linear OC-Co-CO arrangement,TABLE 1Infrared data (cm-l) for cobalt-silyl complexes in Nujolmulls, except where indicated otherwiseComplexCCo(SiF3) (CO),(PPh3)][Co( SiF,) (CO) ,( PMe,Ph)][Co(SiF,) (CO),(PEt,)] a[Co( SiF,) (CO),( PBu,)] a[Co(SiF,) (CO),(AsMe,Ph)] a[CO{S~(OE~),)(CO)~(PM~,P~)] aCo(SiPh,) (CO),(PPh,)]Co(SiPh,) (CO),(PMePh,)]Co(SiPh,) (CO),(PEt,)] aCo( SiPh,) (CO),( AsPh,)]Co( SiPh,) (CO),( SbPh,)].Co(SiF3) (CO)2(PPh,)z][Co(SiF3) (co) 8 (Pph.9) 21[Co{si(oEt),}(Co)z(PPh,),l[Co(SiPh,) (CO),(PMePh,),][Co(SiPh,) (CO)2(dppe)l *[Co(SiF3) (co) (PPh3) 31v(C-0)1980m,1936s1962m,1 905s1965m,1910s1963m,1 908s1970m,1917s1968m.1919s1950vs1 940vs1 940vs1945vs1935vs1965s,1920s2 ooos,1935s1965s,1925s1940m,1870vs1960m,1 880vs1945sc Isomerv(Si-F)848m,820s852m,810s865m,815s860m,812s872m,820s870m,825s840m,800s875m,805sv (Co-Si)3283243 50340340ba In toluene.Obscured. (3). from [CoH(CO),-(PPh,),] + SiR,H. ,I Isomer (2), from [CoH,(SiF,)(PPh,),]+CO. *Isomer (4), from [Co(SiPh,)(CO),] + ZPMePh, (ordPP4-would give only one strong C-0 stretching band in the i.r.The highest C-0 stretching frequency observed (2 000 cm-l)is consistent with a CO group trans to the SiF, group, i.e.isomer (2) ; the isomer with the smaller difference betweenthe two frequencies, that obtained here from SiF,H and[CoH(CO),(PPh,),], must be (3).(iv) With [CoH(CO) (PPh,),]. The complex [CoH(CO)-(PPh,),] in benzene reacted with SiF,H with evolution ofhydrogen (identified by mass spectrometry) and pre-cipitation of a yellow air-sensitive solid, the i.r.spectrum ofwhich showed a single C-0 stretching band at 1945 cm-l.A product obtained previously by this route showed i.r.absorption at 1 935 cm-l, and its solution gave a broad lHn.m.r. signal at 7 22.6. No gas evolution was observed, andthe product was tentatively formulated as [CoH,(SiF,)-(CO) (PPh,),]. The present product showed no high-fieldn.m.r. signal, which is consistent with the evolution ofhydrogen and suggests that the dihydride has undergonereductive elimination to give [Co(SiF,) (CO) (PPh3)J. Noother silanes were found to react with [CoH(CO)(PPh,),]under a variety of conditions.(v) With [CoHL,].The complexes [CoHL,] [L = PMePh,,P(OPh),, or P(OMe),] did not react with tertiary silanes,although long-term (4 months) exposure of [CoH (PMePh,),]to SiF,H gave a solid showing i.r. absorption at 808 and862 cm-l characteristic of SiF, groups. The complex[CoH (dppe),] (dppe = Ph,PCH,CH,PPh,) was unreactive toa variety of silanes. The only exceptions were silanes con-taining at least one Si-Cl bond; in agreement with ourearlier report,'l [CoCl(dppe),] is formed.Reactions of [Co(SiR,) (C0)J with Tertiary Phosphines.-The complex [Co(SiPh,) (CO),] reacted readily with PPh,with rapid evolution of 1 mol equivalent of carbon monoxideand formation of [Co(SiPh,) (CO),(PPh,)] identical to thatisolated from the reaction of SiPh,H with [CoH(CO),(PPh,)].Analogous products were obtained using PMePh,, PEt,,AsPh,, and SbPh,, but the PEt, derivative could not beisolated as a solid.The i.r. spectra of these products aresimilar to those of other complexes of this stoicheio-metry.2~~9 l oThe progress of the reactions with PPh, and PMePh, weremonitored by following the i.r. spectra, which are shownschematically in the Figure. The initial and final spectraare consistent with the presence of [Co(SiPh,) (C0)J and[Co(SiPh,)(CO),L] (L = PPh, or PMePh,) respectively. InSi F, tI fcoSiF, coF,Si -1 -L\ /cothe early stages of the reactions (1-2 h) additional bandsare seen at (L = PPh,) 1 978s, 2 050m, and 2 095mw cm-l,clearly due to intermediate complexes, and analogouschanges are seen for L = PMePh,.Evolution of carbonmonoxide occurred only during the first few minutes of thereaction.In the majority of cases only monosubstitution occurred,regardless of the amount of ligand added. However, withPMePh,, further reaction occurred readily. With an excessof this phosphine, a bright yellow product with a complexi.r. spectrum was obtained but, with careful control of thestoicheiometry, 2 mol equivalents of carbon monoxide wereevolved and [Co(SiPh,) (CO),(PMePh,),] was isolated. Thei.r. spectrum of this product in the C-0 stretching region wasvery different from those of the two forms of [Co(SiF,) (CO),-(PPh,),] described above, consisting of two bands at lowerfrequencies and of unequal intensities (Table 1).When thereaction was repeated using 1 mol equivalent of dppe aproduct with a very similar spectrum was obtained, [Co-(SiPh,) (CO),(dppe)]. In this complex the phosphine groupsmust of necessity occupy adjacent positions, but the i.r.spectrum is clearly incompatible with structures analogousto (2) or (5), and it is unlikely that the bidentateligand woul1980 925span two equatorial positions. Structures of type (4) arelikely for both these complexes.The complex [Co(SiEt,) (CO),] reacted very differently.With 1 mol equivalent of PPh, there was immediatevigorous evolution of gas and a colour change to deep red.On standing, [{Co(CO),(PPh,) j2] was precipitated. Frac-tional distillation and g.1.c. analysis of the supernatant liquidshowed Si,Et, to be present. Similar results were obtainedusing PMePh, or dppe.These reactions are in marked con-trast to those reported by Kahn and Bigorne,lo who obtainedsubstituted complexes [Co(SiEt,) (CO),(PEt,)] by thisreaction. Attempts were made t o follow the i.r. spectraI t1 min60 min18 hInfrared spcctra in the C-0 strctching region of niixturcs of[Co(SiPh,)(CO),] with ( a ) PPh, and ( b ) I’MePh, in toluene atvarious tirncs. Bands marltcd with ;in asterisk corrcspondneither to thc starting material nor to tlic product, [Co(Sil’li,)-(C0)d-Iduring the reaction, but resolution was poor owing to thecontinual precipitation of solid. With l’MeI’h, an inter-mediate with strong C-0 absorption a t 1 984 cm-l wasobserved, \vliile with dppe a new band was found a t 1 904c ni-’ .DISCUSSIOXThe range of complexes [Co(SiR,)(CO),L,-,I is nowknown with the sole exception of the member withn = 0.All these derivatives are highly air-sensitive.Other workcrs have found that the salt-eliminat ionroute to compounds of this type is very restricted in itsapplication to silyl derivatives,3 although it is effectivefor the heavier members of Group 4.’ The hydrogen-elimination route described here [equation (l)] works wellwith tertiary silanes, but some of the cobalt hydridesrequired are not convenient starting materials, beingthermally unstable and air-sensitive.[CoH(CO),L,-,I + SiR,H -w[Co(SiRJ(CO)nL4-n] H, (1)The starting complexes [CoH(CO),L,_,] become lessreactive with increasing phosphine substitution, and thesilanes become more reactive as the groups on the siliconincrease in electronegativity.The latter observation(which is usual in oxidative addition of silanes 12) is con-sistent with initiation of the reaction by nucleophilicattack on silicon by the cobalt complex. The nucleo-philicity of the complexes would increase as the value ofn decreases but, at the same time, steric interactionswould increase markedly.Other factors are undoubtedly involved in the stabilityof the cobalt-silyl complexes, however, since we find that[Co(SiEt,) (CO),] decomposes on treatment with PPh, intoluene. Other workers have investigated the reactionsof [Co(SiR,)(CO),] (R = H, Et, or Me) with tertiary phos-phines in non-polar solvents, with various results.Several groups find a CO-displacement reaction withformation of [Co(SiR,)(CO),L] (L = PEt, or PPh,),10*13*14but the heterolysis products [SiR,L][Co(CO),] (R = Meor E t ; L = PEt, or PMe,) have also been reported.13Clearly the reaction is not straightforward, and it maydepend critically on the conditions used.13 The effectobserved here is superficially similar to that of treatingcis-[Fe(SiCl,),(CO),] with PPh3,1a~15 since in both cases adisilane and a phosphine-substituted metal carbonyl areobtained.However, with the iron complex an intra-molecular process is both feasible and likely, whereas inthe cobalt system reaction must occur either intermole-cularly or by a radical mechanism. Absi-Halabi andBrown 16 have studied the reaction of [Co(SnCl,) (CO),]with ligands, wliicli gives [Co(CO),L,][SnCl,] (L = PPh,or AsPh,), and have found evidence for a radical reaction.Attack by the ligand on the tin atom is followcd byhomolysis of the Co-Sn bond.In the present case,attack on thc silicon atom seems unlikely, since anEt,Si group would not have high electrophilicity andwould not be greatly differcnt from a Ph,Si group except,perhaps, in stcric crowding. The C1,Si compounds,which would be stronger Lewis acids, react by simpleCO clisplacement. The prcvious workcrs also found thatthe rate of reaction and the nature of tlic productswere scnsitive to the presence of light or oxygen.lGIn the reaction of [Co(SiPh,) (CO),] with tertiary phos-phines, evolution of carbon monoxide occurs over a muchshorter period than the changes in the i.r.spectrum. I tis probable that there is rapid formation of a mono-substituted complex of configuration different from thatof the final product, followed by a slow isomerisation(Scheme). Assuming the intermediate to have the usualtrigonal-bipyramidal geometry, (6) is the only likely con926 J.C.S. Daltonfiguration and would be consistent with the observed i.r.spectrum, viz. the retention of the high-frequency C-0band corresponding to the axial CO group, and the pre-sence of two other bands separated by ca. 50 cm-l withan intensity pattern similar to that for the equatorial COgroups of isomer (4) of [Co(SiPh,)(CO),L,].Five-co-ordinate complexes usually undergo intra-molecular exchange reactions very rapidly, and manyhave been shown to be fluxional on the n.m.r.time scale.However, it has recently been shown by 13C n.m.r.spectroscopy that the molecules [Co(MR,) (CO),] undergoexchange at rates related to the bulk of the MR, group,showing that steric factors are important in the re-arrangement.17 If two bulky substituents were present,as in [Co(SiPh,) (CO),(PPh,)], rearrangement would beconsiderably slowed, as we observed in the substitutionreaction. This argument is also consistent with ourSiPh, SiPh,- - co [Co(SiPh,)(CO),] OC-1-L\ /OC co OC co(6 1SiPh,oc - I-co\ /OC I LSCHEMEfinding three different isomers (2)-(4) of the type[Co(SiR,) (CO),L,], from three different preparativeroutes.These isomers must be completely inhibitedfrom rearranging by the presence of three bulky sub-s t ituent s.The i.r. spectra of the isolable form of the mono-substituted species [Co(SiR,) (CO),L] are only consistentwith structure (l), as deduced by other workers.1° Thisstructure has (at most) C,, symmetry, for which two C-0stretching modes are i.r. active, A, and E . The E modeis observed for all the complexes, but the intensity of theA, mode is very sensitive to the nature of the substituentsat silicon. When electronegative substituents arepresent (I?, OEt), the A, mode is readily observed, butwith C-bonded substituents it is very weak or absent. Inthe latter case the complexes behave as if the symmetrywere higher.This difference presumably reflects adifference in the degree of coplanarity of the Co(CO),group. If this group were closely planar, the A, modewould involve very little change in dipole moment,resulting in a minimal intensity for the formally allowedi.r. transition. This would be the case when the twosubstituents are similar electronically and sterically, i.e.there can be little difference in the electron distributionin the Co-SiPh, and Co-PPh, bonds. Such a con-figuration is observed for [Co(GePh,) (CO),(PPh,)].*When the effective electronegativity of the silicon isincreased, this equivalence no longer applies and the COgroups move out of the plane towards the silicon, asobserved in several unsubstituted complexes [Co(SiR,)-Finally, the utility of fluorosilanes in these reactionsshould be noted.With chlorine-containing silanes nosilyl complexes were obtained, but only [CoCl(PPh,),] or[CoCl,(PPh,),] were obtained.lb With fluorosilanes, silylcomplexes are readily formed.(CO),] .18-20EXPERIMENTALAll solvents were rigorously dried and degassed immedi-ately before use. Reactions were conducted under drynitrogen or in vacuo in sealed tubes or Schlenk apparatus.The complexes [CoH(N,) (PPh,),], [Co(SiR,)(CO),] (R =Et or Ph), [CoH(CO)(PPh,),], and [{Co(CO),L}J (L = PPh,,PMePh,, PMe,Ph, PEt,, PBu,, or AsMe,Ph) were preparedby literature m e t h ~ d s . ~ l - ~ ~ Analytical data for new com-pounds are displayed in Table 2.TABLE 2Analytical data (yo) for cobalt-silyl complexes, withcalculated values in parenthesesICo(SiF,) (CO),(PPh,)] 53.2 (51.3) 3.6 (3.1):Co(SiF3) (CO)z(PPh3)zl 62.5 (62.9) 4.4 (4.1)ICo(SiF,)(CO) (PPh,),] 69.3 (68.8) 5.0 (4.7)-Co(SiF,) (CO),(PMe,Ph)] 35.8 (36.3) 2.7 (3.0);Co(Si( OEt),} (CO) ,( PPh,)] 66.1 (65.6) 4.8 (5.6)Complex C H;Co(SiPh,) (CO),(PPh,)] 71.3 (70.4) 4.9 (4.5)CCo(SiPh,) (CO),(PMePh,)] 67.1 (67.6) 4.9 (4.7)-Co( SiPh,) (CO) z( PMePh,) 2] 75.7 (71.2) 5.5 (5.3):Co(SiPh,) (CO),(AsPh,)] 66.0 (65.8) 4.2 (4.1):Co( SiPh,) (CO) ,( SbPh,)] 60.4 (62.0) 4.6 (4.0)CCo(SiPh3) (CO) z(dPPe)l 73.7 (72.7) 5.0 (5.0)Tricarbonylh.ydrido( tripheny2phosphine)cobalt (I) .- Thehydride [CoH(CO),(PPh,)] is very unstable, decomposingabove -50 "C to [{Co(CO),(PPh,)},].It is therefore bestprepared in situ from [CoH(CO),] and PPh,.Unfortu-nately, [CoH(CO),] is itself thermally unstable, and couldnot be obtained in quantitative yield, and the [CoH(CO),-(PPh,)] solution was often contaminated with PPh,, [CoH-(CO),(PPh,),], or [{Co(CO),(PPh,)},] ; on occasions thesewere the major products.Dicobalt octacarbonyl was dissolved in an excess ofpyridine, 30% sulphuric acid was added at 0 "C, and [CoH-(CO),] swept out of the reaction vessel with a stream ofnitrogen, through a column of P,O,, and collected in pentaneat -95 "C. This solution was added to a pentane solutionof a stoicheiometric amount of PPh, a t -95 "C. The tem-perature was raised briefly t o -25 "C, when a pale yellowcolour developed and a gas was evolved. On cooling t o-80 "C yellow crystals were formed, which were collectedand stored a t low temperature.Owing to the difficulty ofcontrolling the stoicheiometry and the pronounced air-sensitivity and thermal instability of the product, yieldswere typically ca. 20%.Dicarbonylhydridobis(triphenyZphosphine)cobalt(I) wasobtained similarly using an excess of PPh, a t 0 "C. Theproduct was filtered off and washed with pentane. Yield60% (Found: C, 71.2; H, 5.0. Calc. for C,,H,,CoO,P,:C, 71.2; H, 4.9%).Tricarbonyl (dimethylphenylpho.s~hine)trijluorosilylcobalt ( I)927-(i) From [{Co(CO),(PMe,Ph)},]. The dimeric complex(0.5 g) and solvent (9% v/v hexane in benzene, 5 cm3) wereplaced in a tube and an excess of SiF,H was condensed in.The tube was sealed and shaken at room temperature forseveral hours.The resulting yellow solid was filtered offand washed with hexane. With ligands other than PMe,Ph,products could be obtained only as oils.(ii) From [CoH(CO),(PPh,)]. A pentane solution of[CoH(CO),(PPh,)] at -78 "C was transferred t o a tube,cooled t o - 195 "C, and SiF,H was condensed in. The tubewas sealed, warmed to 0 "C, and the mixture stirred forseveral hours. The resulting yellow solid was filtered off atlow temperature. Reactions of [CoH(CO),(PPh,),] and[CoH(CO) (PPh3),] were carried out similarly.[9/426 Received, 15th March, 19791REFERENCES(a) Part 25, R. N. Haszeldine, R. V. Parish, and B. F. Riley,J.C.S. Dalton, 1980, 705; ( b ) Part 23, N. J. Archer, R. N. Haszel-dine, and R.V. Parish, ibid., 1979, 695.2 B. J. Sylett and J. M. Campbell, J . Chem. SOC. ( A ) , 1969,1910.M. D. 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