Further studies of group 14- cobalt carbonyl chemistry

Abstract

This thesis describes investigations into several areas of group 14-cobalt carbonyl chemistry including substitution of a bridging carbonyl ligand by an R₂GeH₂ species to form a GeCo₂ triangle, reactions of germanium-cobalt carbonyl clusters with transition metal carbonyl anions and the reactions of Et₄NSnCl₃ with group 14-cobalt carbonyl compounds of the form R₃M'Co(CO)₄ (R₃ = Me, ⁿBu, Ph, Cl, Br; M' = Sn, Ge, Si). Further studies of the reaction between MeGeH₃ and Co₂(CO)₈ have led to a new proposal for the reaction scheme. That is: MeGeH₃ + 2Co₂(CO)₈ → MeGeCo₃(CO)₁₁ + HCo(CO)₄ + H₂ + CO Together with the results obtained from a study of the reaction of H₃GeCo(CO)₄ with Co₂(CO)₈, this has allowed the proposal that “In the absence of marked steric effects, where an even number of hydrogen atoms is attached to a germanium hydride species this will react with Co₂(CO)₈ to replace a bridging carbonyl group to form a GeCo₂ triangle with evolution of H₂ and CO; where there is an odd number of attached hydrogen atoms this will react with Co₂(CO)₈ to also give cleavage of the Co-Co bond to yield a GeCo(CO)₄ species and HCo(CO)₄”. It has been found that substitution of both bridging carbonyl groups of GeCo₄(CO)₁₄ by Me₂GeH₂ or MeGeH₃ is possible and the new compounds [Me₂Ge]₂GeCo₄(CO)₁₂ and [MeGeH]₂GeCo₄(CO)₁₂ have been spectroscopically characterised. An X-ray crystal structure determination has been carried out for (Me₂Ge)₂GeCo₄(CO)₁₂ which shows it to comprise of four GeCo₂ triangles connected by Co-Co edges and Ge apices. An analysis of the carbonyl vibrations of [MeGeR]₂GeCo₄(CO)₁₂ (R = Me, H) and GeCo₄(CO)₁₄ has been carried out. Good spectroscopic evidence has been obtained for the formation of (MeGe)₂Co₄(CO)₁₀[Ge(R)Me] (R = Me, H) from the reaction of (MeGe)₂Co₄(CO)₁₁ with Me(R)GeH₂. Similarly, further evidence for the production of [MeGeR]₂Ge₂Co₆(CO)₁₈ from the reaction of Ge₂Co₆(CO)₂₀ with Me(R)GeH₂ has been obtained. The two trigonal pyramidal clusters, [(CO)₄Co]GeC0₃(CO)₉ and MeGeCo₃ (CO)₉, reacted with Me(R)GeH₂ to provide the open-skeleton derivatives [MeGeR]Co₂(CO)₆[GeCo₂(CO)₇] and [MeGeR]Co₂(CO)₆[Ge(Me)Co(CO)₄] respectively. These have been spectroscopically characterised. The thermally initiated ligand substitution reactions of the closo hexanuclear clusters, (RGe)₂Co₄(CO)₁₁ (R = Me, Co(CO)₄), with PPh₃ or P(OEt)₃ resulted in breakdown of the cluster to afford mainly [(R₃P)Co(CO)₃]₂. However, the electron transfer catalysed reaction of (MeGe)₂Co₄(CO)₁₁ with P(OEt)₃ in a 1:1 ratio provided the monosubstituted derivative, (MeGe)₂Co₄(CO)₁₀(POEt)₃, in moderate yields which has been spectroscopically characterised. Similarly, the reaction of (MeGe)₂Co₄(CO)₁₁ with ᵗBuNC at room temperature appeared to yield the monosubstituted derivative (MeGe)₂Co₄(CO)₁₀CNᵗBu. Reaction of [(CO)₄CoGe]₂Co₄(CO)₁₁ with Et₄N[Co(CO)₄] produced the known anionic cluster Et₄N[Ge₂Co₇(CO)₂₁] in comparatively good yields. The same product was obtained from reaction of Ge₂Co₆(CO)₂₀ with Et₄N[Co(CO)₄], however condensation to [(CO)₄CoGe]₂Co₄(CO)₁₁ was required before reaction with the anion takes place. The reactions of Et₄NSnCl₃ with R₃M'Co(CO)₄ (R = Me, ⁿBu, Ph, M' = Sn; R = Ph, M' = Ge; R = Cl, M' = Si) all yielded the known tin-cobalt carbonyl anion, Et₄N[{Cl₂[Co(CO)₄]Sn}₂Co(CO)₃]. Reaction of Et₄NSnCl₃ with Br₃SnCo(CO)₄, however, produced a mixture of anions of the form Et₄N[(BrₓCl₃₋ₓSn)Co(CO)₃(SnClyBr₃₋y)] (x,y = 0-3). This mixture has been characterised by infrared, ¹¹⁹Sn NMR and FAB mass spectroscopy and an X-ray crystal structure determination has been carried out for Et₄N[(Br₂ClSn)₂Co(CO)₃]. Preliminary studies have been carried out for several other related systems.