Reaction mechanisms of metal–metal bonded carbonyls. Part VI. Reactions of µ-carbonyl-µ-diphenylgermanediyl-bis(tricarbonylcobalt) with carbon monoxide, triphenylphosphine, and tri-n-butylphosphine

Abstract

The reversible ‘ring-opening’ reaction of the complex [(OC)₃Co(µ-GePh₂)(µ-CO)Co(CO)₃], (I), with carbon monoxide in decalin to form (µ-GePh₂){Co(CO)₄}₂, (II), proceeds by a path first order in [Complex] and [CO], and the reverse reaction is first order only in [Complex]. Activation and equilibrium parameters have been obtained. Reaction with triphenylphosphine forms the complex (µ-GePh₂){Co(CO)₃L}₂, (III; L = PPh₃), probably via[(OC)₃Co(µ-GePh₂)(µ-CO)Co(CO)₂PPh₃], produced in a rate-determining CO-dissociative process and subsequently attacked by a second phosphine molecule in a rapid ring-opening reaction. Bimolecular attack by triphenylphosphine also occurs and leads directly to the complex (µ-GePh₂){Co(CO)₃L}{Co(CO)₄}, (IV; L = PPh₃). Reaction of the latter with triphenylphosphine produces complex (III; L = PPh₃) by a process first order only in [Complex]. Reaction of complex (II) with triphenylphosphine proceeds via rate-determining formation of (I) which then reacts rapidly with the phosphine as described above. Tri-n-butylphosphine can attack the complexes (II) and (IV; L = PBu₃) by bimolecular processes. The mechanisms of these reactions are discussed in terms, especially, of relative rate constants for bimolecular attack by carbon monoxide and triphenylphosphine on the complexes or reactive intermediates involved.