Electron-Transfer Catalysis. Radical Chain Mechanism for the Ligand Substitution of Metal Carbonyls

Article abstract of DOI:10.1021/ja00375a016

A novel chain process for the ligand substitution of metal complexes is revealed by bulk and transient electrochemical methods.The large turnover numbers that are obtained for the ligand substitution of the tris(acetonitrile) complexes of molybdenum and tungsten carbonyls with phosphines and isocyanides underscore the electrocatalytic phenomenon.The efficient chain process derives from the substitution lability of the cation radicals, which are formed by the one-electron oxidation of metal carbonyls and subsequently undergo rapid electron transfer, as in Scheme II.Th e driving force for ligand substitution is related to the relative stabilities of the cation radicals.Electron-transfer equilibria between these cation radicals can be evaluated from the standart reduction potentials E⁰ or the cyclic voltammetric peak potentials E_p.The initiation of the chain process is finely tuned to the value of E⁰ and E_p for the various metal carbonyls.The effectiveness of metal carbonyls as catalysts in the enhanced oxidation of nucleophiles such as triphenylphosphine is also described.