Evidence for a charge-transfer intermediate in the catalytic epoxidation of alkenes by ruthenium complexes: a comparison between electrochemical and kinetic data

The catalytic oxidation of various olefins by iodosobenzene in the presence of the diphosphino complexes of ruthenium(II) [RuCl(LL)2]PF6, where LL is 1,3-bis(diphenylphosphino)propane (DPP) or 1-diphenylphosphino-2-(2′-pyridyl)ethane (PPY), gives rise to epoxides, obeying the Michaelis–Menten kinetic law. The calculated kinetic parameters (Km) follow a free energy correlation with the one-electron oxidation potentials of the olefins, measured in the reaction conditions, thus suggesting that the reaction intermediate of the epoxidation is substantially charge-transfer in character.