Electrocatalytic dioxygen reduction in the presence of a rhodoxime

Polarographic and voltammetric evidences are reported for the production of intermediates superoxo [Rh]OO and hydroperoxo [Rh]OOH derivatives at the electrode surface, in the reduction of dioxygen in the presence of rhodium bis(dimethylglyoximato) chloro triphenylphosphine, [ClRh(III)(DMG)2(PPh3)] (I), in the absence and in the presence of protons in non-aqueous solvents. In the latter case the electrocatalytic reduction of dioxygen is observed. From the trends of the concentrations of dioxygen vs the rhodium complexes, a mechanism for the electrochemical process is proposed. The molar ratio of dioxygen to the rhodium complex when the latter is completely consumed for the formation of the adduct, as compared with the 1:1 stoichiometric ratio determined by the Hill plot, together with the influence of the electrode material, suggests that the reduction of dioxygen involves adsorbed species.