Electrochemical reduction of a binuclear dioxo-bridged molybdenum(V) complex with cysteine

Summary Electrochemical reduction of the binuclear dioxo-bridged Mo(V)-cysteine complex, Mo 2 O 4 (cys) 2 2− , has been studied at mercury electrodes in pH 7.5–10 borate, phosphate, and NH 4 + /NH 3 buffers. The complex is reduced in a single diffusion-controlled 4-electron step to a binuclear Mo(III) product at ∼−1.2 V vs . SCE. The product is unstable and dissociates by cleavage of the oxygen bridge bonds. The rate of the decomposition reaction was measured by double potential step chronocoulometry and found to depend on the nature of the buffering medium, but not on pH or buffer concentration. A mechanism consistent with these experimental facts is proposed which involves coordination of the buffer species to the Mo(III) product during electrochemical reduction followed by intra-molecular dissociation of the complex.