Inorganic Models for Two-Electron Redox Chemistry in Biological Systems: Ligand-Bridged Molybdenum and Tungsten Dimers

We describe the energetics of concerted two-electron transfer and metal-metal bond cleavage in the sulfido- and phosphidobridged dimers [M 2 (μ-ER n ) 2 (CO) 8 ] 0/2- (M = Mo or W; R n E ― = RS ― or R 2 P ― ). Reduction of the neutral dimers to their corresponding dianions occurs in a single two-electron step accompanied by cleavage of a metal―metal single bond and large changes in the M-M distance and M-E-M and E-M-E bridge angles. These structural reorganizations provide the driving force for concerted two-electron transfer via inversion of the 0/- and -/2- redox potentials.