Hydride Transfer in the Oxidation of Formate Ion by 2+

Article abstract of DOI:10.1021/ja00274a035

The kinetics of oxidation of formic acid/formate ion by <(bpy)2(py)Ru^IV(O)>²⁺ (bpy is 2,2'-bipyridine and py is pyridine) have been studied as a function of pH and temperature, and the kinetics of oxidation of HCO2^- by <(bpy)2(py)Ru^III(OH)>²⁺ have been studied at pH 7.The pH dependence of the Ru^IV reaction is consistent with paths involving oxidation of HCO2H, k (25 deg C, μ = 0.1 M) = 0.01 +/- 0.04 M^-1s^-1, and of HCO2^-, k (25 deg C, μ = 0.1 M) = 4.2 +/- 0.2 M^-1s^-1.For the oxidation of HCO2^- by Ru^III, k (25 deg C, μ = 1.0 M, pH 7) = 0.01 M^-1s^-1.The path involving Ru^IV and HCO2^- exhibits a large kinetic isotope effect with k_HCO2-/k_DCO2- = 19 (25 deg C, μ = 1.0 M) while that involving Ru^III and HCO2^- has a much smaller kinetic isotope effect with k_HCO2-/k_DCO2- = 3 (25 deg C, μ = 1.0 M).Spectral evidence, in conjunction with the isotope effect data, suggests that oxidation of HCO2^- by <(bpy)2(py)Ru^IV(O)>²⁺ occurs by a two-electron, hydride transfer which is discussed in some detail.Oxidation of HCO2^- by <(bpy)2(py)Ru^III(OH)>²⁺ appears to occur by outer-sphere electron transfer.