Electrocatalytic Oxidation of Formate by (Ni(P2RN2R')2(CH3CN))2+ Complexes

New (Ni(P2RN2R')2(CH3CN))2+complexes with R = Ph, R' = 4-MeOPh; R = Cy, R' = Ph and a mixed ligand (Ni(P2RN2R')(Pr2doubleprime N2R')(CH3CN))2+ with R = Cy, R' = Ph, R(doubleprime) = Ph have been synthesized and characterized by single crystal X-ray crystallography. These complexes are shown to be electrocatalysts for the oxidation of formate in solution to produce CO2, protons, and electrons with rates which are first order in catalyst and in formate at formate concentrations below approximately 0.05 M. For the catalysts studied, maximum observed turnover frequencies vary from <1.1 s-1 to 12.5 s-1 at room temperature, which are the highest rates yet reported for formate oxidation by homogeneous catalysts. A mechanistic scheme is proposed which involves an initial nickel complex bound η1-OC(O)H followed by a rate limiting hydride transfer step. An acetate complex demonstrating the η1-OC(O)CH3 binding mode to nickel has also been synthesized and characterized by single crystal X-ray crystallography. The pendant amines have been demonstrated to be essential for this electrocatalytic activity as no activity toward formate was found for the similar (Ni(depe)2)(BF4)2 (depe = diethylphosphinoethane) complex.