Formate oxidation via β-deprotonation in [Ni(PR2NR′2)2(CH3CN)]2+ complexes

Recent studies from our laboratories have shown that the [Ni(PR2NR'2)2(CH3CN)]2+ complexes originally developed as artificial hydrogenases are also active electrocatalysts for formate oxidation (TOF ~16 s-1). The focus of the current work is to develop a detailed understanding of the catalytic mechanism, which would aid in the design of improved CO2/formate interconversion catalysts. Based on electrochemical and spectroscopic experiments, including data for a new [Ni(P2CyN2{sup PhOMe})2(CH3CN)]2+ complex, we propose a mechanism in which the rate-determining step is a proton transfer from the Ni-O2CH β-H to the ligand pendant base coupled with a 2e- transfer to Ni(II), circumventing direct hydride transfer to the metal center.