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 catalysts for the interconversion of CO2 and formate. Based on electrochemical and spectroscopic experiments, including data for a new [Ni(PCy2NPhOMe2)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.