Electrocatalytic Reduction of CO₂ and H₂O with Zn(II) Complexes Through Metal-Ligand Cooperation

Air and water-stable zinc (II) complexes of neutral pincer bis(diphenylphosphino)-2,6-di(amino)pyridine ("(PNP)-P-3") ligands are reported. These compounds, [Zn(kappa(2)-2,6-{Ph2PNR}(2)(NC5H3))Br-2] (R=Me, 1; R=H, 2), were shown to be capable of electrocatalytic reduction of CO2 at -2.3 V vs. Fc(+/0) to selectively yield CO in mixed water/acetonitrile solutions. These complexes also electrocatalytically generate H-2 from water in acetonitrile solutions, at the same potential, with Faradaic efficiencies of up to 90 %. DFT computations support a proposed mechanism involving the first reduction of 1 or 2 occurring at the (PNP)-P-3 ligand. Furthermore, computational analysis suggested a mechanism involving metal-ligand cooperation of a Lewis acidic Zn(II) and a basic ligand.