Electrochemical mechanism of CO2 reduction mediated by NiII(tpa) (tpa = tris(2-pyridylmethyl)amine) complexes: an integral view

Abstract In this paper, we report the synthesis, characterization, as well as electrochemical, spectroelectrochemical, and density functional theory (DFT) calculations of a series of novel NiII complexes with a flexible tetradentate ligand, tris(2-pyridylmethyl)amine) (tpa). The complexes [NiII(tpa)(H2O)(MeCN)](BF4)2, [NiII(tpa)(NO3)2], and [NiII(tpa)Cl2] were studied for their ability to electrochemically reduce CO2. These complexes were compared with the tris-chelate complex [Ni(bpy)3](BF4)2 to understand the role of flexible tetradentate ligands containing a pyridinic ring in the electrochemical reduction of CO2. Spectroelectrochemical experiments and theoretical studies were performed to rationalize the electrochemical reductions occurring and to predict the redox potential and pathway of CO2 reduction.