Manganese-Based Catalysts with Varying Ligand Substituents for the Electrochemical Reduction of CO2 to CO

Abstract

A series of manganese complexes were synthesized with a variety of ligands and ligand substituents. These complexes were then studied using ultraviolet–visible spectroscopy, cyclic voltammetry, density functional theory calculations, and bulk electrolysis. The UV–vis, cyclic voltammetry, and calculation data show that the bipyridine π* level is modulated by the incorporation of different substituents on the bipyridine and through this interaction moderates the observed catalytic activity of the complex toward CO2 reduction. The calculations were correlated to the experimental UV–vis data and cyclic voltammetry data to demonstrate the relationship among these data, and a Hammett plot showed a good correlation between the substituent identity and the MLCT wavelength from UV–vis (R2 = 0.96). When aliphatic substituents were placed on the 4,4′-positions of the bipyridine, the location of the bpy π* was not significantly altered. However, when more electron withdrawing substituents were placed on the 4,4′-posi...