The Influence of para Substituents in Bis(N-Heterocyclic Carbene) Palladium Pincer Complexes for Electrocatalytic CO2 Reduction

The effect of modifying the pyridyl para position of lutidine-linked bis(N-heterocyclic carbene) Pd pincer complexes is studied both experimentally (R = OMe, H, Br, and COOR) and computationally, showing a strong effect on the first reduction potential of the complex and allowing the reduction potential to be tuned over a wide range in relation to the Hammett sigma(p) constant of the para substituent. The effect of the pyridyl para substituent on electron density of the metal center, frontier orbital energies, and dissociation energy of the trans ligand are also investigated in the context of reactivity with CO2 through electrochemical characterization of the complexes under N-2 and CO2 and controlled potential electrolysis experiments where CO2 is reduced to CO.