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

The effect of modifying the pyridyl <i>para</i> 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 σ_p constant of the <i>para</i> substituent. The effect of the pyridyl <i>para</i> substituent on electron density of the metal center, frontier orbital energies, and dissociation energy of the <i>trans</i> ligand are also investigated in the context of reactivity with CO₂ through electrochemical characterization of the complexes under N₂ and CO₂ and controlled potential electrolysis experiments where CO₂ is reduced to CO