Polyannulated Bis(N-heterocyclic carbene)palladium Pincer Complexes for Electrocatalytic CO2 Reduction

Phenanthro- and pyreno-annulated N-heterocyclic carbenes (NHCs) have been incorporated into lutidine-linked bis-NHC Pd pincer complexes to investigate the effect of these polyannulated NHCs on the ability of the complexes to electrochemically reduce CO2 to CO in the presence of 2,2,2-trifluoroacetic acid and 2,2,2-trifluoroethanol as proton sources. These complexes are screened for their ability to reduce CO2 and modeled using density functional theory calculations, where the annulated phenanthrene and pyrene moieties are shown to be additional sites for redox activity in the pincer ligand, enabling increased electron donation. Electrochemical and computational studies are used to gain an understanding of the chemical significance of redox events for complexes of this type, highlighting the importance of anion binding and dissociation.