The electrocatalytic conversion of carbon dioxide (CO2) into commodity chemicals or renewable fuels is an attractive strategy for removing anthropogenic CO2 from the atmosphere and/or storing renewable electricity in the form of chemical bonds. We report the development of a copper complex supported by a redox-active bipyridyl-N-heterocyclic carbene (NHC) based macrocycle and its application to electrocatalytic CO2 reduction. The analogous nickel and cobalt complexes of the same ligand are active catalysts for CO2-to-CO conversion while the copper complex decomposes under reducing conditions in the presence of CO2. Density functional theory (DFT) calculations were employed to investigate the metal-ligand redox chemistry of the copper complex and associated intermediates, which were compared to the previously reported nickel and cobalt systems. A novel decomposition route is proposed based on the DFT calculations that involves CO2 binding to an NHC donor and subsequent demetalation, which is supported by 1H NMR spectroscopy and high-resolution mass spectrometry of the electrolyzed solution. These results may have important implications regarding the stability and reactivity of other complexes bearing NHC donors employed for CO2 reduction and suggest that productive pathways for CO2 activation and conversion could be accessed involving non-innocent metal-bound NHCs.

Synthesis, characterization, and electronic structure calculations of a copper(II) bipyridyl-N-heterocyclic carbene macrocycle

ACS Fall 2021

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