Electrochemical Reduction of N2O with a Molecular Copper Catalyst

Abstract

Deoxygenation of nitrous oxide (N₂O) has significant environmental implications, as it is not only a potent greenhouse gas but is also the main substance responsible for the depletion of ozone in the stratosphere. This has spurred significant interest in molecular complexes that mediate N₂O deoxygenation. Natural N₂O reduction occurs via a Cu cofactor, but there is a notable dearth of synthetic molecular Cu catalysts for this process. In this work, we report a selective molecular Cu catalyst for the electrochemical reduction of N₂O to N₂ using H₂O as the proton source. Cyclic voltammograms show that increasing the H₂O concentration facilitates the deoxygenation of N₂O, and control experiments with a Zn(II) analogue verify an essential role for Cu. Theory and spectroscopy support metal-ligand cooperative catalysis between Cu(I) and a reduced tetraimidazolyl-substituted radical pyridine ligand (MeIm₄P₂Py = 2,6-(bis(bis-2-N-methylimidazolyl)phosphino)pyridine), which can be observed by Electron Paramagnetic Resonance (EPR) spectroscopy. Comparison with biological processes suggests a common theme of supporting electron transfer moieties in enabling Cu-mediated N₂O reduction.