Electrochemical Reduction of NO with a Molecular Copper Catalyst.

Deoxygenation of nitrous oxide (NO) 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 NO deoxygenation. Natural NO 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 NO to N using HO as the proton source. Cyclic voltammograms show that increasing the HO concentration facilitates the deoxygenation of NO, 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 (MeImPPy = 2,6-(bis(bis-2--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 NO reduction.