Proton-Coupled-Electron Transfer Enhances the Electrocatalytic Reduction of Nitrite to NO in a Bioinspired Copper Complex

Abstract

The selective and efficient electrocatalytic reduction of nitrite to nitric oxide (NO) is of tremendous importance, both for the development of NO-release systems for biomedical applications and for the removal of nitrogen oxide pollutants from the environment. In nature, this transformation is mediated by (amongst others) enzymes known as the copper-containing nitrite reductases. The development of synthetic copper complexes that can reduce nitrite to NO has therefore attracted considerable interest. However, there are no studies describing the crucial role of proton-coupled-electron transfer during nitrite reduction when using such synthetic complexes. In this talk, I will describe a system for the electrocatalytic reduction of nitrite to NO in which the role of proton-relaying units in the secondary coordination sphere of the metal can be probed for the first time (ACS Catal. 2018, 8, 5070–5084). Our results suggest that positioning a pendant carboxylate group in close proximity to the copper centre gives an electrocatalyst that is twice as effective for nitrite reduction than the analogous compound that lacks such a proton-relaying moiety. These results highlight the critical role of proton-coupled-electron transfer in the reduction of nitrite to NO and have important implications for the design of biomimetic catalysts for the selective interconversions of the nitrogen oxides. Figure 1