A Terpyridine based Copper Complex for Electrochemical Reduction of Nitrite to Nitric Oxide

In biological systems, nitrite reductase enzymes (NIRs) are responsible for reduction of nitrite (NO2-) to nitric oxide (NO). These NIRs have mostly Cu or Fe containing active sites, surrounded by amine containing ligands. Therefore, mononuclear Cu complexes with N-donor ligands are highly relevant in the development of NIR model systems and in the mechanistic investigation of nitrite reduction reaction. Herein, we report on a terpyridine based CuII complex with a square planar geometry for H+ assisted electrochemical reduction of NO2-. Through electrochemical measurements, spectroscopic characterization and isotope labelling experiments we propose a mechanistic reaction pathway involving an unstable HNO2 state. The CuI intermediate, formed electrochemially was isolated and its molecular structure was deduced, showing linkage isomerism of nitrite ligand. Moreover, qualitatitve and quantitative product analysis by GC-MS shows N2O formed as a side product along with the main product NO. Furthernore, by obtaining single crystals and structural analysis we have managed to determine the structural arrangement and redox state of the complex after electrochemical treatment.