Electrocatalytic Nitrite Reduction With Polynuclear Copper(I) Complexes Supported By 2‐Mercaptopyridine Ligand

Abstract The electrochemical nitrite reduction to ammonia is a growing interest in chemistry as it can be a potential alternative to the energy‐intensive Haber–Bosch. In this work, two copper complexes supported by pyridine‐2‐thiol (PySH), [Cu I 6 (PyS) 6 ] (1), and [Cu I (PySH) 2 (ClO 4 )] n (2) are synthesized and characterized by spectroscopic techniques. The molecular structure of 1 and 2 is determined by single‐crystal X‐ray structure analysis. The complex 1 provides a distorted octahedral core with six copper atoms, whereas the complex 2 shows a unique 1D polymeric arrangement of copper(I) and PySH. However, complex 2 can be converted to complex 1 upon addition of triethyl amine in acetonitrile at room temperature. Moreover, complex 1 reversibly transforms to complex 2 in the presence of perchloric acid and PySH. Complexes 1 and 2 are used as catalysts for the electrocatalytic nitrite reduction (eNO 2 RR) to produce ammonia (NH 3 ) in 0.05 M acetate buffer of pH 3. In comparison to complex 1 , the complex 2 is found to show better activity for the selective conversion of nitrite to ammonia with a turnover frequency of 2 × 10 −3 s −1 , Faradaic efficiency (FE%) of 89% at −0.02 V (vs. RHE) with a yield rate of 3.29 mmol h −1 cm −2 at −0.42 V (vs. RHE). 1 H NMR spectroscopy revealed the formation of NH 3 as the main product.