Effects of Ligand Electronic Environment on Electrocatalytic Proton Reduction by Cobalt Complexes

Here we have synthesized two mononuclear cobalt (II) complexes of type [Co(L)(L^/)]ClO₄, where L = 4-methyl-N,N-bis((1-methyl-1H-benzo[d]imidazol-2-yl)methyl)aniline, L/ = 2,2^/ bipyridine (for 1) and 4,4^/-dimethyl-2,2^/ bipyridine (for 2). The synthesized complexes were characterized by various spectroscopic techniques and the molecular integrity of the complexes was confirmed by the single crystal x-ray diffraction (SCXRD) analysis. The redox properties of the complexes were analyzed by Cyclic Voltammetry (CV). The electrocatalytic proton reduction studies were done using acetic acid as an external proton source in a non-aqueous medium. The overpotential for the electrocatalytic proton reduction was found to be 453 mV for 1 and 470 mV for 2, consistent with increased electron donation to the metal center by the methyl group in 2, which shifts the reduction potential to more negative values and alters the overpotential. The turnover frequencies (TOF) were 217 and 203 s^-1 for 1 and 2, respectively. A plausible catalytic mechanism was proposed based on the experimental observations. The post-catalytic analyses confirmed the structural integrity of the catalysts, indicating homogeneous behavior under catalytic conditions. This study aims to contribute to the development of sustainable and efficient hydrogen production technologies, supporting the transition toward a sustainable energy future.