Electrocatalytic reduction of protons with bis(N-para-carboxyphenyldithiocarbamato)-(1,10-phenanthroline) cobalt(II) and manganese(II) complexes

• Co II and Mn II dithiocarbamate adducts were synthesized and characterized. • They were used as catalysts in hydrogen-evolution electrocatalysis . • Rate constants of 2.02–4.54 s −1 were observed for their catalytic processes. • They yielded theoretical rate constant k cat of 757 and 1526 M −1 s −1 respectively. • They exhibit good catalytic activity via the dominant confirmatory ECEC mechanism. In this study, 1,10-phenanthroline adducts of bis( N - para -carboxyphenyldithiocarbamato)-cobalt (II) ( 1 ) and manganese (II) ( 2 ) possessing Co II/I and Mn II/I redox couples at −1.56 and −1.57 V versus Ag/AgCl reference were carefully synthesized. These complexes are active for proton reduction at relatively low overpotentials of 0.12 – 0.32 V. Adduct 1 displayed metal-centered catalytic currents at −1.52, −1.58, −1.65, and −1.79 V at [TFA] of 1–4 mM culminating in an anodic shift of 40 mV and cathodic shifts of 20, 90, and 230 mV while adduct 2 displayed metal-centered catalytic currents at −1.53, −1.61, −1.85, and −1.89 V at [TFA] of 3–5 mM culminating in an anodic shift of 40 mV and cathodic shifts of 40, 280, and 320 mV. Experimental TOFs ( k obs ) of 2.02–4.54 s −1 were observed for the metal-centred processes while the foot-of-the-wave analysis (FOWA) which was used to examine the kinetics of electrocatalysis yielded theoretical TOFs of 0.45 and 0.92 s −1 that culminated in rate constants k cat of 757 and 1526 M −1 s −1 for adducts 1 and 2 respectively. The controlled potential electrolysis produced TONs and Faradaic efficiencies in the range of 2.9–5.5 and 61–88 % respectively. The outstanding performances of the adducts offer promising prospects for the electrocatalytic reduction of protons.