Redox-active ligand assisted electrocatalytic water oxidation by a mononuclear cobalt complex

In this report, the synthesis, characterization and electrocatalytic oxidation of water by a mononuclear cobalt( iii ) complex, [Co III (dpaq)(Cl)]Cl ( 1 ) featuring a redox-active pentadentate amidate ligand (H-dpaq = 2-[bis(pyridin-2-ylmethyl)]amino- N -quinolin-8-yl-acetamidate) is reported. Complex 1 has been found to be a stable and homogeneous water oxidation catalyst (WOC) in 0.1 M phosphate buffer (pH 8.0). A series of experiments (rinse test, SEM, EDX spectroscopy) confirm that this complex acts as a molecular electrocatalyst, and not a precursor of CoOx. The electrocatalytic water oxidation proceeds with high faradaic efficiency (81%) and fast rate (85 s −1 ). Analysis of the electrochemical reaction kinetics by foot-of-the-wave (FOWA) methodology reveals a high turnover frequency of 1.6 × 10 4 s −1 which is comparable to the best performing Ru-based WOCs. A cobalt complex bearing a redox-active monoanionic amidate ligand is shown to act as an efficient molecular electrocatalyst for water oxidation at a moderate overpotential (∼500 mV) in mildly alkaline medium.