Photo‐Induced Water Oxidation Based on a Mononuclear Cobalt(II) Complex

Photo‐induced water oxidation based on first row transition metal complexes has drawn much attention recently as a part of the efforts to design systems for solar fuel production. Here, the classic tetradentate ligand TPA (tris(2‐pyridylmethyl)amine) is used together with cobalt(II) in CH 3 CN to form a mononuclear cobalt complex [Co(TPA)Cl]Cl. Single crystal X‐ray diffraction shows that [Co(TPA)Cl]Cl is composed of discrete cationic units with a penta‐coordinate cobalt center, along with chloride counter ions. In borate buffer, the Co complex acts as a water oxidation catalyst, as shown by the presence of a catalytic wave in electrochemistry. Under visible light irradiation, in the presence of photosensitizer and electron acceptor, the Co complex catalyzes O 2 evolution with a turnover frequency (TOF) of 1.0 mol(O 2 )·mol(Co) −1 ·s −1 and a turnover number (TON) of 55 mol(O 2 )·mol(Co) −1 in pH 8 borate buffer.