Exploring the Cooperation of the Redox Non‐Innocent Ligand and Di‐Cobalt Center for the Water Oxidation Reaction Catalyzed by a Binuclear Complex

Water oxidation is a crucial reaction in the artificial photosynthesis system. In the present work, density functional calculations were employed to decipher the mechanism of water oxidation catalyzed by a binuclear cobalt complex, which was disclosed to be a homogeneous water oxidation catalyst in pH=7 phosphate buffer. The calculations showed that the catalytic cycle starts from the Co III,III −OH 2 species. Then, a proton‐coupled electron transfer followed by a one‐electron transfer process leads to the generation of the formal Co IV,IV −OH intermediate . The subsequent PCET produces the active species, namely the formal Co IV,V =O intermediate ( 4 ). The oxidation processes mainly occur on the ligand moiety, including the coordinated water moiety, implying a redox non‐innocent behavior. Two cobalt centers keep their oxidation states and provide one catalytic center for water activation during the oxidation process. 4 triggers the O−O bond formation via the water nucleophilic attack pathway, in which the phosphate buffer ion functions as the proton acceptor. The O−O bond formation is the rate‐limiting step with a calculated total barrier of 17.7 kcal/mol. The last electron oxidation process coupled with an intramolecular electron transfer results in the generation of O 2 .