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

Abstract

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 CoIII,III‐OH2 species. Then, a proton‐coupled electron transfer followed by a one‐electron transfer process leads to the generation of the formal CoIV,IV‐OH intermediate. The subsequent PCET produces the active species, namely the formal CoIV,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 O2.