Water Oxidation Catalyzed by a Bioinspired Tetranuclear Manganese Complex: Mechanistic Study and Prediction.

Density functional theory calculations were utilized to elucidate the water oxidation mechanism catalyzed by polyanionic tetramanganese complex a [Mn Mn O (CH COO) (A-α-SiW O )] . Theoretical results indicated that catalytic active species 1 (Mn ) was formed after O formation in the first turnover. From 1, three sequential proton-coupled electron transfer (PCET) oxidations led to the Mn -oxyl radical 4 (Mn -O⋅). Importantly, 4 had an unusual butterfly-shaped Mn O core for the two substrate-coordinated Mn sites, which facilitated O-O bond formation via direct coupling of the oxyl radical and the adjacent Mn -coordinated hydroxide to produce the hydroperoxide intermediate Int1 (Mn -OOH). This step had an overall energy barrier of 24.9 kcal mol . Subsequent PCET oxidation of Int1 to Int2 (Mn -O ⋅) enabled the O release in a facile process. Furthermore, apart from the Si-centered complex, computational study suggested that tetramanganese polyoxometalates with Ge, P, and S could also catalyze the water oxidation process, where those bearing P and S likely present higher activities.