Flexibility Enhances Reactivity: Redox Isomerism and Jahn–Teller Effects in a Bioinspired Mn(4)O(4) Cubane Water Oxidation Catalyst

[Image: see text] Understanding how water oxidation to molecular oxygen proceeds in molecular metal-oxo catalysts is a challenging endeavor due to their structural complexity. In this report, we unravel the water oxidation mechanism of the highly active water oxidation catalyst [Mn(4)V(4)O(17)(OAc)(3)](3–), a polyoxometalate catalyst with a [Mn(4)O(4)](6+) cubane core reminiscent of the natural oxygen-evolving complex. Starting from the activated species [Mn(4)(4+)V(4)O(17)(OAc)(2)(H(2)O)(OH)](1–), we scrutinized multiple pathways to find that water oxidation proceeds via a sequential proton-coupled electron transfer (PCET), O–O bond formation, another PCET, an intramolecular electron transfer, and another PCET resulting in O(2) evolution, with a predicted thermodynamic overpotential of 0.71 V. An in-depth investigation of the O–O bond formation process revealed an essential interplay between redox isomerism and Jahn–Teller effects, responsible for enhancing reactivity in the catalytic cycle. This is achieved by redistributing electrons between metal centers and weakening relevant bonds through Jahn–Teller distortions, introducing flexibility to the otherwise rigid cubane core of the catalyst. These mechanistic insights are expected to advance the design of efficient bioinspired Mn cubane water-splitting catalysts.