Schwiedrzik Ludwig, Brieskorn Vera, González Leticia
Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria.
ACS Catal. 2021 Nov 5;11(21):13320-13329. doi: 10.1021/acscatal.1c03566. Epub 2021 Oct 18.
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 [MnVO(OAc)], a polyoxometalate catalyst with a [MnO] cubane core reminiscent of the natural oxygen-evolving complex. Starting from the activated species [Mn VO(OAc)(HO)(OH)], 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 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.
由于分子金属 - 氧催化剂的结构复杂性，了解水氧化生成分子氧的过程是一项具有挑战性的工作。在本报告中，我们揭示了高活性水氧化催化剂[MnVO(OAc)]的水氧化机制，这是一种具有[MnO]立方烷核心的多金属氧酸盐催化剂，让人联想到天然析氧复合物。从活化物种[MnVO(OAc)(H₂O)(OH)]出发，我们仔细研究了多种途径，发现水氧化通过连续的质子耦合电子转移（PCET）、O - O键形成、另一次PCET、分子内电子转移以及另一次PCET导致氧气析出，预测的热力学过电位为0.71 V。对O - O键形成过程的深入研究揭示了氧化还原异构化和 Jahn - Teller效应之间的重要相互作用，这在催化循环中增强了反应活性。这是通过在金属中心之间重新分配电子并通过 Jahn - Teller畸变削弱相关键来实现 的，从而为催化剂原本刚性的立方烷核心引入了灵活性。这些机理见解有望推动高效仿生Mn立方烷水分解催化剂的设计。
