Multisite Proton‐Coupled Electron Transfer Facilitates Oxidative Photocatalysis in a Molecular Zr‐Based Coordination Compound

Abstract

Abstract The development of mediators that harness visible light to drive proton‐coupled electron transfer (PCET) offers a promising pathway to achieving challenging redox transformations in a more sustainable manner and with enhanced thermochemical efficiency. However, designing photocatalytic systems based on earth‐abundant metals while gaining precise control over their excited‐state reactivity remains a significant challenge. Here, deprotonation of the hydroxy ligands in the Zr₃(O)(OH)₃ nodes of a photoactive coordination cage is shown to unlock the photocatalytic oxidation of strong O─H and C─H bonds (70–100 kcal mol⁻ 1 ). Mechanistic investigations reveal that this oxidative process proceeds via a multisite PCET pathway involving ground‐state, pre‐association followed by a static quenching mechanism. This contrasts with the dynamic quenching mechanism governing the reductive PCET previously reported for the same system. Collectively, these findings establish an unprecedented ambipolar PCET mechanism with a new class of photocatalytic mediators based on an earth abundant metal.