Enzyme‐Like Synthetic Cleft for Light‐Driven Water‐Oxidation Catalysis Via an Oxide Relay Pathway

ABSTRACT Harnessing functional groups in the outer coordination sphere to direct catalytic pathways is characteristic for enzymes, yet rather underexplored for man‐made catalysts. Here, following our earlier work on Ru(bda) water oxidation catalysts (bda = 2,2′‐bipyridine‐6,6′‐dicarboxylate), we demonstrate how a carboxyl‐functionalized Ru(bda)‐based macrocycle enables an oxide relay mechanism in light‐driven water oxidation via an O─O bond formation between carboxylate and Ru V = O units positioned on opposing sides. Through a combination of photocatalytic water oxidation studies, NMR and single crystal analysis, and 18 O‐labeling experiments, we provide evidence for the mechanistically distinct oxide relay pathway under photocatalytic conditions. Our findings underscore the role of second coordination sphere engineering in modulating reaction pathways and advancing molecular catalyst design.