Intermolecular\nO–O Bond Formation between High-Valent\nRu–oxo Species

Despite extensive research on water oxidation catalysts\nover the\npast few decades, the relationship between high-valent metal-oxo intermediates\nand the O–O bond formation pathway has not been well clarified.\nOur previous study showed that the high spin density on O in Ru<sup>V</sup>=O is pivotal for the interaction of two metal-oxyl radical\n(I2M) pathways. In this study, we found that introducing an axially\ncoordinating ligand, which is favorable for bimolecular coupling,\ninto the Ru-pda catalyst can rearrange its geometry. The shifts in\ngeometric orientation altered its O–O bond formation pathway\nfrom water nucleophilic attack (WNA) to I2M, resulting in a 70-fold\nincrease in water oxidation activity. This implies that the I2M pathway\nis concurrently influenced by the spin density on oxo and the geometry\norganization of the catalysts. The observed mechanistic switch and\ntheoretical studies provide insights into controlling reaction pathways\nfor homogeneous water oxidation catalysis.