Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts

Isolation of Ru-III-bda (17-electron specie) complex with an aqua ligand (2-electron donor) is challenging due to violation of the 18-electron rule. Although considerable efforts have been dedicated to mechanistic studies of water oxidation by the Ru-bda family, the structure and initial formation of the Ru-III-bda aqua complex are still controversial. Herein, we challenge this often overlooked step by designing a pocketshape Ru-based complex 1. The computational studies showed that 1 possesses the crucial hydrophobicity at the Ru-V(O) state as well as similar probability of access of terminal O to solvent water molecules when compared with classic Ru-bda catalysts. Through characterization of single-crystal structures at the Ru-II and Ru-III states, a pseudo seven-coordinate ready-to-go aqua ligand with Ru-III...O distance of 3.62 A was observed. This aqua ligand was also found to be part of a formed hydrogen-bonding network, providing a good indication of how the Ru-III-OH2 complex is formed. [GRAPHICS] .

Automated summary

This article investigates the structure and formation process of the Ru-III-bda complex. By designing a pocketshape Ru-based complex and conducting computational studies and single-crystal structure characterization, a Ru-III...O distance of 3.62 A for the aqua ligand was observed, and it was found to be part of a formed hydrogen-bonding network, providing clues for the formation of the Ru-III-OH2 complex.