Axial Ligand Effects of Ru-BDA Complexes in the O-O Bond Formation via the I2M Bimolecular Mechanism in Water Oxidation Catalysis

A detailed computational investigation of the mechanistic aspects of the water oxidation catalysis (WOC) for ruthenium-based catalysts [Ru(bda)(isoq)(2)] (H(2)bda = 2,2 '-bipyridine-6,6 '-dicarboxylic acid; isoq = isoquinoline). Density functional theory (DFT) calculations describe the kinetics by means of the energy barrier that leads to the O-O coupling, the rate-limiting step for WOC. To test the effect of the axial ligand environment, we investigated bda complexes with para-substituted isoquinolines, phthalazines and pyridines. Since previous screening analyses of the potential energy surface revealed a face to face orientation of metal-oxo species to be best for facilitating the O-O bond formation, this paper probes the deeper role of the axial ligands that saturate the Ru(bda) based complexes from a computational point of view.