Efficient molecular ruthenium catalysts containing anionic ligands for water oxidation

Abstract

Two new mononuclear Ru complexes Ru^II(bipa)(pic)₃ (1; H₂bipa = 6-(1H-benzo[d]imidazol-2-yl)picolinic acid, pic = 4-picoline) and Ru^II(pbic)(pic)₃ (2; H₂pbic = 2-(pyridin-2-yl)-1H-benzo[d]imidazole-7-carboxylic acid, pic = 4-picoline) based on anionic ligands were successfully synthesized, and characterized using NMR spectroscopy, mass spectrometry, and X-ray crystallography. These catalysts showed high activities and stabilities in water oxidation in homogeneous systems with a high turnover number of 2100 and a turnover frequency of 0.21 s⁻¹ for complex 1. The O–O band formation mechanism involved water nucleophilic attack. An active catalytic intermediate, i.e., Ru^IV–OH, was detected using high-resolution mass spectrometry.