Efficient molecular ruthenium catalysts containing anionic ligands for water oxidation
Two new mononuclear Ru complexes RuII(bipa)(pic)3 (1; H2bipa = 6-(1H-benzo[d]imidazol-2-yl)picolinic acid, pic = 4-picoline) and RuII(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., RuIV–OH, was detected using high-resolution mass spectrometry.