Ruthenium(II) terpyridine complexes containing heteroaryl-2-imidazole ligands featuring catalytic activity for water oxidation

Water splitting into O2 and H2 by using solar energy is a clean alternative to fossil fuels to supply the world energetic demands. Water oxidation (2H2O  O2 + 4H+ + 4e-) is the most challenging step because it requires the use of overpotentials to obtain a good performance and is kinetically unfavorable as it implies proton-electron transfer steps, so water oxidation catalysts (WOC) have been developed to deal with these challenges. Among several WOC, ruthenium polypyridyl complexes have been widely studied as they meet the requirements needed for high-efficient water oxidation.1 In this work, two new ruthenium(II) terpyridine aquo complexes [Ru(OH2)(Himpy)(tpy)]2+ (1), and [Ru(OH2)(Himpa)(tpy)]2+ (2) have been synthesized and well characterized by UV-vis, 1H-NMR, and ESI-MS. Electrochemical measurements were performed to know the influence of σ-donor/π-acceptor properties of heteroaryl-2-imidazole ligands on water oxidation-catalytic performance.