Influence of substituents on the water oxidation performance for copper–bipyridine catalysts

Since it was first reported in 2012, copper-based molecular catalysts for water oxidation have gained significant attention. While investigations have endeavored to elucidate additional copper molecular catalysts for water oxidation and enhance their catalytic activities, few have systematically explored substituents' impact on their water oxidation performance. In this work, a series of copper-bipyridine catalysts, (2,2′-bipyridine)Cu(OH)2 derivatives with various substituents were synthesized by simply mixing the copper salts with 4,4′-R-2,2′-bipyridine ligands, where R represents seven distinct substituents. The UV–vis and FTIR spectra confirm the successful synthesis of the catalysts. However, only four of them are stable under the experimental conditions. The electrochemical studies show that their water oxidation potential follows the order of Cu-H < Cu-CH3 < Cu–OCH3 < Cu-CH2OH, indicating their water oxidation ability. Computation calculation indicates a linear relationship between the turnover frequency and the HOMO-LUMO energy gap. This work uncovers the influence of substituents on the catalytic properties of copper-bipyridine catalysts, offering valuable insights into the rational design of copper-based catalysts.