Sulfur Coordination Effects on the Stability and Activity of a Ruthenium-Based Water Oxidation Catalyst.

Water oxidation is regarded as the bottleneck of the water splitting and the development of water oxidation catalysts is of importance in the view of reducing reaction barriers and promoting water oxidation efficiency. Recently, the Sun group has disclosed a family of highly active water oxidation catalysts, [Ru(bda)(L)2 ] (bda2- = 2,2'-bipyridine-6,6'-dicarboxylate; L = N-containing ligands). Herein, we replaced the bda2- ligand with a 2,2'-bipyridine-6,6'-dicarbothioate (bct2- ) ligand and prepared a mononuclear ruthenium complex [Ru(bct)(pic)2 ] (Ru-bct, pic = 4-picoline). Less equatorial ligand distortion is observed for RuII -bct which displays improved stability than RuII -bda. The Ru-bct complex undergoes chemical-structural evolution during electrochemical and chemical oxidation, generating Ru-bda as the intrinsic active species to afford water oxidation. This study provides an example to understand structure-stability-reactivity relationship of molecular water oxidation catalysts.