Oxygen Evolution Catalyzed by a Mononuclear Ruthenium Complex Bearing Pendant SO 3 − Groups

Rational molecular design of catalytic systems capable of smooth OO bond formation is critical to the development of efficient catalysts for water oxidation. A new ruthenium complex was developed, which bears pendant SO 3 − groups in the secondary coordination sphere: [Ru(terpy)(bpyms)(OH 2 )] (terpy=2,2′:6′,2′′‐terpyridine, bpyms=2,2′‐bipyridine‐5,5′‐bis(methanesulfonate)). Water oxidation driven by a Ce 4+ oxidant is distinctly accelerated upon introduction of the pendant SO 3 − groups in comparisons to the parent catalyst, [Ru(terpy)(bpy)(OH 2 )] 2+ (bpy=2,2′‐bipyridine). Spectroscopic, electrochemical, and crystallographic investigations concluded that the pendant SO 3 − groups promote the formation of an OO bond via the secondary coordination sphere on the catalyst, whereas the influence of the pendant SO 3 − groups on the electronic structure of the [Ru(terpy)(bpy)(OH 2 )] 2+ core is negligible. The results of this work indicate that modification of the secondary coordination sphere is a valuable strategy for the design of water oxidation catalysts.