Oxygen Evolution Catalyzed by a Mononuclear Ruthenium Complex Bearing Pendant SO3− Groups

Rational molecular design of catalytic systems capable of smooth O-O bond formation is critical to the development of efficient catalysts for water oxidation. A new ruthenium complex was developed, which bears pendant SO3(-) groups in the secondary coordination sphere: [Ru(terpy)(bpyms)(OH2)] (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 SO3(-) groups in comparisons to the parent catalyst, [Ru(terpy)(bpy)(OH2)](2+) (bpy=2,2'-bipyridine). Spectroscopic, electrochemical, and crystallographic investigations concluded that the pendant SO3(-) groups promote the formation of an O-O bond via the secondary coordination sphere on the catalyst, whereas the influence of the pendant SO3(-) groups on the electronic structure of the [Ru(terpy)(bpy)(OH2)](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.