A Molecular Water-Oxidation Catalyst Derived from Ruthenium Diaqua Bis(2,2'-bipyridyl-5,5'-dicarboxylic acid)

Article abstract of DOI:10.1021/ja00256a010

Controlled-potential electrolysis of cis-Ru^IIL2(OH2)2²⁺ (where L is 2,2'-bipyridyl-5,5'-dicarboxylic acid) in 0.5 M H2SO4 solutions leads to the formation of a relatively durable and active molecular water-oxidation catalyst.Detailed analyses by UV-visible absorption spectrophotometry, resonance Raman spectrophotometry, electrochemical measurements, HPLC, and elemental analysis indicate that the water-oxidation catalyst is an oxo-bridged dimer, L2(H2O)Ru-O-Ru(OH2)L2.The synthesis, spectrophotometric, and redox properties of the monomeric and dimeric ruthenium complexes have been characterized.The effectiveness of the oxo-bridged complex as a water-oxidation catalyst has been evaluated by electrochemical and spectrophotometric analyses and by determination of oxygen production.This newly discovered homogeneous catalyst is highly effective in mediating the thermal and visible-light-induced generation of oxygen from water.A comparison is made between the monomer and dimer and various analogues of the complexes.The presence of the COOH groups at the 5,5' positions of the bipyridyl ligands correlates with the unusual and favorable properties of cis-RuL2(OH2)2 and L2(OH2)Ru-O-Ru(OH2)L2.Dimeric ruthenium complexes of similar structure are also formed during the thermolysis and photolysis of Ru(II) tris(2,2'-bipyridyl-5,5'-dicarboxylic acid), RuL3²⁺, in 0.5 M H2SO4 solutions containing peroxodisulfate.