Catalytic Oxidation of Water to Dioxygen by Mononuclear Ru Complexes Bearing a 2,6-Pyridinedicarboxylato Ligand.

The synthesis, purification, and isolation of mononuclear Ru complexes containing the tridentate dianionic meridional ligand pyridyl-2,6-dicarboxylato (pdc2- ) of general formula [RuIII (pdc-κ3 -N1 O2 )(bpy)Cl] (1III ) and [RuII (pdc-κ2 -N1 O1 )(bpy)2 ] (2II ) (bpy is 2,2'-bipyridine) is reported. These two complexes and their derivatives were thoroughly characterized through spectroscopic (UV/Vis, NMR) and electrochemical (cyclic voltammetry, differential pulse voltammetry, and coulometry) analyses, and three of the complexes were analyzed by single-crystal X-ray diffraction techniques. Under a high anodic applied potential, both complexes evolve towards the formation of Ru-aquo/oxo derivative species, namely, [RuIII (pdc-κ3 -N1 O2 )(bpy)(OH2 )]+ (1-O) and [RuIV (O)(pdc-κ2 -N1 O1 )(bpy)2 ] (2-O). These two complexes are active catalysts for the oxidation of water to dioxygen and their catalytic activity was analyzed through electrochemical techniques. A maximum turnover frequency (TOFmax )=2.4-3.4×103  s-1 was calculated for 2-O.