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‐N1O2)(bpy)Cl] (1III) and [RuII(pdc‐κ2‐N1O1)(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‐N1O2)(bpy)(OH2)]+ (1‐O) and [RuIV(O)(pdc‐κ2‐N1O1)(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

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing Ruthenium-Terpyridyl-Bipyridyl Complexes

The irreversible conversion of single-site water oxidation catalysts (WOC) into the more rugged catalysts structurally related to [(trpy)(5,5&rsquo;-X2-bpy)RuIV(&mu;-O)RuIV(trpy)(O)(H2O)]4+ (X = H, 1-dn4+; X = F, 2-dn4+) represents a critical issue in developing active and durable WOC. In this work, the electrochemical and acid-base properties of 1-dn4+ and 2-dn4+ were evaluated. In-situ resonance Raman spectroscopy was employed to characterize species formed upon stoichiometric oxidation of single-site catalysts demonstrating the formation of high oxidation states mononuclear Ru=O and RuO-O complexes. Under turnover conditions, the dinuclear intermediates, 1-dn4+ and 2-dn4+, as well as the previously proposed [RuVI(trpy)(O)2(H2O)]2+ complex (32+) are formed. 32+ is a pivotal intermediate that provides access to the formation of dinuclear species. Single crystal X-ray diffraction analysis of the isolated complex [RuIV(O)(trpy)(5,5&rsquo;-F2-bpy)]2+ reveals a clear elongation of the Ru-N bond located in the trans position to the oxo group, documenting the weakness of this bond which promotes the release of the bpy ligand and the subsequent formation of 32+. &nbsp;</p