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

• Published in: ChemSusChem Vol. 12; no. 9; pp. 1949 - 1957
• Main Authors: Hoque, Md Asmaul, Benet‐Buchholz, Jordi, Llobet, Antoni, Gimbert‐Suriñach, Carolina
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 08.05.2019
• Subjects: Biological evolution; Catalysis; Catalytic activity; Catalytic oxidation; Coulometers; Coulometry; electrochemical characterization; Ligands; meridional ligands; NMR; Nuclear magnetic resonance; Oxidation; redox catalysis; Ru complexes; Ruthenium compounds; Voltammetry; water oxidation; X-ray diffraction
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201802996

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. Complex solutions simplified: Ru complexes containing the pyridyl‐2,6‐dicarboxylato (pdc2−) and bipyridine (bpy) ligands, and their Ru‐OH2 derivatives are described. Two different coordination modes of the pdc2− (κ‐N1O2 or κ‐N1O1) are observed depending on the oxidation state and number of bpy auxiliary ligands. Such flexibility of the pdc2− ligand and its implications on the catalytic oxidation of water to dioxygen are discussed in detail.