Oxo-Bridge Scenario behind Single-Site Water-Oxidation Catalysts

Abstract

<p> High-oxidation-state decay of mononuclear complexes [RuTB(H2O)]2+ (X2+, where B = 2,2&prime;-bpy or bpy for X = 1; B = 5,5&prime;-F2-bpy for X = 2; B = 6,6&prime;-F2-bpy for X = 3; T = 2,2&prime;:6&prime;,2&Prime;-terpyridine) oxidized with a large excess of CeIV generates a manifold of polynuclear oxo-bridged complexes. These include the following complexes: (a) dinuclear [TB-RuIV-O-RuIV-(T)(O)OH2]2+ (1-dn4+), [TB-RuIII-O-RuIII-T(MeCN)2]4+ (1-dn-N4+), and {[RuIII(trpy)(bpy)]2(&mu;-O)}4+(1-dm4+); (b) trinuclear {[RuIII(trpy)(bpy)(&mu;-O)]2RuIV(trpy)(H2O)}(ClO4)56+ (1-tr6+) and {[RuIII(trpy)(bpy)(&mu;-O)]2RuIV(pic)2}(ClO4)4 (1-tr-P4+, where P is the 2-pyridinecarboxylate anion); and (c) tetranuclear [TB-RuIII-O-TRuIV(H2O)-O-TRuIV(H2O)-O-RuIII-TB]8+ (1-tn8+), [TB-RuIII-O-TRuIV(AcO)-O-TRuIV(AcO)-O-RuIII-TB]6+ (1-tn-Ac6+), and [TB-RuII-O-TRuIV(MeCN)-O-TRuIV(MeCN)-O-RuII-TB]6+ (1-tn-N6+). These complexes have been characterized structurally by single-crystal X-ray diffraction analysis, and their structural properties were correlated with their electronic structures. Dinuclear complex 1-dm4+ has been further characterized by spectroscopic and electrochemical techniques. Addition of excess CeIV to 1-dm4+ generates dioxygen in a catalytic manner. However, resonance Raman spectroscopy points to the in situ formation of 1-dn4+ as the active species.</p>