Homogenous Catalysis of the Photoreduction of Water. 6. Mediation by Polypyridine Complexes of Rhuthenium(II) and Cobalt(II) in Alkaline Media

Article abstract of DOI:10.1021/ja00293a035

The emission of (polypyridine)rhutenium(II) complexes (S) is quenched by (polypyridine)cobalt(II) (CoL₃²⁺) complexes via parallel oxidative, reductive, and energy-transfer paths, giving CoL₃ +S⁺, CoL₃³⁺ + S^-, respectively.The oxidative route provides the basis for a new water photoreduction sequence: in mixed acetonitrile-water solvents relatively high cage-escape yields of Ru(4,7-(CH3)2phen)₃³⁺ and Co(bpy)₃⁺(S = Ru(4,7-(CH3)2phen)₃²⁺, phen = 1,10-phenanthroline, bpy = 2,2'-bipyridine) are obtained.The Ru(III) complex is reduced by triethanolamine (TEOA), and the Co(bpy)₃⁺ reacts with water and/or TEOAH⁺ to give H2. the maximum H2 quantum yield obtained is 0.29 in 50percent acetonitrile-water.Unusual features of the system are the fact that, at low TEOA, Co(bpy)₃²⁺ scavenging of Ru(III) reduces the H2 yield and that the cage-escape and limiting H2 yields are strongly solvent dependent: for the Ru(4,7-(CH3)2phen)₃²⁺-Co(bpy)₃²⁺-TEOA system the H2 yield increases from cca.0.02 in H2O to 0.29 in the mixed solvent.Reduction potentials for CoL₃^3+/2+ and CoL₃^2+/+ couples are also reported.