title: Redox mediator effect on water oxidation in a ruthenium-based chromophore-catalyst assembly.
abstract: The synthesis, characterization, and redox properties are described for a new ruthenium-based chromophore-catalyst assembly, [(bpy)(2)Ru(4-Mebpy-4'-bimpy)Ru(tpy)(OH(2))](4+) (1, [Ru(a)(II)-Ru(b)(II)-OH(2)](4+); bpy = 2,2'-bipyridine; 4-Mebpy-4'-bimpy = 4-(methylbipyridin-4'-yl)-N-benzimid-N'-pyridine; tpy = 2,2':6',2"-terpyridine), as its chloride salt. The assembly incorporates both a visible light absorber and a catalyst for water oxidation. With added ceric ammonium nitrate (Ce(IV), or CAN), both 1 and 2, [Ru(tpy)(Mebim-py)(OH(2))](2+) (Mebim-py = 2-pyridyl-N-methylbenzimidazole), catalyze water oxidation. Time-dependent UV/vis spectral monitoring following addition of 30 equiv of Ce(IV) reveals that the rate of Ce(IV) consumption is first order both in Ce(IV) and in an oxidized form of the assembly. The rate-limiting step appears to arise from slow oxidation of this intermediate followed by rapid release of O(2). This is similar to isolated catalyst 2, with redox potentials comparable to the [-Ru(b)-OH(2)](2+) site in 1, but 1 is more reactive than 2 by a factor of 8 due to a redox mediator effect.
authors: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, USA.
authors: Michael R
authors: MR
authors: Norris
authors: Javier J
authors: JJ
authors: Concepcion
authors: Daniel P
authors: DP
authors: Harrison
authors: Robert A
authors: RA
authors: Binstead
authors: Dennis L
authors: DL
authors: Ashford
authors: Zhen
authors: Z
authors: Fang
authors: Joseph L
authors: JL
authors: Templeton
authors: Thomas J
authors: TJ
authors: Meyer
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D012428:Ruthenium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D014867:Water; D012428:Ruthenium