Chemical and photocatalytic water oxidation by mononuclear Ru catalysts

Four mononuclear Ru complexes with different substituents on the para position of the pyridine ligand of Ru(bda)(pic)(2) (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; pic = picoline) were synthesized and characterized by H-1 nuclear magnetic resonance or X-ray crystallography. The electrochemical properties of this series of compounds in acidic and neutral conditions were studied by cyclic voltammetry. Their catalytic activity towards water oxidation was investigated using a chemical oxidant ([Ce(NH4)(2)(NO3)(6)] (Ce-IV) in acidic solution, or driven by visible light in a three-component system containing a photosensitizer ([Ru(bpy)(3)](2+)) and an electron acceptor (S2O82-). For the chemical water oxidation, complex 1 was found to be the most effective, exhibiting a turnover number (TON) of up to 4000. The pyridine substituent at the 4-position in 1 may be protonated giving an intensive electron-withdrawing effect. Complex 2 bears the most electron-withdrawing trifluoromethyl group under neutral conditions and showed the highest photocatalytic activity with a TON of 270 over 2 h. It was concluded that the more electron-withdrawing substituents led to higher activity towards oxygen evolution for this type of Ru catalysts in the oxidation of water.

Av författaren/redakt...: Jiang, Yi; Li, Fei; Huang, Fang; Zhang, Biaobiao; Sun, Licheng

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