Synthesis and Catalytic Water Oxidation Activities of Ruthenium Complexes Containing Neutral Ligands

Synthesis and Catalytic Water Oxidation Activities of Ruthenium Complexes Containing Neutral Ligands: "

Abstract

Two dinuclear and one mononuclear ruthenium complexes containing neutral polypyridyl ligands have been synthesised as pre-water oxidation catalysts and characterised by ¹H and ¹³C NMR spectroscopy and ESI-MS. Their catalytic water oxidation properties in the presence of [Ce(NH₄)₂(NO₃)₆] (Ce^IV) as oxidant at pH 1.0 have been investigated. At low concentrations of Ce^IV (5 mM), high turnover numbers of up to 4500 have been achieved. An ¹⁸O-labelling experiment established that both O atoms in the evolved O₂ originate from water. Combined electrochemical study and electrospray ionisation mass spectrometric analysis suggest that ligand exchange between coordinated 4-picoline and free water produces Ru aquo species as the real water oxidation catalysts.

Homogeneous water oxidation catalysed by two dinuclear and one mononuclear ruthenium complexes containing neutral polypyridyl ligands (see figure) in the presence of Ce(NH₄)₂(NO₃)₆ as the oxidant at pH 1.0 has been achieved with high turnover numbers of up to 4500.

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