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Science 3 April 2009:
Vol. 324. no. 5923, pp. 74 - 77
DOI: 10.1126/science.1168600
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Reports

Consecutive Thermal H2 and Light-Induced O2 Evolution from Water Promoted by a Metal Complex

Stephan W. Kohl,1 Lev Weiner,2 Leonid Schwartsburd,1 Leonid Konstantinovski,2 Linda J. W. Shimon,2 Yehoshoa Ben-David,1 Mark A. Iron,2 David Milstein1*

Discovery of an efficient artificial catalyst for the sunlight-driven splitting of water into dioxygen and dihydrogen is a major goal of renewable energy research. We describe a solution-phase reaction scheme that leads to the stoichiometric liberation of dihydrogen and dioxygen in consecutive thermal- and light-driven steps mediated by mononuclear, well-defined ruthenium complexes. The initial reaction of water at 25°C with a dearomatized ruthenium (II) [Ru(II)] pincer complex yields a monomeric aromatic Ru(II) hydrido-hydroxo complex that, on further reaction with water at 100°C, releases H2 and forms a cis dihydroxo complex. Irradiation of this complex in the 320-to-420–nanometer range liberates oxygen and regenerates the starting hydrido-hydroxo Ru(II) complex, probably by elimination of hydrogen peroxide, which rapidly disproportionates. Isotopic labeling experiments with H217O and H218O show unequivocally that the process of oxygen–oxygen bond formation is intramolecular, establishing a previously elusive fundamental step toward dioxygen-generating homogeneous catalysis.

1 Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
2 Department of Chemical Research Support, The Weizmann Institute of Science, Rehovot 76100, Israel.

* To whom correspondence should be addressed. E-mail: david.milstein{at}weizmann.ac.il

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Science. ISSN 0036-8075 (print), 1095-9203 (online)