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Electron-Transfer Reduction of Dinuclear Copper Peroxo and Bis-μ-oxo Complexes Leading to the Catalytic Four-Electron Reduction of Dioxygen to Water

Authors

  • Dr. Laleh Tahsini,

    1. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
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  • Dr. Hiroaki Kotani,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA (Japan) Science and Technology Agency (JST), Suita, Osaka 565-0871 (Japan), Fax: (+81)-6-6879-7368
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  • Dr. Yong-Min Lee,

    1. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
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  • Dr. Jaeheung Cho,

    1. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
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  • Prof. Dr. Wonwoo Nam,

    Corresponding author
    1. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
    • Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
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  • Prof. Dr. Kenneth D. Karlin,

    Corresponding author
    1. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
    2. Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218 (USA)
    • Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
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  • Prof. Dr. Shunichi Fukuzumi

    Corresponding author
    1. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
    2. Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA (Japan) Science and Technology Agency (JST), Suita, Osaka 565-0871 (Japan), Fax: (+81)-6-6879-7368
    • Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
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Abstract

The four-electron reduction of dioxygen by decamethylferrocene (Fc*) to water is efficiently catalyzed by a binuclear copper(II) complex (1) and a mononuclear copper(II) complex (2) in the presence of trifluoroacetic acid in acetone at 298 K. Fast electron transfer from Fc* to 1 and 2 affords the corresponding CuI complexes, which react at low temperature (193 K) with dioxygen to afford the η22-peroxo dicopper(II) (3) and bis-μ-oxo dicopper(III) (4) intermediates, respectively. The rate constants for electron transfer from Fc* and octamethylferrocene (Me8Fc) to 1 as well as electron transfer from Fc* and Me8Fc to 3 were determined at various temperatures, leading to activation enthalpies and entropies. The activation entropies of electron transfer from Fc* and Me8Fc to 1 were determined to be close to zero, as expected for outer-sphere electron-transfer reactions without formation of any intermediates. For electron transfer from Fc* and Me8Fc to 3, the activation entropies were also found to be close to zero. Such agreement indicates that the η22-peroxo complex (3) is directly reduced by Fc* rather than via the conversion to the corresponding bis-μ-oxo complex, followed by the electron-transfer reduction by Fc* leading to the four-electron reduction of dioxygen to water. The bis-μ-oxo species (4) is reduced by Fc* with a much faster rate than the η22-peroxo complex (3), but this also leads to the four-electron reduction of dioxygen to water.

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