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Catalytic Four-Electron Oxidation of Water by Intramolecular Coupling of the Oxo Ligands of a Bis(ruthenium–bipyridine) Complex

  1. Prof. Dr. Tohru Wada2,
  2. Dr. Hideki Ohtsu1,
  3. Prof. Dr. Koji Tanaka1,*

Article first published online: 16 JAN 2012

DOI: 10.1002/chem.201102236

Issue

Chemistry - A European Journal

Chemistry - A European Journal

Volume 18, Issue 8, pages 2374–2381, February 20, 2012

Additional Information

How to Cite

Wada, T., Ohtsu, H. and Tanaka, K. (2012), Catalytic Four-Electron Oxidation of Water by Intramolecular Coupling of the Oxo Ligands of a Bis(ruthenium–bipyridine) Complex. Chem. Eur. J., 18: 2374–2381. doi: 10.1002/chem.201102236

Author Information

  1. 1

    Department of Life and Coordination – Molecular Science, Institute for Molecular Science, 5-1, Higashiyama, Myodaiji, Okazaki, 444-8787 Aichi (Japan), Fax: (+81) 564-59-5582

  2. 2

    Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishi-ikebukuro, Toshima, 171-8501 Tokyo (Japan)

*Department of Life and Coordination – Molecular Science, Institute for Molecular Science, 5-1, Higashiyama, Myodaiji, Okazaki, 444-8787 Aichi (Japan), Fax: (+81) 564-59-5582

Publication History

  1. Issue published online: 10 FEB 2012
  2. Article first published online: 16 JAN 2012
  3. Manuscript Revised: 6 OCT 2011
  4. Manuscript Received: 21 JUL 2011

Funded by

  • Grant in Aid for Scientific Researches. Grant Numbers: 20002005, 23550084
  • Ministry of Education, Culture, Sports, Science and Technology of Japan

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Keywords:

  • binuclear complex;
  • electrochemistry;
  • oxidation;
  • Raman spectroscopy;
  • ruthenium

Abstract

A bis(ruthenium–bipyridine) complex bridged by 1,8-bis(2,2′:6′,2′′-terpyrid-4′-yl)anthracene (btpyan), [Ru2(μ-Cl)(bpy)2(btpyan)](BF4)3 ([1](BF4)3; bpy=2,2′-bipyridine), was prepared. The cyclic voltammogram of [1](BF4)3 in water at pH 1.0 displayed two reversible [RuII,RuII]3+/[RuII,RuIII]4+ and [RuII,RuIII]4+/[RuIII,RuIII]5+ redox couples at E1/2(1)=+0.61 and E1/2(2)=+0.80 V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E=+1.2 V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [1]3+ ions at E=+1.60 V in water at pH 2.6 (buffered with H3PO4/NaH2PO4) catalytically evolved dioxygen. Immediately after the electrolysis of the [1]3+ ion in H216O at E=+1.40 V, the resultant solution displayed two resonance Raman bands at equation image=442 and 824 cm-1. These bands shifted to equation image=426 and 780 cm−1, respectively, when the same electrolysis was conducted in H218O. The chemical oxidation of the [1]3+ ion by using a CeIV species in H216O and H218O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (Δequation image=16 and 44 cm−1) fully fit the calculated ones based on the Ru[BOND]O and O[BOND]O stretching modes, respectively. The first successful identification of the metal[BOND]O[BOND]O[BOND]metal stretching band in the oxidation of water indicates that the oxygen–oxygen bond at the stage prior to the evolution of O2 is formed through the intramolecular coupling of two Ru–oxo groups derived from the [1]3+ ion.

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