EPR evidence for one-electron oxidation of phenols by a dimeric manganese(IV/IV) triazacyclononane complex in the presence and absence of hydrogen peroxide

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Bruce C. Gilbert, Norbert W. J. Kamp, John R. Lindsay Smith and John Oakes


Abstract

The reaction of [L2Mn2IV(µ-O)3](PF6)2, L = 1,4,7-trimethyl-1,4,7-triazacyclononane (1) with a range of phenols (2–5) in aqueous solution at pH 10.5 has been investigated. At least for electron-rich substrates, the reaction proceeds via a rapid overall one-electron process from the phenolate ion to the MnIV/MnIV species (1) to give, initially, a MnIII/MnIV species (detected via its characteristic 16-line EPR spectrum in frozen solution at 77 K) and the corresponding phenoxyl radical, detected directly for Trolox (3) by EPR spectroscopy in aqueous solution. The dimeric MnIII/MnIV species is ultimately converted to monomeric MnII. In the presence of H2O2, reoxidation of the manganese species is accompanied by an increase in the rate of formation of the phenoxyl radicals. In similar reactions, 4-methoxyphenol (4) and 2,6-dimethoxyphenol (5) are converted into polyphenols (with the formation of phenoxyl radicals trapped in a polymer matrix). Kinetic EPR and UV–VIS studies provide additional evidence of the reaction mechanism in the presence and absence of H2O2. The mechanism of phenolate oxidation by 1 in the presence and absence of H2O2 is discussed.


References

  1. Manganese Redox Enzymes, ed. V. L. Pecoraro, VCH, New York, 1992 Search PubMed.
  2. G. C. Dismukes, Chem. Rev., 1996, 96, 2909 CrossRef CAS.
  3. L. Stryer, Biochemistry, W. H. Freeman, New York, 1988 Search PubMed.
  4. V. K. Yachandra, K. Sauer and M. P. Klein, Chem. Rev., 1996, 96, 2927 CrossRef CAS.
  5. Y. Kono and I. Fridovich, J. Biol. Chem., 1983, 258, 6015 CAS.
  6. K. Wieghardt, Angew. Chem., Int. Ed. Engl., 1989, 28, 1153 CrossRef.
  7. K. Wieghardt, U. Bossek, B. Nuber, J. Weiss, J. Bonvoisin, M. Corbella, S. E. Vitols and J. J. Girerd, J. Am. Chem. Soc., 1988, 110, 7398 CrossRef CAS.
  8. R. Hage, Recl. Trav. Chim. Pays-Bas, 1996, 115, 385 CAS.
  9. R. Hage, J. E. Ilburg, J. Kerschner, J. H. Koek, E. L. M. Lempers, R. J. Martens, U. S. Racherla, S. W. Russel, T. Swarthoff, M. R. P. van Vliet, J. B. Warnaar, L. van der Wolf and B. Krijnen, Nature (London), 1994, 369, 637 CrossRef CAS.
  10. D. E. De Vos, J. L. Meinershagen and T. Bein, Angew. Chem., Int. Ed. Engl., 1996, 35, 2211 CrossRef CAS.
  11. D. E. De Vos and T. Bein, J. Organomet. Chem., 1996, 520, 195 CrossRef CAS.
  12. C. Zondervan, R. Hage and B. L. Feringa, Chem. Commun., 1997, 419 RSC.
  13. D. E. De Vos and T. Bein, Chem. Commun., 1996, 917 RSC.
  14. T. Kobayashi, K. Tsuchiya and Y. Nishida, J. Chem. Soc., Dalton Trans., 1996, 2391 RSC.
  15. K. Wieghardt, U. Bossek, L. Zsolnai, G. Huttner, G. Blondin, J. J. Girerd and F. Babonneau, J. Chem. Soc., Chem. Commun., 1987, 651 RSC.
  16. R. Hage, B. Krijnen, J. B. Warnaar, F. Hartl, D. J. Stufkens and T. L. Snoeck, Inorg. Chem., 1995, 34, 4973 CrossRef CAS.
  17. M. J. Davies, L. G. Forni and R. L. Willson, Biochem. J., 1988, 255, 513 CAS.
  18. M. J. Thomas and B. H. J. Bielski, J. Am. Chem. Soc., 1989, 111, 3315 CrossRef CAS.
  19. C. Suarna, D. C. Craig, K. J. Cross and P. T. Southwell-Keely, J. Am. Chem. Soc., 1988, 53, 1281 CAS.
  20. W. G. B. Huysmans and W. A. Waters, J. Chem. Soc. B, 1966, 1047 RSC.
  21. E. P. Serjeant and B. N. Dempsey, Ionisation Constants of Organic Acids in Aqueous Solution, Pergamon, Oxford, 1979 Search PubMed.
  22. J. Lind, X. Shen, T. E. Eriksen and G. Merenyi, J. Am. Chem. Soc., 1990, 112, 479 CrossRef CAS.
  23. E. Chapoteau, B. P. Czech, A. Kumar, A. Pose, R. A. Bartsch, R. A. Holwerda, N. K. Dalley, B. E. Wilson and J. Weining, J. Org. Chem., 1989, 54, 861 CrossRef CAS.
  24. S. V. Jovanovic, M. Tosic and M. G. Simic, J. Phys. Chem., 1991, 95, 10 824 CrossRef CAS.
  25. S. V. Jovanovic, S. Steenken, M. Tosic, B. Marjanovic and M. G. Simic, J. Am. Chem. Soc., 1994, 116, 4846 CrossRef CAS.
  26. S. Steenken and P. Neta, J. Phys. Chem., 1982, 86, 3661 CrossRef CAS.
  27. L. Eberson, Electron transfer reactions in organic chemistry, Springer-Verlag, Berlin, 1987 Search PubMed.
  28. H. H. Thorp and G. W. Brudwig, New J. Chem., 1991, 15, 479 Search PubMed.
  29. U. Bossek, M. Saher, T. Weyhermuller and K. Wieghardt, J. Chem. Soc., Chem. Commun., 1992, 1780 RSC.
  30. R. Hage, personal communication.
  31. C. Rossi, F. Laschi, R. Pogni, E. Tiezzi, R. Basosi and L. Pogliani, J. Chem. Soc., Faraday Trans. 1, 1988, 84, 3331 RSC.
  32. D. A. Rockcliffe and A. E. Martell, J. Mol. Catal. A: Chem., 1996, 106, 211 CrossRef CAS.
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