ORGANIC
LETTERS
2003
Vol. 5, No. 16
2875-2878
Decatungstate Photocatalyzed Oxidation
of Aryl Alkanols. Electron Transfer or
Hydrogen Abstraction Mechanism?
,†
Ioannis N. Lykakis,† Charles Tanielian,‡ and Michael Orfanopoulos*
Department of Chemistry, UniVersity of Crete, 71409 Iraklion, Greece, and
Laboratoire de Photochimie, Ecole Europeenne Chimie Polymeres Materiaux de
Strasbourg, 25, rue Becquerel, 67087 Strasbourg Cedex 2, France
Received May 27, 2003
ABSTRACT
4-
Decatungstate W O
photosensitized oxidation of a series of para-X-substituted 1-aryl-1-alkanols was investigated. The only oxidation
10 32
product of the side-chain of the 1-aryl-1-alkanol was the aryl ketone. The product analysis and kinetic data of the title reaction support a
hydrogen atom transfer mechanism in the rate-determining step.
4-
Polyoxometalates are efficient photocatalysts and exhibit a
remarkable array of homogeneous oxidation reactions.1 The
most interesting and synthetically valuable properties of these
metal-oxygen anion clusters are (a) the wide range of their
redox potentials, (b) their oxidative and thermal stability,
W10O32 photocatalyzes the activation of the C-H bonds
in saturated hydrocarbons and alcohols (eq 1).3-15 Most of
the recent work3,5-14 has focused on the possible key
intermediates that follow light absorption by the catalyst
W10O32.4- For example, irradiation of W10O324- in acetonitrile
produces a short-lived excited-state intermediate W10O324-*,
which is too short-lived (∼30 ps) to be responsible for
bimolecular substrate-catalyst interactions.10b,11
and (c) the reversibility in their multielectron reductions.
6-
Polyoxometalates such as SiW12O403-, PW12O403-, H2W18O62
,
and W10O324- catalyze the oxidation of a variety of organic
substrates, for example, hydrocarbons, alcohols, substituted
phenols, and amines.2-15 In particular, decatungstate anion
(8) Kothe, T.; Martschke, R.; Fischer, H. J. Chem. Soc., Perkin Trans.
2 1998, 503.
(9) Molinari, A.; Amadelli, R.; Andreotti, L.; Maldotti, A. J. Chem. Soc.,
Dalton Trans. 1999, 1203.
(10) (a) Texier, I.; Delouis, J. F.; Delaire, J. A.; Giannotti, C.; Plaza, P.;
Martin, M. M. Chem. Phys. Lett. 1999, 311, 139. (b) Texier, I.; Delaire, J.
A.; Giannotti, C. Phys. Chem. Chem. Phys. 2000, 2, 1205.
(11) Duncan, D. C.; Netzel, T. L.; Hill, C. L. Inorg. Chem. 1995, 34,
4640.
(12) (a) Tanielian, C.; Mechin, R.; Seghrouchni, R.; Schweitzer, C.
Photochem. Photobiol. 2000, 71, 12. (b) Tanielian, C.; Schweitzer, C.;
Seghrouchni, R.; Esch, M.; Mechin, R. Photochem. Photobiol. Sci. 2003,
2, 297.
† University of Crete.
‡ Ecole Europeenne Chimie Polymeres Materiaux de Strasbourg.
(1) A special issue of Chemical ReViews is devoted to polyoxometa-
lates: Hill, C. L. Ed. Chem. ReV. 1998, 98, 1.
(2) (a) Hill, C. L.; Christina, M.; McCartha, P. Coord. Chem. ReV. 1995,
143, 407. (b) Papaconstantinou, E. Chem. Soc. ReV. 1989, 18, 1.
(3) Tanielian, C. Coord. Chem. ReV. 1998, 178-180, 1165.
(4) (a) Papaconstantinou, E. J. Chem. Soc., Chem. Commun. 1982, 12.
(b) Hiskia, A.; Mylonas, A.; Papaconstantinou, E. Chem. Soc. ReV. 2001,
30, 62.
(5) (a) Yamase, T.; Takabaysashi, N.; Kaji, M. J. Chem. Soc., Dalton
Trans. 1984, 793. (b) Yamase, T.; Usami, T. J. Chem. Soc., Dalton Trans.
1988, 103.
(6) (a) Nomiya, K.; Sugie, Y.; Miyazaki, T.; Miwa, M. Polyhedron 1986,
5, 1267. (b) Nomiya, K.; Miyazaki, T.; Maeda, K.; Miwa, M. Inorg. Chim.
Acta 1987, 65, 127.
(13) (a) Tanielian, C.; Duffy, K.; Jones, A. J. Phys. Chem. B 1997, 101,
4276. (b) Tanielian, C.; Seghrouchni, R.; Schweitzer C. J. Phys. Chem. A
2003, 107, 1102.
(14) Duncan, D. C.; Fox, M. A. J. Phys. Chem. A 1998, 102, 4559.
(15) (a) Jaynes, B. S.; Hill, C. L. J. Am. Chem. Soc. 1993, 115, 12212.
(b) Renneke, R. F.; Pasquali, M.; Hill, C. L. J. Am. Chem. Soc. 1990, 112,
6585. (c) Prosser-McCartha, C. M.; Hill, C. L. J. Am. Chem. Soc. 1990,
112, 3671.
(7) Fox, M. A.; Cardona, R.; Gaillard, E. J. Am. Chem. Soc. 1987, 109,
6347.
10.1021/ol0349211 CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/11/2003