7838
I. N. Lykakis, M. Orfanopoulos / Tetrahedron Letters 46 (2005) 7835–7839
Organic Compounds; Sheldon, R. A., Kochi, J. K., Eds.;
R1
R1
Academic Press: New York, 1981.
O
O
v
W
H
wO
(Ar)2C H
R1= CH3, CD3
O
(Ar)2C
2. (a) Maldotti, A.; Molinari, A.; Amadelli, R. Chem. Rev.
2002, 102, 3811–3836; (b) Mizuno, N.; Misono, M. Chem.
Rev. 1998, 98, 199–217; (c) Neumann, R. Prog. Inorg.
Chem. 1998, 47, 317–370.
α
O
O
(Ar)2 = (Ph)2, fluoro
TS5
3. (a) Aspecial issue of Chemical Reviews is devoted to
polyoxometalates: Hill, C. L., Ed., Chem. Rev. 1998, 98, 1–
390; (b) Hill, C. L.; Christina, M.; Prosser-McCartha, C.
M. Coord. Chem Rev. 1995, 143, 407–455; (c) Hiskia, A.;
Mylonas, A.; Papaconstantinou, E. Chem. Soc. Rev. 2001,
30, 62–69.
4. (a) Dondi, D.; Fagnoni, M.; Molinari, A.; Maldotti, A.;
Albini, A. Chem. Eur. J. 2004, 10, 142–148; (b) Jaynes, B.
S.; Hill, C. L. J. Am. Chem. Soc. 1995, 117, 4704–4705; (c)
Jaynes, B. S.; Hill, C. L. J. Am. Chem. Soc. 1993, 115,
12212–12213; (d) Prosser-McCartha, C. M.; Hill, C. L. J.
Am. Chem. Soc. 1990, 112, 3671–3673.
R1
R1
O2
Et3SiH
(Ar)2C OOH
major
W10O325- + H+
(Ar)2C
RI2
O2
HOO
4-
W10O32
Scheme 4. The proposed mechanism in the decatungstate catalyzed
photooxygenation of 1,1-diphenylethane and methyl-9H-fluorene in
the presence of O2 based on KIEs.
5. (a) Chambers, R. C.; Hill, C. L. Inorg. Chem. 1989, 28,
2511; (b) Giannotti, C.; Richter, C. Trends Photochem.
Photobiol. 1997, 4, 43–54; (c) Ermolenko, L. P.; Delaire, J.
A.; Giannotti, C. J. Chem. Soc., Perkin Trans. 2 1997, 25–
30; (d) Maldotti, A.; Molinari, A.; Bergamini, P.; Amad-
elli, R.; Battioni, P.; Mansuy, D. J. Mol. Catal. A 1996,
113, 147–157; (e) Maldotti, A.; Amadelli, R.; Carassiti, V.;
Molinari, A. Inorg. Chim. Acta 1997, 256, 309–312.
6. Tanielian, C. Coord. Chem. Rev. 1998, 178–180, 1165–1181.
7. (a) Tanielian, C.; Duffy, K.; Jones, A. J. Phys. Chem. B
1997, 101, 4276–4282; (b) Tanielian, C.; Schweitzer, C.;
Seghrouchni, R.; Esch, M.; Mechin, R. Photochem.
Photobiol. Sci. 2003, 2, 297–305; (c) Tanielian, C.;
Seghrouchni, R.; Schweitzer, C. J. Phys. Chem. A 2003,
107, 1102–1111.
8. (a) Duncan, D. C.; Netzel, T. L.; Hill, C. L. Inorg. Chem.
1995, 34, 4640–4646; (b) Texier, I.; Delouis, J. F.; Delaire,
J. A.; Giannotti, C.; Plaza, P.; Martin, M. M. Chem. Phys.
Lett. 1999, 311, 139–145; (c) Yamase, T.; Takabaysashi,
N.; Kaji, M. J. Chem. Soc. Dalton Trans. 1984, 793–799;
(d) Yamase, T.; Usami, T. J. Chem. Soc. Dalton Trans.
1988, 183–190.
1.8–2.2 V.10,22 The presence of a small amount of TMB
did not affect the rate of the decatungstate catalyzed
photooxygenation of 1-d0 and 2-d0. This result confirms
that the hydrogen atom transfer mechanism is the pre-
dominant mechanism in the reaction of wO with 1-d0
and 2-d0, as shown in Scheme 4.
In the first step, under irradiation conditions, decatung-
state anion undergoes conversion into the well estab-
lished long-lived intermediate wO.7–10 The substantial
KIEs measured in this work (kH/kD = 1.78–2.30) sug-
gest a hydrogen atom abstraction from the alpha carbon
(Ca) of the alkylarene in the rate-determining step. Sub-
sequently, a one-electron-reduced species HþW10O5ꢀ is
32
produced along with a radical intermediate (RI2), as
shown in Scheme 4. The RI2, in the presence of molecu-
lar oxygen, decomposes to the corresponding tertiary
hydroperoxide. The one-electron-reduced species of
the decatungstate re-oxidizes in the presence of molecu-
lar oxygen to give again W10O4ꢀ and a molecule of
9. Duncan, D. C.; Fox, M. A. J. Phys. Chem. A 1998, 102,
4559–4567.
10. Texier, I.; Delaire, J. A.; Giannotti, C. Phys. Chem. Chem.
Phys. 2000, 2, 1205–1212.
11. (a) Lykakis, I. N.; Tanielian, C.; Orfanopoulos, M. Org.
Lett. 2003, 5, 2875–2878; (b) Lykakis, I. N.; Orfanopou-
los, M. Tetrahedron Lett. 2004, 45, 7645–7649.
32
hydrogen peroxide. This mechanism has support
from previous kinetic results with aryl alkanols11
and non-aromatic alkanes.4,5,7
In conclusion, both primary and b-secondary kinetic
isotope effects in the decatungstate catalyzed photooxy-
genation of alkylarenes support a hydrogen atom
abstraction in the rate-determining step.
12. For theory and examples on KIEs see: (a) Melander, L.;
Saunders, W. H. Reaction Rates of Isotopic Molecules;
Wiley-Interscience: New York, 1980; (b) Carpender, B. K.
Determination of Organic Reaction Mechanism; John
Wiley: New York, 1984; (c) Matsson, O.; Westaway, K.
C. Adv. Phys. Org. Chem. 1996, 31, 143–248.
Acknowledgement
13. The 1H NMR and 13C NMR data (in parts per million) of
1
the alkylarenes are as follows: 1-d0: H NMR (500 MHz,
This work was supported by the Greek Secretariat of
Research and Technology, grants: PENED 2002 and
PITHAGORAS II 2005.
CDCl3):
d 7.35 (t, 4H, J = 7.7 Hz), 7.30 (d, 4H,
J = 7.2 Hz), 7.25 (t, 2H, J = 7.3 Hz), 4.21 (q, 1H,
J = 7.2 Hz), 1.69 (d, 3H, J = 7.2 Hz). 13C NMR
(125 MHz, CDCl3): d 146.4, 128.3, 127.6, 126.0, 44.7,
21.8. MS m/z = 182 (100, m/z = 167); 1-d3: 1H NMR
(125 MHz, CDCl3): d 7.35 (t, 4H, J = 7.7 Hz), 7.30 (d, 4H,
J = 7.2 Hz), 7.25 (t, 2H, J = 7.3 Hz), 4.20 (s, 1H). 13C
NMR (125 MHz, CDCl3): d 146.3, 128.3, 127.6, 126.0,
44.5, 21.0 (septet, JCD = 19 Hz). MS m/z = 185 (100,
References and notes
1. (a) Activation andFunctionalization of Alkanes ; Hill, C. L.,
Ed.; Wiley: New York, 1989; (b) Selective Hydrocarbons
Activation: Principles andProgress ; Davies, J. A., Watson,
P. L., Greenberg, A., Liebman, J. F., Eds.; VCH: New
York, 1990; (c) The Chemistry of Alkanes andCycloal-
kanes; Patai, S., Rappoport, Z., Eds.; John Wiley and
Sons: Chichester, 1992; (d) Metal-catalyzedOxidation of
1
m/z = 167). 1-d4: H NMR (500 MHz, CDCl3): d 7.35 (t,
4H, J = 7.7 Hz), 7.30 (d, 4H, J = 7.2 Hz), 7.25 (t, 2H,
J = 7.3 Hz). 13C NMR (125 MHz, CDCl3): d 146.3, 128.3,
127.6, 126.0, 43.9 (triplet, JCD = 19 Hz), 20.9 (septet,
JCD = 19 Hz). MS m/z = 186 (100, m/z = 168). 2-d0: 1H