L. Que, Jr., B. L. Feringa et al.
FULL PAPER
Kinetic isotope effect determination: In essentially the procedure descri-
bed above, a cyclohexane/[D12]cyclohexane (1:1) mixture was used. The
KIE was determined by comparing the turnover numbers for cyclohexanol
and [D11]cyclohexanol (determined by GC with the CP-wax 52 CB column)
and corrected for the relative concentrations of cyclohexane and [D12]cy-
clohexane.
N
N
N
N
N
Fe
O
Fe
N
O
N
O
H
O
H
N
N
Acknowledgement
This work was supported by the Unilever Research Laboratory, Vlaardin-
gen (The Netherlands), and the National Institutes ofHealth, Washington
DC (GM-33162).
2
3
Figure 2. Coordination modes for the hydroperoxide ligand in intermedi-
ates 2 and 3.
[
[
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tion mode is the reason for the difference in reactivity remains
to be elucidated.
4
998.
[
[
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Conclusion
We have shown that the N4Py ± Fe system is one ofthe most
reactive non-heme iron catalysts known to date, capable of
oxidizing a wide range oforganic substrates including alkanes,
alkenes, alcohols, benzene, and DMA. Complex 1 reacts with
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6] M. Sono, M. P. Roach, M. P. Coulter, J. H. Dawson, Chem. Rev. 1996,
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III
2
H O2 to give the well characterized [(N4Py)Fe OOH]
2
intermediate 2, with properties strongly reminiscent of
activated BLM. Intermediate 2 reacts through homolysis of
[7] a) R. M. Burger, J. Peisach, S. B. Horwitz, J. Biol. Chem. 1981, 256,
1636 ± 11644; b) J. W. Sam, X. J. Tang, J. Peisach, J. Am. Chem. Soc.
1
IV
2
1994, 166, 5250 ± 5256.
the O ± O bond, affording two species: [(N4Py)Fe O] and
[
8] a) R. M. Burger, Chem. Rev. 1998, 98, 1153 ± 1169; b) J. Stubbe, J. W.
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.
OH. Although OH radicals are involved in substrate
oxidation, the results obtained cannot be explained solely by
3
30; c) R. A. Marusak, C. F. Mearus, in Active Oxygen in Biochemistry
.
the action of OH radicals. Therefore we propose that the
(Eds.: J. S. Valentine, C. S. Foote, A. Greenberg, J. F. Liebman),
Chapman and Hall, Glasgow, 1995, pp. 336 ± 400.
IV
Fe O species also plays a prominent role in oxidation ofthe
[
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Kozarich, Chem. Rev. 1987, 87, 1107 ± 1136.
substrate. The involvement ofthis species and the nature of
the oxidizing complex need to be elucidated further. The
formation of a low-spin iron(iii) intermediate by both 1 and
Fe ± BLM, and their similar oxidation chemistry, lead to the
attractive hypothesis that 1 and Fe ± BLM react through the
same mechanistic pathways. In view ofthe results described
above, the chemistry ofFe ± BLM should be considered in
terms ofhomolysis ofthe O ± O bond in activated bleomycin.
[
[
10] D. L. Boger, T. M. Ramsey, H. Cai, S. T. Hoehn, J. Stubbe, J. Am.
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[
[
[
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7
826 ± 7828.
Experimental Section
[
16] a) R. Y. N. Ho, J. F. Liebman, J. S. Valentine in Active Oxygen in
Biochemistry (Eds.: J. S. Valentine, C. S. Foote, A. Greenberg, J. F.
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Instrumentation and materials: UV/Vis spectra were recorded on a
Hewlett Packard 8453 UV± Visible Spectrophotometer. GC analyses were
performed on a Hewlett Packard 6890 Gas Chromatograph using an HP-1
dimethyl polysiloxane column, an HP-5 5% phenyl methyl siloxane
column, or a CP-wax 52 CB column. Retention times ofoxidation products
were compared with commercial or independently prepared samples.
Complex 1 was prepared according to published procedures.[18a, 47] Caution:
Perchlorate salts are potentially explosive and should be handled with care.
[
1
204; c) A. Kittaka, Y. Sugano, M. Otsuka, M. Ohno, Y. Sugiura, H.
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Catalytic oxidations: All experiments were carried out under argon, unless
noted otherwise, in a water bath thermostatted at 258C.
[
18] a) M. Lubben, A. Meetsma, E. C. Wilkinson, B. Feringa, L. Que, Jr.,
Angew. Chem. 1995, 107, 1610 ± 1612; Angew. Chem. Int. Ed. Engl.
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McKenzie, H. Toftlund, J. P. Tuchagues, J. Chem. Soc., Dalton Trans.
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Az e ma, M. Slany, F. Godde, A. Simaan, F. Banse, T. Kargar-Grisel, G.
In a typical procedure, cyclohexane (0.38 mL, 1000 equiv) was added to a
À4
solution of 1 (8.75 Â 10 m, 4 mL) and a known amount ofbromobenzene
(
internal standard) in acetone. The reaction was started by addition of30%
2 2
H O (35 mL). After 30 min an aliquot (1 mL) was taken from the reaction
and filtered over a small silica column. The silica was washed thoroughly
with diethyl ether or diethyl ether/10% methanol. The sample was
concentrated to 2 mL by passing an argon stream over the solution, then
analyzed by GC.
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