Table 2 Oxidation of oct-1-ene with different iron catalystsa
In summary, we have demonstrated that Fe(TPA) complexes
can catalyse the oxidation of olefins to cis-diols under
conditions of limiting substrate with high conversion efficiency.
Although some epoxide is also generated, these complexes
represent the first examples of iron catalysts capable of olefin
cis-dihydroxylation. These results open the possibility of
developing more environmentally benign metal catalysts to
replace the traditional toxic and more expensive osmium
reagents. Further efforts are in progress to tune the iron ligand
environment to afford cis-diol products even more selectively
and with a high conversion.
Epoxide yield
(%)
Catalyst
3 2
Fe(L)(CH CN)
]2+
Diol yield (%)
[
L = 5-Me
L = 3-Me
L = TPA
L = 6-Me-TPA
L = 6-Me
L = 6-Me
3
-TPA
-TPA
67
62
53
32
3
5
3
1
59
20
19
16
6
1
1
73
1
21
3
2
-TPA
3
-TPA
b
L = BPMEN
L = 6-Me
We thank KOSEF (R03-2001-00028 to W. N.), LG Yonam
Foundation (2001 to W. N.), and NIH (GM-33162 to L. Q.) for
financial support as well as KOSEF and NSF for stimulating
this international cooperative research effort.
-BPMENb
(µ-O)(TPA) (H O)
(µ-O)(L) (OAc)]
2
[
[
Fe
Fe
2
2
2
2
]4+
3+
2
2
L = 5-Me
L = TPA
L = BPMEN
3
-TPA
0
0
0
1
2
2
b
Notes and references
a
Unless otherwise indicated, reaction conditions are the same as listed in
1
H. C. Kolb, M. S. VanNieuwenhze and K. B. Sharpless, Chem. Rev.,
994, 94, 2483.
b
footnote a of Table 1.
added via syringe pump over 10 min to a CH
containing the iron catalyst (3.5 µmol) and the olefin (0.12 mmol) at 4 °C.
Final catalyst+substrate+H ratio = 1+34+51.
H O
2 2
3
(0.18 mmol) diluted in CH CN (0.3 mL) was
1
3
CN solution (0.45 mL)
2
3
4
M. Schröder, Chem. Rev., 1980, 80, 187.
T. Wirth, Angew. Chem., Int. Ed., 2000, 39, 334.
K. Bergstad, S. Y. Jonsson and J.-E. Bäckvall, J. Am. Chem. Soc., 2000,
2 2
O
1
21, 10424.
5
6
7
8
C. Döbler, G. M. Mehltretter, U. Sundermeier and M. Beller, J. Am.
Chem. Soc., 2000, 122, 10289.
R. A. Johnson and K. B. Sharpless in ‘Catalytic Asymmetric Synthesis,
were essentially ineffective catalysts under conditions of
limiting substrate. These observations are in contrast to those
obtained under excess substrate, where conversion efficiencies
were comparable to the complexes with no 6-methyl sub-
stituents.19 Due to the steric effect of the 6-methyl group, these
2
nd ed., Ed. I. Ojima, Wiley-VCH, New York, 2000, pp. 357–398.
B. M. Choudary, N. S. Chowdari, M. L. Kantam and K. V. Raghavan,
J. Am. Chem. Soc., 2001, 123, 9220.
S. Kobayashi, M. Endo and S. Nagayama, J. Am. Chem. Soc., 1999, 121,
III
complexes are expected to give rise to high-spin Fe -OOH
1
1229.
intermediates.24 The 6-Me-TPA complex was found to exhibit
a catalytic efficiency intermediate between those of the TPA
9 A. Severeyns, D. E. De Vos, L. Fiermans, F. Verpoort, P. J. Grobet and
P. A. Jacobs, Angew. Chem., Int. Ed., 2001, 40, 586.
10 D. T. Gibson and V. Subramanian in ‘Microbial Degradation of
Organic Compounds’, Ed. D. T. Gibson, Marcel Dekker, New York,
1984, pp. 181–251.
1 P. Wende, F.-H. Bernhardt and K. Pfleger, Eur. J. Biochem., 1989, 181,
89.
2 K. Lee and D. T. Gibson, J. Bacteriol., 1996, 289, 3353.
and the 6-Me
2
-TPA or 6-Me
3
-TPA complexes. This behaviour
can be rationalised by the expectation that the 6-Me-TPA
III
complex would give rise to both low-spin and high-spin Fe -
1
OOH species.24
1
We also tested whether the (µ-oxo)diiron(III) complexes were
effective catalysts under these conditions (Table 2). The only
1
1
3 S. Beil, B. Happe, K. N. Timmis and D. H. Pieper, Eur. J. Biochem.,
effective dinuclear catalyst found in our survey was [Fe
2
(µ-
1
997, 247, 190.
4+
O)(TPA)
2
(H
2
O)
2
] ; this complex with readily displaceable
14 C. C. Lange and L. P. Wackett, J. Bacteriol., 1997, 179, 3858.
15 M. D. Wolfe, J. V. Parales, D. T. Gibson and J. D. Lipscomb, J. Biol.
Chem., 2001, 276, 1945.
6 B. Kauppi, K. Lee, E. Carredano, R. E. Parales, D. T. Gibson, H. Eklund
and S. Ramaswamy, Structure, 1998, 6, 571.
7 K. Chen and L. Que, Angew. Chem., Int. Ed., 1999, 38, 2227.
8 M. Costas, A. K. Tipton, K. Chen, D.-H. Jo and L. Que, J. Am. Chem.
Soc., 2001, 123, 6722.
aqua ligands showed a catalytic activity comparable to that of its
mononuclear counterpart under conditions of limiting substrate
1
as well as under conditions of excess substrate as reported
earlier.19,25
On the other hand, isolated (µ-oxo)diiron(III)
1
1
complexes supported by an additional carboxylate bridge, such
as [Fe (µ-O)(L) (µ-OAc)]X (L TPA, 5-Me -TPA,
2
2
3
=
3
BPMEN), were essentially ineffective at olefin oxidation,
affording at best 1–2% yield of epoxide from olefin and no cis-
diol. This lack of catalytic activity of the (µ-oxo)(µ-carbox-
1
9 K. Chen, M. Costas, J. Kim, A. Tipton and L. Que, J. Am. Chem. Soc.,
2
002, 124, 3026.
20 K. Chen, M. Costas and L. Que, J. Chem. Soc., Dalton. Trans., 2002,
ylato)diiron(III) complexes is in disagreement with the observa-
672.
tions of White et al.,21 but is precedented in our previously
21 M. C. White, A. G. Doyle and E. N. Jacobsen, J. Am. Chem. Soc., 2001,
123, 7194.
2 C. Kim, K. Chen, J. Kim and L. Que, J. Am. Chem. Soc., 1997, 119,
964.
3 R. Y. N. Ho, G. Roelfes, B. L. Feringa and L. Que, J. Am. Chem. Soc.,
999, 121, 264.
reported studies of hydrocarbon oxidation,19,25,26 where we
demonstrated a requirement for two cis labile sites. The two
labile sites are needed for peroxide binding and its subsequent
activation. We thus attribute the lack of catalytic activity of the
2
2
2
5
1
(
µ-oxo)(µ-carboxylato)diiron(III) complexes to the presence of
the carboxylate bridge, which hinders the facile coordination of
the added H to the metal centers and instead promotes H
disproportionation.
4 Y. Zang, J. Kim, Y. Dong, E. C. Wilkinson, E. H. Appelman and L. Que,
J. Am. Chem. Soc., 1997, 119, 4197.
2
O
2
2
O
2
25 K. Chen and L. Que, J. Am. Chem. Soc., 2001, 123, 6327.
26 K. Chen and L. Que, Chem. Commun., 1999, 137.
CHEM. COMMUN., 2002, 1288–1289
1289