Factors affecting the catalytic epoxidation of olefins by iron porphyrin complexes and H2O2 in protic solvents

Article abstract of DOI:10.1021/jo034493c

The catalytic epoxidation of cyclohexene by iron(III) porphyrin complexes and H₂O₂ has been investigated in alcohol solvents to understand factors affecting the catalyst activity in protic solvents. The yields of cyclohexene oxide an

Full text of DOI:10.1021/jo034493c

F a ctor s Affectin g th e Ca ta lytic Ep oxid a tion
of Olefin s by Ir on P or p h yr in Com p lexes
oxidation of olefins by H
2
O
2
in a solvent mixture of CH
2
-
2
Cl /CH OH/H O. It has been proposed that protic sol-
2 3 2
vents function as general-acid catalysis which facilitates
2 2
a n d H O in P r otic Solven ts
O-O bond heterolysis, resulting in the generation of
2
-4
Wonwoo Nam,*,† So-Young Oh, Ying J i Sun,
†
†
high-valent oxoiron(IV) porphyrin π-cation radicals.
Recently, we5 and others
6,7
have shown that olefin
‡
§
|
J inheung Kim, Won-Ki Kim, Seung K. Woo, and
Woonsup Shin|
epoxidation and alkane hydroxylation by H O can be
achieved in aprotic solvents (e.g., CH CN) when highly
3
electron-deficient iron porphyrins are used as catalysts.
In the studies, oxygenation reactions were found to
depend significantly on the electronic nature of iron
porphyrin catalysts. More recently, we have shown that
2
2
Department of Chemistry and Division of Nano Sciences,
Ewha Womans University, Seoul 120-750, Korea,
Department of Chemical Technology, Changwon National
University, Kyungnam 641-773, Korea, Department of
Pharmacology and Laboratory of Neurodegenerative
Diseases, Ewha Institute of Neuroscience, Seoul 120-750,
Korea, and Department of Chemistry, Sogang University,
Seoul 121-742, Korea
simple counterions of iron porphyrins (e.g., X ) Cl or CF
SO in Fe(Porp)X) and the presence of imidazoles as axial
ligands also affect the oxygenation reactions in aprotic
3
-
3
8
,9
10
solvents.
Other factors such as pHs in aqueous
wwnam@ewha.ac.kr
solution,11 the presence of a proton-shuttle group on
porphyrin ligand, and the robustness of iron porphyrin
catalysts13 were reported to play important roles in the
1
2
Received April 17, 2003
Abstr a ct: The catalytic epoxidation of cyclohexene by iron-
2 2
reactions of iron porphyrin complexes and H O . In the
(III) porphyrin complexes and H2O2 has been investigated
in alcohol solvents to understand factors affecting the
(
2) (a) Traylor, T. G.; Kim, C.; Fann, W.-P.; Perrin, C. L. Tetrahedron
catalyst activity in protic solvents. The yields of cyclohexene
1
998, 54, 7977-7986. (b) Traylor, T. G.; Kim, C.; Richards, J . L.; Xu,
III/II
oxide and the Fe
reduction potentials of iron porphyrin
F.; Perrin, C. L. J . Am. Chem. Soc. 1995, 117, 3468-3474. (c) Traylor,
T. G.; Tsuchiya, S.; Byun, Y.-S.; Kim, C. J . Am. Chem. Soc. 1993, 115,
complexes were significantly affected by the protic solvents,
and there was a close correlation between the product yields
and the reduction potentials of the iron porphyrin catalysts.
The role of alcohol solvents was proposed to control the
electronic nature of iron porphyrin complexes that deter-
mines the catalyst activity in the epoxidation of olefins by
H2O2. We have also demonstrated that an electron-deficient
iron porphyrin complex can catalyze the epoxidation of
olefins by H2O2 under conditions of limiting substrate with
high conversion efficiency in a solvent mixture of CH3OH
and CH2Cl2.
2
775-2781. (d) Traylor, T. G.; Fann, W.-P.; Bandyopadhyay, D. J . Am.
Chem. Soc. 1989, 111, 8009-8010.
(3) (a) Nam, W.; Han, H. J .; Oh, S.-Y.; Lee, Y. J .; Choi, M.-H.; Han,
S.-Y.; Kim, C.; Woo, S. K.; Shin, W. J . Am. Chem. Soc. 2000, 122, 8677-
8
1
684. (b) Lee, K. A.; Nam, W. J . Am. Chem. Soc. 1997, 119, 1916-
922.
(
4) Traylor, T. G.; Xu, F. J . Am. Chem. Soc. 1990, 112, 178-186.
(5) (a) Nam, W.; Goh, Y. M.; Lee, Y. J .; Lim, M. H.; Kim, C. Inorg.
Chem. 1999, 38, 3238-3240. (b) Lee, Y. J .; Goh, Y. M.; Han, S.-Y.;
Kim, C.; Nam, W. Chem. Lett. 1998, 837-838.
(6) (a) Bartoli, J .-F.; Le Barch, K.; Palacio, M.; Battioni, P.; Mansuy,
D. Chem. Commun. 2001, 1718-1719. (b) Bartoli, J . F.; Battioni, P.;
De Foor, W. R.; Mansuy, D. J . Chem. Soc., Chem. Commun. 1994, 23-
2
4.
(
7) Vinhado, F. S.; Martins, P. R.; Masson, A. P.; Abreu, D. G.;
Vidoto, E. A.; Nascimento, O. R.; Iamamoto, Y. J . Mol. Catal. A: Chem.
002, 188, 141-151.
8) (a) Nam, W.; Lim, M. H.; Oh, S.-Y.; Lee, J . H.; Lee, H. J .; Woo,
S. K.; Kim, C.; Shin, W. Angew. Chem., Int. Ed. 2000, 39, 3646-3649.
b) Nam, W.; Lee, H. J .; Oh, S.-Y.; Kim, C.; J ang, H. G. J . Inorg.
Biochem. 2000, 80, 219-225.
9) The effect of axial ligands on product yields, selectivities, and
The importance of iron(III) porphyrin complexes as
chemical models of heme-containing enzymes and their
use as catalysts for selective and controlled oxygenation
reactions have prompted extensive studies of their reac-
tions with a variety of oxidants including iodosylbenzene,
2
(
(
(
1
peracids, hypochlorite, and hydroperoxides. In particu-
turnover rates has been well documented in metalloporphyrin- and
metallosalen-mediated epoxidation reactions: (a) Lai, T.-S.; Lee, S. K.
S.; Yeung, L.-L.; Liu, H.-Y.; Williams, I. D.; Chang, C. K. Chem.
Commun. 2003, 620-621. (b) Adam, W.; Roschmann, K. J .; Saha-
Moller, C. R.; Seebach, D. J . Am. Chem. Soc. 2002, 124, 5068-5073.
lar, the reactions of iron porphyrin complexes with
hydrogen peroxide have attracted much attention in the
communities of bioorganic, bioinorganic, and oxidation
(c) Kerrigan, N. J .; Langan, I. J .; Dalton, C. T.; Daly, A. M.; Bousquet,
2 2
chemistry, since H O is a biologically important and
C.; Gilheany, D. G. Tetrahedron Lett. 2002, 43, 2107-2110. (d)
J itsukawa, K.; Shiozaki, H.; Masuda, H. Tetrahedron Lett. 2002, 43,
1491-1494. (e) Liu, S.-Q.; Pecaut, J .; Marchon, J .-C. Eur. J . Inorg.
Chem. 2002, 1823-1826. (f) Collman, J . P.; Chien, A. S.; Eberspacher,
T. A.; Zhong, M.; Brauman, J . I. Inorg. Chem. 2000, 39, 4625-4629.
environmentally clean oxidant. Traylor and co-workers
demonstrated for the first time that electron-deficient
iron porphyrin complexes are capable of catalyzing ep-
(g) Nam, W.; Lim, M. H.; Lee, H. J .; Kim, C. J . Am. Chem. Soc. 2000,
*
To whom correspondence should be addressed. Tel: +82-2-3277-
122, 6641-6647. (h) Suzuki, N.; Higuchi, T.; Urano, Y.; Kikuchi, K.;
Uekusa, H.; Ohashi, Y.; Uchida, T.; Kitagawa, T.; Nagano, T. J . Am.
Chem. Soc. 1999, 121, 11571-11572. (i) Battioni, P.; Renaud, J .-P.;
Bartoli, J . F.; Reina-Artiles, M.; Fort, M.; Mansuy, D. J . Am. Chem.
Soc. 1988, 110, 8462-6647.
2
392. Fax: +82-2-3277-2384.
†
Ewha Womans University.
Changwon National University.
Ewha Institute of Neuroscience.
Sogang University.
‡
§
|
(10) Sul’pin, G. B J . Mol. Catal. A: Chem. 2002, 189, 39-66 and
(1) (a) Meunier, B.; Robert, A.; Pratviel, G.; Bernadou, J . In The
references therein.
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic: New York, 2000; Vol. 4, Chapter 31, pp 119-187. (b)
McLain, J .; Lee, J .; Groves, J . T. In Biomimetic Oxidations Catalyzed
by Transition Metal Complexes; Meunier, B., Ed.; Imperial College
Press: London, 2000; pp 91-169. (c) Sono, M.; Roach, M. P.; Coulter,
E. D.; Dawson, J . H. Chem. Rev. 1996, 96, 2841-2887. (d) Ortiz de
Montellano, P. R. Cytochrome P450: Structure, Mechanism, and
Biochemistry, 2nd ed.; Plenum Press: New York, 1995.
(11) (a) Yang, S. J .; Nam, W. Inorg. Chem. 1998, 37, 606-607. (b)
Labat, G.; Meunier, B. J . Org. Chem. 1989, 54, 5008-5011.
(12) Chang, C. J .; Chng, L. L.; Nocera, D. G. J . Am. Chem. Soc. 2003,
125, 1866-1876.
(13) (a) Cunningham, I. D.; Danks, T. N.; Hay, J . N.; Hamerton, I.;
Gunathilagan, S.; J anczak, C. J . Mol. Catal. A: Chem. 2002, 185, 25-
31. (b) Cunningham, I. D.; Danks, T. N.; Hay, J . N.; Hamerton, I.;
Gunathilagan, S. Tetrahedron 2001, 57, 6847-6853.
1
0.1021/jo034493c CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/27/2003
J . Org. Chem. 2003, 68, 7903-7906
7903

TABLE 1. Yield s of Cycloh exen e Oxid e F or m ed in th e Ep oxid a tion of Cycloh exen e by Ir on (III) P or p h yr in Com p lexes
III/II
Red u ction P oten tia ls of th e Ir on P or p h yr in Com p lexesa
a n d H2O2 a n d th e F e
A. Effect of Alcohol Solventsb
CF3CH2OH
CH3OH
CH3CH2OH
(CH3)2CHOH
(CH3)3COH
product yielde,f (%)
E° vs ferrocene, V
17 ( 2
-0.11
71 ( 6
-0.33
67 ( 5
-0.34
65 ( 5
-0.35
3 ( 1
-0.49
g,h
B. Effect of 5-Chloro-1-methylimidazole as an Axial Ligandb,c
CF3CH2OH
CH3OH
CH3CH2OH
(CH3)2CHOH
(CH3)3COH
product yielde,f (%)
E° vs ferrocene, V
70 ( 5
-0.23
72 ( 6
-0.20
69 ( 6
-0.20
68 ( 5
-0.20
35 ( 3
-0.23
g,h
C. Effect of Electronic Nature of Iron(III) Porphyrinsd
1
2
3
4
5
6
7
product yielde,f (%)
E° vs ferrocene, V
0
0
41 ( 3
-0.50
64 ( 5
-0.45
71 ( 6
-0.33
46 ( 3
-0.17
11 ( 2
0.02
g,h
-0.61
-0.56
a
See the Experimental Section for detailed reaction conditions. b Fe(TPFPP)Cl was used as a catalyst. c 5-Chloro-1-methylimidazole
d
e
(
0.1 mmol) was present in reaction solutions. Reactions were run in CH3OH/CH2Cl2 (3:1). Only small amounts (<3% based on H2O2
used) of cyclohexenol and cyclohexenone were formed. Based on the amounts of H2O2 added. Experimental details for electrochemical
measurements have been described previously.
f
g
3
a
h
+
In V versus Fc/Fc (ferrocene/ferrocinium) couple.
present work, we have studied the catalytic epoxidation
of olefins by iron porphyrin complexes and H in protic
2
O
2
solvents, to understand factors affecting the catalyst
activity in protic solvents. We found from the studies that
III/II
the yields of epoxide product and the Fe
reduction
potentials of iron porphyrin complexes are significantly
influenced by the protic solvents and that there is a close
correlation between the product yields and the reduction
potentials of the iron porphyrin catalysts. These results
led us to propose that alcohol solvents coordinating to
iron porphyrins as axial ligands control the electronic
nature of iron porphyrin complexes and determine the
2 2
catalyst activity in the epoxidation of olefins by H O .
We first explored the effect of alcohol solvents on the
catalytic epoxidation of cyclohexene by an electron-
deficient iron(III) porphyrin complex, Fe(TPFPP)Cl (TPF-
PP ) meso-tetrakis(pentafluorophenyl)porphinato dian-
F IGURE 1. Plot of the percent yields of cyclohexene oxide
formed in the catalytic epoxidation of cyclohexene by Fe-
(
TPFPP)Cl and H
2
O
2
vs volumes (%) of alcohols in the solvent
Cl : O, CH OH; (, (CH CHOH.
mixture of alcohol/CH
2
2
3
3 2
)
2 2 2 2
ion), and H O in a solvent mixture of alcohol/CH Cl at
2
room temperature. The results in Table 1A show that
the yields of cyclohexene oxide were markedly influenced
the FeIII/II reduction potentials results from the coordina-
tion of alcohols as axial ligands (vide infra).
Then, the effect of alcohol concentration on the epoxi-
by alcohol solvents; the yields were high in CH
CH OH, and (CH CHOH, whereas only small amounts
of cyclohexene oxide were yielded in (CH OH and CF
CH
OH. In addition, when the FeIII/II reduction potentials
3 3
OH, CH -
2
3 2
)
dation of cyclohexene by Fe(TPFPP)Cl and H
2 2
O was
3
)
3
3
-
investigated in CH OH and (CH CHOH. Figure 1 shows
3
3 2
)
2
that epoxide yields increased with the increase of alcohol
concentrations and the increase of the product yields was
of Fe(TPFPP)Cl were determined with cyclic voltammetry
under the identical reaction conditions employed in the
faster in CH
increase of alcohol concentratons shifted the Fe
3 3 2
OH than in (CH ) CHOH. In addition, the
epoxidation reactions,3 the Fe
a
III/II
reduction potentials
were found to vary significantly depending on the alcohol
solvents; the E° values were similar in CH OH, CH CH
OH, and (CH CHOH but quite different in (CH OH
and CF CH OH (see Table 1A). The Fe reduction
III/II
reduc-
tion potentials to less negative values (Supporting In-
formation, Table S1), indicating that the iron porphyrin
complex became more electron-deficient with the increase
of the amounts of alcohols in reaction solutions. As we
3
3
2
-
3
)
2
3 3
)
III/II
3
2
+
potentials of the Fe(TPFPP) complex also indicate that
the electron-richness of the iron porphyrin complex in
have discussed above, the results of the concentration
III/II
effect on the product yields and the Fe
reduction
alcohol solvents is in the order of (CH
CHOH‚CH CH OH‚CH OH > CF CH OH. Since it has
been demonstrated previously that alcohols bind to
3
)
3
OH > (CH
3 2
) -
potentials are illustrated with the axial ligand effect.
Indeed, it has been reported that the reduction potentials
of Mn(TPP)Cl (TPP ) meso-tetraphenylporphinato dian-
ion) were dependent on methanol concentrations, and
this phenomenon was illustrated with the replacement
3
2
3
3
2
metalloporphyrins as axial ligands,1
4,15
we propose that
the effect of alcohol solvents on the catalyst activity and
3
of an axial chloride ligand by CH OH upon the increase
of methanol concentrations.
To probe that the alcohol solvent effect was resulted
from the coordination of alcohol solvents as axial ligands,
(
14) Nee, M. W.; Lindsay Smith, J . R. J . Chem. Soc., Dalton Trans.
999, 3373-3377.
15) Hashimoto, S.; Mizutani, Y.; Tatsuno, Y.; Kitagawa, T. J . Am.
Chem. Soc. 1991, 113, 6542-6549.
16
1
(
7
904 J . Org. Chem., Vol. 68, No. 20, 2003

the catalytic epoxidation of cyclohexene by Fe(TPFPP)-
Cl and H was carried out in the presence of 5-chloro-
-methylimidazole (5-Cl-1-MeIm) in alcohol solvents.
TABLE 2. Ca ta lytic Ep oxid a tion of Olefin s by
F e(TP F P P )Cl a n d H2O2 u n d er Con d ition s of Lim itin g
Su bstr a tea
2
O
2
8
b
1
+
conversionb (%)
b
The binding of 5-Cl-1-MeIm to the Fe(TPFPP) complex
substrate
products
yields (%)
was monitored by taking UV-vis spectra of the reaction
cyclohexene
99 ( 1
cyclohexene oxide
cyclohexenol
cyclohexenone
cyclooctene oxide
cis-stilbene oxide
trans-stilbene oxide
benzaldehyde
90 ( 5
5 ( 1
∼0
solutions (data not shown).3
b,17
The results in Table 1B
show that when the epoxidation reactions were carried
out in the presence of 5-Cl-1-MeIm, the yield of cyclo-
cyclooctene
cis-stilbene
99 ( 1
99 ( 1
95 ( 5
95 ( 4
2 ( 1
<1
hexene oxide increased from 17% to 70% in CF
solution and high yields of epoxide product were obtained
in CH OH, CH CH OH, and (CH CHOH. In (CH OH
solution, the yield of cyclohexene oxide increased from
% to 35%, and this result was ascribed to a fast
3 2
CH OH
3
3
2
3
)
2
3 3
)
a
See the Experimental Section for detailed reaction conditions.
Based on the amount of substrates used.
b
3
degradation of the Fe(TPFPP)Cl catalyst under the
which the Fe(TPFPP)+ complex in (CH
CH OH is the most electron-rich and -deficient, respec-
3 3 3
) OH and CF -
reaction condition (data not shown). In addition, the
2
III/II
Fe
reduction potentials of the imidazole-bound low-
were identical within
tively, and in these solvents, the yields of epoxide product
are low (see Table 1A). On the basis of the results, we
conclude that alcohol solvents coordinating as axial
ligands play an important role in controlling the elec-
tronic nature of iron porphyrin complexes and that the
electronic nature of iron porphyrin catalysts is an im-
spin Fe(TPFPP)(5-Cl-1-MeIm)
2
experimental error in all alcohol solvents (see Table 1B).
When 1-methylimidazole (1-MeIm) was used instead of
5
-Cl-1-MeIm, the yields of epoxide product were low
III/II
(
about 15% based on H
potentials of the imidazole-bound low-spin Fe(TPFPP)-
1-MeIm)
2
O
2
used) and the Fe
reduction
21
portant factor in determining the catalyst activity.
(
2
were identical (∼ -0.32 V) in all alcohol
Finally, the catalytic epoxidation of olefins by Fe-
8
b
solvents. On the basis of the observations that the
alcohol solvent effect disappeared when the axial posi-
tions of the Fe(TPFPP)+ complex were coordinated by
imidazoles, we conclude that the chloride ligand of Fe-
(
TPFPP)Cl and H
limiting substrate (catalyst/substrate/H
400), since the development of efficient and practical
methods that utilize environmentally benign and inex-
pensive H as a terminal oxidant is an important
objective in preparative oxidation chemistry. Treatment
of olefins with 1.2 equiv of H in the presence of 0.05
mol % catalyst in a solvent mixture of CH OH/CH Cl
2
O
2
was attempted under conditions of
2
O
2
) 1:2000:
2
(
TPFPP)Cl is replaced by alcohol solvents and the Fe-
2
O
2
+
(TPFPP) complexes binding different alcohols show
22
different reactivities in the epoxidation of olefins by
2
O
2
1
8
2 2
H O .
3
2
2
The electronic effect of iron porphyrin complexes on
the catalytic epoxidation of cyclohexene by H was also
afforded the complete conversion of olefins with high
product yields and stereoselectivity (Table 2). By taking
UV-vis spectra of reaction solutions before and after the
addition of the oxidant, the destruction of the iron
porphyrin catalyst was found to be minimal (i.e., less
than 5%). These results demonstrate that the Fe(TPF-
PP)Cl complex can catalyze the epoxidation of olefins by
2
O
2
investigated with iron porphyrins bearing different sub-
stituents on meso-phenyls and pyrrole positions of por-
3
phyrin ligand in CH OH (Supporting Information, Figure
1
9
S1 for the structures of iron porphyrin complexes). As
we have shown previously,3 electron-rich iron porphyrins
did not produce cyclohexene oxide in the epoxidation of
a
2 2
H O efficiently and selectively under conditions of limit-
ing substrate.
2 2
cyclohexene by H O (see data of 1 and 2 in Table 1C).
As the iron porphyrin catalysts became electron-deficient,
the yields of cyclohexene oxide increased (see data of 3-5
in Table 1C). Interestingly, the epoxide yields diminished
In summary, we have shown here that the electronic
nature and catalytic activity of iron porphyrin complexes
are markedly influenced by alcohol solvents. This phe-
nomenon was illustrated with the binding of alcohols as
axial ligands that controls the electronic nature of iron
porphyrin complexes. We have also demonstrated that
the electronic nature of iron porphyrin catalysts is an
important factor in determining the catalyst activity and
that an electron-deficient iron porphyrin complex can
as the iron porphyrins became more electron-deficient
0
(
see data of 6 and 7 in Table 1C).2 These results indicate
that iron complexes of electron-rich or too electron-
deficient porphyrin ligands are poor catalysts. This trend
is also seen in the studies of alcohol solvent effect, in
(
16) (a) Mu, X. H.; Schultz, F. A. Inorg. Chem. 1995, 34, 3835-3837.
b) Mu, X. H.; Schultz, F. A. Inorg. Chem. 1992, 31, 3351-3357.
17) Quinn, R.; Nappa, M.; Valentine, J . S. J . Am. Chem. Soc. 1982,
04, 2588-2595.
18) When the anionic chloride ligand of Fe(TPFPP)Cl was replaced
(
2 2
catalyze the epoxidation of olefins by H O under condi-
tions of limiting substrate with high conversion efficiency.
(
1
(
-
-
by nonligating anions such as CF
3
SO
3
and ClO
4
, the catalytic
Exp er im en ta l Section
efficiency of the iron porphyrin complex increased markedly and the
yields of oxygenated products were high in olefin epoxidation and
Ma ter ia ls a n d In str u m en ta tion . All reagents purchased
from Aldrich Chemical Co. were the best available purity and
used without further purification unless otherwise indicated.
alkane hydroxylation reactions by H
2
O
2
in aprotic solvents.
TPFPP ) â-octachloro-
TDCPP )
(
19) Abbreviations of porphyrin ligands: â-Cl
8
meso-tetrakis(pentafluorophenyl)porphinato dianion; â-Cl
8
â-octachloro-meso-tetrakis(2,6-dichlorophenyl)porphinato dianion; TD-
FPP ) meso-tetrakis(2,6-difluorophenyl)porphinato dianion; TDCPP
(21) At this moment, we do not rule out the possibility that the
polarity and acidity of alcohol solvents also play an important role in
)
meso-tetrakis(2,6-dichlorophenyl)porphinato dianion; TMP ) meso-
tetramesitylporphinato dianion.
20) In these reactions, the iron catalysts degraded at a fast rate,
determining the catalytic activity of iron porphyrin complexes in H O
2 2
2,4
(
reactions.
confirming a previous observation that iron porphyrin complexes
bearing halogen-substituents on pyrrole positions lose their stability
against oxidative degradation: Porhiel, E.; Bondon, A.; Leroy, J .
Tetrahedron Lett. 1998, 39, 4829-4830.
(22) (a) Lane, B. S.; Burgess, K. J . Am. Chem. Soc. 2001, 123, 2933-
2934. (b) White, M. C.; Doyle, A. G.; J acobson, E. N. J . Am. Chem.
Soc. 2001, 123, 7194-7195. (c) Ryu, J . Y.; Kim, J .; Costas, M.; Chen,
K.; Nam, W.; Que, L., J r. Chem. Commun. 2002, 1288-1289.
J . Org. Chem, Vol. 68, No. 20, 2003 7905

Methanol (anhydrous) and dichloromethane (anhydrous) were
purified by distillation over CaH prior to use. H (30%
aqueous) was purchased from Aldrich. Fe(TPFPP)Cl and Fe-
analyzed by GC or GC/MS, and product yields were determined
by comparison against standard curves prepared with known
authentic samples.
2
2 2
O
(
(
TPP)Cl were purchased from Aldrich Chemical Co. Other iron-
III) porphyrin complexes were obtained from Mid-Century
The catalytic epoxidation reactions under conditions of limit-
ing substrate were carried out as follows: H (3 mmol, diluted
2
O
2
Chemicals. The purity of the iron porphyrins was examined by
in a solvent mixture (0.5 mL) of CH OH/CH Cl (3:1)) was added
3
2 2
1
H NMR in CD
2
Cl
2
.
via syringe pump over 40 min to a reaction solution containing
-
3
Product analyses were performed on either a Hewlett-Packard
890 II Plus gas chromatograph equipped with a FID detector
Fe(TPFPP)Cl (1.25 × 10 mmol) and substrate (2.5 mmol) in a
5
solvent mixture (5 mL) of CH OH/CH Cl (3:1). The reaction
3
2
2
using 30-m capillary column (Hewlett-Packard, HP-1 and HP-
) or a SUMMIT HPLC (DIONEX) with a variable-wavelength
mixture was further stirred for 10 min and directly analyzed
by GC or HPLC.
5
UVD 170S and a Phenomenex LUNA C18 reversed-phase
Ack n ow led gm en t. We thank the Ministry of Sci-
ence and Technology of Korea through the Creative
Research Initiatives Program, the Korea Science and
Engineering Foundation (R02-2003-000-100), and the
Korea Research Foundation (Grant No. DP0270) for
financial support.
column. UV-vis spectra were recorded on a Hewlett-Packard
1
8
453 spectrophotometer. H NMR spectra were recorded on a
Bruker AM 250. All electrochemical experiments were performed
under N atmosphere in a glovebox using BAS 50W voltammetric
analyzer.
2
Rea ction Con d ition s. Reactions were performed at ambient
temperature under argon atmosphere unless otherwise indi-
cated. All reactions were run in at least triplicate, and the data
reported represent the averages of these reactions. In general,
Su p p or tin g In for m a tion Ava ila ble: Table S1 reports the
III/II
yields of cyclohexene oxide and the Fe
reduction potentials
-
3
an iron porphyrin complex (1.25 × 10 mmol) was dissolved in
a solvent mixture (2.5 mL) of alcohol/CH Cl (3:1) containing
(0.1 mmol, 30% aqueous, diluted in
(3:1)) was slowly added to the reaction
of Fe(TPFPP)Cl determined in different alcohol concentrations.
Figure S1 shows structures of iron(III) porphyrin complexes
used in this study. This material is available free of charge
via the Internet at http://pubs.acs.org.
2
2
cyclohexene (1 mmol). H
.2 mL of CH OH/CH Cl
2
2
O
2
0
3
2
solution over a period of 3 min, and the resulting solution was
stirred for 10 min. An aliquot of the reaction mixture was directly
J O034493C
7
906 J . Org. Chem., Vol. 68, No. 20, 2003