Biomimetic alkene epoxidation and alkane hydroxylation with sodium periodate catalyzed by Mn(III)-salen supported on amberlite IRA-200

Article abstract of DOI:10.1007/s00706-007-0672-8

The Mn(III)-salen, containing phosphonium groups at the 5,5′-positions of the salen ligand supported on Amberlite IRA-200 via electrostatic binding was used for the oxidation of alkenes and alkanes with sodium periodate at room temperature in the presence of imidazoles as axial ligands, and the effect of solvent, different axial ligands, and various oxygen donors was investigated. This heterogenized catalyst shows high catalytic activity in alkene epoxidation and alkane hydroxylation. It showed high selectivity in the epoxidation of stilbenes, α-pinene, and (R)-(+)-limonene, and exhibits a particular ability to epoxidize linear alkenes. The stability and reusability of this new heterogenized metallo-salen complex was also investigated. The catalyst was characterized by FTIR, UV-Vis, SEM, and thermal analysis.

Full text of DOI:10.1007/s00706-007-0672-8

Monatshefte fu¨r Chemie 138, 1303–1308 (2007)
DOI 10.1007/s00706-007-0672-8
Printed in The Netherlands
Biomimetic Alkene Epoxidation and Alkane Hydroxylation with Sodium
Periodate Catalyzed by Mn(III)-salen Supported on Amberlite IRA-200
Valiollah Mirkhani1;ꢀ, Majid Moghadam1;2, Shahram Tangestaninejad1, and Bahram Bahramian3
1
Department of Chemistry, University of Isfahan, Isfahan, Iran
2
Department of Chemistry, Yasouj University, Yasouj, Iran
3
Department of Chemistry, Shahrood University, Shahrood, Iran
Received February 13, 2007; accepted (revised) February 28, 2007; published online August 27, 2007
# Springer-Verlag 2007
Summary. The Mn(III)-salen, containing phosphonium
olefins [3–6]. Among these reported metallo-salen
groups at the 5,50-positions of the salen ligand supported
complexes, Manganese(III) Schiff base complexes
on Amberlite IRA-200 via electrostatic binding was used
are know to be highly active homogeneous catalysts
for the oxidation of alkenes and alkanes with sodium per-
in the epoxidation of olefins with various oxidants,
iodate at room temperature in the presence of imidazoles as
such as iodosylbenzene, sodium hypochlorite, hy-
drogen peroxide, and periodate [7–11]. The electro-
nic and steric nature of the metal complex can be
tuned by introducing electron-withdrawing and elec-
tron-releasing substituents and bulky groups in the
ligand. However, the instability of Schiff base com-
plexes toward oxidative degradation and difficulties
in recovering of these catalysts limit their practical
applications in both synthetic and industrial pro-
cesses. One way to achieve stable Schiff base com-
plexes is to immobilize them onto solid supports.
Such immobilization offers the combined advan-
tages of homogeneous (mild reaction conditions)
and heterogeneous (easy separation) catalysts, and
may improve the selectivities and activities because
of the support environment.
In our search for new heterogeneous Schiff base
catalysts [12] we report the attachment of a water-
soluble manganese(III)-salen complex containing
phosphonium groups at the 5,50-positions of the
salen ligand on amberlite IRA-200, [Mn(salen)-Ad
IRA-200], and its catalytic activity in the epoxida-
tion of alkenes and hydroxylation of alkanes with
various oxygen atom donors at room temperature
(Scheme 1).
axial ligands, and the effect of solvent, different axial ligands,
and various oxygen donors was investigated. This heteroge-
nized catalyst shows high catalytic activity in alkene epoxida-
tion and alkane hydroxylation. It showed high selectivity in
the epoxidation of stilbenes, ꢀ-pinene, and (R)-(þ)-limo-
nene, and exhibits a particular ability to epoxidize linear
alkenes. The stability and reusability of this new heteroge-
nized metallo-salen complex was also investigated. The
catalyst was characterized by FTIR, UV-Vis, SEM, and
thermal analysis.
Keywords. Epoxidation; Hydroxylation; Periodate; Manga-
nese(III)-salen; Supported catalyst.
Introduction
Cytochrome P-450 enzymes constitute an interest-
ing family of catalysts, which enable the transfer of
an oxygen atom to a wide range of organic com-
pounds [1, 2]. Designing of biomimetic models based
on metalloporphyrins and Schiff base complexes
is one of the most important topics in chemistry.
Metallo-salen complexes such as Mn(III)-salen,
Cr(III)-salen, Ni(II)-salen, and Cu(II)-salen have
been synthesized and used for the epoxidation of
ꢀ
Corresponding author. E-mail: mirkhani@sci.ui.ac.ir

1304
V. Mirkhani et al.
Scheme 1
Results and Discussion
bilized metal complex. The decomposition behavior
of the free complex and the immobilized complex was
compared in order to understand the effect of im-
mobilization. The free complex [Mn(III)-salen]OAc
decomposes during heating to 535ꢁC in several well-
defined steps. The immobilized complex showed less
defined steps of weight loss and maxima peak. A
broad exothermic DTA peak is observed between
235 and 530ꢁC. The free complex showed a weight
loss of 33% at temperatures below 400ꢁC. However,
for the corresponding immobilized complex, a 6%
weight loss appears at temperatures below 400ꢁC.
This behavior indicates thermal stability and im-
mobilization of the complex on to the Amberlite.
A clear change in morphology of the Amberlite sup-
ported complex was also observed by SEM.
Preparation and Characterization of the Polymer
Supported Catalyst, [Mn(salen)-Ad IRA-200]
Mn(III)-salen containing the phosphonium groups at
the 5,50-positions of the salen ligand was immobilized
onto the Amberlite IRA-200, [Mn(salen)-Ad IRA-
200], via electrostatic binding by simple absorption
of dicationic manganese(III)-salen on Ambelite IRA-
200 in aqueous acetone at 80ꢁC. The catalyst loading,
which was determined by neutron activation analysis
(NAA), is 0.076mmol per gram of Amberlite. The dif-
fuse reflectance spectra of [Mn(salen)-Ad IRA-200]
in a BaSO4 matrix clearly indicated that Mn(III)-salen
complex was immobilized on the Amberlite IRA-200.
The FTIR spectrum of the supported catalyst showed
signals at 3053 (Carom–H), 1627, 1542, 1463, 1438,
1307, 749, and 509cmꢂ1, which are assigned to the
manganese(III)-salen complex, where the Amberlite
does not show any peak in this region.
Catalytic Alkene Epoxidation with NaIO4 in the
Presence of [Mn(salen)-Ad IRA-200]
The epoxidation of olefins with NaIO4 and
[Mn(salen)-Ad IRA-200] in the presence of imidaz-
ole yielded the corresponding oxidized products in
Differential thermal analysis and thermogravi-
metric analysis were used to characterize the immo-
Table 1. Epoxidation of alkenes with NaIO4 catalyzed by [Mn(salen)-Ad IRA-200]
Entry
Alkene
Conversion=%a
Epoxide yield=%a
Time=min
1
2
3
4
5
Cyclooctene
Cyclohexene
Styrene
ꢀ-Methylstyrene
(R)-(þ)-Limonene
97
100
94
100
90
97
95b
35
35
35
35
35
89c
96d
75 (1,2-Epoxide)
15 (8,9-Epoxide)
95
6
7
8
Indene
(E)-Stilbene
(Z)-Stilbene
95
69
78
35
35
35
69 (trans-Epoxide)e
41 (cis-Epoxide)e
37 (trans-Epoxide)e
9
10
11
1-Heptene
1-Dodecene
ꢀ-Pinene
63
52
100
63
52
85f
45
50
35
a
GLC yield based on the starting alkene; b the by-product is 5% allylic ketone; c the by-product is 3% benzaldehyde; d the by-
product is acetophenone; e both 1H NMR and GLC data approved the reported yields; f the by-products are 4% verbenone and
11% verbenol

Biomimetic Alkene Epoxidation and Alkane Hydroxylation
1305
Scheme 2
aqueous acetonitrile at room temperature (Table 1).
Cyclooctene was converted to cyclooctene oxide in
high yield. In the oxidation of cyclohexene, only
trace amount of cyclohexenone was produced.
Epoxidation of styrene and ꢀ-methylstyrene pro-
duced only 5% benzaldehyde and 4% acetophenone
as by-products. This catalytic system showed high
regioselectivity in the case of (R)-(þ)-limonene.
The ratio among 1,2- and 8,9-epoxides was found
to be 5:1. In the case of stilbenes, the (E)-stilbene
was converted into the trans-epoxide in 69% yield,
but (Z)-stilbene afforded a 41:37 mixture of the cis-
and trans-epoxides. The catalytic system exhibits a
particular ability to epoxidize linear alkenes such as
1-heptene and 1-dodecene. In the case of ꢀ-pinene,
the major product is ꢀ-pinene oxide (85%), and
allylic oxidation products verbenone and verbenol
were produced as minor products (Scheme 2).
Bu4NIO4, H2O2, KHSO5, tert-BuOOH, and urea-
H2O2, was examined in the epoxidation of cyclo-
octene at room temperature. As shown in Table 2,
NaOCl, H2O2, tert-BuOOH, and urea-H2O2, either
in acetonitrile or dichloromethane, are less efficient
than NaIO4 to oxidize cyclooctene. Oxone (KHSO5),
which is a strong, cheap, and versatile oxidizing
agent was not used further on because of disadvan-
tages, such as need of buffered media and bleaching
of the metal catalyst during oxidation reactions.
Sodium periodate was used as the oxygen source
because of the following advantages: (i) it gives good
oxidation conversion; (ii) it is inert in the absence of
catalyst; and (iii) it is readily soluble in CH3CN=H2O.
The Effect of Different Solvents on the Epoxidation of
Cyclooctene Catalyzed by [Mn(salen)-Ad IRA-200]
In order to choose the reaction media, mixtures of
methanol, ethanol, acetone, and acetonitrile with water
and wet chloroform, carbontetrachloride, and di-
chloromethane were tested in the epoxidation of cy-
clooctene. The obtained results are shown in Table 3.
The aqueous acetonitrile was chosen as the reaction
medium because higher epoxidation yields were
observed. The higher catalytic activity in acetonitrile
The Effect of Different Oxidants on the Epoxidation
of Cyclooctene by [Mn(salen)-Ad IRA-200]
In the catalytic epoxidation of alkenes the choice of
oxygen donor and solvent is of crucial importance.
In order to design the best catalytic system, the abil-
ity of different oxidants, such as NaOCl, NaIO4,
Table 2. The effect of different oxidants on the epoxidation
of cyclooctene catalyzed by [Mn(salen)-Ad IRA-200] at room
temperature after 30 mina
Table 3. The effect of solvent on the epoxidation of cyclo-
octene with NaIO4 catalyzed by [Mn(salen)-Ad IRA-200] at
room temperature after 30 mina
Oxidant
Solvent
Epoxidation yield=%
Solvent
Epoxidation yield=%
NaIO4
Oxone (KHSO5)
H2O2
H2O2=urea
NaOCl
CH3CN=H2O
CH3CN=H2O
CH3CN
CH3CN
CH3CN
97
87
61
25
32
15
38
CH3CN=H2O
CH3COCH3=H2O
CH3OH=H2O
CH3CH2OH=H2O
Wet CHCl3
97
68
56
44
38
35
15
tert-BuOOH
Bu4NIO4
CH3CN
CH3CN
Wet CH2Cl2
Wet CCl4
a
a
Cyclooctene (0.5 mmol), oxidant (1 mmol), imidazole
(0.14 mmol), catalyst (0.018 mmol), CH3CN (5 cm3), H2O
(2.5 cm3)
Cyclooctene (0.5 mmol), NaIO4 (1 mmol), imidazole
(0.14 mmol), catalyst (0.018 mmol), CH3CN (5 cm3), H2O
(2.5 cm3)

1306
V. Mirkhani et al.
is attributed to the polarity of the solvent and the
solubility of NaIO4 in the solvent.
formation of epoxide under the same reaction condi-
tions and in the absence of imidazole was only 29%.
We also investigated the effect of different axial
ligands upon the epoxidation of cyclooctene. Pure
ꢀ-donor amines, with very high pKb values are rela-
tively poor co-catalysts in the epoxidation of cy-
clooctene (Table 4). Pyridine and methyl-substituted
pyridines with weak ꢁ-donating ability and pKb val-
ues much smaller than those of ꢂ-donor amines gen-
erally show co-catalytic activities similar to those of
amines. The observed order of co-catalytic activities,
4-tert-butyl-pyridine>pyridineꢃ4-cyanopyridine,
seems to be directly related to both the ꢂ- and
ꢁ-donor abilities of those nitrogen donors. Electron-
withdrawing substituents, such as CNꢂ, essentially
display no co-catalytic activity. However, substituted
pyridines having electron-releasing methyl groups,
such as 4-tert-butylpyridine, showed 82% conver-
sion in the epoxidation of cyclooctene, which is
higher than for the unsubstituted pyridine. Addition
of Ph3PO and DMF as donor ligands have no signifi-
cant influence on the epoxide yields. Among nitro-
gen bases, which are used as axial ligands, imidazole
and methyl-substituted imidazoles exhibited higher
activity toward the epoxidation of cyclooctene with
sodium periodate. Strong ꢁ-donors ImH and MeImHs
are generally better co-catalysts than all the nitrogen
donors presented in Table 3. The strong coordination
of imidazole should result in an increase of electron
density on metal and thus allows a facile cleavage of
the O–IO3 bond of NaIO4.
The Effect of Different Axial Ligands on the
Epoxidation of Cyclooctene with NaIO4 Catalyzed
by [Mn(salen)-Ad IRA-200]
It is well known that the catalytic ability of manga-
nese Schiff bases is improved by the use of a nitrogen
base as co-catalyst [13, 14]. Epoxidation of cyclo-
octene with the [Mn(salen)-Ad IRA-200]=NaIO4
catalytic system in the presence of imidazole pro-
duced the oxide product in high yield, whereas the
Table 4. The effect of different axial ligands on the epoxida-
tion of cyclooctene catalyzed by [Mn(salen)-Ad IRA-200]=
NaIO4 system after 30 mina
Axial ligand
Epoxidation yield=%
No axial base
Triethylamine
Diethylamine
Piperidine
29
30
33
54
51
25
55
58
82
97
92
93
79
69
32
41
34
30
Pyridine
4-Cyanopyridine
2-Methylpyridine
4-Methylpyridine
4-tert-Butylpyridine
Imidazole
2-Methylimidazole
4(5)-Methylimidazole
2-Ethylimidazole
Pyrazine
Quinaldine
Morpholine
Triphenylphosphine oxide
DMF
Alkane Hydroxylation with NaIO4 in the Presence
of [Mn(salen)-Ad IRA-200]
a
Cyclooctene (0.5 mmol), NaIO4 (1 mmol), axial ligand
(0.14 mmol), catalyst (0.018 mmol), CH3CN (5 cm3), H2O
(2.5 cm3)
Selective partial alkene oxidation is a particularly
challenging problem in organic chemistry. The cat-
Table 5. Hydroxylation of alkanes with NaIO4 catalyzed by [Mn(salen)-Ad IRA-200]
Entry
Alkane
Conversion=%a
Ketone yield=%a
Alcohol yield=%a
Time=min
1
2
3
4
5
6
7
Cyclooctane
Cyclohexane
1,2,3,4-Tetrahydronaphthalene
Ethylbenzene
Adamantane
66
55
38
45
91
42
12
41
81
36
10
–
–
58
–
55
60
55
60
55
60
55
91b
42c
70
Propylbenzene
Fluorene
41d
81
–
a
GLC yield based on starting alkane; b only the ꢀ-position was oxidized; c the product is acetophenone; d the product is ethyl
phenyl ketone

Biomimetic Alkene Epoxidation and Alkane Hydroxylation
1307
alytic hydroxylation of alkanes and arylalkanes
with sodium periodate was performed in the presence
of [Mn(salen)-Ad IRA-200] under the same con-
ditions described for alkene epoxidation (Table 5).
The obtained results showed that in this catalytic
system cyclooctane, cyclohexane, and adamantane
produced a mixture of alcohol and ketone, whereas
1,2,3,4-tetrahydronaphthalene, ethylbenzene, pro-
pylbenzene, and fluorene only were converted
to the corresponding ketones. The regioselectivity
observed for the oxidation of adamantane showed a
significant preference for position 1 over position 2.
This can be attributed to the unique microenvi-
ronment constituted by the Schiff base macrocycle
and support matrix. In the case of 1,2,3,4-tetrahy-
dronaphthalene, only the ꢀ-position was oxidized
and ꢀ-tetralon was obtained in high yield. Oxida-
tion of alkylaromatics, such as ethylbenzene and
propylbenzene led to producing acetophenone and
ethyl phenyl ketone.
Fig. 1. The UV-Vis spectra of A) non-supported solid
Mn(III)-(salen)OAc and B) Mn(salen)-Ad IRA-200
Experimental
All chemicals were used as received from Merck, Aldrich,
and Fluka. Amberlite IRA-200 was purchased form Fluka.
Alkenes and alkanes were purified prior to use by passing
through a column containing active alumina to remove per-
oxidic impurities.
Catalyst Reuse and Stability
Preparation of the Complex
The Schiff base ligand was prepared by the standard procedure
of refluxing ethanolic solutions of the corresponding diamine
and salicylaldehyde derivative in a 1:2 molar ratio according
to Refs. [16, 17]. Thus, salicylaldehyde was chloromethylated
and reacted with triphenylphosphine, to give 2-hydroxy-5-(tri-
phenylphosphinomethyl)benzaldehyde chloride, which in the
condensation with ethylenediamine in a 1:2 molar ratio gave
N,N0-bis{[5-(triphenylphosphonium)methyl]salicylidene}-1,2-
ethanediamine chloride. Finally, the ligand was complexed
with manganese acetate to give [Mn(III)-salen]OAc.
To assess long-term stability and reusability of
[Mn(salen)-Ad IRA-200], cyclooctene was used as
a model substrate, and recycling experiments were
carried out with a single sample of the catalyst. After
each experiment, the catalyst was removed by sim-
ple filtration, washed with water and acetonitrile, and
reused. The resulting yields are listed in Table 6. The
loss of activity observed in the reused catalyst may
be attributed to the degradation of the salen complex
during the reaction [16]. The filtrates were used for
determination of manganese leaching. The amounts
of manganese leached after each run was determined
by atomic absorption spectroscopy (Table 6). The
nature of the recovered catalyst was followed by
IR and UV-Vis spectra. The results indicated that
the catalyst after reusing several times, showed no
change in its IR and UV-Vis spectra.
Immobilization of Schiff Base Complex on Amberlite IRA-200
To a solution of 0.5 g of the complex in 100 cm3 of a 1:1
acetone:water mixture was added 5 g Amberlite IRA-200 and
stirred at 80ꢁC for 24h. After cooling to room temperature,
the brown solids were washed with H2O until no metallo-salen
could be detected in the filtrates by UV-Vis analysis. The
catalyst was dried under vacuum prior to use.
The content of manganese(III)-salen on the Amberlite IRA-
200 support was calculated from the manganese content in
heterogenized catalyst as determined by NAA. Diffuse reflec-
tance spectra were recorded on a Shimadzu UV-265 instrument
using optical grade BaSO4 as the reference. Themogravimetric
analysis of the catalyst was carried out on a Mettler TA4000
instrument.
Table 6. The results obtained from catalyst reuse and stability
in the oxidation of cyclooctene with sodium periodate by
[Mn(salen)-Ad IRA-200]
FTIR spectra were obtained for KBr pellets in the range
400–4000 cmꢂ1 with a Nicolet Impact 400D spectrometer.
Scanning electron micrographs of the catalyst and resin were
taken on a SEM Philips XL 30 instrument. Gas chromatogra-
phy experiments (GC) were performed with a Shimadzu
GC-16A instrument using a 2 m column packed with silicon
DC-200 or Carbowax 20 m.
Run
Epoxide yield=%a
Time=min
Mn leached=%b
1
2
3
97
79
60
30
30
30
5
3
1
a
GC yield; b determined by atomic absorption spectroscopy

1308
V. Mirkhani et al.: Biomimetic Alkene Epoxidation and Alkane Hydroxylation
[6] Zolezzi S, Spodine E, Decinti A (2003) Polyhedron 22:
1653
General Procedure for Catalytic Epoxidation of Alkenes and
Hydroxylation of Alkanes
[7] Routier SB, Bernier JL, Catteau MP, Bailly C (1997)
Bioorg Med Chem Lett 7: 63
[8] Muller JG, Paikoff SJ, Rokita SE, Burrow CJ (1994)
J Inorg Biochem 54: 199
[9] Samide MJ, Peters DG (1998) J Electroanal Chem 44:
395
[10] Hamada T, Irie R, Mihara J, Hamachi K, Katsuki T
(1998) Tetrahedron 54: 10017
All of the reactions were carried out at room temperature
under air in a 25 cm3 flask equipped with a magnetic stirring
bar. A solution of 1 mmol NaIO4 in 2.5 cm3 H2O was added to
a mixture of 0.5 mmol alkene or alkane, 0.018 mmol catalyst,
and 0.14mmol imidazole in 5 cm3 CH3CN. The progress of
the reaction was monitored by GC. The reaction mixture
was diluted with 10 cm3 CH2Cl2 and filtered. The resin was
thoroughly washed with CH2Cl2 and the combined washings
and filtrates were purified on silica-gel plates or a silica-gel
column. IR and 1H NMR spectral data confirmed the identities
of the product.
[11] Hu YJ, Hung XD, Yao ZJ, Wu YL (1998) J Org Chem
63: 2456
[12] a) Bahramian B, Mirkhani V, Tangestaninejad S,
Moghadam M (2005) J Mol Catal A Chem 224: 139;
b) Bahramian B, Mirkhani V, Moghadam M,
Tangestaninejad S (2006) Appl Catal A General 301:
169; c) Bahramian B, Mirkhani V, Moghadam M,
Tangestaninejad S (2006) Catal Commun 7: 289; d)
Mirkhani V, Moghadam M, Tangestaninejad S,
Bahramian B (2006) Appl Catal A General 311: 43;
e) Mirkhani V, Moghadam M, Tangestaninejad S,
Bahramian B (2006) Appl Catal A General 313: 122;
f) Mirkhani V, Moghadam M, Tangestaninejad S,
Bahramian B (2006) Polyhedron 25: 2904
[13] Collman PJ, Zeng L, Brauman IJ ( 2004) Inorg Chem 43:
2672
Acknowledgement
The support of this work by Center of Excellence of Chem-
istry of University of Isfahan (CECUI) is acknowledged.
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