Olefin epoxidation with tert-BuOOH catalyzed by vanadium polyoxometalate immobilized on ionic liquid-modified MCM-41

Article abstract of DOI:10.1080/00958972.2011.636038

Preparation and characterization of vanadium-containing polyphosphomolybdates supported on ionic liquid-modified MCM-41, MCM-41-Im, are reported. The catalyst, [PVMo@MCM- 41-Im], was characterized by elemental analysis, X-ray diffraction, scanning electron microscopy and also FT-IR, and UV-Vis spectroscopic methods. This heterogeneous catalytic system was applied for efficient epoxidation of various olefins in the presence of tert-BuOOH in 1,2-dichloroethane under reflux. The catalyst can be reused several times without apparent loss of its catalytic performance.

Full text of DOI:10.1080/00958972.2011.636038

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Olefin epoxidation with tert-
BuOOH catalyzed by vanadium
polyoxometalate immobilized on ionic
liquid-modified MCM-41
a
a
Robabeh Hajian , Shahram Tangestaninejad , Majid Moghadam
a
a
a
,
Valiollah Mirkhani , Iraj Mohammadpoor-Baltork & Ahmad
a
Reza Khosropour
a
Department of Chemistry, Catalysis Division , University of
Isfahan , Isfahan 81746-73441 , Iran
Published online: 18 Nov 2011.
To cite this article: Robabeh Hajian , Shahram Tangestaninejad , Majid Moghadam , Valiollah
Mirkhani , Iraj Mohammadpoor-Baltork & Ahmad Reza Khosropour (2011) Olefin epoxidation with
tert-BuOOH catalyzed by vanadium polyoxometalate immobilized on ionic liquid-modified MCM-41,
Journal of Coordination Chemistry, 64:23, 4134-4144, DOI: 10.1080/00958972.2011.636038
To link to this article: http://dx.doi.org/10.1080/00958972.2011.636038
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Journal of Coordination Chemistry
Vol. 64, No. 23, 10 December 2011, 4134–4144
Olefin epoxidation with tert-BuOOH catalyzed by vanadium
polyoxometalate immobilized on ionic liquid-modified MCM-41
ROBABEH HAJIAN, SHAHRAM TANGESTANINEJAD*,
MAJID MOGHADAM*, VALIOLLAH MIRKHANI,
IRAJ MOHAMMADPOOR-BALTORK and AHMAD REZA KHOSROPOUR
Department of Chemistry, Catalysis Division, University of Isfahan,
Isfahan 81746-73441, Iran
(
Received 14 July 2011; in final form 14 October 2011)
Preparation and characterization of vanadium-containing polyphosphomolybdates supported
on ionic liquid-modified MCM-41, MCM-41-Im, are reported. The catalyst, [PVMo@MCM-
41-Im], was characterized by elemental analysis, X-ray diffraction, scanning electron
microscopy and also FT-IR, and UV-Vis spectroscopic methods. This heterogeneous catalytic
system was applied for efficient epoxidation of various olefins in the presence of tert-BuOOH in
1,2-dichloroethane under reflux. The catalyst can be reused several times without apparent loss
of its catalytic performance.
Keywords: Immobilized ionic liquid; tert-BuOOH; MCM-41; Epoxidation; Polyoxometalate;
Heterogeneous catalyst
1. Introduction
Olefin epoxidation is an important reaction for the production of epoxides, a major
industrial organic intermediate and is used in the synthesis of drugs, agrochemicals and
food additives [1–3].
Due to the unique properties of polyoxometalates (POMs), their syntheses have
become an important area of research [4–8]. The catalytic function of POMs has attracted
great attention [9–11], due to their hydrolytic and thermal stability, solubility in various
solvents and tunable acid and redox properties at the molecular or atomic levels [12–16].
Although the efficiency of homogeneous catalysts is rather high, they suffer from
drawbacks such as the non-reusability of the catalyst, degradation, tedious work up for
separation of catalyst from products and reactants and decrease in stability toward air,
moisture, and temperature. The best way to overcome these problems is immobilization
on solid support without loss of their intrinsic activity. Organic and inorganic materials
have been used as supports for immobilization of POMs [17–23]. However, inorganic
supports exhibit some advantages over organic supports due to higher surface area and
chemical stability. A new class of supports in heterogeneous catalysis is MCM-type
*
Corresponding authors. Email: stanges@sci.ui.ac.ir; moghadamm@sci.ui.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2011.636038

Vanadium polyoxometalate
4135
O
TBHP, 1,2-dichloroethane
[
MCM-41-Im@PVMo], reflux
Scheme 1. Olefin epoxidation with TBHP catalyzed by vanadium polyoxometalate immobilized on ionic
liquid-modified MCM-41.
mesoporous materials as appropriate host matrices for finely dispersion of POMs within
regular pores and channels [24–30]. Large surface areas, hydrophobicity and acidity of
these materials can effectively improve their catalytic activity.
Ionic liquids are thermally stable, odorless, and unaffected by moisture. They have no
detectable vapor pressure and are immiscible with organic and inorganic solvents. Due
to these excellent properties, these materials are used as reaction media for a broad
range of catalytic applications [31]. Supported ionic liquid catalysis is a concept that
combines the advantages of ionic liquids with those of heterogeneous catalysts [32].
Ionic liquid-modified supported catalysts provide a hydrophobic environment for
organic reactions [33–35]. The simple separation and high reusability of these systems
make them potentially environmentally benign catalysts in organic reactions.
In this article, the preparation and characterization of vanadium-containing
polyphosphomolybdates supported on ionic liquid-modified MCM-41 and its catalytic
activity in olefin epoxidation with tert-butyl hydroperoxide (TBHP) is reported
(scheme 1).
2
. Experimental
All chemicals were commercial reagent grade and obtained from Merck and Fluka.
Polyoxometalate was prepared according to the literature [36]. The MCM-41
was prepared according to the method reported by Beck et al. [37]. The prepared
catalyst was characterized by elemental analysis, X-ray diffraction (XRD), scanning
electron microscopy (SEM), FT-IR, and UV-Vis spectroscopic methods [38]. FT-IR
ꢀ
1
spectra were obtained as potassium bromide pellets in the range 400–4000 cm with
a Jasco Impact 6300D spectrometer. SEM of the catalyst and support were taken
on a SEM Philips XL 20 instrument. UV-Vis spectra were obtained from 200
ꢀ1
to 800 cm with a Jasco V-670 spectrometer. Powder X-ray diffraction patterns were
ꢁ
obtained on a D8 Advanced Bruker using Cu-Ka radiation (2ꢀ ¼ 5–60 ). Gas
chromatography (GC) experiments were performed with a Shimadzu GC-16A
instrument using a 2 m column packed with silicon DC-200 or Carbowax 20 m.
1
In GC experiments, n-decane was used as internal standard. H NMR spectra were
recorded on a Bruker-Avance AQS 300 MHz. The ICP analyzes were performed on an
ICP-Spectrociros CCD instrument. Atomic absorption analyses were carried out on a
Shimadzu 120 spectrophotometer.
2
.1. Synthesis of chloropropylated MCM-41, MCM-41-Cl
To a solution of 3-chloropropyl(trimethoxy)silane (10 mmol, 1.98 g) in toluene (40 mL)
was added MCM-41 (2.0 g) with stirring under reflux for 24 h. The chloropropylated

4
136
R. Hajian et al.
MCM-41 (MCM-41-Cl) was filtered, washed with Et O and dried under vacuum at
2
ꢁ
5
0 C overnight.
2.2. Synthesis of ionic liquid-modified MCM-41, MCM-41-Im
To a suspension of chloropropylated MCM-41 (1 g) in CH CN (20 mL) was added
3
N-methylimidazole (10 mmol) and stirred under reflux for 48 h. After the reaction was
completed, the MCM-41-Im was filtered, washed consecutively with water and acetone,
ꢁ
and dried under vacuum at 70 C overnight.
2
.3. Preparation of PVMo immobilized on ionic liquid-modified MCM-41,
PVMo@MCM-41-Im
To a solution of Na [PMo V O ] (1 g) in a mixture of water/acetone (30 mL, 1 : 1 v/v)
5
10
2
40
was added MCM-41-Im (4 g) and refluxed for 24 h. Finally, the catalyst was filtered and
dried at room temperature.
2
.4. General procedure for epoxidation of alkenes with tert-BuOOH catalyzed by
PVMo@MCM-41-Im under reflux
In a 25 mL round-bottom flask equipped with a magnetic stirring bar, to a mixture of
alkene (0.5 mmol) and PVMo@MCM-41-Im (50 mg, 0.003 mmol) in 1,2-dichloroethane
(5 mL) was added tert-BuOOH (0.005 mmol) and refluxed. The progress of the
reactions was monitored by GC. At the end of the reaction, the catalyst was filtered and
washed with Et O (20 mL). The organic layer was separated, concentrated and after
2
chromatography on a short column of silica gel the pure product was obtained. IR and
1
H NMR spectral data confirmed the identities of the products.
3
3
. Results and discussion
.1. Preparation and characterization of catalyst, PVMo@MCM-41-Im
Scheme 2 shows the preparation procedure for PVMo@MCM-41-Im catalyst. First,
MCM-41 was reacted with 3-chloropropyl(trimethoxy)silane in which methoxy groups
of silane were replaced by silanol groups to produce MCM-41-Cl. Then, 3-chloropropyl
ꢁ
functionalized MCM-41-Cl was reacted with N-methylimidazole at 80 C to prepare the
supported ionic liquid. The FT-IR spectrum of MCM-41-Im (figure 1) shows the
ꢀ
1
) at 1638 cm . The four typical
characteristic band of the parent ionic liquid (ꢁ
C¼N
skeletal vibrations of the Keggin polyoxoanions appear at 1063 (ꢁP–O), 951 (ꢁ
), 867
Mo¼O
ꢀ
1
ꢀ1
and 786 cm (ꢁM–O–M) [39]. Owing to the overlap of 867 cm of M–O–M and P–O
bands with those of Si–O–Si stretching vibrations of mesoporous support, only the
bands corresponding to (Mo¼O and Mo–O–Mo) are discernable after immobilization
on the support (figure 2a). FT-IR spectra indicated that PVMo had been successfully
supported on ionic liquid-modified MCM-41. Diffuse reflectance (DR) UV-Vis spectra
of PVMo showed a broad absorption peak at 304 nm, which was associated with

Vanadium polyoxometalate
4137
Si OH
Si OH
Si OH
Si OH
O
O
O
O
O
O
Si
Si
O
OH
Toluene,Reflux
(
CH O) Si(CH ) Cl
MCM-41
Si
Cl
MCM-41
+
3
3
2 3
O
OH
OH
Si
Si
N
Me
N
CH CN, Reflux
3
Si OH
O
O
O
Si
Si
O
OH
+
MCM-41
Si
N
N
Me
O
Cl
OH
Si
Na [PMo V O ]
5
10 2 40
Aqueos acetone
Si OH
O
O
O
Si
Si
O
O
OH
+
MCM-41
Si
N
N
Me
–
5
[PMo V O ]
1
0 2 40
OH
Si
Scheme 2. The preparation route for catalyst.
6
þ
octahedral Mo , and can be attributed to a ligand metal charge transfer (LMCT) [40].
This absorption appeared in UV-Vis spectra of PVMo@MCM-41-Im and since pure
MCM-41-Im shows no UV absorption in this area (figure 3). These observations clearly
proved the presence of PVMo on the support.
The nitrogen content of the MCM-41-Im was about 3.07%. The results are listed in
table 1. According to this value, the amount of the ligand, which was attached to
ꢀ
1
MCM-41, was 1.1 m mol g of support. The amounts of Mo and V were measured by
ꢀ
1
ICP. Both values showed that the catalyst loading is about 0.06 m mol g . The Keggin
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
type PVMo showed diffraction peaks at 2ꢀ ¼ 8.9 , 9.8 , 10.3 , 27.4 , and 29.5 [41]. The
XRD patterns of MCM-41-Im, PVMo and PVMo@MCM-41-Im are shown in
figure 4. From these patterns, it is clear that primary Keggin structure has been
introduced in MCM-41-Im. Figure 5 shows SEM images of MCM-41-Im and
PVMo@MCM-41-Im. A clear change in the morphology of catalysts indicated that
the PVMo has been supported on the MCM-41-Im.

4
138
R. Hajian et al.
Figure 1. FT-IR spectra of MCM-41-Im.
3.2. Catalytic activity
Since heterogeneous catalysts are recoverable, heterogenization of homogenous
catalysts is of great interest. Therefore, we decided to immobilize PVMo on MCM-
41-Im and investigate its catalytic activity in the epoxidation of various olefins with tert-
BuOOH under reflux. First, the reaction parameters were optimized in reaction of
cyclooctene with TBHP in the presence of PVMo@MCM-41-Im. In order to choose the
reaction media, different solvents were checked in the epoxidation of cyclooctene. From
1
,2-dichloroethane, dichloromethane, chloroform, carbon tetrachloride, acetonitrile,
acetone and methanol, 1,2-dichloroethane was chosen as reaction media because the
highest epoxide yield was observed (table 2).
The catalytic activity of this catalyst was investigated in epoxidation of different
alkenes (table 3). The reactions were continued until no further progress was observed.
In the epoxidation of cis-cyclooctene with TBHP, the conversion was 92% with
9
0% epoxide selectivity and 1,2-cyclooctanediol was produced as by-product.
In epoxidation of cyclohexene, the corresponding epoxide was obtained with 79%
conversion and 58% epoxide selectivity, and allylic oxidation products (cyclohexene-1-
one and cyclohexene-1-ol) were detected in the reaction mixture. In the case of indene,
the major product was epoxide. Epoxidation of limonene with 89% conversion and
1
00% epoxide selectivity led to 74% of 1,2-epoxide and 15% of 8,9-epoxide.
In oxidation of ꢂ-pinene, the major product was ꢂ-pinene oxide (57%), while
verbenone and verbenol were produced as minor products. Oxidation of linear alkenes
such as 1-octene and 1-heptene was accompanied by allylic oxidation. Blank
experiments in the absence of the catalyst were also investigated and the amount of
product is negligible.
The catalytic activity of Na MoO and NaVO supported on MCM-41-Im were
2
4
3
also investigated in the oxidation of cyclooctene with TBHP. In the case of

Vanadium polyoxometalate
4139
Figure 2. FT-IR spectra of: (a) MCM-41-Im@PVMo and (b) recovered PVMo@MCM-41-Im.
MoO @MCM-41-Im, the conversion was 44% and epoxide selectivity was 93%, while
4
in the case of VO @MCM-41-Im, the conversion was 8% and the epoxide selectivity
3
was 63%.
Recently, we reported the use of supported PVMo in alkene epoxidation [17–22]. No
doubt, all of these methods are good in terms of reactivity and reusability; the present
method also has advantages over previous systems such as thermal stability, ease of

4
140
R. Hajian et al.
Figure 3. DR UV-Vis spectra of: (a) MCM-41-Im and (b) PVMo@MCM-41-Im.
Table 1. Analytical data of supported ionic liquid and catalyst.
Compound
C (%)
H (%)
N (%)
Mo (%)
V (%)
MCM-41-Im
PVMo@MCM-41-Im
10.61
7.76
1.94
1.89
3.07
1.24
–
5.75
–
0.62
Figure 4. XRD patterns of: (a) MCM-41-Im, (b) PVMo, and (c) PVMo@MCM-41-Im composite.

Vanadium polyoxometalate
4141
Figure 5. Scanning electron micrographs of: (a) MCM-41-Im and (b) PVMo@MCM-41-Im.
Table 2. The effect of solvent on the epoxidation of cis-cyclooctene
catalyzed by PVMo@MCM-41-Im under reflux.
a
b
Entry
Solvent
Epoxide (%)
Time (h)
1
2
3
4
5
6
CH
CHCl
(CH CO
CH OH
CH CN
Cl
2
Cl
2
6
21
57
25
30
90
25
25
25
25
25
25
3
3 2
)
3
3
C
2
H
4
2
a
Reaction conditions: cis-cyclooctene (0.5 mmol), catalyst (50 mg, 0.003 mmol), 5 mL
solvent, TBHP (0.005 mmol).
GC yield based on the starting cyclooctene.
b

4
142
R. Hajian et al.
a
Table 3. Oxidation of alkenes with THBP catalyzed by PVMo@MCM-41-Im under reflux.
Row
1
Substrate
Product
Time (h) Conversion (%)b Epoxide selectivity (%) TOF (h–1
)
OH
O
25
92
90
12.27
OH
O
OH
2
3
24
23
79
60
58
40
10.97
8.70
O
O
O
1
00
4
5
26
22
89
65
1,2-epoxide (74%)
,9-epoxide (15%)
11.41
9.85
O
O
8
O
57
O
OH
OH
6
7
22
25
70
92
26
40
10.61
12.27
O
OH
O
a
Reaction conditions: alkene (0.5 mmol), TBHP (0.005 mmol), catalyst (50 mg, 0.003 mmol), 1,2- dichloroethane (5 mL).
GC yield based on the starting alkene.
b
Table 4. The results obtained from catalyst reuse and stability in the oxidation
of cyclooctene with THBP by PVMo@MCM-41-Im under reflux.
a
Conversion
(%)
Time
(h)
Mo
leached (%)
b
c
Run
1
2
3
4
5
6
7
8
9
92
90
90
90
90
90
90
90
90
90
25
25
25
25
25
25
25
25
25
25
1.59
0.77
–
–
–
–
–
–
–
1
0
–
a
Reaction conditions: alkene (0.5 mmol), TBHP (0.005 mmol), catalyst (50 mg, 0.003 mmol),
1
,2- dichloroethane (5 mL).
GC yield based on the starting alkene.
b
c
Determined by AA.
preparation and low cost of the catalyst. On the other hand, this catalytic system is
superior in terms of conversion and/or epoxide selectivity.
3.3. Catalyst reuse and stability
The reusability of a supported catalyst is one of the most important benefits of
heterogeneous catalysts, because transition-metal complexes are often expensive to

Vanadium polyoxometalate
4143
purchase or prepare. Therefore, heterogenization of homogeneous catalysts makes them
useful for commercial applications. To assess stability and reusability, the catalyst was
separated from the reaction mixture after each experiment, washed thoroughly with
acetonitrile and n-hexane successively and dried before being used in the subsequent
run. The catalyst was consecutively reused ten times without any loss of its catalytic
activity (table 4). The filtrates were used for determination of the catalyst leaching by
atomic absorption spectroscopy (AAS). The results showed that in the first two runs
some catalyst is leached from support (1.59% in the first run and 0.77% in the second
run), but in the next runs no leaching was observed. FT-IR spectroscopy of the
recovered catalyst after using for ten times showed no change in its IR spectra
(figure 2b).
4
. Conclusion
We have prepared a recyclable catalyst based on immobilization of vanadium
polyoxometalate on ionic liquid-modified MCM-41 which is an efficient catalyst for
epoxidation of alkenes with tert-BuOOH. The catalyst could be easily separated from
the reaction system and reused.
Acknowledgements
The support of this work by the Center of Excellence of Chemistry of University of
Isfahan (CECUI) is acknowledged.
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