POSS-derived mesoporous ionic copolymer-polyoxometalate catalysts with a surfactant function for epoxidation reactions

Article abstract of DOI:10.1039/c5nj01541c

A series of novel polyoxometalate (POM)-based stable polymeric hybrids were successfully synthesized using polyhedral oligomeric vinylsilsesquioxanes (POSS) and ionic liquids (IL) bearing hydrophobic alkyl chains as the building blocks, followed by ion exchange with Keggin-type phosphotungstic acid (PW). The obtained hybrids POSS-IL_x-PW were demonstrated to be mesostructured and amphiphilic materials with good thermal stability. Catalytic tests for the H₂O₂-based epoxidation of cyclooctene have shown that these newly designed catalysts exhibit extraordinary catalytic activities, catalytic rates, and quite stable reusability. The unique amphiphilic property and the mesoporous structure are revealed to be responsible for the catalysts' excellent performance in epoxidation reactions with H₂O₂.

Full text of DOI:10.1039/c5nj01541c

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DOI: 10.1039/C5NJ01541C
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New Journal of Chemistry
►
Journal Name
ARTICLE TYPE
POSS-Derived Mesoporous Ionic Copolymer-Polyoxometalate Catalysts with
Surfactant Function for Epoxidation Reactions
a
a
a
b
a
Jiwei Zhao, Yan Leng,* Pingping Jiang, Jun Wang , and Chenjun Zhang
Received (in XXX, XXX) XthXXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
A series of novel polyoxometalate (POM)-based stable polymeric hybrids were successfully synthesized
using polyhedral oligomeric vinylsilsesquioxanes (POSS) and ionic liquids (IL) bearing hydrophobic
alkyl chains as the building blocks, followed by ion exchange with Keggin-type phosphotungstic acid
(PW). The obtained hybrids POSS-ILx-PW were demonstrated to be mesostructured and amphiphilic
1
0
materials with good thermal stability. Catalytic tests for H O -based epoxidation of cyclooctene have
2
2
shown that these newly designed catalysts exhibit extraordinary catalytic activities, catalytic rate, and
quite stable reusability. The unique amphiphilic property and the mesoporous structure are revealed to be
responsible for the catalysts’ excellent performance in epoxidation reactions with H O .
2
2
mesoporous POM-based polymeric catalysts with optimized
amphipathicity is needed.
Polyhedral oligomeric silsesquioxanes (POSS) are recently
1
. Introduction
1
2
2
3
3
4
4
5
0
5
0
5
0
5
Polyoxometalates (POMs) is a class of transition-metal oxygen
5
5
6
6
7
7
8
0
5
0
5
0
5
0
regarded as ideal building blocks for constructing organic-
[
1,2]
anion clusters with structural versatility
. Owing to their well-
[19,20]
inorganic hybrid materials
. POSS is a class of typical
defined physical and chemical properties and reversible electron
transformation abilities, POMs have been extensively
investigated as catalysts in a variety of oxidation reactions,
organic-inorganic molecules with the general formula R Si O ,
8
8
12
where R is hydrogen or organic groups, such as alkyl, aryl or any
of their derivatives. They have unique star-shaped nanostructures
and chemical properties, such as facile chemical modification,
[
3-6]
including epoxidation of alkenes
. However, their rich redox
properties are strongly hindered by good solubility in common
polar solvents and hydrophilcity, which causes difficulty in
separation and recycling of the catalysts. To overcome this
obstacle, a numbers of strategies have been developed for the
heterogenisation of POM catalysts, including phase
transformation, microemulsion formation, encapsulation by
inorganic or organic cations, and immobilization into polymer or
good pH tolerance, high temperature and oxidation resistance
[21-23]
properties
. So far, micro/mesoporous materials based on
POSS precursors have been prepared by various chemical routes
including hydrosilation methods, thermolysis, and copper-
[24-27]
mediated coupling
. However, there are little reports on the
preparation of POSS-derived micro/mesoporous poly(ionic liquid)
materials for catalysis.
Very recently, we have synthesized a series of POSS-
containing porous ionic polymer materials for epoxidation
[
7-10]
silica matrix
. In this context, assembling of POMs with
polymeric organic cations is revealed to be a successful example
for preparing heterogeneous POM catalysts, which is beneficial
for adjusting the solubility, redox properties, and surface
reactions, but the pore size distribution of these materials is too
[28,29]
wide
. Herein, we demonstrate a successful preparation of
[
11]
microenvironment of POM. For example, Doherty
prepared a
mesoporous POM-based polymeric hybrids by copolymerization
of octavinyl POSS with IL monomers without using any
templates, followed by ion exchange with the Keggin-type
H PW O . With the concept of adjusting of interfacial
POM-based linear cation-decorated polymeric hybrid and used it
as an efficient and recyclable catalyst for the epoxidation of
allylic alcohols and alkenes. We have prepared a series of POM-
based polymeric ionic hybrids by combining poly(ionic liquid)
cations which heteropolyanions, and the resulting ionic solids
turned out to be effective catalysts for acid-catalyzed or oxidative
organic transformations
POM polymeric hybrids are always nonporous, and limited the
heterogeneous catalytic activity in mass-transfer-controlled
3
12 40
microenvironment of POM catalysts in mind, a series of
imidazole IL bearing hydrophobic alkyl chains with different
lengths were synthesized and introduced into the polymeric
hybrids. The catalysts not only exhibit enhanced catalytic
activities for the epoxidation of alkenes using H O but also
[
12-16]
. Nevertheless, the self-assembled
2
2
provide easy catalyst recovery from the reaction system. The
excellent catalytic performance of the catalysts is mostly
attributed to the contributions of the mesoporous structure and the
amphiphilic interfacial microenvironment of the catalysts.
[
17,18]
systems
. Moreover, the hydrophilic or hydrophobic
frameworks of polymeric cations may hinder the interaction of
the POM catalytic centers with the hydrophobic organic
substrates or hydrophilic oxidizing agent H O , which results in
2
2
limited catalytic efficiency. Therefore, a rationally designed
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 |1

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DOI: 10.1039/C5NJ01541C
New Journal of Chemistry
Page 2 of 8
2
. Experimental section
TMS) for HIM: δ (ppm) =0.83 (t, 3H, -CH
), 1.27 (m, 26H, -CH ),
3 2
1
.93 (m, 2H, -CH ), 3.67 (m, 2H, -CH ), 5.38 (d, 1H, -CH), 6.01
2
2
2
.1 Materials and methods
(
d, 2H, -CH ), 7.26 (d, 2H, -CH), 7.54 (d, 1H, -CH) (Figure S4 in
2
1
1
All chemicals were analytical grade and used as received. H-
SI). The H NMR spectra are shown in the Supporting
NMR spectra were measured with
a
Bruker DPX 300 45 Information (SI) Figures S1-S4. Positive-ion electrospray
5
0
5
spectrometer at ambient temperature in D O or CDCl using TMS
ionization mass spectrometry (ESI-MS) m/z: 151.1 [3-butyl-1-
2
3
+
as internal reference. FT-IR spectra were recorded on a Nicolet
vinylimidazolium] (Figure S5A in SI), 207.5 [3-octyl-1-
-
1
+
3
60 FT-IR instrument (KBr discs) in the 4,000-400 cm region.
vinylimidazolium] (Figure S6A in SI), 264.2 [3-dodecyl-1-
+
TG analysis was carried out with a STA409 instrument in dry air
vinylimidazolium] (Figure S7A in SI), and 320 [3-hexadecyl-1-
+
at a heating rate of 10 °C/min. SEM image was performed on a 50 vinylimidazolium] (Figure S8A in SI). Negative-ion electrospray
-
1
HITACHI S-4800 field-emission scanning electron microscope.
TEM images were obtained with JEOL JEM-2100 electron
microscope operated at 200 Kv. The pore size distribution was
ionization mass spectra show the patterns at 79 and 81 (Br )
(Figures S5B-S8B).
2.2.2 Preparation of octavinyl POSS
derived from the desorption branch of N isotherms using Barrett-
Octavinyl POSS was prepared according to the previous
2
[
30,31]
Joyner-Halenda (BJH) method. Electrospray ionization mass 55 literature
. Typically, in a 250 mL flask, vinyltriethoxysilane
1
spectra (ESI-MS) were recorded with a Finnigan mat APISSQ
(19 g, 0.1 mol) was dissolved in 50 mL anhydrous ethanol. Then
10 mL hydrochloric acid and 8 mL deionized water were added
into the above solution with vigorous stirring. The above reaction
mixture was allowed to react for 48 h at room temperature. On
completion, the white crystalline powder was filtered, washed
7
2
2
10 mass spectrometer.
.2 Catalyst preparation
60
.2.1 Preparation of IL monomers
with
anhydrous
ethanol,
recrystallized
in
Typically, [3-octyl-1-vinylimidazolium]Br (OIM) was
2
2
3
3
4
0
5
0
5
0
prepared as follows: N-vinylimidazole (4.71 g, 50 mmol) and 1-
bromooctane (9.66 g, 50 mmol) were dissolved in ethanol (25 mL)
at 80C for 48 h under nitrogen atmosphere with stirring. On
completion, the solvent was removed by reduced pressure
distillation, the remained liquid mixture was washed with
anhydrous diethyl ether for three times, and then dried in vacuum
tetrahydrofuran/methanol (volume ratio: 1:3) and dried in
2
9
vacuum at 80°C for 10 h. Si NMR (400 MHz, CDCl
(ppm) = 80.19 (Figure S9 in SI).
, TMS) δ
3
65
2.2.3 Preparation of POSS-ILs
POSS-IL (x stands for the molar ratio of IL to POSS) were
x
synthesized through free radical polymerization of octavinyl
1
at 50°C for 12 h to give the IL product OIM. H NMR (300 MHz,
POSS and IL. As a typical run for the synthesis of POSS-OIM
,
8
CDCl , TMS) δ (ppm) =0.72 (s, 3H, -CH ), 1.13 (m, 10H, -CH ),
the obtained octavinyl POSS (0.63 g, 1 mmol), OIM (2.30 g, 8
3
3
2
1
.78 (m, 2H, -CH ), 3.51 (m, 2H, -CH ), 5.25 (d, 1H, -CH), 5.95 70 mmol ), and azodiisobutyronitrile (AIBN, 0.06 g) were dissolved
2
2
in a mixture solvent (1,4-dioxane 20 mL and ethanol 20 mL).
(
d, 2H, -CH ), 7.32 (d, 2H, -CH), 7.62 (d, 1H, -CH) (Figure S2 in
2
o
Then the solution was stirred at 75 C for 24 h. After reaction, the
Supporting
vinylimidazolium]Br (BIM), [3-dodecyl-1-vinylimidazolium]Br
DIM), and [3-hexadecyl-1-vinylimidazolium]Br (HIM) were
Information
(SI)).
The
ILs
[3-butyl-1-
above mixture was added dropwise into ethyl acetate (100 mL) to
(
afford the solid product. Then the solid product POSS-OIM
was
8
1
prepared in the same way. H NMR (300 MHz, CDCl , TMS) for 75 filtered, washed with ethanol and dried under vacuum. The ionic
3
BIM: δ (ppm) =0.94 (t, 3H, -CH ), 1.35 (m, 2H, -CH ), 1.92 (m,
polymers POSS-OIM
, POSS-OIM12, POSS-OIM16, POSS-BIM ,
4 8
3
2
POSS-DIM , and POSS-HIM were prepared accordingly.
2H, -CH ), 3.68 (m, 2H, -CH ), 5.36 (d, 1H, -CH), 6.01 (d, 2H, -
8
8
2
2
1
2
.2.4 Preparation of POSS-ILs-PW
Polymeric hybrids POSS-IL -PW were prepared from the
CH ), 7.27 (d, 2H, -CH), 7.67 (d, 1H, -CH) (Figure S1 in SI). H
2
NMR (300 MHz, CDCl , TMS) for DIM: δ (ppm) =0.9 (s, 3H, -
x
3
CH ), 1.3 (m, 18H, -CH ), 1.97 (m, 2H, -CH ), 3.74 (m, 2H, - 80 reaction between POSS-IL
and H
the starting molar ratio of POSS-OIM
Typically, POSS-OIM and PW were dissolved in anhydrous
x
PW12
O
40 (PW). For example,
to PW was 1:(x/3).
3
2
2
x
3
CH ), 5.43 (d, 1H, -CH), 5.93 (d, 2H, -CH ), 7.33 (d, 2H, -CH),
x
2
2
1
7.60 (d, 1H, -CH) (Figure S3 in SI). H NMR (300 MHz, CDCl ,
3
Figure 1. Figure 1. Schematic preparation of the POSS-derived mesoporous catalysts.

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DOI: 10.1039/C5NJ01541C
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New Journal of Chemistry
1
00
9
8
7
6
5
0
0
0
0
0
(
a)
(b)
1
00
200
300
400
500
600
700
800
o
Temperature ( C)
8 8
Figure 2. TG curves of (a) POSS-OIM -PW and (b) POSS-OIM .
(a)
800 1600 1300
2
3000
(b)
Figure 4. SEM images of (A) POSS-OIM
TEM images of (C) POSS-OIM
8
-PW and (B) OIM-PW, and
8
8
and (D) POSS-OIM -PW.
1
160
121
080
1
893
were obtained by the anion-exchange of POSS-OIMx with
H PW O in aqueous solution. The TG profile of POSS-OIM8
1
978
3
12 40
817
30 shows that the small weight loss of 2-3% around 100-110°C
4
000
3500
3000
1500
1000
500
results from the loss of the adsorbed water. However, POSS-
-1
o
Wavenumber (cm )
OIM -PW is quite stable up to ca. 400 C. The weight loss of
8
nearly 38% and 70% for POSS-OIM -PW and POSS-OIM ,
respectively, are attributed to the decomposition of organic
8
8
8 8
Figure 3. FTIR spectra of (a) POSS-OIM and (b) POSS-OIM -PW.
3
4
4
5
5
6
5
0
5
0
5
0
groups. Thus, the content of PW on the POSS-OIM -PW was
calculated to be 45.7%, suggesting a high PW loading capacity of
POSS-OIM8.
8
ethanol (20 mL) and deionized water (20 mL), respectively. Then
the aqueous solution of PW was added into the POSS-OIMx
solution, followed by stirring at room temperature for 2 h. The
Figure 3 illustrates the FT-IR spectra of the prepared samples
POSS-OIM -PW and POSS-OIM . The FT-IR spectrum of
solid product POSS-OIM -PW was filtered, washed with
8
8
8
5
deionized water and ethanol, and dried. The polymeric hybrids
POSS-BIM -PW, POSS-DIM -PW and POSS-HIM -PW were
-1
POSS-OIM clearly shows the strong band at 1121 cm assigned
8
8
8
8
to asymmetric vibration of Si-O-Si and the characteristic bands at
prepared accordingly.
-1
-1
1
300~1600 cm and 2800~3000 cm that are assigned to organic
groups, indicating the coexistence of POSS and IL units. After
the combination of POSS-OIM8 with H PW O , the
2
.3 Catalytic tests
Cyclooctene (10 mmol), acetonitrile (10 mL), and catalyst (0.1
3
12 40
3-
characteristic vibration bands for the [PW O ] species are
1
2
40
1
0
g, 0.025 mmol) were added into a 25 mL flask. Then 30 wt.%
-1
observed at 1080, 978, 893 and 817 cm , assignable to vibrations
of P–O , W=O , W–O –W and W–O –W, respectively
o
H O (12 mmol) was added into the solution at 70 C within 10
[32-35]
2
2
.
a
d
b
c
min under vigorous stirring. After reaction, the reaction mixture
was centrifuged to remove the solid catalyst, and the liquid was
analyzed by a gas chromatography (GC). Other alkene substrates
were tested accordingly. A five-run catalyst recycling was carried
out for testing the reusability of catalyst.
Moreover, the position of the peaks assigned to POSS and
organic moiety in POSS-OIM -PW are well consistent with those
8
of the IR spectrum for POSS-OIM8.
1
5
Figure 4 illustrates the SEM images of POSS-OIM -PW and
8
OIM-PW. It is demonstrated that the POSS-OIM -PW (Figure 4A)
8
have irregular honeycomb-shaped morphology with micrometer
size and nanoscale hollow structure. In the case of POSS-free
hybrid OIM-PW (Figure 4B), the morphology changed to angular
blocks with a smooth surface. In the TEM image of POSS-OIM8,
the black micelles with size of 15-20 nm are clearly seen,
demonstrating the existence of POSS unites (Figure 4C). The
black portion was obviously increased in the TEM image of
3
. Results and discussion
3
.1 Catalyst preparation and characterization
The preparation of the POM-paired polymeric hybrids was
2
0
carried out according to the procedures shown in Figure 1.
Typically, the IL monomer OIM was first prepared and
1
characterized by H NMR. The POSS-containing ionic copolymer
POSS-OIM -PW (Figure 4D), which indicates that the introduced
8
was synthesized by the free radical copolymerization of octavinyl
POSS and OIM using AIBN as the initiator. By varying the molar
ratio of OIM to POSS and the types of alkyl side chain in
PW has been uniformly dispersed in the copolymer network.
The surface area and pore structure of POSS-OIM -PW was
8
2
5
examined by nitrogen sorption measurements. As shown in
imidazole IL, a series of ionic copolymers POSS-IL could be
x
Figure 5A, the isotherm of POSS-OIM -PW is IV type with a
8
prepared in the same way. The final catalysts POSS-OIM -PW
x
65 clear H1-type hysteresis loop at a relatively higher partial

View Article Online
DOI: 10.1039/C5NJ01541C
New Journal of Chemistry
Page 4 of 8
Table 2. Catalytic performances of various catalysts for epoxidation of
cyclooctene with H O .
2 2
(
A)
(B)
a
b
c
d
e
a
b
c
Solubility in
reaction
Con
Sel
Entry
Catalyst
-
(
a)
(%)
(%)
(
(
(
(
b)
c)
d)
e)
.0
1
2
3
Homogeneous
Homogeneous
Heterogeneous
-
-
H PW O
11
1.3
85
37
0
0.2
0.4
0.6
0.8
1.0
2
10
50 100
3
12 40
Relative pressure (p/p )
o
Pore diameter d (nm)
p
POSS-OIM8
(C)
(D)
a
b
c
POSS-OIM4-
PW
4
5
Heterogeneous
81
＞99
＞99
＞99
＞99
＞99
＞99
＞99
d
POSS-OIM
PW
8
-
Heterogeneous ＞99
Heterogeneous ＞99
(
a)
b)
(
POSS-OIM12
-
6
(
c)
d)
.0
PW
(
POSS-OIM -
16
7
Heterogeneous
Heterogeneous
Heterogeneous
Heterogeneous
97
90
99
98
0
0.2
0.4
0.6
0.8
1.0
2
10
50 100
PW
POSS-BIM8-
PW
POSS-DIM8-
PW
POSS-HIM8-
PW
Relative pressure (P/P )
Pore diameter dp (nm)
o
8
Figure 5. (A) Nitrogen adsorption–desorption isotherms and (B) BJH
pore size distributions of (a) POSS-OIM -PW, (b) POSS-OIM12-PW,
c) POSS-OIM16-PW, (d) POSS-OIM -PW, (e) OIM-PW, and (C)
Nitrogen adsorption–desorption isotherms and (D) BJH pore size
8
9
(
4
10
distributions of (a) POSS-OIM
8
-PW, (b) POSS-DIM
8
-PW, (c) POSS-
11
BIM-PW
OIM-PW
DIM-PW
HIM-PW
Heterogeneous
Heterogeneous
Heterogeneous
Heterogeneous
45
52
77
80
＞99
98
HIM -PW, (d) POSS-BIM -PW.
8
8
1
1
1
2
3
4
98
Table 1. The textural parameters of various samples.
98
a
b
Dvc
S
V
p
BET
a
Entry
Catalyst
2
-1
3
-1
Reaction conditions: catalyst (0.03 mmol), cyclooctene (10 mmol),
o b
(
m g ) (cm g )
(nm)
3
2 2
0% H O (12 mmol), acetonitrile (10 mL), 70 C, 2 h. Conversion of
c
cyclooctene. Selectivity for the epoxide product.
1
2
3
4
5
6
7
OIM-PW
POSS-OIM -PW
POSS-OIM -PW
2.1
7.1
25.0
18.7
12.7
8.2
0.006
0.057
0.175
0.129
0.099
0.038
0.122
0.037
11.0
32.4
22.0
21.6
30.3
11.5
24.2
18.4
4
8
2
0
For example, when the molar ratio of OIM to POSS is 16:1, the
BET surface area and the pore volume are 12.7 m /g and 0.099
cm /g, respectively, and when the molar ratio of OIM to POSS is
POSS-OIM -PW
POSS-OIM -PW
1
2
2
1
6
3
POSS-BIM -PW
POSS-DIM -PW
POSS-HIM -PW
8
2
18.6
5.9
4:1, the BET surface area and the pore volume are only 7.1 m /g
8
3
8
and 0.051 cm /g, respectively. Therefore, the surface area and
8
a
b
c
BET surface area, Total pore volume, Average pore size.
25 pore structure can be adjusted flexibly through turning the POSS
content. These results further confirm that the POSS is significant
for the pore formation. With POSS and ILs at molar ratio of 1:8,
we further studied the effect of ILs bearing different length of
alkyl chains on the pore structure. As can be seen in Firgure 5C
pressure region of P/P0 = 0.8−1.0, indicating the presence of
mesoporosity. The BET surface area and the total pore volume
are 25.0 m /g and 0.175 cm /g, respectively (Table 1, entry 3).
The most probable distribution in mesopores appears at 22.0 nm.
However, the POSS-free polymeric hybrid OIM-PW is a
2
3
3
3
4
0
5
0
and 5D, although all the samples show typical type-IV isotherms,
giving a steep increase at a pressure of 0.8< P/P <1, the rather
0
5
0
5
short length or long length of alkyl chains led to low BET surface
2
nonporous material, with a surface area of only 3.4 m /g (Table 1,
2
areas (less than 10 m /g), pore volumes, and the most probable
entry 1). These results demonstrate that the POSS plays important
roles in the formation of mesotructures. The primary result
encouraged us to prepare and test a series of catalysts POSS-
pore sizes. This is probably due to that the ILs bearing short alky
chain is difficult to form micelle during the catalyst preparation
process, which is not beneficial for the formation of porous
structure, and the ILs bearing long alky chain may block up the
already formed channel of the final catalyst. Therefore, the
1
OIM -PW with different molar ratio of OIM to POSS, with the
x
nitrogen sorption isotherms and pore size distribution curves for
the resultant samples displayed in Fig 5(A) and (B), respectively.
Clearly, all the samples POSS-OIM -PW, POSS-OIM -PW, and
2
3
optimum specific surface 25.0 m /g and pore volume 0.175 cm /g
were obtained when the mole ratio of POSS to OIM was 1:8.
4
12
POSS-OIM -PW give typical type-IV isotherms at the pressure
1
6
1
of 0.8< P/P <1 and relative wide pore size distribution curves
3.2 Catalytic activity in the epoxidation reaction
0
with the most probable pore sizes of 25-35 nm (Table 1, entries
The catalytic performances of various catalysts were assessed
in the epoxidation of the probe substrate cyclooctene with
aqueous H O as oxidant and acetonitrile as solvent, and the
2
-5), reflecting a typical mesostructure. However, the low content
or high content of POSS tends to give less porous systems and
causes continuous decline in BET surface areas and pore sizes.
2
2

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New Journal of Chemistry
1
00
(A)
100
80
60
40
20
0
(B)
(a)
8
6
4
2
0
0
0
0
0
a
b
c
a
b
c
(b)
d
d
(c)
0
20 40 60 80 100 120 140 160 180
0
20 40 60 80 100 120 140 160 180
Reaction time (min)
Reaction time (min)
Figure 6. (A) Catalytic kinetics of (a) POSS-OIM
OIM -PW, (c) POSS-OIM12-PW, (d) POSS-OIM16-PW, and (B) catalytic
kinetics of (a) POSS-BIM -PW, (b) POSS-OIM -PW, (c) POSS-DIM
PW, (d) POSS-HIM -PW.
4
-PW, (b) POSS-
4000
3500
3000
1500
1000
500
-1
Wavenumber (cm )
8
8
8
8
-
Figure 7. FT-IR spectra of (a) fresh POSS-OIM
recycled POSS-OIM
8
-PW, (b) two
8
8 8
-PW, and (c) five recycled POSS-OIM -PW.
2 2
Table 3. Epoxidation of various alkenes with H O catalyzed by POSS-
a
8
OIM -PW .
b
c
Reaction
time (h)
Con
(%)
Sel
Entry
Substrate
(%)
100
94
d
1
Cyclooctene
Cyclohexene
1-octene
2
4
6
6
3
100/100/99/99/99
2
3
4
5
93
51
57
81
99
1-hexene
95
Bipentene
83
8
Figure 8. Catalytic activities of POSS-OIM -PW in epoxidation of
[a]
cyclooctene with H
Reaction conditions: catalyst (0.03 mmol), cyclooctene (10 mmol),
2
O
2
in different solvents.
Cis-3-
hexenol
[a]
6
7
4
6
90
72
97
66
o
3
2 2
0% H O (12 mmol), solvent (10 mL), 70 C.
Styrene
a
Reaction conditions: catalyst (0.03 mmol), substrates (10 mmol), 30%
25 that the POSS units are indispensable for the high activities of the
target PW catalyst for epoxidation of cyclooctene with H O .
Moreover, the polymer hybrid catalysts bearing hydrophobic tails
of different lengths might supply a different microenvironment on
the surface of the catalyst for the reactions and strongly affect the
30 catalytic activity.
o
b
H
2
O
2
(12 mmol), acetonitrile (10 mL), 70 C.
Conversion of
2
2
c
d
cyclooctene. Selectivity for the epoxide product. Five-run recycling
test. Byproducts for entry 2: 2-cyclohexen-1-ol ; entry 3: octylaldehyde;
entry 4: 2-hexenone; entry 5: 3,4-epoxyhexane-1-aldehyde; entry 6: 1,2-
ene-p-menth-8,9-epoxy; entry 7: benzaldehyde.
The results in Table 2 demonstrate that most of the catalysts
results are summarized in Table 2. In the absence of catalyst, the
POSS-IL -PW could catalyze the epoxidation of cyclooctene with
x
reaction did not proceed at all (entry 1). The POSS-OIM and
H O in the reaction time of 2 h, giving satisfactory activities and
8
2
2
pure H PW O display very low activities and poor selectivity
selectivity. However, during the reaction process, we found that
3
12 40
(entries 2 and 3). We were glad to find that the newly synthesized 35 the catalytic reaction rate of POSS-IL -PW has the obvious
x
5
0
5
0
mesoporous catalyst POSS-OIM -PW caused a heterogeneous
catalysis, and exhibit very high conversion of 99% with 100%
difference. Thus, we tested the catalytic kinetics of POSS-IL -PW
8
x
for the epoxidation of cyclooctene in acetonitrile solvent. The
results are illustrated in Figure 6A and 6B. For all these catalysts,
the increase of the reaction time led to a smoothly increase in the
selectivity (entry 5). Other mesoporous samples POSS-OIM -PW
x
with different molar ratio of OIM to POSS also show excellent
activities (> 95%) (entries 6 and 7), with the exception of POSS- 40 cyclooctene conversion, the maximum conversions were
1
1
2
OIM -PW that offer a 81% conversion (entry 4), but it is still
achieved at the reaction time of 3 h. Among which, POSS-OIM8-
PW exhibits the fast reaction rate, the conversion reached nearly
90% at the reaction time of only 30 min, and the reaction can be
completed within 1 h.
Encouraged by the above results, other alkene substrates such
as cyclohexene, 1-octene, 1-hexenel, bipentene, cis-3-hexeno and
4
much higher than that of POSS-free nonporous sample OIM-PW,
which shows a 52% conversion with 98% selectivity (entry 11).
The above results suggest that the excellent performance of
POSS-OIM -PW may be relates to the mesoporous structure. For
45
x
the catalysts POSS-IL -PW containing different IL, POSS-BIM -
8
8
PW having a C4 hydrophobic tail displays a 90% conversion
entry 8), which is lower than those of the catalysts POSS-OIM8-
PW, POSS-DIM -PW and POSS-HIM -PW carrying C8, C12,
styrene were also investigated on the catalyst POSS-OIM -PW,
8
(
with the results list in Table 3. It can be seen that the present
catalyst POSS-OIM -PW could be applied to the epoxidation of
8
8
8
and C16 alkyl chain, respectively (entries 5, 9 and 10). Also 50 various alkenes using H O , and optimum results of activities and
2
2
notably, for the POSS-free samples containing different IL, the
increase of the length of alkyl chain in IL leads to continuous
increase in the catalytic conversion from 45% to 80% (entries 11-
selectivity were obtained as well. To assess catalytic reusability
POSS-OIM -PW was recovered simply by filtration and then
8
reused for the next run without adding any fresh catalyst. Table 3
entry 1 displays the result of the five-run recycling test of POSS-
1
4). However, they are much lower than those of the POSS-
containing ones. The above special comparisons further indicate 55 OIM -PW for the epoxidation of cyclooctene. There is no
8

View Article Online
DOI: 10.1039/C5NJ01541C
New Journal of Chemistry
Page 6 of 8
Figure 9. Possible mechanism for biphasic epoxidation of alkenes over amphiphilic catalysts.
decrease in the conversion is observed in the recycling runs,
implying good potential for catalyst reuse. Further, the IR spectra
structure of the catalyst allows a more efficient extractiion and
mass transfer of the substrate to interact with the W peroxo active
of the recycled catalysts (Figure 7) are well consistent with that 45 species and thus promote the catalytic epoxidation performance.
of the fresh one, revealing a durable catalyst structure.
5
0
5
0
Figure 8 shows the catalytic performances of POSS-OIM -PW
4. Conclusion
8
in the epoxidation of cyclooctene with H O in different solvents
2
2
In summary, we have demonstrated the successful application
of octavinyl Polyhedral oligomeric silsesquioxanes (POSS) and
ionic liquids as building blocks for constructing mesostructured
amphiphilic Polyoxometalates (POM)-paired ionic hybrids
POSS-ILx-PW via free radical polymerization and ion exchange
reaction. The obtained hybrids were found to be highly efficient
catalysts for epoxidation of cyclooctene with H O as the oxidant.
The catalyst was recovered easily and reused for five runs
without observing loss in catalytic activity. The overall superior
catalytic activity, high selectivity and excellent recyclability of
POSS-ILx-PW as a heterogeneous catalyst could be attributed to
its amphiphilic surface and mesoporous structure, which allow
for a rapid diffusion of the reactants into the reactive PW centers.
over the reaction times of 1 h, 2 h, and 3 h, respectively. During
the reaction process, the catalyst POSS-OIM -PW was insoluble
8
in all cases, and exhibited different catalytic activities with
satisfying selectivity above 99%. In the acetonitrile, ethanol, and
methanol solvent, liquid-solid heterogeneous catalysis system
was observed, and excellent conversions were obtained after the
reaction time of 2 h. With ethyl acetate and dichloroethane as the
solvent, a liquid-liquid biphasic reaction system was formed due
to the immiscibility of these solvents with aqueous H O . To our
5
0
1
1
2
2
2
55
2
2
delight, the catalyst POSS-OIM -PW also afforded very high
8
activities and selectivity. It is worth noting that an emulsion states
emerged in these biphasic reaction system after the catalyst
POSS-OIM -PW was added and stirred. Similarly, the polymeric
8
hybrids with longer alkyl side chains also acted as very active
emulsion catalysts. Therefore, we suggest that the excellent
60
Acknowledgements
catalytic activity of POSS-OIM -PW for epoxidation of alkenes
largely arises from its unique amphiphilic catalyst structure.
x
The authors thank the National Natural Science Foundation of
China (Nos. 21206052 and 21136005), the Opening Foundation
of the State Key Laboratory of Materials-Oriented Chemical
Engineering (No. KL13-09), and MOE & SAFEA for the 111
Project (No. B13025).
3
.3 Insight into the catalystic behavior of POSS-IL -PW
x
65
2
3
3
4
5
0
5
0
In order to confirm the amphipathicity of these polymeric
hybrid catalysts, the emulsifying property of POSS-OIM -PW in
8
Notes and references
H O /cyclooctene are examined and shown in Figure 9. The
2
2
a
catalyst tends to migrate toward the oil/aqueous interface, and
metastable emulsions with droplet size of about 0.4 mm are
formed after stirring. The phenomenon observed here well
The Key Laboratory of Food Colloids and Biotechnology, Ministry of
Education, School of Chemical and Material Engineering, Jiangnan
University, Wuxi 214122, China. Fax: +86-510-85917763; Tel: +86-510-
85917090; E-mail: lengyan1114@126.com.
7
7
0
5
demonstrates the amphiphilic nature of POSS-OIM -PW, and is
8
b
State Key Laboratory of Materials-Oriented Chemical Engineering,
[
36-
well consistent with that of the Pickering Interfacial Catalysis
College of Chemistry and Chemical Engineering, Nanjing Tech
University, Nanjing 210009, China.
† Electronic Supplementary Information (ESI) available: Catalyst
characterizations. See DOI: 10.1039/b000000x/.
3
7]
,
that the amphiphilic solid catalysts distributed mainly on the
surface of the emulsion droplets, allowing facile separation and
recycling. In terms of the above control experiments and the
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New Journal of Chemistry
Page 8 of 8
View Article Online
DOI: 10.1039/C5NJ01541C
Graphical Abstract
POSS-Derived Mesoporous Ionic Copolymer-Polyoxometalate
Catalysts with Surfactant Function for Epoxidation Reactions
[
a]
[a]
[a]
[b]
[a]
Jiwei Zhao ,Yan Leng* , Pingping Jianj , Jun Wang , and Chenjun Zhang
a
The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and
Material Engineering, Jiangnan University, Wuxi 214122, China;Tel: ++86-510-85917090;
E-mail: lengyan1114@126.com
b
State Key Laboratory of Materials-Oriented Chemical Engineering,College of Chemistry and Chemical
Engineering, Nanjing Tech University, Nanjing 210009, China.
Novel Mesoporous POSS-derived POM-paired polymeric hybrids were demonstrated to be
2 2
highly efficient interfacial solid catalysts for epoxidation of alkenes with H O .