Palladium nanoparticles immobilized onto supported ionic liquid-like phases (SILLPs) for the carbonylative Suzuki coupling reaction

Article abstract of DOI:10.1039/c5ra00443h

Crosslinked polymeric materials based on poly(ionic liquid)s, also named supported ionic liquid-like phases (SILLPs) were prepared by copolymerization of dication imidazole ionic liquids with divinylbenzene (DVB). Using the SILLPs-related polymeric materials as supports, palladium (Pd) metal nanoparticles were immobilized and stabilized, which can efficiently catalyze the carbonylative Suzuki coupling reaction of aryl iodides with aryl boronic acids, affording the corresponding products in good to excellent yields. The Pd nanoparticles immobilized onto SILLPs were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TG), and X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR). The size and dispersion of the Pd nanoparticles supported on polymers are influenced possibly by varying the contents of the ionic liquid units and the introduction of amine groups. Furthermore, hot filtration and mercury poisoning tests indicated that the palladium species leached into the solvent during the reaction and returned to the polymers after the reaction was completed. In addition, the catalyst was easily recovered from the reaction mixture by filtration and reused over five consecutive cycles without a significant decrease in its activity. This journal is

Full text of DOI:10.1039/c5ra00443h

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Palladium nanoparticles immobilized onto
supported ionic liquid-like phases (SILLPs) for the
Cite this: RSC Adv., 2015, 5, 26913
carbonylative Suzuki coupling reaction†
ab
a
a
a
a
Nianming Jiao, Zelong Li, Yan Wang, Jianhua Liu* and Chungu Xia
Crosslinked polymeric materials based on poly(ionic liquid)s, also named supported ionic liquid-like phases
SILLPs) were prepared by copolymerization of dication imidazole ionic liquids with divinylbenzene (DVB).
(
Using the SILLPs-related polymeric materials as supports, palladium (Pd) metal nanoparticles were
immobilized and stabilized, which can efficiently catalyze the carbonylative Suzuki coupling reaction of
aryl iodides with aryl boronic acids, affording the corresponding products in good to excellent yields.
The Pd nanoparticles immobilized onto SILLPs were characterized by transmission electron microscopy
(TEM), thermogravimetric analysis (TG), and X-ray photoelectron spectroscopy (XPS), Fourier transform
infrared spectroscopy (FT-IR). The size and dispersion of the Pd nanoparticles supported on polymers
are influenced possibly by varying the contents of the ionic liquid units and the introduction of amine
groups. Furthermore, hot filtration and mercury poisoning tests indicated that the palladium species
leached into the solvent during the reaction and returned to the polymers after the reaction was
completed. In addition, the catalyst was easily recovered from the reaction mixture by filtration and
reused over five consecutive cycles without a significant decrease in its activity.
Received 9th January 2015
Accepted 4th March 2015
DOI: 10.1039/c5ra00443h
www.rsc.org/advances
nanoparticles on suitable supports to prepare heterogeneous
catalysts has attracted much attention in the eld of catalysis.
Introduction
Biaryl ketones are multipurpose building blocks in the eld of Different supports have been used to stabilize the nano-
6
7
8
pharmaceuticals, natural products, agrochemicals and biolog- particles, such as carbon, silica, molecular sieves and
1
9
ically active compounds. Among many synthetic well- polymers.
documented methods, Friedel–Cras acylation of substituted
Recently, ionic liquids (ILs) have been one of interesting
2
aromatic rings and the acylation of aryl metal species with subjects of scientic study because of their interesting and
functional carboxylic acid derivatives are two usual potentially useful physicochemical properties, including high
3
approaches. But the former is incompatible with many func- ion conductivity, chemical stability, non-ammability and near
10,11
tional groups due to using Lewis acids, and the latter could not absence of vapor pressure.
ILs are proving to be an excellent
avoid the formation of biaryl side products. The palladium- ‘green’ solvent with signicant potential for the traditional
12
catalyzed carbonylative Suzuki coupling reaction of aryl organic synthesis and catalytic reactions. Although ILs have
halides or triates, carbon monoxide (CO) and aryl boronic become commercially available, they are still relatively expen-
acids (or aryl metal reagents) is an attractive route for the sive compared with traditional solvents. Nowadays, the immo-
4
synthesis of biaryl ketones. Although the palladium-catalyzed bilization of ILs onto a solid support, which providing a simple
three component cross-coupling reactions have been reported way for reducing the amount of IL, has been widely investi-
5
13
extensively, most of them were homogeneous without any gated. The immobilized ionic liquids as catalyst supports not
consideration of recyclability and separation of catalyst and only take advantage of excellent physicochemical properties of
product, which limited their applications. In this context, it is ionic liquid, but also realize recycling catalysis and ease
14
desirable to develop heterogeneous and ligand free palladium catalyst-product separation. Many immobilized ionic liquids
catalysis protocols. Immobilization of the palladium have been used to stabilize Pd catalysts. For example, Babak
Karimi and coworkers anchored an imidazolium ionic liquid
bearing triethylene glycol moieties on the surface of silica-
a
State Key Laboratory of Oxo Synthesis and Selective Oxidation, Lanzhou Institute of
coated iron oxide nanoparticles as Pd catalyst support, which
Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China.
E-mail: jhliu@licp.cas.cn; Fax: +86-931-827-7088; Tel: +86-931-496-8058
15
could recover Pd catalyst magnetically. Recently, Mart ´ı nez and
coworkers used laponite clay to immobilize ionic liquid [bmim]
b
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
[
PF ], and then Pd nanoparticles were stabilized into it. The
6
†
Electronic supplementary information (ESI) available: See DOI:
0.1039/c5ra00443h
1
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resulting catalysts showed excellent catalysis activity and recy- demonstrated that the size and dispersion of the Pd nano-
16
clability for the Mizoroki–Heck reaction.
particles in SILLPs are inuenced by varying the contents of IL
The immobilization of ILs onto a solid support is oen units and introduction of amine groups.
realized by either covalent or noncovalent bonds using various
methods, including simple physisorption, self-assembly or
polymerization. Poly(ionic liquid)s, also called polymerized Results and discussion
ionic liquids or polymeric ionic liquids, refer to polymeric
Two kinds of SIILPs were prepared by the synthetic approaches
compounds that feature an IL species in each monomer
repeating unit, connecting through a polymeric backbone,
which are obtained by polymerization of ILs having polymer-
outlined in Scheme 1. Differences between them focused
mainly on whether dication imidazole ionic liquids were
modied with amine groups. The SIILPs modied with amine
groups were prepared based on the different DVB–NDIIL mole
17
izable groups. The major advantages for such polymeric forms
of ILs are enhanced stability, improved processability, exi-
bility, and durability in applications. Obviously, the crosslinked
polymeric materials based on poly(ionic liquid)s, also named
supported ionic liquid-like phases (SILLPs), in which the IL-like
1
1
x
1
ratio. We obtained P(DVB –DIIL ) and P(DVB –NDIIL ) with x ¼
0
.5, 1, 3, 6. The ‘x’ means the DVB–NDIIL mole ratio. Then the
2
ꢀ
PdCl
4
as Pd precursor was absorbed in the polymers by ion
, the
exchange with halogen anion. Aer reduction by NaBH
4
18
fragment is covalently attached to the support is better.
1
1
x
catalysts were denoted as P(DVB –DIIL )–Pd and P(DVB –
NDIIL )–Pd. The exact contents of ILs in polymers were deter-
The framework of our continuous efforts is to develop
effective and green processes for the carbonylative coupling
1
mined by element analysis, listed in Table 1. In order to
investigate the effect of ionic liquid units, we xed the input
amount of Pd to be 2 wt%, and the exact loading amounts were
determined by AAS, as shown in Table 1.
TEM was used to examine the size and size distribution of Pd
nanoparticles supported on SIILPs (Fig. 1). The TEM images
19
reaction. In this paper, we report the synthesis of two kinds of
SILLPs based on dication imidazole ionic liquids supported
palladium catalysts and illustrate its application in the car-
bonylative Suzuki coupling reaction to synthesize biaryl ketones
without the addition of any phosphine ligands. The results
Scheme 1 Synthesis of SIILPs immobilized Pd nanoparticles.
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Table 1 The data of element analysis of SIILPs and Pd contents
1
1
6
1
3
1
1
1
0.5
1
Element
P(DVB –DIIL )
P(DVB –NDIIL )
P(DVB –NDIIL )
P(DVB –NDIIL )
P(DVB –NDIIL )
C (wt%)
50.6
9.75
43
84.9
1.9
4
71.0
8.8
23
56.8
12.6
41
50.8
14.7
54
N (wt%)
IL (mol%)
Pd (wt%)
1.86
1.99
2.14
2.06
2.24
showed that the polymers modied with amine groups metal nanoparticles (Fig. 1f and g). Only when the proportion of
distributed Pd nanoparticles better than the one without amine ILs came up to a higher level, could Pd nanoparticles be
1
1
1
2
groups. As shown in Fig. 1e, agglomeration apparently appeared dispersed well. P(DVB –NDIIL ) and P(DVB –NDIIL ) had rela-
1
1
1
1
on the P(DVB –DIIL ), which was attributed to P(DVB –DIIL ) tively high proportion of ILs, so we can see Pd nanoparticles
not being modied with amine groups. P(DVB –NDIIL ) and disperse well on them (Fig. 1a and c), and the particle sizes are
P(DVB –NDIIL ) did not disperse Pd nanoparticles well, because so small that the characteristic diffraction peaks of Pd are not
there are not enough units of ILs with amine groups to stabilize observed under X-ray diffraction patterns. When we used these
6
1
3
1
Fig. 1 TEM and distribution of particle size images of the catalysts.
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Fig. 2 The FT-IR spectra of polymers and catalysts.
1
1
1
1

ve catalysts to catalyze carbonylative Suzuki coupling reaction pyrolysis of P(DVB –NDIIL ) and P(DVB –NDIIL )–Pd appearing
ꢁ
ꢁ
of iodobenzene with phenyl boronic acid, the obtained yields between 230 C and 350 C, which was attributed to the elimi-
were 56% [P(DVB –DIIL )–Pd], 49% [P(DVB –NDIIL )–Pd], 79% nation of the dication ionic liquids immobilized on the poly-
1
1
6
1
3
1
1
1
ꢁ
[P(DVB –NDIIL )–Pd],
85%
[P(DVB –NDIIL )–Pd],
87% mers. The weight loss above 390 C was due to the
0
.5
1
1
[
P(DVB –NDIIL )–Pd]. On the one hand, the polymer P(DVB – decomposition of PDVB. The results show that the catalyst can
1
ꢁ
NDIIL ) prepared by DVB (mol)/NDIIL (mol) ¼ 1 could disperse tolerate up to 230 C.
1
1
Pd nanoparticles very well. On the other hand, increasing
The catalyst P(DVB –NDIIL )–Pd was used to catalyze car-
content of NDIIL in polymers did not improve yield drastically. bonylative Suzuki reaction. In order to optimize the reaction
Therefore, in order to save expensive ionic liquid, we chose
1
1
P(DVB –NDIIL )–Pd as catalyst to catalyze carbonylative Suzuki
Table 2 The effect of reaction parameters on catalytic activity of
carbonylative Suzuki–Miyaura reaction of iodobenzene with phenyl
boronic acid
coupling reaction.
1
1
1
The polymer SIILPs, P(DVB –DIIL )–Pd and P(DVB –
a
1
NDIIL )–Pd were characterized by FI-IR, and the results are
shown in Fig. 2. Both spectra show an asymmetric broad band
ꢀ1
at around 3420 cm , which is attributed to the stretching
vibration of the C–H in imidazole rings and the N–H in amine
groups. From Fig. 2a and b, we can see that the spectra are very
similar before and aer immobilizing Pd nanoparticles, sug-
gesting that the structures of polymers remain intact. Fig. 2c
ꢁ
b
Entry
Solvent
Base
Time (h)
Temp ( C)
Yield (%)
ꢀ
1
shows that the broad bands at around 3420 cm become small
gradually, which is consistent with the proportions of ionic
liquid in polymers.
The effect of the solvent
1
2
3
4
5
6
Toluene
Anisole
THF
Acetonitrile
Water
K2CO3
CO
K2CO3
12
12
12
12
12
12
120
120
120
120
120
120
85
80
46
34
15
20
K
2
3
1
1
1
1
The polymers P(DVB –NDIIL ) and catalyst P(DVB –NDIIL )–
K
2
K
2
K
2
CO
CO
CO
3
3
3
Pd were characterized by thermogravimetric analysis. The
ꢁ
thermograms are shown in Fig. 3. The weight loss before 230 C
NMF
resulted from the loss of the adsorbed water. There were the
The effect of the base
7
8
9
Toluene
Toluene
Toluene
Na
Cs
Et
2
CO
3
12
12
12
120
120
120
45
62
20
2
CO
N
3
3
The effect of time
10
11
12
Toluene
Toluene
Toluene
K
K
K
2
CO
CO
CO
3
3
3
10
8
14
120
120
120
75
64
85
2
2
The effect of CO pressure
c
1
1
3
4
Toluene
Toluene
K
K
2
CO
CO
3
12
12
120
120
67
86
d
2
3
The effect of temperature
1
1
5
6
Toluene
Toluene
K
K
2
CO
CO
3
12
12
100
140
61
85
2
3
a
Reaction conditions: iodobenzene (1 mmol), phenyl boronic acid (1.4
1
1
mmol), P(DVB –NDIIL )–Pd (1.0 mol%), base (3 mmol), solvent (10 mL),
CO (3 MPa). Isolated yield. CO pressure 2 MPa. CO pressure 4 MPa.
b
c
d
1
1
1
1
Fig. 3 The thermogram of P(DVB –NDIIL )–Pd and P(DVB –NDIIL ).
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a
Table 3 Carbonylative Suzuki coupling reaction of aryl iodides with various aryl boronic acids
b
Entry
1
Aryl iodide
Aryl boronic acid
Product
Yield (%)
85
87
2
3
4
5
85
80
61
6
7
83
60
8
9
71
88
85
65
1
1
0
1
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Table 3 (Contd.)
b
Entry
Aryl iodide
Aryl boronic acid
Product
Yield (%)
12
13
14
67
72
71
1
1
5
6
67
75
1
1
1
7
8
9
57
79
N.R
2
0
N.R
a
1
1
Reaction conditions: aryl iodide (1 mmol), aryl boronic acid (1.4 mmol), P(DVB –NDIIL )–Pd (1.0 mol%), K
2
CO
3
(3 mmol), toluene (10 mL), CO (3
ꢁ
b
MPa), 120 C, 12 h. Isolated yield.
conditions, various reaction parameters such as solvent, base, different solvents on the carbonylative Suzuki coupling reaction
reaction time, CO pressure and temperature were investigated, was studied (Table 2, entries 1–6). According to the evaluated
and the results are shown in Table 2. Firstly, the inuence of results of solvents, when nonpolar solvents, such as anisole and
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toluene, were used a relatively good yield of the carbonylative which may be attributed to that the methoxy group on m-posi-
cross-coupling product, benzophenone, could be obtained. tion led to reduction of the electron density of C-1 position
However, the yield of the carbonylative cross-coupling product connecting with boronic acid. The reaction of sterically
was relatively low in polar solvents, such as THF, DMF, ethanol hindered o-tolylboronic acid with iodobenzene provided lower
and water. These may be attributed to that nonpolar solvents yield (57%) of the desired product compared with 3,5-dime-
are more advantageous to the C–I insertion than polar solvents, thylphenylboronic acid, whose yield was 75% (Table 3, entries
20
which is consistent with previous study. Next, we chose 16 and 17). Moreover, 2-naphthaleneboronic acid also reacted
toluene as reaction solvent to screen suitable base (Table 2, with iodobenzene, affording 79% yield of the corresponding
entries 7–9). Compared with the organic base (Et
3
N), the inor- ketone (Table 3, entry 18). It should be pointed out that the
ganic bases (Na CO , K CO and Cs CO ) showed better activi- carbonylative coupling reaction of bromobenzene (or chloro-
2
3
2
3
2
3
ties. Among the three inorganic bases, K CO gave the best benzene) with phenyl boronic acid did not occur (Table 3,
2
3
yields. We also investigated the effect of the pressure of CO, with entries 19 and 20), because the dissociation energy of the C–Cl
ꢀ
1
decreasing the pressure of CO from 3 to 2 MPa, the yield or C–Br bond is comparatively high (402, 339, and 272 kJ mol
21
decreased from 85 to 65%, respectively. However, with for PhCl, PhBr, and PhI, respectively, at 298 K).
increasing the pressure of CO, the improving of the product To obtain information about the heterogeneity or homoge-
yield was not observed (Table 2, entries 13 and 14), which might neity of the catalytic reaction, hot ltration and mercury
22
indicate that when the CO pressure came up to 3 MPa, continue poisoning tests were carried out. At rst, the relationship
to increase CO concentration played little role in reaction. In the between the progress of reaction and time was depicted in Fig. 4
ꢁ
case of temperature study, at 100 C, the yield of the desired (reaction conditions: 1 mmol iodobenzene, 1.4 mmol phenyl
ꢁ
1
1
product was lower than the one at 120 C (Table 1, entry 15). boronic acid, 1.0 mol% P(DVB –NDIIL )–Pd, 3 mmol K CO ,
2
3
ꢁ
ꢁ
However, when the temperature increased to 140 C, the yield of 10 mL toluene, 3 MPa CO, 120 C), which revealed that the
the desired product did not increase obviously (Table 1, entry reaction rate was maximum at the range of 5–7 h. Thus, we
ꢁ
1
6), suggesting that in this catalysis system, 120 C might reach chose the point of 6 h for the following experiments. The cata-
ꢁ
the vertex of the catalyst activity. Therefore, the optimum lyst was ltered out at above 100 C aer the reaction proceeded
reaction conditions for carbonylative Suzuki coupling reaction for 6 h and the yield of benzophenone was 49% determined by
of iodobenzene with phenyl boronic acid were found to be: GC. The obtained ltrate with additional 1.0 mmol phenyl
P(DVB –NDIIL )–Pd (53 mg, 1.0 mol% relative to iodobenzene), boronic acid was continually stirred under the reaction condi-
toluene (10 mL) as solvent, K CO (3 mmol) as base, under tions. Aer 10 hours the conversion was determined to be 56%.
1
1
2
3
ꢁ
3
MPa of CO pressure at 120 C for 12 hours.
The same approach was applied to mercury test. Aer the rst
With the optimized reaction conditions, we extended the stage, the yield of benzophenone was 49%. In the second stage,
scope of carbonylative Suzuki reaction to a variety of different aer mercury (0.5 mL, 6.8 g) was added into the ltrate, the
aryl iodides with various phenyl boronic acids. As shown in ltrate was stirred for another ten hours under the reaction
Table 3, various electron-donating and electron-withdrawing conditions. The yield of benzophenone remained to be 49%.
groups such as –Me, –OMe, –NH , –COMe, –NO , –OH, –Br These phenomena show that a small amount of catalytically
2
2
and –Cl on both aryl iodide and aryl boronic acid smoothly active palladium species may have leached to the reaction
underwent carbonylative Suzuki coupling reaction giving mixture. But the contents of Pd in catalyst before and aer
desired products with appreciable yields. Iodobenzene reacted reaction were 2.06% and 2.04% respectively, determined by
with phenyl boronic acid giving 85% yield of benzophenone AAS. These indicate that most of Pd species leaching into
(Table 3, entry 1). It was observed that the p-iodoaryl with
electron-donating groups such as –CH and –OCH gave excel-
3
3
lent results (Table 3, entries 2 and 3) while iodoaryl with
electron-withdrawing groups such as –NO2 and –COMe
decreased the yields of the corresponding products (Table 3,
entries 7 and 8). The iodoaryl with ortho-substituents also
decreased the yield due to the steric effect (Table 3, entries 4–6).
p-Chloroiodobenzene and o-bromoiodobenzene could react
with phenyl boronic acid to convert into corresponding prod-
ucts, and excellent yields were obtained (Table 3, entries 9 and
10). Aryl boronic acids with various substituent groups were also
investigated and the corresponding products were also
obtained (Table 3, entries 11–18). It indicated that p-aryl
boronic acids containing the electron-withdrawing groups, such
as –Cl and –Br (Table 3, entries 11 and 12), produced relatively
lower yields of the carbonylative coupling products than the
ones with the electron-donating groups, such as –OCH
3
and
Fig. 4 Yield vs. reaction time plot for carbonylative Suzuki reaction of
1
–
CH (Table 3, entries 13 and 14). However, 3-methoxy-
3
iodobenzene with phenyl boronic acid catalyzed by catalyst P(DVB –
1
phenylboronic acid did not improve the yield (Table 3, entry 15), NDIIL )–Pd.
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1
1
XPS spectra were measured for the catalyst P(DVB –NDIIL )–
th
Pd before reaction and aer the 5 recycle, and the results are
shown in Fig. 6. It can be seen that in the Pd 3d region, two
1
1
peaks at 341.0 eV and 335.8 eV for P(DVB –NDIIL )–Pd corre-
spond to 3d5/2 and 3d3/2 for Pd(0) species. The peaks of 337.0
2
+
2+
(
Pd 3d5/2) and 342.2 eV (Pd 3d3/2) also appear in spectra,
2
+
suggesting that a small number of unreduced Pd ions still
th
exist in catalyst. As for the catalyst aer 5 recycle, the area of
2
+
2+
Pd ions is smaller than the fresh one, suggesting that Pd was
th
slightly reduced by CO aer 5 recycle.
Conclusions
In conclusion, SIILPs based on DVB and dication imidazole
ionic liquids modied with amine groups were synthesized and
proved to be an effective support for palladium nanoparticles.
The precursor of Pd was adsorbed and dispersed effectively by
1
1
Fig. 5 Recyclability of P(DVB –NDIIL )–Pd catalyst in carbonylative
Suzuki reaction of iodobenzene with phenyl boronic acid.
ꢀ
2ꢀ
ion-exchange of Cl for PdCl
4
. By comparison, amine groups
solution are recaptured onto the polymers aer completion of
the reaction. Furthermore, according to the recyclability exper-
iment (Fig. 5), Pd recaptured by the polymers remained active
when it was used in the next cycle. The results show that ionic
liquid units graed on the polymers provide a micro-
environment analogous to ionic liquids so as to prevent the
agglomeration of Pd nanoparticles. In addition, such results are
consistent with the previous reports, in which the Pd nano-
particles can realize the decoordination and coordination again
in this system.
modied in polymers are necessary for stabilizing Pd nano-
particles. Furthermore, a relatively high proportion of ionic
liquid units in polymers is advantageous to disperse Pd nano-
particles. The Pd nanocatalysts immobilized on the ionic liquid
polymers exhibited high catalytic activity in the carbonylative
Suzuki coupling reaction of aryl iodides with aryl boronic acids.
In addition, the catalyst could be easily separated from the
products and recycled up to ve consecutive times.
23
In order to evaluate the recyclability of the catalyst, the Experimental section
reusability was examined for the carbonylative coupling reaction
of iodobenzene with phenyl boronic acid, and the results are
presented in Fig. 5 (reaction conditions: 1 mmol iodobenzene,
All chemicals are analytical grade. Divinylbenzene (DVB) was
purchased from Alfa Aesar. N-Vinylimidazole, bis(2-chloroethyl)
amine hydrochloride, 1,4-dibromobutane, aryl iodides and aryl
2 4
boronic acids was provided by Energy Chemical. Na PdCl was
provided by Shanxi Kaida Chemical Engineering Co. Ltd. The
other chemicals were purchased from Tianjin Kaitong Chemical
Reagent Co. Ltd. The chemicals were used without further
purication except azobis(isobutyronitrile) (AIBN) used aer
recrystallization.
1
1
1
3
.4 mmol phenyl boronic acid, 1.0 mol% P(DVB –NDIIL )–Pd,
ꢁ
mmol K
2
CO
3
, 10 mL toluene, 3 MPa CO, 120 C, 12 h). The
1
1
catalyst P(DVB –NDIIL )–Pd could be reused effectively in ve
consecutive cycles, although the yield decreased slightly, which
might be attributed to leaching of Pd and slight aggregation of
the Pd nanoparticles (Fig. 1h). The content of Pd in catalyst aer
ve cycles was 1.75 wt%, determined by AAS analysis.
2 4 2
Preparation of [(VIM) C N]Cl (NDIIL)
0
0
To prepare the monomer 3,3 -(2,2 -azanediylbis(ethane-2,1-
diyl))bis(1-vinyl-1H-imidazol-3-ium)chloride (NDIIL), 1-vinyl-
imidazole (11.3 g, 0.12 mol), bis(2-chloroethyl)amine hydro-
chloride (8.92 g, 0.05 mol) and ethanol (80 mL) were added to a

ask equipped with a magnetic stirrer under an argon atmo-
ꢁ
sphere. The mixture was reuxed at 90 C for 4 days. Then, the
white precipitate was centrifuged and washed by acetone (50
ꢁ
mL ꢂ 3) and ethanol (50 mL ꢂ 3). Aer drying at 40 C under
0
0
vacuum, 3,3 -(2,2 -azanediylbis(ethane-2,1-diyl))bis(1-vinyl-1H-
1
imidazol-3-ium)chloride hydrochloride was obtained. H NMR
(
400 MHz, MeOD) d 9.54 (s, 2H), 8.04 (t, J ¼ 1.8 Hz, 2H), 7.90 (t, J
¼
1.8 Hz, 2H), 7.28 (dd, J ¼ 15.6, 8.7 Hz, 2H), 5.97 (dd, J ¼ 15.6,
2
3
.7 Hz, 2H), 5.48 (dd, J ¼ 8.7, 2.7 Hz, 4H), 4.80 (t, J ¼ 5.9 Hz, 4H),
1
3
.74 (t, J ¼ 5.9 Hz, 4H), 3.30 (dt, J ¼ 3.3, 1.6 Hz, 1H). C NMR
(101 MHz, MeOD) d 137.71, 129.92, 124.66, 121.40, 110.70,
Fig. 6 XPS spectrum of the Pd 3d edge of fresh and used catalyst
1
1
P(DVB –DIIL )–Pd.
48.39, 46.99. Element analysis: C (44.9%), N (18.7%), H (7.2%).
26920 | RSC Adv., 2015, 5, 26913–26922
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Preparation of [(VIM)
2
C
4
]Br
2
(DIIL)
replaced by CO, the autoclave was lled with 3 MPa CO. The
reaction mixture was heated at 120 C for 12 h. Aer reaction,
ꢁ
0
1,4-butanediyl-3,3 -bis-l-
To
prepare
the
monomer
24
the autoclave was cooled to room temperature and the
remaining CO gas was carefully released. The autoclave was
thoroughly washed with MeOH. The clear liquid was obtained
by ltration and the carbonylative product was puried by
column chromatography (silica gel, 100–200 mesh; petrol ether/
ethyl acetate ¼ 10 : 1). All isolated products were characterized
vinylimidazolium dibromine, 1-vinylimidazole (9.42 g, 0.10
mol), 1,4-dibromobutane (10.80 g, 0.05 mol) and acetone (50
mL) were added to a ask equipped with a magnetic stirrer. The
mixture was reuxed at 60 C with stirring for over 24 h under
an argon atmosphere. Then, the white precipitate was centri-
ꢁ
fuged and washed by acetone (30 mL ꢂ 3) and chloroform (30
1
13
ꢁ
by FT-IR, H and C NMR spectra. The spectral data of known
mL ꢂ 3). Aer drying at 40 C under vacuum, 1,4-butanediyl-
25,26
0
1
compounds are consistent with those reported.
3
,3 -bis-l-vinylimidazolium dibromine was obtained. H NMR
(
400 MHz, DMSO) d 9.51 (s, 1H), 8.23 (t, J ¼ 1.8 Hz, 1H), 7.94 (t, J
Procedure for recycle reaction
¼
1.7 Hz, 1H), 7.31 (dd, J ¼ 15.6, 8.8 Hz, 1H), 5.97 (dd, J ¼ 15.6,
2
2
1
.4 Hz, 1H), 5.45 (dd, J ¼ 8.7, 2.4 Hz, 1H), 4.26 (s, 2H), 1.85 (s, Aer reaction, the catalyst was obtained by centrifugation
13
H). C NMR (101 MHz, DMSO) d 135.45, 128.87, 123.23, separation and washed with distilled water (10 mL ꢂ 3) and
19.16, 108.68, 48.37, 25.69. Element analysis: C (41.3%), N methanol (10 mL ꢂ 3). Aer dried under vacuum, the resulting
(
13.5%), H (6.7%).
catalyst was used for the next carbonylation reaction.
Preparation of P(DVB–NDIIL)
Characterization
To prepare P(DVB–NDIIL), DVB (1.302 g, 10.0 mmol), AIBN (0.10
g, 2 wt%) and NDIIL (3.66 g, 10.0 mmol) were dissolved in
methanol (60 mL) under argon. The mixture was reuxed at 90
Transmission electron microscopy (TEM) images were per-
formed in a TECNAI G2 TF20 with a working voltage of 200 kV.
X-ray photoelectron spectroscopy (XPS) analyses of the catalysts
were performed on a Thermon Scientic ESCALAB250xi spec-
trometer. NMR spectra were recorded on a Bruker Avance TM III
ꢁ
19a
C with stirring under argon. Aer 12 h, a white solid was
centrifuged and was washed with deionized water (50 mL ꢂ 3)
and methanol (50 mL ꢂ 3). The nal product was treated with
equimolar NaOH and washed with water before being dried in
1
13
spectrometer operating at 400 MHz for H and 100 MHz for
C
with reference to tetramethylsilane (TMS) internal standard.
The FT-IR spectra were collected on a Bruker IFS120HR spec-
trometer. The elemental analysis was detected by Element vario
EL analyzer. X-ray photoelectron spectroscopy (XPS) data were
obtained using an Thermo Fisher Scientic KAlpha ESCALAB
ꢁ
vacuum at 80 C for 12 h. The other polymers were synthesized
with the desirable proportions under the same conditions.
Preparation of P(DVB–DIIL)
2
50Xi spectrometer. TG measurements were performed on a
To prepare the DVB-cross-linked polymers, DVB (1.302 g, 10.0
thermal analyzer (NETZSCH STA449F3) with a heating rate of 10
2 4 2
mmol), AIBN (0.11 g, 2 wt%) and [(VIM) C ]Br (4.041 g, 10
ꢁ
ꢀ1
19a
C min . Pd contents in the catalysts were examined by AAS
mmol) were dissolved in DMSO (60 mL) under argon. The
ꢁ
analysis using contrAA700 made in Germany. High resolution
mass spectrum (HRMS) were obtained on a Bruker Daltonics
micro TOF-QII spectrometer. GC-MS were measured on an
Agilent 7890/5795 GC-MS.
mixture was reuxed at 75 C with stirring under argon. Aer 12
h, a white solid was centrifuged and washed with deionized
water (50 mL ꢂ 3) and methanol (50 mL ꢂ 3) before being dried
ꢁ
in vacuum at 60 C for 12 h.
Preparation of the catalysts
Acknowledgements
The process for synthesis of catalyst is schematically shown in
Scheme 1. The metal precursor of Pd was adsorbed by ion-
This work was nancially supported by the National Natural
Science Foundation of China (no. 21373248 and no. 21133011).
ꢀ
2ꢀ
exchange of Cl for PdCl
dispersed in water and mixed with 28 mg Na
h, the solid was then separated by centrifugation and washed
several times by water. Finally, NaBH (40 eq.) aqueous solution
4
. 0.5 g of ionic liquid polymer was
18a
2
PdCl
4
.
Aer 10
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