Synthesis and characterization of Pd-poly(N-vinyl-2-pyrrolidone)/KIT-5 nanocomposite for Heck reaction

Article abstract of DOI:10.1016/j.materresbull.2011.09.018

Pd-poly(N-vinyl-2-pyrrolidone)/KIT-5 nanocomposite was prepared and characterized by XRD, FT-IR, UV-vis, BET and TEM techniques. The catalytic performance of this novel heterogeneous catalyst was determined for Heck reaction. Its stability was excellent and it could be reused eight times without much loss of activity in Heck reaction.

Full text of DOI:10.1016/j.materresbull.2011.09.018

Materials Research Bulletin 47 (2012) 160–166
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Short communication
Synthesis and characterization of Pd-poly(N-vinyl-2-pyrrolidone)/KIT-5
nanocomposite for Heck reaction
Roozbeh Javad Kalbasi *, Neda Mosaddegh
Department of Chemistry, Shahreza Branch, Islamic Azad University, 311-86145 Shahreza, Isfahan, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Pd-poly(N-vinyl-2-pyrrolidone)/KIT-5 nanocomposite was prepared and characterized by XRD, FT-IR,
UV–vis, BET and TEM techniques. The catalytic performance of this novel heterogeneous catalyst was
determined for Heck reaction. Its stability was excellent and it could be reused eight times without much
loss of activity in Heck reaction.
Received 26 May 2011
Received in revised form 21 August 2011
Accepted 22 September 2011
Available online 29 September 2011
ß 2011 Elsevier Ltd. All rights reserved.
Keywords:
A. Composites
A. Nanostructures
B. Chemical synthesis
D. Catalytic properties
1
. Introduction
Palladium-catalyzed Heck reaction between aryl halides and
Among the mesoporous materials, those consisting of inter-
connected large-pore cage-type mesoporous systems with three-
dimensional (3D) porous networks are highly interesting, and
promise supports for heterogeneous catalysis. In addition, they are
considered to be more advantageous than porous materials that
had a hexagonal pore structure with a two-dimensional (2D) array
of pores because they allow for a faster diffusion of reactants, avoid
pore blockage, provide more adsorption sites, and can be used for
processing large-sized molecules. SBA-16, SBA-1, and KIT-5 are a
few examples of porous materials possessing three-dimensional
cage-type porous structures [13–15]. Among them, KIT-5, discov-
ered by Ryoo et al., is a highly well-ordered cage type mesopore
with cubic Fm3m closely packed symmetry, high surface area, large
pores, and high specific pore volume [16]. Recently, Ryoo et al. have
reported the preparation of mesoporous silica KIT-5 materials
using tetraethyl orthosilicate (TEOS) as a silica source and Pluronic
F127 as a structure-directing agent in an aqueous solution at low
HCl concentration regime, without addition of any salt or organic
additives [17]. Furthermore, it was demonstrated that a simple
application of hydrothermal treatments at various temperatures
ranging from 45 8C to 150 8C facilitates the tailoring of the primary
mesopores, cages, and the apertures. These excellent tunable
parameters and interesting structure of KIT-5 potentially allow
one to use them as inorganic support for making heterogeneous
catalysts.
alkenes is one of the most valuable methods for carbon–carbon
bond formation in organic synthesis [1]. Most Heck coupling
reactions have been carried out in the presence of homogeneous
palladium catalysts [2,3]. However, the separation and recovery of
such homogeneous catalysts are not easy, and the resulting
products are often contaminated by Pd. Such problems can be
overcome by applying reusable and recoverable heterogeneous
catalysts [4].
In catalytic applications, a uniform dispersion of nanoparticles
and an effective control of particle size are usually expected.
However, nanoparticles frequently aggregate to yield bulk-like
materials, which greatly reduce the catalytic activity and
selectivity. Therefore, they must be embedded in a matrix such
as polymer [5], or immobilized in the pores of heterogeneous
supports [6] like ordered mesoporous silica. However, nanoparti-
cle-polymer composites usually suffer from disadvantages such as
absence of complete heterogeneity [1]. On the other hand,
although nanoparticle-mesoporous materials are completely
heterogeneous, the hydrophilicity of these catalysts causes a
reduction in the activity of such catalysts in organic reactions.
Therefore, preparation of polymer–inorganic hybrid catalysts
based on mesoporous silica materials with a hydrophobe–
hydrophile nature is interesting [7–12].
In continuing the previous activities to develop new organic–
inorganic hybrid materials as heterogeneous catalysts [9–12],
herein, a heterogeneous catalyst is introduced using a cage-type
mesoporous system with 3D porous networks. The catalytic activity
of this nanocomposite (Pd-poly(N-vinyl-2-pyrrolidone)/KIT-5) was
*
Corresponding author. Tel.: +98 321 3213211; fax: +98 321 3213103.
E-mail addresses: rkalbasi@iaush.ac.ir, rkalbasi@gmail.com (R.J. Kalbasi).
0025-5408/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2011.09.018

R.J. Kalbasi, N. Mosaddegh / Materials Research Bulletin 47 (2012) 160–166
161
1
13
tested for Heck reaction. This catalyst could be reused several times
at least 8) without significant loss of activity/selectivity.
isolated yield). The product was identified with H NMR, C NMR
and FT-IR spectroscopy techniques.
(
2
. Experimental method
3. Results and discussion
2.1. Catalyst characterization
3.1. Catalyst characterization
The samples were analyzed using FT-IR spectroscopy (using a
ꢀ1
Fig. 1 shows the powder XRD patterns of the silica KIT-5, PVP/
Perkin Elmer 65 in KBr matrix in the range of 4000–400 cm ). The
BET specific surface areas and BJH pore size distribution of the
samples were determined by adsorption–desorption of nitrogen at
liquid nitrogen temperature, using a Series BEL SORP 18. The X-ray
powder diffraction (XRD) of the catalyst was carried out on a
KIT-5 and Pd-PVP/KIT-5. Purely siliceous KIT-5 exhibits three
reflections in the region 2 = 0.7–38 which can be indexed to the
1 1 1), (2 0 0), and (2 2 0) reflections of cubic space group Fm3m
15]. The PVP/KIT-5 and Pd-PVP/KIT-5 (2 = 0.7–108) samples
u
(
[
u
show the same pattern indicating that the structure of the KIT-5
1 0 0) is well retained even after immobilization (Fig. 1). However,
Bruker D8Advance X-ray diffractometer using nickel filtered Cu K
a
(
radiation at 40 kV and 20 mA. Moreover, X-ray photoelectron
spectra (XPS) was recorded on ESCA SSX-100 (Shimadzu) using a
non-monochromatized Mg Ka X-ray as the excitation source. The
thermal gravimetric analysis (TGA) data were obtained by a
Setaram Labsys TG (STA) in a temperature range of 30–650 8C and
heating rate of 10 8C/min in N atmosphere. Transmission electron
2
microscope (TEM) observations were performed on a JEOL
JEM.2011 electron microscope at an accelerating voltage of
the intensity of the characteristic reflection peaks of the PVP/KIT-5
and Pd-PVP/KIT-5 samples are found to be reduced (Fig. 1). This
may be attributed to the symmetry destroyed by the hybridization
of KIT-5 which is also found in the ordered mesoporous silica
loading with guest matter [18].
The length of the cubic cell a
0
is calculated by using the formula
pffiffiffi
a
0
¼ d1 1 1 3 (Table 1). Compared to the d-spacing (or the pore
0
center distance a ) of KIT-5 and PVP/KIT-5, the incorporation of the
2
00.00 kV using EX24093JGT detector in order to obtain informa-
tion on the size of Pd nanoparticles and the DRS UV–vis spectra
were recorded with JASCO spectrometer, V-670 from 190 to
Pd nanoparticles into PVP/KIT-5 pores leads to the expansion of the
KIT-5 pore array (Table 1). These results are in good agreement
with that obtained in BET observations.
2
700 nm.
The wide-angle XRD pattern of the Pd-PVP/KIT-5 nanocompo-
site (2
7.908 and 81.848; and these peaks correspond to (1 1 1), (2 0 0),
2 2 0) and (3 1 1) lattice planes of Pd nanoparticles [19]. Planes
were assigned by being compared with Pd standard, and they
correspond to the fcc crystal lattice structure of Pd (JCPDS, Card No.
u = 30–908) (Fig. 1) shows the reflections at 39.928, 46.548,
2
.2. Catalyst preparation
6
(
The cage-type mesoporous silica KIT-5 was prepared through
the method described in the literature recently [15].
Pd-poly(N-vinyl-2-pyrrolidone)/KIT-5 was synthesized in two
steps. At first, poly(N-vinyl-2-pyrrolidone)/KIT-5 (PVP/KIT-5) was
prepared. N-vinyl-2-pyrrolidone (NVP) (0.5 mL, 4.6 mmol) and
KIT-5 (0.5 g) in 7 mL tetrahydrofuran (THF) were placed in a round
bottom flask. Benzoyl peroxide (0.034 g) was added and the
mixture was heated to 65–70 8C for 5 h while being stirred under
2
N gas. The resulting white fine powder composite (PVP/KIT-5) was
collected by filtration, washed several times with THF, and finally
dried at 60 8C under reduced pressure.
In the second step, PVP/KIT-5 (0.5 g) and 10 mL of an aqueous
acidic solution (CHCl = 0.09 M) of Pd(OAc)
were placed in a round bottom flask. The mixture was heated to
0 8C for 5 h while being stirred under N gas. Then, 0.6 mL
9.89 mmol) aqueous solution of hydrazine hydrates (N O)
ꢁH
80 vol.%) was added to the mixture drop by drop in 15–20 min.
2
(0.053 g, 0.236 mmol)
8
2
(
(
2
H
4
2
After that, the solution was stirred at 60 8C for 1 h. Afterwards, it
was filtered and washed sequentially with chloroform and
methanol to remove excess N
temperature to yield Pd-poly(N-vinyl-2-pyrrolidone)/KIT-5 (Pd-
PVP/KIT-5) nanocomposite. The Pd content of the catalyst
2
H
4
ꢁH
2
O, and was dried in room
ꢀ1
estimated by ICP-AES was 0.374 mmol g
.
2.3. General procedure for Heck reaction
In the typical procedure for Heck coupling reaction, a mixture of
iodobenzene (1 mmol), styrene (2 mmol), K CO (5 mmol), and
catalyst (0.14 g, Pd-PVP/KIT-5) in MeOH/H O (3/1, v/v) (5 mL) was
2
3
2
placed in a round bottom flask. The suspension was stirred at 60 8C
for 2 h. The progress of reaction was monitored by TLC using n-
hexane as eluent. After completion of the reaction (monitored by
TLC), for the reaction work-up, the catalyst was removed from the
reaction mixture by filtration, and then the reaction product was
extracted with CH
reduced pressure. The crude product was purified by flash column
chromatography to afford the desired coupling product (96%
2
Cl
2
(3ꢂ 5 mL). The solvent was removed under
Fig. 1. The powder XRD pattern of (a) mesoporous silica KIT-5, (b) PVP/KIT-5 and (c)
Pd-PVP/KIT-5.

1
62
R.J. Kalbasi, N. Mosaddegh / Materials Research Bulletin 47 (2012) 160–166
Table 1
Physicochemical properties of mesoporous silica KIT-5, PVP/KIT-5 and Pd-PVP/KIT-5 samples obtained from XRD and N
2
adsorption.
2
ꢀ1
3
ꢀ1
a
b
Sample
BET surface area (m g
)
V
P
(cm g
)
BJH pore diameter (nm)
2.62
d
1 1 1 (nm)
0
a (nm)
Mesoporous
silica KIT-5
PVP/KIT-5
1090
0.71
10.38
17.98
611
305
0.41
0.40
2.68
5.48
10.51
11.13
18.20
19.27
Pd-PVP/KIT-5
a
Total pore volume.
b
Unit cell parameter.
0
5-0681). The crystallite size of Pd particles was evaluated using
corresponding to carbonyl bond of PVP, is shifted to lower wave
ꢀ1
Scherrer equation which was found to be approx. 7 nm in size. The
size of the Pd nanoparticles, determined by using TEM analysis, is
more reliable than that determined by using Scherrer formula in
XRD analysis.
Fig. 2 presents the FT-IR spectra of KIT-5 (a), PVP/KIT-5 (b), and
Pd-PVP/KIT-5 (c). Similar to mesoporous silica KIT-5 (Fig. 2a), PVP/
KIT-5 and Pd-PVP/KIT-5 samples show the typical vibrations of
asymmetric and symmetric stretching as well as the rocking of Si–
O–Si at around 1080, 816, and 458 cm (Fig. 2). The existence of
PVP in the PVP/KIT-5 composite is evidenced by the appearance of
typical PVP vibration on the FT-IR spectrum (Fig. 2b). In the FT-IR
spectrum of PVP/KIT-5 (Fig. 2b), the new band at 1663 cm
corresponds to the carbonyl bond of PVP [20]. Moreover, the
numbers (1639 cm ). Moreover, the peak intensity of the
carbonyl bond in the spectrum of Pd-PVP/KIT-5 is lower than
that of PVP/KIT-5. This may be due to the interaction between Pd
nanoparticles and C 55 O groups. This means that the double bond
CO stretches become weak by being coordinated with Pd
nanoparticles [20].
Fig. 3 presents the TGA curves of KIT-5 (a), PVP (b), PVP/KIT-5
2
(c) and Pd-PVP/KIT-5 (d) under N atmosphere. The mass loss at
ꢀ
1
temperature <100 8C (around 3.5%, w/w) is attributed to
desorption of water present in the surfaces of the KIT-5
(Fig. 3a). The TGA curve of PVP shows a small mass loss (around
7.5%, w/w) in the temperature range of 50–150 8C, which is
apparently associated with adsorbed water (Fig. 3b). At
temperatures above 200 8C, PVP shows one main stage of
degradation. The mass loss for PVP in the second step is equal to
77% (w/w) which corresponds to the effective degradation of the
polymer (Fig. 3b). Thermo analysis of PVP/KIT-5 shows two steps
of mass loss (Fig. 3c). The first step (around 3%, w/w) that occurs
at 70 8C is related to desorption of water. The second step
ꢀ
1
ꢀ
1
presence of peaks at around 2800–3000 cm corresponds to the
aliphatic C–H stretching in PVP/KIT-5 (Fig. 2b). As shown in
Pd-PVP/KIT-5 spectrum (Fig. 2c), the band around 1663 cm
ꢀ
1
,
(
around 9%, w/w) which appeared at 270 8C is attributed to
degradation of the polymer, which ended at 580 8C (Fig. 3c). By
comparing the PVP and PVP/KIT-5 curves, one can find that the
weight loss of PVP/KIT-5 occurs at a higher temperature, it
illustrates that PVP/KIT-5 has higher thermal stability and
slower degradation rate than PVP (Fig. 3b and c). However, for
Pd-PVP/KIT-5 sample, two separate weight loss steps are seen
(
Fig. 3d). The first step (around 3%, w/w) appearing at
temperature <100 8C corresponds to the loss of water. The
second weight loss (about 500–580 8C) of around 8% (w/w) is
related to the degradation of the polymer. Obviously, the hybrid
Pd-PVP/KIT-5 shows slower degradation rate than PVP/KIT-5,
which may be attributed to the presence of Pd nanoparticles
in the composite structure. By comparing the TGA curves of
Fig. 2. FT-IR spectra of (a) mesoporous silica KIT-5, (b) PVP/KIT-5 and (c) Pd-PVP/
Fig. 3. TGA curves of (a) mesoporous silica KIT-5, (b) PVP, (c) PVP/KIT-5 and (d) Pd-
KIT-5.
PVP/KIT-5.

R.J. Kalbasi, N. Mosaddegh / Materials Research Bulletin 47 (2012) 160–166
163
2
Fig. 4. N adsorption-desorption isotherms of mesoporous silica KIT-5, PVP/KIT-5
and Pd-PVP/KIT-5. Inset: pore size distribution.
PVP/KIT-5 (Fig. 3c) and Pd-PVP/KIT-5 (Fig. 3d), it can be found
that polymer content of composite was not significantly changed
after the Pd loading. Therefore, the assumption that palladium
nanoparticles interact with the polymer carbonyl groups
(
present in the FT-IR section) can be proved. Because the
amounts of polymer in composites are approximately equal, it
can be found that the weakness of carbonyl bond vibration is due
to the interaction between Pd nanoparticles and the polymer and
that the decrease in the intensity of carbonyl bond after Pd
loading is not related to the decrease in the polymer contents of
the composite.
Fig. 6. TEM images for Pd-PVP/KIT-5.
The BET specific surface areas and the pore sizes of KIT-5, PVP/
KIT-5 and Pd-PVP/KIT-5 were calculated using BET and BJH
methods (Table 1). All the samples exhibit a type IV adsorption
isotherm with an H2 hysteresis loop, typically observed for the
mesoporous samples with a cage-type pore structure (Fig. 4). The
corresponding BJH pore size distribution curves for the KIT-5, PVP/
KIT-5 and Pd-PVP/KIT-5 materials are shown in Fig. 4. It is clear
that PVP/KIT-5 and Pd-PVP/KIT-5 exhibit a smaller specific surface
area in comparison to those of pure KIT-5 (Table 1). However, there
is a noticeable increase in pore diameter for Pd-PVP/KIT-5 which
may be due to the incorporation of Pd nanoparticles into PVP/KIT-
5. Similar results were reported for Pt encapsulated in SBA-15 [21].
Fig. 5 displays the result of UV–vis spectra of Pd-PVP/KIT-5. The
2
UV–vis spectra of Pd(OAc) which reveal a peak at 400 nm refer to
the existence of Pd(II) [22]. As mentioned in the experimental
section, Pd(0)-PVP/KIT-5 was prepared by adding hydrazine
hydrate to Pd(II)-PVP/KIT-5. However, as can be seen in Fig. 5,
there is not any peak at 400 nm in the UV–vis spectra of Pd-PVP/
KIT-5, which indicates complete reduction of Pd(II) to Pd
nanoparticles.
The TEM micrographs of Pd-PVP/KIT-5 showed that the ordered
cubic Fm3m mesostructure of KIT-5 was retained, and no damage
in the periodic structure of the silicate framework was observed
(Fig. 6a). The places with darker contrasts could be assigned to the
Fig. 5. UV–vis spectra of Pd-PVP/KIT-5.

1
64
R.J. Kalbasi, N. Mosaddegh / Materials Research Bulletin 47 (2012) 160–166
Table 2
a,b
Effect of different bases and solvents on Heck reaction.
.
c
Base
Yield (%)
Time (h)
d
e
K
K
2
CO
CO
3
96
80
60
25
2
6
2
2
2
3
d
3 4
Na PO
d
Et
3
N
a
Reaction conditions: Pd-PVP/KIT-5 (0.14 g), iodobenzene (1 mmol), styrene
(
2 mmol), base (5 equiv.), 60 8C.
b
(
E)/(Z) stereoselectivity was higher than 99:1.
c
Isolated yield related to E isomer.
d
e
2
Solvent: MeOH/H O (3:1, v/v) (5 mL).
Solvent: H O (5 mL).
2
binding energy. As we know, the position of Pd 3d peak is usually
influenced by the local chemical/physical environment around Pd
species besides the formal oxidation state, and shifts to lower
binding energy when the charge density around it increases [25].
Fig. 7. XPS spectrum of Pd 3d of Pd-PVP/KIT-5.
0
So, the peaks at (334.3 and 339.5 eV) should be due to Pd species
bound directly to O of carbonyl group or N of PVP. The contribution
0
presence of Pd particles with different dispersion. This assumption
was confirmed by EDX data, in which the estimated Pd/Si ratio was
about 0.04 and it correlated with the loaded Pd amount. The small
dark spots in the images could be ascribed to Pd nanoparticles,
probably located in the support channels. The larger dark areas
over the channels most likely corresponded to Pd nanoparticle
agglomerate on the external surface.
of the charge transfer of N and O of PVP to Pd results in the
0
increase in the charge density around Pd and the decrease in
binding energy.
The full XPS spectrum of Pd-PVP/KIT-5 showed peaks of carbon,
oxygen, silicium and palladium. Silicium peaks correspond to
mesoporous silica KIT-5 structure and carbon is related to the PVP
structure (Fig. 8).
Fig. 6b shows that the sizes of Pd nanoparticles were around 3–
5
nm, which were a little larger than the silica mesopore diameter
3.2. Catalytic activity
(2.6 nm). With the incorporation of the nanoparticles larger than
the structure directing agent, pore size can expand the entire
mesopore structure uniformly [23]. These are in accordance with
BET and XRD results.
To obtain information on the structural features of the Pd-PVP/
KIT-5 catalyst, X-ray photoelectron spectroscopy (XPS) study has
been carried out on the Pd-PVP/KIT-5 catalyst. The XPS result of Pd
nanoparticles dispersed in PVP/KIT-5 media for Pd 3d spectrum
with the binding energies of Pd 3d5/2 and Pd 3d3/2 lying at about
Pd-PVP/KIT-5 nanocomposite was used as a catalyst for Heck
reactions of various aryl halides with styrene.
To optimize the reaction conditions, a model reaction was
carried out by taking iodobenzene and styrene in different solvents
and bases at 60 8C. Solvent plays a crucial role in the rate and
product distribution of Heck reactions. In this context, two kinds of
2 2
green solvents were used: H O or MeOH/H O (3:1, v/v); and the
reaction was catalyzed with 0.14 g of Pd-PVP/KIT-5 (Table 2). The
experimental results showed that the time it took for the reaction
3
34.3 and 339.5 eV, respectively (see Fig. 7). It means that Pd
nanoparticles are stable as metallic state in PVP/KIT-5 media (the
XPS spectrum of Pd(II) ions reveals two peaks at about 337 and
to be completed was rarely shorter in the case of using MeOH/H
(3:1, v/v) as a solvent and the yield was higher. Hence, MeOH/H
(3:1, v/v) was chosen as solvent.
2
O
O
2
3
42 eV refer to Pd 3d5/2 and 3d3/2 [24]). In comparison to the
0
standard binding energy (Pd with Pd 3d5/2 of about 335 eV and
Pd3/2 of about 340 eV) [25], it can be concluded that the Pd peaks in
The effect of base on the coupling reaction was evaluated by
taking iodobenzene with styrene in MeOH/H O (3:1, v/v) at 60 8C
in the presence of Pd-PVP/KIT-5 with various bases (K CO , Et N,
and Na PO ) (Table 2). The results revealed that the inorganic bases
which were used were more effective than Et N; and hence, the
was chosen as the base for the
2
0
Pd-PVP/KIT-5 shifted to lower binding energy than Pd standard
2
3
3
3
4
3
economically cheaper K
coupling reactions.
2 3
CO
In order to discriminate the effect of Pd-PVP/KIT-5, the reaction
occurred over palladium nanoparticles in the same reaction
conditions, and no activity was seen in this condition.
Heck reactions of different aryl halides and styrene over Pd-
PVP/KIT-5 as catalyst were investigated (Table 3) [3,26]. The
turnover frequency (TOF) value indicates that the Pd-PVP/KIT-5
is a potential candidate for this kind of reaction, TOF being
defined as the mol product/(mol catalyst h); and this was
calculated from the isolated yield, the amount of palladium
used and the reaction time.
Reusability of the catalyst was tested by carrying out repeated
runs of the reaction on the same batch of the catalyst in the case of
the model reaction (Table 4). The results showed that this catalyst
could be reused eight times without any modification and that no
significant loss of activity/selectivity performance was observed. In
addition, there was very low Pd leaching during the reaction (Table
4). Compared to our previous work on composites based on SBA-15
Fig. 8. Full XPS spectrum of Pd-PVP/KIT-5.

R.J. Kalbasi, N. Mosaddegh / Materials Research Bulletin 47 (2012) 160–166
165
Table 3
a,b
Heck reaction of aromatic aryl halides and styrene catalyzed by Pd-PVP/KIT-5.
R
X
Pd-PVP/KIT-5
+
K CO , MeOH/H O, 60 °C
2
3
2
R
.
c
ꢀ1 d
)
Entry
Substrate
Product
Yield (%)
TOF (h
9.25
Time (h)
Mp (8C)
Found
Reported [Ref.]
I
1
2
96
97
2
122–124
136–138
121–123 [3]
135–137 [3]
OCH3
1.56
3.66
18.5
12
OCH
3
I
CH3
3
4
95
96
5
117–119
38–40
116–118 [3]
38–39 [22]
CH
3
I
Cl
I
1
Cl
Br
5
6
7
96
63
85
2.31
1.01
1.36
8
122–124
142–144
122–124
121–123 [3]
142–145 [3]
121–123 [3]
12
Br
COCH
3
O
Cl
12
a
b
c
Reaction conditions: Pd-PVP/KIT-5 (0.14 g), iodobenzene (1 mmol), styrene (2 mmol), K
E)/(Z) stereoselectivity was higher than 99:1.
2
CO
3
(5 equiv.), MeOH/H
2
O (3:1, v/v), 60 8C.
(
Isolated yield related to E isomer.
d
Turn-over frequency.
[
9–12], Pd-PVP/KIT-5 showed more recyclability, which could be
Table 4
a,b
The catalyst reusability for the Heck reaction.
.
related to the interconnected large-pore cage-type mesoporous
KIT-5 with 3D porous networks in comparison to SBA-15 with a 2D
array of pores because three-dimensional porous network of KIT-5
allows for a faster diffusion of reactants, avoids pore blockage,
provides more adsorption sites and can prevent leaching of Pd
nanoparticles. The XRD patterns of the used catalyst showed that
the structure of the catalyst was maintained.
Table 5 shows a comparison between the catalyst used in the
present study and other Pd catalysts reported in the literature for
Heck reaction [27–31]. As can be seen, Pd-PVP/KIT-5 catalyst
shows good activity and reasonable yield for Heck reaction of
iodobenzene and styrene in a reasonable time with high yields in
the presence of a green solvent. In addition, the reusability of Pd-
PVP/KIT-5 was considerable.
c
Cycle
Yield (%)
Pd content of catalyst (mmol)
Fresh
96
96
96
96
94
94
93
93
91
0.0519
0.0519
0.0519
0.0519
0.0519
0.0518
0.0518
0.0518
0.0517
1
2
3
4
5
6
7
8
a
Reaction conditions: Pd-PVP/KIT-5 (0.14 g), iodobenzene (1 mmol), styrene
CO (5 equiv.), MeOH/H O (3:1 v/v) (5 mL), 60 8C, 2 h.
E)/(Z) stereoselectivity was higher than 99:1.
Isolated yield related to E isomer.
(
2 mmol), K
b
2
3
2
(
c

1
66
R.J. Kalbasi, N. Mosaddegh / Materials Research Bulletin 47 (2012) 160–166
Table 5
Comparison of catalytic activity of Pd-PVP/KIT-5 with other catalysts.
Catalyst
Pd-TiO
Substrate
Product
Solvent
Temperature (8C)
Yield (%)
Time (h)
Ref.
2
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
E-Stilbene
E-Stilbene
E-Stilbene
E-Stilbene
E-Stilbene
E-Stilbene
NMP
120
80
98
98
97
99
89
96
0.5
5
[27]
Pd-complex
Toluene–PEG600 (3:1)
DMF
[28]
Pd/NF300
80–140
80
4
[29]
Polyion complex
Pd-polymer composite
Pd-PVP/KIT-5
H
2
O
20
8
[30]
DMF
80
[31]
MeOH/H
2
O (3:1, v/v)
60
2
This work
[
[
[
[
10] R.J. Kalbasi, M. Kolahdoozan, M. Rezaei, Mater. Chem. Phys. 125 (2011) 784–
90.
11] R.J. Kalbasi, A.A. Nourbakhsh, F. Babaknezhad, Catal. Commun. 12 (2011)
955–960.
4
. Conclusion
7
A novel polymer–inorganic hybrid material, Pd nanoparticle-
12] R.J. Kalbasi, M. Kolahdoozan, K. Shahabian, F. Zamani, Catal. Commun. 11 (2010)
PVP/KIT-5, was prepared by a simple method. The catalytic activity
of this novel catalyst was excellent for Heck reaction of aryl
chloride, bromide and iodides under aerobic conditions. This
heterogeneous catalyst can practically replace a homogeneous
catalyst in view of the following advantages: (a) high catalytic
activity under mild reaction conditions and (b) reusability of the
catalyst for several times without any significant loss in the yield of
the reaction.
1109–1115.
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1
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