Synthesis and characterization of mesoporous poly(N-vinyl-2-pyrrolidone) containing palladium nanoparticles as a novel heterogeneous organocatalyst for Heck reaction

Article abstract of DOI:10.1016/j.molstruc.2014.01.071

Mesoporous poly(N-vinyl-2-pyrrolidone) (MPVP) was prepared through a nanocasting technique based on mesoporous silica KIT-6 as sacrificial templates, and served as an efficient scaffold for supporting Pd nanoparticles. The physical and chemical properties

Full text of DOI:10.1016/j.molstruc.2014.01.071

Journal of Molecular Structure 1063 (2014) 259–268
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Journal of Molecular Structure
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Synthesis and characterization of mesoporous poly(N-vinyl-2-
pyrrolidone) containing palladium nanoparticles as a novel
heterogeneous organocatalyst for Heck reaction
⇑
Roozbeh Javad Kalbasi , Meysam Negahdari
Department of Chemistry, Shahreza Branch, Islamic Azad University, 311-86145 Shahreza, Isfahan, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Mesoporous poly(N-vinyl-2-pyrrolidone) containing Pd nanoparticles was prepared and used as a novel
purely organic heterogeneous catalyst. The catalyst showed high catalytic activity in Heck reaction and
could be reused at least nine times.
ꢀ
Mesoporous poly(N-vinyl-2-
pyrrolidone) was prepared based on
mesoporous KIT-6.
ꢀ
ꢀ
ꢀ
Pd-MPVP was prepared as a novel
heterogeneous organocatalyst.
The mesoporous organocatalyst was
used for the Heck reaction.
The stability of the catalyst was
excellent and could be reused 9 times.
a r t i c l e i n f o
a b s t r a c t
Article history:
Mesoporous poly(N-vinyl-2-pyrrolidone) (MPVP) was prepared through a nanocasting technique based
on mesoporous silica KIT-6 as sacrificial templates, and served as an efficient scaffold for supporting
Pd nanoparticles. The physical and chemical properties of Pd-MPVP were characterized using FT-IR,
XRD, BET, DRS UV–Vis, SEM, TEM and TGA techniques. The application of this novel purely organic het-
erogeneous catalyst, which combine the advantage of organic polymers and mesoporous materials, was
investigated for CAC bond formation through the Heck coupling reaction of aryl iodides, bromides and
chlorides with styrene. It was observed that the activity of this catalyst decreased just 5% after nine
regeneration processes were performed. This unique result opens new perspectives for application of
purely organic mesoporous polymers as structurally defined hydrophobic catalyst in catalytic reactions.
Ó 2014 Elsevier B.V. All rights reserved.
Received 19 October 2013
Received in revised form 8 January 2014
Accepted 27 January 2014
Available online 1 February 2014
Keywords:
Mesoporous polymer
Poly(N-vinyl-2-pyrrolidone)
Pd-nanoparticles
Heck reaction
1
. Introduction
these reactions, the Heck reaction has been widely used for
construction of a carbon–carbon bond [1]. Many Pd complexes
Reactions leading to the formation of CAC bonds are impor-
tant to the synthesis of complex organic molecules. Among
have been used as homogeneous catalysts in this reaction [2–
5]. Although some of the Pd complexes have potential for recy-
cling [2,6], the separation and recovery of most of them are not
easy, and the resulting products are often contaminated by Pd
metal. Thus, it is necessary to develop heterogeneous catalysts
⇑
Corresponding author. Tel.: +98 321 3212522; fax: +98 321 3213103.
E-mail address: rkalbasi@iaush.ac.ir (R.J. Kalbasi).
http://dx.doi.org/10.1016/j.molstruc.2014.01.071
022-2860/Ó 2014 Elsevier B.V. All rights reserved.
0

2
60
R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
which can easily be recovered from the reaction system and re-
used [7–10].
2.2. Catalyst preparation
In heterogeneous catalysts, various support matrices such as
organic polymers [11–13] and inorganic silicas, especially porous
inorganic materials with high surface areas, have been employed
2.2.1. Preparation of KIT-6
Synthesis of mesoporous silica KIT-6 was obtained following
the method reported by Kleitz et al. [57]. Briefly, 6 g (1.03 mmol)
of triblock copolymer Pluronic P123 (EO20PO70EO20) (as a soft tem-
plate and structure directing agent to preparation of KIT-6) and 6 g
(81 mmol) of n-butanol were dissolved in 270 g (15 mol) of dis-
tilled water and 11.4 g (0.115 mol) of concentrated hydrochloric
acid (37 wt% HCl). The mixture was left stirring at 35 °C for 1 h.
Then 12.9 g (0.061 mol) of tetraethyl orthosilicate (TEOS) was
added to the homogeneous clear solution. This mixture was left
stirring at 45 °C for 24 h for the formation of mesostructured prod-
uct, followed by aging at 95 °C for 24 h under a stirring condition.
The solid product was then filtered, washed with deionized water
and dried at 100 °C. Finally, the samples were calcined at 550 °C for
6 h to remove the template.
[
14–16]. Compared with organic polymers, inorganic supports
with nanopores can provide high surface area, large pore vol-
ume, and 3-dimensional pore architecture, which are favorable
for mass transfer in catalysis. However, the disadvantages of
inorganic supports including relatively low stability in alkaline
media and complex functionalization of them are challenges
for preparation of heterogeneous catalysts with high activity
and excellent recyclability. For example, SiAOASi bonds in or-
dered mesoporous silicas are not stable in alkaline media, and
immobilization of palladium species on silica surface generally
requires unique organic linkers [17,18]. On the other hand, the
organic mesoporous materials with some significant advantages
such as flexibility, toughness, hydrophobicity and versatility for
further functionalization are quite different from their inorganic
counterparts as a result of the intrinsic characteristics of organic
molecules [19].
2.2.2. Preparation of mesoporous poly(N-vinyl-2-pyrolidone)
Poly(N-vinyl-2-pyrolidone) (PVP) was deposited inside the
porosity of KIT-6. This was carried out by in situ polymerization.
As a typical run, at first, N-vinyl-2-pyrrolidone (NVP) (1 mL,
9.2 mmol), KIT-6 (0.5 g) and Divinylbenzene (0.061 mL,
0.441 mmol) in 7 mL tetrahydrofuran (THF) were placed in a round
bottom flask. The solution was stirred with magnetic stirrer and re-
fluxed for 6 h at 65 °C to achieve a uniform distribution of organic
monomers inside the pores of KIT-6 prior to polymerization. Then,
Mesoporous polymeric materials have gained much attention
for the adsorption, separation, and catalysis of large molecules
[
20–22], and also as dielectric materials [23], due to their high
specific surface area [24,25], uniform pore diameter [26–29],
and chemical stability for recyclability [30,31]. Nevertheless,
among the different researches on these materials, there are
relatively a few reports on the application of mesoporous poly-
meric materials as a heterogeneous catalyst [32–37]. Mesoporous
polymers can be prepared by various routes, including phase
separation [38,39], controlled foaming [40,41], imprinting with
large molecules or nanoparticles [42,43], ion track etching [44],
0
2,2 -azobis(isobutyronitrile) (AIBN) (5 mol% with respect to VP)
was added to start the polymerization and the mixture was heated
to 65–70 °C for 17 h while being stirred under N gas. The resulting
2
white fine powder nanocomposite (PVP/KIT-6) was collected by fil-
tration, washed several times with THF to remove remaining
monomers, and finally dried at 60 °C under reduced pressure.
The resulting PVP/KIT-6 nanocomposite was immersed in a
10 wt% HF solution (water/ethanol = 1/1) at room temperature
for 18 h to remove the silica framework. Then, it was filtered and
washed sequentially with water/ethanol solution and the
precipitate was dried in room temperature to yield mesoporous
poly(N-vinyl-2-pyrolidone). The synthesized mesoporous poly(N-
vinyl-2-pyrolidone) was briefly denoted as MPVP.
selective decomposition within
a block copolymer assembly
[
45–48], assembly of resin precursors by surfactants [26,28,29],
and polymerization inside a removable porous template or with
embedded template particles [49,50]. Among these methods,
the porous template method is also referred to as ‘hard-templat-
ing’, ‘nanocasting’, or ‘template synthesis’. Most synthetic strate-
gies for fabricating mesoporous polymers have been dependent
on the hard template approach [51–53]. The template mesopor-
ous polymeric replicas are obtained after the selective removal
of the silica framework in the polymer/silica composites. In this
way, a porous polymeric material is obtained.
2.2.3. Preparation of Pd nanoparticle–mesoporous poly(N-vinyl-2-
pyrrolidone)
In continuing our previous activities to develop new meso-
porous polymers as heterogeneous catalysts [54], herein, we
will introduce a novel mesoporous polymer as a heterogeneous
catalyst prepared using a cubic-type mesoporous silica tem-
plate with 3D porous networks. The catalytic activity of this
catalyst (Pd-mesoporous poly(N-vinyl-2-pyrrolidone)) was
tested for Heck reaction in aqueous medium under aerobic con-
dition. In addition, the catalytic activity of this mesoporous
polymeric catalyst was compared with polymer–inorganic hy-
brid materials which were prepared in our previous works
Mesoporous poly(N-vinyl-2-pyrrolidone) (MPVP) (0.25 g) and
10 mL of an aqueous acidic solution (CHCl = 0.09 M) of Pd(OAc)
(0.0066 g, 0.029 mmol) were placed in a round bottom flask. The
mixture was heated to 80 °C for 5 h while being stirred under N
gas. Then, 0.15 mL (2.47 mmol) aqueous solutions of hydrazine hy-
drate (N O) (80 vol.%) was added to the mixture drop by drop
2
2
H ꢁH
2 4 2
in 15–20 min. After that, the solution was stirred at 60 °C for 1 h.
Afterwards, it was filtered and washed sequentially with chloro-
form and methanol to remove excess N
2
H
4
ꢁH
2
O, and was dried at
room temperature to yield palladium nanoparticle-mesoporous
poly(N-vinyl-2-pyrrolidone) (Pd-MPVP) (Scheme 1). The Pd con-
tent of the catalyst was estimated by decomposing the known
amount of the catalyst by nitric acid, hydro-chloric acid, and Pd
content was estimated by inductively coupled plasma atomic
[
55,56], to investigate the advantages of mesoporous polymeric
catalysts.
2
. Materials and methods
emission spectrometry (ICP-AES). The Pd content of the catalyst
ꢂ1
estimated by ICP-AES was 0.0864 mmol g
.3. Instruments and characterization
.
2.1. Chemicals supply
2
N-vinyl-2-pyrrolidinone (VP, 97%) as monomers, p-Divinylben-
0
zene (DVB, 85%) as crosslinker and 2,2 -azobis(isobutyronitrile)
(
The samples were analyzed using FT-IR spectroscopy (using a
ꢂ1
AIBN) as initiator were purchased from Sigma–Aldrich. All other
chemicals were obtained from Sigma–Aldrich, Merck and were
used without further purification.
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

R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
261
Scheme 1. Schematic showing the procedure for the preparation of Pd-MPVP.
nitrogen at liquid nitrogen temperature, using a Series BEL SORP
8. The X-ray powder diffraction (XRD) of the catalyst was carried
1
out on a Bruker D8Advance X-ray diffractometer using nickel fil-
tered Cu Ka radiation at 40 kV and 20 mA. The thermal gravimet-
ric analysis (TGA) data were obtained by a Setaram Labsys TG
(
1
(
STA) in a temperature range of 30–700 °C and heating rate of
0 °C/min in atmosphere. Scanning electron microscope
SEM) studies were performed on Philips, XL30, SE detector.
N
2
Transmission electron microscope (TEM) observations were per-
formed on a JEOL JEM.2011 electron microscope at an accelerating
voltage of 200 kV using EX24093JGT detector in order to obtain
information on the size of Pd nanoparticles and the DRS UV–Vis
spectra were recorded with JASCO spectrometer, V-670 from
1
90 to 2700 nm.
The products were characterized by H NMR and 13C NMR spec-
1
tra (Bruker DRX-500 Avance spectrometer at 400 and 100 MHz,
respectively). Melting points were measured on an Electrothermal
9
100 apparatus and they were uncorrected. All the products were
1
known compounds and they were characterized by FT-IR, H NMR
and C NMR. All melting points are compared satisfactorily with
those reported in the literature.
1
3
2.4. General procedure for Heck reaction
In the typical procedure for Heck coupling reaction, a mixture of
iodobenzene (1 mmol), styrene (2 mmol), K
catalyst (0.14 g, Pd-MPVP) in MeOH/H O (volume ratio: 3:1)
5 mL) was placed in a round bottom flask. The suspension was
2 3
CO (5 mmol), and
2
(
Fig. 1. FT-IR spectra of (a) mesoporous silica KIT-6, (b) PVP/KIT-6, (c) MPVP and (d)
Pd-MPVP.
stirred at 45 °C for 4 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 re-
moved from the reaction mixture by filtration, and then the reac-
tion product was extracted with CH Cl
3. Results and discussion
2
2
(3 mL ꢃ 5 mL). The
3.1. Catalyst characterization
solvent was removed under reduced pressure. The crude product
was purified by flash column chromatography to afford the desired
coupling product (97% isolated yield). The product was identified
Fig. 1 presents the FT-IR spectra of KIT-6 (a), PVP/KIT-6 (b),
MPVP (c), and Pd-MPVP (d). A broad band at around 3400–
1
13
ꢂ1
with H NMR, C NMR and FT-IR spectroscopy techniques.
3450 cm is observed in all samples. It is mainly caused by the

2
62
R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
OAH stretching vibration of the adsorbed water molecules. The
characteristic bands at around 1080, 820 and 480 cm may be as-
Table 1
ꢂ1
Physicochemical properties of mesoporous silica KIT-6, PVP/KIT-6, MPVP and Pd-
MPVP samples obtained from N adsorption.
2
signed to SiAOASi asymmetrical stretching vibration, symmetrical
stretching vibration and bending vibration, respectively, as seen in
Fig. 1a and b. The existence of PVP in the PVP/KIT-6 composite is
evidenced by the appearance of typical PVP vibration on the FT-
IR spectrum (Fig. 1b). In the FT-IR spectrum of PVP/KIT-6, the
BET surface area (m2
g
ꢂ1
)
V
(cm3
g
ꢂ1
)a
Sample
P
P
D (nm)
KIT-6
PVP/KIT-6
MPVP
988
794
226
168
1.35
1.17
0.52
0.11
8.1
7.1
4.2
3.3
ꢂ1
Pd-MPVP
new band at 1677 cm corresponds to the carbonyl bond of PVP
ꢂ1
a
[
58]. Moreover, the presence of peaks at around 2900–3000 cm
Total pore volume.
ꢂ1
and 1439 cm correspond to the aliphatic CAH stretching and
bending in PVP/KIT-6, respectively. The appearance of the above
bands shows that PVP has been attached to the surface of KIT-6
and PVP/KIT-6 has been obtained. Similar to PVP/KIT-6 (Fig. 2b),
MPVP sample shows the characteristic bands for PVP, while the
ꢂ1
bands at around 1080, 820 and 480 cm which are related to
the asymmetric and symmetric stretching as well as the rocking
of SiAOASi are omitted (Fig. 2c). These results have shown that
the silica framework has been successfully removed and MPVP
has been prepared as a replica of KIT-6.
As shown in Pd-MPVP spectrum (Fig. 1d), the band at
ꢂ1
1
681 cm which corresponds to carbonyl bond of PVP, is shifted
ꢂ1
to lower wave numbers (1665 cm ) (red shift). This may be due
to the interaction between the Pd nanoparticles and C@O group.
This means that the double bond CO stretches become weak by
coordinating to Pd nanoparticles [58,59]. Thus, it is confirmed that
PVP molecules exist on the surface of the Pd nanoparticles and
coordinate to the Pd nanoparticles.
The low angle XRD patterns of KIT-6, PVP/KIT-6, MPVP and Pd-
MPVP are shown in Fig. 2. The XRD pattern of KIT-6 (Fig. 2a) shows
one intense peak at 2h about 0.95° and two weak peaks at 2h about
Fig. 3. Pore size distribution of MPVP and Pd-MPVP.
1
.65° and 1.9° which can be indexed as (211), (220), and (320)
reflections associated with three-dimensional cubic symmetry
(Ia3d) [60]. The PVP/KIT-6 (2h = 0.6–10) sample show the same
pattern indicating that the structure of the KIT-6 is retained even
after the support of the surface of the KIT-6 with PVP (Fig. 2b).
The pattern of MPVP shows a typical mesoporous structure with
a peak at 2h around 1.5–2.5° corresponding to a mesoporous
framework. However, the peak position is shifted to a higher angle
(
in comparison to KIT-6) which can be attributed to a decrease in
the dimension of d-spacing (the inter-planar spacing) of MPVP,
according to the Bragg’s law. However, it can be expected because
MPVP is a negative replica of KIT-6 [51]. Moreover, the intensity
and sharpness of the characteristic reflection peak of MPVP is
reduced, indicating the loss of long-range order to some extent
because of organic nature of MPVP.
The wide angle XRD pattern of the Pd-MPVP (Fig. 2d) shows the
reflections at 2h = 39.92°, 46.54°, 67.90°, 81.84° and 85.50°. These
peaks correspond to (111), (200), (220), (311) and (222) lattice
planes of Pd nanoparticles [61]. Planes were assigned by compar-
ing them with the standard Pd and these planes correspond to
the fcc crystal lattice structure of Pd (JCPDS, Card No. 05-0681).
The pattern displays a broad diffraction with 2h ranging from 15°
to 30°, which suggests the amorphous structure of the polymeric
base. The crystallite size of Pd particles was evaluated using Scher-
rer equation which was found to be approx. 5 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. It should be mentioned that the wide-angle XRD pattern
of Pd-MPVP is similar to MPVP (data not shown).
The BET specific surface areas, the pore volumes and the pore
sizes of KIT-6, PVP/KIT-6, MPVP and Pd-MPVP samples were calcu-
lated using BET and BJH methods (Table 1). The surface area, pore
2
ꢂ1
3
ꢂ1
volume and pore size of KIT-6 are 988 m g , 1.35 cm g , and
.1 nm, respectively. After hybridization with PVP through in situ
8
polymerization, PVP/KIT-6 exhibits a smaller pore size and pore
volume than those of KIT-6, which may be concluded that poly-
merization of PVP occurs in the channels of the KIT-6.
Fig. 2. Powder XRD patterns of (a) mesoporous silica KIT-6, (b) PVP/KIT-6, (c)
MPVP, and (d) Pd-MPVP.

R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
263
pore volume which makes it suitable to act as a catalyst for Heck
reaction.
The TGA curves of the KIT-6 (a), PVP (non-porous) (b), PVP/KIT-
6
2
(c) and MPVP (d) under N atmosphere are presented in Fig. 4.
The TGA curve of KIT-6 shows a small mass loss (around 5%,
w/w) at temperature <150 °C, which is apparently associated with
adsorbed water on the surfaces of KIT-6. No other changes in the
weight are observed for KIT-6 at 150–700 °C (Fig. 4a). However,
TG curve of PVP (non-porous) shows 2 steps; the first step (around
5
%, w/w) appearing at temperature 50–120 °C corresponds to the
loss of water. The second weight loss (around 65%, w/w) begins
at 150 °C because of thermo degradation of PVP polymer chains,
and the degradation ends at 550 °C (Fig. 4b).
Thermo analysis of PVP/KIT-6 shows two steps of mass loss
(Fig. 4c). The first step (around 2%, w/w) that occurs at tempera-
tures less than 150 °C is related to desorption of water. The second
step (around 15%, w/w) which appears at 170 °C is attributed to
degradation of the polymer chains, and the degradation ends at
Fig. 4. TGA curves of (a) mesoporous silica KIT-6, (b) PVP (nonporous), (c) PVP/KIT-
6
and (d) MPVP.
5
70 °C (Fig. 4c). MPVP sample exhibits just one weight loss step
(
around 40%, w/w), which begins at 350 °C because of thermo deg-
radation of PVP polymer chains, and the degradation ends at 600 °C
(Fig. 4d). Obviously, the MPVP shows a higher thermal stability
than that of PVP (nonporous), which may be related to the ordered
mesoporous structure of MPVP. Actually, the ordered structure of
MPVP causes to increase the degree of crystallinity of the polymer
(producing semi crystalline form) and thermal stability of MPVP is
increased. Therefore, it is very important for the catalyst applica-
tion that the thermal stability be enhanced greatly.
The morphological characteristics of KIT-6, MPVP and Pd-MPVP
which are illustrated by the SEM microphotographs are shown in
Fig. 5. A comparison of MPVP (Fig. 5b) with KIT-6 template
(Fig. 5a) reveals that the morphology of the silica template is rela-
tively retained in the mesoporous polymer. This suggests that with
the appropriate template it may be possible to prepare polymeric
structure with a pre-selected shape.
The corresponding BJH pore size distribution curves for the
MPVP and Pd-MPVP materials are shown in Fig. 3. As it can be seen,
MPVP which is obtained after the selective removal of the silica
template from PVP/KIT-6, exhibits a relatively narrow pore size
distribution centered at 4.2 nm. However, the pore size distribu-
tion of MPVP is smaller than that of KIT-6 which is expected and
it is in good agreement with the XRD result (shift of peak position
to a higher angle). Although the specific surface area of MPVP
2
ꢂ1
(
226 m g ) is smaller than that of PVP/KIT-6 (Table 1), MPVP still
has a large channel-like pores and a high surface area which indi-
cates that MPVP is a true replica of the mesoporous silica KIT-6,
and makes it suitable to act as a mesoporous organic support. In
this regard, Pd-MPVP exhibits a relatively narrow pore size distri-
bution like MPVP, which means that Pd nanoparticles are well dis-
tributed on the channels and surfaces of MPVP (Fig. 3 and Table 1).
Moreover, Pd-MPVP has a reasonable surface area, pore size and
By comparing the SEM images of MPVP and Pd-MPVP, we can
see that there are some agglomerate particles (lighter spots) on
Fig. 5. SEM photographs of (a) KIT-6, (b) MPVP and (c) Pd-MPVP.

2
64
R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
Fig. 6. TEM images of Pd-MPVP.
Table 3
Effect of different bases on Heck reactiona,b.
Base
Yieldc (%)
None
Trace
97
2
K CO
3
Na
Et
3
PO
N
4
70
50
3
a
Reaction conditions: Pd-MPVP (0.14 g), iodobenzene
(
2
1 mmol), styrene (2 mmol), base (5 mmol), MeOH/H O
(
5 mL), 45 °C, 4 h.
b
E/Z stereoselectivity was higher than 99:1 (determined
1
by H NMR spectroscopy).
c
Isolated yield of the E isomer.
Fig. 7. UV–Vis spectrum of Pd-MPVP.
which is referred to the existence of Pd(II) [62]. As mentioned in
Section 2, Pd-MPVP is prepared by adding hydrazine hydrate to
the Pd(II)–mp-PVP. However, as can be seen in Fig. 7, there is no
peak at 400 nm in the UV–Vis spectrum of Pd-MPVP, which indi-
cates complete reduction of Pd(II) to Pd nanoparticles.
the surface of Pd-MPVP which are related to the Pd nanoparticles
distributed on the outer surface of the support (Fig. 5c).
The TEM micrographs of Pd-MPVP are depicted in Fig. 6. TEM
experiment demonstrates that palladium nanoparticles were uni-
formly dispersed on the surface of MPVP (Fig. 6). This is due to
the existence of a large number of organic groups, as anchoring
sites, on the surface of MPVP. The places with darker contrast
can be assigned to the presence of Pd particles with different dis-
persion. The small dark spots in the image can be ascribed to Pd
nanoparticles with average diameter around ꢄ4 nm (Fig. 6), prob-
ably located into the support channels. The dark spherical particles
most likely correspond to Pd nanoparticles which are located on
the external surface with average diameter of ꢄ10–18 nm or more
than that (40–120 nm according to SEM results) (Fig. 6). These are
in accordance with SEM results.
3.2. Catalytic activity
This novel organocatalyst was synthesized and characterized
with different methods. The main goal of this catalytic synthesis
was to compare this purely organic nanocatalyst (Pd-MPVP) with
a polymer–inorganic nanocomposite (Pd-PVP/KIT-6, which was
prepared in our previous work [56]) or respective non-porous
polymer (Pd-PVP) and to expand the use of these types of purely
organic nanocatalyst for organic reactions. High thermal stability,
high surface areas, narrow pore size distributions, regular frame-
works and hydrophobic surface nature of Pd-MPVP are some of
advantages of this nanocatalyst which make it as a good candidate
to catalyze organic reactions. In this regard, a Heck reaction of var-
ious aryl halides with styrene under aerobic condition was chosen
to test the catalytic activity of Pd-MPVP as a purely organic
nanocatalyst.
Fig. 7 displays the result of UV–Vis spectrum of Pd-MPVP. Nor-
mally, the UV–Vis spectrum of Pd(OAc) , reveals a peak at 400 nm
2
Table 2
Effects of various solvents on Heck reactiona,b.
To optimize the reaction conditions, a model reaction was car-
ried out by taking iodobenzene and styrene in different solvents
and bases at 45 °C. Solvent plays a crucial role in the rate and prod-
uct distribution of Heck reactions. In this context, we used a kind of
solvents; and the reaction was catalyzed with 0.14 g of Pd-MPVP
(containing about 0.92 wt% palladium) (Table 2). The experimental
results showed that the time it took for the reaction to be com-
Solvent
Yieldc (%)
Methanol/water (3:1 v/v)
Methanol
Water
Dioxane
Acetonitrile
97
92
80
60
67
a
Reaction conditions: Pd-MPVP (0.14 g), iodobenzene
CO (5 mmol), solvent (5 mL),
pleted was rarely shorter in the case of using MeOH/H
v) as a solvent and the yield was higher. Hence, MeOH/H
v/v) was chosen as optimized solvent.
2
O (3:1, v/
O (3:1,
(
4
1 mmol), styrene (2 mmol), K
5 °C, 4 h.
2
3
2
b
E/Z stereoselectivity was higher than 99:1 (determined by 1
H
NMR spectroscopy).
Careful selection of the base in terms of its solubility and basi-
city in the reaction mixture was crucial. The role of the base in the
c
Isolated yield of the E isomer.

R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
265
Table 4
a,b
Heck reaction of aromatic aryl halides and styrene catalyzed by Pd-MPVP
Pdo
R
(CH
N
CH2)n
R
O
K CO , MeOH/H O
2
3
2
X
45
°
C , 4 h
X= -I, -Br, -Cl
R= -CH3 , -OCH3 , -COH , ...
.
Yield (%)c
Time (h)
TOF (h )d
ꢂ1
Mp (°C)
Entry
Substrate
Product
Found
Rep. Ref.
I
1
97
4
20.04
120–122
120–122
122–123 [64]
Cl
Br
2
97
8e
10.02
122–123 [64]
122–123 [64]
3
4
93
87
6
7
12.81
10.27
120–122
131–135
I
135.4–137.1 [64]
MeO
MeO
Br
Br
5
78
4e
16.11
111–114
115-116 [64]
H
O
H
O
6
82
5e
13.55
138–141
140–144 [64]
O
O
Br
7
8
76
90
6
6
10.46
12.39
115–118
117–119 [65]
NC
Cl
NC
Cl
Br
72–73
71–72 [66]
(
continued on next page)

2
66
R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
Table 4 (continued)
Entry Substrate
Yield (%)c
Time (h)
TOF (h )d
ꢂ1
Mp (°C)
Product
Found
Rep. Ref.
I
9
84
7
9.91
117–119
116–118 [67]
Me
Me
a
b
c
Reaction conditions: Pd-MPVP (0.14 g), aryl halide (1 mmol), styrene (2 mmol), K
E/Z stereoselectivity was higher than 99:1 (determined by H NMR spectroscopy).
Isolated yield of the E isomer.
Turn-over frequency.
Reflux condition.
2
CO
3
2
(5 mmol), MeOH/H O (3:1 v/v) (5 mL), 45 °C.
1
d
e
Table 6
Table 5
Catalyst reusability for the Heck reactiona,b
Comparison of catalytic activity in Heck reaction over different catalysts.
.
ꢂ1
Yield (%)c
Pd content of catalyst (mmol in 0.14 g)d
Catalyst
Time (h)
4c
Yield (%)a
TOF (h )b
Ref.
Cycle
Pd-MPVP
Pd-PVP/KIT
Pd-PVP (non-porous)
97
97
20.04
0.88
–
This work
56
70
Fresh
97
97
97
97
97
95
95
95
92
92
0.0121
0.0121
0.0121
0.0119
0.0119
0.0118
0.0118
0.0118
0.0117
0.0116
d
8
4
1
2
3
4
5
6
7
8
9
e
f
93
a
b
c
Isolated yield of the E isomer.
Turn-over frequency.
Reaction conditions: Pd-MPVP (0.14 g, 0.92 wt% palladium), iodobenzene
CO (5 mmol), MeOH/H O (3:1, v/v) (5 mL), 45 °C.
Reaction conditions: Pd-PVP/KIT-6 (0.14 g, 10.5 wt% palladium), iodobenzene
1 mmol), styrene (2 mmol), K CO (5 mmol), MeOH/H O (3:1, v/v) (5 mL), 60 °C.
Reaction conditions: Pd-PVP (1 wt% palladium), iodobenzene (1 mmol); styrene
(1.2 mmol), K CO (2 mmol), ethanol (2.0 mL), 80 °C.
(
(
1 mmol), styrene (2 mmol), K
2
3
2
d
2
3
2
e
a
2
3
Reaction conditions: Pd-MPVP, iodobenzene (1 mmol), styrene (2 mmol), K
5 mmol), MeOH/H O (3:1 v/v) (5 mL),45 °C, 4 h.
E/Z stereoselectivity was higher than 99:1 (determined by 1H NMR
spectroscopy).
2 3
CO
f
GC–MS yield to the E isomer.
(
2
b
c
any products. These results show the important role of the support
and catalyst in this reaction.
Isolated yield of the E isomer.
Measured by ICP-AES.
d
In further studies, Heck reactions of a wide range of other aryl
halides with styrene with 0.14 g of Pd-MPVP as catalyst were con-
ducted under similar conditions [64–67]. The results are shown in
Table 4. It is observed that the reaction goes well not only with aryl
iodides and bromides but also with aryl chlorides. It is well known
that activation of CACl bond is much more difficult than CABr and
CAI bonds, and in general requires harsher reaction conditions in
heterogeneous catalysis system [8,68,69]. Therefore, activation of
aryl chlorides remains a major challenge which has to be met by
a highly active catalyst system. However, chlorobenzene afforded
excellent coupling product over Pd-MPVP as catalyst (entry 2),
but needed more time and temperature than that of aryl iodide
and aryl bromide. Additionally, when aryl halides are changed with
electron donating and withdrawing groups, the Pd-MPVP catalyst
is still active (76–87% yield, entries 4–7 and 9), suggesting a good
suitability for this catalyst in Heck reaction. Furthermore, when
both bromo and chloro groups are present in the reactant, chemo
selective reaction is possible. For example, meta-bromocheloro-
benzene reacts with styrene to form meta-chlorostilbene in 90%
yield (entry 8). So, Pd-MPVP can be act as a chemo selective
catalyst.
Fig. 8. Heterogeneity test for Heck coupling reaction. Reaction conditions: Pd-
MPVP (0.14 g), iodobenzene (1 mmol), styrene (2 mmol), K CO (5 mmol), MeOH/
O (3:1 v/v), 45 °C.
2
3
H
2
mechanistic cycle is to reactivate the Pd species in solution, making
it available to be recycled [63]. The results revealed that the inor-
ganic bases used were more effective than Et
probably due to their complete solubility in solvent. Hence, cheap-
er K CO was chosen as the base for the coupling reactions. From
the data obtained, it can be concluded that the nature of the base
play a significant role in the conversion using Pd-MPVP as the
catalyst. These observations agree with a previous report in the
literature [2].
In order to discriminate the effect of the support (MPVP), the
reaction occurred over palladium nanoparticles or MPVP in the
same reaction conditions, and no activity was seen in this condi-
tion. In addition, in the absence of the catalyst, there were not
3
N (Table 3), most
Another important issue concerning the application of a heter-
ogeneous catalyst is its reusability and stability under reaction
conditions. To gain insight into this issue, catalyst recycling exper-
iments were carried out using a Heck reaction of iodobenzene and
styrene over Pd-MPVP. The results are shown in Table 5. After each
cycle, the catalyst was filtered off, washed with water (10 mL)
diethylether and acetone (3 times with 5 mL). Then, it was dried
in an oven at 60 °C and reused in Heck reaction. It should be men-
tioned that after each run, some of the catalyst was lost in the fil-
tration process. Therefore, to solve this problem, after each run the
amount of remaining catalyst was determined and the molar ratio
2
3

R.J. Kalbasi, M. Negahdari / Journal of Molecular Structure 1063 (2014) 259–268
267
of the reactants was changed according to the remaining amount
of catalyst.
The results show that Pd-MPVP can be reused without any
modification 9 times, and no significant loss of activity/selectivity
performance is observed. Moreover, there is low Pd leaching (about
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centrifugation. Then, the reaction progress in the filtrate was mon-
itored (Fig. 8). No further coupling reaction occurred even at ex-
tended times, indicating that the nature of reaction process is
heterogeneous and there is not any progress for the reaction in
homogeneous phase.
The catalytic activity of MPVP in Heck reaction was compared
with Pd-PVP/KIT-6 nanocomposite (prepared in our previous
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Pd-MPVP shows higher activity in Heck reaction at shorter time
and milder condition (45 °C). It can be related to the hydrophobic
nature of Pd-MPVP in compared with Pd-PVP/KIT-6. It should be
mentioned that Pd-MPVP is hydrophobe and Pd-PVP/KIT-6 because
of existence of KIT-6, is hydrophile. Therefore, the organic reac-
tants have more tend to adsorbed on the surface of Pd-MPVP and
consequently the yield and TOF (Turn-Over-Frequency) will be
higher in the case of using Pd-MPVP as catalyst.
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