A green method for the synthesis of gelatin/pectin stabilized palladium nano-particles as efficient heterogeneous catalyst for solvent-free Mizoroki-Heck reaction

Article abstract of DOI:10.1016/j.molcata.2014.12.013

A green method for the synthesis of gelatin/pectin stabilized palladium nano-particles has been described. These particles were prepared under green conditions without addition of any external reducing agent and ligand. All properties of the supported pal

Full text of DOI:10.1016/j.molcata.2014.12.013

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Title: A green method for the synthesis of gelatin/pectin
stabilized palladium nano-particles as efficient heterogeneous
catalyst for solvent-free Mizoroki–Heck reaction<!–<query
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Author: Ardeshir Khazaei Marzieh Khazaei Sadegh Rahmati
PII:
S1381-1169(14)00573-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.12.013
MOLCAA 9375
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Journal of Molecular Catalysis A: Chemical
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26-7-2014
28-11-2014
15-12-2014
Please cite this article as: Ardeshir Khazaei, Marzieh Khazaei, Sadegh Rahmati, A
green method for the synthesis of gelatin/pectin stabilized palladium nano-particles as
efficient heterogeneous catalyst for solvent-free MizorokindashHeck reaction, Journal
of Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2014.12.013
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A green method for the synthesis of gelatin/pectin stabilized palladium nano-
particlesas efficient heterogeneous catalyst for solvent-free Mizoroki–Heck
reaction
a,
a
b,
Ardeshir Khazaei *, Marzieh Khazaei , Sadegh Rahmati *
a
Faculty of Chemistry, Bu-Ali Sina University, P.O. Box 651783868, Hamedan, Iran
b
Department of Chemistry, Payame Noor University (PNU),19395-3697, Tehran, Iran
Abstract
A green method for the synthesis of gelatin/pectin stabilized palladium nano-particles has
been described. These particles were prepared under green conditions without addition of any
external reducing agent and ligand. All properties of the supported palladium particles on
gelatin/pectin mixture were showed by UV–Vis spectra and also by EDX, XRD, TEM and
FESEM images. The synthesized palladium nanoparticles were studied in Mizoroki–Heck
reaction between different aryl halides and n-butyl acrylate. The reaction was performed under
solvent-free conditions and no complicated work up process was needed for the isolation of the
nano-particles. Also the products were obtained in highly short reaction times with excellent
yields.
Keywords: Mizoroki-Heck reaction; Palladium nano-particles; Solvent-free; Gelatin; Pectin.
*Corresponding Authors: Tel & Fax: +98-813-8257407
E-mail addresses : khazaei_1326@yahoo.com (A. Khazaei), rahmati61@yahoo.com (S. Rahmati)
1

1
. Introduction
Lately, the application and development of green catalysts have possessed a large number
of studies in academic and industrial groups to degrade or eliminate the use of dangerous
substances [1,2]. Heterogenization of the catalysts to solid supports can provide opportunities for
recycling of the catalysts from reaction environments. Heterogenization of the catalysts to solid
supports by their immobilization on organic [3] or inorganic [4] polymers [5–7] is of great
interest, because of having many benefits such as easy isolation, low extra production and the
reduced cost.
In recent years, immobilization of the palladium nano-particles on solid supports to
prepare active and stable catalytic systems is an interesting topic. Different supports have been
used to stabilize the nano-particles [8–15]. Along this line, Pd/gellan [16], Pd/arabinogalactan
[17], Pd/agarose [18], Pd/starch [19] and Pd/chitosan [20] have been prepared using
polysaccharides as the bed. In order to develop the use of carbohydrate-based materials as the
support for palladium nano-particles, we decided to introduce gelatin/pectin mixture as a suitable
and naturally degradable support for stabilization of palladium nano-particles.
Gelatin is a colorless, fragile, translucent, nearly tasteless solid. It is a water soluble
protein and is an irreversibly hydrolyzed form of collagen [21]. Gelatin contains free carboxyl
groups on its backbone and has the potential for chelating and reducing transition metals [22].
Pectin is a family of complex polysaccharides that is found extensively in nature [23].
Unique properties of pectin, such as biodegradability, flexibility, non-toxicity, low price and
carrying freely available hydroxyl groups make it suitable and ideal candidate for many practices
in different areas of science.
2

Therefore, using gelatin/pectin mixture as a support for palladium species has two
advantages; first it has the ability to reduces Pd(II) to Pd(0) via its available free carboxyl groups
2
by liberation of CO gas and the second is to act as a highly functionalized support, which
stabilizes the reduced form of the palladium particles by ligation.
Palladium-catalyzed Mizoroki–Heck coupling reaction is one of the most powerful
synthetic methods for the formation of carbon-carbon bonds, which allows the arylation,
alkylation or vinylation of various alkenes through their reaction with aryl, vinyl, benzyl or allyl
halides in the presence of palladium and a suitable base [7,24]. Total synthesis of complex
organic molecules has benefited extraordinary from the Mizoroki–Heck reaction. The Mizoroki–
Heck coupling products find good applications as intermediates in the preparation of materials,
natural products, and bioactive compounds [25]. Herein, we report that palladium nano-particles
stabilized by gelatin/pectin mixture can be successfully used in the Mizoroki–Heck cross-
coupling reaction between the activated and non-activated aryl halides and n-butyl acrylate under
solvent-free conditions.
2
. Experimental
2
.1. General
Chemicals were purchased from Fluka, Merck and Aldrich Chemical Companies and
were used as purchased, without further purification. 1H and 13C NMR spectra were measured
with Bruker Avance III-400 (at 400.2 and 100.6 MHz) spectrometer in pure CDCl3 solvent with
tetramethylsilane (TMS) as the internal standard. Mass spectra were recorded on an Agilent
Technologies (HP) 5973 mass spectrometer operating at an ionization potential of 70 eV. X-ray
diffraction spectrum of the catalyst was obtained by XRD (Ital structures, APD 2000). The
3

transmission electron micrographs (TEM) was obtained using TEM apparatus (100 kV Philips,
EM208) for characterization of the nanoparticles. Field emission scanning electron micrographs
(FE-SEM) were obtained by FE-SEM (Hitachi japan, S4160 at 20 kV). UV-Vis spectra were
recorded on Agilent, 8453, UV-Vis spectrometer. The amount of palladium nanoparticles
supported on gelatin/pectin was measured by SEM-EDX analyzer (Tescan Vega II, with a
Rontec detector) and also by ICP analyzer (Varian, Vista-pro).
2
.2. Synthesis of palladium nano-particles supported on gelatin/pectin mixture
Pectin (0.5 g) and gelatin (0.5 g) were dissolved in water (100 mL) at room temperature.
2
To this solution was added a solution of PdCl (100 mL, 1 mM) and diluted with water (100 mL).
◦
The reaction mixture was refluxed at 100 C for 5h to ensure the complete conversion of Pd(II) to
Pd(0). The mixture was cooled down to room temperature and the solvent was evaporated. The
obtained dark gray composite was dried by the flow of air over night and then under vacuum for
24 h.
2
.3. General method for the Mizoroki–Heck reaction using the nano-catalyst
To a flask, a mixture of gelatin/pectin supported Pd-nano-particles (0.05 g of the
composite, contains 0.002 mmol of palladium), aryl halide (1 mmol), n-butyl acrylate (1.5 mmol,
0
3
.21 mL) and n-Pr N (1.5 mmol, 0.29 mL) were added under solvent-free conditions. The
◦
mixture was stirred at 140 C in the air. After completion of the reaction (monitored by TLC),
ethylacetate (10 mL) was added to the flask. The catalyst was separated by simple filtration.
Water (3× 15 mL) was added to the ethylacetate phase and decanted. The organic layer was dried
4

2 4
over anhydrous Na SO . After evaporation of the solvent, the crude product was purified by
column chromatography.
2
.4. Spectral data for products
1
(
Product 1a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 0.99 (t, 3H, J= 7.2 Hz), 1.47 (sex,
2
H, J= 7.6 Hz), 1.72 (quint, 2H, J= 6.8 Hz), 4.24 (t, 2H, J= 6.4 Hz), 6.51 (d, 1H, J= 16 Hz), 7.39
13
(
t, 3H, J= 4 Hz), 7.54 (m, 2H), 7.71 (d, 1H, J= 16 Hz); C NMR (CDCl3, 100 MHz): δ (ppm):
13.78, 19.23, 30.81, 64.42, 118.31, 128.06, 128.88, 130.22, 134.50, 144.55, 167.08; MS (m/e):
+
-1
2
04 [M ]; FT-IR ν(cm ): 1715 (C=O).
1
(
Product 2a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 1.00 (t, 3H, J= 7.2 Hz), 1.48 (sex,
2
1
H, J= 7.2 Hz), 1.73 (quint, 2H, J= 6.8 Hz), 2.46 (s, 3H), 4.25 (t, 2H, J= 6.8 Hz), 6.40 (d, 1H, J=
13
6 Hz), 7.23 (t, 2H, J= 7.2 Hz), 7.11 (m, 1H), 7.58 (d, 1H, J= 7.2 Hz), 8.01 (d, 1H, j=16 Hz); C
NMR (CDCl3, 100 MHz): δ (ppm): 13.79, 19.25, 19.79, 30.82, 64.42, 119.32, 126.34, 126.41,
+
-1
1
29.97, 130.79, 133.46, 137.62, 142.26, 167.17; MS (m/e): 218 [M ]; FT-IR ν(cm ): 1715
(C=O).
1
(
Product 3a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 1.00 (t, 3H, J= 7.6 Hz), 1.47 (sex,
2
1
1
1
H, J= 7.2 Hz), 1.72 (quint, 2H, J= 6.4 Hz), 2.39 (s, 3H), 4.23 (t, 2H, J= 6.4 Hz), 6.42 (d, 1H, J=
1
3
5.6 Hz), 7.21 (d, 2H, J= 8 Hz), 7.45 (d, 2H, j=8 Hz), 7.69 (d, 1H, J= 16 Hz); C NMR (CDCl3,
00 MHz): δ (ppm): 13.79, 19.24, 21.47, 30.83, 64.35, 117.20, 128.07, 129.62, 131.77, 140.61,
+
-1
44.57, 167.31; MS (m/e): 218 [M ]; FT-IR ν(cm ): 1715 (C=O).
1
(
Product 4a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 0.97 (t, 3H, J= 7.2 Hz), 1.45 (sex,
2
1
H, J= 7.6 Hz), 1.69 (quint, 2H, J= 6.8 Hz), 3.83 (s, 3H), 4.21 (t, 2H, J= 6.8 Hz), 6.32 (d, 1H, J=
13
6 Hz), 6.90 (d, 2H, J= 8.8 Hz), 7.48 (d, 2H, j=8.8 Hz), 7.65 (d, 1H, J= 16 Hz); C NMR
5

(CDCl3, 100 MHz): δ (ppm): 13.77, 19.23, 30.84, 55.32, 64.24, 114.30, 115.76, 127.20, 129.68,
+
-1
1
44.20, 161.34, 167.40; MS (m/e): 234 [M ]; FT-IR ν(cm ): 1713 (C=O).
1
(
Product 5a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 0.98 (t, 3H, J= 7.2 Hz), 1.46 (sex,
2
1
H, J= 7.6 Hz), 1.72 (quint, 2H, J= 7.2 Hz), 2.54 (s, 3H), 4.25 (t, 2H, J= 6.8 Hz), 6.48 (d, 1H, J=
13
6 Hz), 7.68 (d, 1H, J= 8.4 Hz), 7.93 (d, 1H, j=16 Hz), 8.08 (m, 2H); C NMR (CDCl3, 100
MHz): δ (ppm): 13.74, 19.19, 19.93, 30.70, 64.88, 121.41, 123.34, 125.49, 127.30, 138.98,
+
-1
1
39.77, 139.87, 148.16, 166.22; MS (m/e): 263 [M ]; FT-IR ν(cm ): 1715 (C=O).
1
(
Product 6a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 1.04 (t, 3H, J= 7.2 Hz), 1.52 (sex,
2
7
1
1
H, J= 7.6 Hz), 1.78 (quint, 2H, J= 6.8 Hz), 4.31 (t, 2H, J= 6.8 Hz), 6.58 (d, 1H, J= 15.6 Hz),
.49-7.62 (m, 3H), 7.78 (d, 1H, j=7.2 Hz) 7.91 (t, 2H, j=6 Hz) 8.23 (d, 1H, j=8.4 Hz), 8.57 (d,
1
3
H, j=15.6 Hz); C NMR (CDCl3, 100 MHz): δ (ppm): 13.84, 19.30, 30.87, 64.57, 120.97,
23.42, 125.02, 125.48, 126.24, 126.87, 128.76, 130.49, 131.44, 131.85, 133.71, 141.61, 167.02;
+
-1
MS (m/e): 254 [M ]; FT-IR ν(cm ): 1714 (C=O).
1
(
Product 7a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 0.98 (t, 3H, J= 7.2 Hz), 1.45 (sex,
2
H, J= 7.6 Hz), 1.71 (quint, 2H, J= 6.8 Hz), 4.24 (t, 2H, J= 6.4 Hz), 6.57 (d, 1H, J= 16 Hz), 7.67
13
(
m, 3H), 8.25 (d, 2H, j=8.4 Hz); C NMR (CDCl3, 100 MHz): δ (ppm):13.73, 19.17, 30.67,
+
6
4.90, 122.61, 124.16, 128.63, 140.61, 141.57, 148.46, 166.11; MS (m/e): 249 [M ]; FT-IR
-1
ν(cm ): 1709 (C=O).
1
(
Product 8a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 0.97 (t, 3H, J= 7.2 Hz), 1.45 (sex,
2
1
H, J= 7.6 Hz), 1.69 (quint, 2H, J= 6.8 Hz), 3.83 (s, 3H), 4.21 (t, 2H, J= 6.8 Hz), 6.32 (d, 1H, J=
13
6 Hz), 6.90 (d, 2H, j= 8.8 Hz), 7.48 (d, 2H, j=8.8 Hz), 7.65 (d, 1H, j= 16 Hz); C NMR
(CDCl3, 100 MHz): δ (ppm): 13.77, 19.23, 30.84, 55.32, 64.24, 114.30, 115.76, 127.20, 129.68,
+
-1
1
44.20, 161.34, 167.40; MS (m/e): 234 [M ]; FT-IR ν(cm ): 1713 (C=O).
6

1
(
Product 9a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 0.99 (t, 3H, J= 7.2 Hz), 1.47 (sex,
2
H, J= 7.6 Hz), 1.72 (quint, 2H, J= 6.8 Hz), 4.24 (t, 2H, J= 6.4 Hz), 6.51 (d, 1H, J= 16 Hz), 7.39
13
(
t, 3H, J= 4 Hz), 7.54 (m, 2H), 7.71 (d, 1H, J= 16 Hz); C NMR (CDCl3, 100 MHz): δ (ppm):
13.78, 19.23, 30.81, 64.42, 118.31, 128.06, 128.88, 130.22, 134.50, 144.55, 167.08; MS (m/e):
+
-1
2
04 [M ]; FT-IR ν(cm ): 1715 (C=O).
1
(
Product 10a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 1.00 (t, 3H, J= 7.6 Hz), 1.47 (sex,
2
1
1
1
H, J= 7.2 Hz), 1.72 (quint, 2H, J= 6.4 Hz), 2.39 (s, 3H), 4.23 (t, 2H, J= 6.4 Hz), 6.42 (d, 1H, J=
1
3
5.6 Hz), 7.21 (d, 2H, J= 8 Hz), 7.45 (d, 2H, j=8 Hz), 7.69 (d, 1H, J= 16 Hz); C NMR (CDCl3,
00 MHz): δ (ppm): 13.79, 19.24, 21.47, 30.83, 64.35, 117.20, 128.07, 129.62, 131.77, 140.61,
+
-1
44.57, 167.31; MS (m/e): 218 [M ]; FT-IR ν(cm ): 1715 (C=O).
1
(
Product 11a): H NMR (CDCl
3
, 400 MHz): δ (ppm): 0.99 (t, 3H, J= 7.2 Hz), 1.46 (sex,
2
H, J= 7.6 Hz), 1.72 (quint, 2H, J= 7.2 Hz), 4.25 (t, 2H, J= 6.8 Hz), 6.54 (d, 1H, J= 16 Hz), 7.37
1
3
(
m, 1H), 7.69 (d, 1H, J= 16.4 Hz), 7.87 (d, 1H, J= 8 Hz), 8.63 (s, 1H), 8.78 (s, 1H); C NMR
(CDCl3, 100 MHz): δ (ppm): 13.75, 19.19, 30.73, 64.74, 120.60, 123.83, 130.35, 134.32, 140.76,
+
-1
1
49.58, 150.82, 166.40; MS (m/e): 205 [M ]; FT-IR ν(cm ): 1715 (C=O).
3
. Results and discussion
palladium nano-particles supported on gelatin/pectin mixture were prepared by disposal
of aqueous solution of PdCl
2
(100 mL, 1 mmol) to pectin and gelatin (0.5 g of each dissolved in
100 mL water) without using any extra reducing agent under reflux conditions for 5h (Fig. 2).
This solution was refluxed giving a gray solution and by drying in vacuum gave a dark gray
solid.
<
Fig. 1>
7

The UV–Vis spectroscopy of the resulted Pd supported nano-particles to ascertain the
conversion of Pd(II) to Pd(0) by the disappearance of the peak at around 450 nm (Fig. 3). This
change showed the pectin and gelatin can form complexes with Pd(II) ions and reduce them to
Pd(0). The process of reduction is performed by oxidation of carboxyl groups and liberation of
CO gas at the reflux conditions [24b].
2
<
Fig. 2>
The energy dispersive X-ray analysis (EDX) showed the presence of palladium and its
loading amount was measured to be 1.75% (w/w) in the Pdnp/gelatin/pectin catalyst. The EDX
spectrum also shows signals of carbon, nitrogen and oxygen which are present in the gelatin and
pectin (Fig. 4).
<
Fig. 3>
The XRD of Pdnp/gelatin/pectin catalyst confirmed the formation of Pd nano-particles.
The XRD showed the three characteristic peaks at (1 1 1), (2 0 0) and (3 1 1) can be clearly
observed for Pd particles (Fig. 5). These characteristic peaks shows crystallographic planes of
the Pd(0) nano-particles. Generally, Solid material can be classified as being either amorphous or
crystalline. In crystalline materials the ions engross specific locations in a regular lattice. The
simplest such lattice is a simple cube with ions on each of the corners of the cube. The most
common simple structures are the face centered cubic (fcc) and the body centered cubic (bcc).
The fcc structure consists of a cube of ions with six additional ions located at the centers of each
8

of the six faces of the cube [26]. According to crystallographic planes in the diffraction pattern of
the spectrum the face centered cubic (fcc) crystalline structure was indicated for Pd(0).
<
Fig. 4>
The TEM image of the catalyst showed that the Pd nano-particles with near spherical
morphology were formed onto the surface of gelatin and pectin with relatively good
monodispersity. The TEM image indicates that the size of the palladium particles to be in the
range 2–5 nm (Fig. 6a).
<
Fig. 5>
The FESEM image of the Pdnp/gelatin/pectin catalyst shows the size of the particles to be
in the range 2–5 nm (Fig. 7).
<
Fig. 6>
In order to optimize the reaction conditions, first we studied the effect of media upon the
reaction. For this purpose, the coupling reaction of iodobenzene with n-butyl acrylate was used
as a model reaction to investigate the catalytic performance of Pdnp/gelatin/pectin.The influence
of bases, solvents and reaction temperature on the yield was investigated (Table 1). Employing
◦
DMSO and DMF as the solvent in the presence of n-Pr
3
N at 140 C gave 100% conversion of the
starting material after 13 min (Table 1, entries 1 and 2). The use of other organic solvents (Table
, entries 3 and 6) or protic solvents (Table 1, entries 4 and 5) was not beneficial to the process.
1
We have also studied the reaction in solvent-free condition and in the presence of DMSO and
DMF as the solvent after 3 min. The desired product was obtained in 42, 39 and 98% yields,
◦
respectively at 140 C. Comparison of the results clearly shows that the reaction in solvent-free
9

conditions (Table 1, entry 11) proceeded better than in solvents with an excellent yield and
shorter reaction time.
The reaction was also studied at various temperatures under non-solvent conditions. The
results demonstrated that the temperature plays a significant role in the reaction rate. The activity
of the catalyst was increased in high temperatures (Table 1, entries 7–11) with the activity being
◦
very high at 140 C. During our optimization studies, various bases were examined and it was
found that the catalyst was very active and selective for the reaction in the presence of n-Pr
3
N
(Table 1, entry 11) as a liquid organic base, while the reaction rate was very slow when inorganic
bases were used (Table 1, entries 12–14). Remarkably, the reactions were carried out in air
indicating that the Pdnp/gelatin/ pectin catalyst was highly stable and insensitive to oxygen.
<
Table 1>
In order to show the ability of synthesized Pd nano-particles and their application in
organic synthesis, we applied Pdnp/gelatin/pectin as the catalysts in the Mizoroki–Heck reaction.
Employing the optimized reaction conditions (Table 1, entry 11) a range of aryl iodides and
bromides with various substituent groups were examined in the Mizoroki–Heck reaction (Table
2
).
<
Table 2>
The reaction was carried out in the presence of aryl halide (1mmol), alkene (1.5 mmol),
N (1.5mmol) and Pd- nano-particles supported on gelatin and pectin (0.05 g, containing
.002 mmol of Pd).
n-Pr
3
0
10

In the Mizoroki–Heck reaction, various substituents on aryl halides can influence on the
rate of reaction. Therefore, electron-withdrawing substituents (such as NO , CH CO and F) on
aryl halides increase the reaction rate and electron-donating substituents (such as Me, OMe and
2
3
NH
2
) on aryl halides decrease the reaction rate [27].
According to results, high reaction rates and yields were obtained with both activated and
non-activated aryl iodides (Table 2, entries 1–6). Aryl iodides without any substituent and
activated aryl iodides with electron-withdrawing substituents are reactive substrates in Mizoroki–
Heck reaction and the related reactions were completed in shorter times. As an example, the
reaction of iodobenzene with n-butyl acrylate was completed within 3 min giving the desired
product in 98% isolated yield (Table 2, entry 1). Non-activated aryl iodides with
electrondonating substituents (such as Me and OMe) on the aromatic ring are not reactive
substrates in Mizoroki–Heck reaction and the related reactions were completed in longer reaction
times (Table 2, entries 2–4).
The observed longer reaction time for the reaction of 4-iodoanisole in compare with 4-
iodotoluen is due to electrondonating ability of substituents on aromatic rings (Table 2, entries 3
and 4). As shown in Table 2, the coupling reaction of butyl acrylate with o-substituted in
compare with p-substituted aryl iodides performed in longer reaction times (Table 2, entries 2
and 3).
The synthesized Pdnp/gelatin/pectin catalytic system was also applied for the substituted aryl
bromides and hetero aryl bromide giving the desired products in moderate to high yields (Table
2
, entries 7–11).
There are many reports in the applying palladium nano-particles for the Mizoroki–Heck
reaction. To show the catalytic activity of Pdnp/gelatin/pectin system, we compare the previously
11

reported systems with this system in Mizoroki–Heck reaction. Bhaumik et al. reported the
application of Pdnp tethered into mesoporous polymer MPTA1 in the Mizoroki–Heck reaction of
2 3 2
iodobenzene with n-butyl acrylate in the presence of K CO as a base in H O at reflux. Under
these conditions, the reaction was completed within 5 h [28]. While for the similar reaction with
our catalytic system gave the desired product within 3 min in 98% yield (Table 2, entry 1). Also
the synthesis of poly(N-vinyl imidazole) grafted silica-containing palladium nano-particles has
been applied as a catalyst in Mizoroki–Heck reaction of 4-iodoanisole with n-butyl acrylate
2 3
using DMF as solvent in the presence of K CO under phosphine free conditions and the reaction
was completed within 1 h [29]. While for the similar reaction, using the Pdnp/gelatin/pectin the
reaction was completed after 18 min (Table 2, entry 4). In another report, palladium supported on
super para magnetic nano-particles was used as a catalyst for Mizoroki–Heck reaction of
iodobenzene with n-butyl acrylate. The reaction was completed within 5 h in the presence of
◦
K
2
CO
3
in NMP as the solvent at 130 C [30], whereas, the similar reaction, as mentioned above,
went to completion within 3 min. Wang and coworkers reported the application of Pd nano-
particles supported on functionalized mesoporous silica in the Mizoroki–Heck reaction of
◦
iodobenzene with n-butyl acrylate in the presence of Et
3
N as a base in DMF at 120 C. Under
these conditions, the reaction was completed within 1 h [31]. Similar reaction under our
conditions gave the desired product within only 3 min in 98% yield (Table 2, entry 1).
The notable properties of Pdnp/gelatin/pectin system are in situ generation of nano-particles
without addition of any external reducing agents, stability toward air and humidity, easy
handling and recycle ability. It is worth noting, some of the reactions proceeded in the presence
of Pdnp/gelatin/pectin system under solvent-free conditions, are among the fastest ever reported.
12

The importance of using heterogeneous catalyst is due to their application in industry and
the reusability of catalyst is the major area of interest. The reusability of the catalyst was checked
upon the reaction of iodobenzene with n-butyl acrylate as the substrates in the presence of the
◦
catalyst and n-Pr3N at 140 C. After completion of the reaction in the first time, the organic
compounds were separated from the reaction mixture by a simple extraction and the resulting
solid mass was reused for the six times. At the first time, the reaction was completed within 3
min in 98% yield. The Pdnp/gelatin/pectin has been recovered for six times with some decrease in
the catalytic activity of the catalyst. At the sixth time, the reaction was completed within 20 min
in 82% yield (Fig. 7).
<
Fig. 7>
It is interesting that among the recycling process the shape and size of the nano-catalyst
does not change notably. The TEM picture of the recovered nanocatalyst after sixth run showed
that the morphology and the size of the particles were not disturbed notably in comparison with
the TEM picture of the fresh catalyst (Fig. 6a and 6b).
In order to get more information about the leaching of palladium in reaction, the reaction of
iodobenzene with n-butyl acrylate as a model reaction was studied. After completion of the
reaction and the workup for the first run, the amount of leaching was determined by ICP analysis
to be <2.5%. The amount of Pd leaching after the 6th run was also determined by ICP analysis to
be only 14%.
4
. Conclusion
Pdnp/gelatin/pectin as a new category of nano-composite was obtained easily by the in
situ reduction of PdCl under green conditions without addition of any external reducing agents.
2
13

The Pdnp/gelatin/pectin system showed a high activity toward the Mizoroki–Heck cross-coupling
reaction of various aryl halides (I and Br) under solvent-free conditions. The catalyst was very
stable and could be easily separated from the products and reused for six times.
Acknowledgements
We sincerely acknowledge the financial supports from Bu-Ali Sina University Research
Councils, Center of Excellence in Development of Chemistry Methods (CEDCM) and PNU
University.
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17

Table captions
Table 1. Optimization studies for the reaction of iodobenzene with n-butyl acrylate in the presence of
a
Pdnp/gelatin/ pectin.
Table 2. Reaction of aryl halides with n-butyl acrylate catalyzed by Pdnp/gelatin/pectin.
Figure captions
Fig. 1. Preparation of Pdnp/gelatin/ pectin.
Fig. 2. UV–Vis spectroscopy of (a) Pd(II) before reduction and (b) Pd(0) after reduction with gelatin and
pectin.
Fig. 3. The EDX spectrum of Pdnp/gelatin/pectin.
Fig. 4. The XRD spectrum of Pdnp/gelatin/pectin.
Fig. 5. TEM image of the fresh Pdnp/gelatin/pectin catalyst that shows the morphology of Pd nano-
particles on the surface (a), TEM image of the Pdnp/gelatin/pectin catalyst after the 6th run of recycling of
the catalyst (b).
Fig. 6. FESEM image of the Pdnp/gelatin/pectin catalyst that shows the morphology of Pdnp on the
surface.
Fig. 7. Recoverability of Pdnp/gelatin/ pectin
18

Table section:
Table 1. Optimization studies for the reaction of iodobenzene with n-butyl acrylate in the presence of Pdnp/gelatin/
a
pectin.
◦
b,c
Entry
Base
Solvent
DMSO
DMF
T( C)
Time
13 min
13 min
12 h
Yield(%)
94 (100)
90 (100)
12 (24)
31 (37)
48(53)
1
2
3
4
5
6
7
8
9
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
3
N
140
3
N
140
3
N
Toluene
EtOH
Reflux
Reflux
Reflux
Reflux
80
3
N
12 h
3
N
2
H O
12 h
3
N
THF
12 h
8 (12)
3
N
None
None
None
None
None
None
None
None
None
6 h
12 (18)
82 (87)
90 (100)
92 (100)
98 (100)
70 (75)
80 (84)
91 (93)
94 (100)
3
N
100
5 h
3
N
120
85 min
30 min
3 min
14 h
10
11
12
13
14
15
3
N
130
n-Pr
3
N
140
NaOH
KOAc
140
140
14 h
2
K CO
3
140
15 h
DABCO
140
1 h
The bold values (entry 11) show our selected conditions for Mizoroki-Heck reaction.
a
Reactions were carried out using 1 mmol of idobenzene, 1.5 mmol of n-butyl acrylate and 1.5 mmol of base.
Yields are given for isolated products.
b
c
The data presented in the parenthesis refer to the conversion of iodobenzene.
19

Table 2. Reaction of aryl halides with n-butyl acrylate catalyzed by Pdnp/gelatin/pectin.
O
X
O
Pd np /gelatin /pectin
O
+
o
R
n-Pr N, 140 C ,solvent-free
O
3
R
Entry
Aryl halide
Product
Time
Yield(%)
98
I
O
O
1
2
3 min
1
a
I
O
O
25 min
14 min
92
95
Me
Me
2
a
I
O
O
3
Me
Me
3
a
I
O
O
4
5
6
7
18 min
23 min
30 min
70 min
93
93
90
93
MeO
MeO
4
a
I
O
O
O2N
Me
O2N
Me
O
5
a
I
O
6
a
O
Br
O
O2N
O2N
7
a
Br
O
8
9
16 h
14 h
72
84
O
MeO
MeO
8a
Br
O
O
9
a
20

O
Br
O
1
1
0
1
16 h
75
80
Me
Me
10a
Br
O
O
7.5 h
N
N
11a
Figure section:
Fig. 1. Preparation of Pdnp/gelatin/ pectin.
21

Fig. 2. UV–Vis spectroscopy of (a) Pd(II) before reduction and (b) Pd(0) after reduction with gelatin and pectin.
Fig. 3. The EDX spectrum of Pdnp/gelatin/pectin.
Fig. 4. The XRD spectrum of Pdnp/gelatin/pectin.
22

Fig. 5. TEM image of the fresh Pdnp/gelatin/pectin catalyst that shows the size and morphology of Pd
nano-particles on the surface (a), TEM image of the Pdnp/gelatin/pectin catalyst after the 6th run of
recycling of the catalyst (b).
Fig. 6. FESEM image of the Pdnp/gelatin/pectin catalyst that shows the morphology of Pdnp on the surface.
23

Fig. 7. Recoverability of Pdnp/gelatin/pectin
24