Palladium nanoparticles immobilized on poly(vinyl chloride)-supported pyridinium as an efficient and recyclable catalyst for suzuki-miyaura cross-coupling reaction

Article abstract of DOI:10.1155/2011/313102

The palladium nanoparticles immobilized on the polymeric surface of poly(vinyl chloride)-supported pyridinium (PVC-Py-Pd⁰) were achieved by a simple procedure by applying the corresponding functionalized polymer and palladium chloride in ethanol solution. The as-prepared catalyst (PVC-Py-Pd ⁰) was found to be air and moisture stable and exhibits significant catalytic activity for Suzuki-Miyaura cross-coupling reaction of various aryl halides and phenylboronic acid under milder operating conditions. The procedure presented here showed several merits such as short reaction time, simple experimental and isolated procedure and excellent yields of products. Furthermore, the catalyst can be easily recovered and reused for at least six times with consistent activities. Copyright E-Journal of Chemistry 2004-2011.

Full text of DOI:10.1155/2011/313102

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(4), 1490-1497
http://www.e-journals.net
Palladium Nanoparticles Immobilized on
Poly(vinyl chloride)-Supported Pyridinium as an
Efficient and Recyclable Catalyst for
Suzuki-Miyaura Cross-Coupling Reaction
BO ZHOU and YI-QUN LI*
Department of Chemistry, Jinan University
Guangzhou 510632, PR China
tlyq@jnu.edu.cn
Received 8 August 2010; Revised 19 November 2010; Accepted 15 December 2010
Abstract: The palladium nanoparticles immobilized on the polymeric surface
of poly(vinyl chloride)-supported pyridinium (PVC-Py-Pd0) were achieved by
a simple procedure by applying the corresponding functionalized polymer and
palladium chloride in ethanol solution. The as-prepared catalyst (PVC-Py-Pd0)
was found to be air and moisture stable and exhibits significant catalytic
activity for Suzuki-Miyaura cross-coupling reaction of various aryl halides and
phenylboronic acid under milder operating conditions. The procedure
presented here showed several merits such as short reaction time, simple
experimental and isolated procedure and excellent yields of products.
Furthermore, the catalyst can be easily recovered and reused for at least six
times with consistent activities.
Keywords: Nanopalladium, Poly(vinyl chloride), Pyridinium, Heterogeneous catalyst, Suzuki-
Miyaura reaction
Introduction
The palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of aryl halides with
arylboronic acids, is one of the most powerful tool for the preparation of unsymmetrical
biaryl compounds1-5, which has been applied to many areas, including herbicides6 and
natural product syntheses7-9. In the past decades, numerous efforts have been made to
develop efficient catalyst systems for Suzuki-Miyaura cross-coupling reaction10-11. The
traditional protocols for the Suzuki-Miyaura cross-coupling reaction prescribe a palladium
species with phosphine ligands as the catalyst. However, phosphine ligands are expensive,
poisonous, difficultly to recover, air sensitive and subject to P-C bond degradation at elevated

1491
YI-QUN LI et al.
temperatures12. Therefore, the development of phosphine-free catalytic systems to overcome
these drawbacks is considered to be one of the most challenging fields in organic chemistry.
From the standpoint of environmentally benign organic synthesis, development of
immobilized palladium catalysts is challenging and important13-15. In an ideal system, they
can be recovered from the reaction mixture by simple filtration and re-used infinitely and
contamination of products by palladium is prevented. Recently, the preparation and
application of polymer-supported catalysts has drawn dramatic attention during the past few
years, serious interest in these catalysts originated with efforts to develop catalytic systems
displaying the high activity, convenient work-up, easy separability and recovery,
lowtoxicity16.
Metal nanoparticles exhibit unique properties on optical, electronic and chemical behavior
which is quite different from bulk metal materials due to quantum size effect, surface effect
and others effects17-19. Transition metal nanoparticles as good catalysts for organic synthesis
have attracted much attention over the past decade20-23. But the liquid suspensions of metal
nanoparticles in catalysis will bring some problems such as in recycle and the separation of the
catalyst from reaction system. Thus, some work focused on immobilizing metal nanoparticles
on suitable support materials. Actually, many immobilization methods and polymeric support
materials used to catalyze the Suzuki-Miyaura reaction have been reported in literature24-27. All
these catalysts show good catalytic activity for the Suzuki-Miyaura reaction, but the
preparations of the catalyst supports involve many steps. Poly(vinyl chloride) (PVC) modified
by functional group can be prepared via displacement reaction directly without
chloromethylation and makes its inexpensive and practical support for heterogeneous catalyst.
To development of simple and reliable protocols for the immobilization of catalytically active
palladium nanoparticles on functionalized PVC, herein, we report the synthesis and
characterization of one kind of poly(vinyl chloride)–pyrudinium resin supported
nanopalladium catalyst and the application of it in Suzuki-Miyaura reaction of aryl halides
with arylboronic acids that can afford excellent yield in the air.
Experimental
Melting points were measured by X6 micromelting point apparatus and uncorrected.
1
Infrared spectra were recorded using KBr pellet on a Nicolet 2700 spectrometer. H NMR
spectra were recorded on a Bruker AVANCE 300 instrument at 300 MHz in DMSO-d6 using
TMS as the internal standard. The elemental analyses were performed on a Perkin Elmer
EA2400II elemental analyzer. The contents of elemental palladium in the polymeric catalyst
were determined by Perkin Elmer Optima 2000DV inductive coupled plasma (ICP)
spectroscopy. Scanning electron microscopy (SEM) was performed with Philips XL
30ESEM instrument. Transmission electron microscopy (TEM) was performed with a
Philips Tecnai instrument operating at 40–100 kV. All chemicals used were of commercial
grade without further purification.
General procedure for the synthesis PVC-Py-Pd0 catalyst
To a 250 mL three-necked flask was added pyridine (30.0 mL, 0.375 mol), sodium hydroxide
(24.0 g, 0.6 mol) and water (45 mL). To the solution poly(vinyl chloride) (15.0 g) was added and
the reaction mixture and stirred below 60 °C for 3 h, then stirred at 95-100 °C for another 16 h.
After cooling to the room temperature, the mixture was poured into 500 mL water, filtered and
washed with water (3×20 mL) and 95% ethanol (3×20 mL).The as-prepared resin was then
treated with PdCl2 (2.0 g, 9.4 mmol) in 95% ethanol (100.0 mL) for 48 h yielding the elemental
analysis. Metal content of PVC-Py-Pd0 was found to be 0.22 mmol/g by ICP.

Pyridinium as an Efficient and Recyclable Catalyst
1492
General procedure for the PVC-Py-Pd0 catalyzed Suzuki-Mayaura cross-coupling
reaction
The PVC-Py-Pd0 catalyst (3.6 mol% Pd), phenylboronic acid (150 mg, 1.2 mmol), K2CO3
(280 mg, 2.0 mmol) and aryl halides (1.0 mmol) were added to a 25.0 mL reaction flask
containing 95% ethanol (10.0 mL). The mixture was heated to 78 °C and stirred for the
specific time indicated in Table 2. The progress of the reaction was monitored by TLC.
After the completion of the reaction, the catalyst was filtered off and washed with 95%
ethanol for several times by suction. The filtrate was poured into 50.0 mL distilled water and
the solid materials were filtered and treated with 95% ethanol. The products were further
purified with recrystallisation. All of the products are known and the data are found to be
identical with those that reported in literature elsewhere.
Results and Discussion
Preparation and characterization of PVC-Py and PVC-Py-Pd0
Since ‘naked’ nanoparticles are kinetically unstable in solution, all preparation methods
must use stabilizing agents, which adsorb at the particle surface. There are three types of
nanoparticles stabilization: electrostatic stabilization (anions and cations associate with the
NPs), steric stabilization, (aggregation is prevented through the adsorption of large
molecules) and electrosteric stabilization (combining both steric and electrostatic effects)28.
To obtain the stable nanopalladium immobilized on the surface of polymer via electrosteric
stabilization effects, we design a new polymer-supported pyridinium cation resin and use it
as both steric and electrosteric stabilizing agents. The palladium nanocluster stabilized
model was illustrated in Figure 1.
PVC-Py =
Figure 1. Schematic model illustrating the palladium nanocluster immobilized on the
surface of the ionic polymer
The preparation of the PVC-Py involved the addition of an excess of pyridine to
commercial available PVC resin in water at 80 °C for the specific time to afford the
corresponding functionalized resin. The catalyst PVC-Py-Pd0 is directly prepared by simple
in situ reduction of ethanolic solution of palladium chloride in the presence of PVC-Py
support (Scheme 1).
OH
CH
CH
Cl
C
H
CH
CH
CH
N
2
+
CH
CH
Cl
2
2
n
H O
2
z
y
x
N
OH
CH
PdCl
2
C
H
CH
CH
CH
N
CH
CH
N
CH
Cl
2
2
2
z
y
x
95%EtOH
0
Pd
Scheme 1. Preparation of PVC-Py-Pd0 catalyst

1493
YI-QUN LI et al.
The IR spectrum of the PVC-Py showed the characteristic absorption of double bond
(C=C and C=N) group at 1640 cm-1. The nitrogen content was found to be 5.06 mmol/g.
Metal content in PVC-Py-Pd0 catalyst was found to be 0.22 mmol/g by ICP. The
morphology of PVC-Py-Pd0 as well as the polymer support PVC-Py, was studied using
transmission electron microscopy (TEM). TEM images showed the presence of palladium
nanoparticles of ≤40 nm size with the distribution on the surface of polymer matrix (Figure 2).
Figure 2. TEM image of fresh prepared PVC-Py-Pd0
Thermal stability of the PVC-Py-Pd0 has great effect on its catalytic activity and
recyclability because Suzuki-Miyaura reaction is usually carried out under heat conditions.
Figure 3 shows the TG curves of PVC–Py-Pd0 respectively at atmospheric conditions. TG
analysis shows that PVC–Py–Pd0 are stable up to 174.25 ºC respectively.
Temperature, oC
Universal V4.5A TA Instruments
Exo Up
Figure 3. TG curve of PVC-Py-Pd0.
Effect of the base on the catalytic performance
In order to explore the PVC-Py-Pd0 nanoparticles catalyst for the Suzuki-Miyaura coupling
reaction, the coupling of p-nitrobromobenzene and penylboronic acid was chosen as the
model reaction to study the effect of different base. As shown in Table 1, the rate of reaction

Pyridinium as an Efficient and Recyclable Catalyst
1494
and the activity of the catalyst were significantly influenced by the base used. NaHCO3,
NaOH, K2CO3 and Na3PO4⋅12H2O were found to be effective in the reaction, Na2CO3, CaO
and Cs2CO3 led to moderate yields of product, while KOH resulted in a lower yield. Among
the bases screened, K2CO3 was so chosen for the base in the Suzuki-Miyaura reaction with
yield up to 99% and reaction time is less than 1 h.
Table 1. Effect of base on the PVC-Py-Pd0 catalyzed Suzuki-Miyaura cross-coupling
reaction of p-nitrobromobenzene with penylboronic acid
Entry
Base
Na2CO3
NaHCO3
KOH
Reaction time, h
Yields, %a
89.5
94.5
78
1
2
3
4
5
6
7
8
7
14.5
1.2
12
9.5
1
CaO
NaOH
K2CO3
83.5
92.5
99
6
12
92
89
Na3PO4⋅12H2O
Cs2CO3
Isolated yield was based on p-nitrobromobenzen
Effect of the amount of the catalyst on the Suzuki-Miyaura reaction
It is a key issue to note that the amount of palladium catalyst plays an important role in the
product yields. The Suzuki-Miyaura reaction of p-nitrobromobenzene and penylboronic acid
was studied with the amount of catalyst ranging from 0.8 to 5.0% (Table 2).
Table 2. Effect of the ammount of catalyst on the catalytic performance
Reaction time, h Yields, %b
Entry
Amount of catalyst, mol% Pd
1
2
3
4
0.8
2.0
3.6
5.0
1
1
1
1
91.5
93.3
96.0
95.4
Isolated yield was based on p-nitrobromobenzene
It was found that the arylation could be carried out efficiently even with low amount of
the catalyst (0.8 mol% Pd) at 78 °C, the yield of the product was 91.5%. Increasing the
amount of palladium catalyst gave higher yield until the amount of the catalyst increases to
3.6 mol%. The yield slightly decreases with the increasing of the amount of palladium
catalyst to 5.0 mol%.
Suzuki-Miyaura reaction of aryl halides with arylboronic acid catalyzed by PVC-Py-Pd0
On the basis of the optimized reaction conditions, the coupling reactions between a variety
of aryl halides and arylboronic acids were carried out to explore the general effectiveness of
the PVC-Py-Pd0 nanoparticles catalyst (Scheme 2).
0
PVC-Py-Pd
X
(HO) B
2
R
2
+
R
2
R
1
R
1
1
2
3
Scheme 2. Suzuki-Miyaura coupling reaction catalyzed by PVC-Py-Pd0
The results were listed in Table 3.

1495
YI-QUN LI et al.
Table 3. PVC-Py-Pd0 catalyzed Suzuki-Mayaura cross-coupling reaction of different aryl
halides and aryboronic acids
Entry
ArX (1)
Arylboronic acid (2)
Products (3)
Time, h Yields, %b
1
2
3
4
5
6
7
I
I
1
1
68
97
B(OH)2
H3CO
Cl
B(OH)2
OCH3
Cl
B(OH)2
1
90
I
Br
Br
Br
Cl
3
66
B(OH)2
B(OH)2
H3CO
1
91
OCH3
B(OH)2
3.5
48
86
Cl
Cl
trace
B(OH)2
Cl
Cl
8
H3CO
Cl
48
48
1
trace
trace
92
H3CO
B(OH)2
B(OH)2
Cl
9
Cl
H3CO
H3CO
H3CO
H3CO
H3CO
H3CO
10
11
12
13
14
I
B(OH)2
B(OH)2
B(OH)2
OCH3
Cl
H3CO
H3CO
H3CO
H3CO
H3CO
Cl
1
95
I
I
1
93
Br
Br
Br
1
90
B(OH)2
B(OH)2
H3CO
OCH3
1
87
15
16
17
18
19
20
21
22
23
24
H3CO
B(OH)2
1
1
90
83
95
75
62
66
54
96
95
90
H3CO
H3C
H3C
H3C
H3C
H3C
H3C
O2N
O2N
O2N
O2N
Cl
Cl
H3C
H3C
H3C
H3C
H3C
H3C
O2N
O2N
O2N
I
I
I
B(OH)2
B(OH)2
B(OH)2
B(OH)2
B(OH)2
B(OH)2
1
H3CO
Cl
OCH3
Cl
3.5
2
Br
Br
Br
I
1
H3CO
Cl
OCH3
Cl
9.5
1
B(OH)2
B(OH)2
B(OH)2
OCH3
0.5
1
I
H3CO
I
Cl
Cl
F
F
B(OH)2
25
1
96
I
O2N
O
N
F
F
B(OH)2
B(OH)2
26
27
28
29
2
1
1
1
1
95
99
96
96
O2N
O2N
Br
Br
O2N
O2N
OCH3
Cl
O2N
O2N
Br
Br
H3CO
Cl
B(OH)2
B(OH)2
O2N
I
30
31
32
3.5
1.1
17
96
94
98
B(OH)2
B(OH)2
B(OH)2
O2N
O2N
O2N
I
OCH3
H3CO
Cl
O2N
Cl
I
O2N
H2N
H2N
H2N
O2N
H2N
33
34
35
I
I
I
B(OH)2
B(OH)2
B(OH)2
1
1
92
96
93
H3CO
Cl
H2N
H2N
OCH3
Cl
12
Isolated yield was based on the aryl halides

Pyridinium as an Efficient and Recyclable Catalyst
1496
As illustrated in Table 3, the PVC-Py-Pd0 catalyst was applicable to a wide range of
aryl iodides and bromides substrates to give the products with good to excellent yields.
Under the same condition mentioned above, when aryl bromides were employed, a longer
reaction time was required and lower yields were observed than those of aryl iodides. Most
importantly, aryl iodides with either eletron-donating or eletron-withdrawing substituents
have no obvious effect on the yields.
Reusability of PVC-Py-Pd0 catalyst
One of the main aims of our study was to investigate the reuse of and recycling the catalyst.
Finally, we explored the reusability of the PVC-Py-Pd0 catalyst using the reaction of
p-nitrobromobenzene with phenylboronic acid for the model reaction. After the first run, the
catalyst (3.6 mol% Pd) was filtered and extensively washed with EtOH, Et2O and dried
in vacuo. Then the catalyst was directly reused under the same conditions mentioned above.
The results listed in Table 4.
Table 4. Recycling and reuse of PVC-Py-Pd0 in Suzuki-Miyaura reaction
Entry
Reaction time, h
Yields, %a
98.5
1
2
3
4
5
6
2
3.5
4
96.0
95.0
4
4
93.5
93.5
4
95.0
Isolated yield was based on p-nitrobromobenzene
It can be seen from the results that the catalyst could be reused up to 6 runs while
retaining the catalytic activity. Characterization of the reused catalysts by transmission
electron microscopy (TEM) showed that the nanopalladium has no apparently deactivation
could be correlated to the no agglomeration of size ≤40 nm (Figure 4).
Figure 4. TEM image of PVC-Py-Pd0 after reused 6 runs
Conclusion
In conclusion, PVC-Py-Pd0 has been prepared easily by using inexpensive support and
exhibit high activity toward the Suzuki-Miyaura reaction of aryl halides with arylphenyl
boronic acids in the air. This procedure offers several advantages such as short reaction time,
simple experimental and isolated procedure, satisfactory yields of products, as well as
excellent catalytic activity and reusability. Further application of the catalyst system to other
palladium-catalyzed transformations is on progress.

1497
YI-QUN LI et al.
Acknowledgment
This work was financially supported by the National Natural Science Foundation of China
(No 21072077) and the Guangdong Natural Science Foundation (No 10151063201000051).
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