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Published on the web October 16, 2010
Polystyrene-anchored Palladium(II) Complex as an Efficient and Reusable Catalyst
for Suzuki Cross-coupling Reaction in Water Medium
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1
2
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1
Manirul Islam,* Paramita Mondal, Kazi Tuhina, Dildar Hossain, and Anupam Singha Roy
1
Department of Chemistry, University of Kalyani, Kalyani, Nadia, 741235, W. B., India
2
Department of Chemistry, Bankim Sardar College, S-24 P. G. S., Tangrakhali-743329, W. B., India
(
Received September 3, 2010; CL-100755; E-mail: manir65@rediffmail.com)
H2N
A new polystyrene-anchored palladium(II) catalyst has been
Dioxane
P
CH2Cl +
P
CH2 NH
prepared and characterized by conventional spectroscopic
methods and elemental analyses. The catalyst was found to be
highly effective for the Suzuki cross-coupling reactions of aryl
halides with arylboronic acid in water medium under phosphine-
free reaction conditions. The optimal reaction conditions of the
coupling were determined. The present heterogeneous Pd(II)
catalyst was reusable as well as air-stable to allow easy use.
N
reflux/ 120 °C
N
(
1)
(2)
Pd(OAc)2
AcOH
P
CH2 NH
P
= polystyrene
framework
N
AcO Pd
OAc
(
3)
PS-Pd(II) Cat
Scheme 1. Synthesis of polymer-anchored Pd(II) complex.
Transition metal catalyzed coupling reactions have contrib-
uted greatly to the straightforward and facile construction of
carboncarbon bonds.1 Among them, the SuzukiMiyaura
coupling reaction of aryl halides with arylboronic acids is one of
Herein, we report an effective catalyst system composed of a
palladium complex with polystyrene support. The aim of our
studies is to evaluate the effect of this new heterogeneous
palladium catalyst on the reactivity in the Suzuki cross-coupling
reactions and to further determine the extent of their recovery
and recycling in water.
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4
7
the most powerful tools for the synthesis of biaryl derivatives.
Among the reasons for its appeal are the commercial availability
of a large range of boronic acids, the ease with which these
reagents can be handled and their high functional group
The synthesis of the polymer-supported palladium(II) com-
plex was accomplished according to Scheme 1. The polymer-
anchored ligand 2 was prepared according to a literature
compatibility. Significance progress in this area has been
achieved with a variety of palladium catalyst.8
13
Various
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4
homogeneous as well as heterogeneous Pd catalysts have been
proposed for the Suzuki coupling, the latter recognized clearly
as more advantageous with respect to cost, ease of handling,
method. First, the chloromethylated polystyrene 1 (1 g) was
reacted with 2-aminopyridine (3 mL) in dioxane (10 mL) under
reflux condition for 48 h to afford polymer-anchored 2-amino-
pyridine ligand 2. In the next step, polymer-anchored ligand
(1 g) subsequently reacted with palladium acetate (0.5 g) in acetic
acid (10 mL) at 80 °C for 10 h to generate the corresponding
polystyrene-supported palladium(II) complex 3.
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reusability, and selectivity and purity of obtained products.
Different materials have been employed as supports including
2
0
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mesoporous silicas, activated carbons, polymers, zeolites,
2
4
and hydrotalcite. Organic polymer supports can induce specific
control over the catalytic and complexing ability of the ligand.
Palladium coordinating with functionalized polymer ligands is
increasingly attracting attention in recent time because of their
fascinating molecular topologies and their application potential
in developing new catalytic materials. Polystyrene is one of the
most widely employed macromolecular supports. Very recently
our group has reported the synthesis of Pd(II) compound
anchored on functionalized polystyrene and its efficient use as a
heterogeneous catalyst for various organic reactions.2
The characterization of the catalyst was done on the basis of
elemental analysis, IR spectroscopy, thermogravimetric analysis,
and scanning electron microscopy. The complete incorporation
of organic substructure in the material was confirmed by
elemental analyses. The metal content in the catalyst determined
by atomic absorption spectroscopy suggested 4.37 wt % metals
loading in the immobilized palladium complex. The mode of
attachment of 2-aminopyridine and metal onto the polymeric
support was confirmed by IR spectral bands. The pure
chloromethylated polystyrene beads show a sharp characteristic
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Although the Suzuki cross-coupling reactions catalyzed by
the polymer-anchored palladium complexes in organic solvents
is well-developed, its potential utility in water is largely limited.
Recently, the use of water as an environmentally benign solvent
has received considerable attention from the view point of green
¹1
IR peak at 1266 cm (¯: CH2Cl group in polymer). The
¹
1
disappearance of the peak at 1266 cm and the appearance of
¹
1
a strong band in the region 16501660 cm due to sec-amine
(NH) stretching vibration confirmed the attachment of 2-
aminopyridine with chloromethylpolystyrene. The polymer-
anchored ligand exhibited medium to broad intensity bands in
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033
chemistry.
The organic solvents, which are usually used as
the reaction media, often creat a great deal of safety, health, and
environmental issues due to their flammability, toxicity, and
volatility. The use of water in transition metal catalyzed
reactions has become popular because water-base synthetic
processes are inherently safer as well as being inexpensive.
Furthermore, the use of water-insoluble metal complexes allows
an easy separation and the products can be isolated easily by
extraction.
¹
1
the region 31003500 cm which may be assigned to the NH
stretching as well as the CH stretching mode of the pyridine.
Pyridyl ring breathing vibrations were observed as strong bands
¹
1 35
in the region 14001600 cm
.
Slight shifting of these bands
toward lower frequency in the palladium complex suggests
possible coordination through the nitrogen of the pyridine ring.
More conclusive information on the coordination of the ligand
Chem. Lett. 2010, 39, 12001202
© 2010 The Chemical Society of Japan