Highly efficient recyclable heterogeneous palladium catalyst for C-C coupling, amination and cyanation reactions

Article abstract of DOI:10.1016/j.jorganchem.2010.07.006

An inexpensive, air-moisture stable and reusable PS-Pd(II)-anthra complex was synthesized by reacting chloro-methylated polystyrene with anthranilic acid to get polymer anchored ligand which was then reacted with PdCl₂ to get polymer anchored complex. This complex was characterized by different spectroscopic and elemental analyses. The activity of the Pd-complex as catalyst was tested for the Suzuki, Heck, Sonogashira cross-coupling and also for amination and cyanation reactions under various conditions. The catalyst exhibits high catalytic activities for the coupling of various aryl halides with organoboronic acid, alkene, alkyne and amine along with the cyanation of aryl halides providing excellent yields of desired product. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to five times without sufficient loss of its catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2010.07.006

Journal of Organometallic Chemistry 695 (2010) 2284e2295
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Highly efficient recyclable heterogeneous palladium catalyst for CeC coupling,
amination and cyanation reactions
Manirul Islam a, , Paramita Mondal , Kazi Tuhina , Anupam Singha Roy , Sanchita Mondal ,
Dilder Hossain
a
a
b
a
a
*
a
Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, W.B., India
Department of Chemistry, B.S. College, S-24 P.G.S., Canning 743329, W.B., India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 April 2010
Received in revised form
An inexpensive, airemoisture stable and reusable PSePd(II)eanthra complex was synthesized by
reacting chloro-methylated polystyrene with anthranilic acid to get polymer anchored ligand which was
then reacted with PdCl to get polymer anchored complex. This complex was characterized by different
2
spectroscopic and elemental analyses. The activity of the Pd-complex as catalyst was tested for the
Suzuki, Heck, Sonogashira cross-coupling and also for amination and cyanation reactions under various
conditions. The catalyst exhibits high catalytic activities for the coupling of various aryl halides with
organoboronic acid, alkene, alkyne and amine along with the cyanation of aryl halides providing
excellent yields of desired product. Further, the catalyst can be easily recovered quantitatively by simple
filtration and reused up to five times without sufficient loss of its catalytic activity.
Ó 2010 Elsevier B.V. All rights reserved.
1
July 2010
Accepted 6 July 2010
Available online 14 July 2010
Keywords:
Supported catalyst
CeC coupling
Cyanation
Amination
Aryl halides
1. Introduction
respect to their soluble counterpart. The use of heterogeneous cata-
lysts in organic synthesis has now become a common practice
Transition metal-catalyzed carbonecarbon and carbonenitrogen
couplingreactionsare probablyamongthe mostfrequentlyemployed
methods of CeC and CeN bond formation in organic synthesis [1e6].
They have been applied to the synthesis of many organic compounds,
especially those of complex natural products, supramolecular
chemistry, and engineering materials such as conducting polymers,
molecularwires,andliquidcrystals[7e10]. Withvariousmetalsbeing
employed in coupling reactions, palladium probably is the most
versatile metal in promoting or catalyzing reactions involving CeC
and CeNbond formationduetoitsexcellentcatalyticefficiencyinthis
type of reactions [11e14]. In recent years, various homogeneous
palladiumephosphine catalysts [15e18] have been developed for the
efficient cross-coupling reactions. However, these catalysts usually
need to be handled under inert atmosphere or dry conditions. In
addition, they sometimes suffer from significant PeC bond degrada-
tion at elevated temperatures, which leads to palladium aggregation
and eventually affects the overall catalytic performance. Supported
metal complexes continuouslyattract the interestof a growing part of
the scientific community for the advantages that they offer with
[19e22], especially followingthe rapiddevelopmentofcombinatorial
chemistry. Solid-supported palladium complexes having high activity
and selectivity, offer several significant practical advantages in
synthetic and industrial chemistry; among those, the ease of sepa-
ration of the catalyst from the desired reaction products and the ease
of recovery and re-use of the catalyst are most important. A large
number of materials have been used to support, including activated
carbon, silica gel, polymers containing covalently bound ligands,
metal oxides, porous aluminosilicates, clays and other inorganic
materials, and microporous and mesoporous supports [23e29].
Polystyrene is one of the most widely studied heterogeneous
supports due to its environmental stability and good catalytic
activity. Polymer-supported palladium catalysts derived from
chloro-methyl polystyrene resin have been employed in various
coupling reactions [30e38], and have shown lower leaching of
palladium during cross-coupling. Suzuka et al. have reported
PSePEG resin-bound palladium complex for Sonogashira reaction
[39]. Linear polystyrene-supported Pd nanoparticle was devel-
oped by Ohtaka et al. for the SuzukieMiyaura cross-coupling
reaction in water medium [40]. These results encouraged us to
investigate the anthranilic acid-functionalized polystyrene resin-
supported Pd(II) complex, PSePd(II)eanthra, for the coupling and
cyanation reactions. We have already reported the use of an
*
Corresponding author. Tel.: þ91 33 2582 8750; fax: þ91 33 2582 8282.
E-mail address: manir65@rediffmail.com (M. Islam).
0
022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.07.006

M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
2285
polystyrene anchored Pd(II) complexes as an air-stable, active,
and reusable catalyst in CeC coupling reactions [41e43].
In the present work, we have prepared heterogeneous Pd(II)
catalyst on polystyrene and used it in the Suzuki, Heck, Sonoga-
shira, amination and cyanation reactions of aryl halides in the
presence of inorganic or organic bases. The catalyst was charac-
terized by various physicochemical and spectroscopic techniques.
The effects of the various reaction parameters on the catalytic
activity were studied. The key features of the catalyst include rapid
reactions with excellent conversion without the use of phosphine
ligands and total stability under the reaction conditions. Further
this polymer-supported catalyst demonstrated outstanding reus-
ability for these reactions.
analyzed by GCeMS. All the prepared compounds are known and
compared with authentic sample.
2.3. General experimental procedure for Sonogashira reaction
A
round-bottomed flask was charged with aryl iodide
(1.0 mmol), phenylacetylene (1.5 mmol), catalyst (1.0 mol% Pd),
triethylamine (2.0 mmol) and DMF (6 mL) and n-dodecane
(15e20 mg) as an internal GC standard. The resulting mixture was
ꢀ
stirred at the appropriate temperature (90 C). The reaction
mixtures were withdrawn periodically and analyzed by GC/GCeMS.
GC yields are based on the amount of aryl halide employed. Upon
completion of the reaction, the reaction mixture was cooled and
filtered to remove the catalyst which could be used for further
reaction. The filtrate obtained was purified by flash column chro-
matography on silica gel to afford the desired product, which was
confirmed by GCeMS. All the prepared compounds are known and
compared with authentic sample.
2
. Experimental
All the reagents were analytical grade and used as such without
further purification. Solvents were purified and dried according to
standard procedures. Chloro-methylated polystyrene was purchased
from Aldrich and PdCl was procured from Arora Matthey. Other
2
2.4. General experimental procedure for amination reaction
reagents were purchased from Merck.
The palladium content was determined by Varian, USA, AA240
atomic absorption spectrophotometer (AAS). A PerkineElmer, USA,
t
A mixture of aryl halide (1.0 mmol), amine (1.0 mmol), KO Bu
(
1.5 mmol), toluene (6 mL) n-dodecane (15e20 mg) and 1.0 mol%
ꢀ
Pd of catalyst was stirred at 120 C under nitrogen atmosphere. To
study the progress of the reaction, the reaction mixtures were
collected at different time interval and quantified by GC analysis. At
the end of the reaction, the catalyst was separated by simple
2
400C elemental analyzer was used to collect microanalytical data
(
C, H and N). Surface morphology of functionalized polystyrene
ligand and metal complex were analyzed using a scanning electron
microscope (ZEISS EVO40, England) equipped with EDX facility.
Fourier transform infrared (FTIR) spectra for the catalyst and its
precursors were recorded on a PerkineElmer, USA, FTIR 783 spec-
trophotometer using KBr pellets. UVevis spectrum was taken using
a Shimadzu, Japan, UV-2401PC double beam spectrophotometer
having an integrating sphere attachment for solid samples. The
thermal stability of the immobilized catalyst was determined using
a Mettler Toledo, Switzerland, TGA/DTA 851e instrument. The
reaction products were analyzed using a Varian, USA, 3400 gas
chromatograph equipped with a 30 m CP-SIL8CB capillary column
and a flame ionization detector. All reaction products were identi-
fied by using an Agilent, USA, GCeMS (QP-5050) equipped with
a 30 m HP-5ms capillary column.
2 4
filtration. Filtrate was dried over Na SO , filtered, concentrated and
the residue was purified by flash column chromatography on silica
gel. The product was analyzed by GCeMS. All the prepared
compounds are known and compared with authentic sample.
2
.5. General experimental procedure for cyanation reaction
A mixture of K Fe(CN) (1.0 mmol), aryl halides (1.5 mmol),
catalyst (1.0 mol% Pd), triethylamine (2.0 mmol) and DMF (6 mL)
was stirred for 24 h under air at 100 C. The progress of reaction
was monitored by gas chromatography. After completion, the
reaction mixture was cooled and filtered to remove the catalyst
which could be used for further reaction. The filtrate obtained was
purified by flash column chromatography on silica gel to afford the
desired product, which was confirmed by GCeMS. All the prepared
compounds are known and compared with authentic sample.
4
6
ꢀ
2.1. General experimental procedure for Suzuki coupling reaction
A mixture of aryl halide (1.0 mmol), arylboronic acid (1.2 mmol),
K
2
CO
3
(2.0 mmol), DMF (6 mL), n-dodecane (15e20 mg) as an
2
.6. Synthesis of catalyst
ꢀ
internal GC standard and 0.5 mol% of catalyst was stirred at 70 C in
air. Progress of the reaction was monitored by withdrawing the
reaction mixtures periodically and analyzed by GC/GCeMS. GC
yields were based on the amount of aryl halide employed. At the
end of the reaction, the catalyst was separated by simple filtration.
The synthetic procedure of polymer anchored palladium
complex is illustrated in Scheme 1. The complex was prepared
according to the literature procedure [44]. Firstly, the chloro-
methylated polystyrene (1) (1 g) was reacted with anthranilic acid
2 4
Filtrate was dried over Na SO , filtered, concentrated and the
(500 mg) in DMF (10 mL) under reflux condition for 36 h to afford
residue was purified by flash column chromatography on silica gel.
The product was analyzed by GCeMS. All the prepared compounds
are known and compared with authentic sample.
polymer anchored ligand (2). This polymer anchored anthranilic
acid ligand (1 g) subsequently reacted with palladium chloride
ꢀ
(0.1 g) in methanol (10 mL) at 80 C for 10 h to generate the cor-
responding polymer anchored Pd(II) complex (3).
2.2. General experimental procedure for Heck reaction
3. Results and discussions
2 3
A mixture of aryl halide (1.0 mmol), styrene (2.0 mmol), K CO
(
2.0 mmol), DMF (6 mL) n-dodecane (15e20 mg) and 0.5 mol% of
3.1. Characterization of the PSePd(II)eanthra complex
ꢀ
catalyst was stirred at 90 C under air. To study the progress of the
reaction, the reaction mixtures were collected at different time
interval and quantified by GC analysis. At the end of the reaction,
the catalyst was separated by simple filtration. Filtrate was dried
Due to insolubility of the polymer anchored Pd(II) complex in all
common organic solvents, its structural investigations were limited
only to its physicochemical properties, SEMeEDX, TGAeDTA, IR and
UVevis spectral data. The complete incorporation of the organic
substructure in the material was confirmed by elemental analysis.
over Na
2 4
SO , filtered, concentrated and the residue was purified by
flash column chromatography on silica gel. The product was

2286
M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
CH2
NH2
DMF
NH
CH Cl
2
+
-HCl
OH
O
C
O
OH
C
(
1)
(
2)
O
O
C
CH2
PdCl2
00C Ethanol
7
NH
Cl
Cl
Pd
Pd
O
HN
CH2
C
O
(
3)
Scheme 1. Synthesis of PSePd(II)eanthra complex.
Pure chloro-methyl polystyrene group contained 19.18 wt% of Cl
per gram of resin (5.5 mmol Cl per gram of resin).The remaining
chloride content of 1.86% in polymer anchored ligand suggested
nearly 89% conversion of the available chloro-methyl group to the
corresponding polymer anchored ligand. The metal content of
polymer anchored Pd(II) complex determined by AAS suggested
5
.28 wt% metal loading in the immobilized palladium complex
(
degree of loading of palladium is 0.49 mmol/g of resin). The SEM
images of polymer anchored ligand and metal complex clearly
show the morphological change which occurred on the surface of
the polymer matrix after loading of the metal (Fig. 1). EDX data also
supports the metal attachment on the surface of polymer matrix
Fig. 2. EDX spectra of PSeanthra ligand (A) and PSePd(II)eanthra complex (B).
(
Fig. 2).
Thermogravimetric analyses of supported catalyst and its
precursor, polymer anchored anthranilic acid, were taken in air
ꢁ
1
of
n
(eC-Cl) band and appearance of a strong band at 3455 cm
(n
eNH, secondary amine) on anchoring with anthranilic acid
suggests the covalent bond formation through nitrogen atom [45].
ꢀ
ꢁ1
atmosphere at a heating rate of 10 C min . The polymer anchored
palladium complex is stable upto 385 C whereas polymer
anchored ligand decomposes at 360 C (Fig. 3). After complexation
ꢀ
Other characteristic peaks at 3448 (
asym COO) and 1422 ( sym COO) also supports the formation of
ligand [46]. After metal loading, shifting of these bands toward
lower frequency regions (3280 NeH, 1555 asym eCOO and 1410
eCOO) suggests the involvement of the amine and carboxylic
n eOH), 1706 (n C]O), 1589
ꢀ
(
n
n
with metal, the thermal stability of the ligand is slightly improved.
DTA study reveals that the decomposition stages are exothermic in
nature (not shown).
n
n
n
sym
The mode of attachment of anthranilic acid and metal onto the
polymeric support is confirmed by IR spectral data both in the mid
groups of the anthranilic acid in complex formation. More
conclusive information on the coordination of the ligand to the
ꢁ
1
ꢁ1
(
4000e400 cm ) and far (600e50 cm ) IR regions. The pure
central metal ion comes from the new bands due to
n
(PdeN)
ꢁ1
n (PdeCl, bridged) 332 cm [48] and n (PdeO,
ꢁ
1
chloro-methylated polysterene beads show a sharp characteristic
450 cm [47],
ꢁ
1
ꢁ1
IR peak at 1260 cm
(
n
eCH
2
-Cl group in polymer). Disappearance
bridged) 358 cm [49].
Fig. 1. FE-SEM images of PSeanthra ligand (A) and PSePd(II)eanthra complex (B) respectively.

M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
2287
453
365
307
400
600
800
1000
Wave length (nm)
Fig. 3. Thermogravimetric weight loss plots for PSeanthra ligand and PSePd(II)e
anthra complex, respectively.
Fig. 4. UVevis spectrum for PSePd(II)eanthra complex.
The UVevis spectra provided further evidence for the presence
of palladium on polymer support. The electronic spectra of the
polymeric Pd(II) catalyst has been recorded in diffuse reflectance
spectrum mode as BaSO disc due to its solubility limitations in
4
common organic solvents. The low-spin Pd(II) complex may exhibit
We started our investigation for Suzuki reaction (Scheme 2)
with the coupling of 4-bromoacetophenone and phenylboronic
acid as model reaction. The performance of a palladium-catalyzed
Suzuki reaction is known to be governed by the number of factors
such as the bases, solvents, reaction temperatures etc. To verify the
solvent effect in Suzuki cross-coupling reactions, a series of reac-
tions were investigated by taking the model reaction in different
solvents. The reaction conducted in polar solvent medium like DMF
and DMSO, were found to be most effective. The use of THF, MeOH
and ACN as solvents led to slower reactions and no desired cross-
coupling products were observed while reactions were carried out
in nonpolar solvents like toluene and dichloromethane. Conse-
quently, DMF was chosen as the medium of choice for this coupling.
This coupling reaction was found to be highly sensitive to the
three spin-allowed ded transitions from lower lying d orbital to
higher empty d
2
2
orbital. The bands are observed at 307 nm,
x ꢁy
1
1
3
65 nm and 453 nm, which may be designated as
g
A1g/ E ,
1
1
1
1
A
1g/ B1g and A1g/ A2g transitions respectively [50,51] (Fig. 4).
The room-temperature magnetic moment of the polymeric Pd(II)
8
complex has been found to be diamagnetic due to spin paired d
system [52]. This diamagnetic nature supports the formation of
a low-spin square-planar geometry around Pd(II). Based on the
above results of elemental analysis, IR, electronic spectra, magnetic
moment measurements and thermal analysis, the structure of the
Pd(II) complex is suggested and are given in Scheme 1.
ꢀ
reaction temperature. At lower temperatures (30e50 C) only low
ꢀ
to moderate yield was obtained. A reaction temperature of 70 C
was found to be optimal for the model reaction. The influence of
base on the catalytic performance of this system was investigated
by employing various bases. Comparison of inorganic bases utilized
showed that carbonate bases were more stable than the other ones.
Within a short time the reaction proceeded in high yield in pres-
3
3
.2. Catalytic activities
.2.1. Suzuki cross-coupling reaction
Suzuki cross-coupling reaction represents a powerful method
for the CeC bond formation [53e55]. Construction of biaryl
compounds via the palladium-catalyzed Suzuki reaction is an
interesting area in organic synthesis. The importance of biaryl units
as molecular components in pharmaceuticals, herbicides and
natural products, as well as in engineering materials such as con-
ducting polymers, molecular wires and liquid crystals, has attracted
enormous interest [56e58]. The reaction represents an attractive
alternative over other methods using organometallics because
organoboranes are air- and moisture-stable with relatively low
toxicity.
ence of Na
2
CO
3
or K
2
CO
3
. We found that using K
2
CO
3
as base in DMF
ꢀ
at 70 C gave the coupled product in 99% yields. The other inorganic
bases such as NaOH, K
not as effective as K
coupling products. The quantity of K
important. The baseesubstrate molar ratio of 2:1 was found to be
ideal for present catalytic system.
To examine the scope of this coupling reaction, a variety of aryl
halides were coupled with different phenylboronic acids in DMF in
2 3
the presence of a catalytic amount of PSePd(II)eanthra using K CO
3
PO
4
, NaOAc and organic bases like Et
, only affords moderate to low yields of
CO was also found to be
3
N were
2
CO
3
2
3
PS-Pd(II)-anthra
R1
X + (HO) B
R2
R1
R2
2
K CO , DMF
2
3
X = Cl, Br, I
R = H, CH , OMe, COMe, NO ,
1
3
2
R = H, CH , COMe
2
3
Scheme 2. Suzuki cross-coupling reaction.

2288
M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
Table 1
Suzuki cross-coupling reaction of aryl halides and arylboronic acids using PSePd(II)eanthra.
a
Entry
ArX
Productb
Time
5
Yieldc (%)
100
I
1
Me
I
Me
2
3
5
5
98
O N
2
I
O N
2
100
I
4
6
93
Br
5
6
7
8
9
6
8
8
6
6
97
98
95
99
99
Me
Br
Me
MeO
Br
MeO
MeOC
Br
MeOC
O N
2
Br
O N
2
NO2
Br
NO2
1
1
0
1
8
6
89
94
Br
Cl
N
N
1
1
1
2
3
4
12
12
8
72
83
98
MeOC
Cl
MeOC
I
Me

M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
2289
Table 1 (continued)
Entry
ArX
Productb
Time
8
Yieldc (%)
15
99
I
COMe
a
b
c
2 2 3
Reaction conditions: ArX (1.0 mmol), ArB(OH) (1.2 mmol), K CO (2.0 mmol), DMF (6 mL), catalyst (0.5 mol% of Pd); All the reactions were carried out in air.
Products were identified by comparison of their IR, GCeMS and HNMR spectral data those reported in the literature.
Yield of product was determined by GC and GCeMS analysis using dodecane as internal standard.
1
as base. The experimental results are summarized in Table 1.
A control experiment indicated that the coupling reaction did not
occur in the absence of catalyst. Aryl halides bearing either elec-
tron-donating or electron-withdrawing substituents in the para
positions, afforded the corresponding biphenyls in good to excel-
lent yields. Heteroarylbromide, 2-bromopyridine, was coupled
efficiently with phenylboronic acid to give the desired product in
excellent yield (Table 1, entry 11). The cross-coupling of sterically
hindered aryl halides, 1-iodonaphhalene and 2-nitrobromo
benzene also proceed quite well (Table 1, entries 4,10). The reaction
of 4-methyl or 4-acetyl boronic acid with iodobenzene provided
the corresponding biaryls in high yields (Table 1, entries 14, 15). The
coupling reaction of chloroarenes also took place under similar
reaction conditions, though the reactivity was lower than their iodo
and bromo counterpart (Table 1, entries 12, 13).
on the aromatic ring of the aryl halides had a significant effect on
the yields. It was observed that aryl halides with electron-with-
drawing functionality undergo Heck coupling reaction efficiently to
afford the corresponding products in excellent yields. Aryl halides
with electron donating functionality gave moderate to good yields
of coupled product. Iodobenzene gave excellent yield of coupled
product (Table 2, entry 1). Compared with substituted aryl
bromides, the reaction of bromobenzene with styrene gave slight
lower product yield (Table 2, entry 6). Sterically hindered 1-iodo-
naphthalene also coupled with styrene to give desired product in
good yield (Table 2, entry 5). The entire coupled products showed
E-stereochemistry. These results showed that the scope of the
reaction is quite broad and the conditions are tolerant of various
functional groups of substituted on aryl bromides and iodides with
an extremely good selectivity to the trans-isomer. However no
coupling product was obtained in the reaction of less reactive
chlorobenzene (Table 2, entry 11).
3.2.2. Heck cross-coupling reaction
The Heck cross-coupling reaction, the palladium-catalyzed
coupling of aryl halides with alkenes, is an extremely valuable
method for carbonecarbon bond formation [59e62]. It is now
widely used in the special chemical and pharmaceutical
manufacturing industries, because it is simple, versatile, and rela-
tively mild. Our catalyst was next tested for the Heck coupling
reaction (Scheme 3). Initial catalytic studies with 0.5 mol% of
catalyst were performed on the Heck cross-coupling of bromo-
benzene with styrene as a model reaction in different temperature,
solvents and bases under air atmosphere. The reaction was
3.2.3. Sonogashira cross-coupling reaction
The present palladium catalyst was then tested another most
important CeC bond forming process in synthetic organic chem-
istry, known as Sonogashira coupling reaction, the palladium-
catalyzed coupling of aryl halides with terminal alkynes [63e65].
To survey the reaction parameters for the Sonogashira reaction, we
chose to examine K
2 3 2 3 3
CO , NaOH, Cs CO , Et N and piperidine as base
and DMF, DMSO, toluene and DCM as the solvent. It was found that
ꢀ
the reaction performed in DMF with Et
the best performances (Scheme 4).
3
N as base at 90 C showed
ꢀ
conveniently carried out at 90 C. At lower temperature, incom-
plete conversion of bromobenzene was obtained. Several organic
and inorganic bases were screened and it was observed that the
potassium carbonate was the most efficient base for present cata-
lytic reaction. Other bases were significantly less effective and gave
moderate yield. The influence of solvents on Heck coupling reaction
was also examined in different polar and non-polar solvents.
Among different polar solvents, such as DMF, DMSO, NMP, high
catalytic activity was observed in DMF medium. Non-polar solvents
were not favorable for the Heck coupling reaction under present
reaction condition. In the absence of catalyst, the reaction did not
proceed.
With these optimized reaction conditions, the reaction of
various substituted and non-substituted aryl halides with styrene
were examined to explore the scope and generality of this catalyst
for the synthesis of various aryl-alkenes and the results are
summarized in Table 2. As shown in Table 2, the substituent groups
Under optimized reaction conditions, the efficiency of this
catalyst was studied for Sonogashira coupling reaction of various
aryl halides and the results are summarized in Table 3. A control
experiment indicated that the coupling reaction did not occur in
the absence of catalyst. Iodobenzene efficiently reacted with the
phenylacetylene to yield coupled product in good yield (Table 3,
entry 1). Aryl iodides with electron donating group such as methyl
(Table 3, entry 2) and electron-withdrawing groups such as nitro
and acetyl (Table 3, entries 3, 4) were well tolerated under the
present catalytic system. Sterically hindered 1-iodonaphthalene
was also found to react smoothly under present reaction conditions
(Table 3, entry 5). Very small amount homocoupled product was
detected during the reaction. Using aryl bromide instead of aryl
iodide yielded only a small amount of coupled derivatives under
the conditions employed for iodides (Table 3, entry 6). 4-Acetyl-
bromobenzene gave moderate yield of coupled product (Table 3,
entry 7).
3.2.4. Amination reaction
CeN bond formation by palladium-catalyzed cross-coupling
PS-Pd(II)-anthra
reaction is one of the powerful techniques in synthetic organic
chemistry. This method has been widely used in biological, phar-
maceutical, and material sciences for various applications [66,67].
To test the further applicability of the PSePd(II)eanthra catalyst,
we examined the amination reaction (Scheme 5) between aniline
with various aryl halides. In the absence of catalyst the reaction did
R
X
+
R
K CO , DMF
2
3
X = Cl, Br, I
R = H, CH , COMe, NO
3
2
Scheme 3. Heck cross-coupling reaction.

2290
M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
Table 2
Heck cross-coupling reaction of aryl halides and styrene using PSePd(II)eanthra.
a
Entry
ArX
Productb
Time
8
Yieldc (%)
I
1
95
Me
I
2
3
4
Me
8
8
8
89
97
97
O N
2
I
O N
2
MeOC
I
MeOC
I
5
10
92
Br
6
7
8
9
16
16
16
16
84
90
92
86
MeOC
Br
MeOC
O N
2
Br
O N
2
Me
Br
Me
Br
Cl
1
1
0
1
16
24
81
N
No reaction
a
b
c
2 3
Reaction conditions: ArX (1.0 mmol), styrene (2.0 mmol), K CO (2.0 mmol), DMF (6 mL), catalyst (0.5 mol% of Pd); all the reactions were carried out in air.
Products were identified by comparison of their IR, GCeMS and HNMR spectral data those reported in the literature.
Yield of product was determined by GC and GCeMS analysis using dodecane as internal standard. In all the coupling reactions, only E-stereochemistry was observed.
1

M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
2291
PS-Pd(II)-anthra
were investigated. Representative results are summarized in
Table 4. It was observed that the reaction of iodobenzene and
aniline proceeded at 120 C resulting in corresponding coupling
R
X +
R
3
Et N, DMF
ꢀ
X = Br, I
R = H, CH
product in high yield (Table 4, entry 1). Iodoarenes with electron-
withdrawing group (Table 4, entries 2, 3) reacted at a faster rate
than iodoarenes with electron donating group (Table 4, entry 4).
Morpholene was also coupled with iodobenzene to give the desired
aryl amines in good yields (Table 4, entry 6). Substituted anilines
coupled with iodobenzene to give the desired product in moderate
yield (Table 4, entry 5). Bromobenzene remained inactive in ami-
nation reaction under present reaction conditions (Table 4, entry 7).
3
, COMe, NO
2
,
Scheme 4. Sonogashira cross-coupling reaction.
not proceed. Initially we screened typical reaction parameters
including solvents and bases and we varied the temperature and
time. Bases such as K
are found to facilitate this coupling reaction and among them
t
2
CO
3
, Cs
2
CO
3
, Et
3
N, K
3
PO
4
, NaOMe and KO Bu
ꢀ
Although increasing the reaction temperature to 140 C and pro-
longed the reaction time to 48 h, slight conversion of bromo-
benzene was obtained (Table 4, entry 8).
t
KO Bu was the best. Solvents such as DMF, ACN, MeOH, C
H
6 6
and
toluene were investigated and it was found that nonpolar solvents
were more favored. With DMF, ACN, and MeOH, yields were
comparatively low. Consequently toluene is chosen as the medium
of choice for this coupling as highest conversion was obtained. This
arylation is also found to be highly sensitive to reaction tempera-
ture and time. At lower temperatures (30 and 60 C), the reaction
totally fails and with lower reaction time (6 and 12 h) only low to
moderate yield was obtained. It was found that the reactions per-
formed in toluene medium with KO Bu at 120 C for 24 h showed
the best performance.
On the basis of the above optimized reaction conditions, the
coupling reactions between a variety of aryl halides and amines
3.2.5. Cyanation reaction
Cyanation of aryl halides is a common and useful transformation
in organic synthesis as aryl cyanides constitute building blocks for
the synthesis of fine chemicals [68,69] and are integral parts of
several dyes, natural products, herbicides, agrochemicals, and
pharmaceuticals. In this reaction traditionally used cyanide sources
are KCN, Me SiCN, NaCN and Zn(CN) [70e72]. It is evident that the
3 2
utilization of these cyanide sources is connected with a numerous
drawbacks. They are highly poisonous and may contaminate in the
ꢀ
t
ꢀ
4 6
product mixture. Recently, K [Fe(CN) ] has been shown to be
Table 3
a
Sonogashira cross-coupling reaction of aryl halides and phenylacetylene using PSePd(II)eanthra.
Entry
1
ArX
Productb
Time
12
Yieldc (%)
94
I
Me
I
Me
2
3
4
12
12
12
85
96
96
O N
2
I
O N
2
MeOC
I
MeOC
I
5
6
12
87
Br
24
24
14
45
7
MeOC
Br
MeOC
a
3
Reaction conditions: ArX (1.0 mmol), phenylacetylene (1.5 mmol), Et N (2.0 mmol), DMF (6 mL), catalyst (1.0 mol% of Pd); all the reactions were carried out in air.
Products were identified by comparison of their IR, GCeMS and HNMR spectral data those reported in the literature.
Yield of product was determined by GC and GCeMS analysis using dodecane as internal standard.
b
c
1

2292
M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
NH
PS-Pd(II)-anthra
KO Bu, Toluene
R1
X + H
2
N
R2
t
R1
R2
X = Br, I
R = H, CH , COMe, NO
2
1
3
R = H, CH
2
3
Scheme 5. Amination reaction.
Table 4
Amination reaction of aryl halides using PSePd(II)eanthra.
a
Entry
ArX
Productb
Time
24
Yieldc (%)
83
NH
I
1
NH
O N
I
2
2
3
4
5
24
24
24
85
83
74
O N
2
NH
MeOC
I
MeOC
NH
H C
3
I
H C
3
NH
I
24
24
76
84
CH3
I
N
O
6
7
NH
NH
Br
Br
24
48
No reaction
8
26d
a
t
Reaction conditions: ArX (1.0 mmol), amine (2.0 mmol), KO Bu (2.0 mmol), toluene (6 mL), catalyst (1.0 mol% of Pd); all the reactions were carried out in nitrogen
atmosphere.
b
c
Products were identified by comparison of their IR, GCeMS and 1HNMR spectral data those reported in the literature.
Yield of product was determined by GC and GCeMS analysis using dodecane as internal standard.
Temperature ¼ 140 C.
d
ꢀ

M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
2293
X
CN
Table 6, it is seen that present catalyst exhibited higher conversions
and yields compared to the other reported system [76e81]. Reac-
tions conducted at lower temperature and shorter reaction time
was required for these reactions using present catalyst.
PS-Pd(II)-anthra
K Fe(CN) , Et N, DMF
4
6
3
R
R
X = Br, I
3
R = H, CH , COMe, NO2
3.4. Heterogeneity test
Scheme 6. Cyanation reaction.
An important point concerning the use of heterogeneous cata-
lyst is its lifetime, particularly for industrial and pharmaceutical
applications of the coupling reaction. Heterogeneity and the
palladium leaching of this catalyst were examined by the “hot-
filtration test” and “solid phase poisoning test” for the Suzuki
coupling reaction of 4-bromoanisole and phenylboronic acid.
effective as a source of cyanide since it is nontoxic, commercially
available, cheaper and easily handled [73e75].
We finally explored the utility of this PSePd(II)eanthra catalytic
system for cyanation reaction of aryl halides (Scheme 6). After
screening a range of usual inorganic and organic bases and
exploring the scope of various solvents, it was found that this
catalyst is most efficient for the cyanation reaction in the presence
3.4.1. Hot-filtration test
ꢀ
Hot-filtration test was performed in the Heck cross-coupling
reaction of 4-bromoanisole with phenylboronic acid to investigate
whether the reaction proceeded in a heterogeneous or a homoge-
neous fashion. After continuing the reaction for 3 h, the catalyst
was removed by filtration and the determined conversion was 46%.
The resulting filtrate was subjected to heating for further 6 h. From
GC result it reveals that after separation of the catalyst no conver-
sion takes place in the filtrate part. This confirms that the reaction
did not proceed upon the removal of the solid catalyst. Further, no
evidence for leaching of palladium or decomposition of the
complex catalyst was observed during the catalytic reaction and no
palladium could be detected by atomic absorption spectroscopic
measurement of the filtrate after removal of catalyst. These studies
clearly demonstrated that palladium was intact to a considerable
extent with the heterogeneous support, and there is no significant
amount of leaching occurred during reaction.
of Et
3
N as base and DMF as solvent at 100 C. The control experi-
ments showed that the coupling reaction did not occur in the
absence of the catalyst or base. Iodobenzene efficiently reacted
[Fe(CN) ] to yield the nitrile product in excellent yields
4 6
Table 5, entry 1). Substituted aryl iodides also provided good yield
of nitrile products (Table 5, entries 2e4). 1-iodonaphthalene also
underwent smooth reaction providing 85% yield (Table 5, entry 5).
The results are presented in Table 4. Only aryl iodides are reactive
and other halides remained inert under present reaction conditions
with K
(
(Table 5, entry 6).
3
.3. Comparison with other reported system
Table 6 provides a comparison of the results obtained for our
present catalytic system with those reported in the literature. From
Table 5
Cyanation reaction of aryl halides and K
4
Fe(CN)
6
using PSePd(II)eanthra.a
Entry
1
ArX
Productb
Time
18
Yieldc (%)
98
I
CN
Me
I
I
I
Me
CN
2
3
4
18
18
18
91
98
97
O N
2
O N
CN
2
MeOC
MeOC
CN
I
I
5
24
24
85
6
No reaction
Br
CN
a
ꢀ
4 6 3
Reaction conditions: K Fe(CN) (1 mmol), aryl halide (1.5 mmol), catalyst (1.0 mol% Pd), Et N (2.0 mmol), DMF (6 mL), 100 C.
Products were identified by comparison of their IR, GCeMS and HNMR spectral data those reported in the literature.
Yield determined by GC and GCeMS analysis using dodecane as internal standard.
b
c
1

2294
M. Islam et al. / Journal of Organometallic Chemistry 695 (2010) 2284e2295
Table 6
Comparison of catalytic activity of the present catalyst in the cross-coupling and cyanation reactions with other related reported systems.
Reaction
Catalyst
Reaction conditions
Yield%
Reference
ꢀ
Suzuki reaction: (bromobenzene þ Phenylboronic acid)
PSePd(II)eanthra
K
K
K
K
Na
Bu
2
2
2
2
CO
CO
CO
CO
3
3
3
3
, DMF, 0.5 mol% catalyst, 70 C, 6 h
, DMF, 110 C, 10 h
97
80
81
84
78
54
94
80
83
82
98
60
Present
[76]
[77]
Present
[78]
[79]
Present
[80]
Present
[81]
Present
[76]
ꢀ
CuO/Pd-3
2þ
ꢀ
Pd sepiolite
PSePd(II)eanthra
Catalyst 2
, DMF, 0.5
m
mol of Pd catalyst, 100 C, 8 h
ꢀ
Heck reaction: (bromobenzene þ styrene)
, DMF, 0.5 mol% catalyst, 90 C, 16 h
ꢀ
2
CO
3
, DMF, 0.5 mol% catalyst, 140 C, 7 h
N, p-xylene, 0.03 mmol Pd catalyst, 140 C, 12 h
N, DMF, 1.0 mol% catalyst, 90 C, 12 h
2
N, ACN, 500 mg cat. (0.1 mmol as Pd(OAc) ), reflux
ꢀ
SieAsePd(0)
PSePd(II)eanthra
I-Pd
PSePd(II)eanthra
Pd (DPPE)
3
ꢀ
Sonogashira reaction: (iodobenzene þ phenylacetylene)
Amination reaction: (iodobenzene þ aniline)
Cyanation reaction: (iodobenzene)
Et
Et
3
3
t
ꢀ
KO Bu, DMF, 1.0 mol% catalyst, 120 C, 24 h
ꢀ
NaOMe, toluene, 0.05 mmol Pd(OAc)
Et N, DMF, K Fe(CN)
DMF, K Fe(CN)
2
, 110 C, 24 h
ꢀ
PSePd(II)eanthra
CuO/Pd-3
3
4
6
, 1.0 mol% catalyst, 100 C, 10 h
ꢀ
4
6
, 120 C, 10 h
3
.4.2. Solid phase poisoning test
Further the heterogeneous nature of the catalyst was checked by
conditions. The catalyst shows unchanged catalytic activity up to
five reaction cycles. No catalyst deterioration was observed, con-
firming the high stability of the heterogeneous catalyst under the
reaction conditions.
the solid phase poisoning test. This test was performed for the
Suzuki coupling reaction of 4-bromoanisole. We used commercially
available 3-mercaptopropyl-functionalized silica as effective
palladium scavenger which selectively coordinates and deactivates
the leached out palladium. For Suzuki reaction, a mixture of 4-
4. Conclusions
bromoanisole (1.0 mmol), phenylboronic acid (1.2 mmol), K
2 3
CO
In conclusion, we have reported the simple preparation of
(
2.0 mmol), DMF (6 mL), 0.005 g 3-mercaptopropyl-functionalized
polystyrene-supported Pd(II) complex and its successful applica-
tion for the coupling and cyanation reactions of aryl halides under
air atmosphere using DMF as solvent. The present system is highly
air and moisture stable and the catalyst can be synthesized readily
from inexpensive and commercially available starting materials.
The system works equally well for wide variety of aryl halides,
alkenes, alkynes, amines and organoboronic acid and tolerates
a variety of functional groups. Moreover the catalyst was reused for
five consecutive cycles with consistent catalytic activity. Further
work is in progress to broaden the scope of this catalytic system for
other organic transformation.
ꢀ
silica and 0.5 mol% of Pd catalyst was stirred at 70 C for 8 h. In this
case no change in conversion was observed which suggests that the
catalyst is heterogeneous in nature since 3-mercaptopropyl-func-
tionalized silica form a complex with the leached palladium and
there by deactivate the catalyst. From this result we may conclude
that no leaching of palladium is occurred during Suzuki coupling
reaction.
3.5. Catalyst reusability
Recovery and catalyst reuse are important issues in the
coupling reactions. Easy catalyst separation and recycling in
successive batch operations can greatly increase the efficiency of
the reaction. We studied the reusability of the present heteroge-
neous palladium catalyst in the Heck cross-coupling reaction
taking the reaction of 4-bromoanisole and phenylboronic acid
Acknowledgments
We gratefully acknowledge the DST & UGC, New Delhi, for award
of grant under FIST and SAP program to the Department of Chem-
istry, University of Kalyani. M.I. acknowledges the Department of
Science and Technology (DST), the Council of Scientific and Indus-
trial Research (CSIR) and the University Grant Commission (UGC),
New Delhi, India for funding. K.T. is thankful to the University
Grants Commission (Eastern Region), India, for financial support.
(Fig. 5). After completion of the reaction, the catalyst was recov-
ered by simple filtration and washed with ethyl acetate followed
ꢀ
by acetone then dried in reduced pressure at 40 C. The recovered
catalyst was employed in the next run with further addition of
substrates in appropriate amount under optimum reaction
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