Palladium nanoparticles supported on modified crosslinked polyacrylamide containing phosphinite ligand: A novel and efficient heterogeneous catalyst for carbon-carbon cross-coupling reactions

Article abstract of DOI:10.1016/j.molcata.2010.02.025

A novel palladium catalyst based on modified crosslinked polyacrylamide containing phosphinite ligand was synthesized and characterized. It exhibits excellent activity and stability in Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions with different aryl halides including inactive aryl chlorides. Short reaction times with good to excellent yields of the desired products express the effectiveness of this catalyst in these reactions. Transmission electron microscopy (TEM) shows that palladium particles are well-dispersed and of typical diameter of 18-30 nm. The X-ray powder diffraction (XRD) pattern of the Pd catalyst is consistent with the metallic Pd(0). The turnover number (TON) of this catalyst reaches up to 9.5 × 10⁴ for these C-C bond forming reactions. Elemental analysis of Pd by ICP-OES and hot filtration test shows low leaching of the metal into solution from the supported catalyst which confirms the full heterogeneous character of the catalytically active species. The catalyst can be used many times in repeating cycles without considerable loss in its activity.

Full text of DOI:10.1016/j.molcata.2010.02.025

Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Palladium nanoparticles supported on modified crosslinked polyacrylamide
containing phosphinite ligand: A novel and efficient heterogeneous
catalyst for carbon–carbon cross-coupling reactions
Bahman Tamami∗, Soheila Ghasemi
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel palladium catalyst based on modified crosslinked polyacrylamide containing phosphinite lig-
and was synthesized and characterized. It exhibits excellent activity and stability in Mizoroki–Heck and
Suzuki–Miyaura cross-coupling reactions with different aryl halides including inactive aryl chlorides.
Short reaction times with good to excellent yields of the desired products express the effectiveness of
this catalyst in these reactions. Transmission electron microscopy (TEM) shows that palladium particles
are well-dispersed and of typical diameter of 18–30 nm. The X-ray powder diffraction (XRD) pattern of
the Pd catalyst is consistent with the metallic Pd(0). The turnover number (TON) of this catalyst reaches
up to 9.5 × 104 for these C–C bond forming reactions. Elemental analysis of Pd by ICP-OES and hot filtra-
tion test shows low leaching of the metal into solution from the supported catalyst which confirms the
full heterogeneous character of the catalytically active species. The catalyst can be used many times in
repeating cycles without considerable loss in its activity.
Received 11 December 2009
Received in revised form 17 February 2010
Accepted 18 February 2010
Available online 25 February 2010
Keywords:
Palladium nanoparticles
Heterogeneous catalysis
C–C cross-coupling reactions
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
bilized and insoluble metal catalyst is challenging and important.
The immobilizations of active catalysts on heterogonous supports
Palladium-catalyzed C–C coupling reactions have been recog-
nized as powerful tools and major area of interest in multiple
organic transformations for academic and industrial processes
[1,2]. Although it is some times since these reactions were
first reported [3], their widespread applications in organic syn-
thesis occurred only during the last decades. Coupling of aryl
halides with alkenes (Mizoroki–Heck reaction) and organoboronic
acids (Suzuki–Miyaura reaction) have significant importance,
and are well-established methodology in modern organic syn-
thesis. These Pd-catalyzed coupling reactions are ranked today
among the most general transformations in organic synthe-
sis, and have great industrial potential for the synthesis of
chemicals, natural products, bioactive compounds, and advanced
materials [4].
Many practical and economical aspects of these reactions have
to be developed for their industrialization. Several important goals
in this regard are; the use of aryl chlorides as substrates, the possi-
bility of using aqueous condition, mild reaction temperature and
the recovery of the catalyst [5,6]. Also, from the standpoint of
environmentally benign organic synthesis, development of immo-
have become a popular strategy to facilitate the recovery and
recycling of potentially expensive ligands and complexes, and con-
tamination of products by metallic species is prevented. However,
some immobilizations suffer from limited lifetime, lack of recycla-
bility and decrease in the catalytic activity in repeated use owing to
leaching of metal from their support. In this regard, stable, reusable
and active catalyst anchored to solid supports is of current inter-
est [7–10]. Many organic and inorganic supports such as polymers,
carbon, silica gel, metal oxides, zeolites, dendronized support and
chitosan have been used in preparation of novel catalyst systems
[11–14] (for reviews on immobilized metal catalyst, see [15]).
Phosphines and phosphinites are among the most important
phosphorous-based ligands in organometallic chemistry. These lig-
ands and their metal complexes anchored on polymeric supports
or silica gel have been used in many catalytic reactions [16,17].
Recently, the phosphinite ligands are one of the most employed
ones in synthetic chemistry for generation of the C–C bonds [18,19].
These ligands indebted their successful application in C–C bond
formation to their influence on palladium. They can stabilize pal-
ladium and increase its reactivity. As known, a phosphine with
both the characters of bulkiness and electron-richness not only
accelerates the rate of oxidative addition of aryl halides to Pd(0)-
phosphine complex, but also speeds up the process of reductive
elimination from Pd(II) center. Although phosphinites as ligands in
homogeneously catalytic processes have been widely studied, their
∗
Corresponding author. Tel.: +98 711 2284822; fax: +98 711 2280926.
E-mail addresses: tamami@chem.susc.ac.ir (B. Tamami),
soheila ghasemi chem@yahoo.com (S. Ghasemi).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.02.025

B. Tamami, S. Ghasemi / Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
99
application as heterogeneous system in the coupling reactions is
limited.
each refluxing in water, ethanol and acetone) and dried under vac-
uum. This was done in order to remove any physisorbed palladium
and to make the process completely heterogeneous. To determine
the Pd content of the catalyst, it was treated successively with
30 cm3 mixture of concentrated H2SO4, HNO3 and HCl, and fil-
tered. The filtrate was diluted to 50 cm3 with distilled water and
subjected to ICP determination using calibration curve method. Pd
In continuation of our studies on using polyacrylamide sup-
port [20], we herein disclose the preparation of a stable and active
heterogeneous palladium catalyst containing phosphinite ligand
based on polyacrylamide for use in C–C cross-coupling reactions.
No reduction step is required to obtain metallic particles of Pd(0).
content = 0.15 mmol g−1
.
2. Experimental
2.3. Typical procedure for Heck cross-coupling reactions
2.1. General
A round-bottomed flask equipped with a condenser and stir bar
was charged with aryl halide (1 mmol), n-butyl acrylate or styrene
(1.2 mmol), K2CO3 (2.0 mmol) and Pd catalyst (13 mg, 0.2 mol%) in
DMF (3 ml). The flask was placed in an oil bath, and the mixture was
stirred and heated at 100 ◦C for the appropriate time. The reaction
was monitored by TLC (or GC if necessary). After completion of the
reaction, the catalyst was easily recovered by filtration and the fil-
trate was extracted with ethyl acetate three times. The combined
organic extracts were washed with water (2× 10 ml) and brine
(10 ml), and dried over anhydrous Na2SO4 and evaporated under
reduced pressure. The mixture was then purified by column chro-
matography over silica gel or recrystallization to afford a product
with high purity. Characterization of the products was performed
by comparison of their FT-IR, 1H NMR, 13C NMR, and physical data
with those of the authentic samples.
Acrylamide (Fluka) was recrystallized from chloroform. Other
reagents and solvents were of commercial reagent grade and
obtained from Merck or Fluka and used without further purifica-
tion. All products were characterized by comparison of their FT-IR
and NMR spectra and physical data with those reported in the liter-
ature. All yields refer to the isolated products. Progress of reactions
was followed by TLC on silica-gel Polygram SILG/UV 254 plates or
by GLC on a Shimadzu model GC 10-A instrument with hydrogen
flame ionization detector. IR spectra were run on a Shimadzu FT-IR-
8300 spectrophotometer. NMR spectra were recorded on a Bruker
Avance DPX instrument (250 MHz). The Pd analysis and leaching
test was carried out by ICP-OES analyzer (Varian, Vista-Pro). CHN
analysis was carried out on Thermo Finningan FIASHEA 1112 series
instrument. X-ray diffraction data obtained with XRD, D8, Advance,
Bruker, axs. TEM analyses were performed on a Philips model CM
10 instrument. Scanning electron micrographs were obtained by
SEM, XL-30 FEG SEM, Philips, at 20 kV. UV–vis diffuse reflectance
spectroscopy (UV–vis DRS) was performed on Cary 5 instrument
by photometric mode with 300 nm/min scan rate.
2.4. Typical procedure for Suzuki cross-coupling reactions
A round-bottomed flask equipped with a condenser and stir
bar was charged with aryl halide (1 mmol), phenylboronic acid
(1.2 mmol), K2CO3 (2.0 mmol) and Pd catalyst (7 mg, 0.1 mol%) in
DMF (3 ml). The flask was placed in an oil bath, and the mixture was
stirred and heated at 80 ◦C for the appropriate time. After comple-
tion of the reaction, the procedure outlined above was followed.
2.2. Preparation of catalyst
2.2.1. Preparation of crosslinked polyacrylamide
N,Nꢀ-Methylene-bis-acrylamide (NNMBA) (1.13 g, 0.007 mol)
and acrylamide (10 g, 0.14 mol) were dissolved in ethanol (250 ml).
K2S2O8 (62 mg, 0.23 mmol) was added to this solution and stirred at
70–75 ◦C for 5 h. The polymer formed was filtered off, washed sev-
eral times with ethanol, THF and acetone, and then dried at 60 ◦C
under reduced pressure.
2.5. General procedure for recycling reactions
When the corresponding Heck or Suzuki reaction according to
the procedure described in previous sections was finished, the sus-
pension was cooled down to room temperature and filtered off. The
polymer was washed with DMF, water and acetone. It was dried
under vacuum and reused without any pretreatment for repeating
cycles.
2.2.2. Preparation of poly(N-hydroxy acrylamide)
Crosslinked polyacrylamide (5%) (1 g) was suspended in ethanol,
and to this were added 5-fold excess NH2OH/HCl (4.8 g,70 mmol)
and aqueous solution of NaOH (10 ml, 7 M) in small portions. The
mixture was heated while stirring at 90–100 ◦C for 18 h. The resul-
tant mixture was cooled, filtered and washed thoroughly with
water, ethanol and acetone and dried under vacuum overnight to
give the desired product.
3. Results and discussion
3.1. Synthesis and characterization of the palladium catalyst
The Pd catalyst was designed by the sequence of reactions
given in Scheme 1. Crosslinked polyacrylamide 3 (5%) was prepared
by free radical solution polymerization of acrylamide 1 and N,Nꢀ-
methylene-bis-acrylamide 2 mixture in ethanol using K2S2O8 as
initiator. Polar nature of the crosslinking agent provides its compat-
ibility with polymer backbone and polar solvents. We found that
polymers with less than 5% NNMBA will become sticky in the next
step and not physically proper for further reactions. The IR spec-
trum of the polymer showed the characteristic absorption of amide
(N–H amide stretching) at 3193 and 3360 cm−1, and carbonyl group
(C O amide stretching) at 1668 cm−1. The signal at 2933 cm−1
was due to methylene groups. Poly(N-hydroxy acrylamide) 4 was
obtained by transamidation reaction of crosslinked polyacrylamide
with excess of hydroxylamine in ethanol. IR spectrum of the poly-
mer showed a broad band at 3408 cm−1 due to overlapping of OH
stretching and amide NH. The hydroxyl group capacity of the resin
was determined by CHN analysis and was found to be 7.46 mmol/g.
2.2.3. Preparation of polymeric phosphinite ligand
To the crosslinked poly(N-hydroxy acrylamide) (1 g) in THF at
an ice-cooling bath (0 ◦C), a solution of chlorodiphenylphosphine
(2.1 ml, 11.2 mmol) in THF was added dropwise in a period of 15 min
while stirring. The reaction mixture was then stirred for additional
10 h at rt, and then filtered off. The corresponding solid was washed
with water, THF and ethanol and then dried under reduced pres-
sure.
2.2.4. Preparation of palladium catalyst
The phosphinite ligand (1 g) was treated with a solution of
pd(OAc)2 (0.28 g) in DMF (15 ml) at 100 ◦C for 8 h. After complex-
ation, the mixture was filtered and washed thoroughly with DMF,
water and acetone. It was then conditioned for a total of 18 h (3 × 2 h

100
B. Tamami, S. Ghasemi / Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
Scheme 1. Synthetic strategy for the preparation of modified polyacrylamide-supported Pd nanoparticles.
Fig. 1. (A) SEM image of Pd catalyst and (B) SEM close-up of image A.
The polymeric phosphinite ligand 5 was prepared by the reaction of
poly(N-hydroxy acrylamide) with ClPPh2 in THF. The phosphorous
content of the resin was obtained by iodometric titration method
and was found to be 2.8 mmol/g. Palladium complex 6 was obtained
by mixing Pd(OAc)2 with polymer 5 in DMF. The active Pd(0) cata-
lyst as a black insoluble mass was formed by coordination of two P
atoms to Pd(II) center, followed by the reduction to Pd(0) by another
phosphinite group. This reduction pathway is generally known for
Pd(II) compounds [18b–d,21]. Determination of Pd content was car-
ried out on catalyst digestion followed by elemental analysis. ICP
analysis revealed that resin 6 contained an average of 0.15 mmol/g
of Pd.
To obtain a visual image of the supported catalyst, scanning
electron microscopy (SEM) was carried out. By SEM images some
information about the morphology of the catalyst particles was
obtained as presented in Fig. 1. The SEM image shows parti-
cles with diameters in the range of nanometers to micrometers.
Transmission electron microscope (TEM) image clearly shows that
Pd nanoparticles were formed and well-defined spherical parti-
cles dispersed in the polymer matrix with a size in the range of
18–30 nm (Fig. 2). The X-ray powder diffraction (XRD) pattern of
the Pd catalyst is consistent with the metallic Pd(0) data in the lit-
erature [22]. Fig. 3 shows the (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2)
crystallographic planes of the Pd(0) nanoparticles. The Pd nanopar-
ticle size was estimated from the XRD pattern using the Scherrer
equation and was found to be 30.1 nm, close to the size observed
in TEM. Further characterization of polymeric Pd complex was per-
formed using UV–vis diffuse reflectance spectroscopy, as shown in
Fig. 4. We investigated the UV–vis absorption spectra of polymeric
Fig. 2. TEM image corresponding to Pd catalyst.

B. Tamami, S. Ghasemi / Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
101
Table 1
Optimization of base and solvent for Heck reaction of iodobenzene with n-butyl acrylatea.
Entry
Base
Solvent
Pd (mol%)
Time
Conversion (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
THF
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.01
0.001
3 h
3 h
3 h
3 h
1 h
3 h
3 h
3 h
3 h
3 h
3 h
14 h
18 h
N.R
60
10
55
100
90
50
40
55
20
CH3CN
EtOH
H2O
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
NaOAc
KF
K3PO4·12H2O
–
K2CO3
K2CO3
K2CO3
100
100
100
a
Reaction conditions: iodobenzene (1 mmol), n-butyl acrylate (1.2 mmol), base (2 mmol), pd catalyst (0.2–0.001 mol%), and 3 ml of solvent at 100 ◦C.
Conversions based on iodobenzene.
b
band was not significantly affected by chelation and just changed
from 308 to 300 nm on complexation with palladium. Because all
of the phosphinite groups of the polymeric ligand do not partici-
pate on complexation with Pd, the complex shows a wide but weak
absorbance band due to n → ␲* on the range of 380–450 nm. No
d → d transition was observed for this complex. The formation of
deep black colored complexes and the absence of this transition
were attributed to t62geg4 configuration or metallic Pd(0) complex.
3.2. Catalytic activity of the catalyst in C–C coupling reactions
To check the potency of modified polyacrylamide-supported
Pd catalyst, it was first used in Heck coupling reactions, which is
a versatile and most studied method for generation of C–C bond
in organic synthesis. The coupling of iodobenzene with n-butyl
acrylate was initially studied as a model reaction. The reaction con-
ditions were optimized, and the results are presented in Table 1.
It was found that the best system for this reaction was DMF in
combination with K2CO3, which yielded a 100% conversion of
iodobenzene within 1 h using 0.2 mol% of Pd catalyst (entry 5). Also,
we examined the effect of catalyst loading on the coupling reaction
of iodobenzene with n-butyl acrylate. The loading of the catalyst
can be reduced down up to 0.001 mol% of Pd (TON = 9.5 × 104) by
prolonging the reaction time in order to get full conversion. This is
the indication of an effective catalytic system.
Fig. 3. Powder XRD patterns of Pd catalyst.
ligand before and after complexation in the range of 200–750 nm.
The polymeric phosphinite ligand shows an absorbance shoulder
at 308 nm due to the ␲ → ␲* transition and another wide band in
the range of 410–470 nm due to the n → ␲* transition. The ␲ → ␲*
To survey the generality of the catalytic protocol, we investi-
gated the reaction using a variety of aryl iodides and bromides
with n-butyl acrylate or styrene under the optimized condition
(Scheme 2). The results are shown in Table 2 . The electron-neutral,
electron-rich and electron-poor aryl iodides and bromides reacted
with olefins very well. The catalytic performance was excellent for
the substrate with electron-withdrawing groups (entries 4–7, 12,
14, and 21–24). Nevertheless the efficiencies were only slightly
lower for the substrates with electron-donating groups (entries 2,
8, 15, 19 and 25). This cross-coupling reaction was also tolerant
Fig. 4. UV–vis diffuse reflectance spectra for the polymeric phosphinite ligand (a)
and its corresponding palladium catalyst (b).
Scheme 2. Mizoroki–Heck cross-coupling reactions.

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B. Tamami, S. Ghasemi / Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
Table 2
Heck reaction of n-butyl acrylate or styrene with aryl halidesa.
Entry
1
Aryl halides
R2
Time
1 h
Yieldb (%)
92
CO2Bun
2
3
CO2Bun
CO2Bun
1.5 h
2 h
95
89
4
5
6
7
8
CO2Bun
CO2Bun
CO2Bun
CO2Bun
CO2Bun
40 min
40 min
5 h
93
90
85
80
83
5 h
6 h
9
CO2Bun
CO2Bun
8.5 h
14 h
87
75
10
11
12
CO2Bun
CO2Bun
15 h
2 h
70c
92c
13
CO2Bun
24
65c
14
15
CO2Bun
CO2Bun
5 h
9 h
82c
82c
16
17
CO2Bun
CO2Bun
24
10
60c
65c
18
19
Ph
Ph
3.5 h
4 h
92
93

B. Tamami, S. Ghasemi / Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
103
Table 2 (Continued )
Entry
Aryl halides
R2
Time
5 h
Yieldb (%)
80
20
Ph
21
22
23
24
Ph
Ph
Ph
Ph
Ph
3 h
90
90
80
84
81
3 h
10 h
10 h
15 h
25
a
Molar ratio of the reagents ArX:n-butyl acrylate or styrene:K2CO3:palladium catalyst = 1.0:1.2:2.0:0.002. Reaction conditions: DMF, 100 ◦C.
Isolated yields.
With additional tetrabutylammonium bromide (0.05 mmol).
b
c
for substrate with ortho substitution, which is sterically hindered,
and meta substitution and led to good yields (entries 9, 10, 13, 16
and 17). In general, the reaction with less reactive styrene proceeds
slower compared to n-butyl acrylate.
recovery and reusability of the supported catalyst have been
investigated using iodobenzene with n-butyl acrylate as model sub-
strates. The catalyst is highly reusable. It was used for 10 cycles
and retained its catalytic activity in these repeating cycles. The Pd
catalyst exhibited only a slight loss in its activity and required a
bit longer time to achieve full conversion even after 10 cycles. The
results are tabulated in Table 4.
The more easily accessible and cheaper aryl chlorides have not
been employed much, in palladium-catalyzed coupling reactions,
primarily because the oxidative addition of C–Cl bond to Pd(0)
species is usually difficult. Few heterogeneous Pd catalysts were
found to convert activated aryl chlorides at high temperature [23].
It is clear that aryl chlorides are best activated by Pd complex con-
taining electron-rich bulky phosphine [24]. The electron-releasing
properties of these phosphine ligands not only favor the difficult
oxidative addition of aryl-chloro bond, but also the bulk of the
ligand favors the final reductive elimination step in the catalytic
cycle. In our catalytic system, the reaction with chlorides had to be
run in the presence of tetrabutylammonium bromide (TBAB) (Jef-
fery Catalyst) as an additive [25] (entries 11–17). The reaction of
aryl chlorides with styrene is sluggish and do not give the desired
products in acceptable times.
The polyacrylamide-supported Pd catalyst can also be applied
in the Suzuki reaction which is one of the most powerful and ver-
satile method for the generation of new biaryls (Scheme 3). As
shown in Table 3 different aryl halides react with phenylboronic
acid to give the corresponding biaryls. Compared to Heck reaction
described in the previous paragraph, Suzuki reaction was per-
formed under milder reaction condition (80 ◦C) and less palladium
catalyst (0.1 mol%). Moreover, similar to Heck reaction aryl chlo-
rides can also give the coupling products in the presence of TBAB.
In view of multiple recycling and continuous processing, fixation
of Pd particles on solid supports should provide catalysts prepared
at low cost and allow easy separation by filtration, however, a major
drawback of this technique reported in the publications is leaching
[26]. Therefore, the low contamination of residual metal in the iso-
lated products is an important characteristic for supported metal
catalyst. To probe the issue of palladium leaching in our system,
the filtrate of the reaction between iodobenzene and n-butyl acry-
late was analyzed by ICP in 10 repeating cycles. Low palladium
contamination was observed during this experiment. Analysis of
the crude reaction mixture for the first reaction indicates a leach-
ing of 0.48% of the palladium. Residual palladium levels present
in product in different catalytic runs was analyzed. This catalytic
system shows 6.1% palladium leaching after 10 runs. We did not
observe the palladium black formation in the reaction even after
the 10th cycle. For further investigation, the organic phase of the
first run of reaction between bromobenzene and n-butyl acrylate
was separated from the solid and then new portions of reactants
(bromobenzene, n-butyl acrylate and K2CO3) were added to the
clear filtrate. The composition of the reaction mixture was deter-
mined by GLC. Then after 24 h reaction time, the composition was
determined again. The reaction had not progressed and 94% bro-
mobenzene was remained in the reaction mixture. This observation
confirmed negligible palladium leaching from the supported sys-
tem.
In order to ascertain whether the catalyst was behaving in a truly
heterogeneous manner, or whether it is merely a reservoir for more
active soluble form of Pd, hot filtration test was performed. In a typ-
ical experiment, Pd complex (0.2 mol%), bromobenzene (1 mmol),
n-butyl acrylate (1.2 mmol), K2CO3 (2.0 mmol) and DMF (3 ml) were
taken in a round-bottomed flask and stirred at 100 ◦C for 30 min.
At this stage (25% conversion), the catalyst was filtered off and
the experiment was continued with the filtrate for another 24 h.
There was no detectable increase in the product concentration, as
is evident from the GC analysis. It is confirmed the heterogeneous
character of the catalytically active species.
3.3. Heterogeneity test and catalyst reuse
The reusability of supported catalysts is very important theme
and makes them useful for commercial applications. Thus, the
Scheme 3. Suzuki–Miyaura cross-coupling reactions.

104
B. Tamami, S. Ghasemi / Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
Table 3
Suzuki reaction of phenylboronic acid with aryl halidesa.
Entry
1
Aryl halides
Time
Yieldb (%)
96
40 min
2
3
1 h
1 h
92
85
4
5
6
7
40 min
40 min
1.5 h
95
95
85
80
2 h
8
9
3.5 h
3.5 h
80
70
10
11
12
13
4 h
81
40 min
7 h
90
75c
90c
1.5 h
14
7 h
75c
15
16
2 h
2 h
88c
91c
17
18
7 h
70c
5 h
75c
85c
19
16 h
a
Molar ratio of the reagents ArX:phenylboronic acid:K2CO3:palladium catalyst = 1.0:1.2:2.0:0.001. Reaction conditions: DMF, 80 ◦C.
Isolated yields.
With additional tetrabutylammonium bromide (0.05 mmol).
b
c

B. Tamami, S. Ghasemi / Journal of Molecular Catalysis A: Chemical 322 (2010) 98–105
105
Table 4
Recycling of Pd catalyst for the Heck reaction of iodobenzene with n-butyl acrylatea.
c
Entry
Cycle
Time
Isolated yield (%)
TONb
TOF (h−1
)
1
2
3
4
5
6
7
8
9
10
1st
1 h
1 h
1.5 h
1.5 h
1.5 h
1.5 h
2
2
3
3
95
96
93
95
92
96
92
95
93
95
475
480
465
475
460
480
460
475
465
475
475
480
310
316.7
306.7
320
230
237.5
155
2nd
3rd
4th
5th
6th
7th
8th
9th
10th
158.3
TON for 10 runs
4795
Av. TOF (h−1
)
298.92
a
Reaction conditions: molar ratio of iodobenzene:n-butyl acrylate:K2CO3:Pd catalyst = 1.0:1.2:2.0:0.002 in DMF at 100 ◦C. All reactions were carried out with 100%
conversion of iodobenzene.
b
TON = mmol of products/mmol of catalyst.
TOF = TON/time.
c
4. Conclusion
[12] (a) R.S. Varma, K.P. Naicker, P.J. Liesen, Tetrahedron Lett. 40 (1999) 2075–2078;
(b) V. Polshettiwar, R.S. Varma, Tetrahedron 64 (2008) 4637–4643.
[13] (a) C.A. McNamara, M.J. Dixon, M. Bradley, Chem. Rev. 102 (2002) 3275–3300;
(b) I.P. Beletskaya, A.R. Khokhlov, E.A. Tarasenko, V.S. Tyurin, J. Organomet.
Chem. 692 (2007) 4402–4406;
(c) V. Polshettiwar, A. Molnar, Tetrahedron 63 (2007) 6949–6976.
[14] H. Zhou, G.L. Zhuo, X.Z. Jiang, J. Mol. Catal. A: Chem. 248 (2006) 26–31.
[15] (a) P.T. Anastas, J.C. Warner, Green Chemistry: Theory and Practice, Oxford Uni-
versity Press, Oxford, 1998;
In conclusion,
a new palladium catalyst based on modi-
fied crosslinked polyacrylamide was designed and applied in
Mizoroki–Heck and Suzuki–Miyaura cross-coupling reactions.
Through TEM and XRD we can observe high metal dispersion and
small particle sizes in nanoscale. Short reaction times, high yields,
easy purification, recyclability and low Pd leaching are main char-
acteristic of the process. This supported catalyst is air-stable and
all reactions can be conducted in air.
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Acknowledgments
The authors gratefully acknowledge the partial support of this
study by Shiraz University Research Council. We are also grate-
ful from Mr. Mostafavi and Institute for Advanced Studies in Basic
Sciences in Zanjan for running UV–vis DR spectra.
(b) N. Iranpoor, H. Firouzabadi, R. Azadi, Eur. J. Org. Chem. 13 (2007) 2197–2201;
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