Polymer supported Pd catalyzed carbonylation of aryl bromides for the synthesis of aryl esters and amides

Article abstract of DOI:10.1039/c4ra05365f

A polymer-anchored palladium(ii) catalyst was synthesized and characterized using various spectroscopic techniques. Its catalytic activity was evaluated for the alkoxycarbonylation and aminocarbonylation reactions. These carbonylation reactions were carried out for various substituted aryl bromides using alcohols and amines. Both the reactions were optimized by varying the bases, temperature and solvents. These experiments were carried out under high CO pressure. The catalyst was very stable and can be facilely recovered and reused six times without a significant decrease in its activity and selectivity. the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra05365f

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PAPER
Polymer supported Pd catalyzed carbonylation of
aryl bromides for the synthesis of aryl esters and
amides†
Cite this: RSC Adv., 2014, 4, 38986
*
Sk Manirul Islam, Kajari Ghosh, Anupam Singha Roy‡ and Rostam Ali Molla‡
A polymer-anchored palladium(II) catalyst was synthesized and characterized using various spectroscopic
techniques. Its catalytic activity was evaluated for the alkoxycarbonylation and aminocarbonylation
reactions. These carbonylation reactions were carried out for various substituted aryl bromides using
alcohols and amines. Both the reactions were optimized by varying the bases, temperature and solvents.
These experiments were carried out under high CO pressure. The catalyst was very stable and can be
facilely recovered and reused six times without a significant decrease in its activity and selectivity.
Received 5th June 2014
Accepted 15th August 2014
DOI: 10.1039/c4ra05365f
www.rsc.org/advances
(>150 C) or multistep operations.23–27 Alternatively, transition-
ꢀ
Introduction
metal catalyzed amino carbonylation has emerged as an effi-
cient strategy towards such types of compounds.28 Amino-
carbonylation is a constructive method for the direct synthesis
of aromatic amides via coupling of aryl, heteroaryl, or alkynyl
halides with primary/secondary amines.9
Carbonylation processes using carbon monoxide (CO) as a C1
building block have proven to be a powerful tool to construct
important scaffolds in natural products, pharmaceuticals,
agrochemicals, and functional materials.1,2 Over the past few
decades, extensive efforts have been made to develop transition-
metal catalyzed carbonylation of organic halides3–5 or organic
pseudohalides6,7 for the synthesis of carboxylic acids, esters,
amides, and so on.
Carbonylation of aryl halides with alcohols or amines cata-
lyzed by palladium complexes is a convergent and direct route
for the synthesis of aromatic esters and amides.8 Aromatic
esters are important building blocks for various pharmaceuti-
cals and agrochemicals.9 Traditionally, these esters were
synthesized via reaction of the carboxylic acid with alcohols.10
Carbonylation of the aryl halides in the presence of an alcohol is
an attractive alternative method that tolerates a wide range of
substrates, thus demonstrating a great advantage for the
synthesis of substituted aromatic esters and its derivatives.11–13
In this regard, various palladium-based catalytic systems have
been explored for alkoxycarbonylation reaction.14–18
Literature reports reveal that alkoxycarbonylation and ami-
nocarbonylation have been well explored by using a variety of
homogeneous Pd complexes using various air and moisture-
sensitive N/P-containing ligands.29–35 But the recovery and
recycling of the homogeneous palladium catalyst is a chal-
lenging task. To get rid of these serious issues, some hetero-
geneous catalysts have been reported.36 However, these
methods require prolonged reaction time, exotic reaction
condition and the important issue is that most of these reported
methods used phosphine containing complex which is toxic in
nature. On the other hand most of the alkoxy and amino
carbonylations used aryl iodides as the choice of substrate, and
quantitative yields were reported.37,9 Therefore, developing a
simple and versatile method for the preparation of aryl esters
and amides from less expensive aryl bromides catalyzed by
heterogeneous palladium catalyst under phosphine free
condition is still a matter of interest in organic synthesis.
Herein we report the synthesis and characterization of a
newly synthesized polymer anchored palladium(II) Schiff base
complex and its catalytic applications towards alkox-
ycarbonylation and aminocarbonylation reactions of aryl
bromides under the phosphine free conditions.
Amides are also important chemicals that exist in pharma-
ceuticals, natural products, and many functional materials.19,20
Arylacetamides have gained considerable attention because of
their pharmacological and biological activities.21 Some hetero-
cyclic amides are potential CNS (central nervous system)-active
compounds.22 Among the methods documented for the prepa-
ration of amides, most of them require harsh conditions
Experimental
Materials and instruments
Department of Chemistry, University of Kalyani, Kalyani, Nadia, 741235, W.B., India.
E-mail: manir65@rediffmail.com; Fax: +91-33-2582-8282; Tel: +91-33-2582-8750
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra05365f
Analytical-grade reagents and freshly distilled solvents were
used throughout the experiment. Chloromethylated polystyrene
was supplied by Sigma-Aldrich chemicals Company, USA. Other
‡ These authors contributed equally to this manuscript.
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reagents were obtained from Merck Co. The chemical analysis CH2Cl) was converted into PS-CHO according to literature.39 2-
was done by the usual procedure. The purity of solvents and Amino phenol was added (1 : 1 molar ratio) with polymer
substrates were checked by gas chromatography. Carbon aldehyde in methanol solvent with stirring for 24 h under reux
monoxide (99.9%) purchased from IOL Bombay and palladium condition to prepare the yellow Schiff base compound. The
acetate from Arora Matthey, India, were used as received. Liquid mixture was cooled to room temperature and then ltered. The
substrates were predistilled and dried using appropriate residue was washed with ethanol until the ltrate became
molecular sieves. Distillation and purication of the solvents colorless and was dried under vacuum.
and substrates were done by standard procedures.38
Preparation of polymer-bound Pd(II) complex. The polymer-
1H NMR spectra were recorded on a Bruker DPX-400 NMR anchored Schiff base ligand (2 g) in acetic acid (20 mL) was
spectrometer in pure deuterated solvents with TMS as internal placed in a round bottom ask. 5 mL acetic acid (17.4 molar)
standard. A Perkin-Elmer 2400C elemental analyzer was used to solution (2%, w/v) of Pd(OAc)2 were added with constant stirring
collect micro-analytical data (C, H and N). FTIR spectra of the and then reuxed for 24 h. The colour of the complex changed
samples were recorded on a Perkin-Elmer FTIR 783 spectro- from yellow to deep brown. The polymer-anchored metal
photometer using KBr pellets. A Mettler Toledo TGA/SDTA 851 complex obtained by this process, was ltered and washed
instrument was used for the thermogravimetric (TGA) analysis. successively with acetic acid, methanol and nally dried under
The morphology of the functionalized polystyrene and complex vacuum.
was analyzed using
a
scanning electron microscope
General procedure for alkoxycarbonylation reaction cata-
(SEM)(ZEISS EVO40, England) equipped with EDAX facility. lysed by PS-AMP-Pd. To a 50 mL autoclave, aryl bromide (1
The metal content in the catalyst was determined using a Varian mmol), alcohol (5 mL), PS-AMP-Pd (4 Â 10À4 mmol), and Et3N
AA240 atomic absorption spectrophotometer (AAS).
(3 mmol) were added. The autoclave was closed, purged three
times with carbon monoxide, pressurized with 1 atm of CO, and
heated at 70 ꢀC for 3 h. Aer the completion of the reaction, the
reactor was cooled to room temperature, and the remaining CO
gas was carefully vented, and the reactor was opened. The
reactor vessel was thoroughly washed with ethyl acetate
(2 Â 10 mL) to remove any traces of the product and catalyst if
present. The catalyst was ltered, and the reaction mixture was
evaporated under vacuum. The obtained residue was puried by
column chromatography (silica gel, 100–200 mesh; petroleum
ether–ethyl acetate, 95 : 05) to afford the desired product.
General experimental procedure for aminocarbonylation
reaction. To a 50 mL high pressure autoclave, aryl bromide
(1 mmol), amine (2 mmol), PS-AMP-Pd (4 Â 10À4 mmol),
toluene (10 mL), and Et3N (3 mmol) were added. The autoclave
Synthesis of catalyst
Preparation of polymer-bound ligand. Polymer anchored
ligand was readily prepared in two steps (Scheme 1). Firstly,
chloromethylated (5.5 mmol Cl per g of resin) polystyrene (PS-
Table 1 Chemical composition of polymer anchored ligand and
polymer supported catalyst
Compound
Colour
C%
H%
Cl%
N%
Metal%
PS-AMP
PS-AMP-Pd
Yellow
Brown
75.50
68.11
5.96
5.34
5.89
4.09
2.32
2.37
—
8.79
Fig. 1 FT-IR spectra of polymer anchored ligand (a) and polymer anchored Pd(II) catalyst (b).
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Scheme 1 Synthesis of polymer anchored Pd(II) complex.
was closed, purged three times with carbon monoxide, pres- characteristic peak of CO at 1702 cmÀ1 (ESI, Fig. S1†) which was
surized with 3 atm of CO and heated at 100 ꢀC for 8 h. Aer the strongly reduced in the ligand and catalyst (Fig. 1). IR spectra
completion of the reaction, the reactor was cooled to room show a stretching vibration for –CH2 at 2919 cmÀ1 for the
temperature, and the remaining CO gas was carefully vented polymer bound ligand and its complex. The stretching vibration
and the reactor was opened. The reactor vessel was thoroughly of C]N bond appeared at 1698 cmÀ1 for the polymer-bound
washed with ethyl acetate (2 Â 10 mL) to remove any traces of Schiff base ligand which is shied to 1690 cmÀ1 in the metal
the product and catalyst if present. The catalyst was ltered, and complex.40,41 Characteristic peak of free OH appeared at
the reaction mixture was evaporated under vacuum. The residue 3377 cmÀ1 for the ligand and its intensity is reduced in the
obtained was puried by column chromatography to afford the complex.42 A peak is observed at 1246 cmÀ1 (v C–O, phenolic) in
desired product.
the ligand and at 1243 cmÀ1 in the complex.43 The polystyrene
anchored Pd(II) complex exhibited important IR peaks at
Results and discussion
Characterization of the polymer anchored Pd catalyst
Due to the insolubilities of the polymer-supported metal
complex in all common organic solvents, its structural investi-
gation was limited to their physicochemical properties, chem-
ical analysis, SEM, TGA, FTIR and UV-vis spectral data. Table 1
provides the data of elemental analysis of polymer supported
ligand and the polymer supported palladium catalyst. The
palladium content of the polymer-supported catalysts was
estimated by atomic absorption spectrometer and it suggests
8.79 wt% Pd in the catalyst.
The attachment of metal onto the support was conrmed by
comparison of the FT-IR spectra (Fig. 1) of the polymers
before and aer loading with metals, both in the mid-IR (4000–
400 cmÀ1) region. The IR spectrum of pure chloromethylated
polystyrene has an absorption band at 1261 cmÀ1 due to the
C–Cl group, which was weak in the ligand and in the catalyst.
Aldehyde functionalized polystyrene, PS-CHO shows its Fig. 2 DRS-UV vis spectra of polymer anchored Pd(II) complex.
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may be designated as 1A1g / 1Eg, 1A1g / 1B1g and 1A1g / 1A2g
transitions respectively.47,48
Field emission-scanning electron micrographs of single
bead of polymer anchored ligand (PS-L) and its complex (PS-
AMP-Pd) were recorded and it was observed that the morpho-
logical changes occurred on the polystyrene beads at various
stages of the synthesis. The SEM images of polymer anchored
ligand (A) and the immobilized palladium(II) complex (B) on
functionalized polymer are shown in Fig. 3. The pure chlor-
omethylated polystyrene bead has a smooth surface while
polymer anchored ligand and complex show slight roughening
of the top layer of polymer beads. This roughening is relatively
more in complex. Also the presence of palladium metal can be
further proved by energy dispersive spectroscopy analysis of X-
rays (EDAX) (Fig. 4) which suggests the formation of metal
complex with the polymer anchored ligand.
Fig. 3 FE SEM images of polymer anchored ligand (A) and polymer
anchored Pd(II) complex (B).
1575 cmÀ1 (vassym COO bridged), 1358 cmÀ1 (vsym COO bridged)
and 1733 cmÀ1 (v C]O),44 which suggest the most probable
structure of our catalyst is depicted in Scheme 1. Peaks for Pd–
N45 and Pd–O46 appeared in the far-IR region.
The electronic spectra (Fig. 2) of the polymer-supported
metal complex were recorded in diffuse reectance spectrum
mode as MgCO3/BaSO4 disks. The present Pd(II) complex shows
a broad spectrum with few shoulders at a region of 260–530 nm.
It may exhibit three spin-allowed d–d transitions. The bands are
observed at 265–285 nm, 340–380 nm and 450–500 nm, which
Thermal stability of complex was investigated using TGA at a
À1
ꢀ
heating rate of 10 C min in air over a temperature range of
30–600 ꢀC. TGA curve of polymer anchored Pd(II) complex is
shown in Fig. 5. Polymer anchored palladium(II) complex
decomposed at 360–400 ꢀC. So from the thermal stability, it
Fig. 4 EDX images of polymer anchored ligand (A) and polymer anchored Pd(II) complex (B).
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Scheme 3 Alkoxycarbonylation of bromobenzene with ethanol.
Table 2 Effect of bases and temperature on the alkoxycarbonylation
of bromobenzenea
Entry
Base
Temperature (ꢀC)
Conversion (%)
1
2
3
4
5
6
7
K2CO3
Cs2CO3
DBU
NaOAc
Et3N
70
70
70
70
70
80
79
85
91
96
96
96
Fig. 5 TGA curve of polymer anchored Pd(II) complex.
Et3N
Et3N
90
100
concludes that polymer anchored metal complex degraded at
considerably higher temperature.
a
Reaction conditions: bromobenzene (1 mmol), alcohol (5 mL), PS-
AMP-Pd (4 Â 10À4 mmol), base (3 mmol), 1 atm CO pressure, temp.
(70 ꢀC), time (3 h).
Catalytic activities
Since supported palladium catalyst exhibit high catalytic
activity in a wide range of industrially important processes and
have been extensively studied for C–C coupling,49 thus we
decided to investigate the catalytic activity of the PS-AMP-Pd in
the eld of carbonylation reactions (Scheme 2).
therefore, 70 ꢀC was considered as an optimum reaction
temperature for further studies.
The reaction was carried out at 1 atm of CO pressure,
providing an excellent yield of the desired product within 3 h.
Various alcohols were reacted with bromobenzene and the
results are summarized in Table 3. Changing the alcohol
substrate from a primary (MeOH, EtOH) (Table 3, entry 1 and 2)
to a secondary alcohol (iPrOH) (Table 3, entry 3) did not have a
signicant effect on product yield. However, moving to a tertiary
alcohol (tBuOH) was not successful, a low product yield being
obtained presumably due to steric bulk (Table 3, entry 4).
Excellent yield was also obtained with benzyl alcohol (Table 3,
entry 5). It was observed that among all the alcohols used, EtOH
gave the maximum yield with bromobenzene. Hence, the
nalized reaction conditions were the following: base, Et3N;
temperature, 70 ꢀC; solvent, alcohol (also as a nucleophile, here
EtOH); time, 3 h; and 1 atm of CO pressure. These reaction
parameters were then successfully applied for carbonylation of
a variety of aryl bromides with EtOH (Table 4, entries 1–17).
Alkoxycarbonylation reaction of aryl bromide and alcohol
catalyzed by PS-AMP-Pd
Alkoxycarbonylation was carried out with bromobenzene and
ethyl alcohol under CO pressure and maintaining basic
medium using the polymer anchored Pd(II) catalyst. Ethyl
benzoate was obtained as a product with 96% yield (Scheme 3).
Initially, the reaction was carried out with various inorganic
bases, such as K2CO3 (80%) and Cs2CO3 (79%), and organic
bases, such as DBU (85%), NaOEt (91%) and Et3N (96%).
Because Et3N provides the maximum yield of the corresponding
product, it was used for further study. The temperature effect
for the reaction was also studied (Table 2). No profound
increase in the yield of the desired product was observed when
the reaction temperature was increased from 70 to 100 ꢀC;
Scheme 2 Palladium catalyzed alkoxy and amino carbonylation of aryl bromides.
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Table 3 Effect of various alcohols on alkoxycarbonylation reactiona
Entry
Alcohol
Product
Yieldb (%)
1
MeOH
95
2
3
4
EtOH
96
93
20
iPrOH
tBuOH
5
Benzyl alcohol
94
a
Reaction conditions: aryl bromide (1 mmol), alcohol (5 mL), PS-AMP-Pd (4 Â 10À4 mmol), Et3N (3 mmol), 1 atm CO pressure, temp (70 ꢀC), time
b
(3 h). Isolated yield.
A range of aryl bromides can be converted to the ethyl esters
including ortho-substituted examples (Table 4, entries 2, 5 and
8). The yields of different electrophiles varied from 70 to 99%.
Functional groups such as methoxy, cyano, ketone, ester, and
nitryl groups were well tolerated (Table 4, entries 5–9, 12–14).
Fluoro and triuoromethyl group at para – positions were also
effectively converted into their corresponding carbonylative
products in excellently high yields (Table 4, entries 10 and 11).
As representatives of hetero-aromatic substrates, 3-bromopyr-
idine, gave a high yield of the desired ester (Table 4, entry 15)
while 2-bromothiophene only resulted in moderate yield,
probably because of the volatility of the product (Table 4, entry
16). 2-Bromonaphthalene and biaryl compound 4-bromobi-
phenyl was effectively converted (Table 4, entries 17 and 18).
Aminocarbonylation reaction of aryl bromide and amine
catalyzed by PS-AMP-Pd
The scope of PS-AMP-Pd was further extended for amino-
carbonylation of aryl bromides with a range of aliphatic,
aromatic, primary, and secondary amines (Scheme 4).
The reaction of bromobenzene with aniline was selected as a
model reaction for optimization. The inuence of solvent and
reaction temperature on the catalytic performance of this
system was investigated by employing various solvents
temperature (Table 5). Various solvents, such as DMF (90%),
water (85%), anisole (64%), and toluene (96%), were screened
for the reaction, but toluene was found to be the best solvent.
Similarly, various temperatures were screened to get the best
result (Table 5).
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Table 4 Alkoxycarbonylation reaction of aryl bromides with EtOHa
Entry
Bromides
Product
Yieldb (%)
TON
2400
1
96
2
3
98
99
2450
2475
4
98
2450
5
6
96
98
2400
2450
7
98
2450
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Table 4 (Contd.)
Entry
Bromides
Product
Yieldb (%)
TON
2450
8
98
9
95
96
95
96
2375
2400
2375
2400
10
11
12
13
96
2400
14
95
2375
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Table 4 (Contd.)
Entry
15
Bromides
Product
Yieldb (%)
TON
2450
98
16
17
70
98
1750
2450
18
98
2450
a
Reaction conditions: aryl bromide (1 mmol), ethanol (5 mL), PS-AMP-Pd (4 Â 10À4 mmol), Et3N (3 mmol), CO (1 atm), temp (70 ꢀC), time (3 h).
b
Isolated yield.
Table 5 Effect of solvents and temperature on the amino carbonyl-
ation of bromobenzenea
Entry
Solvent
Temperature (ꢀC)
Conversion (%)
1
2
3
4
5
6
7
DMF
Water
90
90
90
70
80
90
85
64
68
75
96
96
Anisole
Toluene
Toluene
Toluene
Toluene
Scheme 4 Aminocarbonylation of aryl bromides with various amines.
90
100
a
Further reaction was optimized with respect to other reac-
tion parameters, including time and CO pressure and the best
optimized reaction conditions were then applied for the ami-
nocarbonylation of a variety of bromoaryls and amines (Table 7,
entries 1–13). The conversion of amino carbonylation is
dependent on the CO pressure applied. The effect of the amount
of CO on the amino carbonylation of bromobenzene into cor-
responding amide was studied and the results are shown in
Table 6. The inuence of reaction time was also investigated by
Reaction conditions: bromobenzene (1 mmol), aniline (2 mmol), PS-
AMP-Pd (4 Â 10 À4 mmol), Et3N (3 mmol), solvent (10 mL).
performing the reaction at a time range from 5 h to 10 h with all
other parameters xed. The results are given in Table 6 which
reveals that the conversion is dependent on reaction time and
maximum conversion was recorded at 9 h. Therefore, 9 h was
selected as the optimum reaction time.
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Table 6 Effect of CO pressure and reaction time on the amino
followed for the sample preparation of the reused catalyst.
Analysis of the used catalyst did not show appreciable loss in
the palladium content as compared to the fresh catalyst. IR
spectrum of the recycled catalyst was quite similar to that of
fresh sample indicating the heterogeneous nature of this
complex. Analysis of the product mixtures showed that if any
palladium was present it was below the detection limit. The UV-
vis spectroscopy was also used to determine the stability of this
catalyst. The UV-vis spectra of the reaction solution, at the rst
run, did not show any absorption peaks characteristic of
palladium metal, which indicates that the leaching of metal did
not take place during the course of the reaction. The metal
content of the recycled catalyst was determined with the help of
AAS and it was found that palladium content of the recycled
catalyst remained almost unaltered. These observations
strongly suggest that the present catalyst is truly heterogeneous
in nature.
Heterogeneity test for the alkoxycarbonylation of bromo-
benzene with benzyl alcohol was carried out at 70 ꢀC using PS-
AMP-Pd catalyst, then aer 1.5 h, the PS-AMP-Pd complex
catalyst was ltered off and was allowed to react further. We
found that no further reaction occurred aer this hot ltration
procedure; hence, this experimental nding suggests there is no
palladium leaching from the PS-AMP-Pd complex during the
progress of a reaction. In addition, to reconrm this observa-
tion, ICP-AES analysis of the reaction mixture was carried out
aer 1.5 and 3 h, which revealed a below detectable level (below
0.01 ppm) of palladium in solution.
carbonylation of bromobenzenea
Entry
CO Pressure (atm)
Reaction time (h)
Conversion (%)
1
2
3
4
5
6
7
1
2
3
4
3
3
3
9
9
9
9
5
55
72
96
96
49
74
96
7
10
a
Reaction conditions: bromobenzene (1 mmol), aniline (2 mmol), PS-
AMP-Pd (4 Â 10 À4 mmol), Et3N (3 mmol), toluene (10 mL), temp (90 ꢀC).
Various substituted aryl and heteroaryl bromides reacted
with aromatic and aliphatic amines to give the desired amides
in good to excellent yields. The substitution of electron with-
drawing and electron donating groups on the aromatic ring of
aryl bromides did not have any appreciable inuence on the
outcome of the reaction. Aryl bromides bearing either elec-
tron-donating or electron-withdrawing substituents, afforded
the corresponding carbonylative products in excellent yields.
Strong electron donating groups on aryl halides are generally
known to slow down the oxidative addition step of the catalytic
cycle50 and therefore give lower yields (Table 7, entries 7, 16).
The model reaction of bromobenzene with aniline provides a
96% yield of the desired product under optimized reaction
conditions (Table 7, entry 1). 4-Methoxyaniline reacts with
bromobenzene, providing 93% yield of the desired product
(Table 7, entry 2). Furthermore, aliphatic amines, such as
benzyl amine and cyclohexyl amine, provide excellent yields of
the corresponding product (Table 7, entries 3 and 4). 3-(Tri-
uoromethyl) aniline provides a moderate yield of the desired
product (Table 7, entry 5). A variety of meta- and para-electron
decient and – electron-rich aryl bromides gave excellent
yields ranging from 90–99% (Table 7, entries 6–9). 1-Bromo-
naphthalene furnishes 86% yield of the corresponding amide
product (Table 7, entry 10). Heteroaryl bromides 3-bromopyr-
idine and 3-bromothiophene also performed well in this
reaction (Table 7, entries 11 and 12). Secondary amines, such
as N-methyl aniline and morpholine were also tested with aryl
bromides for the synthesis of the corresponding carbonylative
products (Table 7, entries 13–17).
Recycling of catalyst
The catalyst remains insoluble in the present reaction condi-
tions and hence can be easily separated. Aer completion of the
reaction the catalyst was recovered by centrifuge and then
washed thoroughly with dichloromethane to remove the
substrates from its surface. The recovered catalyst was collected
and dried at 100 ꢀC. Alkoxycarbonylation and amino-
carbonylation reactions were carried out with the recycled
catalyst under the optimized reaction conditions. The catalyst
was recycled in order to test its activity as well as stability. The
obtained results are presented in Fig. 6. As seen from Fig. 6, the
catalyst did not show any appreciable change in its activity
which indicates that the catalyst is stable and can be regen-
erated for repeated use.
Conclusions
Test for heterogeneity
The leaching of palladium from polymer anchored palladium(II) A polymer anchored palladium Schiff base complex was
complex was conrmed by carrying out analysis of the used prepared and characterized. The complex was an active and
catalyst (EDX, IR) as well as the product mixtures (AAS, UV-vis). reusable catalyst for the alkoxycarbonylation and amino-
For AAS analysis, the sample PS-AMP-Pd (0.1 g) was digested carbonylation reactions. The catalyst is stable and recyclable
with minimum amount of conc. H2SO4 and few drops of under the used reaction conditions. This heterogeneous catalyst
hydrogen peroxide. Then it was made up to the mark of 100 mL shows no signicant loss of activity in recycling experiments.
in volumetric ask with millipore water. In this way stock The active sites do not leach out from the support and thus can
solution was prepared. Then four standard solution of palla- be reused without appreciable loss of activity, indicating effec-
dium complex was prepared. From the calibration curve the tive anchoring. The reusability of this catalyst is high without
unknown amount was determined. The same procedure was signicant decrease in its initial activity.
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Table 7 Aminocarbonylation reaction of various aryl bromides catalyzed by PS-AMP-Pda
Entry
Aryl bromides
Amines
Product
Yieldb (%)
TON
2400
1
96
2
3
93
96
2325
2400
4
98
2450
5
82
2050
6
7
97
90
2425
2250
8
90
2250
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Table 7 (Contd.)
Entry
Aryl bromides
Amines
Product
Yieldb (%)
TON
2475
9
99
10
86
2150
11
12
96
98
2400
2450
13
97
2425
14
92
2300
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Table 7 (Contd.)
Entry
Aryl bromides
Amines
Product
Yieldb (%)
TON
2350
15
94
16
88
2200
17
95
2375
a
Reaction conditions: aryl bromide (1 mmol), amine (2 mmol), PS-AMP-Pd (4 Â 10 À4 mmol), Et3N (3 mmol), toluene (10 mL), CO (3 atm) pressure,
temp (90 ꢀC), time (7 h). b Isolated yield.
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Acknowledgements
SMI acknowledges Department of Science and Technology
(DST) and Council of Scientic and Industrial Research (CSIR),
New Delhi, India for funding. RAM acknowledges UGC, New
Delhi, India for his Maulana Azad National Fellowship.
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