Polyaniline-anchored palladium catalyst-mediated Mizoroki-Heck and Suzuki-Miyauraa reactions and one-pot Wittig-Heck and Wittig-Suzuki reactions

Article abstract of DOI:10.1002/aoc.3234

A polyaniline-anchored palladium catalyst was prepared and screened for coupling reactions of aryl halides. The robust and recyclable catalyst was effective in Mizoroki-Heck and Suzuki-Miyaura reactions of aryl bromides and aryl iodides. The catalyst system was further employed for one-pot Wittig-Heck and Wittig-Suzuki combinations to build conjugated compounds in good conversions.

Full text of DOI:10.1002/aoc.3234

Full Paper
Received: 14 July 2014
Revised: 16 September 2014
Accepted: 16 September 2014
Published online in Wiley Online Library: 6 November 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3234
Polyaniline-anchored palladium catalyst-
mediated Mizoroki–Heck and Suzuki–Miyaura
reactions and one-pot Wittig–Heck and
Wittig–Suzuki reactions
Heta A. Patel, Arun L. Patel* and Ashutosh V. Bedekar*
A polyaniline-anchored palladium catalyst was prepared and screened for coupling reactions of aryl halides. The robust and recy-
clable catalyst was effective in Mizoroki–Heck and Suzuki–Miyaura reactions of aryl bromides and aryl iodides. The catalyst system
was further employed for one-pot Wittig–Heck and Wittig–Suzuki combinations to build conjugated compounds in good conver-
sions. Copyright © 2014 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
Keywords: polyaniline-Pd; heterogeneous catalyst; Mizoroki–Heck; Suzuki–Miyaura; one-pot reactions
choosing a material for heterogenization of palladium species. In
this paper we report our study of the immobilization of palladium
Introduction
Polyaniline (PANI) and polyamines with conjugated systems have
considerable applications in material science due to their electrical,
optical and redox properties.[1] Research has also been greatly
aided by the development of modern analytical and characteriza-
tion techniques.[2] The preparation of PANI can be achieved by a
well-established simple protocol from quite inexpensive materials
(Scheme 1).[3]
Because of the ability of PANI to bind well with metal ions and its
low solubility in organic solvents and water, it can be used as a sup-
port in heterogeneous catalysis. Few reports of the use of PANI-
supported metal ions as heterogeneous catalysts for organic trans-
formations are available.[4] The heterogeneous support system has
also been applied for a few coupling reactions.2c,5
Coupling of an aryl halide with an alkene in the presence of pal-
ladium catalyst and a base, known as the Mizoroki–Heck reaction,[6]
is one of the most widely explored methods for accessing deriva-
tives of stilbene and cinnamic acid. Many researchers have exhaus-
tively utilized this reaction for the synthesis of useful natural
products, drugs or materials with specific properties.[7] Similarly,
coupling of aryl halides with arylboronic acids in the presence of
palladium catalyst and a suitable base furnishes biaryls via the
Suzuki–Miyaura reaction.[8]
Both reactions are effectively catalysed by palladium salts or
complexes and the coupling products are obtained in high yield
in the presence of a very small quantity of the catalyst. However,
the high cost of palladium, in addition to toxicological and environ-
mental concerns, means that there is a growing need to develop ef-
fective means of its immobilization on solid supports for
heterogeneous catalytic reactions.[9] These materials need to have
strong binding interactions with metal ions as well as to offer effec-
tive access to reagents for smooth chemical transformations. It is
important to have a good balance of both these concepts while
salts on PANI support, their basic characterization and their screen-
ing as catalysts for some important coupling reactions.
Synthetic one-pot processes in which more than one step are
carried out simultaneously offer a number of advantages to chem-
ists. The appropriate combination of operations results in the lower-
ing of overall consumption of reagents for the reactions and work-
up, reduces the total reaction time, eliminates the need for purifica-
tion of unstable, volatile intermediates, and often satisfies some of
the requirements of green chemical synthesis. In recent decades
several procedures have been developed for the construction of
useful molecules and intermediates by adopting one-pot or dom-
ino or tandem synthetic schemes.[10] In the study reported here
we also screened this catalyst system for a few one-pot
palladium-mediated coupling reactions.
Experimental
Preparation of PANI
Freshly distilled aniline (10 ml, 109.5 mmol) was carefully dissolved
in aqueous HCl (1.5M, 125 ml). To this a solution of ammonium per-
sulfate (12.5g, 54.8mmol) in HCl (1.5M, 125ml) was added at 0 °C.
Since aniline polymerization is quite exothermic, the oxidant must
*
Correspondence to: Arun L. Patel and Ashutosh V. Bedekar, Department of
Chemistry, Faculty of Science, M. S. University of Baroda, Vadodara 390 002,
India. E-mail: arunpatel_5376@yahoo.co.in (A. L. Patel); avbedekar@yahoo.co.in
(A. V. Bedekar)
Department of Chemistry, Faculty of Science, M. S. University of Baroda, Vadodara
390 002, India
Appl. Organometal. Chem. 2015, 29, 1–6
Copyright © 2014 John Wiley & Sons, Ltd.

H. A. Patel et al.
remove the oligomers and the reaction side products. The polymer
was then vacuum-dried to constant mass. Deprotonation of PANI
hydrochloride was achieved with aqueous ammonia. Deprotonated
polymer was again washed with water, methanol and diethyl ether
and dried to constant mass (4.26 g).1c
Preparation of palladium-loaded PANI
PANI (0.5 g) was charged into a round-bottomed flask containing
palladium chloride (0.1 g, 0.56 mmol) in acetonitrile (25 ml) and
stirred under nitrogen atmosphere for 48 h. The resultant catalyst
was filtered and washed with acetonitrile followed by acetone.
The residue was dried in air for 24 h to afford a black powder of
palladium-loaded PANI (PANI-Pd). The amount of palladium was
measured using inductively coupled plasma atomic emission spec-
trometry (ICP-AES) as 3.86% (w/w).
Scheme 1. Synthesis of PANI.
be added slowly over a period of 1 h. After the addition of the oxi-
dant, the reaction was further stirred (4h) and the precipitated PANI
hydrochloride was separated by filtration and washed with water
(3× 30 ml), methanol (2× 25 ml) and diethyl ether (2× 15 ml) to
General Procedure for Mizoroki–Heck Reaction (Scheme 2)
A two-necked round-bottom flask was charged with iodobenzene
(0.20 g, 0.98 mmol), PANI-Pd catalyst (0.06 g, 0.022 mmol of Pd),
dry potassium carbonate (0.27g, 1.96 mmol) and dry
dimethylacetamide (DMA; 6 ml) under nitrogen atmosphere. This
mixture was slowly heated until the temperature reached 65 °C. A
solution of styrene (0.153 g, 1.47 mmol) in DMA (2ml) was then
introduced. The reaction mixture was then heated to 140°C for
40 h. The reaction mixture was quenched with water and ex-
tracted with ethyl acetate (3× 25ml).The combined organic
phase was washed with water and dried over anhydrous so-
dium sulfate. Solvent was removed in vacuum and crude prod-
uct was purified by column chromatography on silica gel to
afford trans-stilbene (1) as a white solid. Yield 0.173 g
(98.3%); m.p. 120–122 °C (lit.[11] 121 °C).
Scheme 2. PANI-Pd-catalysed Mizoroki–Heck reaction.
N
R
R
Ph
1, R = H (98%)
2, R = Me (84%)
R
3, R = H (88%)
4, R = OMe (89%)
MeO
5, R = H (89%)
The supporting information contains the spectral data for
compounds reported in Schemes 3, 5, 7, 9 and 10.
6, R = Me (84%)
R
Ph
COOtBu
General Procedure for Suzuki–Miyaura Reaction
(Scheme 4)
An oven-dried two-necked round-bottom flask equipped with
a stirrer bar was charged with iodobenzene (0.2 g, 0.98 mmol),
potassium carbonate (0.27 g, 1.96 mmol) and PANI-Pd catalyst
(0.06 g, 0.022mmol of Pd) in dioxane–water (1:1). To this reac-
tion mixture an appropriate quantity of phenylboronic acid
(0.14 g, 1.17 mmol, 1.2eq.) was added and the reaction mixture
was kept at 95 °C for 4 h. The reaction mixture was quenched
with water and extracted with ethyl acetate (3 × 25 ml). The
combined organic phase was washed with water and dried
over anhydrous sodium sulfate. Solvent was removed in vac-
uum and crude product was purified by column chromatogra-
phy on silica gel to afford biphenyl (15) as a white solid. Yield
0.16g (91%); m.p. 71 °C (lit.[12] 71 °C).
O2N
MeO
R
8, = (71%)
7, (85%)
9, R = Ph (61%)
10, R = COOtBu (63%)
R
R
MeO
OMe
R
General Procedure for Wittig–Heck Reaction (Scheme 6)
Synthesis of (E)-1-chloro-4-styrylbenzene (28)
R
13, R = H (48%)
14, R = Me (41%)
R
In a dry nitrogen-flushed two-necked round-bottom flask, a
mixture of 4-chlorobenzaldehyde (0.165 g, 1.18 mmol), Wittig
salt, methyltriphenylphosphonium iodide (0.553 g, 1.37 mmol)
and dry potassium carbonate (0.405 g, 2.93 mmol) in dry DMA
(6 ml) was stirred at 60 °C. At this temperature iodobenzene
(0.20 g, 0.98 mmol) and PANI-Pd catalyst (0.06 g, 0.022 mmol
11, R = H (74%)
12, R = Me (77%)
ArI for 1,2,3,4,5,6,7,11 & 12
ArBr for 8,9,10, 13 & 14
Scheme 3. Compounds prepared from the Mizoroki–Heck reaction with PANI-Pd
catalyst.
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Appl. Organometal. Chem. 2015, 29, 1–6

Polyaniline-Pd catalysed Heck, Suzuki and one-pot coupling reactions
Scheme 4. PANI-Pd-catalysed Suzuki–Miyaura reaction.
Ar
Ar
Ph
Ph
Scheme 8. One-pot Wittig–Suzuki reaction catalysed by PANI-Pd.
R
CN
19, (91%)
Ar
15
16
17
18
, R = H (91%)
20
21
, Ar = C6H5 (90%)
, Ar = 2-Me-C6H4 (80%)
, R = OMe (89%)
, R = NO2 (89%)
, R = F (95%)
General Procedure for One-Pot Wittig–Suzuki Reaction
(Scheme 8)
Ph
Ar
Synthesis of 4-(2-([1,1′-biphenyl]-4-yl)vinyl)benzonitrile (39)
Ph
R
In a dry nitrogen-flushed round-bottom flask was placed a mixture
of 4-cyanobenzaldehyde (0.20g, 1.53 mmol), Wittig salt, 4-
bromobenzyltriphenylphoshphonium bromide (0.78 g, 1.53 mmol)
and dry potassium carbonate (0.57 g, 4.13 mmol) in dry DMF
(6ml). The reaction was heated to 130 °C for 6 h and then
phenylboronic acid (0.223 g, 1.83mmol), potassium carbonate
(0.485 g, 3.52 mmol) and PANI-Pd catalyst (0.06 g, 0.022 mmol of
Pd) were added and continued heating at the same temperature
for 24 h. The reaction mixture was added to water (20 ml) and ex-
tracted with ethyl acetate (3× 25ml). The combined organic layer
was washed with water (2× 20 ml), dried with anhydrous sodium
sulfate and concentrated under vacuum. The residue was purified
by column chromatography on silica gel to obtain the desired prod-
uct (39). Yield 0.301g (70.1%); Z:E ratio 58:42 (determined using 1H
NMR analysis).[14]
22
, (81%)
23
24
25
, R = NO2, Ar = 2-Me-C6H4 (90%)
, R = F, Ar = 2-Me-C6H4 (75%)
, R = OMe, Ar = 2-CHO-C6H4 (86%)
17 18 19 20 21 22 23 24
, &
15 16 25
ArBr for
,
,
,
,
,
,
ArI for
,
&
Scheme 5. Compounds prepared from the Suzuki–Miyaura reaction with
PANI-Pd catalyst and PhB(OH)2 or ArB(OH)2.
Scheme 6. One-pot Wittig–Heck reaction catalysed by PANI-Pd.
of Pd) were added. The reaction mixture was then heated to 140 °C
(40 h). The reaction mixture was quenched with water (20 ml) and
extracted with ethyl acetate (3×25ml). The combined organic
phase was washed with water and dried over anhydrous sodium
sulfate. Solvent was removed in vacuum and the crude product
was purified by column chromatography on silica gel to afford 28
as a white solid. Yield 0.183g (87.1%); m.p. 129–130 °C (lit.[13]
129 °C).
General Procedure for Preparation of 1,4-Bis((E)-2-([1,1′-biphe-
nyl]-4-yl)vinyl)benzene (43) (Scheme 10)
In a dry nitrogen-flushed round-bottom flask was placed a mixture
of terephthaldehyde (41; 0.20 g, 1.48 mmol), Wittig salt, 4-
bromobenzyltriphenylphoshphonium bromide (1.53 g, 2.98 mmol)
and dry potassium carbonate (1.11 g, 8.05 mmol) in dry DMF
(6ml). The reaction was heated to 130 °C for 6 h and then
phenylboronic acid (0.435 g, 3.57mmol), potassium carbonate
(0.945 g, 6.85 mmol) and PANI-Pd catalyst (0.15 g, 0.055 mmol of
Pd) were added and continued heating at the same temperature
for 24 h. The reaction mixture was added to water (20 ml) and
extracted with ethyl acetate (3 × 25 ml). The combined organic
layer was washed with water (2 × 20 ml), dried with anhydrous
sodium sulfate and concentrated under vacuum. The residue
was purified by column chromatography on silica gel to obtain
the desired product as a yellow solid.[15] Yield 0.25 g (38%);
m.p. >250 °C.
Results and Discussion
The preparation of PANI in free base form is well established in the
literature. Accordingly, a sample of PANI was prepared from aniline
hydrochloride with a chemical oxidation protocol using ammonium
persulfate followed by neutralization with aqueous ammonia.1c The
sample of PANI free from oligomers was then exposed to a solution
of PdCl2 in acetonitrile to immobilize the metal ions on the support.
The PANI-Pd catalyst was separated, dried and characterized using
the usual spectral and analytical techniques.
Scheme 7. Compounds prepared from the one-pot Wittig–Heck reaction
with PANI-Pd catalyst (all from ArI).
Appl. Organometal. Chem. 2015, 29, 1–6
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H. A. Patel et al.
analysis of the sample of catalyst indicates a 3.86% loading
of palladium metal.
A preliminary study was conducted to measure the particle size
of the PANI-Pd prepared in this work. The particle size distribution
was studied using dynamic light scattering (DLS) with a BIC 90Plus
(Brookhaven) equipped with 35.0mW solid state lasers operating at
660 nm and an avalanche photodiode detector. All measurements
were made at 25 °C, and the synthesized PANI-Pd was dispersed
in ethylene glycol as medium. The recorded DLS spectra give infor-
mation about the hydrodynamic diameter of the nanoparticles. It is
observed that the particle size ranges from 150 to 300 nm in the
sample investigated. This might be due to rapid aggregation of
nanoparticles by Brownian motion because of the smaller size
and larger diffusion coefficient. The intensity of the scattered light
detected in the DLS experiment becomes greatly magnified if ag-
gregates of micrometre-size particles are present in the solution.
However, from the DLS analysis it can be argued that the synthe-
sized material has a particle size in the nanoscale regime.[16]
The immobilized PANI-Pd catalyst was then examined for the
standard Mizoroki–Heck coupling reaction of aryl halides and sty-
rene derivatives in the presence of a mild base (Scheme 2). Prelim-
inary experiments suggest that K2CO3 is an effective base and DMA
is a suitable solvent.
Scheme 9. C6–C6–C2–C6 type compounds prepared by one-pot Wittig–
Suzuki reaction with PANI-Pd catalyst.
Aryl chlorides are unreactive under the conditions used for the
Mizoroki–Heck reaction, while aryl bromides and aryl iodides
furnish the stilbene derivatives in good to excellent yields, isolated
mostly as the E-isomer. A comparison of the reactivity of
bromobenzene and iodobezene reveals the expected pattern, the
latter being considerably more reactive (Table 1).
A series of aryl bromides and aryl iodides were subjected to the
Mizoroki–Heck reaction with appropriate alkenes and the products
1, 5, 8, 9, 11, 13 (styrene), 2, 6, 12, 14 (4-methylstyrene), 3, 4 (4-vi-
nylpyridine) and 7, 10 (tert-butyl acrylate) were isolated. Disubsti-
tuted alkenes are obtained from corresponding aryl halides in
excellent yields, while the dihalogenated arenes (for 9, 10, 11 and
12) or trisubstituted arenes (for 13 and 14) give the alkene products
in slightly lower yields (Scheme 3). All the products were character-
ized using 1H NMR and mass spectroscopy and by comparing the
physical properties with reported values. The series of compounds
prepared using this Mizoroki–Heck reaction clearly establishes the
efficiency of the present heterogeneous PANI-Pd catalyst.
However, the success of a heterogeneous catalyst is measured by
its ability to be recycled and reused for subsequent reactions. This
was established by performing the reaction of PhI with styrene in
the presence of PANI-Pd under the standard conditions. As evident
from Table 2, the catalyst can be easily separated by filtration and
reused for two more cycles, with small loss of activity.
Scheme 10. Preparation of a highly conjugated system by sequential
Wittig–Suzuki reaction with PANI-Pd catalyst.
An X-ray diffraction (XRD) analysis of the sample of purified PANI
and its complex with palladium salt was carried out. This analysis
clearly shows two signals corresponding to 2θ values of 40° and
46°, characteristic of Pd ion (Fig. 1).
PANI was also subjected to Brunauer–Emmett–Teller (BET)
surface analysis to determine its properties. The BET measure-
ment of PANI shows the surface area to be 36.205 m2 gÀ1
,
while that of PANI-Pd increases to 43.086 m2 gÀ1. ICP-AES
Table 1. Comparison of Mizoroki–Heck reaction of PhBr and PhIa
Entry
Temperature (°C)
[time (h)]
PhX
Isolated yield of
(E)-stilbene (%)
1
2
3
4
5
6
80 [8]
80 [8]
PhBr
PhI
4
28
14
86
45
98
120 [8]
120 [8]
80 [40]
120 [40]
PhBr
PhI
PhBr
PhI
aReaction conditions: styrene (1.5 eq.), PANI-Pd (2.25 mol% Pd), K2CO3
(2.0 eq.), DMA.
Figure 1. XRD patterns of PANI (black) and PANI-Pd (red).
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Appl. Organometal. Chem. 2015, 29, 1–6

Polyaniline-Pd catalysed Heck, Suzuki and one-pot coupling reactions
Table 2. Recyclability study of PANI-Pd for
Mizoroki–Heck reaction of PhI and styrenea
of the product.[21] Typically we have detected a ratio of 31 to 59 in
favour of the Z-isomer for the products reported in Scheme 9 with
the PANI-Pd catalyst. This ratio was determined from 1H NMR anal-
ysis of the purified product and comparison with known data.
This one-pot protocol was then extended for the synthesis of
styrylstilbenes, an important class of highly conjugated systems.[22]
We designed the synthesis by starting with terephthaldehyde (41)
as the aldehyde component and condensed it with two molecules
of the phosphonium salt prepared from 4-bromobenzyl bromide to
initially form the Wittig product 42. This derivative was reacted with
the reagents of the in situ Suzuki–Miyaura reaction to finally furnish
43 (Scheme 10). Such compounds are known to possess many in-
teresting electrical and optical properties, and we offer a very sim-
ple and practical process to access their derivatives.
Cycle
Isolated yield (%)
1
2
3
98
95
90
aReaction conditions: styrene (1.5 eq.), PANI-Pd
(2.25 mol% Pd), K2CO3 (2.0 eq.), DMA, 120 °C, 40 h.
The catalyst system was then applied to the Suzuki–Miyaura cou-
pling reaction. The standard reaction conditions are presented in
Scheme 4, where an aryl bromide or aryl iodide is treated with
arylboronic acid in the presence of PANI-Pd catalyst and a suitable
base. The biaryls, products of this coupling reaction, are isolated in
high yields and characterized using the usual spectroscopic tech-
niques and by comparing physical properties.
Conclusions
We have reported the synthesis and applications of a PANI-
supported palladium catalyst for various useful coupling reactions
of aryl halides. The catalyst is suitable for aryl iodides and aryl bro-
mides while not being effective for aryl chlorides; at the same time
the system can tolerate a number of functional groups during
these reactions. The catalyst is easy to prepare and works
efficiently for the important Mizoroki–Heck and Suzuki–Miyaura
reactions. We have also demonstrated the role of the catalyst in
one-pot Wittig–Heck and Wittig–Suzuki combination to construct
conjugated systems.
A series of aryl halides were subjected to the Suzuki–Miyaura re-
action of Scheme 4 with C6H5B(OH)2 (for 15, 16, 17, 18, 19, 20 and
22), with 2-Me-C6H4B(OH)2 (for 21, 23 and 24) or with 2-CHOC6H4B
(OH)2 (for 25) where the required products are isolated generally in
excellent yields (Scheme 5). Many such polyphenylene products are
identified as important substrates due to their special properties.[17]
Recently there has been a growth of interest in one-pot synthe-
ses or processes of performing many chemical steps in tandem to
produce useful molecules.[10] As a part of our ongoing efforts we
have recently reported a few variations of one-pot procedures for
the synthesis of functionalized conjugated molecules from readily
available starting materials.[18–20] One of the key components of
the Mizoroki–Heck reaction is an electron-deficient alkene, com-
monly a styrene derivative. Many substituted styrenes are costly,
difficult to procure or often unstable at high reaction temperatures.
With the objective of overcoming these difficulties, we have re-
cently developed19a a one-pot procedure where styrene is pre-
pared in situ via Wittig reaction of an aldehyde and Ph3PCH3I, and
then subjected to a Mizoroki–Heck reaction. In the present work
we screened the PANI-Pd catalyst for this approach (Scheme 6).
The wider commercial availability of aromatic aldehydes as com-
pared to styrenes also favours such an approach for the construc-
tion of stilbene derivatives. A series of aldehydes were subjected
to a one-carbon homologation reaction with Ph3PCH3I under basic
conditions to obtain styrene derivatives, which in the presence of
aryl halides and PANI-Pd catalyst undergo further Mizoroki–Heck
reaction. A number of stilbene derivatives were synthesized, as pre-
sented in Scheme 7. Since the Wittig reaction is performed with ar-
omatic aldehyde and Ph3PCH3I, the styrene product formed in situ
immediately undergoes a Mizoroki–Heck reaction with aryl halide
in the presence of PANI-Pd. The stereochemistry is determined in
the second step, which favours the formation of E-isomer.
Acknowledgements
We thank the University Grants Commission (UGC), New Delhi, for
financial support and a research fellowship to HAP. We are also
grateful to Dr S. Sahoo of Sun Pharma Pvt. Ltd for some of the anal-
ysis for this work.
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Appl. Organometal. Chem. 2015, 29, 1–6
Copyright © 2014 John Wiley & Sons, Ltd.
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Additional supporting information may be found in the online
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version of this article at the publisher’s web-site.
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