Development of an efficient solvent free one-pot Heck reaction catalyzed by novel palladium (II) complex-via green approach

Article abstract of DOI:10.1016/j.molcata.2012.03.004

A novel 1-glycyl-3-methyl imidazolium chloride-palladium (II) complex [[Gmim]Cl-Pd (II)] was found to be a heterogeneous catalyst for an efficient Heck reaction with good to excellent yield under solvent free condition. Tetra-coordinated palladium complex was prepared by reacting PdCl₂ with 1-glycyl-3-methyl imidazolium chloride and its catalytic function invented for the CC bond formation. Spectroscopic evidence of complex has been proved by powder XRD, SEM, FT-IR and AFM. This protocol provides a simple strategy for the generation of a variety of new CC bonds under environmentally benign condition.

Full text of DOI:10.1016/j.molcata.2012.03.004

Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Development of an efficient solvent free one-pot Heck reaction catalyzed by
novel palladium (II) complex-via green approach
Parasuraman Karthikeyan, Prashant Narayan Muskawar, Sachin Arunrao Aswar,
Pundlik Rambhau Bhagat∗, Suresh Kumar Sythana
Organic Chemistry Division, School of Advanced Sciences, VIT University, Vellore 632 014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel 1-glycyl-3-methyl imidazolium chloride–palladium (II) complex [[Gmim]Cl–Pd (II)] was found to
be a heterogeneous catalyst for an efficient Heck reaction with good to excellent yield under solvent free
condition. Tetra-coordinated palladium complex was prepared by reacting PdCl2 with 1-glycyl-3-methyl
imidazolium chloride and its catalytic function invented for the C C bond formation. Spectroscopic evi-
dence of complex has been proved by powder XRD, SEM, FT-IR and AFM. This protocol provides a simple
strategy for the generation of a variety of new C C bonds under environmentally benign condition.
© 2012 Elsevier B.V. All rights reserved.
Received 19 December 2011
Received in revised form 8 February 2012
Accepted 4 March 2012
Available online 13 March 2012
Keywords:
Palladium complex
Heck reaction
Aryl halide
Alkene
Ambient temperature
1. Introduction
In this regard, we have developed stable, selective, suitable ligand
that leads to efficient heterogeneous palladium complex with high
In recent years, Ionic liquids have emerged as a set of green
solvent with unique properties such as tunable polarity, high ther-
mal stability and immiscibility with a number of organic solvents,
negligible vapor pressure and recyclability. Their non-volatile char-
acter and thermal stability makes the metal complexes potentially
attractive alternatives to environmentally unfavorable organic co-
solvents, notably chlorinated hydrocarbons. They are particularly
promising as solvents for the immobilization of transition metal
catalysts, Lewis acids and enzymes [1–6]. As a result of their green
credential and potential to enhance reaction rate and selectivities,
ionic liquids are finding increasing application in organic synthesis.
The Mizoroki–Heck synthesis is an important task due to
their valuable applications in both laboratory and industry. The
significance of these compounds exist in the organic synthesis,
polymerization processes, UV screens, preparation of hydrocarbons
and in advanced enantioselective synthesis of natural products and
pharmaceutically active heterocyclic compounds [7]. In general,
palladium catalysts suffer the problems concerning extraction from
the reaction mixture, waste production, high toxicity and price,
air-sensitivity and leaching [8]. Hence, we felt it would be keen
interest to eradicate these negative aspects of palladium complex.
turnover and reprocessibility.
In last two years, Petrovi et al. was described the synthesis
of N, N-diethyl ethanolamine ionic liquid in green Heck reaction
[9] and Liu et al. was reported efficient palladium-catalyzed Heck
reaction by the diol-functionalized imidazolium ionic liquid [10].
Furthermore, Vaultier et al. have synthesized binary task specific
ionic liquid and an efficiency of palladium nano particle catalyzed
Heck cross-coupling [11]. However, Salunkhe et al. was illustrated
multi-functional ionic liquid for Pd (II) catalyzed Heck reaction [12].
Li et al. was exemplified the Pd-TPPTS catalyzed Mizoroki–Heck
coupling in halogen-free ionic liquid [13]. Above all the methods
provide good yield, but some have drawbacks such as lengthy work-
up procedure, harsh reaction conditions (organic co-solvents) and
require absolutely dry and inert media. Herein, we report a protocol
based on palladium functionalized 1-glycyl-3-methyl imidazolium
chloride (Fig. 1), which proved to be highly efficient at ambient
temperature for C C bond formation under solvent free condition.
However, recovery and leaching can occur in the extractive work
up leading to a loss of the catalyst in the reaction mixture on the one
hand and requests additional effort to purify the extracted product.
To overcome such problems, novel complex was developed [14] by
covalent linking of organo catalytic unit with an ionic liquid moiety
(often chloroglycine). This imparts a low solubility of catalyst in the
solvents used for extraction of the product on the one hand and
high solubility in the reaction medium on the other hand [15–19].
∗
Corresponding author. Tel.: +91 9047289073; fax: +91 4162240411.
E-mail address: drprbhagat111@gmail.com (P.R. Bhagat).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2012.03.004

P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
113
2.2.3. Chlorination of protected glycine
In 100 mL RB, thionyl chloride (6 mmol) was added and cooled
in an ice-water bath. The protected glycine (4 mmol) was dissolved
in ethanol and added to RB drop wise at (0 ◦C) and stirred at ambi-
ent temperature for 48 h. The resulting solution was concentrated
under vacuo, cooled in an ice-water bath to get the desired precip-
itate. Recrystallization of the product using ethanol–ether affords
the analytically pure chloroglycine.
Fig. 1. 1-Glycyl-3-methyl imidazolium chloride–palladium (II) complex
[Gmim]Cl–Pd (II).
This strategy was applied to Heck reaction providing high yield and
good recyclability of the organocatalyst.
2.2.4. Removal of protecting groups
An about 33% (10 mL) solution of HBr in acetic acid is placed in
a 100 mL RB flask and protected chloroglycine (4 mmol) was added
with stirring. The flask was closed with a cotton filled drying tube
and swirled to effect complete dissolution of the protected chloro-
glycine. The deprotection occurred with evolution of CO2 and heat.
When the gas evolution ceases, dry ether (50 mL) was added with
swirling and the reaction mixture was stored in an ice-bath. The
precipitated chloroglycine ester was collected on a filter, washed
with ether and dried over NaOH in vacuo.
The objectives of the present study are to: (i) prepare tetra
coordinated 1-glycyl-3-methyl imidazolium chloride–palladium
(II) complex and to explore its application as catalyst, (ii) develop
an efficient synthetic process for the facile conversion of Heck reac-
tion. The present method developed for the Heck reaction offer
many advantages including high conversion, short duration and
the involvement of non-toxic reagents.
Furthermore,
a solution chloroglycine ester (4 mmol) in
2. Experimental
methanol (10 mL) was surrounded by water bath at ambient tem-
perature and NaOH (20 mL) was added with stirring. The mixture
was stored at ambient temperature for overnight. Dilute HCl
(10 mL) was added and methanol removed in vacuo. The aque-
ous solution was cooled in ice-water for 2 h. Chloroglycine was
collected on a filter, washed with ether and dried in air [23–25].
2.1. Materials and methods
All solvents and chemicals were commercially available
and used without further purification unless otherwise stated.
[Gmim]Cl–Pd (II) complex was characterized by powder X-ray
diffraction (P-XRD) diffractometer, a Bruker D8 (advance model);
Germany and lynx eye detector operating with nickel filtered
Cu-K radiation. The 1H NMR spectra was record on a Bruker
500 MHz using CDCl3/DMSO-d6 as the solvent and mass spectra
were recorded on JEOL GC MATE II HRMS (EI) spectrometer. FT-IR
was recorded on AVATRA 330 Spectrometer with DTGS detector.
Column chromatography was performed on silica gel (200–300
mesh). Analytical thin-layer chromatography (TLC) was carried
out on precoated silica gel GF-254 plates. AFM and SEM was ana-
lyzed by (Nano Surf Easy Scan-2 Switzerland), (Carl Zeiss EVO MA
15(model)) respectively.
2.2.5. Synthesis of 1-glycyl-3-methyl imidazolium chloride
[Gmim]Cl
First, chloroglycine (0.01 mol) reacted with N-methylimidazole
(0.11 mol) in 50 mL acetonitrile at 70 ◦C for 24 h to gen-
erate chloroglycine ligand modified by imidazole salt (3-
(amino(carboxy)methyl)-1-methyl-1H-imidazol-3-ium chloride)
[Gmim]Cl. The solvent (acetonitrile) was removed under reduced
pressure at 80 ◦C (water bath temperature). Then the residue
was mixed with 50 mL water and extracted with ethyl acetate
(3 × 5 mL). Further, the water phase was evaporated under reduced
pressure at 80 ◦C until the mass of the residue did not change. 1H
NMR (500 MHz, DMSO-d6): ı 2.2 (s, 1H), 3.3 (s, 3H), 5.0 (s, 2H), 6.92
(d, 1H), 7.0 (d, 1H), 7.6 (s, 1H), 9.1 (s, 1H). HRMS (EI): C6H10ClN3O2
(found: 191.10), cal (191.05). FT-IR (KBr, cm−1): 3429, 3372, 2933,
2855, 1628, 1526 and 1382.
2.2. Preparation of [Gmim]Cl–Pd (II) complex
2.2.1. Protection of amino group using di. tert butyl
pyrocarbonate (Boc)
A solution of the glycine (10 mmol) in a mixture of dioxane
(10 mL), water (5 mL) and 0.5 N NaOH (5 mL) was stirred and cooled
in an ice-water bath. Boc (8 mmol) was added and agitation contin-
ued at ambient temperature for 30–45 min. The resulting solution
was concentrated in vacuo, cooled in an ice-water bath, covered
with a layer of ethyl acetate (15 mL). Then, the reaction mixture was
acidified to pH 2–3 using KHSO4. The aqueous phase was extracted
with ethyl acetate (3 × 10 mL). The ethyl acetate extract washed
with water, dried over anhydrous Na2SO4 and evaporated in vacuo.
The residue was recrystallized using ethanol [20,21].
2.2.6. Synthesis of 1-glycyl-3-methyl imidazolium
chloride–palladium (II) complex [Gmim]Cl–Pd (II)
In RB, [Gmim]Cl (0.02 mmol) was stirred with PdCl2 (0.01 mol) in
100 mL methanol at 50 ◦C for 12 h to deliver the [Gmim]Cl modified
by palladium complex [Gmim]Cl–Pd (II). The solvent (methanol)
was removed under reduced pressure at 80 ◦C (water bath temper-
ature). Finally, white [Gmim]Cl–Pd (II) complex was obtained with
95% [26].
2.3. Procedure for Heck reaction
2.2.2. Protection of acid group using methyl ester
In
a
conical flask (50 mL),
a
mixture of 1-bromo-4-
Boc-glycine (10 mmol) was suspended in 2, 2-di
methoxypropane (DMP) (50 mL) and concentrated HCl (5 mL)
was added. The mixture was allowed to stand at ambient temper-
ature over night. The volatile reactants were removed in vacuo at
60 ◦C, the residue dissolved in a minimum amount of dry methanol
and the solution diluted with dry ether (50 mL). The crystalline
methyl ester hydrochloride was collected on a filter, washed
with ether and dried in vacuo over NaOH. Recrystallization from
methanol–ether (9:1 mL) affords the analytically pure ester [22].
methoxybenzene (1 mmol), styrene (1.2 mmol), triethylamine
(1 mmol) and [Gmim]Cl–Pd (II) (0.1 mmol) was added and stirred
at ambient temperature for a period as indicated in Tables 5 and 6
(The reaction was monitored by HPLC and TLC). The resulting
heterogeneous mixture was extracted with ethyl acetate or diethyl
ether (3 × 5 mL). The organic phase was separated and dried
over anhydrous Na2SO4 and evaporated. The resulting crude was
purified by flash chromatography to give the desired pure product
with excellent yield.

114
P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
Fig. 2. FT-IR of (a) chloroglycine, (b) 1-glycyl-3-methyl imidazolium chloride [Gmim]Cl, and (c) 1-glycyl-3-methyl imidazolium chloride–palladium (II) complex [Gmim]Cl–Pd
(II).
[Gmim]Cl was detected at 3340, 3335 cm−1 with doublet, but in the
case of [Gmim]Cl–Pd (II), we also found the doublet at 3372 cm−1
2.4. Recycling of the catalyst for the model reaction of
1-bromo-4-methoxybenzene with styrene using [Gmim]Cl–Pd (II)
under solvent free condition
,
this also shows the formation of Pd NH (431 cm−1) bond in the cat-
alyst [27]. In all spectra, stretching of C H and C N was observed
at 2933 and 1350 cm−1, respectively. Notably, the FT-IR spectra
revealed that a series of new palladium complex with ionizable
groups had been synthesized.
1-Bromo-4-methoxybenzene (1 mmol) was reacted with
styrene (1.2 mmol) in the presence of [Gmim]Cl–Pd (II) (0.1 mmol)
and triethylamine (1 mmol) at ambient temperature. After comple-
tion of the reaction (TLC/HPLC), the product was extracted as stated
in the preceding general method. The white solid [Gmim]Cl–Pd
(II) was isolated by centrifugation. Furthermore, the recovered
complex was washed with diethyl ether and dried in air. The
resulting catalyst was charged to another batch of the similar
reaction. This was repeated for 8 runs to complete the reaction in
6 h to give the desired product with 96–88% yield (Table 7).
3.1.2. Powder XRD analysis
The formation of the Pd (II) catalyst was also supported by the
XRD patterns with those of glycine, chloroglycine, Pd (II) complex.
In comparison with glycine, chloroglycine, Pd (II) complex which
showed major peaks respectively at 32.50, 38.81, 44.98 and 64.07
(confirming palladium peak with JCPDS data care no: 99-200-3904
for Pd (II)), the [Gmim]Cl–Pd (II) pattern was in good agreement
with peak at 38.81 and 44.98 (Fig. 3).
3. Results and discussion
3.1.3. SEM analysis
3.1. Characterization of complex
The SEM image of the catalyst is shown in Fig. 4. From this
image it is clear that [Gmim]Cl–Pd (II) has nano sphere like
[Gmim]Cl–Pd (II) catalyst has been characterized by FT-IR, XRD,
SEM and AFM.
38.81
3.1.1. FT-IR analysis
Compounds
C
H
C
N
C
O
Pd
O
Pd
N
O
–
H
N H
32.50
44.98
64.07
c
[Gmim]Cl–Pd (II) 2933s 1350s 1742s 639m
431m
3340m
Chloroglycine
[Gmim]Cl
2928s 1392s 1625s
2893s 1382s 1626s
–
–
–
–
3378s 3335m
3429s 3372m
25.82
FT-IR spectra of [Gmim]Cl–Pd (II) at different dissociation
degrees are shown in Fig. 2. For carboxylate ion, the broad peak
at 1742 cm−1 corresponds to carbonyl symmetric stretching. The
asymmetric stretching of carboxylate was shifted to 1626 cm−1
[Gmim]Cl in contrast with the shift to 1625 cm−1 in chloroglycine,
which appeared when [Gmim]Cl was treated with PdCl2 and thus
the carbonyl stretching was decreased. However, the plane of
b
a
20.93
OH at 3378, 3429 cm−1 was present in chloroglycine, [Gmim]Cl
0
30
60
90
C
2
θ
respectively, but when the networks were treated with PdCl2 no
signal was noticed for the OH group, indicates the formation of
Pd O (639 cm−1) bond. Although, the NH2 signal in chloroglycine,
Fig. 3. Powder X-ray diffraction patterns of (a) glycine, (b) chloroglycine, and (c)
1-glycyl-3-methyl imidazolium chloride–palladium (II) complex [Gmim]Cl–Pd (II).

P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
115
Table 1
Effect of the base on Heck coupling reaction.a
Entry
Base
Time (h)
48
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
–
Py
Trace
–
–
48
48
48
48
48
48
24
18
12
6
Imidazole
K2CO3
KOH
NaOH
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
40
53
58
96
96
96
96
96
90
83
3
1
a
Reaction condition: 1-bromo-4-methoxybenzene (1 mmol), styrene (1.2 mmol),
different base (1 mmol), and [Gmim]Cl–Pd (II) (0.1 mmol) stirring at ambient tem-
perature for 6 h.
Fig. 4. SEM image of [Gmim]Cl–Pd (II).
b
Yield determined by HPLC.
morphology with particles of dimensions ca. 75–100 nm and these
are distributed uniformly throughout the material.
showed in the rough topography that confirmed the formation of
film with palladium complex in the size of 2.5 ␮m2.
The palladium complex catalyzed Heck reaction was carried out
using styrene and 1-bromo-4-methoxybenzene as a model reaction
to investigate different parameters, such as effect of solvent, diverse
bases, catalysts and its concentration of the catalyst. Initially, the
influence of different bases to the model reaction was studied;
these results are summarized in Table 1. It was observed that,
organic bases showed maximum conversion over the inorganic
bases. Moreover, this reaction was unsuccessful in the absence of
base (Table 1, entry 1). However, there was no product formation
between 1-bromo-4-methoxybenzene and styrene in the presence
of pyridine and imidazole (Table 1, entries 2 and 3). Furthermore,
3.1.4. AFM analysis
The 3D AFM images of the 1-glycyl-3-methyl imidazolium chlo-
ride and [Gmim]Cl–Pd (II) complex is shown in Fig. 5. The 3D image
for 1-glycyl-3-methyl imidazolium chloride was present 10.2 ␮m2
size of the particles. It can be seen that the surface was very smooth,
crystalline ligand are notably different, the grain size and the shape
vary significantly (Fig. 5(a)). After doping the PdCl2 to the [Gmim]Cl,
Fig. 5(b), 3D AFM image was obtained. From this image, the larger
scan size also emphasizes the differences between the [Gmim]Cl
and [Gmim]Cl–Pd (II). The surface of palladium doped ionic liquid,
Fig. 5. (a) AFM image of 1-glycyl-3-methyl imidazolium chloride, and (b) AFM image of 3-(amino (carboxy) methyl)-1-methyl-1H-imidazol-3-ium chloride supported
palladium complex.

116
P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
Table 2
Table 4
Effect of the solvent on the Heck coupling reaction.a
Effect of the catalyst loading on Heck coupling reaction.a
Entry
Solvent
Temp (◦C)
Time (h)
Yieldb (%)
Entry
[Gmim]Cl–Pd (II) mmol
Time (h)
Yieldb
1
2
3
4
5
6
7
8
9
DCM
CHCl3
THF
Methanol
Ethanol
CH3CN
35
50
50
50
65
60
130
Rt
48
48
48
48
48
48
48
6
Trace
Trace
Trace
Trace
Trace
51
67
96
90
96
1
2
3
4
5
6
7
–
48
24
24
24
6
–
58
64
79
96
97
97
0.025
0.05
0.075
0.1
0.125
0.15
6
6
DMF
Solvent free
Solvent free
Solvent free
Water (5 mL)
a
Reaction condition: 1-bromo-4-methoxybenzene (1 mmol), styrene (1.2 mmol),
triethylamine (1 mmol), and [Gmim]Cl–Pd (II) (0.1 mmol) stirring at ambient tem-
perature for 6 h.
20
35
90
6
6
48
10
11
43
b
Yield determined by HPLC.
a
Reaction condition: 1-bromo-4-methoxybenzene (1 mmol), styrene (1.2 mmol),
triethylamine (1 mmol) solvent (5 mL), and [Gmim]Cl–Pd (II) (0.1 mmol) stirring at
ambient temperature for 6 h.
b
Yield determined by HPLC.
[Cemim] Br, [Aemim] Br, PdCl2/[Cemim] Br, PdCl2/[Aemim] Br and
PdCl2/[Gmim]Cl with Et3N, it gave trace to 78% of product respec-
tively (Table 3, entries 1–7). However, when the same reaction was
conducted with [Gmim]Cl–Pd (II) as a catalyst it gave remarkable
yield of product in short duration (Table 3, entry 8). Almost sim-
ilar yield was obtained when increasing the duration of reaction
(Table 3, entry 9).
Heck reaction was carried out using K2CO3, KOH and NaOH, the
formation of (E)-1-methoxy-4-styrylbenzene increases from 40 to
58% (Table 1, entries 4–6). After inventing the best catalyst systems,
we further optimized the reaction conditions in presence of Et3N.
The experiments showed that on decreasing the time from 24 to
6 h gave the same results with full conversion and 96% yield of (E)-
1-methoxy-4-styrylbenzene (Table 1, entries 7–11). However, the
yields were dropped appreciably on decreasing the time from 6 to
1 h (Table 1, entries 12 and 13). By all these experimental results
and discussions it was concluded that 1 mmol Et3N is sufficient to
brought out the complete Heck reaction in 6 h at 25 ◦C.
Subsequently, in order to find a suitable solvent for the reactions,
the coupling of 1-bromo-4-methoxybenzene and styrene was car-
ried out with different solvents and Et3N. According to publications
from Hartwig and co-workers [28], Zapf and Beller [29], Bohm and
Herrmann [30] and Rafiee [1] polar, aprotic solvents tend to give
the best results for the Heck reaction, while Fu [31] obtained high-
activity of catalysts in dioxane solvent. Among the previous reports,
catalysis in absence of solvent was the most productive, as com-
pared with the polar and non-polar solvents (Table 2). This may be
due to the easy coordination of complex with organic co-solvents.
It has also been reported that H2O molecule sometimes is required
to activate the Pd (II) catalyst. In our case, carrying out the reaction
in H2O (5 mL) 90 ◦C gave a negative effect on the product yield in
comparison with solvent free condition. This lower yield could be
due to complex delocalization under aqueous condition.
The catalytic reactions which can be carried out with a small
amount of expensive complexes is the most useful feature of
synthetic reaction involving palladium complex. According to liter-
ature, Petrovic et al. obtained good yield in the green Heck reaction
of aryl halide with olefin using PdCl2 (1.5 mol %) stirred at 100 ◦C for
12–18 h [9]. Using biphenyl-based phosphine in the range between
0.025 and 0.05 mmol, Joshaghani et al. observed acceptable rate
in the Heck reaction [7]. Among the previous reports, increas-
ing the quantity of the catalyst can improve the reaction yield
and shorten reaction time. Initially, C C formation was carried
out in absence of catalyst at ambient temperature; it was found
that no product formed even after 48 h (Table 4, entry 1). Fur-
ther when the amount of the catalyst was increased from 0.025 to
0.075 mmol, albeit the yield was increased 58–79% (Table 4, entries
2–4). However using 0.1 mmol of [Gmim]Cl Pd (II), (E)-1-methoxy-
4-styrylbenzene was obtained with 96% in 6 h (Table 4, entry 5).
Almost similar yield was achieved when escalating the catalyst
amount from 0.1 to 0.15 mmol (Table 4, entry 6 and 7). Moreover,
temperature also plays an important role in the time and amount
of catalyst. When we conducted the Heck reaction of 1-bromo-4-
methoxybenzene and styrene as the model substrate at various
temperatures from 25 ◦C to 100 ◦C, there was a decrease in the
amount of catalyst required and time. Therefore, the Heck reaction
was carried out at the molar radio of 1-bromo-4-methoxybenzene,
styrene, triethylamine and [Gmim]Cl–Pd (II) 1:1.2:1:0.1 mmol at
ambient temperature in absence of solvent.
Next, in order to optimize the reaction conditions for a particular
catalyst the coupling reaction of 1-bromo-4-methoxybenzene and
styrene was executed in presence of Et3N by using different cata-
lysts and the results are given in Table 3. When the reaction was
carried out using various catalysts such as l-glycine, chloroglycine,
In order to test the substrate generality of [Gmim]Cl–Pd (II) com-
plex catalyzed Heck–Mizoroki reaction of substituted aryl halides
with styrene were performed at ambient temperature to give their
corresponding trans-stilbenes in the appropriate reaction times
with excellent yields (Table 5). It can be noticed that a wide range
of aromatic halides can efficiently contribute in the Heck reactions.
However, both electron-rich and electron-poor aryl halides could
be successfully converted to the desired products in (6–10 h) at
room temperature. On the other hand, the reaction of aryl chlo-
rides with styrene is usually very slow with low yields (Table 5,
entries 1–3).
Finally, the reaction of methyl acrylate with different aromatic
halides was investigated. In these reactions, variety of aryl halides
were stirred with methyl acrylate in the presence of [Gmim]Cl–Pd
(II) at room temperature in absence of solvent. The reaction
proceeded smoothly with the formation of trans-isomers with
80–95% yields. In addition, it was found that, aromatic halides with
Table 3
Effect of the various catalysts on Heck coupling reaction.a
Entry
Catalyst
Time (h)
Yieldb
1
2
3
4
5
6
7
8
9
l-Glycine
Chloroglycine [Cl-gly]
[Cemim] Br
48
48
48
48
48
48
48
6
Trace
Trace
Trace
Trace
65
70
78
96
97
[Aemim] Br
PdCl2/[Cemim] Br
PdCl2/[Aemim] Br
PdCl2/[Gmim]Cl
[Gmim]Cl–Pd (II)
[Gmim]Cl–Pd (II)c
7
a
Reaction condition: 1-bromo-4-methoxybenzene (1 mmol), styrene (1.2 mmol),
triethylamine (1 mmol), and catalyst (0.1 mmol) stirring at ambient temperature for
6 h.
b
Yield determined by HPLC.
Reaction duration 7 h.
c

P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
117
Table 5
Heck–Mizoroki
coupling
of
different
aryl
halides
with
styrene
in
the
presence
[Gmim]Cl–Pd
(II)
and
Et3N
as
base.a.
Entry
Aryl halides
Product
Time (h)
Yieldb (%)
1
8
83
2
3
4
5
9
9
6
8
80
76
94
83
6
7
5
7
96
83
8
10
80
a
Reaction condition: Aryl halide (1 mmol), Olefin (1.2 mmol), triethylamine (1 mmol), and [Gmim]Cl–Pd (II) (0.1 mmol) stirring at ambient temperature for 6 h.
b
Yield determined by HPLC. All the products were characterized by spectroscopic analysis (IR, 1H NMR) known compounds were compared with authentic data [32–34].
withdrawing group were more imprudent than that of electron
donating group (Table 6, entries 1–8).
important factors. For the comparative study, Heck reaction was
carried out with model reaction at the optimized conditions in
presence of Pd/C catalyst. However, a significant difference in Pd
leaching was observed. Without exclusion of air about 32% of the
total palladium amount were lost from the Pd/C and found in
solution (AAS) compared to [Gmim]Cl–Pd (II) where no leaching
detected.
Isolation of the heterogeneous catalyst was easily performed by
extraction or centrifugation. The isolated catalyst was washed with
diethyl ether and dried in air. The regenerated catalyst was used for
the reaction of 4-bromoanisole with styrene for eight runs to afford
trans-stilbene with 96–88% isolated yields (Table 7).
For practical application in the Heck reaction, the lifetime
of the heterogeneous catalysts and their reusability are very
For those conformation, [Gmim]Cl–Pd (II) catalyst was collected
after the completion of the reaction and analyzed by powder X-ray

118
P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
Table 6
Heck reaction of methyl acrylate with some represented aryl bromides/chlorides.a.
Entry
Aryl halides
Product
Time (h)
Yieldb (%)
1
8
93
2
3
7
9
95
90
4
5
6
9
15
18
85
86
80
7
19
24
84
84
8
a
Reaction condition: Aryl halide (1 mmol), Olefin (1.2 mmol), triethylamine (1 mmol), and [Gmim]Cl–Pd (II) (0.1 mmol) stirring at ambient temperature for 6 h.
b
Yield determined by HPLC. All the products were characterized by spectroscopic analysis (IR, 1H NMR) known compounds were compared with authentic data [32–34].
diffraction method and the diffraction patterns are given in Fig. 6.
The analysis specifies that the [Gmim]Cl–Pd (II) do not undergo
any chemical and structural changes, thus proving its surface
catalytic activity towards the coupling reaction of 1-bromo-4-
methoxybenzene with styrene. On the other hand, presence of
peaks due to metallic palladium is noted in the powder XRD
pattern of the complex in the case of ‘Pd (II)’ (Fig. 6(a and b)).
Moreover, surface and size of that reused catalyst was captured
by AFM. The surface of reused palladium complex showed in
the rough topography evidence and reduced size of the particle
755 nm (Fig. 7). However, the extracted product was analyzed by
P-XRD, which indicates the absence of peak at 38.81 that gave an
evidence for ‘no leaching’ of the complex. Furthermore, Pd leaching
was also studied by inductively coupled plasma-atomic emission
spectroscopy (ICP-AES) analysis, indicating that the product mix-
ture contained zero ppm of palladium accounting for 0.1 mmol of
the initially added amount of Pd. From those three experimental
results, we believe that no Pd leaching observed in Heck reactions,
it is due to immobilized palladium in amino acid functionalized
ionic liquid binding site located on the surface, which acts as a lig-
and through metal–ligand interaction. The anchoring of Pd species
by amino acid sites supported on ionic liquid minimizes catalyst

P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
119
Table 7
O
O
H2
N
Recycling of the catalyst for the reaction of 4-bromoanisole with styrene.a
N
Cl
N
N
Cl
Pd
Run
N
N
O
H2
HB+X-
O
1
2
3
4
5
6
7
8
Yieldb (%)
96
96
94
94
92
90
90
88
a
Reaction condition: 1-bromo-4-methoxybenzene (1 mmol), styrene (1.2 mmol),
triethylamine (1 mmol), and [Gmim]Cl–Pd (II) (0.1 mmol) stirring at ambient tem-
perature for 6 h.
B
Ph
ArX
b
Yield determined by HPLC.
Ar
H
Ph
X
Ar
Ar
X
Heterogenous catalyst
b
Ar
Ph
Ph
X
Ph
Ar
a
X
0
30
60
90
2 (θ)
Scheme 1. Proposed catalytic mechanism.
Fig. 6. Powder X-ray diffraction patterns of the [Gmim]Cl–Pd (II) complex (a) before
reaction and (b) after reaction (8th run).
7.16–7.22 (m,1H), 7.30 (t, J 7.5 Hz, 2H), 7.35 (d, J 8.3 Hz, 2H), 7.44
(d, J 7.5 Hz, 2H); 13C NMR: ı 26.2, 130.3, 130.4, 132.3, 132.7, 135.6,
138.3, 144.5, 147.4, 147.5; IR (KBr, cm−1) 3021, 2917, 2855, 1589,
1506, 967, 804, 527.
deterioration and no metal leaching and therefore allows efficient
catalyst recycling. The precise mechanism of the catalytic reaction
needs to be elucidated, but it is noticeable that the mechanism
is strongly modified depending of the halobenzene employed,
obtaining trans-stilbene as the main product (Scheme 1).
4-Methoxy-trans-stilbene (Table 5, entry 6) 1H NMR (500 MHz,
CDCl3, TMS): ı 3.83 (s, 3H), 6.82 (d, J 8.3 Hz, 2H), 6.90 (d, J 15.9 Hz,
1H), 7.01 (d, J 16.6 Hz, 1H), 7.15–7.31 (m, 4H), 7.38–7.44 (m, 3H); 13
C
NMR: ı 60.8, 110.1, 123.3, 127.7, 129.2, 129.7, 130.2, 130.7, 136.2,
140.7, 160.3; IR (KBr, cm−1) 3020, 2915, 2850, 1602, 1517, 1243,
1039, 824, 540.
The [Gmim]Cl–Pd (II) complex stumble on superiority over most
of the reported catalysts [9,10] with many advantages: facile syn-
thesis, thermal stability and structural versatility, easy handling,
catalytic performance in air at 25 ◦C, without any additives, no inert
atmosphere required without leaching of catalyst.
3-Styrylpyridine (Table 5, entry 8) 1H NMR (500 MHz, CDCl3,
TMS): ı 7.06 (d, J 16.4 Hz, 1H), 8.70 (s, 1H), 7.16 (d, J 16.4 Hz, 1H),
7.31–7.25 (m, 2H), 7.39–7.35 (m, 2H), 7.55 (d, J 7.5 Hz, 2H), 7.83 (d,
J 8.0 Hz, 1H), 8.45 (d, J 4.0 Hz, 1H); 13C NMR: ı 123.5, 125.9, 128.7,
129.2, 129.8, 131.8, 133.6, 134.0, 136.6, 150.6.
trans-1,2-Diphenylethene (Table 5, entry 1) 1H NMR (500 MHz,
CDCl3, TMS): ı 7.03 (s, 2H), 7.15–7.20 (m, 2H), 7.32 (t, J 7.6 Hz, 4H),
7.46 (d, J 7.5 Hz, 4H); 13C NMR: ı 125.7, 127.2, 129.4, 138.3; IR (KBr,
cm−1) 3027, 2930, 1600, 1450, 970, 680.
trans-4-Nitrostilbene (Table 5, entry 2) 1H NMR (500 MHz,
CDCl3, TMS): ı 7.17 (d, J 18 Hz, 1H), 7.42–7.33 (m, 4H), 7.56 (d, J
6 Hz, 2H), 7.65 (d, J 9 Hz, 2H), 8.22 (d, J 6.0 Hz, 2H); 13C NMR: ı
126.2, 128.3, 130.9, 132.1, 133.9, 133.9, 137.4, 137.9, 145.6, 148.8.
4-Methyl-trans-stilbene (Table 5, entry 3) 1H NMR (500 MHz,
CDCl3, TMS): ı 2.32 (s, 3H), 7.04 (s, 2H), 7.15 (d, J 8.4 Hz, 2H),
4. Conclusions
In this study, for the first time, we have introduced [Gmim]Cl–Pd
(II) as a catalyst for Heck–Mizoroki reaction with Et3N in the
absence of an organic co-solvent. Aryl bromides were reacted effi-
ciently with styrene and methyl acrylate at ambient temperature
in the presence of the catalyst. The procedure is easy and does not
require special precautions. All the reactions were conducted in
the air without the use of an organic co-solvent. In addition, it
was found that, aromatic halides with withdrawing group were
more reactive than that of electron donating group. Noteworthy
features of this catalyst system are (1) synthesized a novel green 1-
glycyl-3-methyl imidazolium chloride–palladium (II) complex; (2)
its catalytic activity was tested in Heck reaction; (3) 0.1 mmol of
catalyst was sufficient to furnish the trans-stilbenes with excellent
yields (up to 96%). (4) The catalyst can be readily recovered and
reused without significant loss of its activity.
Acknowledgments
We gratefully acknowledge the management of VIT University
for providing required facilities and SAIF (IITM) for providing the
spectral data.
Fig. 7. AFM image of 3-(amino (carboxy) methyl)-1-methyl-1H-imidazol-3-ium
chloride supported palladium complex after 8th run.

120
P. Karthikeyan et al. / Journal of Molecular Catalysis A: Chemical 358 (2012) 112–120
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