Polymer supported Pd catalyzed thioester synthesis via carbonylation of aryl halides under phosphine free conditions

Article abstract of DOI:10.1039/c4ra03338h

A new polymer supported phosphine free Pd(ii) complex has been synthesized and characterized. The catalytic performance of the complex has been tested for the carbonylation of aryl halides into aryl thioesters under mild reaction conditions. Thioesters were obtained in excellent yields from various aryl iodides and thiols in the presence of carbon monoxide and polymer supported palladium catalyst. The effects of solvent, base, reaction time and catalyst amount for the thioester synthesis were reported. This catalyst showed excellent catalytic activity and recyclability. The polymer supported Pd(ii) catalyst could be easily recovered by filtration and reused more than five times without appreciable loss of its initial activity.

Full text of DOI:10.1039/c4ra03338h

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PAPER
Polymer supported Pd catalyzed thioester synthesis
via carbonylation of aryl halides under phosphine
free conditions†
Cite this: RSC Adv., 2014, 4, 26181
*
Sk Manirul Islam, Rostam Ali Molla, Anupam Singha Roy and Kajari Ghosh
A new polymer supported phosphine free Pd(II) complex has been synthesized and characterized. The
catalytic performance of the complex has been tested for the carbonylation of aryl halides into aryl
thioesters under mild reaction conditions. Thioesters were obtained in excellent yields from various aryl
iodides and thiols in the presence of carbon monoxide and polymer supported palladium catalyst. The
effects of solvent, base, reaction time and catalyst amount for the thioester synthesis were reported. This
catalyst showed excellent catalytic activity and recyclability. The polymer supported Pd(II) catalyst could
be easily recovered by filtration and reused more than five times without appreciable loss of its initial activity.
Received 13th April 2014
Accepted 4th June 2014
DOI: 10.1039/c4ra03338h
www.rsc.org/advances
established; biological systems use their relative reactivity in
many enzymatic reactions by employing, for example, acetyl
Introduction
coenzyme A, cysteine proteases or polyketide and fatty acid
synthases.13 Also, thioesters have distinct chemical properties
compared to ordinary esters and their enhanced reactivity has
been employed successfully in a wide range of synthetic organic
reactions.14,15 Therefore, developing a simple and versatile
method for the preparation of thioester is still a challenge in
organic synthesis.
Recently, several methods have been reported in the litera-
ture for the synthesis of thioesters.16–18 However, these methods
require prolonged reaction time and exotic reaction condition.
Alper's group has developed a number of other Pd-catalyzed
thiocarbonylation reactions.19 All of these reported protocols
used homogeneous catalysts. Homogeneous catalysts have
some disadvantages, such as they may easily be destroyed
during the course of the reaction and they cannot be easily
recovered aer the reaction for reuse.20 To get rid of these
serious issues, we have synthesized and reported several sup-
ported metal catalysts21 and we focused our effort to develop an
The palladium-catalyzed cross-coupling reaction for the
formation of carbon–carbon bonds is a dynamic method in
organic synthesis. The palladium-catalyzed coupling of an aryl
halide with an aryl boronic acid (Suzuki coupling) or terminal
alkyne (Sonogashira coupling) is recognized as the most
successful method for forming a C(sp2)–C(sp2) or a C(sp)–C(sp2)
carbon–carbon bond, respectively. These reactions have been
widely employed in the synthesis of natural products, biologi-
cally active molecules and materials science.1
On the other hand, palladium-catalyzed carbonylation of aryl
halides has become a powerful tool in organic synthesis.2 As an
inexpensive and readily available C1 source, carbon monoxide
can be used to synthesize various carbonyl products, such as
aldehydes, ketones, carboxylic acids, esters, and amides.3
Among the different types of carbonylation reactions, palla-
dium-catalyzed coupling carbonylation reaction of aromatic
halides has been one of the most important methodologies for
the synthesis of valuable carbonyl containing compounds both
from academic and industrial perspectives.4 Palladium cata-
lyzed carbonylations serves as powerful tools for the conversion
of aryl halides to carboxylic acid derivatives.5 Thioesters are
activated carboxylic acid derivatives which exhibit acylating
properties similar to those of acid anhydrides.6–11 Thioesters are
becoming increasingly important compounds due to their
distinctive chemical properties; the reduced electron delocal-
ization provides for the enhanced reactivity compared to
oxoesters.12 The importance of thioesters in the cell is well
efficient
methodology
for
palladium-catalyzed
thio-
carbonylation reaction.
Pd-catalyzed thiocarbonylation of aryl halides are less well-
known. Two previous reports in the literature have demon-
strated the feasibility of this transformation with aryl iodides. In
2008, Alper and co-workers reported the Pd-catalyzed thio-
carbonylation of aryl iodides using a phosphonium salt-based
ionic liquid solvent in combination with 14 atm of CO pressure.
Later, Lei et al. in mechanistic studies on Pd-catalyzed
carbonylation reactions demonstrated that the same trans-
formation could be carried out using a sodium thiolate in a
thiol–THF solvent mixture and CO pressure of 10 atm.22–24 Thus,
the development of a new method for the synthesis of thioester
derivatives from aryl halides would be highly desirable. At the
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/c4ra03338h
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same time, only a few examples have been reported for the use
of supported counterparts of the homogeneous palladium
catalysts for the carbonylation reactions of aryl halides.25–31 To
the best of our knowledge, there is only one report of reusable
palladium-catalyzed thiocarbonylation reaction of aryl halides
and thiols.18
We are the rst to report the polymer supported palladium-
catalyzed thiocarbonylation of aryl iodides with thiols. Herein,
we report the synthesis and characterization of a polymer sup-
ported palladium catalyst and illustrate its application for the
synthesis of aryl thioesters via carbonylation of aryl iodides
under mild reaction conditions. This polymer supported Pd(II)
catalyst could be easily separated from the reaction mixture by
simple ltration and can be reused more than ve times
without appreciable loss of its activity.
Experimental section
Materials
Analytical grade reagents and freshly distilled solvents were
used throughout. All reagents and substrates were purchased
from Merck. Liquid substrates were predistilled and dried by
molecular sieve and solid substrates were recrystallized before
use. Distillation, purication of the solvents and substrate were
done by standard procedures.32 5.5% crosslinked chloro-
methylated polystyrene and palladium acetate were purchased
from Aldrich Chemical Company; U.S.A. and used without
further purication.
Scheme 1 Synthesis of the polymer supported Pd(II) catalyst.
ligand (1 g) in acetic acid (20 mL) was treated with 5 mL 1% (w/v)
AcOH solution of Pd(OAc)2 over a period of nearly 30 minutes
under constant stirring. Then the reaction mixture was reuxed
for 24 h. The brown coloured palladium complex thus formed
was ltered and washed thoroughly with ethanol and dried at
room temperature under vacuum.
Physical measurements
NMR spectra were recorded on a Bruker DPX-400 NMR spec-
trometer (1H NMR at 400 MHz and 13C NMR at 100 MHz) in
pure deuterated solvents with TMS as internal standard. The FT-
IR spectra of the samples were recorded from 450 to 4000 cmꢀ1
on a Perkin Elmer FT-IR 783 spectrophotometer using KBr
pellets. UV-vis spectra were taken using a Shimadzu UV-2401PC
doubled beam spectrophotometer having an integrating sphere
attachment for solid samples. Thermogravimetric analysis
(TGA) was carried out using a Mettler Toledo TGA/DTA 851e.
Surface morphology of the samples was measured using a
scanning electron microscope (SEM) (ZEISS EVO40, England)
equipped with EDX facility. Palladium content in the catalyst
was determined using a Varian AA240 atomic absorption spec-
trophotometer (AAS).
General procedure for the synthesis of thioester
A 50 mL high-pressure reactor was charged with dimethoxy-
ethane (DME) (5.0 mL, 4.35 mol), NaOAc (22.6 mg, 0.275 mmol),
aryl iodide (0.25 mmol), palladium catalyst (25 mmol) and CO (1
atm) before heating at 85 ꢁC for 16 h. Aer cooling the reactor,
the CO was vented from the reactor and the desired compound
was puried by chromatography on silica gel using a pentane–
CH2Cl2 eluent system. All the prepared compounds were
1
conrmed by H and 13C NMR spectra.
Results and discussion
Characterization of the polymer supported Pd catalyst
Synthesis of the metal complex
Due to insolubilities of the polymer supported palladium cata-
The synthesis of the immobilized polymer supported palladiu- lyst in all common organic solvents, its structural investigation
m(II) catalyst illustrated in Scheme 1. It was readily prepared was limited to its physicochemical properties, chemical
through a two-step procedure. In step I, 0.2 g of chloromethy- analysis, SEM-EDX, TGA, IR and solid UV-vis spectroscopic data.
lated polystyrene (5.5 mmol Cl per g of resin) (2) was treated Table 1 provides the data of elemental analysis of polymer
with 0.979 g of b-alanine (1) in N,N0-dimethylformamide (DMF) supported ligand and the polymer supported palladium cata-
to produce the corresponding white coloured polymer sup- lyst. Palladium content in the catalyst determined by AAS
ported ligand (PS-ala). The polymer was washed thoroughly suggests 9.08 wt% Pd in the catalyst.
with DMF to remove excess b-alanine. Finally, it was washed
Various frameworks bonding present in the polymer sup-
with double distilled water, dried and stored at room temper- ported metal catalyst were obtained from the FT-IR spectra
ature for further use. In step II, the polymer supported b-alanine (Fig. 1). A new strong band appeared at 3436 cmꢀ1 showed the
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Table 1 Chemical composition of polymer anchored ligand and
polymer supported catalyst
Compound
Colour
C %
H %
Cl %
N %
Metal %
PS-ala
PS-ala-Pd
White
Deep grey
72.04
64.15
5.87
5.07
6.10
4.33
2.41
1.40
—
9.08
presence of a secondary (–NH–) amine group in the ligand. The
(C]O), nasym(COO) and nsym(COO) stretching vibrations are
observed at 1733, 1675 and 1513 cmꢀ1 for polymer anchored
ligand30 and this ligand is bidentate ligand and bound to the
central metal ion through the carboxylic OH and the secondary
amino group; (–NH–). The bands at 1675 and 1513 cmꢀ1, due to
nasym(COO) and nsym(COO) of the amino acids, appear in the
complex at 1670 and 1510 cmꢀ1. The shi of these two bands
suggests the involvement of the carboxylic groups of the poly-
mer supported ligand in complex formation. The decrease in
the intensity of N–H stretching frequency of the secondary
amine group in the complex indicates that the ‘N’ of amino
group may be coordinated to the metal. Weak bands in the far
IR region at ꢂ340–360 cmꢀ1 and ꢂ440–450 cmꢀ1 have been
assigned to nPd–O and nPd–N vibrations.33–35 Thus, making precise
assignments to distinguish Pd–O from Pd–N bands in the far IR
region is rather difficult.
The scanning electron micrographs (Fig. 2) of the polymer
supported ligand and palladium catalyst clearly show the
morphological change which occurred on the surface of poly-
styrene aer loading of metal on it. Energy dispersive spec-
troscopy analysis of X-rays (EDAX) data for the polymer
anchored ligand and palladium catalyst are given in (Fig. 3). The
EDX data also conrm the attachment of metal on the surface of
the polymer matrix.
Fig. 2 FE-SEM images of polymer anchored ligand (PS-ala) (A), PS-
ala-Pd complex (B).
diffuse reectance spectrum mode as BaSO4 disc due to its
solubility limitations in common organic solvents. The low-spin
Pd(II) complex may exhibit three spin-allowed d–d transitions
from lower lying d orbital to higher empty dx2ꢀy2 orbital. The
bands are observed at 305 nm, 365 nm and 420 nm which may
1
1
1
be designated as A1g/1Eg, A1g/1B1g and A1g/1A2g transitions
respectively.36,37
Thermal stability of the complex was investigated using TGA
at a heating rate of 10 ꢁC minꢀ1 in air over a temperature range
of 30–600 ꢁC. TGA curve of the polymer supported palladium
catalyst is shown in Fig. 5. The palladium complex was stable up
to 320–350 ꢁC and above this temperature it decomposed.
Thermogravimetric study suggests that the polymer supported
palladium complex degrade at considerably higher
temperature.
Catalytic activity
Since supported palladium catalyst exhibits high catalytic
activity in a wide range of industrially important processes and
have been extensively studied for C–C coupling, we decided to
investigate the catalytic activity of the PS-ala-Pd in the eld of
carbonylation. Initial studies focused on examining the feasi-
bility of the thiocarbonylation reactions and optimizing
The UV-vis spectra (Fig. 4) provided further evidence for the
presence of palladium on polymer support. The electronic
spectra of the polymeric Pd(II) catalyst has been recorded in
Fig. 1 FT-IR Spectra of polymer anchored ligand PS-ala (a), PS-ala-Pd complex (b).
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Fig. 3 EDAX data of polymer supported ligand (PS-ala) (A) and PS-ala-Pd complex (B).
Fig. 5 Thermogravimetric weight loss plot for the polymer supported
catalyst PS-ala-Pd complex.
Fig. 4 DRS-UV-visible absorption spectra of the polymer supported
ligand and palladium catalyst.
converted to aryl thioester under 1 atm CO pressure. Quanti-
reaction conditions that could be applied to a variety of thiols tative conversion of aryl halide to aryl thioester can be achieved
and aryl halides. by using the polymer supported Pd catalyst (PS-ala-Pd). The
To test the catalytic activity of the present catalyst, the carbonylation reaction of aryl iodide was carried out by using
carbonylation of aryl iodides and thiols were performed as sodium acetate as the base in the DME solvent medium. The
ꢁ
illustrated in Scheme 2. In this reaction aryl halide was reaction was run in a 50 mL autoclave at 85 C under carbon
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Table 3 Effect of solvents on the carbonylation of iodobenzene and
thiophenola
Entry
Solvent
Conversion (%)
1
2
3
4
DME
85
56
72
68
Toluene
Propionitrile
Dioxane
Scheme 2 Palladium catalyzed carbonylation of aryl iodides.
a
Reaction conditions: thiophenol (0.30 mmol), iodobenzene (0.30
mmol), NaOAc (0.275 mmol), CO (1 atm), PS-ala-Pd (25 mmol), time
(16 h) and temperature (85 ꢁC).
monoxide atmosphere for 16 h. In our initial studies, the
iodobenzene was chosen as the reactant for the optimization of
the carbonylation reaction (Scheme 3). The performance of
palladium-catalyzed carbonylation reaction is known to be
governed by a number of reaction parameters. To nd the
appropriate reaction conditions various bases and solvents were
screened (Table 2). In order to identify effective conditions for
promoting the Pd-thiocarbonylation, the reaction was carried
out under various temperature and reaction time (Table 3).
The inuence of base on the catalytic performance of this
system was investigated by employing various bases. Compar-
ison of inorganic bases utilized, showed that inorganic bases
are more effective than organic bases like pyridine and Et3N.
Within a short time the reaction proceeded with high yield in
presence of NaOAc or K2CO3 (Table 2, entries 4 and 7). We
found that using NaOAc as base in DME at 85 ꢁC gave 85%
conversion. Other inorganic bases such as K3PO4, NaHCO3 and
organic bases like Et3N were not as effective as NaOAc, only
afforded moderate to low yields of coupling products (Table 2,
entries 2, 3, 5 and 6).
To verify the solvent effect, a series of solvents were investi-
gated by taking the carbonylation of iodobenzene as the model
reaction. The reactions were that conducted in polar solvent
medium, like DME and propionitrile, were found to be most
effective (Table 3, entries 1 and 3). The use of toluene, dioxane
as solvents led to slower reactions (Table 3, entries 2 and 4).
Consequently, DME was chosen as the medium of choice for
this carbonylation.
This coupling reaction was found to be highly sensitive to the
reaction temperature. At lower temperatures (45–65 ꢁC) only low
to moderate yield was obtained (Table 4, entries 1–3). A reaction
temperature of 85 ꢁC was found to be optimal for the model
reaction (Table 4, entry 5). Also the reaction was carried out for
different time ranging from 10 h to 18 h and it was found that at
16 h the conversion was 85% at given conditions (Table 4,
entries 5 and 7–10).
The inuence of amount of catalyst on the yield was also
investigated (Fig. 6). An increase in the catalyst amount from
10 mmol to 25 mmol resulted in an increase in the yield up to
85%. Further increase in catalyst amount had no profound
effect on the yield of the desired product.
To examine the scope of this carbonylative coupling reac-
tion, a variety of aryl iodides were coupled with different thio-
phenols in DME in the presence of PS-ala-Pd(II) catalyst. The
experimental results are summarized in Table 5. With a dened
Scheme 3 Palladium catalyzed carbonylation of iodobenzene and
thiophenol.
Table 2 Effect of bases on the carbonylation of iodobenzene and Table 4 Effect of temperature and reaction time on carbonylation
thiophenola
reactiona
Entry
Base
Conversion (%) Entry
Temperature (ꢁC)
Time (h)
Conversion (%)
1
2
3
4
5
6
7
8
9
NaOtBu
Et3N
K3PO4
K2CO3
Pyridine
NaHCO3
NaOAc
NaOAc
NaOAc
NaOAc
62
28
37
52
22
26
85
56
72
68
1
2
3
4
5
6
7
8
9
10
45
55
65
75
85
95
85
85
85
85
16
16
16
16
16
16
10
12
14
18
29
43
57
71
85
85
38
51
69
85
10
a
a
Reaction conditions: thiophenol (0.30 mmol), iodobenzene (0.30
Reaction conditions: thiophenol (0.30 mmol), iodobenzene (0.30
mmol), DME (5 mL), CO (1 atm), PS-ala-Pd (25 mmol), time (16 h) and mmol), CO (1 atm). PS-ala-Pd (25 mmol), NaOAc (0.28 mmol), DME
temperature (85 ꢁC).
(5.0 mL).
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harsher reaction conditions. We have tried to synthesize the aryl
thioester from aryl bromide under the optimized reaction
conditions but only trace amount of yield was obtained. Aryl
chloride did not respond to the reaction under the optimized
reaction conditions. Although the exact reaction sequence was
not determined, based on our experimental results and former
mechanistic studies of palladium-catalyzed carbonylations of
aryl halides,38 the reaction mechanism of this thioester
synthesis is proposed in Scheme 4. It is generally accepted that
an organopalladium halide (B) is produced by oxidative addi-
tion of an organic halide to a Pd species (A) formed in the
catalytic system but the later course of the catalytic reaction may
vary depending on the nucleophiles and reaction conditions
employed. The most oen assumed process involves migratory
insertion of a coordinated carbon monoxide in (C) to give an
acylpalladium halide (D), which reacts further with a nucleo-
phile (PhSH) and a base to liberate ArCOSPh.
Fig. 6 Effect of catalyst amount on carbonylation of iodobenzene.
Reaction conditions: thiophenol (0.30 mmol), iodobenzene (0.30
mmol), CO (1 atm), NaOAc (0.28 mmol), DME (5.0 mL), time (16 h),
temperature (85 ꢁC).
Heterogeneity test
An important point concerning the use of heterogeneous cata-
lyst is its lifetime, particularly for industrial and pharmaceutical
applications of the coupling reaction. Heterogeneity of this
catalyst was examined by the “hot ltration test” for the
carbonylation of iodobenzene.
protocol in hand, the substrate scope with various aryl iodides
was explored. As shown in Scheme 2, the protocol well tolerated
diverse electronic and steric substituents of the aryl iodides, as
well as heterocyclic substrates, all resulting in good to excellent
yields. The relative position of substituents had slight impact on
the coupling efficiency: p-iodotoluene and p-iodoanisole resul-
ted in a higher yield than its m- or o-analogues (Table 5, entries
2–7). Almost similar yields were obtained with iodobenzene and
p-tertbutyl-iodobenzene (Table 5, entries 1 and 12). The substi-
tution of electron withdrawing and electron donating groups on
the phenyl ring of aryl iodides did not have any appreciable
inuence on the outcome of the reaction (Table 5, entries 2, 5,
12 and 18–22). Aryl iodides bearing either electron-donating or
electron-withdrawing substituents, afforded the correspond-
ing cabonylative products in good to excellent yields. Strong
electron-donating groups such as methyl and methoxy group
containing aryl iodides resulted in slightly more yields than
aryl iodides with electron-withdrawing groups, such as chlo-
ride and bromide (Table 5, entries 19 and 21). Even hetero-
aromatic iodides proved effective for these carbonylative
couplings as depicted with the indole and thiophene ring
system leading to products (Table 5, entries 9 and14). A few
other aromatic thiols were also successfully tested as repre-
sented by compounds (Table 5, entries 15–17). The di-
substituted alkyl thiol was run, providing the functionalized
thioester (entry 17) in approximately 74% yield. The scope of
Hot-ltration test
Hot-ltration test was performed in the carbonylation of
iodobenzene to investigate whether the reaction proceeded in
a heterogeneous or a homogeneous fashion. Aer continuing
the reaction for 10 h, the catalyst was removed by ltration
and the determined conversion was 66%. The resulting
ltrate was subjected to heating for further 6 h, it has been
found that aer separation of the catalyst no conversion takes
place in the ltrate part. This conrms that the reaction did
not proceed upon the removal of the solid catalyst. Further-
more, no evidence for leaching of palladium or decomposi-
tion of the complex catalyst was observed during the catalytic
reaction and no metal could be detected by atomic absorption
spectroscopic measurement of the ltrate aer removal of
catalyst. These studies clearly demonstrated that metal was
intact to a considerable extent with the heterogeneous
support, and there was no signicant amount of leaching
during the reaction.
Catalyst reusability
the thiocarbonylation procedure with the other electron-poor Recovery and catalyst reuse are important issues in the
aryl iodides were also tested (entries 18 and 23). In most cases, carbonylation reactions. Easy catalyst separation and recycling
good to excellent yields of the thioesters were obtained. Even in successive batch operations, can greatly increase the effi-
in the case of the p-nitro derivative, the desired compound ciency of the reaction. We studied the reusability of the present
(entry 22) was formed.
heterogeneous palladium catalyst in the carbonylation of
An interesting observation was made in the reaction of the iodobenzene with thiophenol. Aer completion of the reaction,
substituted iodobenzenes with either thiophenol or its deriva- the catalyst was recovered by simple ltration and washed with
tive. In all cases, the major products resulted from a thio- ethyl acetate followed by acetone then dried in reduced pressure
ꢁ
carbonylation even though more than 1 atm of CO was applied. at 40 C. The recovered catalyst was employed in the next run
The corresponding less expensive aryl bromides or chlorides are with further addition of substrates in appropriate amount
more attractive substrates, but the reaction oen requires under optimum reaction conditions. The catalyst showed
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Table 5 Polymer supported palladium(II) catalyzed carbonylation of aryl iodidesa
Entry
Aryl halide
Product
Conversion (%)
1
85
2
91
3
88
4
5
6
7
72
95
68
72
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Table 5 (Contd.)
Entry
Aryl halide
Product
Conversion (%)
8
9
93
83
81
10
11
83
12
13
84
74
14
45
85
15b
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Table 5 (Contd.)
Entry
Aryl halide
Product
Conversion (%)
16c
83
74
17d
18
19
20
86
81
88
21
86
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Table 5 (Contd.)
Entry
Aryl halide
Product
Conversion (%)
22
61
23
85
a
Reaction conditions: thiophenols, (0.30 mmol), aryl iodides (0.30 mmol), CO (1 atm), PS-ala-Pd (25 mmol), NaOAc (0.28 mmol), DME (5.0 mL), time
b
c
d
(16 h), temperature (85 ꢁC). p-Methoxythiophenol. m-Methoxythiophenol. 2,6-Di-methylthiophenol used. All the prepared compounds were
conrmed by H and 13C NMR.
1
Fig. 7 Catalyst reusability test of the polymer supported Pd catalyst.
Conclusions
In conclusion, we have reported the preparation and charac-
terization of polystyrene-supported Pd(II) complex and its
successful applications for the thiocarbonylation of aryl iodides
with thiols exploiting a simple setup and reaction conditions,
which use only 1 atm carbon monoxide. Both electron-rich and
electron-decient aryl iodides could be applied and the nature
of the base, temperature and the solvent system proved crucial
for the transformation. The present system is highly air and
moisture stable and the catalyst can be synthesized readily from
inexpensive and commercially available starting materials.
Moreover, the catalyst was reused for six consecutive cycles with
Scheme 4 Proposed reaction mechanism of palladium catalyzed
carbonylation of aryl iodide.
almost the same activity up to six reaction cycles. No catalyst
deterioration was observed, thus conrming the high stability
of the heterogeneous catalyst under the reaction conditions
(Fig. 7).
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consistent catalytic activity. Further work is in progress to
broaden the scope of this catalytic system for other organic
transformation. A protocol, which allows expansion of this
chemistry to other aromatic halides and mechanistic pathway
of this reaction are currently under investigation.
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SMI acknowledges CSIR and DST, New Delhi, Govt. of India, for
nancial support. RAM acknowledges UGC, New Delhi, India
for his Maulana Azad National Fellowship (F1-17.1/2012-13/
MANF-2012-13-MUS-WES-9628/SA-III). ASR acknowledges CSIR,
New Delhi, India for his senior research fellowship.
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