A novel imidazolium-supported palladium-chloroglycine complex: Copper- and solvent-free high-turnover catalysts for the Sonogashira coupling reaction

Article abstract of DOI:10.1002/aoc.2896

A novel, effective 1-glycyl-3-methyl imidazolium chloride-palladium(II) complex ([Gmim]Cl-Pd(II)) was synthesized and studied as an organocatalyst for the Sonogashira coupling reaction under solvent-free conditions at 25 °C. The hydrophobic group on amino acid favors reagent diffusion toward the chloroglycine moiety, increasing the catalytic activity of supported palladium complex. By this protocol, different aryl halides (Cl, Br and I) were reacted with phenylacetylene in good to excellent yields with turnover number 8.0 × 10² to 9.6 × 10². The catalyst was recycled for the reaction of bromobenzene with phenylacetylene for eight runs without appreciable loss of its catalytic activity and negligible metal leaching. Copyright

Full text of DOI:10.1002/aoc.2896

Full Paper
Received: 30 April 2012
Revised: 31 May 2012
Accepted: 31 May 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2896
A novel imidazolium-supported palladium–
chloroglycine complex: copper- and solvent-
free high-turnover catalysts for the
Sonogashira coupling reaction
Parasuraman Karthikeyan, Prashant Narayan Muskawar, Sachin Arunrao Aswar,
Pundlik Rambhau Bhagat* and Suresh Kumar Sythana
A novel, effective 1-glycyl-3-methyl imidazolium chloride–palladium(II) complex ([Gmim]Cl–Pd(II)) was synthesized and
studied as an organocatalyst for the Sonogashira coupling reaction under solvent-free conditions at 25 ꢀC. The hydrophobic
group on amino acid favors reagent diffusion toward the chloroglycine moiety, increasing the catalytic activity of supported
palladium complex. By this protocol, different aryl halides (Cl, Br and I) were reacted with phenylacetylene in good to excellent
yields with turnover number 8.0 Â 102 to 9.6 Â 102. The catalyst was recycled for the reaction of bromobenzene with
phenylacetylene for eight runs without appreciable loss of its catalytic activity and negligible metal leaching. Copyright ©
2012 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: Sonogashira coupling; palladium; amino acid; ionic liquid
During the last two years, Chungu Xia et al. described cross-
Introduction
linked polymer supported palladium-catalyzed carbonylative
Sonogashira coupling reaction in water.[6] Vasundhara Singh et al.
The development of recoverable and recyclable catalysts for
industrial applications has become important from both the
environmental and economical point of view and has been
well reviewed in the literature.[1] In recent years, metal
complex-functionalized ionic liquids have emerged as a set of
green solvents with unique properties such as tunable polarity,
high thermal stability and immiscibility with a number of
organic solvents, negligible vapor pressure and recyclability.
Their non-volatile character and thermal stability make the metal
complexes potentially attractive alternatives to environmentally
unfavorable organic co-solvents, notably chlorinated hydro-
carbons. In particular, they show promise as solvents for the
immobilization of transition metal catalysts, Lewis acids and
enzymes.[2] As a result of their green credential and potential to
enhance reaction rate and selectivities, ionic liquids are finding
increasing applications in organic synthesis.
The Sonogashira–Hagihara reaction is important because of
valuable applications in both laboratory and industry. The
significance of these compounds exists in the organic synthe-
sis, structural units found in natural products, pharmaceuticals,
biologically active molecules, liquid crystalline materials,
conducting polymers and advanced materials. Moreover, the
Sonogashira–Hagihara reaction has emerged as one of the
most powerful, attractive and widely utilized methods for
the formation of Csp2–Csp bonds. In addition, this reaction
exhibits high tolerance to the presence of functional groups
as substituents in substrates, mild reaction conditions, possi-
bility of performing the reaction in water and very often also
in an air atmosphere.[3–5]
reported the synthesis and characterization of recyclable and
recoverable montmorillonite clay-exchanged ammonium-tagged
carbapalladacycle catalyst for Mizoroki–Heck and Sonogashira
reactions in ionic liquid media.[7] Furthermore, Mohammad
Bakherad et al. have reported the copper and solvent-free
Sonogashira coupling reactions of aryl halides with terminal alkynes
catalyzed by 1-phenyl-1,2-propanedione-2-oxime thiosemi-
carbazone-functionalized polystyrene resin supported Pd(II)
complex under aerobic conditions.[8] Nasser Iranpoor et al.
illustrated palladium nanoparticles supported on agarose as
an efficient catalyst and bioorganic ligand for C&bond;
C bond formation via solventless Mizoroki–Heck reaction and
Sonogashira–Hagihara reaction in polyethylene glycol (PEG
400).[9] Haihong Wu et al. exemplified the ionic liquid-
functionalized phosphine-ligated palladium complex for the
Sonogashira reaction under aerobic and CuI-free conditions.[10]
All the above-mentioned methods provide good yields,
whereas some of these reactions are sluggish, requiring at least
24 h for reaction completion, lengthy work-up procedure, harsh
reaction conditions and absolutely dry and inert media. The use
*
Correspondence to: P. R. Bhagat, Organic Chemistry Division, School of Advanced
Sciences, VIT University, Vellore-632 014, India. E-mail: drprbhagat111@
gmail.com
Organic Chemistry Division, School of Advanced Sciences, VIT University,
Vellore632 014, India
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.

P. Karthikeyan et al.
of an eco-friendly reaction medium, minimization of steps, bet-
ter yields and faster reaction remained constant challenges in
the context of green chemistry. Herein, we report a protocol
based on palladium-functionalized 1-glycyl-3-methyl imidazolium
chloride (Fig. 1), which proved to be highly efficient at 25 ꢀC for
C&bond;C bond formation.
many advantages, including high conversion, short duration
and use of non-toxic reagents.
Experimental
However, recovery and leaching can occur in the extractive
workup, leading to a loss of the catalyst in the reaction mixture
and requiring additional effort to purify the extracted product.
To overcome such problems, a novel palladium complex was
developed[11] by covalent linking of the organocatalytic 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 one hand and high solubility in the reaction medium
on the other.[12] This strategy was applied to the Sonogashira
coupling reaction, providing high yield and good recyclability of
the organocatalyst.
General Methods
All solvents and chemicals were commercially available and
used without further purification unless otherwise stated.
The 1-glycyl-3-methyl imidazolium chloride–palladium(II)
([Gmim]Cl–Pd(II)) complex was characterized by powder
X-ray diffraction (P-XRD) diffractometry with a Bruker D8
(advance model, Germany) and lynx eye detector operating
with nickel-filtered Cu-K radiation. 1 H NMR spectra were
recorded on a Bruker 500 MHz instrument using CDCl3–
DMSO-d6 as the solvent and mass spectra were recorded on
JEOL GC-Mate II HRMS (EI) spectrometer. FT-IR spectra were
recorded on an Avatar 330 spectrometer with deuterated
triglycine sulfate detector. Column chromatography was
performed on silica gel (200–300 mesh). Analytical thin-layer
chromatography (TLC) was carried out on pre-coated silica
gel GF-254 plates. Atomic force microscopy (AFM) and scan-
ning electron microscopy (SEM) were performed using a Nano
Surf Easy Scan-2 (Switzerland) and a Carl Zeiss EVO MA 15
instrument, respectively.
Thus the present study focuses on the development of an
efficient synthetic methodology for facile conversion using the
Sonogashira coupling reaction. The developed method offers
Preparation of [Gmim]Cl–Pd(II) Complex
The [Gmim]Cl–Pd(II) complex was synthesized as previously
reported and structural conformation available in Supporting
Figure 1. 1-Glycyl-3-methyl imidazolium chloride–palladium(II) complex
[Gmim]Cl–Pd(II)
Table 1. Effect of the base and time on Sonogashira coupling reactiona
Entry
Base
Time
(h)
Yieldb
(%)
TONc
TOFc
1
—
24
Trace
—
—
25
46
52
96
96
96
96
96
96
96
88
85
80
—
—
—
2
Py
24
24
24
24
24
24
20
18
12
6
—
3
Imidazole
K2CO3
KOH
—
—
4
250
460
520
960
960
960
960
960
960
960
880
850
800
10.41
19.16
21.66
40.00
48.00
53.33
80.00
160.00
320.00
960.00
1173.33
1700.00
3200.00
5
6
NaOH
Et3N
7
8
Et3N
9
Et3N
10
11
12
13
14
15
16
Et3N
Et3N
Et3N
3
Et3N
1
Et3N
0.75
Et3N
0.50
0.25
Et3N
aReaction conditions: bromobenzene (1 mmol), phenylacetylene (1.2 mmol), different base (1 mmol) and [Gmim]Cl–Pd(II) (0.1 mol%), with stirring at
25 ꢀC.
bYield determined by HPLC.
cTON, turnover number; TOF, turnover frequency (mol product molÀ1 catalyst hÀ1).
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A novel imidazolium-supported palladium–chloroglycine complex
Table 2. Effect of the solvent on the Sonogashira coupling reactiona
Entry
Solvent
CH3CN
Temp. (ꢀC)
Time (h)
Yieldb (%)
TONc
TOFc
1
60
130
35
50
50
50
65
25
20
35
90
24
24
24
24
24
24
24
1
40
53
400
530
—
16.66
22.08
—
2
DMF
3
DCM
Trace
Trace
Trace
Trace
Trace
96
4
CHCl3
—
—
5
THF
—
—
6
Methanol
Ethanol
—
—
7
—
—
8
Solvent free
Solvent free
Solvent free
Water (5 ml)
960
900
970
500
960.00
900.00
970.00
20.83
9
1
90
10
11
1
97
24
50
aReaction conditions: bromobenzene (1 mmol), phenylacetylene (1.2 mmol), solvent (5 ml), Et3N (1 mmol) and [Gmim]Cl–Pd(II) (0.1 mol%), with
stirring at different temperatures (see Table 2).
bYield determined by HPLC.
cTON, turnover number; TOF, turnover frequency (mol product molÀ1 catalyst hÀ1).
Table 3. Effect of the various catalysts on Sonogashira coupling reactiona
Entry
Catalyst
L-Glycine
Time (h)
Yieldb
TONc
TOFc
1
2
3
4
5
6
7
24
24
24
24
24
1
Trace
Trace
65
—
—
—
Chloroglycine [Cl-gly]
PdCl2/[Cemim] Br
PdCl2/[Aemim] Br
PdCl2/[Gmim]Cl
—
650
700
750
960
970
27.08
29.16
31.25
960.00
485.00
70
75
[Gmim]Cl–Pd(II)
[Gmim]Cl–Pd(II)d
96
2
97
aReaction conditions: bromobenzene (1 mmol), phenylacetylene (1.2 mmol), triethylamine (1 mmol) and catalyst (0.1 mol%), with stirring at 25 ꢀC.
bYield determined by HPLC.
cTON, turnover number; TOF, turnover frequency (mol product molÀ1 catalyst hÀ1).
dReaction duration 2 h.
information,[2] and the other ionic liquids were synthesized
using the literature procedure reported elsewhere.[13]
acetate or diethyl ether (3 Â 5 ml). The organic phase was
separated, dried over anhydrous Na2SO4 and evaporated. A crude
residue was obtained as the product, which was further purified
by column chromatography (EtOAc–n-hexane) to obtain the
desired coupling product in 80–96% isolated yield.
General Experimental Procedure for the Sonogashira
Coupling Reaction
A mixture of aryl halide (1 mmol), phenylacetylene (1.2 mmol),
triethylamine (1 mmol) and [Gmim]Cl–Pd(II) (0.1 mol%) was
placed in a 50 ml conical flask and stirred at 25 ꢀC for a period
as indicated in Table 5 (the reaction was monitored by high-
performance liquid chromatography (HPLC) and TLC). The
resulting heterogeneous mixture was extracted with ethyl
Recycling of the Catalyst for the Model Reaction of
Bromobenzene with Phenylacetylene using [Gmim]Cl–Pd(II)
Bromobenzene (1 mmol) was reacted with phenylacetylene
(1.2 mmol) in the presence of [Gmim]Cl–Pd(II) (0.1 mol%) and
triethylamine (1 mmol) at 25 ꢀC. After completion of the reaction
Appl. Organometal. Chem. (2012)
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P. Karthikeyan et al.
Table 4. Effect of catalyst loading on Sonogashira coupling reactiona
Entry
[Gmim]Cl–Pd(II) mol%
Time (h)
Yieldb
TONc
TOFc
1
—
0.025
0.050
0.075
0.1
48
24
24
24
24
18
12
6
—
50
62
75
96
96
96
96
96
96
97
97
—
—
2
500
620
750
960
960
960
960
960
960
970
970
20.83
25.83
31.25
40.00
53.33
80.00
160.00
320.00
960.00
970.00
970.00
3
4
5
6
0.1
7
0.1
8
0.1
9
0.1
3
10
11
12
0.1
1
0.125
0.150
1
1
aReaction conditions: bromobenzene (1 mmol), phenylacetylene (1.2 mmol), triethylamine (1 mmol) and [Gmim]Cl–Pd(II) (0.1 mol%), with stirring at
25 ꢀC.
bYield determined by HPLC.
cTON, turnover number; TOF, turnover frequency (mol product molÀ1 catalyst hÀ1).
(TLC/ HPLC), the product was extracted as stated above (’General
Methods’). The white solid [Gmim]Cl–Pd(II) was isolated by
centrifugation. Further, the recovered complex was washed with
diethyl ether and dried in air. The resulting catalyst was charged
to another batch of a similar reaction. This was repeated for eight
runs to complete the reaction in 1 h, to give the desired product
with 86–96% yield (Table 6).
Subsequently, in order to find a suitable solvent for the
reaction, the coupling of bromobenzene and phenylacetylene
was carried out with different solvents and Et3N. According to
publications from Chungu Xia and co-workers,[6] Lei Wang,[14]
Habib Firouzabadi[15] and Mohammad Bakherad,[8] polar, aprotic
solvents tend to give the best results for the Sonogashira
coupling reaction, while Vasundhara Singh[7] and Haihong Wu[10]
obtained high activity of catalysts in ionic liquids. We also
employed several solvents in the model reaction. Among the previ-
ous reports, reaction under solvent-free conditions was the most
productive as compared with the polar and non-polar solvents.
The catalyst was easily coordinated with organic co-solvents. It
has also been reported that H2O molecule is required in some cases
to activate the Pd(II) catalyst. In our case, carrying out the reaction
in H2O (5ml) at 90 ꢀC produced a negative effect on the product
yield in comparison with solvent-free conditions and this lower
yield could be due to delocalization of the complex under aqueous
conditions (Table 2).
Next, in order to optimize the reaction conditions for a
particular catalyst the coupling reaction of bromobenzene and
phenylacetylene was executed in the presence of Et3N using
different catalysts and the results are given in Table 3. When the
reaction was carried out using various catalysts such as L-glycine,
chloroglycine, PdCl2–1-carboxyethyl-3-methylimidazoliumbromide
[Cemim] Br, PdCl2/ 1-aminoethyl-3-methylimidazoliumbromide
[Aemim]Br and PdCl2–[Gmim]Cl with Et3N, it yielded trace
amounts to 75% of product respectively (Table 3, entries 1–5).
However, when the same reaction was conducted with [Gmim]
Cl–Pd(II) as a catalyst it yielded a remarkable yield of product
within a short duration (Table 3, entry 6). An almost similar yield
was obtained when increasing the duration of reaction (Table 3,
entry 7).
Results and Discussion
The palladium complex-catalyzed Sonogashira coupling reaction
was carried out using phenylacetylene and bromobenzene as a
model reaction to investigate different parameters such as effect
of solvent and duration, diverse bases, catalysts and their concen-
tration. Initially, the influence of different bases on 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 phenylacetylene and bromobenzene
in the presence of pyridine and imidazole (Table 1, entries 2 and
3). Furthermore, when the Sonogashira coupling reaction was
carried out using K2CO3, KOH, NaOH and Et3N the formation of
biphenyl increased from 25% to 96% (Table 1, entries 4–7). After
finding the best catalyst systems, we further optimized the reaction
conditions in the presence of Et3N. The experiments showed that
on decreasing the time from 20 h to 1 h, the same results were
obtained, with full conversion and 96% yield of biphenyl (Table 1,
entries 8–13). However, the yields dropped appreciably on decreas-
ing the time from 1 h to 0.25 h (Table 1, entries 14–16). From all
these experimental results and discussion it was concluded that
1 mmol Et3N is sufficient to achieve the complete Sonogashira
coupling reaction in 1 h at 25 ꢀC.
The catalytic reactions which can be carried out with a small
amount of expensive complexes are the most useful feature of
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A novel imidazolium-supported palladium–chloroglycine complex
Table 5. Sonogashira coupling reaction of different aryl halides with phenylacetylene in the presence of [Gmim]Cl–Pd(II) and Et3N as basea,c
Entry
1
Aryl halides
Ph-Br
Product
Time (h)
1
Yieldb (%)
96
TON
960
TOFc
960.00
2
3
4
p-NO2Ph-Br
p-OMePh-Br
p-MeCOPh-Br
1.5
1.5
2
94
92
93
940
920
930
626.66
613.33
465.00
5
1-Bromonaphthalene
1.5
90
900
600.00
6
7
Ph-Cl
2
3
86
83
860
830
430.00
276.66
p-NO2Ph-Cl
8
p-OMePh-Cl
3
82
820
273.33
9
p-MeCOPh-Cl
3
80
96
94
800
960
940
266.66
960.00
10
11
Ph-I
1
p-NO2Ph-I
1.5
626.66
(Continues)
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P. Karthikeyan et al.
Table 5. (Continued)
Entry
12
Aryl halides
Product
Time (h)
2
Yieldb (%)
94
TON
940
TOFc
p-BrPh-I
470.00
13
14
15
p-ClPh-I
2
2
2
93
90
90
930
900
900
465.00
450.00
450.00
p-OMePh-I
p-MeCOPh-I
aReaction conditions: arylhalide (1 mmol), phenylacetylene (1.2 mmol), triethylamine (1 mmol) and [Gmim]Cl–Pd(II) (0.1 mol%), with stirring at 25 ꢀC.
bYield determined by HPLC.
cAll the compounds were characterized by spectroscopy, 1 H NMR, mass and IR from authentic sample.[14]
synthetic reactions involving palladium complex. According to
the literature, Mohammad Bakherad[8] and co-workers obtained
a good yield in the Sonogashira coupling reaction of aryl
halide with phenylacetylene using 1-phenyl-1,2-propanedione-
2-oximethiosemi-carbazone-functionalized polystyrene resin-
supported Pd(II) complex (0.01 mmol) stirred at room temperature
for 3 h under aerobic conditions. Using ionic liquid-functionalized
phosphine-ligated palladium complex in the range between
0.01 and 0.02 mmol, Haihong Wu et al. observed an acceptable
rate in the Sonogashira coupling reaction.[10] Among the
previous reports, increasing the quantity of the catalyst can
improve the reaction yield and shorten reaction time. Initially,
when C&bond;C formation was carried out in the absence of
catalyst at ambient temperature, no product formed even after
48 h (Table 4, entry 1). Further, when the amount of catalyst
was increased from 0.025 to 0.075 mol%, the yield was increased
50–75% (Table 4, entries 2–4). However using 0.1 mol% of
[Gmim]Cl–Pd(II), biphenyl was obtained with 96% yield in 1 h
(Table 4, entries 5–10). A similar yield was achieved when increasing
the catalyst amount from 0.1% to 0.15 mol% (Table 4, entries 11
Table 6. Recycling of the catalyst for the reaction of bromobenzene with phenylacetylenea
Run
0
1
2
3
4
5
6
7
Yieldb (%)
96
96
93
93
90
89
87
86
aReaction conditions: bromobenzene (1 mmol), phenylacetylene (1.2 mmol), triethylamine (1 mmol) and [Gmim]Cl–Pd(II) (0.1 mol%), with stirring
at 25 ꢀC.
bYield determined by HPLC.
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A novel imidazolium-supported palladium–chloroglycine complex
are very important factors. For the comparative study, Sonogashira
coupling reaction was carried out with the model reaction under
optimized conditions in the presence of Pd/C catalyst. However, a
significant difference in Pd leaching was observed. Without exclusion
of air about 34% of the total palladium amount was lost from the
Pd/C and found in solution Atomic absorption spectroscopy (AAS)
compared to [Gmim]Cl–Pd(II), where no leaching was detected.
For those conformations, the [Gmim]Cl–Pd(II) catalyst was
collected after completion of the reaction and analyzed by the
P-XRD method; the diffraction patterns are given in Fig. 2. The
analysis specifies that [Gmim]Cl–Pd(II) does not undergo any
chemical and structural changes, thus proving its surface catalytic
activity towards the coupling reaction of bromobenzene with
phenylacetylene. On the other hand, presence of peaks due to
metallic palladium is noted in the P-XRD pattern of the complex
in the case of ’Pd(II); (Fig. 2). Moreover, surface and size of the
reused catalyst were captured by AFM. The surface of reused
palladium complex evidenced a rough topography and reduced
particle size (755 nm) (Fig. 3). However, the extracted product
was analyzed by P-XRD, which indicates the presence of a peak at
38.81 that provided evidence for ’no leaching’ of the complex.
Furthermore, Pd leaching was also studied by inductively coupled
plasma–atomic emission spectroscopy (ICP-AES), indicating that
the mixture contains less palladium than the limit of detection,
accounting for 0.1 mol% of the initially added amount of Pd. From
those three experimental results, we believe that the absence of
Pd leaching observed in the Sonogashira coupling reaction is due
to immobilized palladium in the amino acid-functionalized ionic
liquid binding site located on the surface, which acts as a ligand
through metal–ligand interaction. The anchoring of Pd species by
amino acid sites supported on ionic liquid minimizes catalyst
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 1,2-diphenylethyne as the main product (Scheme 1).
Figure 2. Powder X-ray diffraction patterns of the [Gmim]Cl–Pd(II)
complex: (a) before reaction; (b) after reaction (eighth run)
and 12). Therefore, the Sonogashira coupling reaction was
carried out at a molar radio of bromobenzene, phenylacetylene,
triethylamine and [Gmim]Cl–Pd(II) of 1:1.2:1:0.001mmol at 25 ꢀC.
The heterogeneous green catalytic copper-free Sonogashira
coupling was examined with a variety of haloarenes under the
reaction conditions identified above and exhibited wide
substrate tolerance. Representative results are summarized in
Table 5. It can be noted that a wide range of aromatic halides can
efficiently contribute in the Sonogashira coupling reaction. How-
ever, both electron-rich and electron-poor aryl halides could be
successfully converted to the desired products in 1–3 h at room
temperature. On the other hand, the reaction of aryl chlorides with
phenylacetylene is usually very slow with modulator yields.
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 bromobenzene with phenylacetylene for eight runs
to afford 1,2-diphenylethyne with 96–86% isolated yields (Table 6).
For practical application in the Sonogashira coupling reaction,
the lifetime of the heterogeneous catalysts and their reusability
Conclusion
In this study, for the first time we have introduced [Gmim]Cl–Pd
(II) as a catalyst for the Sonogashira coupling reaction with Et3N
in the absence of an organic co-solvent. Arylbromides and
iodides reacted efficiently with phenylacetylene at ambient
Figure 3. AFM image of 3-(amino(carboxy)methyl)-1-methyl-1 H-imidazol-3-ium chloride-supported palladium complex after eighth run
Appl. Organometal. Chem. (2012)
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P. Karthikeyan et al.
Scheme 1. Proposed catalytic mechanism
temperature in the presence of our catalyst. The procedure is
easy and does not require special precautions. All the reactions
were conducted in air without the use of an organic co-solvent.
The [Gmim]Cl–Pd(II) complex was shown to be superior to most
of the reported catalysts, with many advantages: facile synthe-
sis, thermal stability and structural versatility, easy handling,
catalytic performance in air at 25 ꢀC, without any additives, inert
atmosphere not required and without leaching of catalyst.
Moreover, the catalyst could be reused for seven consecutive
cycles without significant loss of its catalytic activity. These
advantages make the process highly valuable from the
synthetic and environmental points of view. Further investi-
gation on the application of this kind of catalyst is in progress
in our laboratory.
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We gratefully acknowledge the Management of VIT University for
providing required facilities and SAIF (IITM) for providing the
spectral data.
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2012)