Silica-supported palladium complex: An efficient, highly selective and reusable organic-inorganic hybrid catalyst for the synthesis of E-stilbenes

Article abstract of DOI:10.1016/j.apcata.2012.04.009

A novel, highly efficient and reusable palladium based catalyst has been synthesized by covalent grafting of diphenyldiketone-monothiosemicarbazone on silica gel followed by metallation with palladium chloride, and the resulting organic-inorganic hybrid material was found to be highly effective catalyst for Suzuki-Miyaura cross-coupling reaction of various aryl halides with alkenyl boronic acid to give stilbenes. The catalyst was characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray fluorescence (ED-XRF), BET surface area analysis, solid-state ¹³C CPMAS NMR spectroscopy, atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and elemental analysis. High turnover frequency, mild reaction conditions, high selectivity for E-stilbenes, and easy recovery and reusability of the catalyst renders the present protocol highly indispensable to address the industrial prerequisites and environmental concerns.

Full text of DOI:10.1016/j.apcata.2012.04.009

Applied Catalysis A: General 431–432 (2012) 33–41
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Silica-supported palladium complex: An efficient, highly selective and reusable
organic–inorganic hybrid catalyst for the synthesis of E-stilbenes
∗
R.K. Sharma , Amit Pandey, Shikha Gulati
Green Chemistry Network Centre, Department of Chemistry, University of Delhi, Delhi 110007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel, highly efficient and reusable palladium based catalyst has been synthesized by covalent graft-
ing of diphenyldiketone–monothiosemicarbazone on silica gel followed by metallation with palladium
chloride, and the resulting organic–inorganic hybrid material was found to be highly effective catalyst for
Suzuki-Miyaura cross-coupling reaction of various aryl halides with alkenyl boronic acid to give stilbenes.
The catalyst was characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spec-
troscopy, energy dispersive X-ray fluorescence (ED-XRF), BET surface area analysis, solid-state 13C CPMAS
NMR spectroscopy, atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and ele-
mental analysis. High turnover frequency, mild reaction conditions, high selectivity for E-stilbenes, and
easy recovery and reusability of the catalyst renders the present protocol highly indispensable to address
the industrial prerequisites and environmental concerns.
Received 7 March 2012
Received in revised form 3 April 2012
Accepted 5 April 2012
Available online 16 April 2012
Keywords:
Cross coupling reaction
Reusable catalyst
Silica gel
Immobilization
Microwave
© 2012 Elsevier B.V. All rights reserved.
Stilbenes
1
. Introduction
Palladium catalyzed Suzuki-Miyaura coupling reaction is among
heterogenized alternatives such as nanoparticle-supported, soluble
polymer-supported and various organic/inorganic polymer sup-
ported catalysts has engrossed immense attention because they
combine the advantages of both homogeneous and heterogeneous
catalytic systems [10–16]. Among various inorganic supports for
immobilizing palladium catalysts, silica is very promising because
of its high surface area, good thermal stability, ready availability
and economic viability, and relatively easy covalent modification
with organic or organometallic moieties.
Similar to recoverable catalysts, microwave-promoted synthe-
sis is also an area of escalating interest in both academic and indus-
trial laboratories since microwaves are efficient and non-polluting
mode of heating the reaction mixture [17–24]. So, the combina-
tion of microwave technology and heterogeneous catalysis is likely
to have a great impact on sustainable chemistry, and proved to be
a better catalytic system from both economic and environmental
view point. Recently, we have reported an optimized procedure for
preconcentration, determination and on-line recovery of palladium
using highly selective diphenyldiketone–monothiosemicarbazone
modified silica gel [25]. Following these results, and in con-
tinuation of our work on synthesis of inorganic–organic hybrid
materials, and their applications as metal scavengers, sensors,
and catalysts for various organic transformations [26–32], in
the present paper we investigated the catalytic activity of
silica supported Pd(II)diphenyldiketone–monothiosemicarbazone
the most widespread and highly selective transformations for the
synthesis of stilbenes, as these are the precursors for various
biologically active compounds, pharmaceuticals, liquid crystalline
materials, herbicides and conducting polymers. Over the past
few decades, wide range of palladium based homogeneous cata-
lysts have been used in this coupling reaction due to their high
selectivity [1–9]. In addition, several homogeneous catalysts have
been exploited for directing the stereochemistry of the reac-
tion products. However, despite these benefits and advancement,
homogeneous catalysis contributes only 20% in industrial pro-
cesses due to various drawbacks such as use of large amount
of catalyst, difficulty in purification of products and separation
of soluble catalyst from the reaction mixture. Moreover, these
homogeneous catalysts endow with the metal contamination of
products which may be harmful for human health as well as
for environment. Consequently, there is a huge demand for the
innovation and development of novel catalysts with superior
catalytic activities, lower costs, good recyclability and also less
pollutive to the environment. In this regard, the development of
∗ Corresponding author. Tel.: +91 011 27666250/9958313101;
fax: +91 011 27666250.
(Pd–DKTS–APSG) for the synthesis of stilbenes in microwave reac-
tion system.
E-mail address: rksharmagreenchem@hotmail.com (R.K. Sharma).
0
926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.04.009

3
4
R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
Scheme 1. Preparation of silica supported palladium catalyst (Pd–DKTS–APSG).
2
. Experimental
2.3. Catalyst preparation
2.1. Materials and reagents
Firstly, the surface modification of silica gel was per-
formed using a greener protocol [34] followed by grafting
of diphenyldiketone–monothiosemicarbazone (DKTS) on amino-
propylated silica gel (APSG) [25]. Then, the grafted silica gel,
DKTS–APSG (1 g) was refluxed with PdCl2 (0.4 mmol) in ace-
tone for 4 h. The dark brown solid was filtered off and washed
thoroughly with acetone until the washings were colorless. The
organic–inorganic hybrid catalyst (Pd–DKTS–APSG) thus obtained
was dried in a vacuum oven (Scheme 1).
3
-APTES (98%), silica gel (60–100 mesh) and trans-phenylvinyl
boronic acid were purchased from Sigma–Aldrich. Thiosemicar-
bazide, diphenyldiketone, and all other starting materials and
reagents used in the reactions were obtained commercially from
Spectrochem. Pvt. Ltd., India and used without purification. The
diphenyldiketone–monothiosemicarbazone (DKTS) was prepared
according to the reported procedure [33].
2
.4. General procedure for Suzuki-Miyaura cross coupling
2.2. Characterizations
reaction in microwave
Solid-state 13C cross-polarization magic-angle spinning
CPMAS) NMR spectra were recorded on Bruker DSX-300 NMR
A microwave vessel was charged with aryl halide (1 mmol),
(
trans-2-phenylvinyl boronic acid (1.5 mmol), DMF–H O (3:2, 5 mL),
spectrometer. Elemental analysis (CHN) was performed using
Elementar Analysensysteme GmbH VarioEL V3.00 instrument.
Powder XRD patterns were recorded on Bruker D8 ADVANCE X-ray
diffractometer using graphite monochromatized Cu-K␣ radiation.
Surface area was calculated using the BET method on Gemini-
V2.00 instrument (Micromeritics Instrument Corp.). Samples were
2
K CO (2.5 mmol) and catalyst (25 mg), and the whole reaction
2
3
◦
mixture was irradiated in microwave (120 W) at 110 C for 25 min
Scheme 2). After the completion of reaction, the catalyst was fil-
(
tered, and the reaction contents were subjected to multiple ethyl
acetate extractions. The combined filtrates were washed with sat-
urated sodium bicarbonate solution, and dried over anhydrous
sodium sulfate. The solvent was evaporated under reduced pres-
sure, and the products obtained were analyzed and confirmed by
GC–MS.
◦
outgassed at 100 C for 3 h to evacuate the physically adsorbed
moisture before measurement. Scanning electron microscopy
SEM) images were obtained using a ZEISS EVO 40 instrument.
(
The samples were placed on a carbon tape and then coated with
a thin layer of gold using a sputter coater. Qualitative analysis
of catalyst for metal was performed using energy dispersive XRF
spectrometer (Fischerscope X-ray XAN-FAD BC). The content of
palladium in the catalyst was determined using LABINDIA AA 7000
atomic absorption spectrometer. The Fourier transform infrared
3
. Results and discussion
.1. Solid state 13C CPMAS NMR spectroscopy
3
(
FT-IR) spectra were recorded on a Perkin-Elmer spectrometer
The presence of 3-aminopropyl group after functionalization of
−1
using KBr in the range of 4000–400 cm . Catalytic reactions were
carried out in Anton Paar multiwave 3000 microwave reaction
system equipped with temperature and pressure sensor. The
products obtained were analyzed and confirmed on an Agilent gas
chromatography (6850 GC) using mass selective detector (5975
MSD).
13
silica gel with 3-APTES is confirmed by solid state C NMR spec-
13
troscopy. The C CPMAS NMR spectrum of APSG (Fig. 1a) shows the
presence of three well resolved peaks at 9.44, 20.99 and 42.68 ppm
assigned to the carbons of the propyl group which authenticate the
synthesis of APSG [35]. The covalent linkage between the DKTS and
13
the organic moiety on the silica can also be examined by C CPMAS

R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
35
Scheme 2. Pd–DKTS–APSG catalyzed synthesis of E-stilbenes.
NMR spectroscopy. In 13C CPMAS NMR spectrum of Pd–DKTS–APSG
Fig. 1b), in addition to three peaks of propyl group, new promi-
(
nent peak appeared at 162 ppm which is assigned to carbon of C N
which clearly confirms the covalent grafting of palladium complex
on APSG. Some small peaks in the range of 90–140 ppm and at
1
95 ppm are attributed to aromatic carbons and C S, respectively.
3.2. Elemental and surface area analysis
BET surface area measurements were carried out to analyze the
grafting reactions. The surface area of the bare silica was approxi-
2
−1
mately 235.67 m g . The amine-functionalized silica (APSG) and
immobilized complex (Pd–DKTS–APSG) showed a surface area
2
−1
2
−1
of 152.04 m g
and 69.66 m g , respectively. In general, the
anchoring of organic or organometallic moieties onto the sil-
ica matrix obstructs the access of nitrogen gas molecules, thus
reducing its surface area. So, the reduction in surface area in the
sequence SG > APSG > Pd–DKTS–APSG confirms the functionaliza-
tion of silica gel with 3-aminopropyltriethoxy silane to give APSG,
and its subsequent modification with DKTS and Pd(II) ions to
yield the organic–inorganic hybrid catalyst (Pd–DKTS–APSG). The
results of elemental analysis of APSG (nitrogen wt.% = 2.20, carbon
wt.% = 6.60, hydrogen wt.% = 2.38) gives rise to the grafting capacity
−
1
of 1.57 mmol g , and C/N ratio was found to be ∼3 which is close
to the expected value thereby confirming the 3-APTES grafting on
silica gel.
3.3. XRD studies
Small angle X-ray diffraction patterns of modified silica (APSG)
and silica supported Pd catalyst are shown in Fig. 2. The observed
◦
pattern showed a broad peak at an angle 2Â = 22 which character-
ized the material with low crystallinity or the amorphous nature
of silica. The slight decrease in intensity was observed in the XRD
pattern of Pd–DKTS–APSG confirming the immobilization of DKTS
ligand, and its further metallation with palladium. This decrease
in intensity is attributed to the filling of the pores of silica surface
on metallation or it may be due to reduction in X-ray scattering
contrast between the channel wall of the silicate framework and
ligand. The overall XRD pattern of the catalyst was found to be sim-
ilar to modified silica gel, confirming that crystallinity of silica is
maintained after modification reactions.
Fig. 1. 13C CPMAS NMR spectrum of (a) APSG and (b) Pd–DKTS–APSG.

3
6
R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
3.5. SEM analysis
The morphology of the catalyst was characterized by scanning
electron microscopy. SEM micrographs are presented at two differ-
ent magnifications. SEM image at low magnification (238×) (Fig. 4a)
revealed that silica gel beads do not possess any cracks during the
preparation of catalyst confirming its good mechanical strength.
High magnification (27.60×) SEM micrograph (Fig. 4b) depicted the
uniform dispersion of palladium complex on the surface of silica
which is responsible for its high activity.
3.6. Catalytic activity tests
The optimization of catalytic conditions was carried out
employing the coupling of trans-2-phenylvinyl boronic acid with
p-bromoanisole. p-Bromoanisole was chosen as the test substrate
because it is electronically deactivated (+R-effect) toward oxidative
addition of the catalyst, and gives accurate assessment of catalytic
activity.
Fig. 2. XRD pattern of (a) APSG, (b) Pd–DKTS–APSG, and (c) reused Pd–DKTS–APSG.
3.6.1. Effect of base and solvent
To examine the effect of base on the catalytic activity of
Pd–DKTS–APSG, various bases (Et N, Na CO , K CO and NaHCO )
3
2
3
2
3
3
have been employed using series of solvents such as diox-
ane, toluene, H O, DMF, DMF–H O, and DCM (dichloromethane).
2
2
Selected results are presented in (Fig. 5). It was found that present
catalyst (Pd–DKTS–APSG) gave maximum conversion (96%) using
K CO as base in combination with polar solvent system, i.e.
2
3
DMF–H O (may be due to the high solubility of the substrates in
2
DMF–H O solvent system). As shown in Fig. 5, other combination
2
of solvents/bases gave lower conversion.
3.6.2. Effect of temperature and time
To study the effect of temperature and time on the activity of the
Fig. 3. ED-XRF spectrum of silica supported palladium catalyst (Pd–DKTS–APSG).
catalyst, model reaction was carried out at diverse range of temper-
◦
atures (25–120 C) for different intervals of time (5–25 min). The
3
.4. ED-XRF and atomic absorption spectroscopy
conversion of p-bromoanisole as a function of time and tempera-
ture is shown in Fig. 6. The results showed that at room temperature
no change in the conversion of p-bromoanisole was observed even
if the reaction was continued for 25 min. So, the temperature of
the reaction was raised, and found that maximum conversion of
To determine the metal loading of Pd–DKTS–APSG, the catalyst
was digested in 10 mL of nitric acid in a microwave digester system
for 10 min, and diluted sufficiently by double distilled water. The
resulting solution was then subjected to AAS for metal analysis. The
Pd content of the catalyst was found to be 0.7 wt.% of silica. Further
to support the above observation, the catalyst was also subjected
to energy dispersive X-rays fluorescence spectroscopy. The ED-XRF
spectrum of catalyst (Pd–DKTS–APSG) is shown in Fig. 3, and the
well resolved peak of palladium clearly confirms the presence of
palladium in the catalyst.
p-bromoanisole was obtained when the reaction was carried out at
10 C in microwave for 25 min.
◦
1
3
.6.3. Effect of mass of catalyst
The influence of catalyst mass on its activity was studied in
the range of 5–30 mg of Pd–DKTS–APSG using p-bromoanisole and
Fig. 4. SEM image of Pd–DKT–APS at (a) low magnification (238×) and (b) high magnification (27.60×).

R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
37
to 96% and the selectivity reached 100%. This is because on increas-
ing the amount of catalyst, number of active sites on the porous
surface of catalyst has increased.
3.7. Pd–DKTS–APSG catalyzed Suzuki-Miyaura cross coupling
reaction
In order to evaluate the scope of the present catalytic system,
cross coupling of trans-phenylvinyl boronic acid with various aryl
halides have been studied. The catalyst was able to activate the
carbon halogen bond of both substituted and un-substituted aryl
halides. In all the cases, E-stilbenes were formed depicting the high
selectivity of the present catalytic system. Both electron deficient
and electron rich aryl halides gave products in good yields with high
turnover frequency (TOF) values (Table 2). The present catalytic
system was also compared with some reported catalysts (Table 3)
[
36–40], and found that our organic–inorganic hybrid catalytic sys-
tem (Pd–DKTS–APSG) is better than the reported ones in terms
of yield, cost, reaction time, selectivity, turn over frequency and
reusability.
Fig. 5. Effect of base and solvent on conversion of p-bromoanisole (reaction con-
ditions: p-bromoanisole (1 mmol), phenyl vinyl boronic acid (1.5 mmol), catalyst
◦
(
25 mg), 110 C in microwave (120 W) for 25 min).
3.8. Plausible reaction mechanism
The proposed catalytic route is shown in Scheme 3. It is very
well known that in addition to nature of substrate, cross coupling
reaction is sensitive to both steric and electronic properties of
the catalyst. The present catalytic system (Pd–DKTS–APSG) was
found to be highly effective for activating the carbon halogen
bond of both substituted and un-substituted aryl halides to give
E-stilbenes. This outstanding activity and selectivity of the catalyst
has been attributed to the electronic properties of the DKTS ligand
(
ꢀ donation by N and S atoms) which stabilizes the palladium in
2 oxidation state. In addition, steric properties of the DKTS ligand
two bulky aryl groups) helps in reductive elimination step, and
hence maintained the stereoselectivity of the product.
+
(
3.9. Heterogeneity test
To confirm the heterogeneous nature of the catalyst, the filtra-
tion test was applied. During the reaction, catalyst was separated
from the reaction mixture by filtration (after 15 min). The filtrate
was allowed to react for additional 5–6 min and no increment in
conversion was observed. This confirms that the reaction did not
proceed after the removal of the catalyst. After the completion of
reaction, the liquid phase of the reaction mixture was collected by
filtration and tested with atomic absorption spectrophotometer.
Absence of palladium in the reaction mixture suggested that no
leaching of the catalyst was observed during the reaction.
Fig. 6. Effect of temperature and time on conversion of p-bromoanisole (reaction
conditions: p-bromoanisole (1 mmol), phenyl vinyl boronic acid (1.5 mmol), catalyst
(
25 mg), K2CO3 (3 mmol), DMF–H2O solvent, microwave (120 W)).
◦
phenyl vinyl boronic acid in DMF–H O solvent system at 110 C in
2
microwave. The conversion and yield during each catalyst upload
are shown in Table 1. When the catalyst mass was increased from
5
mg to 30 mg, the conversion of p-bromoanisole increased from 25
3.10. Recycling of catalyst
Table 1
After the completion of reaction, the catalyst was recovered sim-
a
Effect of mass of catalyst on its activity.
ply by filtration and then washed properly with DMF, water and
chloroform. The recovered catalyst was dried under vacuum oven
Amount of catalyst/ (mg (mol%))
Blank
Conversion (%)
Yield (%)
◦
–
25
45
70
95
96
96
–
22
41
68
88
91
91
at 100 C, and then used again in successive cycles (six) under iden-
5
1
1
2
2
3
(0.03)
tical reaction conditions (Table 4). The results showed that there is
no appreciable loss of catalytic activity. Comparison of IR and XRD
spectra of fresh and recovered catalysts suggests that the structural
properties of recycled catalyst remained unaltered after the reac-
tion as none of the vibrations change significantly. The catalyst was
recovered, recycled, and used for 6 consecutive trials without the
loss of its activity and selectivity.
0 (0.06)
5 (0.09)
0 (0.13)
5 (0.16)
0 (0.19)
a
Reaction conditions: p-bromoanisole (1 mmol), phenyl vinyl boronic acid
◦
(
1.5 mmol), K2CO3 (3 mmol), DMF–H2O solvent, 110 C in microwave for 25 min.

3
8
R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
Table 2
Pd–DKTS–APSG catalyzed Suzuki cross coupling reaction of aryl halides with trans-phenylvinyl boronic acid.
a
Entry
Aryl halide
Product
Conv.b (%)
Yieldb (%)
TOFc (h−1
)
1
I
100
95
1404
2
Br
96
92
1360
3
Cl
90
81
1197
4
H C
Br
94
88
1300
3
CH3
5
H CO
3
Br
96
91
1345
OCH3

R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
39
Table 2 (Continued)
Entry Aryl halide
Product
Conv.b (%)
Yieldb (%)
TOFc (h−1
)
6
O
2
N
Br
98
95
1404
NO2
O
C
7
97
92
1360
H C
Br
3
COCH3
O
C
8
98
94
1197
H
Br
CHO
Br
9
96
90
1330
O N
2
NO
2
Br
10
CH3
100
80
1182
CH3
a
b
c
◦
Reaction conditions: aryl halide (1 mmol), phenyl vinyl boronic acid (1.5 mmol), K2CO3 (3 mmol), catalyst (25 mg), DMF–H2O solvent, 110 C in microwave for 25 min.
Conversion and yield were determined by GC.
TOF (turn over frequency) = number of moles of aryl halide converted in to product/mol of active site/time.

4
0
R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
Table 3
Literature precedents for the synthesis of stilbenes.
Entry
Aryl halide
Catalytic system
Reaction conditions
Yield (%)
78
Ref.
[36]
◦
1
Br
Pd(dba)3 (dba-dibenzylidene
acetone)
Aryl vinyl iodide, 70 C, 3 h,
THF solvent.
2
3
Br
Br
Palladium acetate
Trans-phenylvinyl boronic
acid, 150 C, 5 min, H2O–TBAB,
Na2CO3
91
85
[37]
[38]
◦
OCH
OCH
Palladium-N-heterocyclic
carbene complex
Trans-phenylvinyl boronic
3
◦
acid, 80 C, 24 h, dioxane
solvent
4
5
Br
Br
3
2.5 ppm Pd
trans-phenylvinyl boronic acid,
46
[37]
[39]
◦
1
50 C, 5 min., H2O–TBAB,
Na2CO3
CHO
[Pd(C3H5)Cl]2 and tetrapodal
phosphane ligand
Trans-phenylvinyl boronic
100
◦
acid, 20 h Xylene, 130 C, K2CO3
Br
6
7
2.5 ppm Pd
Pd(dba)3
Trans-phenylvinyl boronic
acid, 150 C, 5 min, H2O–TBAB,
Na2CO3
26
72
[37]
[36]
◦
H C
3
◦
Br
CH
Aryl vinyl iodide, 70 C, 5 h,
3
THF solvent.
8
9
Br
Br
Br
Cl
CH
3
Pd(OAc)2
Trans-phenylvinyl boronic
acid, 150 C, 5 min,
H2O/EtOH/TBAB, Na2CO3
91
89
80
90
[37]
[37]
[39]
[40]
◦
COCH
3
3
2.5 ppm Pd
Trans-phenylvinyl boronic
◦
acid, 150 C, 5 min, H2O–TBAB,
Na2CO3
1
1
0
1
COCH
[Pd(C3H5)Cl]2 and tetrapodal
phosphane ligand
Trans-phenylvinyl boronic
◦
acid, 20 h Xylene, 130 C, K2CO3
Pd(dba)3 (dba-dibenzylidene
acetone) and benzoferrocene
Trans-phenylvinyl boronic
acid, 24 h, 1,4-dioxane, Cs2CO3
Table 4
Recycling of the catalyst.
a
Cycle
Conversion (%)
Yield (%)
TOF (h−1)
1
2
3
4
5
6
96
96
96
95
95
94
91
91
91
90
90
89
1345
1345
1345
1330
1330
1315
a
◦
Reaction conditions: p-bromoanisole (1 mmol), phenyl vinyl boronic acid (1.5 mmol), K2CO3 (3 mmol), catalyst (25 mg), DMF–H2O solvent, 110 C in microwave for
2
5 min.

R.K. Sharma et al. / Applied Catalysis A: General 431–432 (2012) 33–41
41
Scheme 3. Proposed reaction mechanisms.
4
. Conclusion
[11] H.-B. Pan, C.H. Yen, B. Yoon, M. Sato, C.M. Wai, Synth. Commun. 36 (2006)
473–3478.
12] A. Fihri, D. Cha, M. Bouhrara, N. Almana, V. Polshettiwar, ChemSusChem 5
2012) 85–89.
[13] A. Datta, K. Ebert, H. Plenio, Organometalllics 22 (2003) 4685–4691.
3
[
We have developed a novel, efficient and reusable silica based
(
organic–inorganic hybrid palladium-catalyst (Pd–DKTS–APSG) for
Suzuki-Miyaura cross-coupling reaction to yield E-stilbenes. The
supported catalyst displayed good activity and selectivity at low Pd
loading (0.7 wt.%). The supported catalyst could be easily separated
and recovered from the reaction mixture (by simple filtration) and
reused several times. The combination of advantages displayed by
the Pd–DKTS–APSG catalytic system such as: economic viability,
easy preparation, high catalytic activity, stability, reusability, and
no measurable Pd leaching, prove that the present catalyst should
be considered as a viable alternative in cross-coupling reactions on
efficiency, environmental concerns and economical grounds.
[
[
[
14] M. Heiden, H. Plenio, Chem. Eur. J. 10 (2004) 1789–1797.
15] K.C.Y. Lau, H. He, P. Chiu, P.H. Toy, J. Comb. Chem. 6 (2004) 955–960.
16] R. Sharma, S. Dhingra, Designing and Synthesis of Functionalized Silica Gels
and their Applications as Metal Scavengers, Sensors, and Catalysts: A Green
Chemistry Approach, LAP Lambert Academic Publishing, Germany, 2011.
17] R.K. Sharma, D. Rawat, Inorg. Chem. Commun. 17 (2012) 58–63.
18] R.K. Sharma, C. Sharma, I.T. Sidhwani, J. Chem. Educ. 88 (2011) 85–87.
[
[
[19] R.K. Sharma, S. Gulati, S. Sachdeva, Green Chem. Lett. Rev. 5 (2012) 83–87.
[20] R.K. Sharma, G. Ahuja, I.T. Sidhwani, Green Chem. Lett. Rev. 2 (2009) 101–105.
[
[
21] Y. Liu, C. Khemtong, J. Hu, Chem. Commun. (2004) 398–399.
22] K. Hayashi, S. Kim, Y. Kono, M. Tamura, M. Chiba, Tetrahedron Lett. 47 (2006)
171–174.
[23] R.K. Leadbeater, N.E. Mack, T.L. Kormos, Tetrahedron Lett. 47 (2006) 217–220.
[
[
24] F. Chanthavong, N.E. Leadbeater, Tetrahedron Lett. 47 (2006) 1909–1912.
25] R.K. Sharma, A. Pandey, S. Gulati, A. Adholeya, J. Hazard. Mater. 209–210 (2012)
285–292.
Acknowledgements
[26] R.K. Sharma, D. Rawat, G. Gaba, Catal. Commun. 19 (2012) 31–36.
[27] R.K. Sharma, C. Sharma, Catal. Commun. 12 (2011) 327–331.
[28] R.K. Sharma, C. Sharma, J. Mol. Catal. A: Gen. 332 (2010) 53–58.
The financial assistance from University Grant Commission,
Delhi, India is acknowledged. The authors also thank USIC-CLF, DU,
Delhi, India for NMR data; AIRF, JNU, Delhi, India for SEM analysis
and IISc, Bangalore, India for solid state NMR measurements.
[29] R.K. Sharma, C. Sharma, Tetrahedron Lett. 51 (2010) 4415–4418.
[30] R.K. Sharma, D. Rawat, J. Inorg. Organomet. Polym. 20 (2010) 698–705.
[31] R.K. Sharma, D. Rawat, J. Inorg. Organomet. Polym. 21 (2011) 619–626.
[32] R.K. Sharma, D. Rawat, P. Pant, J. Macromol. Sci. Pure Appl. Chem. 45 (2008)
394–399.
[
[
33] E. Offiong, Transit. Met. Chem. 20 (1995) 126–131.
34] A.M. Donia, A.A. Atia, W.A. Al-amrani, A.M. El-Nahas, J. Hazard. Mater. 161
References
(
2009) 1544–1550.
[
[
[
[
[
[
[
[
[
1] L. Yin, J. Liebscher, Chem. Rev. 107 (2007) 133–173.
2] O. Baudoin, Eur. J. Org. Chem. (2005) 4223–4229.
[35] S.B. Hartono, S.Z. Qiao, J. Liu, K. Jack, B.P. Ladewig, Z. Hao, G.Q.M. Lu, J. Phys.
Chem. C 114 (2010) 8353–8362.
[36] M.S. Kabir, A. Monte, M. Cook, Tetrahedron Lett. 48 (2007) 7269–7273.
[37] R.K. Arvela, N.E. Leadbeater, M.S. Sagi, V.A. Williams, J. Org. Chem. 70 (2005)
161–168.
[38] A. Tudose, A. Maj, X. Sauvage, L. Delaude, A. Demonceau, A.F. Noels, J. Mol. Catal.
257 (2006) 158–166.
[39] E. Peyroux, F. Berthiol, H. Doucet, M. Santelli, Eur. J. Org. Chem. (2004)
1075–1082.
3] A. Suzuki, Proc. Jpn. Acad. Ser. B: Phys. Biol. Sci. 80 (2004) 359–371.
4] J.H. Clark, D.J. Macuarrie, S.J. Tavernier, Dalton Trans. (2006) 4297–4309.
5] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457–2483.
6] A. Suzuki, J. Organomet. Chem. 653 (2002) 83–90.
7] R.B. Bedford, C.S.J. Cazin, D. Holder, Coord. Chem. Rev. 248 (2004) 2283–2321.
8] A.C. Frisch, M. Beller, Angew. Chem. Int. Ed. 44 (2005) 674–688.
9] S. Jana, B. Dutta, R. Bera, S. Koner, Inorg. Chem. 47 (2008) 5512–5520.
[10] Y. Li, X.M. Hong, D.M. Collard, M.A. El-Sayed, Org. Lett. 2 (2000) 2385–2388.
[40] M. Thimmaiah, X. Zhang, S. Fang, Tetrahedron Lett. 49 (2008) 5605–5607.