Synthesis and characterization of recyclable and recoverable MMT-clay exchanged ammonium tagged carbapalladacycle catalyst for Mizoroki-Heck and Sonogashira reactions in ionic liquid media

Article abstract of DOI:10.1016/j.molcata.2010.10.015

An efficient synthesis of an ammonium tagged carbapalladacycle 5, in modest yield, has been achieved. Further, the clay-nanocomposite 6 was prepared by ion exchange of 5 into clay interlayers as a new organic-inorganic hybrid catalytic system. The ionic t

Full text of DOI:10.1016/j.molcata.2010.10.015

Journal of Molecular Catalysis A: Chemical 334 (2011) 13–19
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Synthesis and characterization of recyclable and recoverable MMT-clay
exchanged ammonium tagged carbapalladacycle catalyst for Mizoroki–Heck and
Sonogashira reactions in ionic liquid media
Vasundhara Singh∗, Rajni Ratti, Sukhbir Kaur
Department of Applied Sciences, PEC University of Technology, Chandigarh 160012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 August 2010
Received in revised form 13 October 2010
Accepted 16 October 2010
Available online 5 November 2010
An efficient synthesis of an ammonium tagged carbapalladacycle 5, in modest yield, has been achieved.
Further, the clay-nanocomposite 6 was prepared by ion exchange of 5 into clay interlayers as a new
organic–inorganic hybrid catalytic system. The ionic tag of the ammonium supported carbapalladacycle
5 assists in the pillaring process and enhances the organophilicity of catalyst 6 in the interlayers of
clay. The catalytic activity in ammonium based ionic liquid [TMBA] NTf2 of both the homogeneous and
heterogeneous recyclable catalysts 5 and 6 respectively in micromolar concentration of palladium has
been tested for Mizoroki–Heck and Sonogashira reactions in good yields with high TON/TOF and negligible
metal leaching. Effect of solvent and temperature on the catalytic activity has also been examined.
© 2010 Elsevier B.V. All rights reserved.
Keywords:
Carbapalladacycle
MMT-clay
Organic–inorganic hybrid materials
Mizoroki–Heck
Sonogashira
1. Introduction
Palladium catalyzed C–C and C–heteroatom bond forming reac-
tions are firmly positioned as one of the most important tools in
Development of recoverable and recyclable catalysts for indus-
trial applications has become important from both environmental
and economical point of view and has been well reviewed in litera-
ture [1]. To achieve this objective several catalysts are anchored or
immobilized onto polymeric and inorganic supports [2,3]. Despite
the advantages and the progress, homogeneous catalysis has a
share of less than 20% in industrial processes because of the issues
related to recoverability and recyclability of expensive metal cat-
alysts. In contrast, heterogeneous catalysis exhibits the advantage
of easy separation of the catalyst from the products and can be
easily adapted to continuous flow processes [4,5]. However, het-
erogeneous catalysis lacks complete characterization, mechanistic
details regarding factors affecting activity and selectivity. Hence,
there is a need to synthesize homogeneous–heterogeneous cata-
lysts to overcome the drawbacks of each system and to combine
the advantages of both [6]. Successful methods include immobiliz-
ing or supporting the active homogeneous catalysts onto various
inorganic supports such as zeolites, mesoporous materials, alu-
mina, silica, clays and high surface carbons [7–9] which assists
in controlling reactivity, selectivity besides the advantage of easy
workability.
organic synthesis [10]. During the last decade very active systems
have been developed in order to improve the stability and efficiency
of palladium based catalysts [11]. Carbometallated PdII complexes,
particularly palladacycles have emerged as promising catalysts for
various cross-coupling reactions [12]. Of these the potential of
oxime derived palladacycles as catalyst precursors for important
carbon–carbon coupling reactions has been well explored [13].
The highlighting features of these palladacycles are their extraor-
dinary thermal stability, insensitivity to air or moisture, ready
and economic synthetic access and modulation of electronic and
steric properties by simple variations in structure. Several dimeric
chloro-bridged palladacycles derived from a wide variety of aro-
matic and aliphatic oximes from benzaldehyde, acetophenone and
benzophenone, pinacolone and acetylferrocene have been reported
and their catalytic activity checked in different cross-coupling pro-
cesses [14,15].
Previously, numbers of attempts have been made to immobilize
the active oxime carbapalladacycle onto to various supports like
silica [16], polystyrene [17], MCM-41, polystyrene–divinylbenzene
[18], periodic mesoporous organosilica (PMO) [19], alumina [20]
and recently Kaiser resin [21] in an effort to develop supported
Pd–ligand complexes thereby enhancing the recyclability of ligand
and reducing the metal leaching considerably.
Lately, reports of the use of ionic supported catalysts immobi-
lized in ionic liquids as efficient recyclable catalysts have appeared
∗
Corresponding author. Tel.: +91 172 2753263.
E-mail address: vasun7@yahoo.co.in (V. Singh).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.10.015

14
V. Singh et al. / Journal of Molecular Catalysis A: Chemical 334 (2011) 13–19
Fig. 1. Preparation of clay nanocomposite catalyst 6.
in literature [22]. The ionic support enhances the interaction and
immobilization of the tagged moiety in the ionic media resulting in
high turn over numbers, frequencies with negligible metal leaching
and has been recently reviewed in literature [23].
into the ammonium based ionic liquid-phase facile thus creating
a homogeneous supported catalytic system. Further, for the het-
erogenization of active catalytic species, the ammonium tagged
carbapalladacycle 5 has also been supported on to inexpensive and
readily available Na+-MMT clay by ion-exchange method to create
an organic–inorganic hybrid catalytic system 6. The catalytic activ-
ities of both in homogenous and heterogeneous phase have been
studied for Mizoroki–Heck and Sonogashira reactions.
Montmorillonite clay having a layered 2:1 structure, high cation
exchange capacity can be chemically modified by immobilization
involving a simple ion exchange of organic and inorganic moi-
eties which can be fine tuned as per industrial requirements and
are being considered as potentially cost effective and environmen-
tally benign nano-materials for the future [24,25], especially with
amines or quaternary ammonium salts which provides a simple
method for the preparation of organic–inorganic hybrid materials.
Recently, Kim et al. have reported the preparation of cationic nan-
oclays by immobilizing ionic liquids as a modifier in the interlayers
of clays [26]. A supported ionic-liquid film (SILF) of nanomet-
ric thickness containing bis (oxazoline)–copper complexes in clay
has been used as recoverable catalysts for enantioselective cyclo-
propanation reaction [27]. Tao et al. prepared palladium-sepiolite
catalysts by immobilizing Pd2+ on sepiolite using ionic liquid and
used them as efficient catalysts for hydrogenation of alkenes and
Heck reaction [28].
Previously, oxime carbapalladacycle with an ionophilic imida-
zolium tag and its heterogenisation with Al/MCM-41 was described
by Corma et al. [20] which showed unsatisfactory results for both
Mizoroki–Heck and Suzuki couplings due to the specific nature
of the imidazolium tag. In continuation to our program involv-
ing development of robust recyclable and recoverable catalysts
[29–31], we hereby present our work which involves designing the
Najera’s oxime carbapalladacycle by the introduction of an inert
ammonium tag to the main structure, making its immobilization
2. Experimental
2.1. Synthesis of ammonium tagged carbapalladacycle catalyst 5
The synthetic route adopted to prepare ammonium tagged car-
bapalladacycle is as shown in Scheme 1.
4-Hydroxyacetophenone was treated with hydroxylamine
hydrochloride to obtain the corresponding oxime 2 as a white
solid which on reaction with 1,5-dibromopentane gave compound
3. Carbapalladation of compound 3 with sodium tetrachloropal-
ladate at room temperature gave 4 as a green solid. The NMR,
IR, mass spectroscopic data of compound 4 is in agreement with
that reported in literature [20]. The ammonium pendant was then
appended to compound 4 using five fold excess of trimethylamine
in THF at 50 ◦C for 36 h, resulting in the formation of compound 5
as a greenish powder (overall yield 20%). IR (KBr, cm−1): 3443.2,
3183.7, 3023.8, 2939.3, 2862.4, 1635.0, 1578.8, 1559.5, 1456.3,
1376.3, 1334.0, 1263.0, 1206.8, 1097.8, 1034.7, 963.0, 907.8, 804.0,
737.9, 638.0, 603.2, 522.8. 1H NMR (400 MHz, DMSO): ı ppm: 7.19
(m, 1H), 7.07 (d, 1H, J = 7.76 Hz), 6.55 (d, 1H, J = 6.48 Hz), 3.95 (t,
2H), 3.34 (s, 2H), 3.05 (s, 9H), 2.15 (s, 3H), 1.75 (4H, s),1.42 (s, 2H);
13C NMR (400 Mz, DMSO): ı ppm: 162.9, 157.0, 153.6, 137.7, 129.0,
120.3, 109.5, 63.4, 53.5, 31.0, 28.4, 22.9, 22.4, 11.3. MS ESI+: Isotopic
distribution for M+-C16H38N2 compatible with 2 Pd and 2 Cl (%):
m/z 587.2 (0.453), 587.7 (0.997), 588.2 (1.722), 588.7 (3.241), 589.2
(4.827), 589.7 (6.27), 590.2 (7.728), 590.7 (8.612), 591.2 (8.97),
591.7 (7.88), 592.2 (8.27), 592.7 (5.417), 593.2 (5.66), 593.7 (3.059),
594.2 (2.629), 594.7 (1.337), 595.2 (1.110), 595.7 (0.725).
2.2. Preparation of clay nanocomposite catalyst 6
The complex 5 is intercalated into the clay interlayers to obtain
a heterogeneous catalyst as shown in Fig. 1. To the suspension of
the complex 5 (100.8 mg, 0.12 mmol) in CH2Cl2 (15 ml) was added
Na+-MMT clay (100 mg) in small portions with vigorous stirring at
room temperature and continued for 48 h. The resulting suspension
was filtered and the solid was exhaustively soxhlet-extracted with
dichloromethane (4 × 10 ml) to remove excess complex. The result-
Fig. 2. XRD patterns of (a) Na+–MMT clay, (b) catalyst 6.

V. Singh et al. / Journal of Molecular Catalysis A: Chemical 334 (2011) 13–19
15
O
N
N
1,5-dibromopentane,K2CO3
OH
NH2OH,NaOAc
H2O,reflux,1h
OH
O
Br
acetone,reflux,48h
3
HO
HO
Na2PdCl4,NaOAc
Methanol,72h
2
1
OH
2Br
(CH3)3N,THF
500C,36h
OH
Pd
O
Br
Pd
N
O
Cl
2
4
Cl
5
Scheme 1. Synthetic route for the preparation of ammonium tagged oxime carbapalladacycle 5.
ing product was dried under vacuum to get the clay nanocomposite
6, as a free flowing powder.
grated MS “MD 800” [TMBA] NTf2 [(trimethylbutylammonium
bis(trifluoromethylsulfonyl)imide] was prepared by quaterniza-
tion of trimethylamine with butyl chloride followed by anion
exchange with LiNTf2 [32].
2.3. Catalyst characterization
2.5. Typical experimental procedure for Mizoroki–Heck reaction
with catalysts 5 and 6
Palladium content of 5 as determined by AAS was found
to be 2.39 mmol/g. The carbon, nitrogen and hydrogen content
determined by elemental analysis is 32.78, 4.329 and 4.404%
respectively. The unmodified Na+–MMT clay and catalyst 6 were
characterized by using XRD, IR, BET and TGA analysis to determine
the structure, surface area and thermal stability respectively. The
powder XRD patterns of Na+–MMT clay and catalyst 6 are presented
in Fig. 2. The characteristic peak at 7.44◦ corresponds to d0 0 1 spac◦-
Catalyst 5 (0.1 mg, 0.005 mol% Pd)/catalyst 6 (0.2 mg, 0.005 mol%
Pd) was dissolved in [TMBA] NTf2 (0.5 ml) taken in a 25 ml
round bottom flask. To this were added iodobenzene (816 mg, 4.0
mmol), t-butyl acrylate (512 mg, 4.0 mmol), triethylamine (606 mg,
6.0 mmol). The mixture was magnetically stirred in a pre-heated oil
bath at 80 ◦C for 3 h. The solution was allowed to cool, extracted
with diethyl ether (5 × 5 ml) and the ethereal phase was con-
centrated, purified by column chromatography and analyzed by
GC–MS and 1H NMR. The catalyst was recycled seven times with
negligible loss of activity.
+
˚
ing of 11.86 A in case of Na –MMT clay. Similarly, the peak at 7.07
˚
corresponds to a d0 0 1 spacing of 12.49 A in case of catalyst 6 indicat-
ing expansion of the interlayers due to exchange of smaller Na+ ions
with the bulkier carbapalladacycle cation. The IR spectra of oxime 2
shows a characteristic C N stretching vibration of 1675 cm−1 and
the corresponding C N vibration in 4 was shifted to 1635 cm−1
indicating N–Pd coordination (Fig. 3). Further, the presence of a
band at 1636.5 cm−1 in the IR spectrum of catalyst 6, as shown in
Fig. 4, confirms the successful intercalation of catalyst 5 in the clay
interlayers. The nitrogen adsorption–desorption isotherms of MMT
and catalyst 6 at 77 K were evaluated using an adsorption analyzer.
The BET surface area and micropore volume increased from 11.89
to 14.37 m2/g and 0.0253 to 0.0566 cm3/g for MMT clay and cata-
lyst 6 respectively as given in Table 1, which further supports the
intercalation process. TGA analysis of catalyst 5 and 6 showed that
catalyst 5 was thermally stable up to 450 ◦C after which it degraded
rapidly while catalyst 6 showed thermal stability up to 700 ◦C which
is probably because the ionic liquid is sandwiched in the layers of
MMT clay in catalyst 6. In each case, the specimens were heated
from 50 to 750 ◦C at the rate of 10 ◦C/min under nitrogen flow.
2.5.1. (E)-tert-Butyl-cinnamate
1H NMR (400 MHz, CDCl3): ı ppm: 7.56–7.60 (d, 1H, J = 15.9 Hz),
7.49–7.52 (m, 2H), 7.36–7.38 (m, 3H), 6.35–6.39 (d, 1H, J = 15.9 Hz),
1.55 (s, 9H).
2.6. Typical experimental procedure for Sonogashira reaction
with catalyst 5 and 6
Catalyst 5 (0.1 mg, 0.047mol% Pd)/catalyst 6 (0.2 mg, 0.047 mol%
Pd) was dissolved in [TMBA] NTf2 (0.5 ml) taken in a 10 ml round
bottom flask and 4-iodoacetophenone (123 mg, 0.5 mmol),
3-ethynylbenzene (58 mg, 0.5 mmol), triethylamine (75 mg,
0.742 mmol) were added. The mixture was magnetically stirred in
a pre-heated oil bath at 80 ◦C for 12 h. The solution was allowed
to cool, extracted with diethyl ether (5 × 5 ml) and the ethereal
phase was dried over Na2SO4, filtered, concentrated and purified
by chromatography using hexane–ethyl acetate (8:2) to elute the
desired coupling product which was analyzed by GC–MS and 1H
NMR. The catalyst was recycled seven times without any loss of
activity.
2.4. Methods and materials
1H NMR was recorded in CDCl3 on a 400 MHz Bruker instru-
ment using TMS as the internal standard. IR spectra were recorded
on a Bio-Rad-Win-IR spectrometer. Na+-montmorillonite clay
(Na+–MMT) with cation exchange capacity of 120 meq/100 g clay,
was provided by Kunimine Co. Ltd., Japan. XRD analysis was
done using Rigaku D-Max IIIC using Ni-filtered Cu-Ka radia-
tion. BET surface area and pore volume were determined using
micromeritics autosorb automated gas sorption system. TGA anal-
ysis was carried out using TGA Mettler Toledo system. AAS
was determined by GBC Avanta instrument. Elemental analy-
sis was carried out using Analytischer Funktiontest vario EL II.
GC–MS had been recorded on a Fisons “GC 8000” with inte-
2.6.1. 1,2-Diphenyl ethyne
1H NMR (400 MHz, CDCl3): ı ppm: 7.48–7.42 (m, 4H), 7.34–7.27
(m, 6H).
2.7. Leaching tests
Leaching of catalytically active species was tested by allowing
the reaction to proceeded to less than 50% conversion. The product

16
V. Singh et al. / Journal of Molecular Catalysis A: Chemical 334 (2011) 13–19
Fig. 3. IR spectrum of catalyst 5.
Fig. 4. IR spectrum of catalyst 6.
was extracted with diethyl ether and this extracted product was
allowed to react for addition 48 h which was then analyzed by NMR
spectroscopy for any further progress of reaction.
change in number and pattern of aromatic protons from A2B2 to
ABM. Moreover, the shift in position of band at 1675 cm−1 in case
of 3 assigned for C N stretching to 1635 cm−1 further confirmed
the formation of the palladacycle. The simplest carbapalladacycle
has been reported to be a dimeric species because of the tendency
of palladium to form tetra coordinated complexes. In our case also
the molecular ion clusters arising from natural isotopic distribu-
tion of palladium and chlorine suggests the formation of a dimeric
species as inferred from the mass spectrum. On quarternization of
trimethylamine with compound 4 gave the ammonium tagged car-
bapalladacycle 5 wherein the presence of the ammonium tag was
confirmed by NMR (ı ppm: 3.05, s, 9H; 3.95, t, 2H) and mass spec-
tral analysis. The mass spectral analysis of 5 showed a molecular
ion clusters in consistence with the presence of dimeric species
which is contrary to the monomeric oxime carbapalladacycle with
an ionophilic imidazolium tag as described by Corma et al. [20].
The intercalation of complex 5 into clay interlayers by ion
exchange resulted in the formation of heterogeneous catalyst 6. As
expected, on intercalation the d0 0 1 interlayer spacing showed an
2.8. Recovery and reuse of catalyst 6
The recovery and reuse of catalyst was done on running a bigger
batch using 4.0–8.0 mmol of the reactants in a typical reaction pro-
cedure and vacuum filtered while hot. The remaining solid catalyst
6 was washed with dichloromethane (30 ml per 10 mg of the solid)
and was dried for 1 h under reduced pressure. The dry solid was
weighed and reused in next run by adding proportional amounts
of reactants.
3. Results and discussion
The synthetic route followed as shown in Scheme
1
resulted in moderate yield of the catalyst 5. The formation of
palladium–carbon bond in compound 4 has been confirmed by
Table 1
Physico-chemical characterization of Na+-MMT clay and clay nanocomposite 6.
Multipoint BET surface area (m2/g)
Pore volume (cm3/g)
Elemental analysis (AAS)
˚
Sample
Basal spacing (A)
Na+-MMT clay
Catalyst 6
11.86
12.49
11.89
19.83
0.0253
0.0566
–
Pd: 1.178 mmol/g

V. Singh et al. / Journal of Molecular Catalysis A: Chemical 334 (2011) 13–19
17
Table 2
100
Optimized results of Mizoroki–Heck reaction of variously substituted iodobenzenes
with t-butyl acrylate at 80 ◦C using catalyst 5 and 6 in [TMBA] NTf2.
80
60
40
20
0
S.No. Haloarene
Catalyst Time (h) Yielda (%) TON
TOF (h−1
)
catalyst 5
catalyst 6
1
2
3
4
5
Iodobenzene
4-Iodoanisole
4-Iodotoluene
5
6
3
3
94
95
18,800 6,266
19,000 6,333
5
6
12
12
92
92
18,400 1,533
18,400 1,533
5
6
12
12
87
89
17,400 1,450
17,800 1,483
1
2
3
4
5
6
7
Run
1-Iodo-3-nitrobenzene 5
3
3
96
96
19,200 6,400
19,200 6,400
6
Fig. 5. Recycling studies for Mizoroki–Heck reaction of iodobenzene and t-butyl
4-Iodo-acetophenone
5
6
3
3
97
98
19,400 6,466
19,600 6,533
acrylate.
a
Isolated yield.
100
80
˚
˚
increase from 11.86 A to 12.49 A and the BET surface area increased
from 11.89 m2/g to 19.83 m2/g as shown in Table 1. The IR spec-
tra of catalyst 6 showed the peaks characteristic of palladacycle
thus confirming the exchange of cationic catalyst 5. The extent of
exchange of 5 in clay was determined by the palladium content as
determined by AAS and found to be 1.0 meq/1 g of clay. TGA analy-
sis showed the thermal stability of 5 and 6 up to a temperature of
450 ◦C and 750 ◦C respectively.
catalyst 5
catalyst 6
60
40
20
0
Complex
5
in
homogenous
phase
and
6
in
1
2
3
4
5
6
7
homogenous–heterogeneous phase were checked for their
catalytic activity in Heck and Sonogashira couplings using [TMBA]
NTf2 as solvent. The immobilization of catalyst 5 and 6 in [TMBA]
NTf2 ionic liquid was confirmed by repeated extraction using
diethyl ether with negligible presence of both the catalysts in the
ethereal phase.
Mizoroki–Heck and Sonogashira reaction, as shown in
Schemes 2 and 3, were carried out under optimized conditions in
ionic liquid media resulting in excellent yield and conversion with
high TON and TOF of the desired products as confirmed by NMR
and GC–MS analysis. The optimization of reaction conditions was
done by varying the reaction temperature and catalyst loading.
The reaction proceeds at micromolar concentration of palladium at
lower temperature of 80 ◦C. Significantly, the Sonogashira reaction
gave good results without the use of copper (I) salts as co-catalyst
as compared to previous reports [33]. Alonso et al. carried out Sono-
Run
Fig. 6. Recycling studies for Sonogashira reaction of 4-iodoacetophenone and 3-
ethynylbenzene.
in both reactions indicating the stability of the catalyst 5 in ionic
liquid media and catalyst 6 due to immobilization in the interlayers
of clays and in ionic liquid media. Recoverability of the heteroge-
neous catalytic system 6 has been measured by the “Quantitative”
catalyst recovered after each cycle.
Kinetics of both the reactions was also studied using catalyst
5 and 6 under optimized conditions. The results are as shown in
Figs. 7 and 8.
The hot filtration test performed to ensure that the activity is
actually because of the heterogenized palladacycle or due to the sol-
uble palladium leached out from the supported catalyst suggested
that there is negligible leaching of catalytically active species which
indicates a heterogeneous catalysis operational in case of catalyst
6 as the filtered solution did not exhibit any further reactivity.
Good results were obtained for Sonogashira at room tem-
perature also though longer reaction time of 24 h is required
for complete conversion. Typical Mizoroki–Heck and Sonogashira
gashira reaction catalyzed by untagged oxime carbapalladacycle
о
using 0.1–0.5 mol% of catalyst at a higher temperature of 110
C
with no recyclability reports of catalyst [34]. Contrary to this, the
ammonium tagged carbapalladacycle 5 and 6 are recyclable and
required in a comparatively smaller amount of 0.047 mol% giving
good conversions at 80 ◦C. GC–MS analysis indicated the absence
of Glaser type homocoupling products. Further both reactions
were studied on various substrates containing electron releasing
and electron withdrawing groups to examine the versatility of the
catalyst 5 and 6. The results are summarized in Tables 2 and 3.
The analysis of the results in Tables 2 and 3 showed that the
coupling of deactivated electron-rich haloarenes took longer hours
while the reactions with activated electron poor iodoarenes were
accomplished in lesser time duration. High yields and excellent
TONs and TOFs were achieved in all the cases.
For recycling studies, the typical reactions as discussed in Sec-
tions 2.5 and 2.6, were carried out under optimized conditions.
After every cycle the catalytic system remains as a clear solu-
tion though there is an increase in viscosity due to the formation
of a quaternary ammonium salt by reaction of triethylamine and
the haloarene. Negligible loss of activity of catalysts 5 and 6 was
noticed even after seven cycles for both Mizoroki–Heck and Sono-
gashira reaction. The results for the recycling studies are as shown
in Figs. 5 and 6. No precipitation of palladium black was observed
100
90
80
70
60
catalyst 5
50
catalyst 6
40
30
20
10
0
0
1
2
3
Time,h
Fig. 7. Kinetic curves of Mizoroki–Heck reaction of iodobenzene and t-butyl acry-
late.

18
V. Singh et al. / Journal of Molecular Catalysis A: Chemical 334 (2011) 13–19
O
I
OR'
OR'
catalyst 5/6,800C
C
+
[TMBA]NTf2,Et3N
O
R
R
R'=CH3,t-Bu
R=alkyl,keto,
alkoxy,nitro etc
Scheme 2. Mizoroki–Heck reaction using catalysts 5 and 6.
I
catalyst 5/6,800C
[TMBA]NTf2,Et3N
C
C
C
C
R'
+
R
R'
R
R'=NH2,alkyl,
halogen,alkoxy
R=alkoxy,keto,
alkyl
Scheme 3. Sonogashira reaction using catalysts 5 and 6.
Table 3
Optimized results for Sonogashira of various haloarenes with aryl acetylenes at 80 ◦C using catalyst 5 and 6 in [TMBA] NTf2.
S.No.
1
Haloarene
Substituted acetylenes
1-Phenylacetylene
Catalyst
Time (h)
Yielda (%)
TON
TOF (h−1
159
)
Iodobenzene
5
6
12
12
90
92
1914
1957
163
2
3
4
5
6
7
8
Iodobenzene
3-Ethynylaniline
1-Phenylacetylene
3-Ethynylaniline
3-Ethynylaniline
3-Ethynylaniline
3-Ethynylaniline
3-Chloro-1-ethynylbenzene
3-Ethynylaniline
5
6
12
12
94
95
2000
2021
166
168
4-Iodo-acetophenone
4-Iodo-acetophenone
4-Iodotoluene
5
6
12
12
94
94
2000
2000
166
166
5
6
12
12
96
97
2042
2063
170
171
5
6
15
15
88
90
1872
1914
124
127
4-Iodoanisole
5
6
15
15
90
90
1914
1914
127
127
1-Iodo-3-nitrobenzene
1-Iodo-3-nitrobenzene
1-Bromo-4-nitrobenzene
5
6
12
12
97
99
2063
2106
171
175
5
6
12
12
90
93
1914
1978
159
164
9
5
6
24
24
80
82
1702
1744
70
72
a
Isolated yield.
100
90
80
70
60
50
40
30
20
10
0
reaction were also carried in toluene and water as reaction media
which gave products in satisfactory yield, however, there were
problems related to recoverability and formation of palladium
black in toluene.
catalyst 5
catalyst 6
4. Conclusion
In summary, catalyst 5 with enhanced ionophilicity has been
synthesized by anchoring it to a catalytically inert ammonium
tag which assists in improving the solubility of carbapalladacy-
cle in ionic liquid media and reduces the palladium leaching. The
ammonium tag facilitates the heterogenisation of catalyst 5 into
the layers of montmorillonite clay resulting in the formation of an
organic-inorganic hybrid catalyst 6. Micromolar concentrations of
recyclable 5 and recyclable and recoverable catalyst 6 efficiently
promote the Mizoroki–Heck and Sonogashira couplings both in
0
2
4
6
8
10
12
Time, h
Fig. 8. Kinetic curves of Sonogashira reaction of 4-iodoacetophenone and 3-
ethynylbenzene.

V. Singh et al. / Journal of Molecular Catalysis A: Chemical 334 (2011) 13–19
19
homogeneous as well as heterogeneous forms. In particular, Sono-
gashira reaction was performed under copper free condition with
no cross coupling side products.
[13] E. Alacid, D.A. Alonso, L. Botella, C. Najera, M.C. Pacheco, Chem. Rec. 6 (2006)
117–132.
[14] E. Alacid, C. Nájera, J. Org. Chem. 73 (2008) 2315–2322.
[15] E. Alacid, C. Nájera, Eur. J. Org. Chem. (2008) 3102–3106.
[16] C. Baleizao, A. Corma, H. Garcia, A. Leyva, Chem. Commun. (2003) 606–607.
[17] F.T. Luo, C. Xue, S.L. Ko, Y.D. Shao, C.J. Wu, Y.M. Kuo, Tetrahedron 61 (2005)
6040–6045.
Acknowledgements
[18] C. Baleizao, A. Corma, H. Garcia, A. Leyva, J. Org. Chem. 69 (2004) 439–446.
[19] A. Corma, D. Das, H. Garcia, A. Leyva, J. Catal. 229 (2005) 322–331.
[20] A. Corma, H. Garcia, A. Leyva, Tetrahedron 60 (2004) 8553–8560.
[21] E. Alacid, C. Najera, J. Organomet. Chem. 694 (2009) 1658–1665.
[22] N. Audic, H. Clavier, M. Maudit, J.C. Guillemin, J. Am. Chem. Soc. 125 (2003)
9248–9249.
The authors (RR and SK) are thankful to IFCPAR (3405-2), New
Delhi for fellowship and financial support, RIL (R&D), Vadodara and
RSIC, Chandigarh for the analytical data.
ˇ
[23] R. Sebesta, I. Kmentova, S. Toma, Green Chem. 10 (2008) 484–496.
[24] R.S. Varma, Tetrahedron 58 (2002) 1235–1255.
References
[25] R.A. Schoonheydt, Clay Clay Miner. 50 (2002) 411–420.
[26] N.H. Kim, S.V. Malhotra, M. Xanthos, Micropor. Mesopor. Mat. 96 (2006) 29–35.
[27] M.R. Castillo, L. Fousse, J.M. Fraile, J.I. García, J.A. Mayoral, Chem. Eur. J. 13 (2007)
287–291.
[28] R. Tao, S. Miao, Z. Liu, Y. Xie, B. Han, G. An, K. Ding, Green Chem. 11 (2009)
96–101.
[29] V. Singh, V. Sapehiyia, G.L. Kad, J. Mol. Catal. A: Chem. 210 (2004) 119–124.
[30] V. Singh, S. Kaur, V. Sapehiyia, J. Singh, G.L. Kad, Catal. Commun. 6 (2005) 57–60.
[31] R. Ratti, S. Kaur, M. Vaultier, V. Singh, Catal. Commun. 11 (2010) 503–507.
[32] C. Tiyapiboonchaiya, D.R. Mac Farlane, D.R. Sung, M. Foreyth, Macromol. Chem.
Phys. 203 (2002) 1906–1911.
[1] J.A. Gladysz, Pure Appl. Chem. 73 (2001) 1319–1324.
[2] C.E. Song, S.G. Lee, Chem. Rev. 102 (2002) 3495–3524.
[3] T.J. Dickerson, N.N. Reed, K.D. Janda, Chem. Rev. 102 (2002) 3325–3344.
[4] C. Wiles, P. Watts, Eur. J. Org. Chem. (2008) 1655–1671.
[5] G.J. Hutchings, J. Mater. Chem. 19 (2009) 1222–1235.
[6] A. Corma, H. Garcia, Top. Catal. 48 (2008) 8–31.
[7] V. Polshettiwar, A. Molnar, Tetrahedron 63 (2007) 6949–6976.
[8] A.P. Wight, M.E. Davis, Chem. Rev. 102 (2002) 3589–3614.
[9] B. Desai, C.O. Kappe, Top. Curr. Chem. 241 (2004) 177–208.
[10] X. Chen, K.M. Engle, D-Hui Wang, J-Quan Yu, Angew. Chemie. Int. Ed. 48 (2009)
5094–5115.
[33] E.M. Marza, A.M. Segarra, C. Claver, E. Peris, E. Fernandez, Tetrahedron Lett. 44
(2003) 6595–6599.
[34] D.A. Alonso, C. Najera, M.C. Pacheco, Adv. Synth. Catal. 345 (2003) 1146–1158.
[11] J. Tsuji, Palladium Reagents and Catalysts, Wiley, Chichester, 2004.
[12] J. Dupont, C.S. Consorti, J. Spencer, Chem. Rev. 105 (2005) 2527–2572.