Palladium(II) supported on polycarbosilane: Application as reusable catalyst for Heck reaction

Article abstract of DOI:10.1016/j.molcata.2015.06.012

Heck reaction catalyzed by palladium(II) attached polycarbosilane is reported. Polycarbosilane (PCS), which is an organic-inorganic hybrid polymer containing both Si and C in its back bone structure, was synthesized by the polycondensation of trichloromethylsilane and trimethoxyvinylsilane in the presence of sodium metal. Palladium acetate was attached to the polycarbosilane (Pd-PCS) and its catalytic activity was investigated. Heck reaction in which C-C coupling between aryl halides or vinyl halides and activated alkenes in the presence of a base has been selected for the study. Palladium ions supported on PCS have been used as a catalyst for the first time and it efficiently catalyzed Heck reaction and an yield of 75-90% was obtained with different substrates. For comparison, catalytic activities of Pd ions supported on SBA-15, activated charcoal and amorphous silica were also investigated. Results indicate the superior activity of Pd-PCS.

Full text of DOI:10.1016/j.molcata.2015.06.012

Journal of Molecular Catalysis A: Chemical 407 (2015) 87–92
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Palladium(II) supported on polycarbosilane: Application as reusable
catalyst for Heck reaction
Kunniyur Mangala, P.S. Sinija, Krishnapillai Sreekumar∗
Department of Applied Chemistry, Cochin University of Science and Technology, Cochin 682022, Kerala, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Heck reaction catalyzed by palladium(II) attached polycarbosilane is reported. Polycarbosilane (PCS),
which is an organic-inorganic hybrid polymer containing both Si and C in its back bone structure, was
synthesized by the polycondensation of trichloromethylsilane and trimethoxyvinylsilane in the presence
of sodium metal. Palladium acetate was attached to the polycarbosilane (Pd-PCS) and its catalytic activity
was investigated. Heck reaction in which C–C coupling between aryl halides or vinyl halides and activated
alkenes in the presence of a base has been selected for the study. Palladium ions supported on PCS have
been used as a catalyst for the first time and it efficiently catalyzed Heck reaction and an yield of 75–90%
was obtained with different substrates. For comparison, catalytic activities of Pd ions supported on SBA-
15, activated charcoal and amorphous silica were also investigated. Results indicate the superior activity
Received 4 December 2014
Received in revised form 23 May 2015
Accepted 11 June 2015
Available online 17 June 2015
Keywords:
Polycarbosilane
Heck reaction
Palladium catalyst
Heterogeneous catalysis
of Pd-PCS.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
for materials which are used as solid supports in heterogeneous
catalysis.
Polycarbosilane (PCS) has considerable technological impor-
tance due to its high thermal, chemical and oxidative stability.
It is not hard to envision a variety of potential applications that
are opening up for these polymers in areas such as nanotech-
nology [1], surface science, catalysis [2–6], liquid crystals [7–9],
new ceramic materials [10–14], organic-inorganic hybrids etc. PCS,
which contains both Si and C in their back bone structure, have
been of particular importance as precursor to SiC [15–21]. PCS can
be prepared in one step from simple silane monomers or mix-
tures containing vinyl, halo or halomethyl moieties in the presence
of an active metal. Several investigators have explored the use of
alkali metals for the reductive coupling of silanes and vinyl silanes
[11–14,16,18–21]. The participation of vinyl groups produces par-
tial branching. The Wurtz type coupling reaction, which employs
alkali metals, can be used for the preparation of PCS. It gener-
Homogeneous catalytic processes often exhibit high activity and
selectivity, in most cases, but the catalyst-product separation is
generally nontrivial. In addition, the metal catalysts and ligands
can be very expensive. These limit the practical application of
many outstanding catalytic systems. Immobilization of analogues
of homogeneous catalysts on a solid support is one of the promising
ways to prepare well-defined catalytic systems, a task of great eco-
nomic and environmental importance [22–24]. Palladium catalysts
deposited over different types of solid supports such as silica matri-
ces, charcoal etc have been reported [25–28]. However, activated
charcoal and non-functionalized polymers have drawbacks such as
relatively low stability or lack of active functional groups for bind-
ing Pd ions and hence the inherent restrictions for reuse [28]. Since
C and SiO2 have only a small residual charge, their affinity for metal
ions will be weak. Silica is a favorable solid support, but if silica is
used directly, the main problem of these catalytic systems seems
to be the metal leaching from the support during the reaction even
though they adsorb back to the support after the completion of the
reaction [27]. Polymer supported transition metal ions have signif-
icant role as catalysts in various organic reactions [4,5,29,30]. The
metal ions are attached to the polymer support through a chemical
bond. This reduces the possibility of leaching of metal ions from the
solid support. Considering Pd ions as a homogeneous catalyst, they
easily lose catalytic activity by forming Pd clusters and also they
are highly expensive. A heterogeneous catalyst is desirable in this
ally leads to extensive crosslinking and appreciable Si Si and C
C
bonding in addition to SiC bonding [15–17]. A reasonable ceramic
yield is obtained after sufficient crosslinking which increases the
softening temperature and decreases the solubility. The highly
crosslinked nature of the PCS provides scope for high surface area
for the polymer [4,5]. High surface area is one of the main criteria
∗
Corresponding author. Fax: +91 484 2577595.
E-mail address: ksk@cusat.ac.in (K. Sreekumar).
http://dx.doi.org/10.1016/j.molcata.2015.06.012
1381-1169/© 2015 Elsevier B.V. All rights reserved.

88
K. Mangala et al. / Journal of Molecular Catalysis A: Chemical 407 (2015) 87–92
Scheme 1. Synthesis of polycarbosilane.
case, especially for recycling, though it is not always as reactive as
compared to homogeneous catalysts.
Palladium catalysis has achieved the status of an indispens-
able tool for both common and state-of-the art organic synthesis.
Among basic types of palladium catalysed transformations, the
Heck reaction and related chemistry occupies a special space.
Heck reaction is the catalytic arylation and alkenylation of olefins
[31–35]. The reaction presents one of the simplest ways to
obtain variously substituted olefins, dienes, and other unsaturated
compounds. Aryl, benzyl, and styryl halides react with olefinic com-
pounds in the presence of hindered amines and a catalytic amount
of palladium ions to form vinyl derivatives in which the aryl, ben-
zyl, or styryl group has replaced a vinyl hydrogen of the original
olefin. To satisfy both recyclability and reactivity, immobilization
of a reactive homogeneous catalyst was devised by binding the Pd
catalyst on a polymer. Polycarbosilane is an active support for the
heterogeneous catalysis. The PCS shows high thermal stability and
have crosslinked structure. By altering the monomers and reaction
time, it is possible to get sufficient crosslinking and active sites in
the polymer. The metal salts react with the active sites of the PCS
and stable bonds are formed between them, thus developing an
efficient heterogeneous catalyst. Pd(OAc)2 was chosen as Pd source
for the current study. For comparison, catalytic activities of Pd ions
supported on SBA-15 (Pd-SBA), activated charcoal (Pd-C) and amor-
phous silica (Pd-SiO2) were also investigated. Pd-PCS show high
stability, negligible metal leaching and can be reused with same
activity. This indicates the superiority of PCS with other supports
under consideration.
Scheme 2. Conversion of chloride groups of PCS to hydroxyl groups.
Scheme 3. Incorporation of palladium ion to PCS.
analyzer. The metal ion concentration was estimated using Thermo
Electron Corporation Atomic Absorption Spectrometer. 1H NMR
spectra were recorded on Bruker 400 MHz instrument with TMS
as the internal standard in CDCl3 (SAIF-CUSAT). In catalytic activity
study, all the reactions were analyzed, by HPLC on Shimadzu CLASS
´
˚
VP Ver 6.1. Column: Phenomenex Luna 5u C18 (2) 100 A, for yield
and purity of the products. Solvent ratio (CH3OH:H2O) was 75:25
with a run time of 30 min. The flow rate, detector wavelength and
the temperature were 1 mL/min, 254 nm and 28 ◦C, respectively.
2.3. Synthesis of PCS
In
108.75 mmol) was refluxed in anhydrous toluene (50 mL)
and stirred vigorously to make dispersion. mixture of
a 250-mL round-bottom flask, sodium metal (2.5 g,
2. Experimental
A
trichloromethylsilane (6.4 mL, 54.38 mmol) and trimethoxyvinyl-
silane (8.3 mL, 54.38 mmol) was added drop wise carefully
(Scheme 1). The reaction was highly exothermic. After the addition
of monomers, the reaction mixture was refluxed for 12 h. The
whole process was carried out in a fume hood and under Nitrogen
atmosphere. The reaction mixture was cooled and the suspension
obtained was filtered and washed initially with methanol, then
with water in a Soxhlet extractor for 24 h, and dried under vacuum.
Yield was 47%. Chlorine estimation was done by the modified
Volhard’s method [4,6,37].
2.1. Materials
Monomers, trichloromethylsilane and trimethoxyvinylsilane,
palladium acetate, SBA-15 and palladium(II) attached charcoal
were purchased from Sigma–Aldrich, USA. DMF, triethyl amine,
sodium, amorphous silica and sodium sulphate were purchased
from Loba Chemie Pvt. Ltd., India. Chloroform, dichloromethane,
diethyl ether, ethanol, methanol, toluene and all the substrates for
catalytic activity studies were purchased from Spectrochem Pvt.,
Ltd., India; and all the solvents were purified according to standard
procedures [36].
2.4. Preparation of hydroxyl substituted PCS
2.2. Characterization
PCS was treated with water to substitute chloro substituent with
hydroxyl groups. The reaction was conducted in a round bottom
flask; the polymer was refluxed in water for 24 h (Scheme 2). It was
cooled and the precipitate obtained was filtered and dried under
vacuum.
FT-IR spectra were recorded on JASCO model 4100 FT-IR spec-
trometer as KBr pellets. 29Si-CP-MAS NMR and 13C CP-MAS-NMR
spectra were obtained from NMR Research Center, IISc., Banga-
lore and National Chemical Laboratory, Pune. Thermogravimetric
analysis was done on PerkinElmer Diamond model Pyris 6 TG/DTA
system using Platinum as standard. Samples were heated under
nitrogen atmosphere from 50 ◦C-1000 ◦C at a rate of 20 ◦C/min. The
X- Ray Diffraction analysis was carried out using Rigaku (D-MAX
Cu-K␣) X-ray Photometer. The sample was scanned over the range
of 20–90◦ angles with an increment of 0.05◦ angle and with the rota-
tion speed of 5◦/min. (SAIF-CUSAT). Surface Area & porosity were
measured using Micromeritics TriStar 3000 V6.07 A Surface area
2.5. Preparation of polycarbosilane supported palladium ion
(Pd-PCS)
1 g of PCS was stirred in 15 mL of dry toluene for 12 h to swell.
Ethanolic solution of palladium acetate (1.35 g, 6 mmol) was added
drop wise to the swollen PCS and was stirred for 12 h under reflux
condition (Scheme 3). The reaction mixture was cooled, filtered,

K. Mangala et al. / Journal of Molecular Catalysis A: Chemical 407 (2015) 87–92
89
and washed with methanol in a Soxhlet extractor and dried under
vacuum.
2.6. Catalytic activity study
Heck reaction was considered as the model reaction to study
the catalytic activity of Pd-PCS. The optimum quantity of the cata-
lyst was found out first and the catalytic activity was generalized by
conducting the reaction with diverse sets of substrates. To optimize
the concentration of catalyst, the reaction between 1-iodo-4-
nitrobenzene and acrylonitrile was conducted in the presence of
Pd-PCS by varying the concentration as 2, 3, 5 and 10 mol%. Yield of
the reaction was analyzed in each case. General procedure for Heck
reaction: To a round bottom flask containing 3 mol% of Pd-PCS, mix-
ture of organic halide (1 equiv.), olefinic compound (1 equiv.) and
triethyl amine (1 equiv.) were added. DMF was used as the solvent.
A water cooled condenser was placed on the flask and stirred for
about 8 h at 100 ◦C. The reaction mixture was cooled, filtered and
washed initially with dichloromethane and then with water. The
filtrate was extracted with diethyl ether. The ether layer was col-
lected and dried over anhydrous sodium sulphate. It was filtered
and solvents were removed in a rotary vacuum evaporator. The
residue was recrystallized from dichloromethane.
Fig. 1. 29Si CP-MAS NMR spectrum of PCS.
For the comparative study of catalytic activity, Heck reaction in
the presence of Pd-SBA, Pd-C and Pd-SiO2 were also conducted. [Pd-
SBA and Pd-SiO2 were prepared by stirring an ethanolic solution of
palladium acetate (1.35 g of palladium acetate in 15 mL of ethanol)
with 1 g of SBA-15/SiO2 for 12 h under reflux condition. The reac-
tion mixture was cooled, filtered, and washed with methanol in
a Soxhlet extractor and dried under vacuum. The supports were
heated to 300 ◦C prior to use]. The reaction was conducted between
1-iodo-4-nitrobenzene and acrylonitrile in the presence of 3 mol%
of catalyst.
due to SiCH3 stretching, 1270 cm−1 corresponding to SiCH3 defor-
mation,1082 cm−1 due to CH2 wagging in SiCH2Si bond and
783 cm−1 due to SiCH3 wagging. 1032 cm−1 seen as superimposed
on 1082 cm−1 was assigned to SiO bonds. The peaks assigned to
SiOSi bonds (around 1040 cm−1) was observed since this peak
intensified with prolonged air exposure, the side chains of the poly-
mer might have got oxidized during the handling and recording
processes.
29Si CP-MAS NMR spectrum of PCS is shown in Fig. 1. Spec-
trum gives a clear idea about the structure of the polymer. Peaks
were mainly distributed in two regions. Peak around −10.45 ppm
corresponds to CH3SiCl(CH2)2 linkage and −48.77 ppm peak is of
SiSi linkage; formed by the head to head polymerization of the
monomers. A small peak at 18.79 ppm corresponds to Si O link-
age which might be formed by the oxidation of the polymer side
chains.
2.6.1. Recycling of catalysts
Recycling of the catalysts were performed as follows: The Heck
reaction between 1-iodo-4-nitrobenzene and acrylonitrile was car-
ried out by taking equimolar amounts of substrates and trimethyl
amine in a round bottom flask containing 3 mol% of catalyst. DMF
was used as the solvent and the reaction was carried out for
about 8 h at 100 ◦C. The reaction mixture was cooled and cata-
lyst was removed by simple filtration. It was washed thoroughly
with methanol, chloroform and acetone and dried under vacuum
for 24 h. The recovered catalyst was used again for carrying out the
reaction in each cycle.
Fig. 2 shows the 13C CP-MAS NMR spectrum of PCS. It exhibits
two major broad peaks at 6.03 and 14.45 ppm, which are mainly
assigned to the signal of SiSiCH3 units and CH2-CH2 respectively.
The absence of signal around 60 ppm indicates the absence of unre-
acted alkoxy group in the prepared polymer.
3. Results and discussion
In the TG curve (Fig. 3), 3% weight loss below 300 ◦C is attributed
to the vaporization of low molecular weight oligomers and phys-
ically adsorbed water from the polymer surface. From 300–800 ◦C
the main weight loss indicates that the polymer undergoes Kumada
rearrangement and releases gaseous products such as methane and
hydrogen during the conversion of the Si Si bond to Si C bond. No
obvious weight loss was observed in the range of 800–1000 ◦C. The
total weight loss of the polymer at 1000 ◦C was found to be only 14%.
High temperature stability is attributed to substantial crosslinking
in PCS [16].
3.1. Preparation of PCS
The preparation of PCS by the polycondensation of chlorosi-
lane and vinyl silane in the presence of a metallic reducing agent
has been demonstrated in Scheme 1. Trichloromethylsilane and
trimethoxyvinylsilane were used as monomers. The mixture of
monomers was refluxed with sodium in toluene for 12 h; polymer
was formed by Wurtz-type coupling reaction which led to the for-
mation of hyper branched PCS back bone with appreciable Si Si
and C C bonding, in addition to Si C bonding [12–14,18,38,39].
The quantitative estimation of chlorine in PCS was done by the
modified Volhard’s method. The result showed that 4.10 m.equiv./g
of chlorine was present in the polycarbosilane.
The FT-IR spectrum of the polymer showed the correspond-
ing peaks of PCS [20]. Peaks at 1453, 1270, 1082, 783 cm−1
could be clearly seen in the spectrum which corresponded to
the CHSiCH3 and SiC. The spectrum showed a peak at 2929 cm−1
which was corresponding to the CH stretching, 1635, 1453 cm−1
The XRD pattern of the PCS (Fig. 4) clearly reveals its amorphous
nature; which can be explained because of it’s highly crosslinked
structure.
From the spectral data, it is clear that the PCS has Si Si, Si C and
C
C linkage and also all the methoxy groups have been reacted to
form the polymer. Halide estimation implies the presence of chlo-
rine in polycarbosilane. The polymerization was conducted in an
oxygen free atmosphere. Hence the SiO linkage might be formed
by the oxidation of the polymer side chains.

90
K. Mangala et al. / Journal of Molecular Catalysis A: Chemical 407 (2015) 87–92
Fig. 5. 29Si CP-MAS NMR spectrum of Pd-PCS.
Fig. 2. 13C CP-MAS NMR spectrum of polycarbosilane.
Fig. 6. 13C CP-MAS NMR spectrum of Pd-PCS.
The metal content of the polymer was determined using AAS
technique. The AAS result showed that 4.28 m.equiv/g of palladium
ion was present on the polycarbosilane.
Fig. 3. TG curve of polycarbosilane.
29Si CP-MAS NMR spectrum of Pd-PCS is shown in Fig. 5. New
peaks in the region around −102.64 and −111.97 ppm correspond
to the PdOSi linkage. It is seen that there is a total up field shift of the
polycarbosilane peaks. Peak around −10.45 ppm has been shifted to
−22.15 ppm and −48.77 ppm to −68.34 ppm and small peak around
18.79 ppm was shifted to 7.77 ppm. This trend is explained due to
the presence of palladium ion attached to the polycarbosilane.
13C CP-MAS NMR spectrum of Pd-PCS is shown in Fig. 6. Sig-
nals around 130 ppm and −0.79 ppm are observed. Peak around
−0.79 ppm is due to the polycarbosilane and the former one ie,
130 ppm corresponds to the peaks of acetate moiety.
Fig. 4. X-ray diffraction pattern of polycarbosilane.
From the above data it could be confirmed that the palladium ion
4. Preparation of Pd-PCS
was attached to the PCS through Si
O Pd linkage and the acetate
moiety was also attached to the metal.
PCS was refluxed in water, to substitute the chloro groups
with hydroxyl groups (Scheme 2). The hydroxyl group substitu-
tion was confirmed from the infrared spectrum, which showed a
The thermogravimetric analysis of Pd-PCS shows very small
weight loss, which might be because of the evaporation of adsorbed
water molecule and low molecular weight fractions of the polycar-
bosilane.
Surface area of the prepared polycarbosilane and Pd-PCS were
determined by BET surface area analyzer. Results are shown in
Table 1. The surface area of both the PCS and Pd-PCS were found to
be high. The high surface area of PCS can be explained by its meso-
porous nature. The high surface area is a supportive aspect for the
application of PCS in catalysis.
peak around 3448 cm−1
.
The hydroxyl substituted PCS was allowed to swell in toluene.
Palladium acetate was added to it as an ethanolic solution and
stirred at reflux condition (Scheme 3). Pd-PCS was characterized
by FT-IR, 29Si-CP-MAS NMR, 13C CP-MAS NMR spectroscopic tech-
niques, TG-DTA, AAS and surface area analysis.
The FT-IR spectrum of the Pd-PCS showed the peak correspond-
ing to SiOPd at 980 cm−1
.

K. Mangala et al. / Journal of Molecular Catalysis A: Chemical 407 (2015) 87–92
91
Table 1
Table 4
Results of BET surface area analysis.
Metal content on solid supports.
Sample
Surface area (m2/g)
Catalyst
Pd(II) content (m. equiv./g)
BET
679
311
Langmuir
1171
480
Pd-PCS
Pd-SBA
Pd-SiO2
Pd-C
4.28
0.88
0.57
0.94
PCS
Pd-PCS
Table 2
Optimization of amount of the catalyst*
Table 5
Recycling of catalysts*
.
Entry
Mol (%) of the catalyst
Yield (%)
Catalyst
Yield (%)
1st cycle
1
2
3
4
2
3
5
10
83
92
93
98
2nd cycle
3rd cycle
Pd-PCS
Pd-SBA
Pd-SiO2
Pd-C
92
90
93
92
90
50
40
40
89
26
23
24
*
Catalyst- Pd-PCS and time 8 h.
*
Catalyst- 3% Pd-PCS, temperature 100 ◦C and time 8 h.
Table 3
Heck reaction with different substrates*
Entry
Organic halide
Olefinic compound
Yield (%)
J = 16 Hz), 7.43 (d, 2H), 7.20 (d, 2H), 6.41, 6.37 (d, 2H, J = 16 Hz), 3,80
(s, 3H), 2.37 (s, 3H); Pale yellow oil.
1
2
3
4
5
6
7
8
9
10
4- Iodotoluene
1-Iodo-4-nitrobenzene
4- Iodotoluene
1-Iodo-4-nitrobenzene
4- Iodotoluene
1-Iodo-4-nitrobenzene
4- Iodotoluene
1-Iodo-4-nitrobenzene
4-Iodobenzoic acid
4-Iodobenzoic acid
Acrylonitrile
Acrylonitrile
Styrene
Styrene
Methyl acrylate
Methyl acrylate
Methyl methacrylate
Methyl methacrylate
Acrylonitrile
83
92
75
79
77
80
79
83
86
90
Entry 7: (E)-Methyl 2-methyl-3-p-tolylacrylate, C12H14O2
LCMS ES+ (M++1) m/z: 191; FT-IR (KBr, cm−1): 3087, 2932, 1747,
1320, and 967; H1 NMR (400 MHz, CDCl3) ı: 8.15 (m, 1H), 7.89
(d,1H), 7.76 (m, 1H), 7.74 (d,1H), 7.25, 7.21 (d, 1H, J = 16 Hz), 3.54
(m, 3H), 2.51 (s, 1H) 1.94 (m, 3H). Oily in nature.
It is clear that Pd-PCS efficiently catalyzed the reaction, almost
75–90% yields were obtained for all substrates under consideration.
The product analysis gives an idea about the trans-selectivity of
catalyst.
In order to compare the catalytic activity of Pd-PCS, Heck
reaction in the presence of Pd-SBA, Pd-C and Pd-SiO2 were also con-
ducted. The metal ion content of the Pd-C, Pd-SBA and Pd-SiO2 were
determined using AAS technique. The results are listed in Table 4.
It is evident from the result that the metal ion attachments were
low compared to Pd-PCS and it might be because; palladium ions
were attached to the solid supports only by adsorption.
Methylmethacrylate
*
Reaction condition- equimolar conc. of aryl halide and olefinic compound in the
presence of 3 mol% of Pd-PCS at 100 ◦c and time 8 h.
4.1. Catalytic activity study
Palladium ions attached to the polymer were considered as the
catalytic sites and polycarbosilane as solid support. The amount
of catalyst was estimated in terms of the palladium ions with
respect to the substrates. The catalytic activity study was done
by conducting the Heck reaction in the presence of Pd-PCS. To
examine the effect of catalyst concentration, the reaction of 1-iodo-
4-nitrobenzene and acrylonitrile in the presence of Pd-PCS was
conducted. The study proceeded by conducting the reaction using
different amounts of Pd-PCS. The results of the study are given in
Table 2.
It was observed that, as the metal concentration was increased,
the rate of the reaction was also increased. From the results
obtained and by considering the expense of palladium salts, the
optimum concentration of catalyst was selected as 3 mol% with
respect to the aryl halide; and DMF as the solvent, 100 ◦C as reaction
temperature and time period of the reaction as 8 h.
4.1.1. Comparative study of catalytic activity
For the comparative study of catalytic activity, Heck reaction
was conducted between 1-iodo-4-nitrobenzene and acrylonitrile
in presence of 3 mol% of Pd-SBA, Pd-SiO2 and Pd-C.
Experiments were also carried out to examine the recy-
clability of catalysts, by conducting the Heck reaction of
1-iodo-4-nitrobenzene and acrylonitrile under optimized reaction
conditions. The results are entered in Table 5. The results indicate
that catalysts show almost similar activity in the first cycle. The
reaction proceeded smoothly for the three cycles when Pd-PCS was
used as the catalyst. But in the case of other catalysts, as the num-
ber of cycles increases the activity reduces. It may be because of
the leaching out of metal ions from the support in each cycle. As a
result, the product yield gradually decreased in successive cycles.
The AAS analysis of the recycled catalysts shows that the leach-
ing of Pd(II) ion from the PCS support was insignificant. But Pd-SBA,
Pd-SiO2 and Pd-C show significant leaching. The dramatic decrease
in the Pd dispersion during the reaction leads to a significant
decrease in catalytic activity of the catalysts in further cycles.
Pd-PCS shows high thermal stability, which may be neces-
sary for Heck reaction. The PCS is an active support so that when
Pd(OAc)2 was added a stable chemical bond was formed. The unfa-
vorable leaching was minimized because of this linkage.
The catalytic activity of Pd-PCS was generalized by conducting
the Heck reaction with diverse sets of substrates, which are listed
in Table 3. The products were known compounds and identified
by comparing the spectral data (FT-IR, 1H NMR spectra and mass
spectra by LCMS) and melting points with those reported. All the
reactions were analyzed by HPLC for yield and purity of the prod-
ucts. One of the benefits of the Heck Reaction is its outstanding trans
selectivity. The spectral data of selected entries are listed below.
Entry 1: (E)-3-p-tolylacrylonitrile, C10H9N
LCMS ES+ (M+-1) m/z: 142; FT-IR (KBr, cm−1): 3037, 2932, 2258,
1587, 1320, and 977; H1 NMR (400 MHz, CDCl3) ı: 7.39, 7.35 (d,
1H, J = 16 Hz), 7.49,7.33 (d, 1H), 7.22, 7.20 (d, 1H), 5.84, 5.80 (d, 1H,
J = 16 Hz), 2.38 (s, 3H); M. p.: 48 ◦C.
5. Conclusion
Entry 5: (E)-Methyl 3-p-tolylacrylate, C11H12O2
LCMS ES+ (M++1) m/z: 177; FT-IR (KBr, cm−1): 3055, 2930, 1747,
1346 and 987; H1 NMR (400 MHz, CDCl3) ı: 7.69, 7.65 (d, 1H,
Highly crosslinked PCS was successfully synthesized and char-
acterized. The study showed the application of PCS in the area

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K. Mangala et al. / Journal of Molecular Catalysis A: Chemical 407 (2015) 87–92
of heterogeneous catalysis. The cross linked nature increases the
surface area of the polycarbosilane, which is one of the main advan-
tages in catalysis. Heck reaction was considered for the catalytic
activity study of Pd-PCS. Reaction with a diverse set of substrates
was examined and good to excellent yield was obtained. Catalysts
such as Pd ions supported on SBA-15, activated charcoal and amor-
phous silica were also used in order to compare the catalytic activity
of Pd-PCS. Results indicate the superior activity of Pd-PCS.
In summary, the article demonstrates an environmentally
benign, economically friendly and sustainable Heck reaction,
employing Pd(OAc)2 supported on PCS. The catalyst was air-stable
and thermally stable to allow easy use and storage without any pre-
cautions and shows high recyclability, which would enable wide
application in various Pd-catalyzed reactions.
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