Nano–silica supported palladium catalyst: Synthesis, characterization and application of its activity in Sonogashira cross–coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2017.10.006

This study deals about preparation of palladium(II) complex of 3,5–bis(2–benzothiazolyl)pyridine supported on nano silica functionalized with trimethoxysilylpropyl chloride, Pd(II)Cl₂–BTP@TMSP–nSiO₂. The synthesized heterogeneous cat

Full text of DOI:10.1016/j.jorganchem.2017.10.006

Accepted Manuscript
Nano–silica supported palladium catalyst: Synthesis, characterization and application
of its activity in Sonogashira cross–coupling reactions
Zahra Dehbanipour, Majid Moghadam, Shahram Tangestaninejad, Valiollah Mirkhani,
Iraj Mohammadpoor–Baltork
PII:
S0022-328X(17)30582-X
10.1016/j.jorganchem.2017.10.006
JOM 20126
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 23 July 2017
Revised Date: 26 September 2017
Accepted Date: 5 October 2017
Please cite this article as: Z. Dehbanipour, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor–Baltork, Nano–silica supported palladium catalyst: Synthesis, characterization and
application of its activity in Sonogashira cross–coupling reactions, Journal of Organometallic Chemistry
(2017), doi: 10.1016/j.jorganchem.2017.10.006.
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ACCEPTED MANUSCRIPT
Nano‒silica supported palladium catalyst: Synthesis, characterization
and application of its activity in Sonogashira cross‒coupling reactions
Zahra Dehbanipour, Majid Moghadam, Shahram Tangestaninejad,* Valiollah Mirkhani,*
Iraj Mohammadpoor–Baltork
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746–73441, Iran
Abstract‒ This study deals about preparation of palladium(II) complex of 3,5–bis(2–
benzothiazolyl)pyridine supported on nano silica functionalized with trimethoxysilylpropyl chloride,
Pd(II)Cl2–BTP@TMSP–nSiO2. The synthesized heterogeneous catalyst was characterized by FT‒IR,
UV–Vis spectroscopies, field emission scanning electron microscopy, energy dispersive X‒ray
analysis, transmission electron microscopy and elemental analysis. Furthermore, the Pd(II)Cl2–
BTP@TMSP–nSiO2 was found as a highly efficient catalyst in the Sonogashira cross‒coupling of aryl
halides (iodides, bromides and chlorides) with phenyl acetylene. This heterogeneous catalyst was easily
recyclable and reused several times without significant loss of reactivity. Finally, its catalytic activity
was compared with homogeneous catalyst to demonstrate the effect of supporting on the catalytic
activity.
Keywords: Sonogashira cross‒coupling; Palladium complex; Nano silica; Aryl halide.
Corresponding authors: Tel: +98-31-3793-4920; Fax: +98-31-36689732; E-mails: moghadamm@sci.ui.ac.ir (M.
Moghadam); mirkhani@sci.ui.ac.ir (V. Mirkhani); stanges@sci.ui.ac.ir (S. Tangestaninejad).
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1. Introduction
The palladium catalyzed C−C coupling reactions are considerably powerful tools in synthetic organic
chemistry [1]. These include Suzuki‒Miyaura, Mizoroki‒Heck, Sonogashira‒Hagihara, Stille,
Fukuyama and Negishi reactions [2]. Among them, the Sonogashira‒Hagihara cross‒coupling is one of
the most successful methods for the carbon–carbon bond forming between sp2‒hybridized carbon
atoms of aryl, heteroaryl, and vinyl halides and sp‒hybridized carbon atoms of terminal acetylenes
[3−10]. The products of these reactions have been widely used for the synthesis of substituted alkynes
[8] natural products, pharmaceutical compounds, polymeric materials [4] and optical materials [11-13].
The traditional procedure for the Sonogashira–Hagihara reaction requires the presence of Pd‒complex
of phosphines as a catalyst and copper iodide salt as a co‒catalyst. However, using copper salts as
co‒catalysts sometimes leads to the homo‒coupling reaction of terminal alkynes (Glaser‒type reaction)
upon exposure of the copper‒acetylide intermediate to air or other oxidizing agents [14−16]. However,
the separation of these unpleasant by‒products is difficult [17−19]. Therefore, several attempts have
been done to eliminate the copper co‒catalyst from the Sonogashira–Hagihara reaction [20,21]. Thus,
the design and synthesis of palladium catalysts for this reaction under copper free and mild reaction
conditions are highly desirable [22].
The palladium salts are expensive to purchase and therefore homogeneous palladium catalysts suffer
from disadvantages such as high price, low chemical and thermal stability, and difficulties in the
isolation and recovery of the catalyst from the reaction mixture. These problems limit the large‒scale
applications of these catalysts. A way to overcome these difficulties is to immobilize the palladium
catalysts on suitable supports. In this respect, several heterogeneous palladium catalysts have been
reported for Sonogashira C−C coupling reactions [2, 23−31]. Sardarian and co‒workers reported the
reaction of different aryl halides with alkynes in water in the presence of nanosilica dendritic polymer
supported palladium nanoparticles [32]. Also, our group reported the synthesis of mono‒, di‒, and
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trialkynylaromatics by Sonogashira cross‒coupling reaction in water by Pd nanoparticles immobilized
on nanosilica triazine dendritic polymer as catalyst [33]. Zhang and co‒workers reported the
Sonogashira coupling reactions between aryl halides and aryl acetylenes at 120 °C using a novel
magnetic composite nanoparticles anchored palladium nanocatalyst [34]. Also, an efficient copper and
solvent free Sonogashira cross-coupling reaction catalyzed by polymer supported 3-benzoyl-1-(1-
benzylpiperidin-4-yl)-2-thiopseudourea-Pd(II) complex, was reported [27].
One of the most applied supports is nano‒silica due to its excellent (chemical and thermal) stability,
economic aspects, good accessibility and reusability and good dispersion of catalytic active sites on it
[35].
Here, we report the preparation of palladium complex of bis‒thiazole ligand and investigation of its
catalytic activity in the Sonogashira C−C coupling reaction under copper ion and phosphorous ligand
free conditions. Also, the catalyst was supported on silica nanoparticles and characterized by different
analytical techniques. Finally, its catalytic activity was studied in the Siniogashira reaction and the
results were compared with homogeneous counterpart (Scheme 1).
Scheme 1. Sonogashira cross‒coupling catalyzed by Pd(II)Cl2–BTP@TMSP–nSiO2.
2. Experimental
2.1. Materials and methods
All the reagents were obtained from commercial sources. The FT‒IR spectra were recorded by a
JASCO 6300 spectrophotometer. The UV‒vis spectra were recorded by a JASCO V‒670
1
spectrophotometer. H NMR and 13C NMR (400 and 100 MHz) spectra were taken on a Bruker
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Avance 400 MHz spectrometer. The morphological features were obtained on a SIGMA VP‒500 field
emission‒scanning electron microscope (FE‒SEM), equipped with an energy dispersive X‒ray analysis
(EDAX) detector. Elemental analysis was performed on a LECO, CHNS‒932 analyzer. The palladium
content of the catalyst was determined by a Jarrell‒Ash 1100 ICP analysis. The transmission electron
microscopy (TEM) was carried out on a Zeiss EM10C transmission electron microscope operating at
100 kV. The silica nanoparticles were activated and chloropropylated by known procedures [36, 37].
2.2. Synthesis of Pd(II)Cl2‒BTB catalyst
In a 25 mL round bottom flask equipped with a condenser, a mixture of triphenylphosphite (TPP, 0.52
ml, 2 mmol), tetrabutylammonium bromide (TBAB, 0.88 g, 3 mmol), 2–aminothiophenol (0.212 ml, 2
mmol), and 1,3‒benzenedicarboxylic acid (0.164 g, 1 mmol) was prepared and stirred at 100 ºC for 120
min. At the end of the reaction, MeOH (15 ml) was added to the viscous solution to precipitate the
product. The resulting solid was filtered off and washed with cold MeOH to give the desired
1,3‒bis(2‒benzothiazolyl)benzene(BTB) ligand. Then, the residue was purified by recrystallization
from ethanol to afford the pure product [38]. 1H NMR (400 MHz, CDCl3) 8.83 (t, J = 1.6, 1H), 8.25
(dd, J = 7.6, 1.6 Hz, 2H), 8.15 (d, J = 8, 2H), 7.97 (dd, J = 8, 0.4 Hz, 2H), 7.66 (t, J = 8, Hz, 1H),
7.53‒7.58 (td, 2H, aromatic H ), 7.43‒7.47 (td, 2H, aromatic H), FT‒IR (KBr disc): 1560 (m), 1424
(m), 1315 (m), 954 (s), 893 (m), 752 (s), cm‒1.Elemental analysis: calcd for C20H12N2S2 (344) C, 69.76;
H, 3.49; N, 8.17; S, 18.62; found: C, 71.39; H, 3.79; N, 7.75; S, 18.66.
A mixture of 1,3‒bis(2‒benzothiazolyl)benzene, BTB, ligand (1 mmol) and PdCl2 (1 mmol) in EtOH
(3 mL) was stirred under reflux conditions for 5 h. After the homogeneous catalyst was synthesized, the
resulting solid was filtered off and washed with EtOH to give the desired Pd(II)Cl2‒BTB complex.
2.3. Synthesis of Pd(II)Cl2–BTP@TMSP–nSiO2 catalyst
First, in a 25 mL round bottom flask equipped with a condenser, a mixture of triphenyl phosphite
(TPP, 0.52 ml, 2 mmol), tetrabutylammonium bromide (TBAB, 0.88 g, 3 mmol), 2–aminothiophenol
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(0.212 ml, 2 mmol), and pyridine–3,5–dicaboxylic acid (0.164 g, 1 mmol) was prepared and stirred at
100 ºC for 120 min. At the end of the reaction, MeOH (15 ml) was added to the viscous solution to
precipitate the product. The resulting solid was filtered off and washed with cold MeOH to give the
desired 3,5–bis(2–benzothiazolyl)pyridine, BTP, ligand. Then, the residue was purified by
recrystallization from ethanol to afford the pure product [39].1H NMR (400 MHz, CDCl3) 9.42 (d, J =
2Hz, 2H), 9.06 (t, J = 2.4, 1H), 8.18 (d, J = 8.4, 2H), 8 (dd, J = 8, 0.4Hz, 2H), 7.59 (td, J = 8.2, 0.26
Hz, 2H), 7.47–7.51 (td, 2H, aromatic H), FT–IR (KBr disc): 1690 (s), 1417 (m), 1265 (s), 957 (m), 751
(s), 720 (s), cm–1. Elemental analysis: calcd for C19H11N3S2 (345.18) C, 66.08; H, 3.18; N, 12.17; S,
18.55; found: C, 66.32; H, 3.67; N, 12.35;S, 18.10.
For attachment of BTP ligand to nanosilica and preparation of BTP@TMSP–nSiO2, a mixture of
chloropropylated nanosilica (1 g), BTP ligand (0.24 g, 1 mmol) and NaI (0.17 g, 1.2 mmol) in dry
DMF (25 mL) was stirred under reflux conditions overnight. The yellow solid material was separated
by filtration, washed with CHCl3 (2×15 mL) to remove the unreacted 3,5–bis(2–
benzothiazolyl)pyridine ligand. The final nanocatalyst, Pd(II)Cl2–BTP@TMSP–nSiO2, was obtained
by addition of PdCl2 (0.33 g, 1 mmol) to silica supported BTP@TMSP–nSiO2 in ethanol (25 mL)
under reflux conditions for 24 h. The resulting catalyst was washed with ethanol (2×15 mL) to remove
the unreacted PdCl2, and finally dried under air.
2.4. General Procedure for the Sonogashira cross‒coupling of aryl halides with phenyl acetylene
catalyzed by pd(II)Cl2–BTP@TMSP–nSiO2
A round‒bottom flask was charged with aryl halide (1 mmol), phenylacetylene (1.1 mmol), DIPEA (1
mmol), Pd(II)Cl2–BTP@TMSP–nSiO2 (0.15 mol% Pd) and H2O/DMF (0.5 mL,1:1). The reaction
mixture was stirred at at room temperature for the time indicated in Table 2 and its progress was
monitored by TLC (n‒hexane/ethyl acetate, 6:1). After completion of the reaction, ethyl acetate (15
mL) was added to reaction mixture, and the catalyst was separated by centrifugation. The resulting
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mixture was washed with H2O (2×10 mL). Then, the organic layer was dried over anhydrous MgSO4
and the solvent was removed under reduced pressure. The residue was recrystallized from ether and
ethyl acetate (3:1) to afford the pure product (Table 2).
3. Results and discussion
3.1. Preparation and characterization of catalysts
Scheme 2 demonstrates the preparation route for homogeneous catalyst. As can be seen,
1,3‒bis(2‒benzothiazolyl)benzene (BTB) was prepared by the reaction of 2–aminothiophenol with
1,3‒benzenedicarboxylic acid in the presence of triphenylphosphite [38]. Then, the produced ligand
reacted with PdCl2 to give the Pd(II)Cl2‒BTB. The homogeneous catalyst was characterized by FT‒IR,
1H NMR, and UV‒vis spectroscopies. From the FT‒IR spectra presented in Fig. 1, the absorption band
at 1690 cm‒1 corresponds to the stretching vibration mode of imine bond in BTB. This band appears at
1585 cm‒1 in the FT‒IR spectrum of the synthesized homogeneous catalyst indicating the coordination
of the ligand to the metal.
In the UV‒vis absorption spectrum of the BTB ligand, two absorption peaks were observed at 260 and
300 nm (Fig. 2). Upon complexation, the Pd(II)Cl2‒BTB complex exhibits a peak at 400 nm, which is
pertained to d‒d charge transfer (Fig. 3).
The preparation path for heterogeneous catalyst is demonstrated in Scheme 3. First, the BTP ligand,
3,5–(bis(2–benzothiazolyl))pyridine, was prepared by the reaction of 2–aminothiophenol with 3,5–
pyridinedicarboxylic acid. Then, the prepared ligand was attached to the surface of 3‒chloropropylated
nanosilica and finally a heterogeneous catalyst, Pd(II)Cl2–BTP@TMSP–nSiO2, was obtained by the
reaction of the nanosilica supported BTP ligand with PdCl2. The prepared heterogeneous catalyst was
characterized by elemental analysis, FT‒IR and UV‒vis spectroscopies, SEM, TEM and ICP analyses.
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In the FT−IR spectrum, the bands at 1101 (Si−O−Si), 1427 (C=N) and 2955 cm‒1 (C−H stretching
vibration) confirmed the attachment of the catalyst on the surface of nano SiO2 (Fig. 4).
In the diffuse–reflectance UV–vis spectrum of the BTP@TMSP–nSiO2, the peak at 347 nm was
attributed to n→π∗ transitions in the BTP@TMSP–nSiO2 (Fig. 5). In the case of the Pd catalyst, the
peak at 485 nm was assigned to the d–d transition of Pd in Pd(II)Cl2–BTP@TMSP–nSiO2 (Fig. 6).
To study the morphology and particle size of the Pd(II)Cl2–BTP@TMSP–nSiO2, FE‒SEM images of
the catalyst were taken (Fig. 7). As can be seen, the nano‒SiO2 particles are spherical and have
diameters in the range of 24 nm (Fig. 8). Furthermore, the energy‒dispersive X‒ray spectroscopy
(EDX) obtained from SEM shows the presence of Pd atoms as well as, Si, N, S, and O atoms in the
texture of Pd(II)Cl2–BTP@TMSP–nSiO2 catalyst (Fig. 9). Also, the elemental mapping showed that
palladium species have been distributed uniformly in the catalyst texture (Fig. 10).
The catalyst was further characterized by transmission electron microscopy (TEM). According to the
TEM images, the Pd complex has been well dispersed within the nanosilica matrix (Fig. 11).
The amount of palladium deposited on the surface of nanosilica was determined by an inductively
coupled plasma (ICP) analyzer. The ICP analysis showed that the amount of Pd is about 0.31 mmol of
Pd/g of the heterogeneous catalyst. The nitrogen content of the catalyst, determined by CHN
ananalysis, was about 1.52%. According to this value, the amount of ligand on the nanosilica is 0.35
mmol g‒1.
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Scheme 2. The preparation route for homogeneous catalyst
Scheme 3. The preparation route for heterogeneous catalyst
3.2. Investigation of catalytic activity of both catalysts in the C–C coupling reactions
The catalytic activity of the heterogeneous catalyst was investigated in the Sonogashira‒Hagihara
cross‒coupling of aryl halides with aliphatic alkyne. As shown in Table 1, the reaction conditions such
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as kind of base and solvent, and the amount of catalyst were optimized in the coupling of
4‒iodoanisole with phenylacetylene in the presence of Pd(II)Cl2–BTP@TMSP–nSiO2 catalyst as a
model reaction (Table 1).
First,
a
wide range of bases such as NaOH, Na2CO3, K2CO3, NEt3 and DIPEA
(N,N‒diisopropylethylamine) were screened, and amongst them, DIPEA (1 mmol) was found to be the
most efficient base both in terms of reaction time and yield. Note that in the absence of base, only 15%
of the corresponding product was produced. This shows that the presence of base is crucial in this
reaction (entries 1-6). Lower amount of base (0.75 mmol) gave lower yield but increasing it to 1.5
mmole had no significant effect on the product yield (entries 7 and 8).
To study the effect of the solvent, different solvents including H2O, DMF, THF, EtOH, H2O/DMF (1:1)
and H2O/EtOH (1:1) were used as reaction media in the presence of Pd(II)Cl2–BTP@TMSP–nSiO2 at
room temperature and the highest yield obtained in H2O/DMF (1:1)(entries 5 and 10-14).
Finally, the effect of the catalyst amount on the yield of the desired product in model reaction was
investigated, and the best result was obtained with 0.15 mol% of the palladium catalyst (entries 15-17).
In the absence of catalyst, no product was detected in the reaction mixture (entry 18). Consequently,
from the observations summarized in Table 1, we conclude that 0.15 mol% of the catalyst, DIPEA (1
mmol) as the base, in H2O/DMF (1:1) at room temperature, are the appropriate reaction conditions for
this transformation (Table 1). To study the effect of immobilization of Pd species on its catalytic
activity, the model reaction was carried out using 15 mol% of PdCl2 as catalyst. The results revealed
that the homogeneous PdCl2 is less efficient than heterogeneous Pd(II)Cl2–BTP@TMSP–nSiO2 (entry
19).
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Table 1. Optimization of conditions for the Sonogashira cross‒coupling of 4‒iodoanisole with
phenylacetylene catalyzed by Pd(II)Cl2–BTP@TMSP–nSiO2.a
Entry
1
Catalyst amount
(mol%)
Base (mmol)
NaOH (1)
Solvent
H2O/DMF
H2O/DMF
H2O/DMF
H2O/DMF
H2O/DMF(1:1)
H2O/DMF(1:1)
H2O/DMF(1:1)
H2O/DMF(1:1)
‒
Time
(h)
6
Yield
(%)b
15
0.15
2
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.3
Na2CO3 (1)
K2CO3 (1)
NEt3 (1)
6
6
6
2
2
2
2
2
2
3
5
5
5
2
5
5
5
2
32
34
81
95
15
67
96
23
81
76
51
60
72
95
60
57
0
3
4
5
DIPEA (1)
DIPEA (0)
DIPEA (0.75)
DIPEA (1.5)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
DIPEA (1)
6
7
8
9
10
11
12
13
14
15
16
17
18
19c
H2O
DMF
THF
EtOH
H2O/EtOH(1:1)
H2O/DMF
H2O/DMF
H2O/DMF
H2O/DMF(1:1)
H2O/DMF(1:1)
0.06
0.04
0
0.15
33
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aReaction conditions: 4‒iodoanisole (1 mmol), phenylacetylene (1.1 mmol), base (1 mmol), Pd(II)Cl2–
BTP@TMSP–nSiO2, solvent (0.5 mL), room temperature.
bIsolated yield.
cThe PdCl2 was used as catalyst.
Under the optimized reaction conditions, various aryl iodides, bromides and chlorides were
cross‒coupled with phenylacetylene in the presence of Pd(II)Cl2–BTP@TMSP–nSiO2 at room
temperature to give the desired products in high yields (Table 2, entries 1–7). As expected; aryl iodides
were found to be more reactive than aryl bromides and chlorides.
In order to show the effect of supports on the catalytic activity, some of the reactions were repeated
using the 0.15 mol% of Pd(II)Cl2‒BTB complex (Table 2). The same trend observed for the
heterogeneous catalyst was also observed for its homogeneous counterpart. Comparison of the turnover
frequencies (TOFs) of both catalysts showed that the homogeneous catalyst is more reactive than the
heterogeneous one. But the main disadvantage of the homogeneous catalyst is its lack of recoverability
and reusability in the catalytic experiments.
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Table 2. Sonogashira cross‒coupling of aryl halides with phenylacetylene catalysed by Pd(II)Cl2–
BTP@TMSP–nSiO2.a
Entry
X
I
R1
H
R2
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Time (h)b
2
Yield (%)b,c
96
TOF (h‒1)b
320
1
2
3
4
5
6
7
I
4‒MeO
H
2 (1.5)
4
95 (97)
95
316 (422)
158
Br
Br
Br
Cl
Cl
4‒MeO
Ac
4 (3)
4 (3)
7 (5)
7 (5)
91 (90)
93 (94)
85 (83)
89 (90)
152 (200)
155 (207)
81 (111)
85 (120)
H
4‒MeO
aReaction conditions: aryl halides (1 mmol), phenylacetylene (1.1 mmol), DIPEA (1 mmol), Pd(II)Cl2–
BTP@TMSP–nSiO2 (0.15 mol% Pd), H2O /DMF (0.5 mL) at room temperature.
bThe numbers in the parentheses refer to homogeneous catalyst.
cIsolated yield.
The proposed mechanism is demonstrated in Scheme 4. The first step is activation the catalyst and
producing the chloride free catalytic species. Then, aryl halide is added to this active complex via an
oxidative‒addition process. The third step is addition of phenylacetylene and formation of a Pd-
acetylide complex. The final step is formation the product via a reductive‒elimination process and
releasing the catalyst for the next catalytic cycle.
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Scheme 4. Proposed mechanism for the Sonogashira coupling catalyzed by Pd(II)Cl2–BTP@TMSP–
nSiO2
3.3. Catalyst recovery and reuse
As mentioned above, the homogeneous catalyst is not reusable but the main advantage of
heterogeneous catalysts is their recovery and reuse. This property is important for industrial
applications of catalysts. Therefore, the reusability of the catalyst was examined in the reaction of
4‒iodoanisole with phenylacetylene under the optimized conditions. After completion of the reaction,
the heterogeneous catalyst was separated, dried and reused for six consecutive trials without any
remarkable loss of its catalytic activity (Fig. 12). Furthermore, The amount of palladium leaching from
the Pd(II)Cl2–BTP@TMSP–nSiO2 catalyst was determined by ICP analysis. It was observed that only
trace amounts of Pd are leached in the first run.
a
4. Conclusion
In conclusion, we have catalyzed the Sonogashira cross‒coupling of aryl halides (iodides, bromides,
and chlorides) with phenylacetylene. This manner uses homogeneous and nano‒silica supported
palladium(II) complex derived from 3,5–bis(2–benzothiazolyl)pyridine (BTP) as catalysts. Both
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homogeneous and heterogeneous catalysts were applied in the Sonogashira cross‒coupling with
excellent yield. As expected, aryl iodides and bromides were more reactive than chloride ones. Despite
the higher catalytic activity of the homogeneous catalyst, it could not be reused even one time while the
heterogeneous catalyst can be recovered and reused, several times without significant loss of its
activity.
Acknowledgements. The support of this work by The Research Council of the University of Isfahan is
acknowledged.
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Polyhedron (2017) http://dx.doi.org/10.1016/j.poly.2017.08.032
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Fig. 1. The FT–IR spectra of: a) Pd(II)Cl2‒BTB; b) BTB ligand
Fig. 2. The UV–vis spectrum of the BTB ligand
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Fig. 3. The UV–vis spectrum of the Pd(II)Cl2‒BTB complex
Fig. 4. The FT–IR spectra of: a) TMSP–nSiO2; b) BTP@TMSP–nSiO2; c) Pd(II)Cl2–BTP@TMSP–
nSiO2
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Fig. 5. Diffuse–reflectance UV–vis spectrum of the BTP@TMSP–nSiO2
Fig. 6. Diffuse–reflectance UV–vis spectrum of the Pd(II)Cl2–BTP@TMSP–nSiO2
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Fig. 7. SEM images of catalyst.
Fig. 8. Particle size distribution of catalyst
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Fig. 9.EDX spectrum of catalyst
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Fig. 10. Elemental Mapping of The catalyst
Fig. 11. TEM image of catalyst
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Fig. 12. Reusability of the Pd(II)Cl2–BTP@TMSP–nSiO2 catalyst in the reaction of 4‒iodoanisole
with phenylacetylene
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u A new palladium complex supported on nano‒silica was prepared u This heterogeneous
catalyst was used for Sonogashira C-C coupling reaction u The results of heterogeneous
catalyst was compared with homogeneous counterpart u The heterogeneous catalyst was
reusable.