Synthesis and characterization of a host (a new thiol based dendritic polymer)-guest (Pd nanoparticles) nanocomposite material: An efficient and reusable catalyst for C-C coupling reactions

Article abstract of DOI:10.1039/c6ra16704g

The catalytic activity of a new thiol based dendritic polymer immobilized on nano silica containing palladium nanoparticles was studied in C-C coupling reactions. In this manner, functionalized silica nanoparticles were reacted with 1,3,5-benzenetricarbonyl and then with 1,2-ethanedithiol. Finally, this new dendritic material was used as host for carrying of Pd nanoparticles. Thermogravimetric and elemental analyses are in a proper correlation and confirm the successful synthesis of the dendritic polymer. The characterization of the catalyst by transmission electron microscopy, EDX and elemental mapping, show a uniform dispersed, nano-scaled Pd particles in denderimer's cavities and also on the surface functional groups. This insoluble nanosilica thiolated dendritic polymer-supported Pd nanoparticles, showed a set of favorable properties to be used as a heterogeneous and reusable catalyst in the Suzuki-Miyaura and Heck C-C coupling reactions.

Full text of DOI:10.1039/c6ra16704g

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Synthesis and characterization of a host (A new
thiol based dendritic polymer)ꢀguest (Pd
nanoparticles) nanocomposite material: An
efficient and reusable catalyst for C‒C coupling
reactions
sCite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
Maryam Zakeri, Majid Moghadam,* Valiollah Mirkhani,* Shahram
Tangestaninejad, Iraj Mohammadpoor−Baltork, Zari Pahlevanneshan
www.rsc.org/
The catalytic activity of a new thiol based dendritic polymer immobilized on nano silica containing
palladium nanoparticles was studied in CꢀC coupling reactions. In this manner, functionalized
silica nanoparticles were reacted with 1,3,5ꢀbenzenetricarbonyl and then with 1,2ꢀethanedithiol.
Finally, this new dendritic material was used as host for carrying of Pd nanoparticles.
Thermogravimetric and elemental analyses are in a proper correlation and confirm the
successful synthesis of the dendritic polymer. The characterization of the catalyst by
transmission electron microscopy, EDX and elemental mapping, show a uniform dispersed,
nano−scaled Pd particles in denderimer's cavities and also on the surface functional groups. This
insoluble nanosilica thiolated dendritic polymerꢀsupported Pd nanoparticles, showed a set of
favorable properties to be used as a heterogeneous and reusable catalyst in the Suzuki−Miyaura
and Heck CꢀC coupling reactions.
for the encapsulated particles by different methods such as
covalent bond formation, electrostatic interactions, hydrogen
Introduction
Dendrimers are a group of nanosized, three dimensional
polymers and a class of macromolecules having highly
branched architecture.1 This family of polymers is considered as
bonding and etc.9,25
Palladium nanoparticles (Pd−NPs), consisting of only several or
tens of atoms, are novel catalytic materials, also have a number
one of the best synthetic molecules, which suggest perfect of other applications, including hydrogen storage,26 sensing,27
coatings, polymer membranes,28 and fuel cells.29
properties, such as high degree of branching units, high density
Pd nanoparticles are excellent catalysts for hydrogenation,30
of facial functional group, nanosized scale, internal cavities and
dehydrogenation31 and also coupling reactions such as
also high ability of monodispersion of metallic nanoparticles.2−5
Due to these specific characteristics, dendrimers have potential
applications in various high technologies, such as
pharmaceutical, biomedical and industrial uses.6, 7
Dendrimers are synthesized by stepwise growth from core to
first and second or maybe more generations,8 thus designing a
new dendrimer with new interior and surface functional groups
is a tricky and challenging issue. Dendrimer bearing higher
generations are almost spherical and the cavities inside the
dendrimers are approximately in the range of nanometer,9,
which can be used as a host for encapsulation of nanoparticles,
mostly transition metals, such as Pd,11−13 Cu,14−16 Au,17−19 Ag,20
Pt,21, 22 and Ru.23, 24
Multiple internal and external functional groups enable the
dendrimer to act as proper host for a various range of ions and
molecules. These functional groups can easily act as a stabilizer
Department of Chemistry, Catalysis Division, University of
Isfahan, Isfahan, 81746–73441 (Iran) Fax: +98–31–36689732;
Tel: +98–31–37934920. E–mail: moghadamm@sci.ui.ac.ir,
mirkhani@sci.ui.ac.ir
carbon−carbon,32 carbon−sulfur33 and carbon‒nitrogen.34
The recovery and reusability of this precious metal catalyst
represent a key issue for the sustainable development of any
catalytic applications. For this purpose, palladium nanoparticles
have been supported by a variety of conventional and
non−conventional
metal−organic frameworks,39 anthracene derivatives,40 ion
exchange and
resins,41 ligands,42 surfactants,43,44
supports,
such
as,
polymers,35−38
dendrimers.45,46 The strong interactions between the palladium
and soft sulfur based donors, make sulfur−containing supports
highly efficient stabilizers for nanoparticles.47−49 The size and
morphology of the resulting palladium nanoparticles depend on
several different reaction conditions. These conditions include
the surfactant used, the type and amount of reducing agent
employed, the reaction time and the properties of stabilizing
agent.50, 51
10
In continuation of our previous works on the application of
dendriticꢀbased catalysts in organic synthesis,11,14,52ꢀ57, here we
wish to report the synthesis of a host (a new thiol based
dendritic polymer)ꢀguest (Pd nanoparticles) nanocomposite
material and its application as catalyst for the Suzuki–Miyaura
and Heck CꢀC coupling reactions (Scheme 1).
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DOI: 10.1039/C6RA16704G
was cooled to 0 °C and stirred overnight. The solid material was
filtered, washed overnight with hot tetrahydrofuran (THF) in a
Soxhlet extractor. Then dried in a vacuum oven at 60 °C.
Nano−Silica Supported Thiolated Dendritic Polymer (G1)
BCC1−nSiO2 (1 g) in dimethylformamide (DMF) (12 mL) was
treated with 1,2−ethanedithiol (8.11 mmol, 0.7 mL) and DIPEA
°
(8 mmol, 1.4 mL) at 80 C for 16 h. The solid material was
filtered and washed overnight with hot ethanol in a Soxhlet
extractor and dried in a vacuum oven at 60 °C.
Scheme 1. Suzuki–Miyaura cross−coupling and Heck reacꢀons catalyzed by Pdnp−nSTDP
BCC2−nSiO2
Experimental
G1 (1 g) was added slowly to
a
solution of
Materials and reagents
1,3,5−benzenetricarbonyl trichloride (2.4 g, 9 mmol) and
DIPEA (9 mmol, 1.55 mL) in THF (20 mL). The reaction
All commercially available reagent grade chemicals were
purchased from Merck, Fluka and Sigma–Aldrich. All reagents
and solvents were used without further purification. FT−IR
spectra were recorded on a Jasco 6300D instrument in the range
of 400–4000 cm−1. Thermal gravimetric analysis (TGA) was
recorded on a Mettler TG50, under air flow at a consistent
heating of 5 °C min−1 in the range of 0ꢀ600 °C. Elemental
analysis was obtained on LECO CHNS−932 analyzer. The
X−ray photo−electron spectroscopy (XPS) measurements were
performed on XPS–Auger Perkin Elmer 8025ꢀBesTec electron
°
mixture was cooled and stirred at 0 C for 16 h. The reaction
mixture was filtered and the solid was washed overnight with
hot THF in a Soxhlet extractor. The BCC2−nSiO2 was dried in
a vacuum oven at 60 °C.
Nano−Silica Supported Thiolated Dendritic Polymer (G2 or
nSTDP)
To a solution of BCC2−nSiO2 (1 g) in DMF (20 mL),
1,2−ethanedithiol (9.5 mmol, 0.8 mL) and DIPEA (9.5 mmol,
1.65 mL) were added slowly and the reaction mixture was
spectrometer, using
a
Gammadata−scienta ESCA200
hemispherical analyzer equipped with an Al (Kα = 1486.6 eV)
X−ray source. The Pd content of the catalyst was measured by
an inductively coupled plasma optical emission spectrometry
(ICP−OES), via a Jarrell−Ash 1100 ICP analyzer. Scanning
electron microscopy images were performed on a Hitachi
S−4700 field emission−scanning electron microscope
(FE−SEM). Transmission electron microscopy (TEM)
measurements were carried out on a Philips CM10 analyzer
operating at 100 kV. Substances were identified and quantified
by gas chromatography (GC) on an Agilent GC 6890 equipped
with a 19096C006 80/100 WHP packed column and a flame
ionization detector (FID). In GC experiments anisole was used
as internal standard.
°
stirred at 80 C for 16 h. The resulting nano−silica supported
dendritic polymer (G2 or nSTDP) was filtered and washed with
hot ethanol overnight in a Soxhlet extractor and dried in a
vacuum oven at 60 °C.
Nano−Silica Thiolated Dendritic Polymer Supported Palladium
Nanoparticles (Pdnp−nSTDP)
Initially, Na2PdCl4 solution was prepared by mixing and
dissolving of PdCl2 (240 mg, 1.36 mmol) and NaCl (176 mg, 3
mmol) in methanol (10 mL), under stirring at room temperature
for 24 h and then filtered. Methanol (40 mL) and nSTDP (1 g)
°
was added to this solution. The slurry was then stirred at 60 C
for 24 h. After cooling the mixture to room temperature,
sodium acetate (0.76 g, 9.28 mmol) was added and stirred for 1
h. The solid was filtered, washed with methanol, water and
acetone continuously, to remove the unreacted precursors, and
finally dried in vacuum and Pdnp−nSTDP catalyst (1.09 g) as a
dark brown solid was prepared. Palladium analysis (ICP): 0.14
mmol Pd/ g catalyst. Average particle diameter: 3.6 ± 0.5 nm
(based on TEM and particle size analyses).
The procedure for the preparation of nanosilica thiolated
dendritic polymerꢀsupported Pd particles (Pdnp−nSTDP) was as
follows:
Propylthiol−Functionalized Nano−Silica (PT−nSiO2)
(
3−Mercaptopropyl)trimethoxysilane (8.5 mL) was added
dropwise via a syringe to a stirred solution of activated nano‒
silica (3 g) in dried toluene (50 mL) under reflux conditions for
12 h. The reaction medium was cooled to room temperature and
filtered. The solid was washed overnight with dried toluene by
soxhlet extractor to remove the unreacted starting materials.
The white solid was dried in a vacuum oven at 110 °C.
Typical Procedure for Suzuki–Miyaura Cross−Coupling
Catalyzed by Pdnp−nSTDP
Aryl halide (1 mmol), phenylboronic acid (1.1 mmol), K2CO3
(1.5 mmol) and the Pdnp−nSTDP catalyst (5 mg, 0.07 mol%)
were added to 3 ml of DMF/H2O (2:1). The reaction mixture
was stirred at desired temperature under air atmosphere. The
results are summarized in Table 3. The yields were quantified
by GC analysis. After the end point, the solution was filtered
and the products were extracted with ethyl acetate (3×10 mL).
BCC1−nSiO2
To a solution of 1,3,5−benzenetricarbonyl trichloride (2.65 g,
10 mmol) and diisopropylethylamine (DIPEA) (10 mmol, 1.7
mL) in anhydrous THF (10 mL) was slowly added the
previously synthesized PT−nSiO2 (2 g).The reaction mixture
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The organic phase was washed with water (2×10 mL), dried the characteristic bands for C─Haliph appear at 1450 and 2950
over anhydrous Na2SO4 and concentrated in vacuum to afford cm−1.11 In the FT−IR spectra of BCC1−nSiO2, G1,
the pure product.
BCC2−nSiO2 and G2 (Fig. 1b–e), in addition to the above
mentioned vibrations, the bands at 1690–1710 cm−1 (C=O) is a
good indication for the presence of carbonyl groups on the
nano−silica.59
Typical Procedure for Heck Reaction Catalyzed by Pdnp−nSTDP
Aryl halide (1 mmol), styrene (1.1 mmol), K2CO3 (1.5 mmol)
and Pdnp−nSTDP (10 mg, 0.14 mol% Pd) were added in 3 mL
of DMF/H2O (1:2). The reaction mixture was stirred at 95 C
°
under an air atmosphere for desired time summarized in Table
5. The progress of the reaction was tracked by GC. After
completion, the reaction mixture was cooled, poured in water
and extracted by diethyl ether (2×10 mL). The organic phase
was washed with water (3×10 mL) and dried over anhydrous
MgSO4. After evaporation of the solvent the pure product was
afforded.
Results and discussion
Preparation and characterization of nanosilica thiolated
dendritic polymerꢀsupported Pd particles (Pdnp−nSTDP)
The first step for the synthesis of nanosilica thiolated dendritic
polymer was modification of the activated nanosilica with
(3−mercaptopropyl)trimethoxysilane, to obtain the thiol
functionalized nanosilica (PT−nSiO2).58 The addition of 1,3,5ꢀ
benzenetricarbonyl trichloride (BCC) to the surface−attached
propylthiol nanosilica was carried out at 0 °C, to substitute only
one of the chlorine atoms to achieve BCC1−nSiO2. In the next
step, BCC1−nSiO2 was thiolated via addition of
1,2−ethanedithiol to prepare G1. The G2 was achieved by
Fig. 1. FT-IR spectrum of: a) PT−nSiO2, b) BCC1− nSiO2, c) G1, d) BCC2−nSiO2 and
e) G2
The TGA survey scan was run at 5 °C per minute. The TGA
curve of PT−nSiO2, BCC1−nSiO2, G1, BCC2−nSiO2 and G2,
over the temperature range from 0 to 600 °C shows a double
steps descending, which indicates a weight loss occurred. The
first step is due to loss of residual water in the porous sample
and the second step reflects the removal of organic moieties on
the surface. The TGA features are imaged in Figure 2.
addition
of
1,3,5ꢀbenzenetricarbonyl
trichloride
and
1,2−ethanedithiol, successively (Scheme 2).
Fig. 2. TGA spectra of: a) PT−nSiO2; b) BCC1−nSiO2; c) G1; d) BCC2−nSiO2 and e)
G2 (nSTDP)
Elemental analysis calculation is in a good relevance with TGA
data (Table 1).60 The elemental analysis results for sulfur
content showed a decrease from PT−nSiO2 to BCC1−nSiO2 and
also from G1 to BCC2−nSiO2 due to addition of 1,3,5ꢀ
benzenetricarbonyl trichloride. Consequently, this amount
increased via further addition of 1,2−ethanedithiol. As it is
shown in Table 1, the nitrogen content was also investigated.
The presence of nitrogen in the CHNS is due to utilization of
DIPEA as a base trapped in the pores of nanosilica.
Scheme 2. Synthesis of nano−silica Thiolated dendriꢀc polymer (G2 or nSTDP).
Synthesis of dendritic polymer was step by step monitored by
FT−IR spectroscopy, TGA and also elemental analysis. FTꢀIR
spectra were recorded neat and only significant absorption in
cm−1 are indicated. The FT−IR spectrum of PT−nSiO2 (Fig. 1a)
showed a broad O─H stretching band at 3200–3400 cm−1 and a
strong Si─O─Si stretching band about 1000 –1100 cm−1. Also,
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Table 1. TGA and elemental analysis (EA) results for the synthesis of nano−silica thiolated dendritic material
C
H
N
−
−
−
1.72
−
0.38
−
1.43
−
S
9.07
9.01
3.69
O
−
−
6.23
−
7.96
−
12.50
−
12.15
−
Cl
−
−
8.07
−
−
−
10.80
−
−
−
Total
21.26
21.01
35.65
24.36
53.26
47.81
68.92
48.55
84.41
75.46
PT−nSiO2
BCC1−nSiO2
G1
TGA (wt%)
EA (wt%)
TGA (wt%)
EA (wt%)
TGA (wt%)
EA (wt%)
TGA (wt%)
EA (wt%)
TGA (wt%)
EA (wt%)
10.20
10.04
16.61
17.81
28.32
29.66
31.49
32.21
37.81
39.17
1.98
1.96
1.03
1.08
2.80
2.93
1.77
1.97
3.22
3.85
3.72
14.16
14.83
12.35
12.94
31.21
32.19
BCC2−nSiO2
G2
0.25
After synthesis and characterization of nSTDP, the dendritic are also clearly observed in XPS elemental survey of the
polymer was used as host for carrying the palladium catalyst (Figure 6).
nanoparticles. The supported Pd nanoparticles were obtained by
the reaction of Na2PdCl4 with nSTDP in the presence of sodium
acetate as reducing agent (Scheme 3).61 As mentioned in the
literature, the Pd nanoparticles can be trapped by the cavities
and also by the surface functional groups.25 Based on three
dimensional structure of dendrimers, internal sulfides and
oxygenes, and also external thiol groups of this dendritic
material are capable to be as host for a Pd nanoparticles.
The presence of palladium in the catalyst was confirmed by
ICP, which showed a value of about 0.14 mmol Pd per gram of
catalyst.
Figures 3a, b and c present the field emission scanning electron
microscopy (FE−SEM) images of nanosilica, nSTDP and
Pdnp−nSTDP. The size and surface morphologies of the
nSTDP and Pdnp−nSTDP are uniform, as shown in the images,
the nSiO2 particles are spherical and the average diameters are
in the range of 50 to 70 nm.
The energy dispersive X−ray (EDX) results, collected from
SEM analysis, proved the presence of S and Si elements in the
nSTDP and also Pd element in the Pdnp−nSTDP (Figures 3d
and e). Elemental mapping of Pdnp−nSTDP depicted in Figure
4, in which the uniform and homogenous dispersion of C, Si, O,
S and Pd elements can be visualized.
Figure 5A shows the transmission electron microscopy (TEM)
image of the Pdnp−nSTDP. The picture verifies that the particles
are well dispersed and almost no agglomeration was observed.
Also, the catalyst composed of spherical, nanosized Pd particles
range from 2 to 5.5 nm (Figure 5B).
Xꢀray photoelectron spectroscopy (XPS) is a powerful tool to
investigate the electron properties of the species formed on the
surface, such as the electron environment, oxidation state, and
the binding energy of the core electron of the metal. Figure 6
shows the XPS spectrum of catalyst. The calibration was
Scheme 3. Synthesis of the Pdnp−nSTDP catalyst
performed with the C1s peak (E= 284.5 eV). As shown in this
Figure, the peaks at 335.85 (3d5/2) and 340.98 eV (3d3/2),
All these observations confirm that this new thiolated dendritic
correspond to Pd with zero oxidation state.62 The peaks
polymer is an appropriate host and ligand for palladium
corresponding to silicon, oxygen, carbon, sulfur and palladium
nanoparticles.
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Fig. 3. FE−SEM images of: a) nanosilica, b) nSTDP and c) Pdnp−nSTDP. SEM−EDX
spectra of: d) nSTDP and e) Pdnp−nSTDP.
Catalytic experiments
The catalytic activity of the prepared catalyst was investigated
in the SuzukiꢀMiyaura and Heck CꢀC coupling reactions.
Suzuki–Miyaura Coupling of Aryl Halides with Arylboronic
Acids
The Suzuki–Miyaura cross−coupling reactions typically require
careful optimization of base and solvent types, temperature,
amount of catalyst and substrates molar ratios (Table 2). In this
manner, the Suzuki–Miyaura cross−coupling of 4−iodoanisole
with phenylboronic acid in the presence of Pdnp−nSTDP
catalyst was selected as a model for optimization of reaction
parameters such as the base and solvent types, temperature,
amount of catalyst and substrates molar ratios (Table 2).
To optimize the solvent, different types of single and mixed
solvents were employed. The mixture of DMF/H2O (1:2) was
proved to be the optimum reaction medium (Table 2, entries 1ꢀ
7). Several organic and inorganic bases were screened (i.e.,
NEt3, DBU, Na2CO3, K3PO4, NaOH, piperidine and K2CO3), of
which K2CO3 gave the best yield (Table 2, entries 8ꢀ14). A
1:1.1:1.5 ratio of 4−iodoanisole to phenylboronic acid and base
was optimal for product formation. The catalytic loading could
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be lowered to 0.07 mol% Pd (5 mg) with shorter reaction times However, decreasing the catalyst loading, led to longer reaction
and up to 98% yield.
time and lower yield (Table 2, entry 17).
The effect of reaction temperature was also investigated and the
60 °C was suitable for evaluation of the scope of Suzuki–
Miyaura cross−coupling reaction.
Fig. 4. Elemental mapping (S, Si, C, O and Pd) of Pdnp−nSTDP.
Fig. 6. The XPS spectra of catalyst: (a) showing Pd 3d5/2 and Pd 3d3/2 binding
energies, (b) the elemental survey scan, (c) Reused Pdnp−nSTDP
To determine the substrate scope for the Suzuki–Miyaura
cross−coupling reaction, different aryl halides were employed
in the reaction (Table 3). In this case, different substituted aryl
chloride, bromide and iodides were reacted with phenylboronic
acid and 4−methoxyphenylboronic acid in the presence of 0.07
mol% (5 mg) of Pdnp−nSTDP as catalyst, K2CO3 as base and
DMF/H2O (2:1) as solvent. The experimental data showed that
reactions proceeded extremely well and the electronic
properties of the substituents and functional groups on the
aromatic rings had almost negligible effect on the results.
Fig. 5. (A) TEM image for Pdnp−nSTDP and (B) Particle size distribution results for
Pdnp−nSTDP catalyst
.
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Further investigation also revealed that aryl iodides were more was investigated in the Suzuki–Miyaura cross−coupling
reactive than aryl bromides and aryl chlorides in these catalytic reaction of 4−iodoanisole with phenylboronic acid and Heck
reactions. Although, aryl chlorides have less reactivity than aryl reaction of 4−bromoacetophenone with styrene under the
iodides and aryl bromides, but they are economically more optimized conditions. After completion of each catalytic cycle,
available. Due to less reactivity, the coupling reactions with the catalyst was separated by simple filtration and reused. The
aryl chlorides have been performed at 90 °C (Table 3, entries results showed that the catalyst could be reused five
14−18).63,64
consecutive times without significant loss of its catalytic
activity in both reactions (Table 6). The analysis of palladium
leaching from Pdnp−nSTDP catalyst by ICP indicated that only
Heck Reaction of Aryl Halides with Styrenes
The high catalytic activity of this catalyst in the Suzuki– a negligible amount of palladium has been leached in the first
Miyaura cross−coupling reaction prompted us to investigate the two runs in the SuzukiꢀMiyaura reaction and in the first three
catalytic capability of our new designed dendritic polymerꢀ runs in the Heck reaction. The hot filtration test was also
supported palladium particles in the Heck reaction.
carried out in both reactions. In this manner, the hot reaction
For identifying the exact optimized conditions for the coupling mixtures were centrifuged at about 45% conversion to remove
reaction detailed in Table 4, the reaction of the solid particles. The filtrates continue to catalyze the
4−bromoacetophenone and styrene was selected as a model reactions. Compared to the unfiltered reaction (after 15 min for
reactin using Pdnp−nSTDP as catalyst under thermal conditions. SuzukiꢀMiyaura and 12 h for Heck reaction), no further
The
optimized
conditions
were
gained
applying progress was observed.
4−bromoacetophenone (1 mmol), styrene (1.1 mmol), K2CO3 The XPS studies on the recycled catalyst prove the presence of
(1.5 mmol) and Pdnp−nSTDP 0.14 mol% Pd (10 mg) in Pd nanoparticles in the texture. However the spectra shows the
DMF/H2O (1:2) at 95 °C.
existence of small amounts of Pd(II) which was not observed in
The substrate scope of the coupling reaction was investigated freshly prepared catalyst. This indicates that some Pd
using various structurally different aryl halides (Table 5). As it nanoparticles were oxidized to Pd(II) (Fig. 6c).65
is mentioned in Table 5, the yield were decreased from aryl The results of the present study were compared with some
halides to bromides and chlorides. While the nature of results reported in the SuzukiꢀMiyaura crossꢀcoupling and Heck
substituents of R1 and R2 has almost no specific effect on the reaction catalyzed by different Pd containing catalysts. As can
reaction.
be seen, this catalytic system is more efficient than the others in
the SuzukiꢀMiyaura crossꢀcoupling reaction by comparison of
their TOFs (Table 7). Also, in the case Heck reaction, the TOFs
Catalyst Recycling and Reuse
From industrial and economic points of view, the catalyst show that this catalytic system is one of the best catalytic
recycling is the most important issue for a heterogeneous systems (Table 8).
catalyst. Therefore, the reusability of the Pdnp−nSTDP catalyst
Table 2. Optimization of the Suzuki–Miyaura cross−coupling of 4−iodoanisole (IA) with phenylboronic acid (PBA) catalyzed by Pdnp−nSTDP.
Entry
1
2
3
4
5
6
7
8
Base
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
NEt3
Ba:PBA:Base (mmol)
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1:1
Catalyst (mol% Pd)
0.07
Solventa
Toluene
EtOH
EtOH/H2O (1:1)
DMF
T (°C)
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
25
40
Time (min)
45
Yield (%)b
50
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.04
70
50
80
80
25
10
50
50
30
45
50
50
25
25
30
20
63
75
65
59
85
98
54
46
50
50
54
30
80
85
85
90
H2O
DMF/H2O (1:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
9
DBUc
10
11
12
13
14
15
16
17
18
19
20
Na2CO3
K3PO4
NaOH
Piperidine
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
1:1:1.2
1:1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
0.014
0.07
0.07
10
30
25
98
65
80
a) Reaction was performed using 3 ml of solvent.
b) GC yield
c) 1,8ꢀDiazabicyclo [5.4.0] undecꢀ7ꢀene
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RSC Advances
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View Article Online
DOI: 10.1039/C6RA16704G
Journal Name
RSCPublishing
Table 3. Suzuki–Miyaura cross−coupling of aryl halides with arylboronic acids catalyzed by Pdnp−nSTDP.a
Entry
R1
R2
X
Time (min)
Yield (%)b
TOF (h−1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
H
H
4−Ac
4−Ac
4−Me
H
H
4−MeO
H
4−MeO
H
4−MeO
H
4−MeO
H
4−MeO
H
4−MeO
H
4−MeO
H
4−MeO
H
I
I
I
I
10
10
15
13
10
30
25
30
28
32
30
35
32
40
38
65
55
65
95
98
92
95
95
94
95
93
96
91
93
91
93
81
82
85
87
90
8143
8400
5257
6263
8143
2685
3257
2657
2939
2437
2657
2228
2491
1735
1849
1120
1355
1186
I
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
H
4−MeO
4−MeO
4−Ac
4−Ac
4−CHO
4−CHO
Hc
Hc
4−Acc
4−Acc
4−CHOc
H
a) Reaction conditions: Aryl halide (1 mmol), phenylboronic acid (1.1 mmol), K2CO3 (1.5 mmol), Pdnp−nSTDP (0.005 g, 0.07 mol% Pd), H2O/
DMF (1 mL/2 mL) at 60 °C.
b) GC yield
c) The reaction was performed at 90 °C
Table 4. Optimization of the Heck reaction of 4−bromoacetophenone (BA) with styrene (Sty) catalyzed by Pdnp−nSTDP.a
Entry
1
2
3
4
5
6
7
8
Base
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
NEt3
BA:Sty:Base (mmol)
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1:1
Catalyst (mol% Pd)
Solventa
Toluene
EtOH
H2O
T (°C)
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
Time (h)
22
25
15
18
14
12
8
Yield (%)b
55
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.07
0.21
0.14
0.14
50
65
60
65
68
94
50
55
60
60
55
45
70
75
94
85
EtOH/H2O (1:1)
DMF
DMF/H2O (1:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
DMF/H2O (2:1)
20
22
14
18
15
18
14
10
8
9
DBU
10
11
12
13
14
15
16
17
18
Na2CO3
K3PO4
NaOH
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
1:1.1:1.2
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
80
110
12
8
94
a) The reaction was performed using 3 ml of solvent.
b) GC yield
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 8

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Journal Name
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View ArticAle ROnTliInCeLE
DOI: 10.1039/C6RA16704G
Table 5. Heck reaction of aryl halides with styrenes catalyzed by Pdnp−nSTDP.a
Entry
R1
R2
X
Time (h)
Yield (%)b
TOF (h−1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
H
H
4−Ac
4−Ac
4−Me
H
H
4−Me
H
4−Me
H
H
4−Me
H
H
4−Me
H
4−Me
H
4−Me
H
I
I
I
I
7.5
8
8
8
8
11
10
11
12
11
12
12
16
16
15
16
96
94
95
94
95
93
91
92
94
93
91
92
91
89
88
88
91.43
83.93
84.82
83.93
84.82
60.39
65
59.74
55.95
60.39
54.16
54.76
40.62
39.73
41.90
39.28
I
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
H
4−F
4−Ac
4−Ac
4−CHO
4−MeO
H
4−Ac
4−Ac
4−CHO
H
a) Reaction conditions: Aryl halide (1 mmol), styrenes (1.1 mmol), K2CO3 (1.5 mmol), Pdnp−nSTDP (0.01 g, 0.14 mol% Pd), H2O/DMF (1 mL/2 mL) at 95
°C.
b) GC yield
Table 6. Recycling of the Pdnp−nSTDP catalyst in the SuzukiꢀMiyaura cross−coupling of 4−bromoacetophenone with phenylboronic acid in 15 mina and Heck
reaction of 4−bromoacetophenone with styrene after 12 h.b
Run
Yield (%)c
Pd leached (%)d
SuzukiꢀMiyaura
Heck reaction
SuzukiꢀMiyaura
Heck reaction
1
2
3
4
5
92
90
88
88
88
94
90
86
86
86
2
1
0
0
0
4
2
1.5
0
0
a) Reaction conditions: 4−bromoacetophenone (1 mmol), phenylboronic acid (1.1 mmol), K2CO3 (1.5 mmol), Pdnp−nSTDP (0.005 g, 0.07 mol% Pd),
H2O/DMF (1 mL/2 mL) at 60 °C.
b) Reaction conditions: 4−bromoacetophenone (1 mmol), styrene (1.1 mmol), K2CO3 (1.5 mmol), Pdnp−nSTDP (0.01 g, 0.14 mol% Pd), H2O/DMF (1 mL/2
mL) at 95 °C.
c) GC yield.
d) Determined by ICP analysis
Table 7. Comparison of the results obtained in the SuzukiꢀMiyaura coupling
reaction of bromobenzene with phenylboronic acid catalyzed by Pdnp−nSTDP
Conclusion
with those obtained by some recently reported catalysts.
This paper describes the synthesis and characterization of a new
Catalyst
Reaction conditions
TOF
(hꢀ1)
Ref
37
67
66
48
64
11
thiol based dendritic material as a host for carrying of
palladium nanoparticles. The new synthesized nanosilica
thiolated dendritic polymerꢀsupported Pd particles has proven
to be highly effective heterogeneous catalyst for carbon−carbon
couplings in both SuzukiꢀMiyaura and Heck reactions.
Although palladium as a precious metal is quite expensive, we
have shown that they can be easily recovered and reused for
several times, without any significant loss of its catalytic
activity. Therefor it would be possible to use them in further
real−world applications.
Pd(0)/UiOꢀ66ꢀNH2
Pd(PyBNHC)@nSiO2
Pd(0)/MCoSꢀ1
PdTN
DMF/H2O, K2CO3, 60 °C, 697.7
30 min
DMF/H2O, K2CO3, 65 °C, 438
100 min
H2O, K2CO3, 70 °C, 300 98
min
THF/H2O,NaOH, 63 °C, 80
150 min
DMF/H2O, K2CO3, 100 16.6
°C, 1440 min
DMF/H2O, K2CO3, RT, 2666
360 min
Pd Schiff base complex
Pd−nSTDP
Pdnp−nSTDP
DMF/H2O, K2CO3, 60 °C, 3257
25 min
This
work
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 9

RSC Advances
Page 10 of 13
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C6RA16704G
for Suzuki–Miyaura CrossꢀCoupling and Heck Reactions. Adv. Synth.
Catal. 2013, 355, 957–972.
Table 8. Comparison of the results obtained in the Heck reaction of 4ꢀ
bromobenzenel with styrene catalyzed by Pdnp−nSTDP with those obtained
by some reported catalysts.
12 J. H. Noh, R. Patala and R. Meijboom, Catalytic evaluation of
dendrimer and reverse microemulsion template Pd and Pt
nanoparticles for the selective oxidation of styrene using TBHP.
Catalyst
Reaction conditions
TOF
(hꢀ1)
15.5
Ref
Pd(OAc)2/(LHX)
Palladacycle
Pd/USY
Pd(OAc)2/NHC
Pd@PANI
Pd−nSTDP
PEPSIꢀPd NHC
Pdnp−nSTDP
DMF/H2O, K2CO3, 80 °C, 4 h
[nꢀBu4N]Br, Na(OAc), 120 °C, 16 h 62.5
68
69
70
71
72
11
73
This
work
Appl. Catal. A: Gen. 2016, 514, 253–266.
13 J. H and Noh, R. Meijboom, Dendrimerꢀtemplated Pd nanoparticles
an Pd nanoparticles synthesized by reverse microemulsions as
efficient nanocatalyst for the Heck reaction: A comparative study. J.
Colloid Interface Sci. 2014, 415, 57–69.
DMF, NaOAc, H2, 140 °C, 20 h
DMF/H2O, K2CO3, 80 °C, 2 h
DMF, N2, EtN(iꢀPr)2, 120 °C, 48 h
DMF/H2O, K2CO3, 85 °C, 14 h
DMF, K2CO3, TBAB, 140 °C, 2 h
DMF/H2O, K2CO3, 95 °C, 11 h
48
24
14.5
642
100
60.4
14 M. Nasr−Esfehani, I. Mohammadpoor−Baltork, A. R. Khosropour,
M. Moghadam, V. Mirkhani and S. Tangestaninejad, Synthesis and
characterization of Cu(II) containing nanosilica triazine dendrimer: A
recyclable nanocomposite material for the synthesis of
Acknowledgement
benzimidazoles, benzothiazoles, bisꢀbenzimidazoles and bis
ꢀ
Partial support of this work by the Research Council of the
University of Isfahan is acknowledged.
benzothiazoles. J. Mol. Catal. A: Chem. 2013, 379, 243−259.
15 Z. V. Feng, J. L. Lyon, J. S. Croley, R. M. Crooks, D. A. Vanden
Bout and K. J. Stevenson, Synthesis and catalytic evaluation of
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