Immobilized palladium nanoparticles on silica functionalized N-propylpiperazine sodium N-propionate (SBPPSP): Catalytic activity evaluation in copper-free Sonogashira reaction

Article abstract of DOI:10.1007/s13738-013-0271-z

An efficient heterogeneous palladium catalyst system has been developed based on immobilization of Pd nanoparticles on silica-bonded N-propylpiperazine sodium N-propionate (SBPPSP) substrate. SBPPSP substrate can stabilize the Pd nanoparticles effectively

Full text of DOI:10.1007/s13738-013-0271-z

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0271-z
ORIGINAL PAPER
Immobilized palladium nanoparticles on silica functionalized
N-propylpiperazine sodium N-propionate (SBPPSP): catalytic
activity evaluation in copper-free Sonogashira reaction
Khodabakhsh Niknam
•
•
Abdollah Deris
Farhad Panahi M. Reza Hormozi Nezhad
•
Received: 6 January 2013 / Accepted: 9 May 2013
Ó Iranian Chemical Society 2013
Abstract An efficient heterogeneous palladium catalyst
system has been developed based on immobilization of Pd
nanoparticles on silica-bonded N-propylpiperazine sodium
N-propionate (SBPPSP) substrate. SBPPSP substrate can
stabilize the Pd nanoparticles effectively so that it can
improve their stability against aggregation. In addition,
grafted piperazine species on to the silica backbone prevent
the removing of Pd nanoparticles from the substrate sur-
face. Transmission electron microscopy (TEM) of catalyst
is shown the size of Pd nanoparticles, also it confirmed by
particle size analyzer which shown the average size of
Introduction
The most frequently utilized method for the preparation of
alkynylarenes is the Sonogashira–Hagihara reaction, in
which C(aryl)–C(sp) bonds are constructed by the palladium/
copper-catalyzed cross-coupling of aryl halides and terminal
alkynes [1–4]. Since its discovery by Sonogashira and co-
workers in 1975, considerable research has been devoted to
the synthetic application of the reaction as well as to improve
itsefficiency[1]. Oneofthemajorproblemsassociatedwithit
lies in the reaction conditions where the use of both a palla-
dium catalyst and a copper reagent (co-catalyst) is frequently
required to promote the reaction, resulting in contamination
of the coupling products with metal residue. In addition, it has
been well-documented that the Sonogashira coupling often
suffers from the Glaser-type oxidative dimerization of the
alkyne substrate [5], as a side reaction in the presence of a
Cu(I) co-catalyst. Recently, quite a few reports addressing
these problems have appeared, in which the coupling is car-
ried out with an immobilized palladium catalyst and/or under
copper-free conditions [6–10].
2
1 nm for Pd. The catalytic activity of these catalysts was
investigated in the Sonogashira reaction. The catalyst could
be recycled several times without appreciable loss in cat-
alytic activity.
Keywords Heterogeneous palladium nanoparticles Á
Silica-bonded N-propylpiperazine sodium N-propionate Á
Sonogashira reaction Á Aryl halides Á Alkynes
In the recent years, there is considerable attention on
preparation of heterogeneous palladium catalyst based on
the nanometer scale palladium species [11–14]. Palladium
nanoparticles on a suitable support have the ability to be
recoverable and ligand-free catalytic systems with
improved catalyst characteristics [11–24]. Usually, palla-
dium nanoparticle catalysts are prepared from a palladium
salt, on a substrate or stabilizer in the presence of a
reducing agent [14–27]. Steric, electrostatic, and electros-
teric factors are responsible for the stabilization of Pd
nanoparticles during their synthesis.
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-013-0271-z) contains supplementary
material, which is available to authorized users.
K. Niknam (&) Á A. Deris Á F. Panahi
Department of Chemistry, Faculty of Sciences,
Persian Gulf University, Bushehr 75169, Iran
e-mail: niknam@pgu.ac.ir
M. Reza Hormozi Nezhad
Department of Chemistry, Sharif University of Technology,
Tehran 11155-9516, Iran
Recently, we introduced Pd nanoparticles on silica-
bonded N-propylpiperazine (PNP-SBNPP) as an efficient
catalyst for Heck and Suzuki reactions (Scheme 1) [14].
M. Reza Hormozi Nezhad
Institute for Nanoscience and Nanotechnology (INST),
Sharif University of Technology, Tehran 9161, Iran
123

J IRAN CHEM SOC
O
was filtered and dried overnight under vacuum [29]. Sub-
sequently, the mixture was treated with saturated solution
SiO2 O Si
N
N
Pd0
O
of NaHCO (50 mL) over 2 h. Then, the mixture was fil-
3
n
tered and dried overnight under vacuum to afford silica-
Scheme 1 The synthetic rout for preparation of PNP-SBNPP
bonded
SBPPSP) as a white powder (26.7 g). Elemental analysis
gave the results: C, H, and N content to be 13.72, 2.30, and
.78 %, respectively. The C/N relationship observed and
N-propylpiperazine
sodium
N-propionate
(
Herein, we describe the preparation of immobilized pal-
ladium nanoparticles on silica-bonded N-propylpiperazine
sodium N-propionate (PNP-SBPPSP) as catalyst and the
catalytic activity of both PNP-SBPPSP and PNP-SBNPP is
investigated in the Sonogashira cross-coupling reactions.
2
calculated is 4.93 and 4.28, respectively.
Preparation of Pd nanoparticles on silica-bonded
N-propylpiperazine sodium N-propionate (PNP-SBPPSP)
Experimental
To a mixture of (SBPPSP) (1 g) in absolute ethanol
(10 mL), palladium acetate (0.15 g, 0.67 mmol) was added
Chemicals and reagents
and stirred 24 h at room temperature. Then, the mixture
was filtered and washed with ethanol (3 9 10 mL). After
drying in vacuum oven Pd nanoparticles on silica-bonded
N-propylpiperazine sodium N-propionate (PNP-SBPPSP)
was obtained as dark solid (1.1 g).
Chemicals were purchased from Fluka, Merck and Aldrich
Chemical Companies. The products were characterized by
comparison of their spectral and physical data with those
1
reported in literature [7–11]. For recorded H-NMR spectra, we
were using Bruker Avance (DRX 500 MHz) in pure deuterated
General procedure for Sonogashira cross-coupling
reaction
CDCl solvent with tetramethylsilane (TMS) as internal stan-
3
dards. X-ray diffraction (XRD, D8, Advance, Bruker, axs), FT-
IR spectroscopy (Shimadzu FT-IR 8000 spectrophotometer),
and SEM instrumentation (SEM, XL-30 FEG SEM, Philips, at
A mixture of aryl halide (1 mmol), alkyne (1.2 mmol),
triethylamine (4 mmol), PNP-SBPPSP (0.05 g, 2.6 mol %)
[or PNP-SBNPP (0.05 g, 2.8 mol %)], and acetonitrile
20 kV) were employed for characterization of catalyst. Melting
points determined in open capillary tubes in a Barnstead
Electrothermal 9100 BZ circulating oil melting point apparatus.
The reaction monitoring was accomplished by TLC on silica
gel PolyGram SILG/UV254 plates. Column chromatography
was carried out on columns of silica gel 60 (70–230 mesh).
Silica-bonded N-propylpiperazine (SBNPP) and Pd nanopar-
ticles onsilica-bondedN-propylpiperazine (PNP-SBNPP) were
prepared according to our reported procedure [14, 28].
(
3 mL) was stirred under reflux conditions for the time
specified in Table 2. The reaction was followed by TLC.
After completion of the reaction, the mixture was cooled
down to room temperature and filtered, and the remaining
was washed with dichloromethane (3 9 10 mL) to sepa-
rate catalyst. After extraction dichloromethane from water,
the organic phase dried over Na SO . Evaporation of the
2
4
solvent gave products. For further purification if needed,
the products passed through a short column of silica gel
using n-hexane as eluent.
Preparation of silica-bonded N-propylpiperazine methyl
N-propionate (SBPPMP)
Selected NMR data: 2-methyl-phenylethynyl-benzene
1
(
Table 1, entry 10): H-NMR (500 MHz, CDCl ): d (ppm)
3
To a magnetically stirred mixture of SBNPP (25 g) in MeOH
2.56 (s, 3H, CH ), 7.19–7.22 (m, 1H, Ar), 7.26–7.28 (m,
3
(
50 mL), methyl acrylate (25 mL) was added and heated at
0–50 °C for48 h under nitrogen [29]. Then, themixture was
filtered and washed with methanol (2 9 50 mL) and dried
h under vacuum to afford silica-bonded N-propylpiper-
azine methyl N-propionate (SBPPMP) as a white powder
26.6 g). Elemental analysis gave the results: C, H, and N
2H, Ar), 7.36–7.41 (m, 3H, Ar), 7.54 (d, 1H, J = 7.5 Hz,
1
3
4
Ar), 7.56–7.58 (m, 2H, Ar). C-NMR (125 MHz, CDCl3):
d (ppm) 21.17, 94.01, 98.51, 124.10, 126.00, 128.59,
128.72, 128.77, 129.88, 131.93, 132.26, 140.81.
8
(
The recyclability of PNP-SBPPSP as catalyst
content to be 13.47, 2.28, and 2.18 %, respectively.
in the reaction of iodobenzene and phenylacetylene
Preparation of silica-bonded N-propylpiperazine sodium
N-propionate (SBPPSP)
A mixture of iodobenzene (2 mmol, 0.408 g), phenylacet-
ylene (2.4 mmol, 0.245 g), triethylamine (8 mmol), PNP-
SBPPSP (0.1 g), and acetonitrile (5 mL) was stirred under
reflux conditions. The reaction was followed by TLC. After
completion of the reaction (1.0 h), the mixture was cooled
To a magnetically stirred mixture of (SBPPMP) (26.6 g)
was treated with HCl (0.5 M, 50 mL), and then the mixture
1
23

J IRAN CHEM SOC
Table 1 Optimization reaction between iodobenzene and phenylacetylene in the presence of PNP-SBPPSP as a catalyst at various conditions
I
PNP-SBPPSP
or PNP-SBNPP
+
Solvent, Base
Temperature
o
Temp/ C
a,b
Yield * (%)
Entry
Solvent
DMF
Base
Catalyst loading (g)
Time/h
1
2
3
4
5
6
7
8
9
Na
2
CO
CO
3
3
0.075
0.075
0.075
0.075
0.075
0.05
120
1.5 (1.5)
1.0 (1.0)
1.0 (1.0)
2.0 (2.0)
1.0 (1.0)
1.5 (1.5)
12 (12)
85 (83)
25 (28)
25 (26)
66 (67)
92 (92)
87 (86)
60 (60)
32 (30)
93 (92)
H
2
O
O
Na
2
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
H
2
Cs CO
2
3
CH
CH
CH
CH
CH
CH
3
CN
3
CN
3
CN
3
CN
3
CN
3
CN
Na
2
CO
3
Et
Et
Et
Et
Et
3
N
3
N
3
N
3
N
3
N
0.03
0.01
12 (12)
0.1
1.0 (1.0)
Reaction conditions: iodobenzene (1 mmol), phenylacetylene (1.2 mmol) and base (4 mmol) in solvent (3 mL)
a
Isolated yield
b
The times and yields in parenthesis related to PNP-SBNPP
down to room temperature and filtered, and the remaining
was washed with dichloromethane (3 9 10 mL) to sepa-
rate catalyst. After extraction dichloromethane from water,
the organic phase dried over Na SO . Evaporation of the
In addition, the histogram revealing the size distribu-
tions of Pd nanoparticles on SBPPSP substrate is shown in
Fig. 2 and is proposed according to the data obtained from
the TEM image. The average sizes of Pd nanoparticles for
Pd-SBPPSP catalyst are obtained 21 nm.
2
4
solvent gave product which passed through a short column
of silica gel using n-hexane as eluent (0.327 g of product
The microscopic features of the catalyst were observed
with SEM (Fig. 3). In this figure, we can see morphology
of the silica substrate.
9
2 %). The recycled catalyst was used in next run.
The crystalline structure of the PNP-SBNPP catalyst is
displayed by the XRD pattern depicted in Fig. 4. The XRD
pattern of the PNP-SBNPP catalyst also shows palladium
nanoparticles on the silica surface. The strongest peaks of
Results and discussion
Catalyst preparation and characterization
the XRD pattern correspond to SiO , and other peaks are
2
As shown in Scheme 2, immobilized palladium nanopar-
ticles on piperazine-modified silica (Pd-SBPPSP) are pre-
pared in a four-step process. First, activated silica was
reacted with 3-chloropropyl trimethoxysilane in refluxing
toluene to produce 3-chloropropylsilica (3-CPS) [21].
Second, 3-CPS was treated with piperazine to generate the
silica-bonded N-propylpiperazine substrate [14, 28, 29].
Third, silica-bonded N-propylpiperazine treated with
methylacrylate and followed by hydrolysis to obtain silica-
indexed as the (111), (200), (220), and (311) planes of the
palladium nanoparticle [14, 21].
The BET surface area using nitrogen adsorption iso-
therms at the temperature of liquid nitrogen which gave the
2
1.40 m g and the total pore volume
-1
results of a
s,BET
-1
0.2505 cm g (see supplementary material).
3
To confirm the Pd content, the supported catalyst was
treated with concentrated HCl and HNO to digest the Pd
3
species and then analyzed by ICP analysis. The Pd content
for PNP-SBPPSP was determined to be 55.6 ppm
bonded
SBPPSP) [29]. Finally, palladium acetate is reduced on
SBPPSP substrate using ethanol as green reducing agent
22]. The Pd species stabilized by grafted ligand through
N-propylpiperazine
sodium
N-propionate
-
(55.6 mg L = 5.56 % w/w).
1
(
After characterization of catalyst, its catalytic activity is
tested in Sonogashira cross-coupling reactions.
We tested various conditions to optimize the amount of
PNP-SBPPSP and PNP-SBNPP catalysts on the Sono-
gashira reaction between iodobenzene and phenylacetylene
(Table 1). The optimized amount of PNP-SBPPSP catalyst
was 0.05 g (2.6 mol % of Pd) [or PNP-SBNPP catalyst
0.05 g (2.8 mol %)].
[
the amine and carboxylate groups (Scheme 2) [27, 30].
TEM image of PNP-SBPPSP catalyst (Fig. 1) shows
that the Pd nanoparticles with near spherical morphology
are assembled on to the silica bonded N-propylpiperazine
sodium N-propionate support with a relatively good
monodispersity.
123

J IRAN CHEM SOC
NH
OH
O
HN
Et N
O
(
MeO) Si
Cl
3
SiO2 OH
SiO2 O Si
Cl
SiO2 O Si
N
Toluene, Reflux, 18 h
NH
3
O
O
OH
Xylene, Reflux
(SBNPP)
OMe
1
)
O
O
SiO2 O Si
O
O
Pd(OAc)2
SiO2 O Si
N
SBNPP
N
N
Na
N
O
O
EtOH, r.t., 24 h
O
2
) HCl
Pd[o]
O
O
3
) NaHCO3
(
SBPPSP)
(
PNP-SBPPSP)
Scheme 2 The synthetic route for preparation of PNP-SBPPSP
Fig. 1 Transmission electron microscope (TEM), which show the
image of Pd nanoparticle on SBPPSP support
Fig. 3 SEM of PNP-SBPPSP
solvent, base and temperature were optimized and the
result was shown in Table 1. The optimized conditions was
aryl halide (1 mmol), phenylacetylene (1.2 mmol), trieth-
ylamine (4 mmol), and PNP-SBPPSP (0.05 g, 2.6 mol %)
[or PNP-SBNPP catalyst 0.05 g (2.8 mol %)] in 3 mL
acetonitrile as solvent under reflux conditions.
The generality of this protocol was applied for coupling
of various alkynes with aryl halides (Scheme 3; Table 2).
Phenylacetylene was found to couple smoothly with
iodobenzene providing good yield (87 %) of the desired
product (Table 1, entry 6). In addition, phenylacetylene
was coupled with bromobenzene and chlorobenzene in 85
and 45 % yield, respectively (Table 2, entries 2–5). Func-
tional groups like methoxy, methyl, and nitro were well
tolerated under the present catalytic system (Table 2,
entries 6–10). The electron-donating groups on the aryl
ring decreased the reaction rate and also yield of product
(Table 2, entries 8–10). Sterically hindered 2-iodo toluene
was treated with phenylacetylene under optimized condi-
tions providing 82 % yield of the desired product (Table 2,
entry 10). The electron-withdrawing groups on the aryl ring
increased the reaction rate and also yield of product
Fig. 2 Histogram representing the size distribution of Pd nanopar-
ticles on SBPPSP substrate
By decreasing the catalyst to 0.01 g (0.52 mol % of Pd)
[
or PNP-SBNPP catalyst 0.01 g (0.56 mol %)], the yield of
product decreased and the time of reaction was increased
(Table 1, entry 8), while the increase of catalyst to 0.1 g
(5.2 mol % of Pd) [or PNP-SBNPP catalyst 0.1 g
(5.6 mol %)] did not have more effect on the reaction yield
(Table 1, entry 9). In addition, different conditions, such as
1
23

J IRAN CHEM SOC
Fig. 4 XRD of PNP-SBPPSP
efficiency with PNP-SBPPSP in most cases, but as the Pd
contents of PNP-SBNPP is slightly more {PNP-SBPPSP
X
PNP-SBPPSP (0.05 g)
R
+
0.05 g (2.6 mol % of Pd) [or PNP-SBNPP 0.05 g
Et3N (4 mmol)
R
CH3CN 3 mL, Reflux
(2.8 mol %)]} so the reactivity of PNP-SBNPP is lower
than PNP-SBPPSP.
(
1 mmol)
(1.2 mmol)
X = I, Br, Cl
The possibility of recycling the catalyst was examined
using the reaction of iodobenzene with phenylacetylene
under optimized conditions. Upon completion, the reaction
mixture was filtered and the catalyst was washed with
dichloromethane. The recycled catalyst could be reused
four times without any treatment (Fig. 5).
Scheme 3 PNP-SBPPSP catalyzed couper-free Sonogashira cross-
coupling reactions
Table 2 The react ion of phenylacetylene with aryl halides in the
presence of PNP-SBPPSP as catalyst (Sonogashira reaction)
a,b
Yield (%)
Entry Aryl halide
Catalyst
loading (g)
Time/h
Conclusions
1
2
3
4
5
6
7
8
9
1
1
a
C
C
C
C
C
6
6
6
6
6
H
H
H
H
H
5
5
5
5
5
-I
0.075
0.075
0.05
1 (1)
2 (2)
92 (92)
90 (88)
85 (85)
64 (65)
45 (45)
-Br
-Br
-Cl
-Cl
In conclusion, this work shows that palladium nanoparti-
cles stabilized by silica-bonded N-propylpiperazine sodium
N-propionate, which can be prepared by simple operation
4 (4)
0.075
0.05
12 (12)
12 (12)
4-O
4-O
2
N-C
N-C
6
H
H
4
-I
0.05
0.75 (0.75) 92 (92)
2
6
4
-Br
0.05
1.5 (1.5)
7 (7)
86 (85)
86 (85)
65 (63)
82 (80)
85 (84)
4-MeO-C
6
H
4
-I
0.05
4-MeO-C
6
H
4
-Br 0.075
12 (12)
3 (3)
0
1
6 4
2-Me-C H -I 0.05
2-Iodothiophene 0.05
7 (7)
Reaction conditions: aryl halide (1 mmol), alkyne (1.2 mmol), tri-
ethylamine (4 mmol), acetonitrile (3 mL) under reflux conditions
b
Isolated yield
c
The times and yields in parenthesis related to PNP-SBNPP
(
Table 2, entries 6, 7). Iodothiophene was also found to
react smoothly with phenylacetylene in very good yield
Table 2, entry 11). PNP-SBNPP was shown the same
Fig. 5 Recyclability of PNP-SBPPSP in the reaction of iodobenzene
(2 mmol), phenylacetylene (2.4 mmol), triethylamine (8 mmol) and
acetonitrile (5 mL) under reflux conditions. Reaction time = 1.0 h
(
123

J IRAN CHEM SOC
from commercially available and relative cheap starting
materials, efficiently catalyzed the Sonogashira reactions.
It could also be recovered and reused for several times
without noticeable loss of reactivity.
13. J. Cheng, G. Zhang, J. Du, L. Tang, J. Xu, J. Li, J. Mater. Chem.
2
4. K. Niknam, M.S. Habibabad, A. Deris, F. Panahi, M.R. Hormozi
1, 3485 (2012)
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Acknowledgments We are thankful to Persian Gulf University
Research Council for partial support of this work. Also, we are
thankful to the School of Chemistry, Manchester University for
running CHN and SEM.
1
1
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