Palladium nanoparticles immobilized on nano-silica triazine dendritic polymer (Pdnp-nSTDP): An efficient and reusable catalyst for suzuki-miyaura cross-coupling and heck reactions

Article abstract of DOI:10.1002/adsc.201200707

A new catalyst based on palladium nanoparticles immobilized on nano-silica triazine dendritic polymer (Pd_np-nSTDP) was synthesized and characterized by FT-IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy and elemental analysis. The size of the palladium nanoparticles was determined to be 3.1±0.5 nm. This catalytic system showed high activity in the Suzuki-Miyaura cross-coupling of aryl iodides, bromides and chlorides with arylboronic acids and also in the Heck reaction of these aryl halides with styrenes. These reactions were best performed in a dimethylformamide (DMF)/water mixture (1:3) in the presence of only 0.006 mol% and 0.01 mol% of the catalyst, respectively, under conventional conditions and microwave irradiation to afford the desired coupling products in high yields. The Pd_np-nSTDP was also used as an efficient catalyst for the preparation of a series of star- and banana-shaped compounds with a benzene, pyridine, pyrimidine or 1,3,5-triazine unit as the central core. Moreover, the catalyst could be recovered easily and reused several times without any considerable loss of its catalytic activity. Copyright

Full text of DOI:10.1002/adsc.201200707

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DOI: 10.1002/adsc.201200707
Palladium Nanoparticles Immobilized on Nano-Silica Triazine
Dendritic Polymer (Pdnp-nSTDP): An Efficient and Reusable
Catalyst for Suzuki–Miyaura Cross-Coupling and Heck Reactions
Amir Landarani Isfahani,a Iraj Mohammadpoor-Baltork,a,* Valiollah Mirkhani,a,*
Ahmad R. Khosropour,a Majid Moghadam,a Shahram Tangestaninejad,a
and Reza Kiab
a
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
Fax : (+98)-311-6689732; phone: (+98)-311-7932705; e-mail: imbaltork@sci.ui.ac.ir or mirkhani@sci.ui.ac.ir
Department of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, Iran
b
Received: August 8, 2012; Revised: January 22, 2013; Published online: March 19, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200707.
Abstract: A new catalyst based on palladium nano- presence of only 0.006 mol% and 0.01 mol% of the
particles immobilized on nano-silica triazine dendrit- catalyst, respectively, under conventional conditions
ic polymer (Pdnp-nSTDP) was synthesized and char- and microwave irradiation to afford the desired cou-
acterized by FT-IR spectroscopy, thermogravimetric pling products in high yields. The Pdnp-nSTDP was
analysis, field emission scanning electron microscopy, also used as an efficient catalyst for the preparation
energy dispersive X-ray, transmission electron mi- of a series of star- and banana-shaped compounds
croscopy and elemental analysis. The size of the pal- with a benzene, pyridine, pyrimidine or 1,3,5-triazine
ladium nanoparticles was determined to be 3.1ꢀ unit as the central core. Moreover, the catalyst could
0.5 nm. This catalytic system showed high activity in be recovered easily and reused several times without
the Suzuki–Miyaura cross-coupling of aryl iodides, any considerable loss of its catalytic activity.
bromides and chlorides with arylboronic acids and
also in the Heck reaction of these aryl halides with Keywords: Heck reaction; palladium nanoparticles;
styrenes. These reactions were best performed in a di- reusable catalyst; Suzuki–Miyaura cross-coupling;
methylformamide (DMF)/water mixture (1:3) in the triazine dendritic polymer
Introduction
Dendritic polymers are highly branched, spherical
three-dimensional macromolecules, the synthesis and
The application of palladium nanoparticles (PdNPs) properties of which have attracted much attention
as catalysts, especially in Suzuki–Miyaura cross-cou- during the past decades.[5] Due to their three-dimen-
pling and Heck reactions, has attracted great attention sional structure and multiple internal and external
in the last decade.[1] Due to their large surface-to- functional groups, dendritic polymers can selectively
volume ratio, the nanoparticle-based catalytic systems act as suitable hosts for a wide range of ions and mol-
exhibit higher activity than their corresponding bulk ecules.[6] Dendritic polymers with metal ions incorpo-
materials.[2] However, these nanoparticles usually un- rated into their core or on their surface have found
dergo aggregation to form larger, bulk particles and, great applications in catalytic processes.[7]
therefore, their catalytic activities are reduced. Gener-
Immobilization of metal-containing dendritic poly-
ally, the aggregation of nanoparticles can be avoided mers on solid supports is of practical importance in
by using suitable stabilizers or protecting agents.[3] the field of catalysis because of their easy recoverabil-
The immobilization of these nanoparticle-based cata- ity and reusability, as well as their environmentally
lytic systems on solid supports makes the catalyst re- benign and non-polluting nature. Owing to these ad-
cyclable and reusable, and minimizes the leaching of vantages, heterogeneous dendritic polymer-based cat-
the particles. These are very important aspects from alysts have been efficiently used in many important
environmental, economical and safety points of organic transformations.[8]
view.[4]
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Among dendritic molecules, triazine-based dendrit- These processes were monitored by FT-IR, thermog-
ic polymers have received more interest because of ravimetric analysis (TGA) and elemental analysis.
the low cost and chemoselective reactivity of the re-
The presence of bands in the FT-IR spectra at
lated starting material, cyanuric chloride (2,4,6-tri- 1580–1603 (C=N), 1480 and 2990 cmꢁ1 (C Haliph) con-
ꢁ
chlorotriazine).[9] Such chemoselective reactivity is firms the synthesis of AP-nSiO2, CC1-nSiO2, G1 and
temperature dependent, in which the first, second and G2 (Figure 1).[13] Due to the presence of a strong Si
ꢁ
ꢁ1
ꢁ
the third substitutions proceed at 0, 25 and 708C, re- O band at 1000–1100 cm , the C Cl band of CC at
spectively. Consequently, for a wide range of catalytic 1010 cmꢁ1 was masked. Also, it was not possible to
ꢁ
applications, different generations of triazine-based assign the N H band in the FT-IR spectrum, due to
ꢁ
dendritic polymers can be prepared via a stepwise interference from the silica O H band (3200–
functionalization and regulation of the conditions.[10]
In continuation of our efforts on the development
3400 cmꢁ1).
The nitrogen content of AP-nSiO2, determined by
of efficient catalytic systems for useful synthetic or- elemental analysis, was found to be 0.99 mmolgꢁ1 of
ganic transformations,[11] herein we wish to report the nano-silica.
preparation and characterization of a new thermally
The amount of organic moieties in the cyanuric
stable, oxygen insensitive, phosphine-free, air- and chloride-functionalized AP-nSiO2 (CC1-nSiO2) was
moisture-stable, and reusable palladium nanoparticles also determined by TGA and elemental analysis. The
immobilized on nano-silica functionalized triazine total amount of organic moieties on nano-SiO2 was
dendritic polymer (Pdnp-nSTDP) catalyst and its ap- about 0.76 mmolgꢁ1. Also, the amount of released
ꢁ
plication in C C coupling reactions via the Suzuki– chloride ion was determined by titration with AgNO3,
Miyaura cross-coupling and Heck reactions under the results of which were in accordance with the re-
conventional conditions and microwave irradiation sults obtained by TGA and elemental analysis. The
(Scheme 1).
weight loss of the nSTDP between 30–6008C as
a function of temperature was determined using
TGA, which is an irreversible process because of ther-
mal decomposition. The TGA plots of AP-nSiO2,
CC1-nSiO2, CC2-nSiO2, G1 and G2 (Figure 2) depict
a two-step thermal decomposition. The first step of
weight loss in the case of AP-nSiO2 corresponds to
the removal of physically adsorbed water, whereas, in
the other cases, the main weight loss in the second
Results and Discussion
Synthesis and Characterization of Palladium
Nanoparticles Immobilized on Nano-Silica Triazine
Dendritic Polymer (Pdnp-nSTDP)
First, nano-silica was modified with 3-aminopropyltri- step is due to the removal of organic moieties on the
methoxysilane (APTS) according to the literature surface. The TGA results are summarized in Table 1.
procedure[12] to afford aminopropyl-functionalized The observed total weight losses for AP-nSiO2, G1
nano-silica (AP-nSiO2). The reaction of cyanuric chlo- and G2 are 5.757%, 17.77% and 36.64%, respectively.
ride (CC) with the surface-attached propylamine of On the basis of these values, the theoretical conver-
AP-nSiO2 was carried out at room temperature sion is 77% for AP-nSiO2!CC1-nSiO2, 60% for
for substitution of one of the chlorine atoms CC1-nSiO2!G1, 57% for G1!CC2-nSiO2 and 80%
to yield CC1-nSiO2. Then, CC1-nSiO2 was for CC2-nSiO2!G2. A summary of the elemental
reacted
with
bis(3-aminopropyl)amine, analysis and TGA data is included in Table 2. A good
H2NCH2CH2CH2NHCH2CH2CH2NH2, to give G1 agreement was observed between elemental analysis
which in turn was converted to CC2-nSiO2 upon reac- and TGA data for these conversions (Table 2).
tion with cyanuric chloride. Finally, CC2-nSiO2 react-
After preparation and characterization of nSTDP,
ed with H2NCH2CH2CH2NHCH2CH2CH2NH2 which the palladium nanoparticles were immobilized onto
produced the nano-silica triazine dendritic polymer this ligand. As shown in Scheme 3, the palladium
(G2 or nSTDP) as the support for PdNPs (Scheme 2). nanoparticles immobilized on nano-silica trazine den-
Scheme 1. Suzuki–Miyaura cross-coupling and Heck reaction catalyzed by Pdnp-nSTDP.
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Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP)
Scheme 2. Synthesis of nano-silica triazine dendritic polymer (G2 or nSTDP).
Figure 1. The FT-IR spectra of: a) AP-nSiO2; b) CC1-nSiO2;
c) G1 and d) G2 (nSTDP).
Figure 2. TGA spectra of: a) AP-nSiO2; b) CC1-nSiO2; c)
G1; d) CC2-nSiO2 and e) G2.
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Table 1. Thermogravimetric analysis (TGA) results.
electron microscopy (FE-SEM) (Figure 3). The size
and surface morphologies of the nSTDP and Pdnp-
nSTDP were directly visualized by FE-SEM (Fig-
ure 3a and b). As can be seen the nSiO2 particles are
spherical and have diameters in the range of 40 to
70 nm.
The energy dispersive X-ray (EDX) results, ob-
tained from SEM analysis for the nSTDP and Pdnp-
nSTDP, are shown in Figure 3c and d, which clearly
show the presence of Pd nanoparticles in the Pdnp-
nSTDP catalyst.
Sample
Organic
[wt%]
Organic
[mmolgꢁ1
n-SiO2]
Yield
[%]
AHCTUNGTRENNUNG
AP-nSiO2
CC1-nSiO2
G1
CC2-nSiO2
G2
5.757
15.58
17.77
25.301
36.64
0.99
0.76
0.45
0.26
0.21
–
77
60
57
80
Further characterization of Pdnp-nSTDP was per-
formed by transmission electron microscopy (TEM).
The TEM images of Pdnp-nSTDP showed well-defined
spherical Pd particles dispersed in nSTDP (Figure 4).
The size distribution of Pd nanoparticles was about
3.1ꢀ0.5 nm, indicating that palladium nanoparticles
did not aggregate upon immobilization on nSTDP. All
these observations indicate that the triazine dendritic
polymer is a good host and ligand for palladium nano-
particles.
Table 2. TGA and elemental analysis (EA) results for the
synthesis of nano-silica triazine dendritic polymer.
C
H
N
Total
AP-nSiO2
TGA (wt%) 3.636
0.707 1.414
1.020 1.552
5.757
6.291
10.25
10.409
17.783
18.518
EA (wt%)
CC1-nSiO2 TGA (wt%) 5.47
EA (wt%) 5.537
TGA (wt%) 9.722
EA (wt%)
CC2-nSiO2 TGA (wt%) 12.96
EA (wt%) 13.010 1.920 11.216 26.146
TGA (wt%) 20.411 3.590 14.11 38.111
EA (wt%) 20.411 4.209 14.187 38.807
3.719
0.53
4.25
0.832 4.040
1.751 6.310
G1
The palladium content of the catalyst, measured by
10.071 2.100 6.347
1.261 11.08
25.301 ICP, showed a value of 1.27% (0.12 mmolgꢁ1 of
nSTDP).
G2
Suzuki–Miyaura Cross-Coupling of Aryl Halides with
Arylboronic Acids at Room Temperature and under
dritic polymer (Pdnp-nSTDP) were prepared by reduc- MW Irradiation
[14]
tion of Na2Pd2Cl6 (prepared in situ from PdCl2 and
NaCl) in methanol at 608C in the presence of nSTDP. Initially, the Suzuki–Miyaura cross-coupling of 4-bro-
The morphology of the surfaces of nSTDP and moacetophenone with phenylboronic acid in the pres-
Pdnp-nSTDP were studied by field emission scanning ence of Pdnp-nSTDP catalyst was chosen as a model
Scheme 3. Synthesis of the Pdnp-nSTDP catalyst.
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Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP)
Figure 3. FE-SEM images of: a) nSTDP and b) Pdnp-nSTDP.
Figure 4. TEM image and particle size distribution results
SEM-EDX spectra of: c) nSTDP and d) Pdnp-nSTDP.
for Pdnp-nSTDP catalyst.
for optimization of reaction parameters such as the molar ratios of substrates and MW power. The results
base and solvent types, temperature, catalyst loading, are summarized in Table 3. The model reaction was
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Table 3. Optimization of the Suzuki–Miyaura cross-coupling of 4-bromoacetophenone (BA) with phenylboronic acid (PBA)
catalyzed by Pdnp-nSTDP.
Entry Base
Ba:PBA:Base [mmol] Catalyst [mol% Pd] Solvent[a]
Method
Time [h] Yield [%][b]
1
2
3
4
5
6
7
8
NEt3
1:1.1:1.5
1:1.1:1.5
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.004
0.008
0.006
0.006
0.006
0.006
0.004
0.006
0.008
0.006
0.006
DMF/H2O (1:3) r.t.
24
24
24
24
24
14
7
16
18
15
15
14
14
14
11
12
7
35
42
25
58
50
73
95
64
58
70
61
53
60
60
72
70
95
93
94
68
75
73
93
93
62
93
DBU[c]
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:1) r.t.
piperidine 1:1.1:1.5
NaOH
K3PO4
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
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
1:1.1:1.2
1:1.1:1.5
1:1.1: 1.5
1:1.1:1.5
1:1.1:1.5
1:1:1
9
toluene
DMF
H2O
r.t.
r.t.
r.t.
r.t.
10
11
12
13
14
15
16
17
EtOH
H2O/EtOH (1:1) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) r.t.
DMF/H2O (1:3) MW (200 W, 708C) 9 min
DMF/H2O (1:3) MW (200 W, 708C) 8 min
DMF/H2O (1:3) MW (200 W, 708C) 6 min
DMF/H2O (1:3) MW (200 W, 708C) 5 min
DMF/H2O (1:3) MW (200 W, 708C) 5 min
DMF/H2O (1:3) MW (180 W, 508C) 12 min
DMF/H2O (1:3) MW (250 W, 858C) 5 min
18[d] K2CO3
19[e] K2CO3
7
7
20
21
22
23
24
25
26
K2CO3
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
1:1.1:1.5
[a]
[b]
[c]
[d]
[e]
Reaction was performed using 2 mL of solvent.
Isolated yield.
DBU=1,8-diazabicycloACTHNUTRGNEUGN[5.4.0]undec-7-ene.
Reaction was performed under an argon atmosphere.
Reaction was performed under an oxygen atmosphere.
first performed in the presence of different organic
For reaction under MW irradiation, the above-men-
and inorganic bases such as NEt3, DBU, piperidine, tioned molar ratios of the reactants and catalyst with
NaOH, K3PO4, Na2CO3 and K2CO3; amongst them an applied power of 200 W at 708C were found to be
K2CO3 was found to be the most effective base. Then, the optimal conditions (Table 3, entry 23). It is note-
the same reaction was carried out in different single worthy that the model reaction was also carried out
and mixed solvents. Among the solvents examined, under argon and oxygen atmospheres; the results
DMF/H2O (1:3) was proved to be the best reaction were comparable to that obtained in an open system
medium. The effects of the amount of catalyst and (Table 3, entries, 18 and 19), which clearly reveals
the ratios of substrates on the model reaction were that the Pdnp-nSTDP is a stable and oxygen-insensi-
also explored; the best result was obtained using tive catalyst.
0.006 mol% Pd catalyst and the ratio of 4-bromoace-
Encouraged by our initial studies, we then exam-
tophenone to phenylboronic acid was 1:1.1. There- ined the generality and versatility of this supported
fore, it was concluded that the optimum reaction con- palladium-catalyzed Suzuki–Miyaura cross-coupling
ditions involved 4-bromoacetophenone (1 mmol), of aryl halides with arylboronic acids.
phenylboronic acid (1.1 mmol), K2CO3 (1.5 mmol)
As can be seen in Table 4, under the optimized con-
and Pdnp-nSTDP (0.006 mol% Pd) in DMF/H2O (1:3) ditions, a diversity of aryl iodides and bromides con-
at room temperature (Table 3, entry 7).
taining electron-donating and electron-withdrawing
substituents reacted efficiently with phenylboronic
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Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP)
Table 4. Suzuki–Miyaura cross-coupling of aryl halides with arylboronic acids catalyzed by Pdnp-nSTDP.[a]
Entry
R1
R2
X
Room Temperature
Time [h]
Yield [%][b]
MW
Time [min]
Yield [%][b]
1
2
3
4
5
6
7
8
H
H
4-Ac
4-Me
4-Ac
H
H
4-MeO
H
H
4-MeO
H
4-MeO
H
4-MeO
H
4-MeO
H
4-MeO
H
I
I
I
I
2
3
2
2
3
6
7
6
6.5
7
8
10
10
8
95
96
96
95
96
95
94
96
95
95
95
90
92
94
2
2
2
3
3
3
3
3
3
5
5
5
5
4
10
10
7
95
92
93
96
95
94
95
93
94
93
95
92
91
92
94
90
92
93
90
I
Br
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
3-CN
H
9
10
11
12
13
14
15
16
17
18
19
H
4-MeO
H
4-MeO
H
18 (10[c])
24 (14[c])
84 (92[c])
84 (90[c])
83 (92[c])
81 (95[c])
80 (90[c])
H
4-Ac
4-Ac
4-CHO
20ACTHNGUTERNNUG
( 10[c])
18 (10[c])
18 (10[c])
8
8
[a]
Reaction conditions: aryl halide (1 mmol), arylboronic acid (1.1 mmol), K2CO3 (1.5 mmol), Pdnp-nSTDP (0.006 mol%
Pd), DMF/H2O (1:3, 2 mL), r.t. or MW (200 W, 708C).
Isolated yield.
Reaction was performed at 808C.
[b]
[c]
acid and 4-methoxyphenylboronic acid under air at- 808C, the yields increased slightly (90–95%) but the
mosphere at room temperature to afford the desired reaction times decreased significantly (10–14 h)
cross-coupling products in high yields (Table 4, en- (Table 4, entries 15–19).
tries 1–14). The experimental results showed that the
The Suzuki–Miyaura cross-coupling was also inves-
electronic properties of the substituents on the aro- tigated under microwave irradiation. The treatment
matic rings of the starting materials had no significant of a variety of aryl halides (iodides, bromides and
influence on the reaction, however, aryl iodides were chlorides) with arylboronic acids under the optimized
found to be more reactive than aryl bromides.
microwave irradiation, afforded the corresponding
It is important to note that aryl chlorides are cheap- cross-coupling products in 90–96% yields in very
er and more readily available but less reactive than short reaction times (2–10 min) (Table 4). The results
aryl iodides and bromides. Due to lower reactivity, reveal that the yields of the products are comparable
the coupling reactions with aryl chlorides have been under conventional conditions and microwave irradia-
generally investigated using a higher amount of cata- tion, but the reaction times are considerably shorter
lyst.[15] In order to further explore the efficiency and under microwave irradiation (Table 4). It is notable
applicability of this method, the cross-coupling of aryl that various sensitive functional groups such as MeO,
chlorides with arylboronic acids was also checked Ac, CHO and CN are well tolerated under the reac-
under the same conditions. As shown in Table 4, reac- tion conditions.
tion of various aryl chlorides with phenylboronic acid
and 4-methoxyphenylboronic acid proceeded smooth-
ly in the presence of the same catalyst amount as Heck Reaction of Aryl Halides with Styrenes Under
used for aryl iodides and bromides (0.006 mol% Pd) Thermal Conditions and MW Irradiation
at room temperature, resulting in the desired cross-
coupling products in high yields (80–84%) within 18– Encouraged by the obtained results in the Suzuki–
24 h. When the same reactions were performed at Miyaura cross-coupling, we then investigated the po-
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Amir Landarani Isfahani et al.
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tential of our Pdnp-nSTDP catalyst in the Heck reac- reaction was exposed to MW irradiation, the maxi-
tion. In order to obtain the optimum experimental mum yield of the desired product was achieved with
conditions, the reaction of 4-bromoacetophenone with a MW power of 200 W at 708C (Table 5, entry 22).
styrene was considered as a model reaction in the
Using the optimized reaction conditions, a variety
presence of Pdnp-nSTDP catalyst under thermal con- of structurally divergent aryl iodides, bromides and
ditions and microwave irradiation. The effects of the chlorides was coupled with styrene and 4-methylstyr-
reaction conditions such as the type of base and sol- ene to generate the desired coupling products in 88–
vent, temperature, catalyst amount, molar ratios of 95% yields at 858C within 9–22 h (Table 6). The Heck
substrates and MW power were tested and a summary reaction of these aryl halides with styrenes was also
of the optimization experiments is provided in examined under microwave irradiation. Under these
Table 5. As can be seen, under thermal conditions, conditions, the corresponding coupling products were
the best result was obtained using 4-bromoacetophe- obtained in 87—96% yields in 8–20 min (Table 6).
none
(1 mmol),
styrene
(1.1 mmol),
K2CO3 The experimental results show that microwave irradi-
(1.5 mmol) and Pdnp-nSTDP (0.01 mol% Pd) in DMF/ ation has the evident advantage of short reaction
H2O (1:3) at 858C (Table 5, entry 7). When the same times over the traditional heating mode. It is notewor-
Table 5. Optimization of the Heck reaction of 4-bromoacetophenone (BA) with styrene (Sty) catalyzed by Pdnp-nSTDP.
Entry
Base
BA:Sty:K2CO3
[mmol]
Catalyst
ACHTUNGTRENN[UNG mol% Pd]
Solvent[a]
Method
Time
[h]
Yield
[%][b]
U
1
2
3
4
5
6
7
8
NEt3
DBU
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
1:1.1:1.2
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
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:1)
toluene
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
thermal (858C)
30
30
30
30
24
24
15
24
24
24
24
24
24
30
30
30
39
48
48
52
50
92
50
50
65
50
63
50
48
40
piperidine
NaOH
K2CO3
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
9
10
11
12
13
14
15
DMF
H2O
EtOH
H2O/EtOH
(1:1)
16
17
18
19
20
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.5
1:1.1:1.2
0.008
0.012
0.01
0.01
0.01
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
thermal (858C)
thermal (858C)
thermal (708C)
thermal (1008C)
MW (200 W,
708C)
15
15
15
15
65
92
85
92
70
12 min
21
22
23
24
25
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
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
0.008
0.01
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
DMF/H2O (1:3)
MW (200 W,
708C)
MW (200 W,
708C)
MW (200 W,
708C)
MW (250 W,
858C)
12 min
12 min
12 min
12 min
12 min
68
93
93
93
85
0.012
0.01
0.01
MW (150 W,
508C)
[a]
Reaction was performed using 2 mL of solvent.
Isolated yield.
[b]
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Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP)
Table 6. Heck reaction of aryl halides with styrenes catalyzed by Pdnp-nSTDP.[a]
Entry
R1
R3
X
Thermal
Yield [%][b]
MW
Time [h]
Time [min]
Yield [%][b]
1
2
3
4
5
6
7
8
H
H
4-Me
4-Ac
4-Ac
H
H
4-MeO
4-F
H
I
I
I
I
9
9
9
9
95
93
92
95
91
90
92
93
91
90
93
95
92
90
92
89
88
89
91
10
10
8
8
8
95
93
96
96
95
93
95
95
89
92
93
92
93
89
93
89
90
87
89
4-Me
4-Me
H
4-Me
H
4-Me
4-Me
H
4-Me
H
4-Me
H
H
H
H
I
9
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
14
14
15
17
15
10
13
15
15
20
20
22
20
20
12
12
12
10
14
12
13
12
18
17
15
20
20
15
9
10
11
12
13
14
15
16
17
18
19
4-F
4-Me
4-Ac
4-Ac
4-CHO
H
4-MeO
4-Ac
4-Ac
4-CHO
H
4-Me
H
[a]
Reaction conditions: aryl halide (1 mmol), styrene (1.1 mmol), K2CO3 (1.5 mmol), Pdnp-nSTDP (0.01 mol% Pd), DMF/
H2O (1:3, 2 mL), 858C or MW (200 W, 708C).
Isolated yield.
[b]
thy that, based on NMR spectra, in all Heck olefina- liquid crystals,[16] components of organic light-emitting
tion reactions, the trans-product was obtained with devices (OLEDs),[17] field-effect transistors (FETs),[18]
100% selectivity.
single molecular electronics,[19] and non-linear optical
materials.[20] They have also been used in coordination
chemistry,[21] and in the syntheses of dendritic chro-
mophores[22] and hyperbranched conjugated mole-
cules.[23] Accordingly, the development of new and
highly efficient methods for their preparation is a de-
sirable synthetic goal.
Synthesis of Star- and Banana-Shaped Molecules
Containing Benzene, Pyridine, Pyrimidine or 1,3,5-
Triazine Central Cores Catalyzed by Pdnp-nSTDP
Star- and banana-shaped compounds are of great sig-
In order to further widen the applicability of this
nificance due to their wide variety of applications as method, we examined the preparation of a range of
Table 7. Synthesis of star- and banana-shaped molecules via Suzuki–Miyaura cross-coupling catalyzed by Pdnp-nSTDP.
Entry
Substrate
Product
Room Temperature
Time [h]
MW
Yield [%][a]
Time [min]
8
Yield [%][a]
95
1
S1[b]
S2[b]
12
12
92
2
92
8
93
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Table 7. (Continued)
Entry
Substrate
Product
Room Temperature
Time [h]
Yield [%][a]
MW
Time [min]
Yield [%][a]
3
S3[c]
S4[c]
S5[d]
S6[d]
S7[d]
S8[d]
14
14
15
15
15
15
90
8
94
4
5
6
7
89
90
91
83
87
8
92
93
89
87
90
10
10
10
10
8
[a]
Isolated yield.
[b]
[c]
[d]
Reaction conditions: 2,6-dibromopyridine (1 mmol), arylboronic acid (2.3 mmol), K2CO3 (3 mmol), Pdnp-nSTDP
(0.012 mol% Pd), DMF/H2O (1:3, 8 mL), room temperature or MW (200 W, 708C).
Reaction conditions: 1,3,5-tribromobenzene (1 mmol), arylboronic acid (3.8 mmol), K2CO3 (4.5 mmol), Pdnp-nSTDP
(0.018 mol% Pd), DMF/H2O (1:3, 8 mL), room temperature or MW (200 W, 708C).
Reaction conditions: 2,4,6-tricholoropyrimidine or 2,4,6-trichlorotriazine (1 mmol), arylboronic acid (4.2 mmol), K2CO3
(4.5 mmol), Pdnp-nSTDP (0.045 mol% Pd), DMF/H2O (1:1, 8 mL), room temperature or MW (200 W, 708C).
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Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP)
star- and banana-shaped molecules using this catalytic For example, in the preparation of S11 from S9 by
system. The results are summarized in Table 7. As the the Suzuki–Miyaura cross-coupling reaction with phe-
data demonstrated, the Suzuki–Miyaura cross-cou- nylboronic acid catalyzed by Pdnp-nSTDP, the mono-
pling of 2,6-dibromopyridine with phenylboronic acid and bis-cross-coupling products (S13 and S14) were
or 4-methoxyphenylboronic acid was performed effi- also produced (Scheme 5).
ciently in the presence of Pdnp-nSTDP catalyst at
Finally, the efficiency of this catalytic system was
room temperature and under microwave irradiation examined for the synthesis of star-shaped molecules
and the corresponding banana-shaped molecules were by the Heck reaction. As shown in Scheme 6, the
obtained in high yields (Table 7, entries 1 and 2). Heck reaction of 1,3,5-tribromobenzene either with
Also, a series of star-shaped triarylbenzens, triarylpyr- styrene or with 4-methylstyrene proceeded smoothly
imidines and triaryltriazines was obtained in high in the presence of Pdnp-nSTDP at 858C and under mi-
yields using this method by coupling of 1,3,5-tribro- crowave irradiation, affording the corresponding star-
mobenzene, 2,4,6-trichloropyrimidine or 2,4,6- shaped products (S15 and S16) in high yields.
trichloro
perature and under microwave irradiation (Table 7, results of our experiments are compared with some of
entries 3–8). those reported using several Pd-based nanoparticle
A
In Table S1 (Supporting Information) some of the
It is noteworthy that the preparation of some star- catalysts.[24,25] As can be seen, some of the reported
shaped molecules was studied directly from 4-bromo- methods provide higher yields (entries 13, 14 and 16)
and 4-iodoacetophenones as precursors by a combina- and/or shorter reaction times (entries 8, 13 and 17).
tion of cyclotrimerization and the Suzuki–Miyaura However, in the present method, the amount of the
cross-coupling via two synthetic pathways: path a) cy- catalyst (Pdnp-nSTDP) is much lower and the turnover
clotrimerization of 4-haloacetophenones catalyzed by frequencies (TOFs) are higher, and the reaction tem-
H3PW12O40 (HPW)[11a] and then cross-coupling with peratures are comparable (entries 3, 7 and 16) or
arylboronic acids in the presence of Pdnp-nSTDP cata- lower than the others.
lyst; path b) cross-coupling of 4-haloacetophenones
To the best of our knowledge, this is the first report
with arylboronic acids catalyzed by Pdnp-nSTDP and on the synthesis of palladium nanoparticles immobi-
subsequent cyclotrimerization in the presence of lized on a nano-silica triazine dendritic polymer and
ꢁ
HPW (Scheme 4). As can be seen, the path b is more its application in C C coupling reactions.
effective and the desired star-shaped molecules were
obtained in high yields under these conditions.
The structures of the products were determined
from their spectral data. The structure of the product
The path a) is unfavourable due to the formation of S2 was additionally confirmed by X-ray diffraction
two by-products, in addition to the desired product. analysis (Figure 5, CCDC 854353, these data can be
Scheme 4. Synthesis of star-shaped molecules from 4-haloacetophenones.
Adv. Synth. Catal. 2013, 355, 957 – 972
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Amir Landarani Isfahani et al.
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Scheme 5. Reaction of 1,3,5-tris(4-bromophenyl)benzene S9 with phenylboronic acid catalyzed by Pdnp-nSTDP.
Scheme 6. Synthesis of star-shaped molecules by the Heck reaction.
obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif).
Catalyst Recycling and Reuse
The recycling and reusability of a catalyst is very im-
portant from practical, economical and environmental
points of view. Thus, the reusability of Pdnp-nSTDP
was examined in the Suzuki–Miyaura cross-coupling
of 4-bromoacetophenone with phenylboronic acid
under the optimized conditions. After completion of
Figure 5. Crystal structure of compound S2.
the reaction (in the case of MW irradiation, the reac-
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Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP)
Table 8. Recycling and reuse of the Pdnp-nSTDP catalyst in
Suzuki–Miyaura cross-coupling of 4-bromoacetophenone
with phenylboronic acid.[a]
mined with a Stuart Scientific SMP2 apparatus. FT-IR spec-
tra were recorded on a Nicolet-Impact 400D spectropho-
1
tometer. H and 13C NMR (400 and 100 MHz) spectra were
recorded on a Bruker Avance 400 MHz spectrometer using
CDCl3 as solvent. Elemental analysis was performed on
a LECO, CHNS-932 analyzer. Thermogravimetric analysis
(TGA) was carried out on a Mettler TG50 instrument under
air flow at a uniform heating rate of 58Cminꢁ1 in the range
30–6008C. The TGA instrument was re-calibrated at fre-
quent intervals with standards; the accuracy was always
better than ꢀ2.0%. The scanning electron microscope mea-
surement was carried out on a Hitachi S-4700 field emis-
sion-scanning electron microscope (FE-SEM). The transmis-
sion electron microscopy (TEM) was carried out on a Philips
CM10 Transmission Electron Microscope operating at
100 kV. The Pd content of the catalyst was determined by
a Jarrell-Ash 1100 ICP analysis. The microwave system used
in these experiments includes the following items: Micro-
SYNTH labstation, equipped with a glass door, a dual mag-
netron system with pyramid shaped diffuser, 1000 W deliv-
ered power, exhaust system, magnetic stirrer, ꢁquality pres-
sureꢂ sensor for flammable organic solvents, and a ATCFO
fiber optic system for automatic temperature control.
Run
Yield [%][b]
Room Temp.
Pd leached [%][c]
MW
Room Temp.
MW
1
2
3
4
5
6
7
95
92
92
92
92
92
92
93
91
91
91
90
90
90
2
1
0
0
0
0
0
1
1
0
0
0
0
0
[a]
Reaction conditions: 4-bromoacetophenone (1 mmol),
phenylboronic acid (1.1 mmol), K2CO3 (1.5 mmol), Pdnp-
nSTDP (0.006 mol% Pd) in DMF/H2O (1:3, 2 mL), room
temperature for 7 h or MW (200 W, 708C) for 5 min.
Isolated yield.
[b]
[c]
Determined by ICP.
tion mixture was first cooled to room temperature),
ethyl acetate (15 mL) was added, the catalyst was sep-
arated by centrifugation and reused. The results
showed that the catalyst could be reused six consecu-
tive times without significant loss of its catalytic activ-
ity (Table 8). The analysis of palladium leaching from
Pdnp-nSTDP catalyst by ICP indicated that only
Synthesis of Triazine Dendritic Polymer Supported on
Nano-Silica (nSTDP)
Activation of Nano-Silica: In
a round-bottomed flask
a trace amount of palladium has been leached in the equipped with a condenser and a magnetic stirrer, a mixture
of nano-silica (10 g, 40–100 nm) and concentrated HCl
(80 mL, 6M) was heated in an oil-bath at 1208C for 24 h.
The mixture was filtered and the white powder was washed
with distilled water until neutral pH. The solid was dried
under vacuum at 1208C.[26]
first two runs (Table 8).
Conclusions
Preparation of Propylamine-Functionalized Nano-Silica
(AP-nSiO2): In a round-bottomed flask equipped with a con-
denser and a magnetic stirrer, a mixture of activated nano-
silica (3 g) and 3-aminopropyltrimethoxysilane (APTS)
(8 mL) in 50 mL of anhydrous toluene was stirred under
In conclusion, we have demonstrated palladium nano-
particles immobilized on nano-silica triazine dendritic
polymer (Pdnp-nSTDP) to be a highly active, air- and
moisture-stable, oxygen-insensitive and highly reusa-
ble catalyst for the Suzuki–Miyaura cross-coupling reflux conditions for 8 h. The reaction mixture was filtered
and the solid material was washed with toluene in a continu-
ous extraction apparatus (Soxhlet) to remove the unreacted
starting material, and dried in a vacuum oven at 1108C.[12]
Preparation of CC1-nSiO2: The AP-nSiO2 (2 g,
0.99 mmolg)ꢁ1 was added to a solution of cyanuric chloride
(1.85 g, 10 mmol) and diisopropylethylamine (DIPEA)
(10 mmol, 1.7 mL) in THF (10 mL). The reaction mixture
was shaken overnight at room temperature. The solid mate-
rial was separated by filtration, washed with hot THF for
12 h in a Soxhlet apparatus to remove the unreacted starting
and the Heck reaction of aryl iodides, bromides and
chlorides with arylboronic acids and styrenes, respec-
tively, under conventional conditions and microwave
irradiation. This catalytic system was also used effi-
ciently for the synthesis of a series of star- and
banana-shaped molecules. Ease of recovery and reuse
of the catalyst make this method an economic and en-
vironmentally-benign process. In addition, high yields,
short reaction times, wide scope and simple work-up
procedure make this method a valid contribution to materials and then dried in a vacuum oven at 508C.
ꢁ
Preparation of Nano-Silica-Supported Triazine Dendritic
Polymer (G1): To a slurry of CC1-nSiO2 (1 g) in DMF
(12 mL) was added bis(3-aminopropyl)amine (8.11 mmol,
1 mL) and DIPEA (8.11 mmol, 1.4 mL). The reaction mix-
ture was stirred at 808C for 16 h. The solid material was fil-
tered, washed with hot ethanol for 12 h in a Soxhlet appara-
tus to remove the unreacted starting materials and then
dried in a vacuum oven at 508C.
the existing methodologies for C C coupling reac-
tions.
Experimental Section
General Remarks
Preparation of CC2-nSiO2: Nano-silica-supported triazine
dendritic polymer, G1 (1 g, 0.45 mmol) was added to a solu-
tion of cyanuric chloride (1.66 g, 9 mmol) and DIPEA
The chemicals used in this work were purchased from Fluka
and Merck chemical companies. Melting points were deter-
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Amir Landarani Isfahani et al.
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(9 mmol, 1.56 mL) in THF (20 mL). The reaction mixture
was agitated at room temperature for 16 h. The reaction
mixture was filtered and the solid was washed with hot THF
for 16 h in a Soxhlet apparatus to remove the unreacted
starting materials. Finally, the CC2-nSiO2 was dried in
a vacuum oven at 508C.
Preparation of Nano-Silica-Supported Triazine Dendritic
Polymer (G2 or nSTDP): To a slurry of CC2-nSiO2 (1 g,
0.36 mmol) in DMF (20 mL) was added bis(3-aminopropyl)-
amine (9.36 mmol, 1.14 mL) and DIPEA (9.36 mmol,
1.61 mL). The reaction mixture was agitated at 808C for
16 h and then filtered. The resulting nano-silica-supported
dendritic polymer (G2 or nSTDP) was washed with hot eth-
anol for 24 h in a Soxhlet apparatus to remove unreacted
starting materials and dried in a vacuum oven at 508C.
Pd) in 2 mL of DMF/H2O (1:3) was stirred at 858C or irradi-
ated with MW (200 W, 708C) under an air atmosphere for
the desired time according to Table 6. The progress of the
reaction was monitored by TLC (eluent: ether/ethyl acetate,
6:1). At the end of the reaction, the mixture was cooled to
room temperature, ethyl acetate (15 mL) was added and the
catalyst was separated by centrifugation. The organic layer
was washed with water (2ꢃ10 mL) and dried over anhy-
drous MgSO4. Evaporation of the solvent and purification
of the crude product by recrystallization from ethyl acetate
and ether (1:3) afforded the pure product (Table 6).
General Procedure for Synthesis of Star- and Banana-
Shaped Molecules Containing Benzene, Pyridine,
Pyrimidine or 1,3,5-Triazine Central Cores via
Suzuki–Miyaura Cross-Coupling Catalyzed by Pdnp-
nSTDP
Preparation of Nano-Silica Triazine Dendritic
Polymer Supported Palladium Nanoparticles (Pdnp-
nSTDP)
A mixture of 1,3,5-tribromobenzene, 2,6-dibromopyridine,
2,4,6-trichloropyrimidine or 2,4,6-trichlorotriazine (1 mmol),
arylboronic acid (2.3–4.2 mmol), K2CO3 (3–4.5 mmol) and
Pdnp-nSTDP (0.012–010.045 mol% Pd) in 8 mL of DMF/
H2O (1:3) was stirred at room temperature or exposed to
MW irradiation (200 W, 708C) for the appropriate time ac-
cording to Table 7. The work-up was performed as described
for Suzuki Miyaura cross-coupling and the pure product was
obtained by recrystallization of the crude product from
ethyl acetate and ether (1:1).
A mixture of PdCl2 (240 mg, 1.36 mmol) and NaCl (88 mg,
1.52 mmol) in methanol (8 mL) was stirred at room temper-
ature for 24 h and then filtered. The filtrates were diluted
with methanol (40 mL) and nSTDP (1 g, 0.21 mmol) was
added to this solution. The resulting mixture was stirred at
608C for 24 h. At the end of the reaction, the mixture was
cooled to room temperature, sodium acetate (0.76 g,
9.28 mmol) was added and stirred at room temperature for
1 h. The solid was filtered, washed with methanol, water and
acetone, to remove the unreacted starting materials and
then dried in vacuum to afford Pdnp-nSTDP catalyst (1.07 g)
as a light gray solid. Palladium analysis (ICP): 1.27%. Aver-
age particle diameter: 3.1ꢀ0.5 nm (based on TEM and par-
ticle size analyses).
Synthesis of S11 and S12 from S9 and S10 Catalyzed
by Pdnp-nSTDP at Room Temperature and under
MW Irradiation (Scheme 4, Path a)
To a mixture of 1,3,5-tris(4-halophenyl)benzene (S9 or S10,
prepared according to the previously reported method[11a]
)
(1 mmol), arylboronic acid (4.5 mol) and K2CO3 (4.5 mmol)
in 10 mL of DMF/H2O (1:1), was added Pdnp-nSTDP
(0.018 mol% Pd). The reaction mixture was stirred at room
temperature or exposed to MW irradiation (270 W, 708C)
for the time indicated in Scheme 4. The progress of the reac-
tion was monitored by TLC (eluent: ether/EtOAc, 9:1).
After completion of the reaction, ethyl acetate (15 mL) was
added (in the case of the reaction under MW irradiation,
the mixture was first cooled to room temperature) and the
catalyst was separated by centrifugation. The organic phase
was washed with water (2ꢃ10 mL), dried over anhydrous
MgSO4, and evaporated. The resulting crude material was
purified by recrystallization from ethyl acetate and ether
(1:1) to afford the pure product.
General Procedure for Suzuki–Miyaura Cross-
Coupling Catalyzed by Pdnp-nSTDP at Room
Temperature and under Microwave Irradiation
A
mixture of aryl halide (1 mmol), arylboronic acid
(1.1 mmol), K2CO3 (1.5 mmol) and Pdnp-nSTDP
(0.006 mol% Pd) in 2 mL of DMF/H2O (1:3) was stirred at
room temperature or exposed to microwave irradiation
(200 W, 708C) under an air atmosphere for the period of
time indicated in Table 4. The progress of the reaction was
monitored by TLC (eluent: ether/ethyl acetate, 6:1). After
completion of the reaction, ethyl acetate (15 mL) was added
(in the case of the reaction under MW irradiation, the mix-
ture was first cooled to room temperature) and the catalyst
was separated by centrifugation. The organic phase was
washed with water (2ꢃ10 mL), dried over anhydrous
MgSO4 and evaporated. The residue was recrystallized from
ethyl acetate and ether (1:3) to afford the pure product
(Table 4).
Synthesis of S11 and S12 by Suzuki–Miyaura Cross-
Coupling and Subsequent Cyclotrimerization
(Scheme 4, Path b)
In this protocol, the reaction was performed in two steps.
First, the desired 4-arylacetophenone was prepared by the
reaction of 4-haloacetophenone with arylboronic acid ac-
cording to the above-mentioned general procedure for
Suzuki–Miyaura cross-coupling catalyzed by Pdnp-nSTDP
(Table 4, entries 3, 5, 10 and 11). Then, the cyclotrimeriza-
tion of 4-arylacetophenone was carried out according to the
reported procedure.[11a] In this step, a mixture of 4-arylaceto-
General Procedure for Heck Reaction Catalyzed by
Pdnp-nSTDP under Thermal Conditions and
Microwave Irradiation
In a round-bottomed flask equipped with a condenser and
a magnetic stirrer, a mixture of aryl halide (1 mmol), styrene
(1.1 mmol), K2CO3 (1.5 mmol) and Pdnp-nSTDP (0.01 mol%
970
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2013, 355, 957 – 972

Palladium Nanoparticles Immobilized on Nano-Silica Triazine Dendritic Polymer (Pdnp-nSTDP)
phenone (1 mmol) and H3PW12O40 (151 mol%) was subject-
ed to MW irradiation (450 W, 908C) for the appropriate
time according to Scheme 4. After completion of the reac-
tion, as monitored by TLC, hot ethyl acetate (10 mL) was
added and the catalyst was separated by filtration. The sol-
vent was evaporated and the resulting crude material was
purified by recrystallization from ethyl acetate and ether
(1:1) to afford the pure product.
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Synthesis of 1,3,5-Tristyrylbenzenes (S15 and S16) via
Heck Reaction Catalyzed by Pdnp-nSTDP under
Thermal Conditions and Microwave Irradiation
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The 1,3,5-tribromobenzene (1 mmol), styrene (5.5 mmol),
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mixed in DMF/H2O (1:1, 10 mL). The reaction mixture was
stirred at 858C or irradiated with MW (300 W, 858C) for the
appropriate time as mentioned in Scheme 6. The reaction
progress was monitored by TLC (eluent: ethyl acetate/ether,
1:6). After completion of the reaction, the mixture was
cooled to room temperature, ethyl acetate (15 mL) was
added and the catalyst was separated by centrifugation. The
organic phase was washed with water (2ꢃ10 mL), dried
over anhydrous MgSO4, and evaporated. The organic phase
was evaporated and the residue was recrystallized from n-
hexane to afford the pure product.
Acknowledgements
The authors are grateful to the Center of Excellence of
Chemistry and Research Council of the University of Isfahan
for financial support of this work.
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