Ultrasound-assisted C-C coupling reactions catalyzed by unique SPION-A-Pd(EDTA) as a robust nanocatalyst

Article abstract of DOI:10.1039/c3ra45790g

A novel and highly stable Pd(EDTA)^2- salt was synthesized as a catalyst, using a counter-cation of N-methylimidazolium bonded to 1,3,5-triazine-tethered SPIONs (superparamagnetic iron oxide nanoparticles). This well-defined complex efficiently

Full text of DOI:10.1039/c3ra45790g

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Ultrasound-assisted C–C coupling reactions
catalyzed by unique SPION-A-Pd(EDTA) as a robust
nanocatalyst
Cite this: RSC Adv., 2014, 4, 8590
Received 12th October 2013
Accepted 5th December 2013
Marzieh Ghotbinejad, Ahmad R. Khosropour,* Iraj Mohammadpoor-Baltork,*
Majid Moghadam, Shahram Tangestaninejad and Valiollah Mirkhani
DOI: 10.1039/c3ra45790g
www.rsc.org/advances
2ꢀ
A novel and highly stable Pd(EDTA) salt was synthesized as a catalyst,
The palladium catalyzed cross-coupling reactions are the
using a counter-cation of N-methylimidazolium bonded to 1,3,5- most powerful and selective tools for carbon–carbon bond
16–18
triazine-tethered SPIONs (superparamagnetic iron oxide nano- formation.
These cross-coupling reactions have been
particles). This well-defined complex efficiently catalyzed the Mizor- abundantly used in organic synthesis, pharmaceuticals, and the
oki–Heck and Suzuki–Miyaura cross-coupling reactions. The cross- synthetic methodologies of natural products, conducting poly-
1
9,20
coupled products were produced under conventional heating and mers, and liquid crystals.
Among these reactions, the Miz-
21,22
23
ultrasound irradiation at an extremely low catalyst loading (as low as oroki–Heck
.032 mol% Pd). Results indicated that conventional synthesis took recognized as important tools in modern organic synthesis.
longer and gave moderate yields, while in the presence of ultrasound The Heck reaction is a transformation between aryl halides
irradiation, the reaction occurred very fast in high to excellent yields. and olens that leads to the formation of disubstituted
and Suzuki–Miyaura reactions have been
0
24,25
The catalyst could be quickly recovered by an external magnetic field olens.
The Suzuki reaction is the most powerful method for
and could be reused for several reaction cycles without any change in coupling aryl halides with phenylboronic acid, which provides
26–30
catalytic activity.
an effective method for synthesizing biaryls.
These reactions generally proceed in the presence of a
homogeneous palladium catalyst. The difficulties in product
separation and recycling of the catalyst have limited the appli-
3
1,32
Introduction
cations of homogeneous palladium catalysts in recent years.
Therefore, in order to overcome these drawbacks, many inves-
tigations on developing effective methods for immobilization of
Pd complexes on different solid supports, such as microporous
With the increasing environmental consciousness in chemical
research, the challenge of designing sustainable environmen-
tally friendly procedures has become the fundamental aim of
green chemistry. From the rst report on using ultrasound in
33
34
35
polymers, activated carbon, clays, and magnetic nano-
particles (MNPs) have been performed. Magnetic nanoparticle-
supported catalysts are the better choice as they not only show
excellent catalytic activities but the magnetic nature of these
particles also allows for facile recovery and recycling of the
1
organic synthesis, the motivation to use this technique in
organic transformations increased tremendously. Ultrasonic-
assisted organic synthesis (UAOS) is a promisingly useful
2–4
approach to a green technique in organic synthesis. The
physical and chemical effects of ultrasound irradiation are
based on acoustic cavitations resulting from the continuous
formation, growth and implosive collapse of bubbles in a
solution, which results in a high temperature and pressure
36,37
catalyst without use of the traditional ltration method.
Moreover, surface modied superparamagnetic iron oxide
nanoparticles (SPIONs) have received increasing interest in the
past few years both in biomedical and organic trans-
formations. Very recently, we reported synthesis of SPION-ACl2
as a green and powerful nano-catalyst for the efficient synthesis
38
5–8
pulse. The advantages of ultrasound irradiation in organic
synthesis are the formation of purer products in good yields,
short reaction times, improved energy conservation, easier
manipulation, mild conditions and waste minimization which
39
of Betti bases. It was found that due to the high magnetization
of the catalyst it could be satisfactory recovered by a simple
external magnet. Moreover, the catalyst could be easily recycled
and reused without a loss of its activity.
9–15
is comparable to traditional methods.
Now, encouraged by the previous results and our interest in
Catalysis Division, Department of Chemistry, University of Isfahan, 81746-73441, developing efficient, sustainable and greener pathways for
Isfahan, Iran. E-mail: khosropour@chem.ui.ac.ir; imbaltork@sci.ui.ac.ir; Fax: +98
116689732; Tel: +98 3117932700
40
organic transformations, particularly those under ultrasonic
3
8590 | RSC Adv., 2014, 4, 8590–8596
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41
42
irradiation and C–C coupling reactions, we would like to
report herein a new and powerful palladium-EDTA complex-
tagged dicationic ionic liquid with a 1,3,5-triazine core
anchored to superparamagnetic nanoparticles (SPION-ACl2),
and its application in cross-coupling reactions such as the
Mizoroki–Heck and Suzuki–Miyaura reactions, under ultra-
sound irradiation.
Result and discussion
The synthetic pathway for the catalyst is depicted in Scheme 1.
SPION-A-Pd(EDTA) was characterized by means of Fourier
transform infrared spectroscopy (FT-IR), inductively coupled
plasma atomic emission spectroscopy (ICP) thermal gravimetric
analysis (TGA), and high resolution transmission electron
microscopy (HR-TEM).
Fig. 1 illustrates the FT-IR spectra of Fe O (a), silica-
3
4
encapsulated Fe O (b), and the nanocatalyst SPION-A-
3
4
Pd(EDTA) (c), respectively.
The FT-IR spectrum of SPION-A-Pd(EDTA) (Fig. 1c) showed
ꢀ
1
absorption bands at 3421 cm
2
(N–H stretching vibration),
3 4
Fig. 1 Comparison of the FT-IR spectra of (a) Fe O ; (b) silica-
ꢀ
1
ꢀ1
ꢀ1
930 cm (C–H), 1622 cm (C]N) and 635–587 cm (Fe–O) encapsulated Fe O ; (c) SPION-A-Pd(EDTA).
3
4
SPIONs.
Inductively coupled plasma atomic emission spectroscopy
ICP) determined the amount of palladium in SPION-A-
Pd(EDTA) as 3.41 wt%.
(
applied it in the Mizoroki–Heck reaction under ultrasound
irradiation. To optimization the reaction conditions the reac-
tion of iodobenzene (1.0 mmol) and styrene (1.0 mmol) was
chosen as a model, and the role of various bases, solvents and
the output power of the ultrasound apparatus were investigated.
The thermal stability of SPION-A-Pd(EDTA) was also evalu-
ated by thermal gravimetric analysis–differential thermal
analysis (TGA-DTG). According to this curve, two weight loss
ꢁ
steps were observed. In the rst step (below 180 C), the water
(Table 1, entries 1–14).
molecules (4.59%) in the structure were omitted, while the
As illustrated in Table 1, DMF was the best solvent for this
synthesis. Other solvents such as ethanol and toluene gave only
moderate yields of the product (Table 1, entries 1–3).
ꢁ
organic part (11.28%) was lost between 180 and 480 C (Fig. 2).
To study the morphology of SPION-A-Pd(EDTA), an HR-TEM
image was also investigated (Fig. 3).
Among the various bases screened, K CO was found to be
2
3
HR-TEM images of SPION-A-Pd(EDTA) revealed that it
appears to have an almost spherical structure with an average
size of about 10–13 nm (Fig. 3b). Thus, the enormous active
sites of this nanoparticle may display excellent activity levels in
organic transformations.
the most effective base for this transformation (Table 1, entry 4).
Other bases such as Na CO and NEt gave moderate yields
2
3
3
of the product (Table 1, entries 5, 6).
No reaction occurred without the catalyst (Table 1, entry 7).
More examination revealed that the yield reduced drastically
with the replacement of Pd(OAc)2@nano-Fe3O4 or Pd(OAc)
Aer the structure characterization of the catalyst, in order to
evaluate the catalytic activity of SPION-A-Pd(EDTA), we initially
Scheme 1 The synthetic pathway for SPION-A-Pd(EDTA).
Fig. 2 TG-DTG analysis of SPION-A-Pd(EDTA).
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but using lower power (140 W) sharply decreased the conversion
to approximately 85% even with more reaction time (Table 1,
entry 12).
Accordingly, performing the reaction at 170 W in the pres-
ence of 0.094 g of SPION-A-Pd(EDTA) (0.003 mol % Pd), with
ꢁ
K
2
CO
3
as the base, and DMF as the solvent, at 50 C, was
optimal for the Mizoroki–Heck reaction. This optimized sono-
chemical reaction was applied to the synthesis of a variety of
disubstituted olens.
To assess the inuence of ultrasonic irradiation on this
transformation, we initially examined this reaction under
thermal conditions (Table 2). As shown in Table 2, the reaction
takes place efficiently in high TOF between 2 and 14 hours at
ꢁ
9
0 C.
To demonstrate the effect of sonication, the synthesis of all
Fig. 3 (a) HR-TEM image of SPION-A-Pd(EDTA) and (b) SPION-A-
Pd(EDTA) particle size distribution histogram.
the corresponding products was also investigated with ultra-
sonic irradiation (Table 3). It is apparent that the ultrasound
accelerates this transformation under milder conditions.
For instance, at the optimal conditions, 1,2-diphenyl-
ethylene was produced almost quantitatively (96% isolated
Table 1 Optimization of the reaction of iodobenzene with styrene in
a
the presence of SPION-A-Pd(EDTA)
5
-1
yield) with high TOF (5.6 ꢂ 10 h ) aer 10 min sonication at
ꢁ
50
C (Table 3, entry 1), while in silent conditions, a higher
ꢁ
temperature (90 C) was required to obtain the product in only
87% yield and with lower TOF aer 2 h (Table 2, entry 1). This
achievement could be extended to the other products.
We assume that the benecial effect of ultrasound on this
heterogeneous reaction may be attributed to a better mass
b
Entry
Yield (%)
Solvent effect
1
2
3
DMF
Toluene
Ethanol
96
60
55
Table 2 Mizoroki–Heck cross-coupling of aryl halides and styrene
derivatives in the presence of SPION-A-Pd(EDTA) under silent
conditions
Base effect
a
4
5
6
K
2
CO
3
96
87
50
Na CO
2 3
NEt
3
Catalyst effect
7
8
9
—
Pd(OAc)
Pd(OAc)
—
20
15
96
2
@nanoFe
3 4 2
O nanoSiO
2
@nano-SiO
2
1
2
b
c
1
0
SPION-A-Pd(EDTA)
Entry
R
R
X
Product Time (h) Yield (%) TOF
4
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Power effect (watt)
1
2
3
4
5
6
7
8
9
H
H
H
H
H
4-Me
H
I
I
2a
2b
2
8
7
9
6
8
9
8
10
3
5
7
8
10
14
12
87
90
83
85
84
80
83
85
87
88
86
84
84
86
82
87
1.4 ꢂ 10
3.7 ꢂ 10
3.9 ꢂ 10
3.1 ꢂ 10
4.7 ꢂ 10
3.3 ꢂ 10
3.1 ꢂ 10
3.5 ꢂ 10
2.9 ꢂ 10
9.8 ꢂ 10
5.7 ꢂ 10
4.0 ꢂ 10
3.5 ꢂ 10
2.9 ꢂ 10
1.9 ꢂ 10
2.4 ꢂ 10
1
1
1
1
1
2
3
4
120
140
170
200
78
85
96
96
Br 2a
4-Me Br 2b
2c
Br 2b
4-Me Br 2d
4-MeO 4-Me
I
4-Me
4-Me
4-Me
4-Me
4-Ac
4-Ac
4-Ac
4-Ac
4-CHO
4 F
H
a
Reaction conditions: Iodobenzene (1 mmol), styrene (1.5 mmol) and
CO (1.5 mmol) in the presence of the catalyst containing 0.003 mol
Pd in 2 mL of DMF. Isolated yield.
K
%
2
3
b
H
4-Me
H
I
I
I
2b
2d
2e
1
1
1
0
1
2
4-Me Br 2f
Br 2e
4-Me Br 2f
H
2
@nano-SiO2 instead of SPION-A-Pd(EDTA) as the catalyst 13
1
1
1
4
5
6
H
H
Br 2g
Br 2h
(Table 1, entries 8 and 9).
We also found that the output power of the ultrasound
apparatus greatly affected this transformation. The obvious
improvement in the conversion (96%) reached a plateau at
4 F
4-Me Br 2i
a
Reactions were carried out under aerobic conditions in 2 ml of mixture
of DMF, 1 mmol aryl halide, 1.5 mmol styrene derivative, 1.5 mmol
170 W of power. Higher acoustic power (200–400 W) made no
K
2
CO
3
in the presence of SPION-A-Pd(EDTA) (0.003 mol% Pd) and
ꢁ
b
c
ꢀ1
obvious difference in the yield of the product (Table 1, entry 14) 90 C. Isolated yield. [mol product/mol palladium] h
.
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Table 3 Mizoroki–Heck cross-coupling of aryl halides and styrene Table 4 Optimization reaction for the synthesis of phenylbenzene as
derivatives in the presence of SPION-A-Pd(EDTA) by ultrasound a model under ultrasonic irradiation in the presence of SPION-A-
a
irradiation
Pd(EDTA)
1
2
b
c
Entry
R
R
X
Product Time (min) Yield (%) TOF
b
Entry
1
Solvent
DMF
Base
Pd (mol%)
Power
Yield (%)
5
5
5
5
4
4
4
5
5
4
4
4
4
4
4
4
1
2
3
4
5
6
7
8
9
H
H
H
H
H
4-Me
H
I
I
2a
2b
10
8
96
97
88
91
91
87
89
89
91
90
90
88
90
88
86
89
1.9 ꢂ 10
2.5 ꢂ 10
1.0 ꢂ 10
1.2 ꢂ 10
9.2 ꢂ 10
9.1 ꢂ 10
9.9 ꢂ 10
1.1 ꢂ 10
1.2 ꢂ 10
7.1 ꢂ 10
8.1 ꢂ 10
6.8 ꢂ 10
9.1 ꢂ 10
6.9 ꢂ 10
5.9 ꢂ 10
5.1 ꢂ 10
K
2
K
2
K
2
K
2
CO
CO
CO
CO
3
3
3
0.003
0.003
0.003
0.003
0.003
0.003
0.003
0.003
0.003
170
170
160
160
160
160
140
160
200
57
54
95
95
65
47
80
95
95
2
3
4
5
6
7
8
9
H
2
2
2
2
2
2
2
2
O
Br 2a
17
15
20
19
18
16
15
25
22
26
20
25
29
35
a
H
H
H
H
H
H
H
O/DMFa
O/DMFa
O/DMFa
4-Me Br 2b
2c
Br 2b
4-Me Br 2d
3
4-MeO 4-Me
I
Na
2
CO
3
4-Me
4-Me
4-Me
4-Me
4-Ac
4-Ac
4-Ac
4-Ac
4-CHO
4 F
H
O/DMFa
NEt
3
O/DMF
K
2
K
2
K
2
CO
CO
CO
3
3
3
H
4-Me
H
I
I
I
2b
2d
2e
a
O/DMFa
O/DMF
1
1
1
1
1
1
1
0
1
2
3
4
5
6
a
b
4-Me Br 2f
Br 2e
4-Me Br 2f
2
H O/DMF (V/V) 2 : 1. Isolated yield.
H
H
H
Br 2g
Br 2h
Suzuki–Miyaura C–C coupling reactions using SPION-A-
Pd(EDTA) was repeated six times to evaluate the catalyst's
recyclability and stability (Fig. 4). The results illustrated the
excellent stability of the catalyst under the reaction conditions.
Initially, the Suzuki–Miyaura cross-coupling of iodobenzene
with phenylboronic acid in the presence of SPION-A-Pd(EDTA)
was chosen as a template reaction for the optimization of
parameters such as base type, solvent and ultrasonic irradiation
power of the reaction. The results are summarized in Table 4.
Finally, a comparison of this protocol with recent reports was
performed with the Suzuki–Miyaura cross-coupling reaction of
phenyl bromide and phenylboronic acid as a template. As
shown in Table 6, the best TOF was obtained when utilizing
SPION-A-Pd(EDTA).
4 F
4-Me Br 2i
a
Reactions were carried out under aerobic conditions in 2 ml of mixture
of DMF, 1 mmol aryl halide, 1.5 mmol styrene derivative, 1.5 mmol
CO in the presence of SPION-A-Pd(EDTA) (0.003 mol% Pd)
and power: 170 W at 50 C. Isolated yield. [Mol product/mol
K
2
3
ꢁ
b
c
ꢀ
1
palladium] h
.
transfer and dispersion of the nanocatalyst in the medium in
comparison with magnetically stirred reactions, which makes
the catalyst more effective in this transformation.
To continue, for the investigation of the effect of the catalyst–
sonication combination on the other C–C coupling reactions,
we decided to study the Suzuki–Miyaura cross-coupling reaction
of arylboronic acids with a variety of aryl halides in the presence
of SPION-A-Pd(EDTA) under ultrasonic irradiation.
Experimental
As shown in Table 4, the optimal conditions included the All chemicals were purchased from the Merck chemical
reaction of iodobenzene (1 mmol), phenylboronic acid (1.1 company. Fe O nanocomposites and silica-coated magnetite
3
4
mmol), K
2 3
2 3 4
CO (1.5 mmol) and SPION-A-Pd(EDTA) (0.094 g, nanoparticles (SiO @Fe O ) were synthesised according to the
43
0.003 mol% Pd) in DMF/H
2
O (1 : 2) under ultrasound irradia- literature. The Na Pd(EDTA) complex was prepared by the
2
ꢁ
tion at 30 C.
dissolution of Pd(OAc)2 (Aldrich), Na CO and Na H EDTA
2
3
2
2
As with the aforementioned results, the generality of the (Merck) performed on UV-active aluminum-backed plates of
1
13
reaction condition was also examined. The results revealed that silica gel (TLC Silica gel 60 F254). H, and C NMR spectra were
the yields of the corresponding products were comparable measured on a Bruker DPX 400 MHz spectrometer in CDCl3
under silent conditions and ultrasound irradiation, while the with the chemical shi (d) given in ppm. Coupling constants are
sonication was performed with a swi reaction under milder given in Hz.
conditions in comparison to conventional heating (Table 5).
The successful production of the biaryl derivatives indicated spectrophotometer with KBr pellets, and were reported in cm
The FT-IR spectra were taken on a Nicolet-Impact 400D
ꢀ1
.
that this is a powerful procedure for the Suzuki–Miyaura Melting points were determined using a Stuart Scientic SMP2
reaction.
apparatus and are uncorrected. The sonication was performed
The recovered SPION-A-Pd(EDTA) could also be reused easily in a UP 400S ultrasonic processor equipped with a 3 mm wide
using an applied magnetic eld aer the end of the reaction, and 140 mm long probe, which was immersed directly into the
without any signicant loss of its high catalytic performance. reaction mixture. The operating frequency was 24 kHz and the
The examination of the ultrasonic-assisted Mizoroki–Heck and output power was 0–400 Watts through manual adjustment.
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a
Table 5 Suzuki–Miyaura cross-coupling of aryl halides and ArB(OH)
2
in the presence of SPION-A-Pd(EDTA)
b
c
Silent conditions
Ultrasonic conditions
1
2
d
e
b
e
Entry
R
R
X
Product
Time (h)
Yield (%)
TOF
Time (min)
Yield (%)
TOF
3
5
5
5
5
4
5
5
5
4
4
4
5
5
5
5
4
5
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
H
H
H
H
H
4-MeO
H
4-MeO
H
4-MeO
H
4-MeO
H
H
4-MeO
H
4-MeO
H
I
I
3a
3b
3a
3b
3b
3c
3d
3e
3f
3g
3h
3d
3e
3b
3c
3g
3h
3i
4
2
7
6
8
7
8
6
9
6
5
6
5
3
4
8
11
14
92
93
85
87
86
88
86
89
82
83
88
88
90
89
90
86
89
85
7.7 ꢂ 10
10
7
95
96
88
90
89
90
90
92
87
88
91
90
93
91
92
89
90
88
1.9 ꢂ 10
2.7 ꢂ 10
1.1 ꢂ 10
1.3 ꢂ 10
9.3 ꢂ 10
1.2 ꢂ 10
1.1 ꢂ 10
1.4 ꢂ 10
5.0 ꢂ 10
6.9 ꢂ 10
9.2 ꢂ 10
1.3 ꢂ 10
1.4 ꢂ 10
1.1 ꢂ 10
1.3 ꢂ 10
7.8 ꢂ 10
1.0 ꢂ 10
4
1 ꢂ 5 10
3
Br
Br
Br
Br
Br
Br
Br
I
I
I
I
I
4.0 ꢂ 10
16
14
19
15
16
13
35
25
20
14
13
17
14
23
18
24
3
4.8 ꢂ 10
3
4-MeO
4-MeO
4-Me
4-Me
4 F
4-Ac
4-Ac
4-Me
4-Me
4-MeO
4-MeO
4-Ac
4-Ac
4-CHO
3.6 ꢂ 10
3
4.1 ꢂ 10
3
3.6 ꢂ 10
3
4.9 ꢂ 10
3
3.0 ꢂ 10
3
0
1
2
3
4
5
6
7
8
4.6 ꢂ 10
3
5.9 ꢂ 10
3
4.9 ꢂ 10
3
6.0 ꢂ 10
3
9.9 ꢂ 10
3
4-MeO
H
4-MeO
H
I
7.5 ꢂ 10
3
Br
Br
Br
3.6 ꢂ 10
3
2.7 ꢂ 10
3
2.0 ꢂ 10
7.3 ꢂ 104
a
Reactions were carried out under aerobic conditions in 2 ml of mixture of DMF and water (1 : 2), 1 mmol aryl halide, 1.1 mmol arylboronic acid
b
ꢁ ꢁ
2 3
and 1.5 mmol K CO (1.5 mmol) with SPION-A-Pd(EDTA) (0.003 mol% Pd). At 70 C. Applied power: 160 W at 30 C. Isolated yield. [Mol
1
c
d
e
ꢀ
product per mol palladium] h
.
The HRTEM images were taken with a Philips CM30 unit
operated at 150 kV. The TGA curve was obtained with a heating
ꢁ
ꢀ1
rate of 10 C min on a TG 50 Mettler thermogravimetric
ꢁ
ꢁ
analyzer from 30 C to 600 C. The Pd content of the catalyst was
determined by Jarrell-Ash 1100 ICP analysis.
Preparation of SPION-A-Pd(EDTA)
2 3 2
Na CO (0.2 mmol, 0.021 g) was added to a mixture of Na EDTA
(
0.1 mmol, 0.037 g) and PdCl (0.1 mmol, 0.018 g) in water (5 ml)
2
ꢁ
Fig. 4 Reuse of SPION-A-Pd(EDTA) examined on the model reactions at 25 C, and was stirred magnetically for 5 h. In an argon
of Mizoroki–Heck and Suzuki–Miyaura under ultrasonic irradiation.
atmosphere, SPION-ACl2 (0.53 g) in EtOH (5 ml) was added
dropwise to the solution and the resulting mixture was stirred
for a further 12 h at room temperature. Finally, the catalyst was
Table 6 Comparison of the present method with recent Suzuki–Miyaura cross-coupling procedures
Pd amount
(mol %)
a
b
c
Entry
Catalyst
Time (min)
Yield (%)
TOF
Ref.
5
1
2
3
4
5
6
7
SPION-A-Pd(EDTA)
Pd/IL-NH /SiO /Fe
SiO /BisILsR[PdEDTA]
Pd–NHC@Fe -IL (3)
Pd(OAc) @Fe -IL (3)
Fe @SiO @mSiO –Pd(0)
SMNPs-Salen Pd(II)
16
300
600
360
360
360
180
88
87
99
85
91
0.003
0.5
1
0.5
0.5
1.1 ꢂ 10
This work
2
2
3
O
4
34.8
45
44
46
47
48
49
2
99.0
3
O
O
4
28.33
30.33
215.56
6.67
2
3
4
3
O
4
2
2
97
100
0.075
0.5
a
Reactions were carried out under aerobic conditions in 2 ml of mixture of DMF and water (1 : 2), 1 mmol phenyl bromide, 1.1 mmol phenylboronic
b
c
ꢀ1
acid and 1.5 mmol K
2
CO
3
.
Isolated yield. [Mol product per mol palladium] h .
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collected by an external permanent magnet, washed with
Acknowledgements
CH Cl (3 ꢂ 10 ml) and H O, and dried under vacuum.
2
2
2
The support of this work by the Center of Excellence of Chem-
istry, of the University of Isfahan, (CECUI) is acknowledged.
General procedure for heterogeneous Heck reactions
A mixture of an aryl halide (1.0 mmol), an alkene (1.5 mmol),
K CO (207 mg, 1.5 mmol) and SPION-A-Pd(EDTA) (0.094 g,
2 3
Notes and references
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.003 mol % of Pd) in DMF (2 ml) was exposed to ultrasonic
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irradiation at 170 W at 50 C for 8–35 min according to Table 3.
The progress of the reaction was monitored by TLC (eluent:
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. Purication by ash column chroma-
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ꢀ1
1
48 C. IR (KBr) nmax ¼ 2969, 1602, 1495, 1378, 1253, 860 cm
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1
H NMR (400 MHz, CDCl
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1
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2 3
CO (207 mg, 1.5 mmol) and Cat. B (0.094 g,
0
.003 mol % of Pd) in 2 ml DMF–H
2
O (1 : 2 v/v) was exposed to
ꢁ
ultrasonic irradiation at 160 W at 30 C for 7–35 min according
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(
2 ꢂ 1 ml), air-dried, and used directly for the next round of the 17 (a) V. Farina, Adv. Synth. Catal., 2004, 346, 1553; (b)
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4
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13
0
ꢁ
4
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ꢀ
1 1
¼
2938, 1680, 1601, 1490, 1378, 1253, 852 cm . H NMR (400
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H), 3.87 (s, 6H).
3
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