Pd complex of an NNN pincer ligand supported on γ-Fe2O3@SiO2 magnetic nanoparticles: A new catalyst for Heck, Suzuki and Sonogashira coupling reactions

Article abstract of DOI:10.1039/c5nj00344j

In this study, a Pd complex of bis(imino)pyridine as an NNN pincer ligand supported on γ-Fe₂O₃@SiO₂ magnetic nanoparticles (Pd-BIP-γ-Fe₂O₃@SiO₂) was synthesized and characterized by SEM, TEM, FT-IR, TGA, ICP, XRD, XPS, VSM and elemental analysis. The synthesized catalyst was used successfully as a new air- and moisture-stable phosphine-free Pd catalyst for Heck, Suzuki and Sonogashira coupling reactions of aryl iodides, bromides and chlorides with alkyl acrylates, styrene, phenylboronic acid and phenylacetylene. The true heterogeneous magnetically-recyclable catalyst can be separated easily using a magnetic bar and reused ten times without any drastic loss of its catalytic activity.

Full text of DOI:10.1039/c5nj00344j

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Journal Name
RSCPublishing
ARTICLE
Pd Complex of a NNN Pincer Ligand Supported on γꢀ
Fe2O3@SiO2 Magnetic Nanoparticles: A New Catalyst
for Heck, Suzuki and Sonogashira Coupling
Reactions
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2015,
Accepted 00th January 2015
Sara Sobhania* Zohre Zeraatkara, Farzaneh Zarifia
DOI: 10.1039/x0xx00000x
In this paper, Pd complex of bis(imino)pyridine as a NNN pincer ligand supported on γꢀFe2O3@SiO2
magnetic nanoparticles (PdꢀBIPꢀγꢀFe2O3@SiO2) was synthesized and characterized by SEM, TEM, FTꢀ
IR, TGA, ICP, XRD, XPS, VSM and elemental analysis. The synthesized catalyst was used successfully
as a new airꢀ and moistureꢀstable phosphineꢀfree Pd catalyst for Heck, Suzuki and Sonogashira coupling
reactions of aryl iodides, bromides and chlorides with alkyl acrylates, styrene, phenylboronic acid and
phenylacetylene. The true heterogeneous magnetically recyclable catalyst can be separated easily by a
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magnetic bar and reused ten times without any drastic loss of its catalytic activity
.
nitrogen ligand.9 Moreover, pincer ligands offer high stability
towards heat, air and moisture and great control of the steric and
electronic properties of metal centers.10 Recently, synthesis and
application of a complex of BIP with Pd supported on MCMꢀ41 in
Suzuki coupling reaction was reported.11 Despite the high catalytic
activity of this heterogeneous palladium catalyst, its separation
technique was energy and time consuming. Moreover, the catalyst
was used for the coupling reaction of only aryl bromides as aryl
halides with phenylboronic acid. Employing magnetic nanoparticles
(MNPs) as a support for Pd complex can solve the problem of
catalyst separation. This kind of supporting allows Pd catalyst to be
easily separated from the reaction medium by application of an
external permanent magnet. Magnetic separation of MNPs, which is
an alternative to filtration or centrifugation, prevents loss of the
catalyst, and saves time and energy.12 However, MNPs are readily
aggregated due to the self interactions. In order to prevent the
aggregation, the surface of MNPs was usually modified with suitable
coating such as silica layer.13 The outer shell of silica not only
improves the dispersibility but also provides suitable sites (SiꢀOH
groups) for further surface functionalization.14
Introduction
Heck, Suzuki and Sonogashira crossꢀcoupling reactions are
important strategies for the formation of carbonꢀcarbon bonds and
catalyzed originally by homogeneous Pd catalyst.1 However, these
reactions suffer from problems associated with the separation and
recovery of the homogeneous and high cost Pd catalyst, which might
result in undesirable metal contamination of the products. Therefore,
to have an efficient recovery and recycling of Pd catalyst, the
immobilization of homogeneous Pd catalytic systems on different
supporting materials has been the subject of intense research.2 Other
challenge facing this field is the design of the catalysts that are more
robust and efficient using valuable ligands as stabilizers for Pd
species.3 During the past decades, the most common ligands used for
these crossꢀcoupling reactions have been the phoshineꢀbased ones.4
Most of the phosphineꢀbased ligands are air and/or moistureꢀ
sensitive, poisonous, unrecoverable and degradable at elevated
temperature which limited their largeꢀscale application in the
industrial chemistry.5 In recent years, several groups have tried to
develop phosphineꢀfree Pd complexes for crossꢀcoupling reactions.
However, the reported complexes have the drawbacks of requiring
an excess of expensive ligands, multistep syntheses and inert
conditions. Moreover, most of the reported methods are amenable
only for the crossꢀcoupling reactions of aryl iodides and bromides.6
To benefit the valuable applications of MNPs and unique
properties of BIP as a NNN pincer ligand, and in continues of
our recent works on the development of heterogeneous catalysts
in organic transformations,15 herein, we report the synthesis of
an airꢀ and moistureꢀstable phosphineꢀfree Pd complex with
BIP supported on γꢀFe2O3@SiO2 nanoparticles (PdꢀBIPꢀγꢀ
Fe2O3@SiO2). The synthesized catalyst was characterized by
different methods such as TEM (transmission electron
microscopy), SEM (scanning electron microscope), FTꢀIR
Bis(imino)pyridines (BIP) with the central nitrogen donor and
flanking imine arms are known as NNN tridentate pincer ligands,
which coordinate easily with transition metals such as Mn, Zn, Gd,
Ni, Co and Fe to form metal complexes.7 These metal complexes
have mainly applied as highly active and selective catalysts for the
oligoꢀ and polymerization of olefins.8 Metal complexes containing
nitrogen donor pincer ligands present a high stability due to the
formation of two fiveꢀmembered metallacycles with a tridentate
(Fourier
transform
infrared
spectroscopy),
TGA
(Thermogravimetric analysis), ICP (inductively coupled
plasma), XRD (Xꢀray diffraction), XPS (Xꢀray photoelectron
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spectrum), VSM (Vibrating Sample Manetometer) and
elemental analysis and used as a new magnetically recoverable
Pd catalyst for the carbon–carbon coupling reactions of aryl
halides with olefines, phenylboronic acid and phenylacetylene
via Heck, Suzuki and Sonogashira reactions.
Results and discussion
Synthesis and characterization of PdꢀBIPꢀγꢀ
Fe2O3@SiO2
e
Synthesis of PdꢀBIPꢀγꢀFe2O3@SiO2 is schematically described in
Scheme 1. The synthesized silicaꢀcoated γꢀFe2O3 nanoparticles (γꢀ
Fe2O3@SiO2)16
were
functionalized
with
3ꢀ
aminopropyltriethoxysilane by refluxing in dry toluene. The
obtained aminoꢀfunctionalized γꢀFe2O3@SiO2 reacted with pyridineꢀ
2,6ꢀdicarbaldehyde to produce γꢀFe2O3@SiO2 supported with
bis(imino)pyridine (BIPꢀγꢀFe2O3@SiO2). Pd complex of BIP
supported on γꢀFe2O3@SiO2 (PdꢀBIPꢀγꢀFe2O3@SiO2) was
synthesized by refluxing BIPꢀγꢀFe2O3@SiO2 with Pd(OAc)2 in
methanol. The synthesized PdꢀBIPꢀγꢀFe2O3@SiO2 was fully
characterized by SEM, TEM, TGA, FTꢀIR, ICP, XRD, XPS, VSM
and elemental analysis.
NH2
O
Si
OH
OH
OH
OH
OH
OH
Figure 1. (a,b) SEM images, (c,d) TEM images and (e) particle size
distribution histogram of PdꢀBIPꢀγꢀFe2O3@SiO2
O
O
O
O
pyridineꢀ2,6ꢀdicarbaldehyde
MeOH, reflux, 6 h
(EtO)3Si(CH2)3NH2
γꢀFe2O3
γꢀFe2O3
dry toluene, reflux, 48 h
SiO2
SiO2
O
Si
NH2
FTꢀIR spectra of aminoꢀfunctionalized γꢀFe2O3@SiO2, BIPꢀγꢀ
Fe2O3@SiO2 and PdꢀBIPꢀγꢀFe2O3@SiO2 are shown in Figure 2. The
bands at around 565ꢀ684, 1048ꢀ1206 and 2935 cmꢀ1 were assigned to
the stretching vibrations of FeꢀO, SiꢀO and CH2 bonds, respectively.
The peak positioned at around 1471 cmꢀ1 in the FTꢀIR spectrum of
aminoꢀfunctionalized γꢀFe2O3@SiO2 was related to the bending of
the CH2 bonds. The characteristic absorption bands due to the
stretching vibration of C=C and C=N were observed at 1409ꢀ1454
and 1646 cmꢀ1 in the spectrum of BIPꢀγꢀFe2O3@SiO2. Peaks
appeared at 1634 and 1401 cmꢀ1 in the spectrum of PdꢀBIPꢀγꢀ
Fe2O3@SiO2 were related to COO (in acetate) and confirmed the
presence of Pd in the catalyst.
N
N
N
O
Si
Si
N
O
Si
O
O
O
O
O
Pd(OAc)2
MeOH, reflux, 10 h
O
γꢀFe2O3
γꢀFe2O3
SiO2
AcO
OAcꢀ
Pd
N
N
O
O
SiO2
O
O
Si
BIPꢀγꢀFe2O3@SiO2
PdꢀBIPꢀγꢀFe2O3@SiO2
Scheme 1. Synthesis of PdꢀBIPꢀγꢀFe2O3@SiO2
According to the SEM (Fig. 1), it was observed that the synthesized
PdꢀBIPꢀγꢀFe2O3@SiO2 has uniformity and spherical morphology.
TEM images of PdꢀBIPꢀγꢀFe2O3@SiO2 displayed a dark γꢀFe2O3
core surrounded by a gray silica shell with thickness of about 4 nm.
It can be seen that the NPs are spherical in shape and relatively
monodispersed. The particle size distribution of PdꢀBIPꢀγꢀ
Fe2O3@SiO2 was evaluated using TEM and showed that the average
diameter of the particles was 20 nm.
Figure 2. FTꢀIR spectra of (a) aminoꢀfunctionalized γꢀFe2O3@SiO2,
(b) BIPꢀγꢀFe2O3@SiO2 and (c) PdꢀBIPꢀγꢀFe2O3@SiO2
FTꢀIR spectra of BIPꢀγꢀFe2O3@SiO2 and PdꢀBIPꢀγꢀFe2O3@SiO2
were compared with those of unsupported 1 and 2 (Scheme 2, Fig.
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3). Comparison of FTꢀIR spectra of BIPꢀγꢀFe2O3@SiO2 and PdꢀBIPꢀ
γꢀFe2O3@SiO2 with those of 1 and 2 showed that the characteristic
peaks were positioned at the same wave numbers, but with a small
shift in the spectrum of BIPꢀγꢀFe2O3@SiO2 and PdꢀBIPꢀγꢀ
Fe2O3@SiO2 due to the interaction with the support. As shown in
Figure 3, the bands at around 1049ꢀ1110 and 2923 cmꢀ1 were
assigned to the stretching vibrations of SiꢀO and CH2 bonds,
respectively. The characteristic absorption bands related to the
stretching vibration of C=C and C=N were observed at 1455 and
1648 cmꢀ1 in the spectrum of 1. After complexation with palladium,
these two peaks in the spectrum of 2 were shifted to 1454 and 1641
cmꢀ1, respectively, because of the bond formation between the metal
and the ligand. The overlap of these peaks with the COO peak in
acetate causes them to become broad.
Figure 4. TGA diagram of BIPꢀγꢀFe2O3@SiO2
As presented in Figure 5, the reflection planes of (2 2 0), (3 1 1), (4 0
0), (4 2 2), (5 1 1) and (4 4 0) at 2θ = 30.3◦, 35.7◦, 43.4◦, 53.8◦, 57.4◦
and 63.0◦ were readily recognized from the XRD pattern of γꢀFe2O3.
The same set of characteristic peaks was observed in the XRD
pattern of PdꢀBIPꢀγꢀFe2O3@SiO2, which indicates the stability of the
crystalline phase of nanoparticles during the subsequent surface
modification. The observed diffraction peaks was indicated that γꢀ
Fe2O3 NPs mostly exist in faceꢀcentered cubic structure. XRD
pattern of PdꢀBIPꢀγꢀFe2O3@SiO2 showed a weak peak at 2θ = 39.9◦
correspond to (1 1 1) reflection of the supported Pd. This peak is
relatively broad due to the small particle size of the Pd NPs.17
EtO
EtO
EtO
Si
EtO
EtO
EtO
N
N
pyridineꢀ2,6ꢀdicarbaldehyde
MeOH, reflux, 6 h
Si
NH2
N
EtO
EtO
EtO
Si
EtO
EtO
EtO
1
Si
N
Pd(OAc)2
AcO
Pd
N
OAcꢀ
MeOH, reflux, 10 h
EtO
EtO
EtO
N
Si
2
Scheme 2. Synthesis of 1 and 2
γꢀFe2O3
Figure 3. FTꢀIR spectra of 1 and 2
The thermal behaviour of BIPꢀγꢀFe2O3@SiO2 is shown in Figure 4.
A significant decrease in the weight percentage at about 145 °C was
related to the desorption of water molecules from surface. This was
evaluated to be ∼0.5% according to the TGA. Another decreasing
peak started at 234 °C. The organic parts decomposed completely at
around 550 °C. According to the TGA, the amount of BIP
functionalized on γꢀFe2O3@SiO2 calculated to be 0.34 mmol.g−1.
These results are in good agreement with the elemental analysis data
(N = 1.58% and C = 4.96%). The ICP analysis of PdꢀBIPꢀγꢀ
Fe2O3@SiO2 showed that 0.28 mmol of Pd was loaded on 1 g of the
catalyst.
PdꢀBIPꢀγꢀFe2O3@SiO2
Figure 5. XRD patterns of γꢀFe2O3 and PdꢀBIPꢀγꢀFe2O3@SiO2
Xꢀray photoelectron spectroscopy (XPS) was carried out to establish
the oxidation state of Pd in the catalyst (Fig. 6). The binding energies
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CO2Bun
CO2Bun
at 337.6 and 342.1 eV corresponding to Pd 3d5/2 and Pd 3d3/2
respectively, confirmed the presence of Pd (II) in the catalyst. No
peaks corresponding to Pd (0) in the metallic state was detected.
,
PdꢀBIPꢀγꢀFe2O3@SiO2
I
Scheme 3. Heck crossꢀcoupling reaction of iodobenzene with nꢀ
butyl acrylate
.
At first, the model reaction was performed in DMF at 100 °C in the
presence of 0.25 and 0.5 mol% of PdꢀBIPꢀγꢀFe2O3@SiO2 and Et3N
(2 mmol) (Fig. 8a). In both reactions, the yield of the product was
increased in 15 min and remains constant till 0.5 h. Higher yield was
obtained in the presence of 0.5 mol% of the catalyst. The influence
of a variety of solvents such as EtOH, CH3CN, H2O and toluene on
the progress of the reaction were studied (Fig. 8b). Of the tested
solvents, DMF was the best choice, giving the desired product in
shorter reaction time (0.25 h) and with higher yield (98%) (Fig. 8b).
A similar reaction under solventꢀfree conditions proceeded slowly in
1 h. In the screening of various bases, Et3N gave the highest catalytic
efficiency for this coupling reaction (Fig. 8c). The model reaction
Figure 6. Xꢀray photoelectron spectroscopy (XPS) of PdꢀBIPꢀγꢀ was also studied in the presence of PdꢀBIPꢀγꢀFe2O3@SiO2 (0.5
Fe2O3@SiO2
mol%) in DMF in 80 °C. The results of this study suggested that 100
°C is the optimum temperature for this reaction (Fig. 8d). The model
reaction was examined in the absence of the catalyst, Pd(OAc)2 and
2 (Fig. 8e). A trace amount of the product was obtained after 1 h in
the absence of the catalyst. The catalytic activity of PdꢀBIPꢀγꢀ
Fe2O3@SiO2 was higher than that of Pd(OAc)2 and 2.
The magnetization curves of γꢀFe2O3 and PdꢀBIPꢀγꢀFe2O3@SiO2
were measured at room temperature with a vibrating sample
magnetometry (VSM). As shown in Figure 7, the remanence and
coercivity were reduced insignificantly, which indicates that both
unmodified and PdꢀBIPꢀmodified γꢀFe2O3 are superparamagnetic.
The value of saturation magnetic moments of γꢀFe2O3 decreased
with the attachment of SiO2 and the PdꢀBIP from 68.6 emu/g to 53.0
emu/g for PdꢀBIPꢀγꢀFe2O3@SiO2. However, PdꢀBIPꢀγꢀFe2O3@SiO2
with superparamagnetic characteristics and high magnetization
values can quickly respond to an external magnetic field and
redisperse when the external magnetic field is removed. This
supports their potential application for targeting and separation.
(a) 100
90
80
70
0.25 mol%
0.5 mol%
60
50
40
30
20
10
0
80
40
0
0
5
10
15
20
25
30
Time (min)
(b)
100
90
80
70
60
50
40
30
20
10
0
ꢀ15000
ꢀ10000
ꢀ5000
0
5000
10000
15000
DMF
Solvent free
EtOH
PdꢀBIPꢀγꢀFe2O3@SiO2
γꢀFe2O3
ꢀ40
CH3CN
H2O
Toluene
ꢀ80
Field (Oe)
0
10
20
30
40
50
60
Time (min)
Figure 7. Magnetization curves of γꢀFe2O3 and PdꢀBIPꢀγꢀ
Fe2O3@SiO2
(c)
100
90
80
70
60
50
40
30
20
10
0
Catalytic activity of PdꢀBIPꢀγꢀFe2O3@SiO2 in Heck,
Suzuki and Sonogashira crossꢀcoupling reactions
KOH
K2CO3
NaOAc
Et3N
For optimization of the Heck coupling reaction conditions, we chose
the coupling of iodobenzene (1 mmol) with nꢀbutyl acrylate (1.1
mmol) in the presence of PdꢀBIPꢀγꢀFe2O3@SiO2 as a model reaction
(Scheme 3).
0
10
20
30
40
50
60
Time (min)
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Table 1. Heck crossꢀcoupling reaction of aryl halides with olefins
using PdꢀBIPꢀγꢀFe2O3@SiO2
(d)
100
90
80
70
60
50
40
30
20
10
0
R2
R2
PdꢀBIPꢀγꢀFe2O3@SiO2 ( 0.5 mol %)
100°C
80°C
X
Et3N, 100 oC, DMF
R1
R1
Entry
R1
X
R2
Time (h)
Yielda
(%)
98
95
96
92
86
92
92
90
83
88
91
90
88
80
82
93
86
75
75
0
5
10
15
20
25
30
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
H
H
H
I
I
I
I
I
Br
Br
Br
Cl
Cl
Cl
I
CO2Bun
CO2Me
CO2Et
CO2Bun
CO2Bun
CO2Bun
CO2Bun
CO2Bun
CO2Bun
CO2Bun
CO2Bun
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
0.25
0.75
0.75
1.5
1.5
4
2.5
3
5
6
6
2
3
Time (min)
4ꢀCl
4ꢀMeO
H
4ꢀNO2
4ꢀCN
H
4ꢀCN
4ꢀNO2
H
4ꢀCl
4ꢀMeO
H
4ꢀNO2
4ꢀCN
H
(e)
100
90
80
70
60
50
40
30
20
10
0
Catalyst
PdꢀBIP
Pd(OAc)2
No Catalyst
I
I
0
10
20
30
40
50
60
3
3.5
3
3
7
Br
Br
Br
Cl
Cl
Time (min)
4ꢀNO2
7
aIsolated yield. Reaction conditions: aryl halide (1 mmol), olefin (1.1
mmol), Et3N (2 mmol), PdꢀBIPꢀγꢀFe2O3@SiO2 (0.5 mol%), DMF, 100
°C. The products were characterized by comparison of their physical
properties with the authentic samples.6
Figure 8. Effect of the amount of the catalyst (a), different bases (b),
solvents (c), temperatures (d), and type of the catalyst (e) on reaction
conversions.
To explore the scope of this method, the Heck coupling reaction of
various aryl halides and olefins was studied under optimal reaction
conditions (Table 1). Different aryl iodides reacted well with olefins
including methyl/ethyl/nꢀbutyl acrylate and the desired products
were isolated in 86ꢀ98% yields (Entry 1ꢀ5). Aryl bromides reacted
with nꢀbutyl acrylate and generated the corresponding products in
high yields (Entries 6ꢀ8). The applicability of this method for the
coupling reaction of some aryl chlorides (far cheaper and more
widely available than aryl iodides and bromides) with nꢀbutyl
acrylate was also examined. The examined aryl chlorides underwent
the coupling reactions and gave the desired products in relatively
good yields. However, the reaction proceeded in rather longer
reaction times compared with aryl bromides and iodides (Entries 9ꢀ
11). To test the potential for practical synthetic applications, a larger
scale Heck coupling reaction of iodobenzene (50 mmol) with nꢀbutyl
acrylate (55 mmol) was carried out under the present reaction
conditions. The reaction proceeded smoothly (2 h), giving 98% yield
of the desired product.
To check whether Pd was being leached out from the solid catalyst
to the solution or weather the catalyst was truly heterogeneous in
nature, Heck crossꢀcoupling reaction of iodobenzene with nꢀ
butylacrylate was studied. After proceeding of 30% of the coupling
reaction at 100 °C, the catalyst was separated by a magnet and the
remaining solution was stirred for 12 h. In the absence of the
catalyst, any increase in the conversion value (30%) was not
detected. Moreover, ICP analysis of the remaining solution revealed
that there was not any Pd in the reaction mixture. These results
suggested that the Pd was not being leached out from the solid
surface of the catalyst during coupling reaction and the catalyst was
truly heterogeneous. Heterogeneous nature of the catalyst was
further checked by employing a solidꢀphase poisoning test, by using
16
3ꢀmercaptopropylꢀfunctionalized γꢀFe2O3@SiO2 as an efficient Pd
scavenger. In a typical experimental procedure, iodobenzene (1
mmol), nꢀbutyl acrylate (1.1 mmol), Et3N (2 mmol) and DMF (10
ml) were mixed in a round bottom flask along with PdꢀBIPꢀγꢀ
Fe2O3@SiO2 (0.02 g) and 3ꢀmercaptopropylꢀfunctionalized γꢀ
Fe2O3@SiO2 (0.05 g). The whole mixture was stirred in an oil bath
for about 0.5 h at 100 °C. No change in the conversion was observed
compared with the results obtained in the presence of PdꢀBIPꢀγꢀ
Fe2O3@SiO2 (Table 1, entry 1). These results clearly demonstrated
that this novel catalyst was heterogeneous in nature.
3
It is worth to mention that JHꢀH value of 16.0ꢀ16.4 Hz for vinyllic
1
hydrogens of the products was obtained using H NMR spectra and
showed an excellent selectivity for the formation of trans isomer of
the products.
In order to extend the generality of this method, the Heck coupling
reaction of aryl halides with styrene was also studied. The results
showed that this catalytic system was effective for the Heck coupling
reaction of styrene with both activated and deactivated aryl iodides,
bromides and chlorides (Entries 12ꢀ19).
The reusability of the catalyst is a very important theme, especially
for commercial and industrial applications. Therefore, the recovery
and reusability of PdꢀBIPꢀγꢀFe2O3@SiO2 were investigated in the
reaction of iodobenzene with nꢀbutyl acrylate under the present
reaction conditions. After the reaction was completed and allowed to
be cooled, the catalyst was separated by a magnetic bar from the
reaction mixture (Fig. 9b), washed with EtOAc, dried 30 min at 100
°C and reused for a consecutive run under the same reaction
conditions. The catalyst was successfully used in 10 subsequent
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reactions (Table 2). The average isolated yield of the product for ten
consecutive runs was 93.1%, which clearly demonstrates the
practical reusability of the catalyst. The average turnover number
(TON = mmole of product/mmole of Pd catalyst) and average
turnover frequency [TOF (hꢀ1) = TON/time] of the catalyst for 10
runs were 186 and 744 hꢀ1, respectively.
Figure 11. FTꢀIR spectra of PdꢀBIPꢀγꢀFe2O3@SiO2 after (a) first
reuse, (b) tenth reuse
Figure 9. (a) Reaction mixture, (b) Separation of PdꢀBIPꢀγꢀ
Fe2O3@SiO2 from the reaction mixture by a magnetic bar
The activity of various recoverable palladium catalysts with Pdꢀ
BIPꢀγꢀFe2O3@SiO2 in the Heck coupling reaction of n-butyl
acrylate with iodobenzene was compared in Table 3. From Table
3, it is appeared that PdꢀBIPꢀγꢀFe2O3@SiO2 showed good
catalytic activity for the Heck reactions in terms of TON and
TOF compared with the other catalytic systems. More
importantly, among supported palladium catalysts, our catalyst
like the ones which were supported on magnetic nanoparticles
could be easily separated from the reaction mixture by using an
external magnet.
Table 2. Recycling of PdꢀBIPꢀγꢀFe2O3@SiO2 for the Heck
reaction of iodobenzene with nꢀbutyl acrylate
Cycle
1st
2nd
3rd
4th
5th
6th
7th
8th
Yielda (%)
TON
196
196
196
196
192
192
184
180
170
160
TOF(hꢀ1)
784
784
784
784
768
768
736
720
98
98
98
98
96
96
92
90
85
80
Table 3. Catalytic activity of PdꢀBIPꢀγꢀFe2O3@SiO2 compared
with some recoverable catalysts reported for the Heck coupling
reaction of n-butyl acrylate with iodobenzene
9th
10th
680
640
Entry Catalyst (mol%)
Conditions
Yielda TON
(%)ref
TOF
(hꢀ1)
12
aIsolated yield. Reaction conditions: iodobenzene (1 mmol), nꢀbutyl
acrylate (1.1 mmol), Et3N (2 mmol), PdꢀBIPꢀγꢀFe2O3@SiO2 (0.5 mol%),
DMF, 100 °C, 0.25 h.
1
2
3
4
5
SiO2@Fe3O4ꢀPd DMF, K2CO3, 100 °C, 8 h 9718
(1)
97
41
The TEM image of the catalyst after being reused ten times
showed that the Pd nanoparticles were still well dispersed and no
obvious aggregation of Pd was observed (Fig. 10).
PdCl2 (2.3)
/DPPPEGb 200
(6.0)
Solvent free, Pr3N, 80 °C, 9519
5 min
512
Si–PNHCc–Pd NMP, K2CO3, 120 °C, 2 h 9520
(0.5)
190 95
HMMSdꢀNH2ꢀ NMP, K2CO3, 130 °C, 8 h 9821
Pd (4)
24
92
3
SMNPseꢀ
supported 4,5ꢀ
diazafluroenꢀ9ꢀ
oneꢀPd (1)
Solvent free, DABCO, 140 9222
°C, 2 h
46
6
PdCl2/TiO2 (0.5) DMF, Et3N, under 400 W 94f23 188
(mercury vapor lamp) UVꢀ
38
Figure 10. TEM of PdꢀBIPꢀγꢀFe2O3@SiO2 after tenth reuse
visible irradiation 45±3 °C,
5 h
g24
7
8
Fe3O4ꢀNH2ꢀPd
(5)
NMP, K2CO3, 130 °C,
10 h
99
<
20
92
92
92
2
Comparison of FTꢀIR spectra of used catalyst (Fig. 11) with fresh
catalyst demonstrates that the structure of the catalyst retained
after first and tenth recoveries. Furthermore, the ICP and CHN
analysis (N = 1.51% and C = 4.92%) of PdꢀBIPꢀγꢀFe2O3@SiO2
were carried out after ten times reuse and the results showed that
only a very small amount (less than 1%) of Pd metal was
removed from the catalyst.
PdꢀDABCOꢀγꢀ Solvent free, Et3N, 100 °C, 9225
184
9
Fe2O3
(1)
0.5 h
9
TiO2@Pd NPs DMF, Et3N, 140 °C, 10 h 9226
(1)
10
PdꢀSMFh (1)
CH3CN, Et3N, 100 °C,
20 h
9227
5
6 | J. Name., 2015, 00, 1-7
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Journal Name
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View Article Online
ARTICLE
DOI: 10.1039/C5NJ00344J
12
4ꢀNO2
Cl
5
82
11
12
Pd(0)–ZnFe2O4
(4.62)
DMF ,Et3N, 120 °C,
3 h
9028
20
6
aIsolated yield. Reaction conditions: aryl halide (1mmol), phenylacetylene
(1.1 mmol), Et3N (2 mmol), PdꢀBIPꢀγꢀFe2O3@SiO2 (0.5 mol%), DMF,
100°C. The products were characterized by comparison of their physical
properties with the authentic samples.30
PdꢀBIPꢀγꢀ
Fe2O3@SiO2
(0.5)
DMF, Et3N, 100 °C, 0.25 98i
h
196
784
aIsolated yield.
bDPPPEG = bisꢀ(diphenylphosphinite)PEG.
cPNHC = Polymeric Nꢀheterocyclic carbene.
dHMMS = Monodispersed hollow magneticspheres.
eSMNPs = Silicaꢀcoated magnetite nanoparticles.
fConversion.
Conclusion
In summary, we have synthesized complex of Pd with
bis(imino)pyridine as a NNN pincer ligand supported on γꢀ
Fe2O3@SiO2 magnetic nanoparticles (PdꢀBIPꢀγꢀFe2O3@SiO2). After
its characterization by different methods, it was used a new airꢀ and
moistureꢀstable magnetically recyclable phosphineꢀfree Pd catalyst
for Heck, Suzuki and Sonogashira coupling reactions. A wide range
of aryl halides (iodides, bromides and chlorides) was coupled
successfully with alkyl acrylates, styrene, phenylboronic acid and
phenylacetylene to generate the corresponding products in good to
high yields. Any Pd detection in the remaining solution after
separation of the catalyst in the hot filtration test and the results of
poisoning test showed that the observed catalysis was heterogeneous
in nature. The true heterogeneous PdꢀBIPꢀγꢀFe2O3@SiO2 could be
reused by a magnetic bar for ten consecutive cycles without any
drastic loss of its reactivity. Due to the true heterogeneous nature,
simple and efficient recyclability and applicability for large scale
coupling reactions, PdꢀBIPꢀγꢀFe2O3@SiO2 could be a potential
catalyst for using in industrial chemistry. Further investigation on
the application of PdꢀBIPꢀγꢀFe2O3@SiO2 in organic synthesis is
underway in our laboratory.
gDetermined by GC.
hSMF = Siliceous mesocellular foam.
iCurrent work.
Encouraged by the above results of Heck reactions, the catalytic
activity of PdꢀBIPꢀγꢀFe2O3@SiO2 was then evaluated for Suzuki and
Sonogashira coupling reactions (Tables 4 and 5). As shown in
Tables 4 and 5, aryl halides (iodides, bromides and chlorides)
functionalized with electronꢀwithdrawing or electronꢀdonating
groups reacted with phenylboronic acid or phenyl acetylene to
generate the corresponding products in good to high yields.
Table 4. Suzuki coupling reactions of aryl halides with
phenylboronic acid using PdꢀBIPꢀγꢀFe2O3@SiO2
OH
PdꢀBIPꢀγꢀFe2O3@SiO2 ( 0.5 mol %)
X
Ph
B
Ph
OH
Et3N, 100 oC, DMF
R
R
Entry
R
X
Time (h)
Yielda
(%)
98
95
90
92
91
92
91
Experimental
1
2
3
4
5
6
7
8
9
H
4ꢀCl
I
I
I
Br
Br
Br
Br
Cl
Cl
Cl
1
1.5
2
3
3
2.5
2.5
5
4
4
Generals
4ꢀMeO
H
4ꢀMeO
4ꢀNO2
4ꢀCN
H
Chemicals were purchased from Merck Chemical Company. NMR
spectra were recorded in ppm in CDCl3 on a Bruker Advance DPXꢀ
400 and 250 instrument using TMS as internal standard. The purity
of the products and the progress of the reactions were accomplished
by TLC on silicaꢀgel polygram SILG/UV254 plates. FTꢀIR spectra
were recorded on a JASCO FTꢀIR 460 plus spectrophotometer. TEM
analysis was performed using TEM microscope (Philips CM30). The
morphology of the products was determined by using Hitachi Japan,
model s4160 Scanning Electron Microscopy (SEM) at accelerating
voltage of 15 KV. Thermo gravimetric analysis (TGA) was
performed using a Shimadzu thermo gravimetric analyzer (TGꢀ50).
Elemental analysis was carried out on a Costech 4010 CHNS
elemental analyzer. Power Xꢀ ray diffraction (XRD) was performed
on aX’Pert Pro MPD diffractometer with Cu Kα (λ = 0.154 nm)
radiation. Surface analysis spectroscopy of the catalyst was
performed in an ESCA/AES system. This system was equipped with
a concentric hemispherical (CHA) electron energy analyzer (Specs
model EA10 plus) suitable for Xꢀray photoelectron spectroscopy
(XPS). Room temperature magnetization isotherms were obtained
using a vibrating sample magnetometer (VSM, Lake Shore 7400).
The content of Pd in the catalyst was determined by OPTIMA
7300DV ICP analyzer.
82
86
85
4ꢀCN
4ꢀNO2
10
aIsolated yield. Reaction conditions: aryl halide (1 mmol), phenylboronic
acid (1.1 mmol), Et3N (2 mmol), PdꢀBIPꢀγꢀFe2O3@SiO2 (0.5 mol%),
DMF, 100 °C. The products were characterized by comparison of their
physical properties with the authentic samples.29
Table 5. Sonogashira coupling reaction of aryl halides with
phenylacetylene using PdꢀBIPꢀγꢀFe2O3@SiO2
PdꢀBIPꢀγꢀFe2O3@SiO2 ( 0.5 mol %)
X
Ph
Ph
Et3N, 100 oC, DMF
R
R
Entry
1
2
3
4
5
6
7
8
R
H
X
I
I
Time (h)
Yielda (%)
1.5
2.5
4
4
5
5
3
3
5
96
93
94
90
85
82
91
87
85
71
84
4ꢀCl
4ꢀMeO
H
4ꢀMeO
4ꢀMe
4ꢀNO2
4ꢀCN
H
I
Synthesis of aminoꢀfunctionalized γꢀFe2O3@SiO2
Br
Br
Br
Br
Br
Cl
Cl
Cl
14
The γꢀFe2O3@SiO2 (3.5 g) was sonicated in dry toluene (50 mL)
for 30 min. (3ꢀAminopropyl)triethoxysilane (3.5 mL) was added to
the dispersed γꢀFe2O3@SiO2 in toluene, slowly heated to 105 °C and
stirred at this temperature for 48 h. The resulting aminoꢀ
functionalized γꢀFe2O3@SiO2 was separated by an external magnet
9
10
11
4ꢀMe
4ꢀCN
6
5
This journal is © The Royal Society of Chemistry 2015
J. Name., 2015, 00, 1-7 | 7

New Journal of Chemistry
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VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5NJ00344J
and washed with toluene, ethanolꢀwater mixture, deionized water CDCl3), δ 14.2, 60.0, 118.2, 127.9, 128.7, 130.1, 134.3, 144.3, 166.6
and ethanol in turn, and dried under vacuum.
ppm.
(E)-n-Butyl 3-(4-chlorophenyl)acrylate
3
1H NMR (400 MHz, CDCl3): δ 0.90 (t, 3H, J = 7.2 Hz), 1.33ꢀ1.39
Synthesis of BIP supported on γꢀFe2O3@SiO2
(m, 2H), 1.57ꢀ1.64 (m, 2H), 4.13 (t, 2H, 3J = 6.8 Hz), 6.64 (d, 1H, 3J
3
3
A solution of pyridineꢀ2,6ꢀdicarbaldehyde (15 mmol, 2.02 g) in
methanol (20 mL) and aminoꢀfunctionalized γꢀFe2O3@SiO2 (1 g)
was refluxed for 6 h at 60 °C. The resulting light brown solid was
separated by an external magnet, repeatedly washed with hot
methanol and finally dried in oven under vacuum.
= 16.0 Hz), 7.45 (d, 2H, J = 8.0 Hz), 7.63 (d, 1H, J = 16.0 Hz),
7.74 (d, 2H, 3J = 8.0 Hz) ppm; 13C NMR (100 MHz, CDCl3), δ 13.7,
19.2, 30.7, 64.4, 118.8, 129.1, 129.4, 132.9, 136.0, 143.0, 166.7
ppm.
(E)-n-Butyl 3-(4-methoxyphenyl)acrylate
3
1H NMR (400 MHz, CDCl3): δ 0.91 (t, 3H, J =7.0 Hz), 1.35ꢀ1.40
(m, 2H), 1.60ꢀ1.62 (m, 2H), 3.72 (s, 3H), 4.13 (m, 2H, 3J =7.0 Hz),
Synthesis of the PdꢀBIPꢀγꢀFe2O3@SiO2
3
3
3
6.24 (d, 1H, J = 16.0 Hz), 6.81 (d, 3H, J =4.8 Hz), 7.39 (d, 3H, J
3
=4.2 Hz), 7.58 (d, 1H, J = 16.0 Hz) ppm; 13C NMR (100 MHz,
BIP supported on γꢀFe2O3@SiO2 (1 g) was sonicated in methanol
(30 mL) for 0.5 h. A solution of Pd(OAc)2 (0.34 mmol, 0.076 g) in
methanol (10 mL) was added to the dispersed BIP supported on γꢀ
Fe2O3@SiO2 in methanol and stirred under reflux for 10 h. The
reaction mixture was cooled to room temperature. The solid was
separated by an external magnet, washed several times with
methanol and dried in an oven under vacuum.
CDCl3), δ 13.6, 19.1, 30.7, 55.0, 64.0, 114.1, 115.5, 127.0, 129.5,
144.0, 161.2, 167.1 ppm.
(E)-n-Butyl 3-(4-nitrophenyl)acrylate
1H NMR (400 MHz, CDCl3): δ 0.92 (t, 3H, J = 7.2 Hz), 1.35ꢀ1.44
3
3
(m, 2H), 1.62ꢀ1.69 (m, 2H), 4.17ꢀ4.24 (m, 2H), 6.53 (d, 1H, J =
16.0 Hz), 7.63ꢀ7.68 (m, 3H), 8.20 (d, 2H, J = 8.0 Hz) ppm; 13C
3
NMR (100 MHz, CDCl3), δ 13.6, 19.1, 30.6, 64.7, 122.5, 124.0,
128.6, 140.5, 141.5, 148.3, 166.0 ppm.
Synthesis of 1
(E)-n-Butyl 3-(4-cyanophenyl)acrylate
A solution of pyridineꢀ2,6ꢀdicarbaldehyde (15 mmol, 2.02 g) in
methanol (20 mL) and (3ꢀaminopropyl)triethoxysilane (30 mmol, 7.2
mL) was refluxed for 6 h. The resulting solid was separated, washed
with hot methanol (3 × 10 mL) and finally dried in an oven under
vacuum.
3
1H NMR (400 MHz, CDCl3): δ 0.77 (t, 3H, J = 7.0 Hz), 1.30ꢀ1.38
(m, 2H), 1.57ꢀ1.64 (m, 2H), 4.14 (t, 2H, 3J = 6.8 Hz), 6.45 (d, 1H, 3J
= 16.0 Hz), 7.54 (d, 2H, 3J = 8.4 Hz), 7.60 (d, 2H, 3J = 8.0 Hz) ppm;
13C NMR (100 MHz, CDCl3), δ 13.5, 19.0, 30.5, 64.4, 113.0, 118.1,
121.6, 128.3, 132.4, 138.4, 141.8, 165.7 ppm.
(E)-1,2-Diphenylethene
Synthesis of 2
3
1H NMR (400 MHz, CDCl3): δ 7.18 (s, 2H), 7.33 (t, 2H, J = 6.8
3
3
Hz), 7.42 (t, 4H, J = 7.0 Hz), 7.58 (d, 4H, J = 7.2 Hz) ppm; 13
NMR (100 MHz, CDCl3), δ 126.7, 127.8, 128.8, 137.4 ppm.
(E)-1-Chloro-4-styrylbenzene
C
A solution of Pd(OAc)2 (0.34 mmol, 0.076 g) in methanol (10 mL)
was added to 1 (0.34 mmol, 0.19 g) in methanol (10 mL) and stirred
under reflux for 10 h. The reaction mixture was cooled to room
temperature. The solid was separated, washed several times with
methanol and dried in an oven under vacuum.
1H NMR (400 MHz, CDCl3): δ 7.07 (s, 2H), 7.28ꢀ7.39 (m, 5H),
7.43ꢀ7.46 (m, 2H), 7.50ꢀ7.52 (m, 2H) ppm; 13C NMR (100 MHz,
CDCl3), δ 127.7, 128.5, 128.8, 129.0, 129.9, 130.0, 130.4, 134.3,
136.9, 138.1 ppm.
General procedure for the Heck, Suzuki and Sonogashira
coupling reaction
(E)-1-Methoxy-4-styrylbenzene
1H NMR (400 MHz, CDCl3): δ 3.89 (s, 3H), 6.92 (d, 2H, J = 8.4
3
3
3
Hz), 6.99 (d, 2H, J = 16.4 Hz), 7.09 (d, 2H, J = 16.0 Hz), 7.36 (t,
A
mixture of aryl halide (1.0 mmol), alkene/phenylboronic
3
2H, J = 7.6 Hz), 7.46ꢀ7.52 (m, 3H), ppm; 13C NMR (100 MHz,
acid/phenylacetylene (1.1 mmol), Et3N (2 mmol) and PdꢀBIPꢀγꢀ
Fe2O3@SiO2 (0.018 g, 0.5 mol%) was stirred in DMF at 100 °C for
an appropriate time (Tables 1, 4 and 5). After cooling the reaction
mixture to room temperature, the catalyst was separated by a
magnetic bar, washed several times with EtOAc, dried and reused
for a new run. After evaporation of the solvent under vacuum, the
crude product was subjected to silica gel column chromatography
eluted with nꢀhexane/EtOAc (50/1) to afford the pure product.
CDCl3), δ 55.3, 114.1, 126.3, 126.6, 127.2, 127.8, 128.2, 128.7,
130.1, 137.7, 159.3 ppm.
(E)-1-Nitro-4-styrylbenzene
1H NMR (400 MHz, CDCl3): δ 7.06ꢀ7.18 (m, 1H), 7.40ꢀ7.45 (m,
4H), 7.49ꢀ766 (m, 4H), 8.15ꢀ8.26 (m, 2H) ppm; 13C NMR (100
MHz, CDCl3), δ 125.2, 127.4, 128.0, 128.2, 130.0, 134.4, 137.3,
145.0, 147.8 ppm.
(E)-4-Styrylbenzonitrile
1H NMR (400 MHz, CDCl3): δ 7.09 (d, 1H, J = 16.0 Hz), 7.22 (d,
3
(E)-n-Butyl cinnamate
1H, 3J = 16.0 Hz), 7.31ꢀ7.34 (t, 1H, 3J = 4.0 Hz), 7.38ꢀ7.41 (t, 2H, 3J
1H NMR (400 MHz, CDCl3): δ 0.88 (t, 3H, J = 7.6 Hz), 1.34ꢀ1.36
3
3
3
(m, 2H), 1.59ꢀ1.62 (m, 2H), 4.13 (t, 2H, 3J = 6.8 Hz), 6.36 (d, 1H, 3J
= 4.0 Hz), 7.54 (d, 2H, J = 7.2 Hz), 7.58 (d, 2H, J = 8.4 Hz), 7.64
3
(d, 2H, J = 8.4 Hz) ppm; 13C NMR (100 MHz, CDCl3), δ 111.7,
3
= 16.0 Hz), 7.29ꢀ7.30 (m, 3H), 7.43ꢀ7.45 (m, 2H), 7.60 (d, 1H, J =
16.4 Hz) ppm; 13C NMR (100 MHz, CDCl3), δ 13.7, 19.2, 30.8,
64.3, 118.2, 128.0, 128.8, 130.1, 134.4, 144.4, 166.8 ppm.
(E)-Methyl cinnamate
120.2, 127.8, 128.0, 128.1, 129.8, 130.0, 133.5, 133.6, 137.4, 142.9
ppm.
Biphenyl
1H NMR (400 MHz, CDCl3): δ 7.46 (t, 2H, 3J = 7.2 Hz), 7.56 (t, 4H,
1H NMR (400 MHz, CDCl3): δ 3.74 (s, 3H), 6.38 (d, 1H, J = 16.4
3
3J = 8.0 Hz), 7.72 (d, 4H, J = 6.8 Hz) ppm; 13C NMR (100 MHz,
3
3
Hz), 7.31ꢀ7.33 (m, 3H), 7.45ꢀ7.47 (m, 2H), 7.63 (d, 1H, J = 16.4
Hz) ppm; 13C NMR (100 MHz, CDCl3), δ 51.6, 117.7, 128.1, 128.9,
130.3, 134.3, 144.8, 167.3 ppm.
CDCl3), δ 127.2, 127.3, 128.8, 141.3 ppm.
4-Chlorobiphenyl
1H NMR (400 MHz, CDCl3): δ 7.31ꢀ7.49 (m, 5H), 7.51ꢀ7.57 (m,
4H) ppm; 13C NMR (100 MHz, CDCl3), δ 128.1, 128.7, 129.3,
129.5, 130.0, 130.2, 140.8, 141.1 ppm.
(E)-Ethyl cinnamate
1H NMR (400 MHz, CDCl3): δ 1.43 (t, 3H, J = 8.0 Hz), 4.19 (q,
3
2H, 3J = 8.0 Hz), 6.35 (d, 1H, J = 16 Hz), 7.27ꢀ7.28 (m, 3H), 7.41ꢀ
3
7.42 (m, 2H), 7.63 (d, 1H, J = 16.0 Hz) ppm; 13C NMR (100 MHz,
3
4-Methoxybiphenyl
8 | J. Name., 2015, 00, 1-7
This journal is © The Royal Society of Chemistry 2015

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ARTICLE
DOI: 10.1039/C5NJ00344J
3
1H NMR (400 MHz, CDCl3): δ 3.83 (s, 3H), 6.99 (d, 2H, J = 8.8
[6] M. Bakherad, S. Jajarmi, J. Mol. Catal. A Chem., 2013, 370, 152; D.
Wang, D. Denux, J. Ruiz, D. Astruc, Adv. Synth. Catal., 2013, 355,
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Organomet. Chem., 2013, 724, 206.
[7] C. Uerpmann, B. J. L. Henner, C. Guérin, F. Carre, J. Organomet.
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Inorg. Chem., 1999, 1999, 959; K. T. Sylvester, P. J. Chirik, J. Am.
Chem. Soc., 2009, 131, 8772.
[8] B. L. Small, M. Brookhart, A. M. A. Bennett, J. Am. Chem. Soc.,
1998, 120, 4049; R. Duchateau, Chem. Rev., 2002, 102, 3525.
[9] A. J. Canty, J. Patel, B. W. Skelton, A. H. White, J. Organomet.
Chem., 2000, 607, 194.
[10] M. E. van der Boom, D. Milstein, Chem. Rev., 2003, 103, 1759; W.
Leis, H. A. Mayer, W. C. Kaska, Coord. Chem. Rev., 2008, 252, 1787;
J. Takaya, N. Iwasawa, Organometallics, 2009, 28, 6636; J. I. van der
Vlugt, Angew. Chem. Int. Ed., 2010, 49, 252.
3
3
Hz), 7.31 (t, 1H, J = 7.2 Hz), 7.43 (t, 2H, J = 8.0 Hz), 7.55 (t, 4H,
3J = 8.8 Hz) ppm; 13C NMR (100 MHz, CDCl3), δ 56.5, 115.3,
127.8, 127.9, 129.3, 129.9, 134.9, 142.0, 160.3 ppm.
4-Nitrobiphenyl
1H NMR (400 MHz, CDCl3): δ 7.43ꢀ7.52 (m, 3H), 7.62ꢀ7.64 (m,
2H), 7.73ꢀ7.76 (m, 2H), 8.29ꢀ8.30 (m, 2H) ppm; 13C NMR (100
MHz, CDCl3), δ 125.2, 128.5, 128.9, 130.0, 130.3, 139.9, 148.2,
148.7 ppm.
4-Cyanobiphenyl
1H NMR (400 MHz, CDCl3):δ 7.41ꢀ7.51 (m, 3H), 7.56ꢀ7.60 (m,
2H), 7.68ꢀ7.74 (m, 4H), ppm; 13C NMR (100 MHz, CDCl3), δ 112.0,
120.1, 128.3, 128.8, 129.8, 130.2, 133.7, 140.3, 146.8 ppm.
1,2-Diphenylethyne
1H NMR (400 MHz, CDCl3): δ 7.27 (t, 6H, J = 7.5 Hz), 7.34ꢀ7.43
3
[11] K. Dhara, K. Sarkar, D. Srimani, S. K. Saha, P. Chattopadhyay, A.
Bhaumik, Dalton Trans., 2010, 39, 6395.
(m, 4H) ppm; 13C NMR (100 MHz, CDCl3) δ 89.3, 123.2, 128.2,
128.4, 131.6 ppm.
[12] N. E. Leadbeater, M. Marco, Chem. Rev., 2002, 102, 3217; S.
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Heck coupling reaction of iodobenzene and nꢀbutyl acrylate in
large scale
A mixture of iodobenzene (50 mmol), nꢀbutyl acrylate (55 mmol),
Et3N (100 mmol), and PdꢀBIPꢀγꢀFe2O3@SiO2 (0.9 g, 0.5 mol%) was
stirred in DMF at 100 °C. After completion, the reaction mixture
was cooled to room temperature and the catalyst was separated by a
magnetic bar. The solvent was evaporated under vacuum and the
crude product was subjected to silica gel column chromatography
eluted with nꢀhexane/EtOAc (50/1) to afford the pure product in
98% yield.
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Acknowledgement
Financial support of this project by University of Birjand Research
Council is appreciated.
References
aAddress, Department of Chemistry, College of Sciences, University of
Birjand, Birjand, Iran. Fax: +98 56 32202065; Tel: +98 5632202065; E-
mail: ssobhani@birjand.ac.ir, sobhanisara@yahoo.com
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