SPIONs-bis(NHC)-palladium(II): A novel, powerful and efficient catalyst for Mizoroki-Heck and Suzuki-Miyaura C-C coupling reactions

Article abstract of DOI:10.1016/j.molcata.2014.01.001

A novel, stable and powerful nano Pd-NHC complex utilizing N-methylimidazole bounded to 1,3,5-triazine-tethered SPIONs (superparamagnetic iron oxide nanoparticles) as a bidentate NHC ligand is reported. This well-defined complex was used as an efficient (

Full text of DOI:10.1016/j.molcata.2014.01.001

Journal of Molecular Catalysis A: Chemical 385 (2014) 78–84
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
SPIONs-bis(NHC)-palladium(II): A novel, powerful and efficient
catalyst for Mizoroki–Heck and Suzuki–Miyaura C–C coupling
reactions
∗
∗
Marzieh Ghotbinejad, Ahmad R. Khosropour , Iraj Mohammadpoor-Baltork ,
Majid Moghadam, Shahram Tangestaninejad, Valiollah Mirkhani
Catalysis Division, Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 July 2013
Received in revised form
A novel, stable and powerful nano Pd-NHC complex utilizing N-methylimidazole bounded to 1,3,5-
triazine-tethered SPIONs (superparamagnetic iron oxide nanoparticles) as a bidentate NHC ligand is
reported. This well-defined complex was used as an efficient (NHC)-based catalyst for Mizoroki–Heck
and Suzuki–Miyaura cross coupling reactions. These cross coupled products were produced in excel-
lent yields under conventional heating or microwave irradiation at extremely low palladium loading
1
7 December 2013
Accepted 1 January 2014
Available online 8 January 2014
3
6
−1
(
∼0.002 mol%) with perfect high turnover frequencies (TOFs) (10 –10 h ). Moreover, the catalyst could
be quickly and completely recovered by external magnetic field and be reused for seven reaction cycles
without any change in catalytic activity.
Keywords:
Mizoroki–Heck reaction
Suzuki–Miyaura reaction
SPIONs
©
2014 Elsevier B.V. All rights reserved.
TCT
N-Heterocyclic carbenes
1
. Introduction
in pharmaceuticals were set usually as ppm level. So, one way to
overcome these drawbacks is immobilization of Pd-NHC on dif-
ferent solid supports [15–19]. For instance, the immobilization of
Pd-NHCs complexes on polystyrene [20] or silica [21,22] has been
reported. Meanwhile, utilizing of nano-supports in this case has
attracted considerable interest due to their high activity and envi-
ronmental acceptability [23]. Although, these materials offer high
specific surface area of the active component which enhances the
contact between reactants and supported catalyst, they are eas-
ily agglomerated and difficult separated. Moreover, due to specific
nature of the mechanisms of Suzuki and Heck reactions, leaching
of palladium from the support to the reaction mixture is the other
problem [24]. This was a reason for the observed decrease in activ-
ity of recycled catalysts. So, even though the widespread Pd-NHC
catalytic systems described previously, it is essential to design a
more efficient, stable and easily recoverable palladium catalyst for
C–C coupling reactions.
Currently, magnetic separation provides a very useful approach
for removing magnetic nanoparticles (MNPs) with an exter-
nal magnet. Meanwhile, various Pd-NHC immobilized on MNPs
employing the property of magnetic separation have been devel-
oped in a number of C–C coupling reactions [25]. These magnetic
nanoparticles show excellent catalytic activities. The magnetic sep-
aration method presents many advantages over conventional ones.
This can be considered as an environmentally benign that the
consequence caused by filtration steps was omitted in the reaction.
Recently, N-heterocyclic carbenes (NHCs) have emerged as an
extremely useful and versatile class of ligands in homogeneous
transition metal catalysis due to the strong ␴-donor properties, ease
of preparation and effective binding ability to any transition metal
irrespective of their oxidation states [1–6]. Within this context,
these compounds have attracted increasing attention in both aca-
demic and industrial fields owing to their unique catalytic activity
[
2,7]. NHCs complexes as homogeneous catalysts have been used
in a number of organic transformations such as olefin metathe-
sis, and C–C and C–N bond formation reactions [8]. In this regard,
the discovery of catalytic properties of Pd-NHCs complexes in
the Mizoroki–Heck and Suzuki–Miyaura cross-coupling reactions
are considered as particularly useful since these reactions provide
many vast applications in the synthesis of natural products, numer-
ous drugs and high performance modern organic materials [9–14].
Despite the wide application of these homogeneous catalysts in
organic transformations, their recycling is almost complicated and
their separation is very difficult. Moreover, in consequence of tox-
icity of palladium residuals, acceptable limits of palladium traces
∗ Corresponding authors. Tel.: +98 311 7932715; fax: +98 311 6689732.
E-mail addresses: Khosropour@chem.ui.ac.ir (A.R. Khosropour),
imbaltork@sci.ui.ac.ir (I. Mohammadpoor-Baltork).
1
381-1169/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2014.01.001

M. Ghotbinejad et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 78–84
79
To date there are only a few examples of Pd-NHC anchored to
MNPs with the catalytic behavior in the organic transformations
26]. Moreover, based on the character of reactants, tempera-
2.3. Synthesis of SPIONs-bis(NHC)-palladium(OAc)2 (4)
[
In a round bottom flask equipped with mechanical stir-
rer and condenser, mixture of SiO @Fe O (4.03 g) and
ture and catalyst activity of Pd-NHC immobilized on MNPs, the
Suzuki–Miyaura or Mizoroki–Heck have been performed efficiently
at 0.5–72 h using 1–10 mol% of palladium as active site of the
catalyst system [27]. Consequently, there is a demand for the devel-
opment of new Pd-NHC-MNPs with superior catalytic activities,
less palliative and high recyclability. Encourage to our previous
work on C–C-coupling reactions [28a] and also on imidazolium-
tagged box ligands via synthesis of 1,3,5-triazine-functionalized
bisimidazolium dichloride tethered to MNPs and their good perfor-
mance and recyclability in Betti synthesis [28b], we designed and
prepared SPIONs-bis(NHC)-palladium(II) (4) as a new and highly
stable Pd-NHC-tagged MNPs and investigated their performance
in the Mizoroki–Heck and Suzuki–Miyaura reactions.
a
2
3
4
3-aminopropyltriethoxysilane (APTS) (5 mL) was refluxed in dry
◦
toluene (100 mL) at 100 C for 24 h. After this time, the magnetite
nanoparticles were separated from the reaction mixture by an
external permanent magnet, washed with ethanol and Mili-Q water
◦
several times and dried under vacuum at 60 C to obtain 1. For
preparation of supported N-heterocyclic carbene ligand 3, to a mix-
◦
ture of 1 (0.50 g) in dry THF (40 mL) at 0 C, 1,3,5-trichlorotriazine
◦
(TCT) (0.25 g) was added and the mixture was stirred at 0 C for
2 h. After consumption of TCT and producing of 2, as indicated by
TLC, diisopropylethyl amine (1 mL) and N-methylimidazole (5 mL)
were added to this mixture and refluxed in dry toluene for one day.
The residue was separated from the mixture by an external perma-
nent magnet, washed with CH Cl and THF for several times and
2
2
◦
finally dried under vacuum at 60 C to obtain 3. The final catalyst
nanoparticles were obtained as dark-brown solids by addition of
Pd(OAc)2 (101 mg, 0.45 mmol) to a dispersed mixture of 3 (1.01 g)
in DMSO (5 mL) under argon atmosphere at room temperature.
2
. Experimental
2.1. Materials
◦
Next, the mixture was stirred for 4 h at 60 C and then allowed to
◦
All chemicals were purchased from Merck chemical company.
proceed for an additional 30 min at 100 C. The resulting complex
Fe O nanoparticles and silica-coated magnetite nanoparticles
was collected by an external permanent magnet and washed with
ethanol (3 × 10 mL) to remove the unreacted Pd(OAc)2, and finally
dried under air (89% yield upon Pd consumption determined by
ICP).
3
4
(
SiO @Fe O ) were synthesized according to the literature [29].
2 3 4
All known organic products were identified by comparison
of their physical and spectral data with those of authentic
samples. Thin layer chromatography (TLC) was performed on UV-
active aluminum-backed plates of silica gel (TLC Silica gel 60
F254).
2.4. General procedure for Mizoroki–Heck reaction under
thermal conditions and microwave irradiation
2.2. Instrumentation and analysis
In a round-bottomed flask equipped with a condenser and a
2
magnetic stirrer, aryl halide (1 mmol), alkene (1.5 mmol), K CO3
1H and 13C NMR spectra were recorded on a Bruker-avance
(
207 mg, 1.5 mmol) and 4 (0.074 g, 0.002 mol% Pd) in DMF (2 mL)
4
00 MHz spectrometer in CDCl . Coupling constants are given
3
◦
◦
was stirred at 90 C or exposed to MW irradiation (200 W, 70 C)
under air atmosphere. The progress of the reaction was mon-
itored by TLC (eluent:petroleum ether/ethyl acetate, 4:1). After
completion of the reaction, the reaction mixture was cooled to
room temperature, CH Cl (15 mL) was added and the catalyst was
in Hz. The FT-IR spectra were taken on a Nicolet-Impact 400D
−
1
spectrophotometer in KBr pellets and reported in cm . Melting
points were determined using Stuart Scientific SMP2 apparatus
and are uncorrected. The microwave system used in these exper-
iments includes the following items: Micro-SYNTH lab station,
equipped with a glass door, a dual magnetron system with pyra-
mid shaped diffuser, 1000 W delivered power, exhaust system,
magnetic stirrer, ‘quality pressure’ sensor for flammable organic
solvents, and a ATCFO fiber optic system for automatic tempera-
ture control. The coercivities (Hc), the saturation magnetizations
2
2
separated by an external magnetic field. The organic layer was
washed with water (3 × 10 mL) and dried over anhydrous MgSO .
4
The product was isolated by chromatography on a short column
of silica gel to obtain the corresponding products in to 77–90%
yields.
(
Ms) and the remnant magnetizations (Mr) of the samples were
measured with a vibrating sample magnetometer (VSM) (Megh-
natis Daghigh Kavir Co). TGA curve was obtained with a heating
2
.5. General procedure for Suzuki–Miyaura reaction at room
◦
temperature and under microwave irradiation
rate of 10 C/min on a TG 50 Mettler thermogravimetric analyzer
◦
in the range 30–600 C. The TEM images were taken with a Philips
In a round-bottomed flask equipped with a condenser and
a magnetic stirrer, aryl halide (1.0 mmol), aryl boronic acid
CM120 unit operated at 200 kV. A scanning electron microscope
(
SEM) (Philips XL20), equipped with an EDS detector (EDAX) was
(
1.1 mmol), K CO3 (207 mg, 1.5 mmol), and 4 (0.074 g, 0.002 mol%
used to observe the changes in the size and morphology of the
samples. An accelerating voltage of 15 kV was used to obtain the
SEM images. X-ray photoelectron spectra (XPS) were recorded on
an XPS–Auger Perkin Elmer 8025-BesTec electron spectrometer.
This instrument includes an ultra-high vacuum chamber, a hemi-
spherical electron energy analyzer and an X-ray source providing
unfiltered K␣ radiation from its Al anode (hꢀ = 1486.6 eV). The pres-
sure of the main spectrometer chamber during data acquisition
2
Pd) were mixed in DMF-H O (1:2 V/V). The mixture was stirred
2
◦
◦
at 50 C or exposed to microwave irradiation (200 W, 70 C) under
air atmosphere. The progress of the reaction was monitored by TLC
(eluent:petroleum ether/ethyl acetate, 4:1). After completion of the
reaction, CH Cl2 (15 mL) was added (in the case of the reaction
2
under MW irradiation, the mixture was first cooled to room tem-
perature) and the catalyst was separated by a permanent magnet.
−7
The organic phase was washed with H O (3 × 10 mL), dried over
was maintained at ca. 10 Pa. The binding energy (BE) scale was
2
anhydrous MgSO , and the solvent was evaporated under reduced
calibrated by using the peak of adventitious carbon, setting it to
4
pressure. The product was isolated by chromatography on a short
column of silica gel to obtain the corresponding products in 80–91%
yields.
2
84.5 eV. The accuracy of the BE scale was ± 0.1 eV. The Pd content
of the catalyst was determined by a Jarrell-Ash 1100 ICP instru-
ment.

8
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M. Ghotbinejad et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 78–84
Scheme 1. Synthesis of the catalyst SPIONs-bis(NHC)-palladium(II) diacetate 4.
3
. Result and discussion
As shown in this figure, the peaks at 337.26 (3d5/2) and 342.57 eV
(3d3/2), correspond to Pd with two oxidation states.
3.1. Catalyst preparation and characterization
The peaks at 335.1 (3d5/2) and 340.4 eV (3d3/2) indicate that
a small portion of Pd is in zero oxidation state [30]. The peaks
corresponding to oxygen, carbon, nitrogen, silicon and palla-
dium are also clearly observed in XPS elemental survey of the
catalyst.
The preparation of the catalyst follows the steps described
in Scheme 1. First, silica-coated magnetite nanoparticles
Fe O @SiO ) were selected as support, and subsequently these
(
3
4
2
MNPs were reacted with 3-aminopropyltriethoxysilane (APTS)
to obtain the functionalized MNPs 1. Next, TCT was covalently
immobilized onto the surface of the SPIONs by controlling the
temperature and then two other chlorides were replaced with
two equivalents of N-methylimidazole via formation of C–N bond
between imidazole and triazine parts.
The thermal stability of 4 was also evaluated by TGA–DTG, and
the thermograms are given in the Supplementary material (F1).
According to these curves, the weight loss below 600 C is 9.69
◦
and 6%, for 3 and 4, respectively. So, these results approved that
◦
4 has high thermal stability below 600 C. This observation can be
attributed to the formation of a stable Pd complex. Upon increas-
ing the temperature, first the strong Pd–C and Pd–N bonds should
be cleaved which in turns increases the thermal stability of the Pd
complex.
Finally, SPIONs-bis(NHC)-palladium(II) diacetate 4 was pre-
pared by the reaction of Pd(OAc)2 with 3 in DMSO.
The Pd loading of 4, measured by ICP, showed a value of about
0
.27 mmol/g of catalyst. The FT-IR spectrum of 4 showed absorption
The SEM image showed that the shape of Fe O nanoparticles is
3
4
−1
−1
−1
bands at 584–638 cm (Fe–O), 1623 cm (C=N), 2927 cm (C–H)
and 3432 cm (N–H stretching vibration).
spherical (Supplementary material, F2). The presence of the palla-
dium was also confirmed by the EDX detector coupled to the SEM
which showed the presence of C, O, Si, Cl, N and Pd (Supplementary
material, F3).
Transmission electron microscopy (TEM) confirmed the
nanometer dimensions of 4 particles (Supplementary material,
F4). As shown in the particle size histogram, the average size of
the magnetic nanoparticles is about 10–11.5 nm.
−
1
X-ray photoelectron spectroscopy (XPS) is a powerful tool to
investigate the electron properties of the species formed on the
surface, such as the electron environment, oxidation state, and the
binding energy of the core electron of the metal. Fig. 1 shows the
XPS spectrum of 4. The calibration was performed with the C 1s
peak (Eˇ = 284.5 eV).
Fig. 1. The XPS spectra of: (a) 4 showing Pd 3d5/2 and Pd 3d3/2 binding energies, (b) the elemental survey scan of 4.

M. Ghotbinejad et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 78–84
81
Fig. 2. Room temperature magnetization curves of (a) Fe3O4, (b) 4.
Fig. 2 shows the magnetization curves of Fe O and 4. As shown,
some selected geometry parameters on its optimized structure are
listed in the Supplementary material.
3
4
the saturation magnetization for Fe O4 is equal to 69.4 emu/g and
3
the magnetization value of 4 was 27.1 emu/g. This investigation
proved the super paramagnetic behaviour of the catalyst. Due to
the coating of magnetic nanoparticles with silica and also func-
tionalization of silica-encapsulated Fe O , Ms is found considerably
3.2. Catalytic activity of 4
3
4
lower than that of the bulk magnetite.
After structure characterization of the 4, its catalytic activity was
investigated in the Mizoroki–Heck reaction. In this study, the kind
and texture of the catalyst, kind of base, solvent, and reaction tem-
perature were examined in the coupling reaction of iodobenzene
(1.0 mmol) and styrene (1.0 mmol), as model reaction (Table 1). As
illustrated, the semi-heterogeneous catalyst is much more reactive
than the heterogeneous ones.
The optimized geometry and molecular orbitals were also inves-
tigated at the high level computational method. The calculation
was performed with the TURBOMOLE program package, [31,32]
making use of the resolution of the identity (RI) approximation for
the evaluation of the electron-repulsion integrals. The equilibrium
geometry of the ground electronic states (S ) for SiO -APTS-
0
2
1
,3,5-triazin-bis NHC-Pd(II) (compound 4 without consideration
In the outset, the effectiveness of different solvents such as
ethanol, toluene and DMF were examined. DMF appeared to be
superior to the others (Table 1, entry 1). Next, the influence of bases
in this reaction was investigated. In contrast, using different bases
such as NEt3 or Na CO3 instead of K CO3 evidently gave the lower
of the Fe O @SiO @APTS core) has been determined at the MP2
3
4
2
(
Möller–Plesset second order perturbation theory).
The dunning correlation consistent polarized valence dueled
zeta basis set (cc-pVDZ) has been used [33]. The optimized geome-
2
2
try of SiO -APTS-1,3,5-triazin-bisNHC-Pd(II) is shown in Fig. 3 and
yields (Table 1, entries 5 and 6).
2
Fig. 3. The optimized geometry of SiO2-APTS-1,3,5-triazin-bisNHC-Pd(II).

8
2
M. Ghotbinejad et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 78–84
Table 1
Table 2
Optimization of the reaction of iodobenzene with styrene in the presence of 4, under
thermal condition .
Optimization of the reaction of iodobenzene with styrene in the presence of 4, under
microwave irradiation .
a
a
◦
Yield [%]b
◦
Yield [%]b
Entry
Solvent
Base
Pd [mol%]
T [ C]
t [h]
Entry
Solvent
Base
Pd [mol%]
Power [W]
T [ C]
Solvent effect
Solvent effect
1
2
3
DMF
Toluene
Ethanol
K2CO3
K2CO3
K2CO3
0.002
0.002
0.002
90
90
90
2
2
3
90
60
55
1
2
3
DMF
Toluene
Ethanol
K2CO3
K2CO3
K2CO3
0.002
0.002
0.002
200
200
200
70
70
70
96
62
57
Base effect
Base effect
4
5
6
DMF
DMF
DMF
K2CO3
Na2CO3
NEt3
0.002
0.002
0.002
90
90
90
2
2
2
90
50
40
4
5
6
DMF
DMF
DMF
K2CO3
Na2CO3
NEt3
0.002
0.002
0.002
200
200
200
70
70
70
96
55
44
Without Pd
Power effect
7
8
9
DMF
DMF
DMF
K2CO3
K2CO3
K2CO3
–
90
90
90
10
8
7
–
10
15
7
8
9
DMF
DMF
DMF
K2CO3
K2CO3
K2CO3
0.002
0.002
0.002
150
200
250
50
70
80
60
96
83
Fe3O4
nanoSiO2
Pd loading
a
Reaction conditions: mixture of iodobenzene (1.0 mmol), styrene (1.5 mmol),
10
11
12
DMF
DMF
DMF
K2CO3
K2CO3
K2CO3
0.001
0.002
0.003
90
90
90
4
2
3
78
90
81
catalyst, base (1.5 mmol) and solvent (2 mL) was irradiated for 4 min.
b
Isolated yield.
Temperature effect
1
1
1
3
4
5
DMF
DMF
DMF
K2CO3
K2CO3
K2CO3
0.002
0.002
0.0020
80
90
110
5
2
3
66
90
88
compared with the data obtained under microwave irradiation. In
the traditional manner an acceptable result was registered after 2 h,
but quantitative yield of the corresponding product was obtained
under microwave irradiation only after 4 min (Table 2, entry 1).
So, this energy source was used as heating system in this trans-
formation. With this achievement we investigated the reaction
under microwave irradiation with a temperature controlled pro-
gram. During irradiation, the temperature was monitored by a
a
Reaction conditions: iodobenzene (1.0 mmol), styrene (1.5 mmol), catalyst, base
(
1.5 mmol), solvent (2 mL).
b
Isolated yield.
Moreover, no reaction occurred in the absence of the catalyst
◦
(
Table 1, entry 7) and no valuable yield was obtained in the presence
fiber optic sensor for controlling the MW power levels. At 70 C
of nano-SiO , or pure Fe O (Table 1, entries 8 and 9). On the other
and 200 W, 96% of product was registered after 4 min (Table 2,
entry 1). Surprisingly, by increasing the temperature and power
up to 80 C and 250 W, respectively, after 4 min, 83% of the prod-
2
3
4
hand, the influence of palladium loading was also investigated. As
shown in Table 1, the best result was obtained with 0.002 mol% of
catalyst (Table 1, entry 11).
◦
uct was isolated (Table 2, entry 9). Notably, lower yields were
obtained when the same reaction was carried out with utilizing
of lower amount of the catalyst. Under the optimized reaction
conditions, several aryl halides were reacted with olefins in the
presence of 4 and a large spectrum of cross coupling products
was produced through Mizoroki–Heck reaction under microwave
irradiation (Table 3). It was generally observed that high to excel-
lent yields of the products were obtained specially in the case of
aryl halides bearing electron-donating substituents (Table 3, entry
5–9). In the case of iodobenzene the corresponding products were
obtained exclusively with very high turnover frequencies (TOF)
It was also found that the reaction temperature has a great
influence on this transformation. The obvious improvement in the
◦
conversion (90%) was achieved for the reaction at 90 C (Table 1,
entry 14).
◦
Higher reaction temperature (100–120 C) gave no better yield
but at lower reaction temperature (80 C), the yield decreased 66%
◦
even after long reaction times (Table 2, entries 13 and 15). There-
◦
fore, all reactions were carried out at 90 C in the presence of 4.
Next, in order to show the influence of microwave irradiation
on the Mizoroki–Heck reaction, the results obtained in the reac-
tion of iodobenzene with styrene by conventional heating were
3
4
−1
(2.2 × 10 –2.3 × 10 h ) (Table 3).
Table 3
Mizoroki–Heck cross coupling of aryl halides and styrene in the presence of 4.
Entry
R1C H X
R2C H CH=CH
2
X
Conventional heatinga
Microwave irradiationb
6
4
6
4
Yield (%)c
TOF (h )d
−1
Time (min)
Yield (%)c
TOF (h )d
−1
Time (h)
4
5
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
H
H
H
H
H
4-CH3
H
4-CH3
4-CH3
H
4-CH3
H
4-CH3
H
4-CH3
H
4-CH3
H
H
I
I
2
8
7
9
6
8
9
8
10
3
5
7
8
10
8
12
90
87
82
81
82
80
81
78
77
89
85
82
84
86
87
87
2.3 × 10
4
7
4
5
5
6
8
7
9
2
4
5
6
5
4
5
96
92
91
87
90
88
87
83
81
93
90
88
90
91
92
90
6.8 × 10
3
5
5.4 × 10
3.8 × 10
3
5
Br
Br
I
Br
Br
I
I
I
I
Br
Br
Br
Br
Br
5.8 × 10
6.5 × 10
3
5
4.5 × 10
5.4 × 10
3
5
4-CH3O
4-CH3
4-CH3
4-CH3
4-CH3
4-CH3CO
4-CH3CO
4-CH3CO
4-CH3CO
4-CHO
4-F
7.0 × 10
5.6 × 10
3
5
5.0 × 10
4.4 × 10
3
5
4.5 × 10
3.3 × 10
3
5
4.9 × 10
3.4 × 10
3
5
3.8 × 10
2.7 × 10
4
6
0
1
2
3
4
5
6
1.5 × 10
1.5 × 10
3
5
8.5 × 10
6.4 × 10
3
5
5.8 × 10
5.5 × 10
3
5
5.2 × 10
4.5 × 10
3
5
4.3 × 10
5.6 × 10
3
5
5.4 × 10
6.7 × 10
3
5
4-F
4-CH3
7.2 × 10
5.4 × 10
a
Reactions were carried out under aerobic conditions 1.0 mmol aryl halide, 1.5 mmol styrene in 2 mL of DMF and 1.5 mmol K2CO3 in the presence of 4 (0.074 g, containing
of 0.002 mol% Pd).
c
Isolated yield.
b
◦
Applied power: 200 W, 70 C.
d
−1
mol product/mol palladium) (h ).
(

M. Ghotbinejad et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 78–84
83
Table 4
Table 5
Optimization of the reaction of iodobenzene with phenylboronic acid in the presence
of 4 under thermal condition .
Optimization of the reaction of iodobenzene with phenylboronic acid in the presence
of 4 under microwave irradiation .
a
a
◦
Yield [%]b
◦
Yield [%]b
Entry
Solvent
Base
Pd [mol%]
T [ C]
t [h]
Entry
Solvent
Base
Pd [mol%]
Power [W]
T [ C]
Solvent effect
Solvent effect
1
2
3
DMF
H2O
H2O/DMF
K2CO3
K2CO3
K2CO3
0.002
0.002
0.002
50
50
50
3
4
2
65
50
91
1
2
3
DMF
K2CO3
K2CO3
K2CO3
0.002
0.002
0.002
200
200
200
70
70
70
58
42
95
H2O
c
H2O/DMFc
Base effect
Base effect
c
c
c
H2O/DMFc
4
5
6
H2O/DMF
H2O/DMF
H2O/DMF
K2CO3
Na2CO3
NEt3
0.002
0.002
0.002
50
50
50
2
3
4
91
49
42
4
5
6
K2CO3
Na2CO3
NEt3
0.002
0.002
0.002
200
200
200
70
70
70
95
51
39
H2O/DMFc
H2O/DMFc
Temperature effect
Power effect
c
c
c
H2O/DMFc
7
8
9
H2O/DMF
H2O/DMF
H2O/DMF
K2CO3
K2CO3
K2CO3
0.002
0.002
0.002
25
50
60
5
2
3
60
91
87
7
8
9
K2CO3
K2CO3
K2CO3
0.002
0.002
0.002
150
200
250
50
70
80
70
95
84
c
H2O/DMF
H2O/DMFc
Pd loading
a
Reaction conditions: mixture of iodobenzene (1.0 mmol), phenylboronic acid
c
c
c
10
11
12
H2O/DMF
H2O/DMF
H2O/DMF
K2CO3
K2CO3
K2CO3
0.001
0.002
0.003
50
50
50
5
2
3
70
91
75
(
1.1 mmol), catalyst, base (1.5 mmol) and solvent (2 mL) was irradiated for 2 min.
b
Isolated yield.
c
2:1 (V/V).
Without Pd
c
c
c
1
1
1
3
4
5
H2O/DMF
H2O/DMF
H2O/DMF
K2CO3
K2CO3
K2CO3
–
90
90
90
7
5
5
–
15
20
Fe3O4
nanoSiO2
a
Reaction conditions: iodobenzene (1.0 mmol), phenylboronic acid (1.1 mmol),
catalyst, base (1.5 mmol) and solvent (2 mL).
b
Isolated yield.
c
2
:1 (V/V).
We also studied the application of this catalyst for the
Suzuki–Miyaura reaction. In order to optimize the reaction con-
dition, we studied the reaction of iodobenzene with phenylboronic
acid as a model reaction using different bases and solvents (Table 4).
Optimization of the base for the Suzuki reaction was also evalu-
ated by using K CO , Na CO , and NEt . It was found that K CO was
Fig. 4. Reusability of the catalyst.
of view. The separation of 4 is a highly simple process, which is
achieved by using a permanent magnet. In this manner, the catalyst
reusability was checked in the Mizoroki–Heck and Suzuki–Miyaura
reactions. At the end of each reaction, the catalyst was separated,
washed with ethanol and acetone and reused with fresh substrates
in both catalytic systems. As can be seen in Fig. 4, the catalyst
was reused several times (seven consecutive runs were checked)
without loss of its catalytic activity remarkably.
2
3
2
3
3
2
3
the most effective base for this reaction (Table 4, entry 4). Under
microwave irradiation, we found that the best yield was obtained at
◦
7
0 C and a power of 200 W (Table 5, entry 3). Under the optimized
reaction conditions, aryl iodides or aryl bromides, bearing differ-
ent substituents were converted to their corresponding products
in high excellent yields (Table 6).
Compared to the Heck reaction, the Suzuki reaction was per-
formed under milder reaction conditions. The catalyst recycling is
important from economical, environmental and industrial points
The amount of Pd leached in both reactions was measured by ICP
(Supplementary material). It was observed that only small amounts
Table 6
Suzuki–Miyaura cross coupling of aryl halides and ArB(OH)2 in the presence of 4.
Entry
R1C H X
R2C H B(OH)
2
X
Conventional heatinga
Microwave irradiationb
6
4
6
4
Yield (%)c
TOF (h )d
−1
Time (min)
Yield (%)c
TOF (h )d
−1
Time (h)
4
5
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
H
H
H
H
H
I
I
4
5
6
7
6
8
6
9
5
7
5
6
91
87
82
83
85
86
88
81
85
84
88
89
86
84
89
80
84
1.1 × 10
2
3
4
6
7
5
5
5
2
3
4
4
5
7
6
5
4
95
93
88
87
91
92
91
87
90
90
92
93
92
89
90
85
86
1.6 × 10
3
5
4-CH3O
H
4-CH3O
H
4-CH3O
H
H
H
4-CH3O
H
H
4-CH3O
H
4-CH3O
H
8.7 × 10
9.3 × 10
3
5
Br
Br
Br
Br
Br
Br
I
I
I
I
I
6.8 × 10
6.3 × 10
3
5
5.9 × 10
4.4 × 10
3
5
4-CH3O
4-CH3O
4-CH3
7.1 × 10
3.8 × 10
3
5
5.4 × 10
5.8 × 10
3
5
7.3 × 10
5.7 × 10
3
5
4-CN
4.5 × 10
5.4 × 10
3
6
4-CH3CO
4-CH3CO
4-CH3
4-CH3O
4-CH3O
4-CH3CO
4-CH3CO
4-CHO
8.5 × 10
1.5 × 10
3
5
0
1
2
3
4
5
6
7
6.0 × 10
9.0 × 10
4
5
8.8 × 10
6.6 × 10
3
6
7.4 × 10
9.3 × 10
3
5
5
8.6 × 10
6.6 × 10
3
5
Br
Br
Br
Br
10
11
14
12
4.2 × 10
3.7 × 10
3
5
4.0 × 10
4.5 × 10
3
5
3.6 × 10
5.3 × 10
3
5
4-CHO
4-CH3O
3.5 × 10
6.4 × 10
a
Reactions were carried out under aerobic conditions in 2 mL of mixture of DMF and H2O (1:2), 1.0 mmol arylhalide,1.1 mmol arylboronic acid and 1.5 mmol K2CO3 in the
presence of 4 (0.074 g, 0.002 mol% Pd).
c
Isolated yield.
b
d
◦
Applied power: 200 W, 70 C.
Mol product/mol palladium) (h ).
−1
(

8
4
M. Ghotbinejad et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 78–84
of Pd are leached in the first run and no Pd was detected in the next
runs. This can be attributed to the strong attachment of Pd to the
NHC ligand.
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