Mechanistic investigation of Heck reaction catalyzed by new catalytic system composed of Fe3O4@OA-Pd and ionic liquids as co-catalyst

Article abstract of DOI:10.1016/j.molliq.2016.02.055

A simple and efficient protocol has been developed for the Heck coupling reaction catalyzed by a two component catalytic system composed of palladium deposited oleic acid coated-Fe₃O₄ nanoparticles (Fe₃O₄@OA-Pd)

Full text of DOI:10.1016/j.molliq.2016.02.055

Journal of Molecular Liquids 218 (2016) 625–631
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Mechanistic investigation of Heck reaction catalyzed by new catalytic
system composed of Fe3O4@OA–Pd and ionic liquids as co-catalyst
a
Ezzat Rafiee a,b, , Masoud Kahrizi
⁎
a
Faculty of Chemistry, Razi University, Kermanshah 67149, Iran
Institute of Nano Science and Nano Technology, Razi University, Kermanshah 67149, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple and efficient protocol has been developed for the Heck coupling reaction catalyzed by a two component
catalytic system composed of palladium deposited oleic acid coated-Fe3O4 nanoparticles (Fe3O4@OA–Pd) and
thermo-regulated molybdovanadate-based ionic liquid salts (H5PMo10V2O40-IL, Mo10V2-IL) as a novel and recy-
clable catalytic system. In this system, low amounts of Mo10V2-ILs are used as an efficient co-catalyst, which re-
duce cost and increase efficiency in the Heck coupling reaction. These thermo-regulated co-catalysts are thermo-
responsive, and could reversibly transform to precipitate with a decrease in temperature. In this study, the cata-
lytic activities of various types of Mo10V2-IL including Mo10V2-(3-sulfonic acid) propylpyridine (Mo10V2-PyPS),
Mo10V2-(4-sulfonic acid) butylpyridine (Mo10V2-PyBS), Mo10V2-(4-sulfonic acid) butyltrimethyl amine
(Mo10V2-TMABS), Mo10V2-(4-sulfonic acid) butyltriethyl amine (Mo10V2-TEABS) and Mo10V2-(4-sulfonic acid)
butyltributyl amine (Mo10V2-TBABS) were investigated in the Heck reaction. It was shown that all of the
mentioned co-catalysts are efficient. It is apparent from cyclic voltammetric measurements that, these catalytic
systems are electroactive and undergo reversible redox transitions between palladium nanoparticles and
Mo10V2-IL species, also, it contains strong acid sites and mobile protons which can activate Ar–X and Pd–X
bonds in oxidative addition and reductive elimination steps. As evidenced from mechanistic investigations, the
electron transfer properties and Brönsted acidity of Mo10V2-ILs have been most pronounced upon application
of the Fe3O4@OA–Pd and Mo10V2-IL system in the Heck coupling reaction. Fe3O4@OA–Pd and Mo10V2-PyPS
exhibited excellent activities and the methodology is applicable to diverse substrates providing good to excellent
yields of desired products. Moreover, this catalytic system was recycled for four consecutive cycles without any
significant loss in activity.
Received 4 October 2015
Received in revised form 9 February 2016
Accepted 17 February 2016
Available online xxxx
Keywords:
Polyoxometalate
Ionic liquid
Palladium
Nanocatalyst
Heck reaction
Hybrid compound
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
palladium metal aggregation and precipitation [8,9]. Nowadays, the
chemists have been interested in the development of different aspects
Palladium-catalyzed arylation of olefins, known as the Heck reac-
tion, is one of the most important reactions for the formation of C\\C
bonds in organic synthesis, from both the research and industrial points
of view [1–5]. Because of its tolerance to different functional groups, a
variety of applications in the synthesis of pharmaceuticals, fine
chemicals, polymers and natural compounds have been worked out
[6,7]. Despite the importance of palladium catalyzed Heck reaction,
the homogeneous palladium-based catalysis has significant drawbacks
including low catalyst stability, possible toxicity caused by residual
metal species, and inability in catalyst recovery, which have impeded
their large scale application in industry. Moreover, the homogeneous
palladium catalysts tend to lose their catalytic activity because of
of palladium catalysts by deposition of palladium on solid supports
[10–17].
Palladium-supported catalysts mimic their homogeneous counter-
parts and can be considered as ‘soluble’ analogues since they are readily
dispersed and exhibit an intrinsically high surface area, an attribute that
allows excellent accessibility of substrates to the surface bound active
catalytic sites. Magnetic nanoparticles (MNPs) as catalyst supports
have been attracting more and more attention because they can be eas-
ily recovered from the reaction mixture simply by using an external
magnet, thus eliminating the necessity of tedious centrifugation, filtra-
tion, or membrane separation steps [18–20]. Fe3O4 nanoparticles are
reactive especially in an acidic environment and thereby lose their
magnetic properties. Oleic acid (OA) as a protecting shell can be utilized
to coat the Fe3O4 nanoparticles to form a core–shell (Fe3O4@OA) struc-
ture. Meanwhile, the OA shell can prevent the aggregation of the Fe3O4
particles and provide numerous double bonds for location of palladium
nanoparticles on the core–shell structure [21].
⁎
Corresponding author at: Faculty of Chemistry, Razi University, Kermanshah 67149,
Iran.
E-mail addresses: e.rafiei@razi.ac.ir, Ezzat_rafiee@yahoo.com (E. Rafiee).
http://dx.doi.org/10.1016/j.molliq.2016.02.055
0167-7322/© 2016 Elsevier B.V. All rights reserved.

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E. Rafiee, M. Kahrizi / Journal of Molecular Liquids 218 (2016) 625–631
Recently, catalytic systems which contain ionic liquids (ILs) have
2. Experimental
received much attention as promising green catalysts to reuse homoge-
neous catalysts [22–24]. Ionic liquids are normally composed of rela-
tively large organic cations and inorganic or organic anions and have
attracted a lot of interest for their unique properties, such as negligible
volatile pressure, low toxicity, very low flammability, and the ability to
dissolve in many organic and inorganic solvents [25]. The combination
of organic cation parts with polyoxometalates (POMs) can cause the
formation of POM-based ionic liquids (POM-ILs) that are emerging to
be very important in catalysis [26–29]. These interesting organic–
inorganic hybrid materials have properties of both POM anion and IL
cation. POM-ILs with electron transfer ability and Brönsted acid proper-
ty [30–32] can act as excellent co-catalyst and strong activator for reac-
tants in coupling reactions. Despite the advantages of ILs, there exist
some drawbacks about catalysis with IL based systems: high solubility
in most of solvents producing separation problems which is an impor-
tant restriction for catalytic systems. One of the main ways to overcome
this problem is the use of thermo-regulated IL which can convert from
homogeneous to heterogeneous form by reducing temperature.
2.1. General remarks
All of the reagents and solvents were commercially available and
purchased from Fluka, Merck, and Aldrich chemical companies. FT-IR
spectra were recorded with KBr pellets using a Bruker ALPHA FT-IR
spectrometer. UV–vis spectra were obtained with an Agilent (8453)
UV–vis diode-array spectrometer using quartz cells of 1 cm optical
path. The potential variation was measured with a Hanna 302 pH
meter. Thin layer chromatography (TLC) on precoated silica gel Fluores-
cent 254 nm (0.2 mm) on an aluminum plate was used for monitoring
the reactions. The cross coupling products were characterized by their
1H NMR spectra. The electrochemical reduction of catalyst was studied
in phosphate buffer (0.1 M), pH = 7. A glassy carbon electrode was
used as the working electrode and Ag/AgCl as the reference electrode.
Cyclic voltammograms (ν, 0.1 V s−1) were obtained at ambient temper-
ature (20 5 °C).
In order to continue our studies directed towards the develop-
ment of practical procedures for some important transformations
[33–36], we developed new efficient catalytic systems composed of
a family of POM-ILs (Scheme 1). These catalysts incorporate (3-sul-
fonic acid) propylpyridine (PyPS), (4-sulfonic acid) butylpyridine
(PyBS), (4-sulfonic acid) butyltrimethyl amine (TMABS), (4-sulfonic
acid) butyltriethyl amine (TEABS) and (4-sulfonic acid) butyltributyl
amine (TBABS) as cations and H5PMo10V2O40 (Mo10V2) as anion and
palladium deposited oleic acid coated-Fe3O4 nanoparticles (Fe3O4@
OA–Pd). These catalytic systems were employed in the Heck coupling
reaction. All of these catalytic systems exhibited remarkable activities
in a model reaction and the systems tolerate a wide variety of aryl ha-
lide compounds and styrene with good to excellent yields of desired
products. Also the effect of redox properties and Brönsted acidity of
POM-ILs part of mentioned catalytic system were investigated.
2.2. Preparation of Mo10V2
Mo10V2 was prepared according to the following procedure: sodium
metavanadate (24.4 g) was dissolved by boiling in 100 mL of water and
then mixed with 7.1 g of Na2HPO4 in 100 mL of water. Then this solution
was cooled, 5 mL of concentrated sulfuric acid was added, and the
solution developed a red color. An addition of 121.0 g of Na2MoO4·2H2O
dissolved in 200 mL of water was then made. While the solution was
vigorously stirred, 85 mL of concentrated sulfuric acid was added slow-
ly, and the hot solution was allowed to be cooled to room temperature.
Mo10V2 was then extracted with 500 mL of diethyl ether. Evaporation of
the solvent afforded a crude product which dissolved in water, concen-
trated to first crystal formation, and then allowed to crystallize further.
The large red crystals that formed were filtered, washed with water, and
air dried [37].
Scheme 1. Structures of organic–inorganic hybrid compounds (POM-ILs).

E. Rafiee, M. Kahrizi / Journal of Molecular Liquids 218 (2016) 625–631
627
2.3. Synthesis of Mo10V2-IL catalysts
separated by a magnetic field, washed with ethanol and water three
times and dried at vacuum conditions [38].
For the preparation of Mo10V2-IL cations, their respective amine
(pyridine, trimethyl amine, triethyl amine and tributyl amine)
(0.11 mol) and 1,3-propanesultone or 1,4-propanesultone (0.10 mol)
were dissolved in toluene (30 mL) and stirred at 40 °C for 72 h under
nitrogen atmosphere. The produced precipitate was filtered, washed
with diethyl ether three times and dried in vacuum. For the preparation
of POM-IL, the prepared cation (0.1 mol) was added to an aqueous
solution of Mo10V2 (0.02 mol, 5 mL), and then the mixture was stirred
at room temperature for 24 h. Water was removed in vacuum to give
the final product as a solid.
2.6. General procedure for the Heck coupling reaction
For Heck coupling reaction, a reaction tube was charged with aryl
halide (4 mmol), styrene (4 mmol), tetrabutylammonium bromide,
TBAB (4 mmol), Fe@OA–Pd (0.38 mol%), Mo10V2-IL (0.26 mol%) and
5 mL DMF and the resulting mixture was refluxed at 120 °C under a
dry nitrogen atmosphere for appropriate time. Progress of the reaction
was monitored by TLC. Upon completion of the reaction, Fe@OA–Pd
was separated by magnet, washed with diethyl ether (2 × 10 mL) and
water (2 × 10 mL), and then dried under vacuum for reusing. Also the
reaction mixture was then cooled to 5 °C and Mo10V2-IL was separated
by filtration, and washed with diethyl ether (3 × 10 mL) and dried
under vacuum for reusing. The residual mixture was extracted by
CH2Cl2 (3 × 20 mL), and the combined organic layers were dried over
MgSO4. Solvent was evaporated and the crude product was character-
ized by 1H NMR spectroscopy [38].
2.4. Synthesis of oleic acid coated-Fe3O4 nanoparticles
The oleic acid coated-Fe3O4 nanoparticles were prepared by a co-
precipitation method, according to a synthesis route described in our
previous publication [38]. Typically, FeCl2·4H2O (4.3 g) and FeCl3·6H2O
(11.6 g) were mixed with 350 mL of deionized water. The resulting
solution was heated to 80 °C while stirring, vigorously. Then, 20 mL of
25% NH4OH was quickly added into the solution. The resulting suspen-
sion was vigorously stirred for 5 min and then, 1 mL oleic acid was
added into the suspension. After mixing for 25 min, the black precipi-
tates were collected with the help of a magnet and washed repeatedly
with deionized water and ethanol, then dried at vacuum conditions.
3. Results and discussion
In continuation of our studies about the effect of POMs on the
coupling reactions [36], we decided to investigate the role of another
forms of POMs, ionic liquid forms, in these types of organic reactions.
Mo10V2 is soluble in most of polar organic solvents, and cannot be
used as a catalyst here. On the other hand, Mo10V2 based pyridinium
or ammonium sulfonic group ILs have some significant physical proper-
ties such as reversible thermal response. Therefore, we believe that this
type of ILs can be applied as an efficient and recyclable part of our
proposed catalytic system in coupling reactions especially in the Heck
reaction.
2.5. Synthesis of Fe3O4@OA–Pd catalyst
A solution of Na2[PdCl4] (0.011 M) in ethanol was prepared by
reacting PdCl2 (0.50 g, 2.82 mmol) and NaCl (0.33 g, 5.64 mmol) at
room temperature. Fe@OA nanoparticle (0.5 g in 700 mL methanol) so-
lution was held at 25 °C for 1 h and then Na2[PdCl4] (100 mL, 0.011 M)
was added. Then 100 mL of NaOAc (5 M) was added rapidly into the so-
lution. After that, 50 mL of methanol was added, and the product was
In the first step of our investigations, we prepared Fe3O4@OA–Pd and
a series of Mo10V2-ILs with different IL parts, and their structural
Fig. 1. FT-IR spectra of different Mo10V2-ILs.

628
E. Rafiee, M. Kahrizi / Journal of Molecular Liquids 218 (2016) 625–631
Table 1
Comparison of activity of Mo10V2-IL series in the Heck reaction.a
Entry
POM-IL
Time (h)
Yield (%)
TON
1
2
3
4
5
6
–
24
12
16
18
24
24
0
94
88
81
92
82
0
500
468
430
489
436
Mo10V2-PyPS
Mo10V2-PyBS
Mo10V2-TMABS
Mo10V2-TEABS
Mo10V2-TBABS
a
Reaction conditions: styrene (4 mmol), 1-bromobenzene (4 mmol), Fe3O4@OA–Pd
(0.19 mol%), Mo10V2-IL (0.13 mol%), TBAB (4 mmol) and at 120 °C.
features were investigated using FT-IR and TEM techniques (Supple-
mentary information, Figs. S1 and S2).
TEM observations and FT-IR spectrum indicated that Fe3O4@OA–Pd
as a main catalyst in this catalytic system has a uniform morphology.
According to the FT-IR spectrum of Fe3O4@OA–Pd, the broad band
near 3446 cm−1 refers to the OH stretching vibration associated with
absorbed water molecule. Two bands at around 2919 and 2854 cm−1
were attributed to the asymmetric and symmetric stretching of CH2
groups of oleic acid, respectively. The peak at 1641 cm−1 exhibited
the presence of the CC stretching vibration. Meanwhile, two new
bands at 1404 and 1542 cm−1 appeared which are characteristic of
the asymmetric –(COO) and the symmetric –(COO) stretch vibration
band, respectively. The absorption band at 583 cm−1 was attributed
to Fe\\O stretch vibrations which confirm the existence of Fe3O4
nanoparticles. Other characterization results have been presented in
our previous publication[21].
Fig. 2. Potentiometric titration curves of Mo10V2-IL series.
Considering that the Heck reaction is affected by acidity of the
catalyst, the acidity of the Mo10V2-ILs plays an important role in this
transformation. It seems that Mo10V2-ILs can act as bond activator in
Also The FT-IR spectra of Mo10V2-ILs are shown in Fig. 1. As shown in
Fig. 1, the structures of all Mo10V2-ILs were confirmed.
Next we decided to study the roles of Mo10V2-IL series in the Heck
reaction. Initially, we compared the catalytic performances of Fe3O4@
OA–Pd and different Mo10V2-ILs in the reaction of styrene with 1-
bromobenzene as model reaction. As seen in Table 1, in the absence of
the Mo10V2-IL the reaction did not proceed even after 24 h. The results
showed that all of the listed catalytic systems can catalyze the reaction
in a desirable manner and the corresponding product was obtained in
good to excellent yield but in different reaction times.
POMs can affect on the reactions with two different mechanisms:
Brӧnsted acid and electron transfer mechanism. In order to probe
which one is the main mechanism, the acidity of Mo10V2-ILs and cyclic
voltammetry measurements of Mo10V2-PyPS, Fe3O4@OA–Pd and mix-
ture of both catalysts were investigated.
Scheme 2. Proposed mechanism for Heck reaction catalyzed by Fe3O4@OA–Pd and
Fig. 3. Cyclic voltammograms of a) Mo10V2-PyPS, b) Fe3O4@OA–Pd and c) mixture of both
modified glassy carbon electrode in a phosphate buffer solution of pH = 7, 100 mV/s.
Mo10V2-ILs, HPA (heteropoly acid) and PA− (polyoxoanion).

E. Rafiee, M. Kahrizi / Journal of Molecular Liquids 218 (2016) 625–631
629
Table 2
Electrochemical data.
The CV responses of Mo10V2-PyPS, Fe3O4@OA–Pd and mixture of both
component modified glassy carbon electrode in a phosphate buffer so-
lution of pH = 7 are shown in Fig. 3. In the potential range between
E = −0.34 and E = +1.58 V, three pairs of redox peaks were observed
for Mo10V2-PyPS modified electrode (Fig. 3a). It can be attributed to the
electron-transfer reaction of Mo(V)/Mo(IV), Mo(IV)/Mo(III) and V(IV)/
V(V) couples. Also, the oxidation behavior of Fe3O4@OA–Pd was inves-
tigated by means of CV and the oxidation of Pd(0)/Pd(II) was identified
with its characteristic peak located at E = +0.03 V (Fig. 3b) [39, 40]. The
peaks at potential 0.16–0.42 are attributed to Fe(II)/Fe(III) nanocrystals
[41]. In addition, to explore the interaction between Fe3O4@OA–Pd and
Mo10V2-IL, we investigate the CV of mixed Fe3O4@OA–Pd and Mo10V2-IL
glassy carbon electrode. As shown in Fig. 3c, in the potential range
between E = −0.33 and E = +1.42 V, all the redox peaks of
Mo10V2-PyPS and Fe3O4@OA–Pd were observed. Also the shift in
the potential of characteristic peak of Fe3O4@OA–Pd and Mo10V2-PyPS
in glassy carbon electrode, clearly indicates the interaction between
Fe3O4@OA–Pd and Mo10V2-PyPS. The amount of the shifts in different
peaks is reported in Table 2.
To establishing the best reaction conditions, firstly the model reac-
tion was carried out in the absence of the Mo10V2-PyPS, the reaction
did not proceed at all and the starting materials were remained intact
after 24 h (Table 3, entry 1). Increasing the quantity of Mo10V2-PyPS
from 0.13 mol% to 0.26 mol% decreases the reaction time but more
than this amount had no significant effect on the reaction time and
yield (entries 2–4). Improvement in time of the reaction was observed
as the quantity of Fe3O4@OA–Pd as catalyst was increased from
0.188 mol% to 0.376 mol%. Further increasing in the Fe3O4@OA–Pd
quantity showed no improvement in the yield or reaction time (en-
tries 4–6). Therefore, 0.26 mol% of the Mo10V2-PyPS and 0.38 mol%
of Fe3O4@OA–Pd were chosen as the optimum amounts of the cata-
lytic system for further reactions. Moreover the effects of various sol-
vents, such as H2O, dimethylacetamide (DMAc), toluene and DMF
have been studied (Table 3, entries 5, 7–9). DMF at 120 °C is found
to be the choice in terms of yield and reaction time (entry 5).
This catalytic system is efficient for a variety of aromatic bromides
and chlorides (Table 4). The results showed acceptable yields of the
corresponding products using aryl bromides with electron-rich or
electron-poor substituents, except in the case of 4-bromoaniline and
4-chloroaniline, where 43 and 56% yields were obtained (entries 3, 7).
Most reactions using styrene and aryl bromides gave well to excellent
yields regardless of steric effect of the substrates. This catalytic system
showed high selectivity for the trans-configured products in all cases,
and no cis/gem olefin products were observed.
Catalyst
EPc (V)
EPa (V)
Potential shift
Assignment peak
ΔEPc (V)
ΔEPa (V)
Fe3O4@OA–Pd
+0.30
N.A.
+0.21
+0.03
+1.42
+0.00
−0.14
+1.23
+0.28
+0.1
−
−
−
−
Fe(II)/Fe(III)
Pd(0)/Pd(II)
V(IV)/V(V)
Mo(IV)/Mo(III)
Mo(V)/Mo(IV)
V(IV)/V(V)
Fe(II)/Fe(III)
Pd(0)/Pd(II)
Mo(IV)/Mo(III)
Mo(V)/Mo(IV)
Mo10V2-PyPS
+1.46
+0.07
−0.07
+1.30
+0.40
N.A.
−
Mixture of both
components
−0.16
+0.10
N.A.
+0.03
+0.04
−0.19
+0.07
+0.07
+0.02
+0.02
+0.10
−0.03
+0.02
−0.12
oxidative addition and reductive elimination steps in the Heck reaction.
A possible mechanism for the Heck reaction in the presence of Fe3O4@
OA–Pd and Mo10V2-ILs is proposed in Scheme 2. In the first step the
C–X bond of an aryl halide (X = Br, Cl) is oxidatively added to the pal-
ladium atom. At this point, the oxidation of palladium (0) is facilitated
by Mo10V2-ILs. Palladium then forms a π complex with the alkene and
next, the alkene inserts itself in the palladium–carbon bond (Pd\\Ar).
In the next step, β-hydride elimination causes the formation of a new
palladium–alkene π complex. Finally this complex is destroyed and
the desired product is released. As shown in the highlighted part of
Scheme 2, in the reductive elimination step, the Pd–X bond is activated
by Mo10V2-IL acidic hydrogens. H–X is a very good leaving group and
this intermediate is very susceptible to loss of H–X group. Finally, in
the reductive elimination step a formed polyoxoanion with taking
hydrogen in Pd\\H group returns to acidic form and palladium reduces
to palladium (0). Further research is under investigation in our
laboratory.
The difference of IL parts in Mo10V2-IL series, apparently influenced
the acidity of the Mo10V2-ILs, which was probed by a potentiometric
titration with an organic base [38].
As shown in Fig. 2, all kinds of Mo10V2-ILs presented very strong
acid sites, Ei N 100 mV. The presence of pyridine as an electron
withdrawing group in Mo10V2-IL structures was accompanied by a
gradual increase in acidic strength active sites. Strength of acidic
sites of different hybrid materials is as the following trends: PyPS-
Mo10V2 N PyBS-Mo10V2 N TMABS-Mo10V2 N TEABS-Mo10V2 N TBABS-
Mo10V2 (Ei values for these compounds are 345, 303, 253, 245, and
238 mV respectively). As a result, it seems that higher activity of
Mo10V2-PyPS is related to higher acidic strength of this catalyst because
the number of acidic sites in all kinds of co-catalyst is approximately
similar.
In order to probe the electron transfer behavior of Mo10V2-ILs and
Fe3O4@OA–Pd, we decided to investigate this property of Mo10V2-ILs
and Fe3O4@OA–Pd by means of cyclic voltammetry (CV) measurements.
As expected, reactions with aryl chlorides gave slightly lower
yields and higher reaction time leaving some unreacted starting
materials. It should be noted that, aryl halides containing electron-
withdrawing functional groups give higher yields with lower reac-
tion times compared to those containing electron-donating func-
tional groups.
Table 3
Effect of the POM on the Heck coupling reaction.a
Entry
Catalyst
Solvent
Time (h)
Yield (%)b
TON
Fe3O4@OA–Pd (mol%)
Mo10V2-IL
1
2
3
4
5
6
7
8
9
0.19
0.19
0.19
0.19
0.38
0.56
0.38
0.38
0.38
–
DMF
DMF
DMF
DMF
DMF
DMF
H2O
24
12
9
9
7
0
94
89
93
96
90
32
8
0
500
473
494
251
159
85
Mo10V2-PyPS (0.13 mol%)
Mo10V2-PyPS (0.26 mol%)
Mo10V2-PyPS (0.39 mol%)
Mo10V2-PyPS (0.26 mol%)
Mo10V2-PyPS (0.26 mol%)
Mo10V2-PyPS (0.26 mol%)
Mo10V2-PyPS (0.26 mol%)
Mo10V2-PyPS (0.26 mol%)
7
24
24
24
Toluene
DMAc
21
207
78
a
Reaction conditions: styrene (4 mmol), bromobenzene (4 mmol), TBAB (4 mmol) at 120 °C.
Isolated yield.
b

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E. Rafiee, M. Kahrizi / Journal of Molecular Liquids 218 (2016) 625–631
Table 4
Heck reaction of various aryl halides with styrene.
Entry
1
Aryl halide
Time (h)
12
Yield (%)a
74
TON
197
2
3
12
24
88
43
234
114
4
5
6
7
4
6
96
94
86
255
250
229
7
8
9
24
24
12
56
66
87
149
175
231
10
11
12
12
81
83
216
221
12
8
97
258
a
Isolated yield, all products were characterized by comparison of their spectroscopic data with those reported in the literature [21, 42–44].
An important factor in the development of solid acids for most of the
organic reactions is the reusability of the catalysts. This aspect was con-
sidered by recovering of the Fe3O4@OA–Pd after each catalytic run by
magnet and reusing it in a new cycle. But in the case of Mo10V2-PyPS,
considering that this catalyst is insoluble in the reaction medium at
5 °C, the catalyst can be recovered easily by simple filtration.
In order to evaluate the reusability of our catalytic system, a control
test was performed using 0.04 g of the first recycled catalysts (primeval
amount of catalytic system) and 92% yield of the product was obtained
after 12 h. As shown in Fig. 4, the catalytic system revealed a remarkable
activity and was reused up to at least four consecutive cycles without
appreciable reduction in the catalytic activity of the catalyst.
4. Conclusion
In conclusion, we have developed an efficient protocol for the Heck
coupling reaction using Fe3O4@OA–Pd and Mo10V2-ILs as efficient, het-
erogeneous and recyclable catalytic systems. The reaction was carried
out in base and ligand free conditions and could be employed for the
condensation of different aryl halides and styrene. Our investigation
Fig. 4. Reusability of Fe3O4@OA–Pd and Mo10V2-PyPS in the model reaction (after 12 h).

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631
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on the role of Mo10V2-ILs in this study demonstrated that, these co-
catalysts can influence the Heck reaction in two different and simulta-
neous manners: Brӧnsted acid and electron transfer pathways which
make it a highly efficient co-catalyst for this type of organic transforma-
tion. Moreover, the recovery of this system consists of a single filtration
for Mo10V2-ILs albeit after cooling to 5 °C and magnetic separation for
Fe3O4@OA–Pd. Both components of this catalytic system are stable
under the present reaction conditions and after separation from reac-
tion media, can be used up to four catalytic cycles without significant
loss in activity. Further studies on extending the application of this cat-
alytic system in other organic synthesis are ongoing in our laboratory.
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Acknowledgment
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The authors thank the Razi University Research Council for the
support of this work.
Appendix A. Supplementary data
TEM image and FT-IR spectrum of Fe3O4@OA–Pd are available.
Supplementary data associated with this article can be found in the
online version, at http://dx.doi.org/10.1016/j.molliq.2016.02.055.
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