Fe3O4@OA-Pd and Mo10V2@NSiO2 nanoparticles: An efficient and reusable catalytic system for Heck reaction under ligand free conditions

Article abstract of DOI:10.1007/s11164-015-2077-3

This paper reports the use of a novel catalytic system composed of H₅PMo₁₀V₂O₄₀ supported on nano silica (Mo₁₀V₂@NSiO₂) and palladium-deposited, oleic-acid-coated Fe₃O₄ (Fe₃O₄@OA-Pd) nanoparticles, as reusable catalysts for Heck coupling reaction under ligand and base free conditions. The average particle size of catalyst was measured to be about 9 nm by transmission electron microscopy. The immobilized palladium on oleic acid coated Fe₃O₄ was found to be effective in the Heck arylation of various aryl bromides and especially less reactive aryl chlorides with styrene in the presence of heteropoly acid. This method has the advantages of high yields, elimination of ligand and base, simple methodology and easy workup. Interestingly, the novel catalytic system could be recovered in a facile manner from the reaction mixture and recycled several times without any significant loss in catalytic activity. Structural changes of recovered Mo₁₀V₂@NSiO₂ and Fe₃O₄@OA-Pd were investigated before reusing for the next runs. Finally, synchronized reusability of both components of our catalytic system has been investigated in the model reaction.

Full text of DOI:10.1007/s11164-015-2077-3

Res Chem Intermed
DOI 10.1007/s11164-015-2077-3
Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles:
an efficient and reusable catalytic system for Heck
reaction under ligand free conditions
Ezzat Rafiee1,2 Masoud Kahrizi1
•
Received: 17 January 2015 / Accepted: 24 April 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract This paper reports the use of a novel catalytic system composed of
H5PMo10V2O40 supported on nano silica (Mo10V2@NSiO2) and palladium-de-
posited, oleic-acid-coated Fe3O4 (Fe3O4@OA–Pd) nanoparticles, as reusable cata-
lysts for Heck coupling reaction under ligand and base free conditions. The average
particle size of catalyst was measured to be about 9 nm by transmission electron
microscopy. The immobilized palladium on oleic acid coated Fe3O4 was found to be
effective in the Heck arylation of various aryl bromides and especially less reactive
aryl chlorides with styrene in the presence of heteropoly acid. This method has the
advantages of high yields, elimination of ligand and base, simple methodology and
easy workup. Interestingly, the novel catalytic system could be recovered in a facile
manner from the reaction mixture and recycled several times without any significant
loss in catalytic activity. Structural changes of recovered Mo10V2@NSiO2 and
Fe3O4@OA–Pd were investigated before reusing for the next runs. Finally, syn-
chronized reusability of both components of our catalytic system has been inves-
tigated in the model reaction.
Keywords Heck coupling Á Palladium Á Oleic acid Á Heterogeneous catalyst Á
Polyoxometalate Á Nanoparticles Á Magnetically recoverable
&
Ezzat Rafiee
Ezzat_rafiee@yahoo.com; e.rafiei@razi.ac.ir
1
2
Department of Inorganic Chemistry, Faculty of Chemistry, Razi University,
67149 Kermanshah, Iran
Institute of Nano Science and Nano Technology, Razi University, 67149 Kermanshah, Iran
123

E. Rafiee, M. Kahrizi
Introduction
Palladium-catalyzed cross-coupling of aryl halides with olefins, known as Heck
coupling, has contributed greatly to the straightforward and facile construction of
carbon–carbon bonds [1–10]. This reaction is generally considered to be a
homogeneous reaction most commonly catalyzed by soluble Pd(II) species with a
variety of ligands, such as palladium–phosphine complexes [2], oxime palladacy-
cles [3], palladium–salen complexes [4], and palladium–N-heterocyclic carbine
complexes [5]. However, separation of the expensive catalyst from the product for
reusing is often problematic in these homogeneous systems. Moreover, aggregation
and precipitation of palladium metal in the homogeneous systems always leads to
lost activity of the catalysts. Thus, heterogeneous catalysts are highly desirable,
especially in large-scale synthesis, from both environmental and economic aspects.
Much effort has been paid to developing heterogeneous catalytic systems that can be
efficiently reused [6, 9, 10]. Original ways have been found in the elaboration of
magnetic catalysts that can be easily removed using external magnets, and in the use
of supported forms of catalytic systems without practical loss.
Fe3O4 nanoparticles as a catalyst support have been attracting more and more
attention because they can be easily recovered from the reaction mixture simply by
using an external magnet, thus eliminating the necessity of tedious centrifugation,
filtration, or membrane separation steps [11–19].
ItisnoteworthythatFe3O4 nanoparticlestendtoaggregate, whichdeterioratesunique
characteristic properties of nanoparticles. Coating of the nanoparticles with a suitable
protective layer can decrease the degree of agglomeration and increase the stability of
the palladium nanoparticles. Several molecules have been used to coat the surface of
magnetic nanoparticles (MNPs). Oleic acid is particularly useful in this regard [20–23],
since it is readily available and is non-toxic. In addition, oleic acid has a strong affinity
for magnetite particles through interaction between its carboxy groups and iron cations
on the magnetite surface. Furthermore, the twisty hydrocarbon tails of oleic acid may
helptostabilizethe transitionmetal catalystsbychainswrappingupthe individualmetal
nanoparticles, thus preventing them from aggregating with each other.
Recently, there has been a growing number of studies done on the use of
polyoxometalates (POMs) in the coupling reactions [24–27]. The unique results for
coupling reactions catalyzed by palladium and POM systems encourage us to study the
Heck coupling reaction catalyzed by palladium-deposited, oleic-acid-coated Fe3O4
(Fe3O4@OA–Pd) particles and H5PMo10V2O40 supported on nano silica (Mo10V2@
NSiO2) as an efficient, reusable and cost-effective catalytic system. The essential
requirement for the Heck reaction includes a base and a ligand-stabilized active Pd
species. We believe that Mo10V2@NSiO2 is an excellent alternative for bases and a
strong activator for reactants in this reaction. The use of base, ligand and non-
recyclable catalysts in reported systems in the literature is not beneficial to industrial
and synthetic applications. The use of high amounts of bases poses several problems,
such as inability to recover, contamination of the environment, corrosion of equipment
and high toxicity. Hence, there is a need for efficient, ecofriendly and recoverable
alternatives to replace bases in the Heck reaction. Along this line, using heterogeneous
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Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles…
heteropoly acids (HPAs), which are low in toxicity, highly stable towards humidity,
recyclable and air stable, can be useful. HPAs are advantageous over conventional
bases as they can be easily recovered from the reaction mixture by simple filtration and
can be reused without activation, thereby making the process economically and
environmentally viable. This heterogeneous catalytic system can be readily recovered
and reused several times without significant loss of activity.
Materials and methods
General information
All reactions were performed under an atmosphere of dry nitrogen. All chemicals used in
this work were obtained from Fluka, Aldrich or Merck companies, and were used without
further purification. Transmission electron microscopy (TEM) analysis was performed
using the TEM microscope LEO 912AB TEM Netherland. The high-resolution
transmission electron microscopy (HR-TEM) measurements were conducted using a
JEOL JEM-2100F electron microscope operating at 200 kV. X-ray diffraction (XRD)
measurements were performed using a Bruker AXS Company, D8ADVANCE diffrac-
tometer (Germany). Surface areas were calculated from the linear part of the BET plot.
Low temperature nitrogen adsorption experiments were performed using a Quantachrome
instrument (model Nova 2000) for measuring surface area and pore volume. Fourier
transform infrared spectroscopy (FT-IR) spectra were recorded with KBr pellets using a
Shimadzu 470 spectrophotometer. Gas chromatography was performed on a Varian CP-
3800 (column: CP-Sil 8 CB fused silica capillary column). Thin layer chromatography
(TLC) on precoated silica gel, fluorescent 254 nm (0.2 mm), on aluminum plates was
used for monitoring the reactions. The cross-coupling products were characterized by their
1H nuclear magnetic resonance (NMR) spectra.
Synthesis of oleic acid coated-Fe3O4 nanoparticles
The oleic acid coated-Fe3O4 nanoparticles were prepared by the co-precipitation
method, according to a synthesis route described in our previous publication [28].
Typically, FeCl2Á4H2O (4.3 g) and FeCl3Á6H2O (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 suspension was vigorously stirred for 5 min, and then 1 mL oleic acid was
added into the suspension. After mixing for 25 min, the black precipitates were
collected with the help of a magnet and washed repeatedly with deionized water and
ethanol, then dried under vacuum conditions.
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
nanoparticles (0.5 g in 700 mL methanol) solution was held at 25 °C for 1 h and
123

E. Rafiee, M. Kahrizi
then Na2[PdCl4] (100 mL, 0.011 M) was added. Then 100 mL of NaOAc (5 M) was
added rapidly into the solution. After that, 50 mL of methanol was added, and the
product was separated by magnetic field, washed three times with ethanol and water,
and dried under vacuum conditions [28].
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 Na2MoO4Á2H2O dissolved in 200 mL of water was then made. While the
solution was vigorously stirred, 85 mL of concentrated sulfuric acid was added
slowly, and the hot solution was allowed to cool to room temperature. Mo10V2 was
then extracted with 500 mL of diethyl ether. Evaporation of the solvent afforded a
crude product that dissolved in water, concentrated to first crystal formation, and
then was allowed to crystallize further. The large red crystals that formed were
filtered, washed with water, and air dried [29].
Preparation of Mo10V2@NSiO2
Mo10V2@NSiO2 was prepared by impregnating nano silica (3.0 g) with an aqueous
solution of Mo10V2 (with concentration depending upon the loading 40 wt%
Mo10V2 on silica). The mixture was stirred overnight at room temperature, followed
by drying using a rotary evaporator [30–32].
General procedure for the Heck coupling reaction
For the Heck coupling reaction, a reaction tube was charged with aryl halide
(4 mmol), styrene (4 mmol), tetrabutylammonium bromide, TBAB (4 mmol),
Fe@OA–Pd (0.02 g), Mo10V2@NSiO2 (0.004 g) and 5 mL DMF, and the resulting
mixture was refluxed at 120 °C under a dry nitrogen atmosphere for an appropriate
time. Progress of the reaction was monitored by TLC. Upon completion of the
reaction, the reaction mixture was then cooled to room temperature and Fe@OA–Pd
was separated by magnet, washed with diethyl ether (2 9 10 mL) and water
(2 9 10 mL), and then dried under vacuum for reusability. Mo10V2@NSiO2 was
also separated by filtration, and washed with diethyl ether (3 9 10 mL) and dried at
100 °C for reusing. The residual mixture was extracted by CH2Cl2 (3 9 20 mL),
and the combined organic layer was dried over MgSO4.
Results and discussion
In the present work, Mo10V2@NSiO2 and Fe3O4@OA–Pd were used as a highly
efficient nano catalytic system. The catalytic activity of this two-component system
was investigated in Heck reaction under base and ligand-free conditions.
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Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles…
Fig. 1 TEM images and size distribution of Fe3O4@OA–Pd
Fig. 2 XRD patterns of a Mo10V2@NSiO2 and b PMo10V2
At the beginning of our catalytic studies, the structural features of Fe3O4@OA–
Pd catalyst were investigated using TEM techniques (Fig. 1). TEM observations
indicated that Fe3O4@OA–Pd as a main catalyst in this catalytic system has a
uniformity and spherical morphology. The average particle size of catalyst was
about 9 nm. Other characterization results have been presented in our previous
publication [28].
XRD patterns of Mo10V2@NSiO2 and PMo10V2 are presented in Fig. 2; no
obvious peak was found in the catalyst, which indicates that Mo10V2 was
homogeneously dispersed in amorphous silica [33]. The nano silica and Mo10-
V2@NSiO2 have BET surface areas of 628 and 181 m2 g-1, respectively. The
surface area of catalyst decreased remarkably compared to its parent support, but
123

E. Rafiee, M. Kahrizi
still showed very high value. The reduction in the surface area of supported catalyst
may be due to the blockage of smaller pores by active species and good dispersion
of Mo10V2.
Next, for optimization of the reaction conditions, the reaction of 1-bromonaph-
talene (4 mmol) and styrene (4 mmol) at 120 °C and under ligand and base-free
conditions was chosen as a model reaction (Scheme 1). First, the abilities of various
catalytic systems such as H3PW12O40 (PW), Mo10V2, Pd2.5PMo10V2O40 and
Mo10V2@NSiO2 accompanied by Fe3O4@OA–Pd in the model reaction were
investigated (Table 1). As shown in Table 1, among these catalysts, Mo10V2 and
Mo10V2@NSiO2 were found to be excellent catalysts in terms of conversion and
reaction time (entries 3, 4). It may be because of this fact that Mo10V2 and
Mo10V2@NSiO2 are ideal outer-sphere electron-transfer compounds. Electron
transfer between palladium species and POMs in the catalytic cycle of this reaction
may help to increase the reaction efficiency. We have also studied a similar reaction
Scheme 1 Reaction of styrene and 1-bromonaphtalene as a model reaction
Table 1 Effect of the POM on the Heck coupling reaction
Entry
Catalyst
Solvent
Time (h)
Yield (%)a
Fe3O4@OA–Pd (g)
POM (g)
1
0.01
0.01
0.01
0.01
–
–
DMF
DMF
DMF
DMF
DMF
H2O
24
24
24
24
24
24
24
8
0
32
95
70
23
10
0
2
PW (0.001)
3
Mo10V2 (0.001)
4
Mo10V2@NSiO2 (0.004)
Pd2.5Mo10V2 (0.001)
Mo10V2@NSiO2 (0.004)
Mo10V2@NSiO2 (0.004)
Mo10V2@NSiO2 (0.004)
Mo10V2@NSiO2 (0.004)
Mo10V2@NSiO2 (0.008)
Mo10V2@NSiO2 (0.004)
Mo10V2@NSiO2 (0.004)
Mo10V2@NSiO2 (0.004)
5
6
0.01
0.01
0.02
0.03
0.01
0.02
0.02
0.02
7
Toluene
DMF
DMF
DMF
DMF
DMF
DMF
8
90
95
70
0b
6c
73d
9
8
10
11
12
13
24
24
24
24
Reaction conditions: styrene (4 mmol), 1-bromonaphtalene (4 mmol), TBAB (4 mmol) and at 120 °C
a
Isolated yield
b
Reaction proceeded in TBAB free conditions
c
Reaction proceeded in room temperature condition
d
Reaction proceeded at 80 °C
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Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles…
in the absence of POM. The reaction did not proceed and the starting materials
remained intact after 24 h (entry 1). There is a problem here: Mo10V2 in acidic form
is a homogeneous catalyst in this reaction media. The major problem, limiting the
utility of homogeneously catalyzed processes, is a well-known difficulty in catalyst
recovery and recycling. The recycling of POMs as catalysts is the key issue to their
application. Therefore, we chose Mo10V2@NSiO2 as the heterogeneous recoverable
catalyst for the Heck coupling reaction.
To establishing the best reaction conditions, the effects of various solvents, such
as H2O, toluene and DMF, were studied (entries 4, 6, 7). DMF at 120 °C was found
to be the choice in terms of yield and reaction time (entry 4). Next, the model
reaction was carried out in the presence of different amounts of Fe3O4@OA–Pd as
catalyst. Improvement in time of the reaction was observed as the catalyst quantity
increased from 0.01 to 0.02 g. Further increase in the Fe3O4@OA–Pd quantity
showed no improvement in the yield or reaction time (Table 1, entries 8, 9). Also,
more increase in Mo10V2@NSiO2 had no significant effect on the reaction time and
yield (Table 1, entry 10). Having realized the optimum catalysts loading for the
reaction (0.004 g of the Mo10V2@NSiO2 and 0.02 g of Fe3O4@OA–Pd), attention
turned to the evaluation of the influence of TBAB as an additive on the Heck
coupling reaction. In the absence of TBAB, the reaction did not proceed even after
24 h (Table 1, entry 11), while addition of TBAB permitted us to achieve 90 %
yield of the product after 8 h (Table 1, entry 8). The potential and efficiency of the
tetraalkylammonium salts has been illustrated. TBAB is a phase transfer catalyst for
facilitating the regeneration of the zero valent palladium catalyst. The dissociation
of the hydridopalladium halide complex can be more efficient in the presence of
inorganic bases [34]. Also, TBAB can act as stabilizer of palladium nanoparticles,
preventing their aggregation to the bigger size particles, which are usually inactive
or less active. At elevated temperature, TBAB can partially decompose to Bu3N,
and Bu3N can facilitate the reductive elimination step. It is generally accepted that
promoting the oxidative addition and reductive elimination step and prevention of
palladium black formation, thereby enhancing catalyst concentration, are factors of
the high catalytic activity in the presence of tetraalkylammonium salts [34–36].
Finally, the model reaction was performed at various temperatures. As shown in
Table 1, with reduction of the temperature from 120 °C to room temperature, the
yield decreased from 90 to 6 % (Table 1, entries 12, 13). These results demonstrated
that the reaction temperature had a significant effect on the reaction progress, and
further experiments were carried out at 120 °C. Therefore, 0.004 g of the
Mo10V2@NSiO2 and 0.02 g of Fe3O4@OA–Pd at 120 °C in the presence of TBAB
were chosen as the optimum condition of catalytic system for further reactions.
Using the optimized reaction conditions, we explored the general applicability of
Fe3O4@OA–Pd and Mo10V2@NSiO2 as a catalytic system with styrene and other
aryl halides containing electron withdrawing or donating substituents, and the
results are tabulated in Table 2. It should be noted that this catalytic system showed
high selectivity for the trans-configured products in all cases, and no cis/gem olefin
products were observed. Among the various substituted aryl bromides, both
deactivated (electron-rich) and activated (electron-poor) examples were converted
efficiently to the desired products in good to excellent yields (entries 1–7). Aryl
123

E. Rafiee, M. Kahrizi
Table 2 Heck reaction of various aryl halides with styrene
Entry
Aryl halide
Time (h)
Yield (%)b
Br
1
8
90
Br
2
3
8
86
91
Br
12
OHC
Br
4
5
6
12
12
12
82
83
72
Br
H
3C
Br
O
Br
7
8
24
9
71
93
H2N
Cl
NO2
NO2
Cl
9
12
12
91
78
O2
N
Cl
10
OHC
Cl
11
12
86
Cl
12
13
12
24
79
91
NO2
N
Cl
Cl
14
24
40
H2N
Reaction conditions: styrene (4 mmol), aryl halide (4 mmol), TBAB (4 mmol) at 120 °C
a
Isolated yield. All products were characterized by comparing their 1H-NMR data with authentic samples
123

Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles…
bromides containing electron-withdrawing functional groups give higher yields with
lower reaction times compared to those containing electron-donating functional
groups. As expected, aryl bromides were more reactive than aryl chlorides, and the
substituent effects in the aryl bromides appeared to be less significant than in the aryl
chlorides (Table 2, entries 3, 7 and 10, 14). As shown in Table 2, activated aryl
chlorides such as 2,4-dinitrochlorobenzene, 4-nitrochlorobenzene and 4-chloroben-
zaldehyde underwent the Heck reaction with styrene under similar conditions to afford
the corresponding product in excellent yield (entries 8–10), whereas deactivated aryl
chlorides such as 4-chloroaniline gave 40 % yield (entry 14). It is noteworthy that this
catalytic system also had the ability to couple styrene with sterically hindered
substrates such as 1-bromonaphthalene, 4-bromobiphenyl, 1-chloronaphthalene and
2, 4-dinitrochlorobenzene in reasonable yields (Table 2, entries 1, 2, 8, 11).
In recent years, reusable solid acid catalysts have attracted a great deal of interest.
Since most of the catalysts are expensive and contaminate the environment, the
development of efficient methods for recovery and reusing of the catalyst is very
important. Thus, investigations of the factors that affect the reusability of the
catalyst have especially profound importance. We decided to investigate the
structural changes of recovered Mo10V2@NSiO2 and Fe3O4@OA–Pd before
reusing for the next runs. In order to determine the changes of both components
of our catalytic system, Mo10V2@NSiO2 and Fe3O4@OA–Pd were separated from
the model reaction, and their structural changes were determined by FT-IR
technique. As shown in FT-IR spectra of the fresh and recovered Fe3O4@OA–Pd
(Fig. 3), it seems that the reaction media and temperature did not effect the structure
of Fe3O4@OA–Pd. The broad band near 3400–3500 cm-1 in Fig. 3 refers to the OH
stretching vibration associated with absorbed water molecule. Two bands at around
2860–2930 cm-1 were attributed to the asymmetric and symmetric stretching of
CH2 groups of oleic acid, respectively. The peak at about 1625 cm-1 exhibited the
presence of the C=C stretching vibration. From Fig. 3, it is clear that the band at
1710 cm-1, which was assigned to the stretching vibration of C=O in oleic acid, is
absent in the spectrum of Fe3O4@OA particles. Meanwhile, two new bands at about
1415 and 1570 cm-1 appeared, and are characteristic of the asymmetric –(COO-)
and the symmetric –(COO-) stretch vibration bands, respectively. These results
could be explained by the fact that oleic acid was chemically absorbed onto the
surface of Fe3O4 particles. Literature data concerning coordination modes of
carboxylate group and the metal atom show that in our case, the two oxygen atoms
in the carboxylate connected to Fe atoms as a bridging bidentate form [20, 37]. The
absorption bands at 583 cm-1 in fresh and 571 cm-1 in recovered Fe3O4@OA–Pd
were attributed to Fe–O stretch vibrations that confirm the existence of Fe3O4 in the
two samples. The spectrum of recovered Fe3O4@OA–Pd shows that structural
properties of oleic acid to Fe3O4 do not change after completion of the reaction.
Figure 4 shows the FT-IR spectra of the pure Mo10V2, fresh Mo10V2@NSiO2 and
recovered Mo10V2@NSiO2. The bands for the Keggin structure of neat Mo10V2
occurred at 1096, 1042, 944 and 815 cm-1 [30]. The four bands were detected for
fresh Mo10V2@NSiO2, indicating that the Keggin structure of the Mo10V2 was well
preserved. The FT-IR spectra of the recovered Mo10V2@NSiO2 confirmed that there
is no significant change in the structure of the catalyst.
123

E. Rafiee, M. Kahrizi
Fig. 3 FT-IR spectra of fresh and recovered Fe3O4@OA–Pd
Fig. 4 FT-IR spectra of fresh and recovered Mo10V2@NSiO2 and fresh Mo10V2
123

Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles…
The reaction data, along with some literature data for comparison, are given in
Table 3. These catalysts showed good reactivity. However, the use of base, ligand
and non-recyclable catalysts in these reported systems is not beneficial to industrial
and synthetic applications.
Reusability of Fe3O4@OA–Pd and Mo10V2@NSiO2 makes the Heck coupling
more economical, which encouraged us to study the reusability of this catalytic
system in the model reaction. After each run, the desired catalysts were washed with
suitable solvent and dried as described in the experimental section. As shown in
Fig. 5a, to evaluate the reusability of Mo10V2@NSiO2, at the beginning of each run
Fe3O4@OA–Pd was used freshly. In the presence of recovered Mo10V2@NSiO2, the
yield of the product was reduced to an extent of only 15 % from the first run to the
third run. Reusability of Fe3O4@OA–Pd was also investigated in the model
reaction, as shown in Fig. 5b. It should be noted that to evaluate the recovery of the
Fe3O4@OA–Pd at the beginning of each run, Mo10V2@NSiO2 was used freshly.
The results indicated that Fe3O4@OA–Pd can be recycled three times, albeit with
slightly decreasing activity. Finally, synchronized reusability for both components
of our catalytic system in the model reaction has been investigated (Fig. 5c) and
neither of them were used freshly. The results demonstrate that Fe3O4@OA–Pd and
Mo10V2@NSiO2 can be simultaneously reused at least three times without apparent
loss of their catalytic activity.
A possible mechanism for the Heck reaction in the presence of Fe3O4@OA–Pd
and Mo10V2@NSiO2 is proposed in Scheme 2. In a first step, the C–X bond of an
aryl halide (X = Br, Cl) is oxidatively added to the palladium atom. At this point,
the aryl halide bond activation is done by Mo10V2@NSiO2 acidic hydrogens.
Palladium then forms a p complex with the alkene, and next, the alkene inserts itself
in the palladium–carbon bond (Pd–Ar). In the next step, beta-hydride elimination
Table 3 Comparison of the reaction data with other reported methods
Entry Catalyst
Solvent
Temperature
(°C)
Time
(h)
Yield
(%)
References
1
2
3
Pd–Fe3O4
TiO2@Pd
DMF
DMF
H2O
110
140
100
24
24
15
76
91
71
[38]
[39]
[40]
Benzimidazolium salt/
Pd(OAc)2
4
Pd(II)/[BMIM][TPPMS]
Pd(dba)2/P(OPh)3
Pd (0) MCM-41
Pd/(SiO2/Fe3O4)
NHC-Pd/SBA-16-IL
Pd/SiO2
[BMIM][OAc] 140
3
20
24
12
40
20
12
40
43
90
71
94
90
82
[41]
5
DMF
100
[42]
6
DMF
100
[43]
7
CH3CN/H2O
NMP
80–90
140
[44]
8
[45]
9
DMA
135
[46]
11
DMF
120
This work
123

E. Rafiee, M. Kahrizi
Fig. 5 Reusability of Fe3O4@OA–Pd and Mo10V2@NSiO2 in the model reaction (after 8 h). a Model
reaction with recovered Mo10V2@NSiO2. b Model reaction with recovered Fe3O4@OA–Pd. c Model
reaction with recovered Mo10V2@NSiO2 and Fe3O4@OA–Pd
HX
H
H
Pd XH
-
PA
Pd(0)
HPA
Ar
Pd
X
Pd
X
Ph
Ar
Ph
Ph
Ph
X
Pd
Pd
Ar
X
H
H
Ar
Scheme 2 Proposed mechanism for Heck reaction catalyzed by Fe3O4@OA–Pd and Mo10V2@NSiO2
causes formation of a new palladium–alkene p complex. Finally, this complex is
destroyed and desired product is released. The palladium(0) compound is
regenerated by reductive elimination of the palladium(II) compound using Mo10-
V2@NSiO2. Further research is under investigation in our laboratory.
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Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles…
Conclusion
In conclusion, we have come up with a new stable and heterogeneous catalytic
system; Fe3O4@OA–Pd and Mo10V2@NSiO2. The present paper reports Heck
coupling catalyzed by an efficient ligand and base free heterogeneous catalytic
system. The immobilized palladium on oleic acid coated-Fe3O4 was found to be
effective in the Heck arylation of various aryl bromides, and especially of less
reactive aryl chlorides with styrene in the presence of heteropoly acid. Moreover,
the recovery of this system consists of a single filtration for Mo10V2@NSiO2 and
magnetic separation for Fe3O4@OA–Pd. Both components of this catalytic system
are stable under the present reaction conditions, and after separation from reaction
media, can be used up to three catalytic cycles without significant loss in activity.
Further studies on extending the application of this catalytic system in other organic
synthesis are ongoing in our laboratory.
Acknowledgments The authors thank the Razi University Research Council for support of this work.
References
1. R.F. Heck, J.P. Nolley, J. Org. Chem. 37, 2320 (1972)
2. I.P. Beletskaya, A.V. Cheprakov, Chem. Rev. 100, 3009 (2000)
3. M. Shibasaki, E.M. Vogl, J. Organomet. Chem. 576, 1 (1999)
4. J. Mo, L. Xu, J. Ruan, S. Liu, J. Xiao, Chem. Commun. 3591 (2006)
¨
¨
5. W.A. Herrmann, C. Brossmer, K. Ofele, C.-P. Reisinger, T. Proermeier, M. Beller, H. Fischer,
Angew. Chem. Int. Ed. 34, 1844 (1995)
¨
6. W.A. Herrmann, V.P.W. Bohm, C.-P. Reisinger, J. Organomet. Chem. 576, 23 (1999)
7. L. Yin, J. Liebscher, Chem. Rev. 107, 133 (2007)
8. A. Molnar, Chem. Rev. 111(3), 2251 (2011)
9. D. Sengupta, J. Saha, G. De, B. Basu, J. Mater. Chem. A 2, 3986 (2014)
10. B. Basu, S. Das, P. Das, B. Mandal, D. Banerjee, F. Almqvist, Synthesis 1137 (2009)
11. S. Tang, L. Wang, Y. Zhang, S. Li, S. Tian, B. Wang, Fuel Process. Technol. 95, 84 (2012)
12. B.V. Subba Reddy, A. Siva Krishna, A.V. Ganesh, G.G.K.S. Narayana Kumar, Tetrahedron Lett. 52,
1359 (2011)
13. R. Parella, N. Srinivasarao, A. Babu, Catal. Commun. 29, 118 (2012)
14. H.Y. Niu, Z.F. Dizhang, Y.Q.Cai Meng, J. Hazard. Mater. 227, 195 (2012)
15. H. Liu, Z. Jia, S. Ji, Y. Zheng, M. Li, H. Yang, Catal. Today 175, 293 (2011)
16. L. Ai, C. Zeng, Q. Wang, Catal. Commun. 14, 68 (2011)
17. A. Kong, P. Wang, H. Zhang, F. Yang, S. Huang, Y. Shan, Appl. Catal. A: Gen. 183, 417 (2012)
18. J. Liu, Y. Zhou, F. Liu, C. Liu, J. Wang, Y. Pan, D. Xue, RSC Adv. 2, 2262 (2012)
19. G. Li, L. Mao, RSC Adv. 2, 5108 (2012)
20. N. Wu, L. Fu, M. Su, M. Aslam, K.C. Wong, V.P. Dravid, Nano Lett. 4, 383 (2004)
21. G. Kataby, M. Cojocaru, R. Prozorov, A. Gedanken, Langmuir 15, 1703 (1999)
22. R. Tadmor, R.E. Rosensweig, J. Frey, J. Klein, Langmuir 16, 9117 (2000)
23. D. Li, D. Jiang, M. Chen, J. Xie, Y. Wu, S. Dang, J. Zhang, Mater. Lett. 64, 2462 (2010)
24. K.C. Pereira, A.L. Porter, Sh. Potavathri, A.P. LeBris, B. DeBoef, Tetrahedron 69, 4429 (2013)
25. A. Corma, S. Iborra, F.X. Llabres i Xamena, R. Monton, J.J. Calvino, C.J. Prestipino, J. Phys. Chem.
C. 114, 8828 (2010)
26. S. Pathan, A. Patel, RSC Adv. 2, 116 (2012)
27. P. Zhao, Y. Leng, M. Zhang, J. Wang, Y. Wu, J. Huang, Chem. Commun. 48, 5721 (2012)
28. E. Rafiee, A. Ataei, Sh. Nadri, M. Joshaghani, S. Eavani, Inorg. Chim. Acta 409, 302 (2014)
29. G.A. Tsigdinos, C.J. Hallada, Inorg. Chem. 7, 437 (1968)
30. E. Cadot, M. Fournier, A. Teze, G. Herve, Inorg. Chem. 35, 282 (1996)
123

E. Rafiee, M. Kahrizi
31. E. Rafiee, Z. Zolfagharifar, M. Joshaghani, S. Eavani, Appl. Catal. A: Gen. 365, 287 (2009)
32. E. Rafiee, F. Rahimi, J. Chil. Chem. Soc. 58, 1926 (2013)
33. Y. Li, Z. Wang, R. Chen, Y. Wang, W. Xing, J. Wang, J. Huang, Catal. Commun. 55, 34 (2014)
34. T. Jeffery, J.-C. Galland, Tetrahedron Lett. 35, 4103 (1994)
¨
35. R. Brinkmann, R. Koppler, P. Neiteler, J. Richter, Adv. Mater. 4, 804 (1992)
36. I. Pryjomska-Ray, A.M. Trzeciak, J.J. Ziolkowski, J. Mol. Catal. A: Chem. 257, 3 (2006)
37. K. Yang, H. Peng, Y. Wen, N. Li, Appl. Surf. Sci. 256, 3093 (2010)
38. J. Chung, J. Kim, Y. Jang, S.M. Byun, T. Hyeon, B.M. Kim. Tet. Lett. 54, 5192 (2013)
39. M. Nasrollahzadeh, A. Azarian, A. Ehsani, M. Khalaj, J. Mol. Catal. A: Chem. 394, 205 (2014)
¨
40. A. Slamani, S. Demir, I. Ozdemir, Catal. Commun. 29, 141 (2012)
41. Y. Liu, M. Li, Y. Lu, G.H. Gao, Q. Yang, M.Y. He, Catal. Commun. 7, 985 (2006)
´
42. J.C. Cardenas, L. Fadini, C.A. Sierra, Tet. Lett. 51, 6867 (2010)
43. S. Jana, B. Dutta, R. Bera, S. Koner, Inorg. Chem. 47, 5512 (2008)
44. Z. Wang, P. Xiao, B. Shen, N. He, Colloids Surf. A 276, 116 (2006)
45. H. Yang, X. Han, G. Li, Y. Wang, Green Chem. 11, 1184 (2009)
46. L. Huang, Z. Wang, T.P. Ang, J. Tan, P.K. Wong, Catal. Lett. 112, 219 (2006)
123