Heterogeneous Fe3O4@chitosan-Schiff base Pd nanocatalyst: Fabrication, characterization and application as highly efficient and magnetically-recoverable catalyst for Suzuki-Miyaura and Heck-Mizoroki C-C coupling reactions

Article abstract of DOI:10.1016/j.catcom.2015.10.002

An environmentally friendly palladium-based catalyst supported on magnetite nanoparticles was successfully prepared. FT-IR, XRD, VSM, SEM, EDS and TGA studies have been used to characterize the nanocatalyst. The catalytic activity of the as-prepared catalyst was evaluated as a heterogeneous catalyst for the Suzuki-Miyaura carbon-carbon cross-coupling reaction of aryl halides and phenylboronic acid. Furthermore, it was found that the catalyst showed a high activity for the Mizoroki-Heck reaction of aryl halides and n-butyl acrylate. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture and recycled consecutive five runs without any significant loss in activity.

Full text of DOI:10.1016/j.catcom.2015.10.002

Heterogeneous Fe3O4@chitosan-Schiff base Pd nanocatalyst: Fabrication,
characterization and application as highly efficient and magnetically-
recoverable catalyst for Suzuki–Miyaura and Heck–Mizoroki C–C coupling
reactions
A. Naghipour, A. Fakhri
PII:
DOI:
Reference:
S1566-7367(15)30097-2
doi: 10.1016/j.catcom.2015.10.002
CATCOM 4460
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
12 August 2015
30 September 2015
1 October 2015
Please cite this article as: A. Naghipour, A. Fakhri, Heterogeneous Fe3O4@chitosan-
Schiff base Pd nanocatalyst: Fabrication, characterization and application as highly effi-
cient and magnetically-recoverable catalyst for Suzuki–Miyaura and Heck–Mizoroki C–C
coupling reactions, Catalysis Communications (2015), doi: 10.1016/j.catcom.2015.10.002
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ACCEPTED MANUSCRIPT
Heterogeneous Fe3O4@chitosan-Schiff base Pd nanocatalyst: Fabrication,
characterization and application as highly efficient and magnetically
recoverable catalyst for Suzuki–Miyaura and Heck–Mizoroki C-C coupling
reactions
A. Naghipour and A. Fakhri
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
Abstract
An environmentally friendly palladium-based catalyst supported on magnetite nanoparticles
was successfully Prepared. FT-IR, XRD, VSM, SEM, EDS and TGA studies have been used
to characterize the nanocatalyst. The catalytic activity of the as-prepared catalyst was
evaluated as a heterogeneous catalyst for the Suzuki–Miyaura carbon–carbon cross-coupling
reaction of aryl halides and phenylboronic acid. Furthermore, it was found that the catalyst
showed a high activity for the Mizoroki–Heck reaction of aryl halides and n-butyl acrylate.
Interestingly, the novel catalyst could be recovered in a facile manner from the reaction
mixture and recycled consecutive five runs without any significant loss in activity.
Keywords
Magnetically-recoverable nanocatalyst, Fe3O4 nanoparticles, Chitosan-Schiff base complex,
Suzuki–Miyaura coupling, Mizoroki–Heck coupling
1. Introduction
The further development of the catalytic system has been planned based on using advanced
catalysts that can selectively catalyze the specific chemical reactions with a high reactivity,
and also it can be recycled through the simple separation and regeneration process according
to the principles of green chemistry. Homogeneous catalysts due to accessibility of all
catalytic sites, possibility to tune the chemo-, regio- and enantioselectivity of the catalyst,
high selectivities, better yields, and easy optimization of catalytic systems offer many
advantages than heterogeneous catalysts in chemists view [1-2]. Despite of these advantages,
 Address correspondence to A. Naghipour, Department of Chemistry, Faculty of Science, Ilam University,
P.O. Box 69315516, Ilam, Iran; Tel/Fax: +98 843 2227022; E-mail: Naghipour2002@yahoo.com
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homogeneous catalysts separation from the final product is difficult and involving
troublesome work-up. To overcome this aforementioned drawback, heterogenization of the
homogeneous catalysts has been considered greatly as an attractive solution [3-5]. Although
heterogenization of the homogeneous catalysts exhibit obvious advantages of easy separation
and efficient recycling, but most catalysts still suffer from lower catalytic efficiencies than
corresponding homogeneous catalysts. With the advent of nanoscience, chemists achieved
that the best solution to lower activity limitation of heterogeneous catalysts is to keep the size
of the particles in the heterogeneous catalyst as small as possible. Nowadays a wide variety of
nanostructured catalysts or catalytic systems immobilized on nanostructured supports have
been applied in various catalytic reactions and as results heterogeneous catalytic systems
recently have attracted much attention [6-13].
In recent years, magnetic nanoparticles (MNPs), because of providing greater accessibility of
active sites for reaction and thereby, enhancing dramatically the contact between reactants
and catalyst and also unique features including good stability, easy synthesis and
functionalization, high surface area as well as low toxicity and price have emerged as
attractive support for the immobilization of homogeneous catalysts [14-15]. More
importantly, MNPs have great potential in view of facile separation from the reaction mixture
with an external magnet. Among the various MNPs as core magnetic support, most extensive
studies have arguably been devoted to Fe3O4 MNPs [16-18].
Surface-functionalizing of iron oxide MNPs by various materials such as precious metals [19-
21], carbon [22, 23], silica [24-26] and polymers [27-29] were introduced as simple
approaches to stabilize and modify the as-prepared MNPs. Coating of solid surfaces by
polymers imparts various desirable properties to MNPs such as, excellent thermal stability,
extension loading amount of immobilized catalyst, chemical inertness, improvement in
catalyst leaching and ease of succedent functionalization.
Chitosan (CS), the most abundant natural amino polysaccharide, which is extracted from the
partial deacetylation of chitin due to special set of properties including availability, safety,
non-toxicity, biocompatibility, biodegradability, low immunogenicity, and antibacterial
properties [30-33] have demonstrated extensive applications in several fields such as drug
delivery, medicine, adhesives, fuel cells and especially, in catalysis fields. Coating of MNPs
by CS, in addition bearing aforesaid advantages, functionalization of amine and hydroxyl
groups in CS provide coordination sites for variety of chemical modifications. As a result
catalysts based on chitosan have received much attention for different kinds of organic
reaction such as oxidation, C-C coupling, multi-component reactions and etc.
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Suzuki–Miyaura [34] and Heck–Mizoroki [35] C–C cross-coupling reactions are the most
fundamental transformations in organic synthesis. Such reactions have great industrial
potential for the synthesis of a large number of natural products, biologically active
compounds, many organic building blocks and therapeutic drugs and their intermediates [36].
Due to these reactionsʼ wide range of applications, there is considerable interest in this area
with a focus directed towards the development of more efficient and recyclable catalysts for
industrial applications in environmentally benign processes. Even though Suzuki and Heck
C–C cross-coupling reactions catalyzed by palladium–phosphine systems have achieved great
success over the last decade [37], however, phosphine ligands are often quite expensive, air-
sensitive, and virulent, which limit their wide use in large-scale application. Consequently,
the development of new phosphorus free palladium catalysts for higher activity, stability and
substrate tolerance that allow reactions to be carried out under milder reaction conditions is of
practical interest.
In continuation of our efforts in designing greener heterogeneous catalysts, we herein present
the preparation of magnetic core–shell type Fe3O4@CS-Schiff base Pd and its application as
catalyst in Suzuki and Heck C–C cross-coupling reactions.
2. Experimental
2.1 Material and physical measurements
All starting materials were purchased from Merck and Aldrich and were used without any
additional purification. Fourier transform infrared (FT-IR) spectra were recorded on a
VRTEX 70 model BRUKER FT-IR spectrophotometer using KBr pellets. Thermogravimetric
analysis (TGA) was carried out under air atmosphere on Shimadzu DTG-60 instrument. X-
ray diffraction (XRD) was performed on a Rigaku-Dmax 2500 diffractometer with Cu Kα
radiation (λ = 1.5418 A˚). The morphology of the catalyst was observed using a Philips XL30
(scanning electron microscopy) SEM. The magnetization measurement was carried out in a
vibrating sample magnetometer (VSM) MDKFD. The Room-temperature magnetization
curves of the nano catalysis were recorded in an external field up to 15 kOe. The known
products were characterized by comparison of their spectral (1HNMR, Bruker NMR-
Spectrometer FX 400Q) and physical data with those of authentic samples. The content of Pd
in the catalyst was determined by inductively coupled plasma optical emission spectroscopy
(ICP-OES) method using PerkinElmer Optima 8000 ICP-OES.
2.2 Preparation of magnetic Fe3O4@CS-Schiff base Pd catalyst
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Hydrophilic Fe3O4 Nanoparticles were synthesized based on chemical coprecipitation
strategy. For this purpose, under a nitrogen atmosphere and vigorous stirring, 10 mL of
concentrated ammonia solution was added into the mixture of 2mmol FeCl3.6H2O and 1
mmol FeCl2.4H2O in 100 ml deionized water at 70 °C. The black magnetite solid product
formed immediately and stirring was continued for 30 min. After 30 min, the reaction
mixture was cooled; the precipitate was magnetically separated and washed with distilled
water several times. In order to prepare Fe3O4@CS MNPs, 3 g of chitosan in 300 mL of 2%
(v/v) acetic acid solution was slowly added to 1 g of freshly precipitated magnetite were
dispersed in 50 mL of distilled water under ultrasound irradiation. The mixture was then
stirred for 1 h at room temperature and neutralized with 10% (w/v) solution of NaHCO3.
After the foam was subsided, the precipitate was recovered through magnetically separating,
washing twice with deionized water and drying at 60 °C. Fe3O4@CS-Schiff base ligand was
prepared as following: 5 mmol of 2-Pyridinecarboxaldehyde and Fe3O4@CS NPs (1 g) in 40
mL of ethanol was refluxed under nitrogen atmosphere for 30 h. After that, the resultant
mixture was cooled; the solid was separated magnetically, washed thoroughly with ethanol
and then dried under vacuum. In continues, 1.0 g of Fe3O4@CS-Schiff base was added to 60
mL ethanol solution of palladium chloride and the mixture was refluxed for 20 h under
nitrogen atmosphere. The Final product was collected by separation magnetically, copiously
washed with ethanol to remove any loose metal species, and dried under vacuum to give the
magnetic Fe3O4@CS-Schiff base Pd catalyst.
2.3 General procedure for the Suzuki reaction
A mixture of arylhalides (1 mmol), phenylboronic acid (1.2 mmol), K2CO3 (1.5 mmol), PEG
(Polyethylene glycol) (4 mL) and Pd catalyst (10 mg) was stirred at 80 °C temperature for a
given time until the completion of the reaction was achieved as monitored by TLC. After
completion of the reaction, the catalyst was separated with a magnet and washed with EtOH,
dried and reused for a next run under the same reaction conditions. To the resulting mixture
H2O (10 mL) was added followed by extraction with dietyl ether (3 × 50 mL). The extracted
organic phases were dried over Na2SO4, filtered and concentrated in vacuo to get the desired
product. These crude products were purified by a short plug of silica using hexane/ethyl
acetate as eluent.
2-Methylbiphenyl: 1H-NMR (400 MHz, CDCl3): δ (ppm): 7.39-7.68 (m, 9H), 2.3 (s, 3H).
2-Methoxybiphenyl: 1H-NMR (400 MHz, CDCl3):  (ppm): 6.72-7.51 (m, 9H), 3.71 (s, 3H).
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3-Trifluoromethylbiphenyl: 1H-NMR (400 MHz, CDCl3):  = 7.6-8.01 (m, 9H).
2.4 General procedure for the Heck reaction
In a typical reaction, the reaction vessel was charged with arylhalides (1 mmol), n-butyl
acrylate (1.5 mmol), Et3N (1.5 mmol), and the catalyst in N,N-dimethylformamide (DMF, 4
mL). The reaction mixture was heated to 120 °C for appropriate time. At the end of the
reaction (confirmed by TLC analysis), the mixture was cooled to room temperature and the
catalyst was separated with a magnet and washed with EtOH, and then dried under vacuum
for the next run. The resultant residual mixture was diluted with water and extracted with
CH2Cl2 (3 × 50 mL). The combined organic layers was dried over anhydrous Na2SO4, filtered
and concentrated in vacuo to get the desired product. These crude products were purified by a
short plug of silica using hexane/ethyl acetate as eluent.
1
(E)-n-Butyl cinnamate: H NMR (400 MHz, CDCl3): δ (ppm): 7.69 (d, J = 16.0 Hz, 1 H),
7.51-7.55 (m, 2 H), 7.39-7.41 (m, 3 H), 6.42 (d, J = 16.0 Hz, 1 H), 4.23 (t, J = 6.7 Hz, 2 H),
1.64-1.72 (m, J = 7.2 Hz, 2 H), 1.47 (m, J = 7.5 Hz, 2 H), 0.95 (t, J = 7.4 Hz, 3H).
(E)-n-Butyl 3-(4-methoxyphenyl)acrylate: 1H NMR (400 MHz, CDCl3): δ (ppm): 7.62 (d, J =
15.9 Hz, 1 H), 7.48 (d, J = 8.7 Hz, 2 H), 6.90 (d, J = 8.6 Hz, 2 H), 6.31 (d, J = 16.0 Hz, 1 H),
4.21 (t, J = 6.7 Hz, 2 H), 3.84 (s, 3 H), 1.65 (m, J = 7.1 Hz, 2 H), 1.38-1.50 (m, J = 7.5 Hz, 2
H), 0.99 (t, J = 7.4 Hz, 3 H,).
1
(E)-n-Butyl 3-(4-methylphenyl)acrylate: H NMR (400 MHz, CDCl3): δ (ppm): 7.6 (d, J =
16.0 Hz, 1 H), 7.39 (d, J = 8.1 Hz, 2 H), 7.2 (d, J = 7.9 Hz, 2 H), 6.42 (d, J = 15.8 Hz,1 H),
4.23 (t, J = 6.7 Hz, 2 H,), 2.36 (s, 3 H), 1.65-1.72 (m, J = 7.1 Hz, 2 H), 1.46 (m, J = 7.5 Hz, 2
H,), 0.99 (t, J = 7.4 Hz, 3 H).
1
(E)-n-Butyl 3-(2-methylphenyl)acrylate: H-NMR (400 MHz, CDCl3): δ (ppm): 7.88 (d, J=
14.7 Hz, 1 H), 7.41-7.45 (m, 1H), 7.11 (m, 3 H), 6.27 (d, J= 15.9 Hz, 1 H), 4.11 (t, 2 H), 2.35
(s, 3 H), 1.68 (m, 2 H), 1.32 (m, 2 H), 0.85 (t, J= 2.5 Hz, 3 H).
(E)-n-Butyl 3-(2-methoxyphenyl)acrylate: 1H NMR (400 MHz, CDCl3): δ (ppm): 7.89 (d, J =
16.6 Hz, 1H), 7.42 (d, J = 7.5 Hz, 1H), 7.2 (t, J = 9.1 Hz, 1H), 6.95 (d, J = 7.5 Hz, 2H), 6.44
(d, J = 16.6 Hz, 1H), 4.14 (t, J = 6.7 Hz, 2H), 3.81 (s, 3H), 1.62-1.75 (m, 2H), 1.3-1.5 ( m,
2H), 0.94 (t, J = 6.79 Hz, 3H).
(E)-n-Butyl 3-(2-thiophenyl)acrylate: 1H NMR (400 MHz, CDCl3): δ (ppm): 7.79 (d, J = 15.7
Hz, 1 H), 7.36 (d, J = 5.0 Hz, 1 H), 7.22-7.30 (d, J = 3.4 Hz, 1 H), 7.05 (t, J = 4.3 Hz, 1 H),
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6.26 (d, 1 H), 4.21 (t, J = 6.7 Hz, 2 H), 1.70 (m, J = 7.1 Hz, 2 H), 1.47 (m, J = 7.5 Hz, 2 H),
0.98 (t, J = 7.4 Hz, 3 H).
1
(E)-n-Butyl 3-(3-trifluoromethylphenyl)acrylate: H-NMR (400 MHz, CDCl3): δ (ppm):
7.42- 7.68 (m, 5H), 6.52 (d, J = 16.1 Hz, 1H), 4.23 (t, J = 6.4 Hz, 2H), 1.65- 1.72 (m, 2H),
1.42- 1.50 (m, 2H), 0.95 (t, J = 7.2 Hz, 3H).
3. Results and discussion
3.1 Catalyst characterization
The nanoparticle size and morphology of nanocatalyst were characterized by SEM image. As
shown in Fig.1.1. Fe3O4@CS-Schiff base Pd catalyst has uniformity and spherical
morphology and the average size of the catalyst is about 32 nm that is in good agree with
other techniques. The EDS results, obtained from SEM analysis of Fe3O4@CS-Schiff base
Pd, are shown in Fig.1.2. Quantification of the EDS peak gives the main element Pd, Fe, O, N
and C in 3.95%, 10.13%, 42.40% and 43.53% by weight, respectively.
Purity and crystalline nature of synthesized nanocatalyst was investigated by XRD (Fig.1.3.).
the bare Fe3O4 shows diffraction peaks at 2θ = 30.3°, 35.6°, 43.3°, 53.8°, 57.4° and 62.9°
corresponding to the diffractions of (220), (311), (400), (422), (511) and (440). The same
XRD pattern of Fe3O4@CS-Schiff base Pd catalyst is implied retention of the crystalline
spinel ferrite core structure and the grafting process did not induce any phase change of the
Fe3O4 nanoparticles. The appearance of the new peaks at 2θ = 40.1 and 46.5 are attributed to
the Pd species. The average crystallite size of the nanocatalyst is estimated from the XRD
data using the Debye–Scherrer equation [38]:
where d is the particle size of the crystal, k is the Scherrer constant (0.94), λ is the X-ray
wavelength (0.15406 nm), β is the full width at half maximum (FWHM) in radians, and θ is
the position of the diffraction peak maximum of the XRD diffraction peaks. According to the
above equation and by measuring the (311) peak widths of the XRD, the average diameter of
Fe3O4@CS-Schiff base Pd catalyst was calculated to be 31 nm that is in a good agreement
with the SEM observations.
TGA was used to determine the thermal stability and supported components content on the
surface of the magnetic nanoparticles. Fig.1.4. depicts the TGA result of Fe3O4@CS-Schiff
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base Pd under a nitrogen atmosphere. The coated Fe3O4 nanoparticles show an excellent
thermal stability at temperatures up to 800 °C. The weight loss for all samples occurring up to
200 °C was completely attributed to the removal of physically adsorbed solvent molecules
and moisture. The mass loss of approximately 35% at 220-730 °C in the TGA curves of the
magnetic catalyst corresponds to the degradation of chitosan chains and Schiff base Pd
complex, loaded on chitosan.
Fourier transform Infrared spectroscopy was employed to characterize Successful
functionalization of the synthesized MNPs in the range of 4000-400 cm−1. Fig.1.6. showed
the FT-IR spectrum for the samples of Fe3O4 MNPs, Fe3O4@CS, Fe3O4@CS-Schiff base and
Fe3O4@CS-Schiff base Pd catalyst. In Fig.1.6.a., Three Adsorption peaks at 579, 1624 and
3405 cm-1 can be observed in the IR spectrum of the bare Fe3O4 nanoparticles. The band at
579 cm-1 is attributed to the vibration of the Fe-O bonds in the crystalline lattice of Fe3O4
which demonstrate the existence of spinel Fe3O4 components. The bands at 1624 and 3398
cm-1 are related to characteristic bands of -OH group, which cover the surface of the particles
during the preparation of Fe3O4 in an aqueous system. Compared with Fig.1.6.a., two new
bands located in Fig.1.6.b. at 2924 cm−1 and 2854 cm−1 and the band at 1631 cm−1 can be
attributed to the aliphatic C–H and N–H stretching vibrations respectively These bands are
attributed to the characteristic absorptions of the chitosan attached on the ferrite surface.
Diagnostic peaks appeared in Fe3O4@CS-Schiff base at 1592 and 1642 cm−1 correspond to
the stretching vibrations of the C=C and C=N bonds (Fig.1.6.c.). In Fe3O4@CS-Schiff base
Pd catalyst, however, the absorption of C=N bond shifted to lower wave number (1624 cm−1)
after chelated with Pd ions (Fig.1.6.d.).
The magnetic properties of the magnetite nanoparticles were carried out by VSM at room
temperature. Fig. 4 shows the saturation magnetization of Fe3O4@CS-Schiff base Pd catalyst
was 37.4 emu/g and can be separated comfortably from the mixture by using an external
magnet.
<Fig. 1.>
In order to obtain an insight into the accurate amount of Pd grafted on the Fe3O4@CS-Schiff
base, ICP-AES analysis was applied. The ICP analysis showed that 1.03 mmol of Pd was
grafted on 1.0 g of the Fe3O4@CS-Schiff. And also ICP analysis of the recovered catalyst
after consecutive runs indicates no considerable change in the content of Pd in the catalyst.
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3.2 Application of the catalyst in the Suzuki cross coupling reaction
The prepared Fe3O4 supported heterogeneous Pd-catalyst was first evaluated against the C–C
bond formation reaction of aryl halides with aryl boronic acids often referred to as the
Suzuki–Miyaura cross coupling reaction. For initial assessment of the reaction, the Suzuki
coupling reaction of 4-nitrobromobenzene with phenyl boronic acid was chosen as a model
for optimizing reaction parameters such as the solvent, base, temperature and the amount of
the catalyst (Table 1).
Variation of temperature in the range 25–100°C revealed that the optimum temperature for
the reaction was 80 °C (entry 13 versus entries 2, 11, 12 and 14). In the case of 60 °C, the
yield of the desired product was lower than the one at 80 °C. However, when the temperature
increased to 100 °C, the yield of the desired product did not increase obviously. According to
the optimization results and the pivotal goal of green chemistry, the ideal result is obtained by
using PEG as a green solvent. As can be readily seen from the data in Table 1, in the absence
of a base and catalyst or in the presence of only a base or catalyst did not result in any
conversion. Assessment of the test reaction using different kinds of bases such as K2CO3,
NaHCO3, Et3N and CH3COONa shown that in the presence of K2CO3, the catalyst was very
active and high yields of coupled product could also be obtained for the reaction. In addition,
further experiments showed that 10 mg amount of catalyst was sufficient to guarantee a clean
and complete conversion (entry 13). When the amount of catalyst was reduced to 5 mg under
otherwise same conditions as shown in Table 1-entry 7, the yield decreased to 80% in 60 min.
On the other hand, using 15 mg of catalyst did not increase the yield significantly (entry 8).
<Table 1>
With the optimized reaction conditions in hand, the scope of catalytic utility of the
heterogeneous Fe3O4@CS-Schiff base Pd catalyst in Suzuki reaction was extended to the
various aryl iodides, bromides and chlorides with electron-withdrawing and electron-
releasing groups and phenylboronic acid(Table 2). As illustrated in Table 2, excellent yield
was achieved in the reactions of iodobenzene and aryl iodides bearing both electron-
withdrawing and electron-donating groups. Also, the catalyst exhibited high activity toward
bromobenzen and aryl bromides bearing electron-withdrawing. For the aryl bromides bearing
electron-donating substituents still showed a high activity, and the products were obtained in
excellent yield. The substituents in the ortho position gave rise to the corresponding
biphenyls in longer time than the substituents in the para position (entry 4 vs 3 and entry 5 vs
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6) due to steric hindrance. The Suzuki reaction of sterically hindered 2-bromonaphthalene
afforded a moderate yield of the corresponding coupled product. In this work, substrate
which contains bromo and chloro substituents, 1-chloro-4-bromobenzene, was also tested to
evaluate selectivity our catalyst in the suzuki reaction between bromo and chloroarenes (entry
19). Reactions with a functionalized chlorobenzene (entry 21) were not that efficient as
compared with their bromo analogue.
<Table 2>
3.3 Catalyst testing for the Heck–Mizoroki reaction
The Heck cross-coupling reaction, as another typical Pd-catalyzed carbon–carbon bond
formation between aryl halides and olefins in the presence of a base, has occupied a special
place in both fundamental research and industrial application. Encouraged by Fe3O4@CS Pd
Schiff-base catalyst application to the Suzuki reaction, the effectiveness of the catalyst for the
Heck reactions was investigated next. To further improve the efficiency of the product
formation, the effects of solvents, bases, reaction temperature and catalyst loading were
studied through a model reaction of iodobenzene with n-butyl acrylate.
<Table 3>
As illustrated in Table 1, several solvents including H2O, PEG, DMSO and DMF were tested
and DMF was found to be the most appropriate, giving the C-C coupling product in a 98%
yield. In terms of base, NaHCO3 and NaOAc give moderate yields (entries 6 and 7 in Table
3), while organic base, Et3N, improved the yield up to 97% under the same reaction
conditions (entry 2 in Table 3). The use of K2CO3 in place of Et3N resulted in poor
conversion of the substrate. Different amounts of catalyst between 5 and 20 mg were further
investigated for this reaction, and 10 mg catalyst was found to be optimal. For the higher
amounts of catalyst, the desired product was obtained in a nearly quantitative yield (Table 3,
entry 11). An increase of temperature from 100 to 120 °C promote the reaction significantly
(entry 12 and 2).The reaction was conveniently carried out at 120 °C for activated aryl
halides but for activation of bromobenzene, a higher temperature at about 140 °C is required.
Lowering in temperature often results in incomplete conversion of the starting materials.
With the optimized conditions in hand, the scope of the Fe3O4@CS-Schiff base Pd catalyzed
Heck reactions was investigated by employing various substituted aryl halides to react with
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n-butyl acrylate. Satisfactory catalytic activity was observed in the couplings of the aryl
iodides bearing either electron-withdrawing (entries 2, 3) or electron-donating groups (entries
4, 5, 7, 8) with butyl acrylates. The aryl iodides possessing electron-donating group showed a
slight drop in reactivity compared to the aryl iodides possessing electron-withdrawing groups.
In terms of activated bromobenzene, such as p-CN, p-NO2, m-CF3, by prolonging the
reaction, the yields could be obviously improved (entry 9 and 17). Reaction of the aryl
bromide bearing methyl and methoxy group also delivered the coupling product in moderate
yield. Unfortunately, no Heck products were detected even after increasing the reaction
temperature and reaction time for chlorobenzene and functionalized chlorobenzene.
<Table 4>
3.4 Recyclability of the catalyst
As an important aspect of heterogeneous catalysis, the recyclability of the catalyst was tested
in the model Suzuki–Miyaura and Heck–Mizoroki cross-coupling reactions. Each time, after
completion of the reaction, the catalyst was simply separated by an external magnet and then
washed thoroughly with acetone followed by copious amounts of water and finally by EtOH
to remove the base and organic compound present in the used catalyst. After drying, the
catalyst was re-employed directly in the model reaction for the next run. A negligible
reduction in the activity of the catalyst after consecutive five runs, indicate that the catalyst
was not only very active, but also very stable.
<Fig. 2>
4. Conclusions
In summary, Fe3O4@ CS-Schiff base Pd complex have been developed as a novel, green and
highly efficient nanocatalyst. The synthesized catalyst was confirmed by XRD, FT-IR, TGA,
VSM, SEM and EDS techniques. The efficiency of the nanocomposite was verified in Suzuki
and Heck reactions providing target products in excellent yields under relatively mild
experimental conditions. In addition, the catalyst could be readily removed from the reaction
mixture by a permanent magnet and reused up to consecutive five runs without loss of its
catalytic activity.
Acknowledgements
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The authors gratefully acknowledge received support from the Ilam University, Ilam, Iran, on
this work.
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Fig. 1. (1) SEM image of Fe3O4@CS-Schiff base Pd catalyst. (2) EDS spectrum of
Fe3O4@CS-Schiff base Pd catalyst. (3) XRD patterns of a) Fe3O4 MNPs and b) Fe3O4@CS-
Schiff base Pd catalyst. (4) TGA diagram for Fe3O4@CS-Schiff base Pd catalyst. (5) Room
temperature magnetization curves of Fe3O4@CS-Schiff base Pd catalyst. (6) FT-IR spectra of
a) Fe3O4 MNPs, b) Fe3O4@CS, c) Fe3O4@CS-Schiff base and d) Fe3O4@CS-Schiff base Pd.
Fig. 2. Recyclability of catalyst in the Suzuki–Miyaura and Heck–Mizoroki model reaction.
14

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Fig. 1
15

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100
80
60
Heck reaction
suzuki reaction
40
20
0
1
2
3
4
5
Run
Fig.2
16

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Table 1. The optimization of reaction parameters for the Suzuki reaction of
4-nitrobromobenzene with phenyl boronic acid.a
T
(°C)
60
60
60
60
60
60
60
60
60
60
60
RT
40
80
100
Catalyst
(mg)
10
Time
(min)
10 h
60
Yieldb
(%)
-
Entry
Base
Solvent
1
2
-
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
H2O
K2CO3
NaHCO3
NaOAc
Et3N
10
90
70
65
10
-
3
10
60
4
10
60
5
10
60
6
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
-
24 h
60
7
5
80
98
50
60
65
50
70
97
98
8
15
25
9
10
60
10
11
12
13
14
15
DMF
DMSO
PEG
PEG
PEG
PEG
10
60
10
60
10
2 h
60
10
10
30
10
30
a Reaction condition: nitrobromobenzene (1 mmol), phenyl boronic acid (1.2 mmol), base
(1.5 mmol) and solvent (2 ml).
b Yields refer to those of pure isolated products.
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Table 2. Suzuki coupling of aryl iodides / bromides and chlorides
with phenyl boronic acid catalyzed by Fe3O4@CS-Schiff base Pd
catalyst.a
Time
(min)
Yield
(%)b
Mp(°C)
[Ref]
Entry
Aryl halide
1
2
3
10
35
25
98
92
98
69–70 [39]
49-51 [40]
46-48 [41]
Light yellow
liquid [42]
4
5
6
60
20
35
95
97
96
87-89 [43]
Colorless oil
[44]
7
15
96
111-113
8
25
20
20
30
50
25
99
98
98
85
90
95
40-41 [45]
69–70 [39]
46-48 [41]
87-89 [43]
49-51 [40]
83-85 [46]
9
10
11
12
13
18

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14
15
35
70
92
90
57-59 [47]
52–54 [44]
viscous
16
17
18
15
30
99
97
50
liquid [48]
111–113
[41]
2 h
96-98 [49]
19
20
21
45
35
92
95
40
77-79 [50]
69–70 [39]
57-59 [47]
24 h
22
2 h
60
75-78 [51]
a
Reaction condition: aryl halides (1 mmol), phenyl boronic acid (1.2 mmol),
K2CO3 (1.5 mmol), Fe3O4@CS-Schiff base Pd (10 mg) and PEG (2 ml).
b Yields refer to those of pure isolated products.
Table 3. The optimization of reaction parameters for the Heck
reaction of iodobenzene with n-butyl acrylate.a
Catalyst Time Yield
Entry
Base
Solvent T (°C)
(mg)
10
(min) (%)b
1
2
3
Et3N
Et3N
Et3N
H2O
DMF
120
120
120
20
20
20
10
98
85
10
DMSO
10
19

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4
5
Et3N
-
PEG
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
120
120
120
120
120
120
120
120
100
130
10
10
10
10
10
-
20
5 h
20
20
20
24
20
15
20
20
70
-
6
NaHCO3
NaOAc
K2CO3
Et3N
70
80
20
-
7
8
9
10
11
12
13
Et3N
5
70
98
50
98
Et3N
20
10
10
Et3N
Et3N
a Reaction condition: iodobenzene (1 mmol), n-butyl acrylate (1.2 mmol), base
(1.5 mmol) and solvent (2 ml).
b Yields refer to those of pure isolated products.
Table 4. Heck coupling of aryl iodides / bromides with n-butyl
acrylate catalyzed by Fe3O4@CS-Schiff base Pd catalyst.a
Time Yield
Mp(°C)
[Ref]
Entry
Aryl halide
(min)
(%)b
Pale yellow
liquid [52]
Pale yellow
liquid [52]
Pale yellow
liquid [52]
1
2
3
20
98
30
25
95
90
Pale yellow
liquid [52]
4
5
50
80
96
95
Pale yellow
liquid [52]
20

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brown oil
[53]
6
7
60
4 h
90
90
60
65
60
55
40
92
Pale yellow
liquid [52]
Pale yellow
liquid [52]
Pale yellow
liquid [52]
8
9
10
43-46 [54]
colorless oil
[48]
11
12
90
90
80
98
60–64 [54]
a
Reaction condition: aryl halides (1 mmol), n-butyl acrylate (1.2 mmol),
Et3N (1.5 mmol), Fe3O4@CS-Schiff base Pd (10 mg) and DMF (2 ml).
b Yields refer to those of pure isolated products.
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Graphical abstract
22

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Highlights

Environmentally friendly Pd-chitosan Schiff base catalyst supported on magnetic
nanoparticles was successfully prepared.


This magnetic nanoparticle was fully characterized.
The catalytic activity of this magnetic nanocatalyst was evaluated in the Suzuki and
Heck C-C cross-coupling reaction.

This magnetic nanoparticle could be easily recovered from the reaction mixture using
a magnet and recycled.
23