A magnetic porous chitosan-based palladium catalyst: A green, highly efficient and reusable catalyst for Mizoroki-Heck reaction in aqueous media

Article abstract of DOI:10.1039/c5nj01337b

A novel, biodegradable and environmentally benign magnetic porous chitosan-thienyl imine palladium(ii) complex, MPCS-TI/Pd, was prepared and characterized by FT-IR, SEM, TEM, EDX, XRD, BET, VSM and TG-DTA analysis. This complex, with high surface areas and low catalyst loading, was found to be a highly active and robust heterogeneous catalyst for the Mizoroki-Heck reaction of aryl bromides and chlorides with various terminal olefins in aqueous media in good to excellent yields. The catalyst was easily separated using an external magnet and the recovered catalyst was reused for seven cycles without significant loss of catalytic activity.

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Magnetic porous chitosan-based palladium catalyst:
A green, highly efficient and reusable catalyst for
Mizoroki-Heck reaction in aqueous media
Cite this: DOI: 10.1039/x0xx00000x
Barahman Movassagh,* Nasrin Rezaei
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
A novel, biodegradable and environmentally benign magnetic porous chitosanꢀthienyl imine
palladium(II) complex, MPCSꢀTI/Pd, was prepared and characterized by FTꢀIR, SEM, TEM,
EDX, XRD, BET, VSM and TGꢀDTA analysis. This complex, with high surface areas and low
catalyst loading, was found to be a highly active and robust heterogeneous catalyst for the
MizorokiꢀHeck reactions of aryl bromides and chlorides with various terminal olefins in
aqueous media in good to excellent yields. The catalyst was easily separated by an external
magnet and the recovered catalyst was reused in seven cycles without significant loss of
catalytic activity.
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ionic liquids,15 multiꢀwalled carbon nanotubes16ꢀ18 and
polymers such as polystyrene,19ꢀ21 polyethylene glycol,22
Introduction
polyvinyl chlorideꢀpolyethylene,23 and polysaccharides.24
Chitosan is a safe, inexpensive, natural, and biodegradable
polysaccharide which is derived from animal resources such as
the shells of several crustaceans, shrimp shell, fish shell and
some fungi. This biopolymer has been employed for various
applications in agriculture,25 food,26 biosensors,27 biomedical,28
adsorption of heavy metals,29ꢀ32 drug delivery,33 as well as
stable support for Pdꢀcatalyzed crossꢀcoupling reactions.34,35
Chitosan is derived from deacetylation of chitin and is usually
obtained in a powdered or flaked form, but these forms have
relatively low specific surface area.36 Highly porous chitosan
microspheres (PCMS)ꢀsupported palladium catalyst with a high
specific surface area of the porous structure has been reported
to show high catalytic activity, stability, and recyclability for
homocoupling and crossꢀcoupling reactions of aryl halides.37
During the last two decades, magnetically recoverable
nanoparticles have attracted a great attention as heterogeneous
catalysts due to their inherent properties,38,39 such as simple
handling, simple renewability and recovery with magnetic
separation, thermal stability, biocompatibility, large surface
area, and high catalytic activity in various organic reactions.40,41
In the present work, we wish to report a new reusable and
efficient heterogeneous magnetic porous catalyst from chitosanꢀ
supported imine palladium complex for the Heck reaction of
Palladiumꢀcatalyzed carbonꢀcarbon bondꢀforming reactions
have played a crucial role in synthetic organic chemistry. The
palladiumꢀcatalyzed coupling of aryl halides and terminal
alkenes (the MizorokiꢀHeck reaction) is regarded as the most
successful method for the preparation of various substituted
olefins, dienes, and precursors of conjugated polymers.1,2
The MizorokiꢀHeck reaction has shown to have a widespread
application in the synthesis of natural products,3,4
agrochemicals,5 and pharmaceuticals.6 Many catalytic systems
have been developed for this reaction using different palladium
catalysts together with phosphane and phosphorous ligands.7,8
However, phosphane ligands are sensitive to air oxidation, as
well as being toxic, expensive, and unstable at high
temperatures. Efforts have been made to eliminate phosphorous
from this reaction.9,
Moreover, many catalysts used in the
10
Heck reactions are homogeneous, which are impossible to be
recovered and the residual palladium left in the product,
confines the reaction; therefore, in recent years, the
development of heterogeneous catalytic systems has increased.
The advantages of heterogeneous catalysts which make them
valuable for the environment are having more surface areas and
simpler isolation of the reaction products and recyclability of
the catalyst.11,12 The heterogeneous catalysts have been
immobilized onto various supporters, such as zeolites,13 silica,14
Department of Chemistry, K. N. Toosi University of Technology, P. O.
Box 16315ꢀ1618, Tehran, Iran, Fax: +98ꢀ21ꢀ22853650; Tel: +98ꢀ21ꢀ
23064323; Eꢀmail: movassagh@kntu.ac.ir
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spectra of modified chitosan support (
1
, Fig. 2b) to unmodified
chitosan (Fig. 2a) reveals a new band at 720 cmꢀ1 which is
characteristic =CH OOP band for thiophene. At 1637 cmꢀ1, a
noticeably strong band is observed which is caused by C=N
stretching vibration of the imine group. FTꢀIR spectrum of the
S
HOH2C
HOH2C
HO
H2N
N
O
HO
O
HO
O
C
CH3COOH
PEG
O
O
O
O
HO
O
O
H
H2N
HOH2C
H2N
HOH2
C
S
n
n
1
TIꢀfunctionalized chitosanꢀsupported PdCl2 complex (
TI/Pd), Fig. 2c, shows its C=N vibrational band at 1630 cmꢀ1, a
lower frequency than that observed for the free ligand ( ),
supporting the assumption that the ligand coordinates to the
metal ion through the nitrogen atoms of the ligand. Finally, the
crossꢀlinked magnetic porous chitosanꢀthienyl imine Pd
2, PCSꢀ
PdCl2
EtOH
1
Cl
Cl
S
N
FeCl3. 6H2O
H2O, 85 °C, N2
NH4OH
HOH2C
HO
Fe3O4
NP
+
O
HO
O
+
O
O
FeCl2. 4H2O
H2N
HOH2C
O
n
complex, MPCSꢀTI/Pd (3) was prepared by treatment of PCSꢀ
CH3COOH
2
TI/Pd with the suspension of Fe3O4 in glyoxal and aq. acetic
acid solution at room temperature. The vibration band at 569
cmꢀ1 is the typical IR absorbance induced by structure FeꢀO
vibration of the Fe3O4 MNPs (Fig. 2d). Also, in addition to the
O
S
Cl
Pd
2
at 1630 cmꢀ
N
C=N vibrational band of the PCSꢀTI/Pd complex
Cl
HOH2
C
HO
O
1, another band at 1636 cmꢀ1 is observed which is attributed to
the C=N of the imine groups between remained amino groups
O
O
O
O
HOH2C
HO
O
HO
N
HOH2
C
O
S
Cl
N
NH2
P
of the complex 2 and glyoxal crossꢀlinker agent.
d
HO
N
HOH2C
S
Cl
O
HO
HOH2
O
Cl
Cl
O
C
O
N
HOH2C
O
O
O
NH2
HO
CH2OH
O
HO
HO
CH2OH
CH2OH
HO
O
H2
N
O
H2N
O
Fe3O4
NP
N
O
N
O
CH2OH
O
OH
OH
N
HOH2
C
CH2OH
O
HOH2
C
OH
O
O
NH2
O
O
OH
O
O
O
Cl
Cl
S
N
OH
O
d
Cl
P
CH2OH
S
CH2OH
N
N
Cl
NH2
O
OH
CH2OH
CH2OH
OH
O
O
O
O
d
O
OH
CH2OH
N
Cl
P
Cl
S
3
Scheme 1. Preparation of MPCSꢀTI/Pd catalyst.
Fig. 1. The picture of NCSꢀTI(a), BCSꢀTI (b), PCSꢀTI (c).
aryl bromides and chlorides with various olefins in aqueous
media.
Results and discussion
Characterization of MPCS-TI/Pd
The porous chitosanꢀthienyl imine support (PCSꢀTI, 1) was
easily prepared by treating chitosan with an appropriate amount
of 2ꢀ thiophenecarbaldehyde and polyethylene glycol (PEG) in
dilute acetic acid for 24 h at room temperature (Scheme 1).
Then the reaction mixture was dripped into a 1N NaOH aq.
solution through a needle, washed with hot water until neutral,
followed by extraction of the PEG component (Scheme 1).
Similarly, the bead chitosanꢀsupported ligand (BCSꢀTI) was
prepared by the same protocol in the absence of PEG. Also, the
normal chitosanꢀsupported ligand (NCSꢀTI) was produced by
mixing chitosan and 2ꢀthiophenecarbaldehyde in EtOH. Fig. 1,
shows the difference in size and appearance among NCSꢀTI,
BCSꢀTI, and PCSꢀTI supports with the same weight of the
samples. The PCSꢀTI ligand was characterized by elemental
analysis. The sulfur and nitrogen contents of this polymer were
1.65 and 5.32 mmol/g, respectively, indicating that the degree
of substitution was 0.31. The FTꢀIR spectra in Fig. 2 indicate
the differences between unmodified chitosan, modified
chitosanꢀsupported (chelate ligand), and its palladium
complexes; the successful functionalization to an imine is
indicated by several observations. Comparison of the FTꢀIR
Fig. 2. FTꢀIR spectra of chitosan (a), PCSꢀTI (b), PCSꢀTI/Pd
(c), and MPCSꢀTI/Pd complexes (d).
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Fig. 3. SEM images of the NCSꢀTI ligand (a), PCSꢀTI(b), PCSꢀTI/Pd (c), MPCSꢀTI/Pd (d),
and TEM images of MPCSꢀTI/Pd before reaction (e, f), after eight cycles of reaction (g, h).
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Fig. 4. EDX spectra of the PCSꢀTI (a), PCSꢀTI/Pd (b), and MPCSꢀTI/Pd (c).
= 20.60°. The XRD pattern of PCSꢀTI/Pd shows three peaks at
= 40.13°, 46.24°, 68.27° which are attributed to (1 1 1), (2 0
EDX, XRD, XPS, VSM, and TGA. The palladium content of 0) and (2 2 0) facets of elemental palladium (Fig. 5a (ii)). The
the catalyst ( ), as determined by ICP was obtained to be 2.8% XRD measurement of the magnetic MPCSꢀTI/Pd catalyst (Fig.
(0.263 mmol/g). The morphological structures of the NCSꢀTI 5a (iii)) exhibits diffraction peak at 2 = 29.17°, 35.67°, 43.02°,
This catalyst was also characterized by ICP, SEM, TEM,
2θ
3
θ
and PCSꢀTI were examined by SEM, which show the change 53.51°, 57.57°, 62.92°, 71.23°, and 74.09°; these values are in
on the surface of the porous polymer, as compared with the good agreement with the standard XRD pattern of Fe3O4
uniform normal polymer (Fig. 3a and 3b). TEM images of the (JCPDS file No. 19ꢀ0629). Further evidence for the attachment
fresh catalyst (MPCSꢀTI/Pd, 3) at two different magnifications of thiophenecarbaldehyde and metal on to the polymeric
were recorded (Fig. 3e and 3f); these images clearly show that support is confirmed by Xꢀray photoelectron spectroscopy
Pd nanoparticles were formed and wellꢀdefined spherical (XPS) of the complex. The peaks at 285.0, 399.78, 530.14,
particles dispersed in the polymer matrix with a size in the 162.36, and 711.86 eV are attributed to C, N, O, S, and , Fe
range of 6ꢀ8 nm (see ESI). The TEM images of the catalyst atoms, respectively (Fig. 5b); The PdII 3d5/2 and 3d3/2 binding
after eight times of use (Fig. 3g and 3h) exhibits slight energies of the fresh MPCSꢀTI/Pd catalyst were determined to
aggregation of palladium(II) NPs with average size of 6ꢀ12 nm. be 337.58 and 342.98 eV, respectively (Fig. 5c top); also, the
The EDX spectra of PCSꢀTI/Pd and MPCSꢀTI/Pd (Fig. 4bꢀc) binding energies of 334.57 (3d5/2) and 340.82 (3d3/2) eV are
were carried out to examine the existence of palladium and attributed to Pd0. The results showed the presence of 86.2% of
iron; Fig. 4b reveals the presence of palladium on the surface of PdII and 13.8% of Pd0 in the fresh (original) MPCSꢀTI/Pd
chitosan matrix with energy bands of 2.6 and 2.8 KeV (L lines). catalyst, and 93.12% of Pd0 and 6.9% of PdII after reaction (Fig.
The presence of both Fe3O4 MNPs cores (6.43 and 7.2 KeV) 5c bottom).
and palladium of chitosan matrix were also confirmed by EDX
The magnetic properties of Fe3O4 MNPs and the catalyst 3
analysis (Fig. 4c). The XRD patterns of PCSꢀTI, PCSꢀTI/Pd, were investigated by VSM measurement (Fig. 6). Fig. 6a
and the crossꢀlinked magnetic MPCSꢀTI/Pd are shown in Fig. exhibits typical magnetization curves of the pristine Fe3O4
5a. As presented in Fig. 5a (i), the diffraction pattern of MNPs and the catalyst
3 as a function of the applied magnetic
chitosanꢀthienyl imine support shows a characteristic peak at 2
θ
field at 300 K. The two hysteresis loops of supermagnetic
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Fig. 5. (a) Powder XRD patterns of the PCSꢀTI (i), PCSꢀTI/Pd (ii), and MPCSꢀTI/Pd (iii).
(b) XPS spectrum of the MPCSꢀTI/Pd, (c) XPS of the Pd 3d, (d) Cl 2p, (e) S 2p, and up,
before reaction, down, after reaction.
Fe3O4NPs and MPCSꢀ Fe3O4 (66.96 emu/g); this reduced
magnetic strength is due to the chitosan shells covered on recyclability of a catalyst, because CꢀC coupling reactions are
magnetic particles. carried out under high temperature conditions. TGA and DTA
From the N2 adsorption/desorption isotherm of MPCSꢀ with heating in a range varying from room temperature to 850
Thermal stability is necessary for the catalytic activity and
TI/Pd catalyst 3, the BET surface area of the particles is 205.6 °C showed weight losses peaks around 75ꢀ180, 180ꢀ310, and
m2gꢀ1 as calculated by linear part of the BET plot, and the total 310ꢀ440 °C which could be attributed to the evaporation of the
pore volume at P/P0 = 0.98 is 0.4741 cm3gꢀ1. The BET isotherm residual water, chitosanꢀchain of low molecular weight
is of type IV and H3 hysteresis loop (IUPAC classification) is decomposistion, and chitosanꢀthienyl imine over Fe3O4 NPs
the characteristic of mesoporous adsorbents.42 The pore decomposition (see ESI, Fig. S27).
distribution of this catalyst is in the mesoporous regime, with
mean pore diameter of 1.64 nm (see ESI. Fig. S25, S26).
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Fig. 6. (a) Magnetization (M) as a function of field (H) for Fe3O4 nanoparticles (black curve) and 3 (gray curve).
(b) The MPCSꢀTI/Pd in a typical reaction mixture in the absence (i) and the presence of a magnetic field (ii).
(Table 1, entries 1ꢀ3). Similar results were obtained for their
magnetic counterparts (Table 1, entries 4ꢀ6). Among the Pd
catalysts investigated, the porous catalysts PCSꢀTI/Pd and
MPCSꢀTI/Pd (Table 1, entries 3 and 6) showed better catalytic
Catalytic performance of MPCS-TI/Pd catalyst for the
Heck reaction
To explore the catalytic activity of various Pd catalysts, the performances because of high surface area in their structures.
MizorokiꢀHeck reaction of 4ꢀbromoanisole with styrene, as Although the catalytic activity of the former was higher
model substrates, was investigated under various reaction than the latter in the first run (96% vs 91%), the magnetic
conditions. The results are summarized in Table 1. As can be porous catalyst was more reusable, as seen in their run 2. The
seen, the NCSꢀTI/Pd catalyst has considerably lower catalytic effects of the type of solvent, base, temperature, as well as
activity than the corresponding bead and porous catalysts
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catalyst loadings were investigated using MPCSꢀTI/Pd as the TI/Pd catalyst used in the MizorokiꢀHeck reaction of 4ꢀbromoanisole
catalyst. It was revealed that single solvents such as DMF, (1 mmol) and styrene (1.3 mmol) under the reaction conditions.
DMSO, and H2O, and even the solventless condition gave After each cycle, the reaction mixture was cooled down to room
lower yields (Table 1, entries 8ꢀ10 and 12). The best reaction temperature and H2O (10 mL) was added, the catalyst was
solvent was found to be DMF/H2O (v/v = 1:2) (Table 1, entry magnetically separated, washed with water and Et2O, and dried in
6). It was also found that Et3N gives a better result than N,N
ꢀ
vacuum at 50 °C for 2 h before being used for the next round of the
diisopropylethylamine (DIPEA), K2CO3, and NaOAc (Table 1, reaction. The catalyst shows unchanged catalytic activities up to
entries 6, 13ꢀ15). When the reaction was carried out at different seven reaction cycles (Fig. 7); no catalyst deterioration was
temperatures, it was found that increasing the temperature from observed, confirming the high stability of the heterogeneous catalyst
100 to 110 °C increases the yield, while raising the temperature under the reaction conditions.
even further up to 120 °C and 130 °C gives little improvements To determine whether the catalyst is truly functioning in a
(Table 1, entries 6, 17 and 18). It was confirmed that TBAB heterogeneous manner, a hot filtration test was performed in the
was necessary for the reaction; the results listed in Table 1 Heck reaction of 4ꢀbromoanisole and styrene under the reaction
showed that a much poorer yield was obtained in the absence of conditions. During the catalytic reaction, the solid catalyst was
this additive (Table 1, entry 7). When 0.5 equiv. of TBAB was removed from the reaction mixture by using an external magnet after
used, the best result was achieved (Table 1, entry 6). Then, 1 h and the determined conversion was 27%. The residual solution
different catalyst loadings between 0.05 and 0.2 mol% were was, then, allowed to react for a further 4 h and the obtained
studied for the reaction (Table 1, entries 6, 19 and 20. Among conversion was the same (27%). Also, the amount of the Pd species
those, 0.1 mol% of the catalyst was found to be the best. dissolved into solution caused by leaching of the catalyst was
Therefore, it was decided to use DMF/H2O in volume ratio of determined using ICP after evaporation of the solution to dryness.
1:2 as the solvent, Et3N as the base, 0.1 mol% catalyst at 110 The ICP result showed that 0.07% of the total amount of the original
°C as the optimal condition in further studies.
Pd species is lost into solution during the course of the reaction.
Due to the fact that MPCSꢀTI/Pd is an efficient and reusable These results suggested that minimal leaching of palladium takes
catalyst for the MizorokiꢀHeck reaction of 4ꢀbromoanisole with place during the reaction and the catalyst is purely heterogeneous in
styrene under optimized conditions, the catalyst was then nature.
applied to other crossꢀcoupling reactions of aromatic bromides
and chlorides carrying either electronꢀwithdrawing or electronꢀ
releasing constituents in aromatic rings with various vinylic
substrates (styrenes, acrylates, acrylic acid, acrylonitrile, and
acrylamide) (Table 2). The transꢀproducts were selectively
obtained in all cases. The results show that the above catalytic
system is remarkably active and tolerates a range of functional
groups. Table 2 shows that the reaction of aryl bromides with
terminal olefins all proceeded very smoothly within 4 to 6
hours to give the desired products in 83ꢀ96% isolated yields
(Table 2, entries 1ꢀ19). There was no significant difference in
the yield of product between electronꢀdeficient and electronꢀ
rich bromides (Table 2, entries 1ꢀ6, 9ꢀ15). On the basis of the
above results, to extend the scope and generality of this
protocol, the coupling of aryl chlorides was also studied.
Compared with the corresponding bromo analogues, the
reactions of chloro derivatives gave moderate to good yields
Fig. 7. Recycling activity of the MPCSꢀTI/Pd catalyst.
and required longer times (Table 2, entries 20ꢀ27).
Conclusions
Stability and recyclability of MPCS-TI/Pd catalyst
In summary, we have prepared and characterized a novel stable
low leaching magnetic porous chitosanꢀthienyl imine palladium
complex catalyst. This green, heterogeneous and biodegradable
catalyst proved to be a highly active, selective, and recyclable
catalyst for the MizorokiꢀHeck reaction of aromatic bromides
and chlorides with various terminal olefins in aqueous media.
The advantages of this procedure is simple operation, low
catalyst loading (0.1 mol%), easy separation of the catalyst,
excellent yields of the products, and environmental friendliness.
Another point of great concern for heterogeneous catalysts is the
possibility of transition metal leaching when used in a polar medium,
especially for those prepared by adsorption of transition metal on
solid matrices, such as polymer, silica, charcoal, and aluminum
oxide.43 Matrix surface modification by the introduction of special
ligands has been extensively studied to minimize the transition metal
leaching and to enhance chelation of transition metals with the
introduced surface ligands.
The reusability of our magnetic catalyst was also examined by
carrying out repeated runs on the same batch of 0.1 mol% MPCSꢀ
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Table 1. Effect of various Pd catalysts, solvents, bases, and temperatures for the MizorokiꢀHeck reaction.a
Br
Pd cat
+
MeO
solvent, base, 5h
MeO
Base
Entry
Catalyst
Solvent
Temp (°C)
Yield (%)b,c
(mol% of Pd)
1
2
NCSꢀTI/Pd (0.1)
BCSꢀTI/Pd (0.1)
PCSꢀTI/Pd (0.1)
DMF/H2O (v/v = 1:2)
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
DIPEA
K2CO3
NaOAc
Et3N
Et3N
Et3N
Et3N
Et3N
110
110
110
110
110
110
110
110
110
100
110
120
110
110
110
100
120
130
110
110
54(53)
87(78)
96(81)
62(59)
75(73)
91(90)
15d
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF
3
4
MNCSꢀTI/Pd (0.1)
MBCSꢀTI/Pd (0.1)
MPCSꢀTI/Pd (0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.1)
MPCSꢀTI/Pd(0.05)
MPCSꢀTI/Pd(0.2)
5
6
7
8
86
9
DMSO
75
10
11
12
13
14
15
16
17
18
19
20
H2O
72
DMF/H2O (v/v = 1:1)
–
89
53
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
DMF/H2O (v/v = 1:2)
83
73
77
85
91
90
82
91
a Reaction conditions: 4ꢀbromoanisole (1 mmol), styrene (1.3 mmol), base (2 mmol), TBAB (0.5 mmol), in solvent (3 mL) for 5 h.
b Isolated yields.
c
In paranthesis yields obtained in run 2.
d No TBAB was added.
Furthermore, the catalyst can be recovered and reused up to and Aldrich. Polyethylene glycol (PEG, MW = 10000) was
seven times with no significant loss of activity.
purchased from Aldrich. Thermogravimetricꢀdiffraction
thermal analysis (TGꢀDTA) was carried out using a thermal
gravimetric analysis instrument (NETZSCH TG 209 F1 Iris)
with a heating rate of 10 ºC minꢀ1. XRD patterns were recorded
by an EQUINOX 3000, Xꢀray diffractometer using Cu Kα
Experimental
1
radiation H NMR (300 MHz) and 13C NMR (75 MHz) spectra
General
were recorded using a Bruker AQSꢀ300 Avance spectrometer.
Transmission electron microscope, TEM (ZeissꢀEM10Cꢀ80
KV) was used to obtain TEM images. The scanning electron
microscopy (SEM) images were obtained using a scanning
electron microscope MIRA3\\TESCANꢀLMU. The magnetic
As received chitosan (CS) powder with average MW = 100000ꢀ
300000 and the deacetylation degree of 70ꢀ85% (from Acros
company) was used without further purification. All chemicals
were commercial reagent grades and purchased from Merck
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Journal Name
RSCPublishing
ARTICLE
Table 2. MizorokiꢀHeck reaction of aryl bromides and chlorides with various olefins.a
R1
R2
MPCS-TI/Pd (0.1 mol%)
Ar
ArX
+
R2
DMF/H2O,Et3N,110 oC,TBAB
R1
6
4
5
Entry
ArX
PhBr
4ꢀMeCOC6H4Br
4ꢀNCC6H4Br
4ꢀOHCC6H4Br
R1
Ph
Ph
Ph
Ph
R2
H
H
H
H
Product
Time (h)
Yield (%)b
9344
1
2
3
4
6a
6b
6c
6d
4
4
4
5
9344
9044
8945
5
4ꢀO2NC6H4Br
Ph
H
6e
4
9346
6
7
8
9
4ꢀMeOC6H4Br
2ꢀMeC6H4Br
1ꢀBromonaphthalene
PhBr
PhBr
PhBr
4ꢀMeOC6H4Br
PhBr
4ꢀMeC6H4Br
4ꢀO2NC6H4Br
PhBr
1ꢀBromonaphthalene
PhBr
PhBr
Ph
Ph
Ph
H
H
H
H
H
H
H
H
H
H
CH3
H
H
H
H
H
H
6f
5
6
6
5
5
4
5
4
5
3
5
6
6
4
8
7
7
8
8
7
9
7
9146
8645
8545
8847
8745
9623
9123
9224
9422
9546
8348
9248
8745
9445
7944
7744
7344
7145
6947
8123
7548
8145
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
6r
6s
6a
6b
6c
6d
6i
4ꢀClC6H4
4ꢀMeOC6H4
COOH
COOH
CO2Bun
CO2Me
CO2Me
CO2Me
CO2Et
CN
CONH2
Ph
Ph
Ph
Ph
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
PhCl
4ꢀMeCOC6H4Cl
4ꢀNCC6H4Cl
4ꢀOHCC6H4Cl
PhCl
PhCl
PhCl
H
H
H
CH3
H
4ꢀClC6H4
COOH
CO2Me
CONH2
6k
6p
6s
PhCl
a Reaction conditions: aryl halide (1 mmol), olefin (1.3 mmol), Et3N (2 mmol), catalyst (0.1 mol %), TBAB (0.5 mmol), in DMF/H2O
(v/v =1:2, 3 mL), at 110 °C.
b Isolated yields.
c References provided for the known compounds.
measurement of samples were carried out in a vibrating sample
magnetometer (VSM) (4 inch, Daghigh Meghnatis Kashan Co.,
Kashan, Iran) at room temperature. FTꢀIR spectra were
obtained using a Shimadzu model FTꢀIR8400 instrument. The
Pd content of the complex was determined using inductively
coupled plasma (ICP, Varian vistaꢀmpx), and surface
morphology of the catalyst was analyzed using Energyꢀ
dispersiveꢀXꢀray (MIRA3, TESCANꢀLMU) equipped with
EDX facility. The XꢀRay photoelectron spectroscopy (XPS)
data were recorded with 8025ꢀBesTec twin anode XR3E2 Xꢀ
ray source system. Micro analytical data was collected by a
PerkinꢀElmer, USA, 2400C elemental analyzer. The N2ꢀ
sorption was carried out in a BelsorpꢀminiꢀBEL Japan, Inc. at
298 K (see ESI).
Preparations
Fe3O4
The synthesis of Fe3O4 was achieved using the procedure described
by Luo and coꢀworkers.49 In a typical preparation procedure, ferric
chloride hexahydrate FeCl3.6H2O (5.5 g, 20.35 mmol) and ferrous
chloride tetrahydrate FeCl2.4H2O (2.0 g, 20.1 mmol) were dissolved
in deionized water (125 mL) under nitrogen atmosphere with
mechanical stirrer at 85 °C. The pH value of the solution was
adjusted to 9ꢀ11 using aqueous NH3 (25 %). After continuous
stirring for 4 h, the magnetite precipitates were washed with distilled
water until the pH value descended to 7.0. The black precipitate
(Fe3O4) was collected with a permanent magnet at the bottom of the
reaction flask (Scheme 1).
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Porous chitosan-thienyl imine support, PCS-TI (1)
In a 200 mL roundꢀbottom flask equipped with a magnetic stirring
bar, chitosan (1 g) was allowed to dissolve slowly in aqueous acetic
acid solution (0.87 M, 100 mL), for 1 h at room temperature; then
PEG (1 g) was added to the above flask and stirred for 10 min,
followed by addition of 2ꢀthiophenecarbaldehyde (2.24 g, 20 mmol)
and the mixture was stirred for 24 h under N2 atmosphere. The
reaction mixture was dripped into a 1 N NaOH aqueous solution
(250 mL) through a needle of 0.9 mm diameter. The gelatin like CSꢀ
TI was collected and washed with hot distilled water until neutral
(pH ~ 7), followed by extraction of the PEG component with about 2
liters of hot water (Scheme 1). Similarly, the bead chitosanꢀ
supported ligand (BCSꢀTI) was prepared by the same protocol in the
absence of PEG. Also, the normal chitosanꢀsupported ligand (NCSꢀ
TI) was produced by mixing chitosan and 2ꢀthiophenecarbaldehyde
in EtOH (10 mL).
Acknowledgements
Financial support from K.N. Toosi University of Technology
Research Council is gratefully acknowledged. The authors are
grateful to Dr. Sogand Noroozizadeh for revising the English
language of the manuscript.
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2:1, 3 mL), and the catalyst (0.001 mmol, 0.1 mol% Pd) was
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combined organic extracts were washed with brine (2 × 10
mL), dried (MgSO4), and concentrated in vacuum. The crude
product was further purified by preparative TLC (silica gel)
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DOI: 10.1039/C5NJ01337B
We have prepared a highly active and recyclable heterogeneous catalyst for the Heck reaction in aqueous
media in high yields.
S
N
ArX
S
Et3N
R1
S
N
N
N
Ar
Fe3O4
NP
H2O/DMF
R2
R1
N
S
TBAB
Up to 96% yield
27 examples
S
N
S
R2