Pd nanoparticles immobilized on magnetic chitosan as a novel reusable catalyst for green Heck and Suzuki cross-coupling reaction: In water at room temperature

Article abstract of DOI:10.1002/aoc.4112

A novel type of magnetically responsive chitosan nanocomposite was successfully synthesized as a green and high powerful palladium-based heterogeneous catalyst and its efficiency in Heck and Suzuki cross-coupling was evaluated. This catalyst promote a large library of functional substrates of these reactions under mild and sustainable conditions (water or ethanol as solvent, at room temperature, in significantly short reaction time (20?minutes)) and stand as recyclable, metal scavenging catalytic systems.

Full text of DOI:10.1002/aoc.4112

Received: 8 July 2017
DOI: 10.1002/aoc.4112
Revised: 17 August 2017
Accepted: 17 August 2017
F U L L P A P E R
Pd nanoparticles immobilized on magnetic chitosan as a
novel reusable catalyst for green Heck and Suzuki
cross‐coupling reaction: In water at room temperature
Abdol R. Hajipour1,2
| Ali R. Sadeghi1 | Zahra Khorsandi1
1 Department of Chemistry, Isfahan
University of Technology, Isfahan 84156,
IR Iran
2 Department of PharmacologyUniversity
of Wisconsin, Medical School, 1300
University Avenue, Madison 53706‐1532,
WI USA
A novel type of magnetically responsive chitosan nanocomposite was success-
fully synthesized as a green and high powerful palladium‐based heterogeneous
catalyst and its efficiency in Heck and Suzuki cross‐coupling was evaluated.
This catalyst promote a large library of functional substrates of these reactions
under mild and sustainable conditions (water or ethanol as solvent, at room
temperature, in significantly short reaction time (20 minutes)) and stand as
recyclable, metal scavenging catalytic systems.
Correspondence
Abdol R. Hajipour, Department of
Chemistry, Isfahan University of
Technology, Isfahan 84156, IR Iran.
Email: haji@cc.iut.ac.ir
KEYWORDS
heck and Suzuki reaction, magnetic chitosan, room temperature conditions, water
Funding information
Isfahan University of Technology (IUT);
Center of Excellence in Sensor and Green
Chemistry Research (IUT)
1 | INTRODUCTION
Numerous heterogenization methods applying various
solid supports such as charcoal, inorganic silica, alumina
One of the most ideal strategies is to perform coupling
reactions in low‐cost, safe and environmentally friendly
conditions, such as ambient temperature and water as
the only solvent.[1,2] The use of this solvent alone has fun-
damental merit in that water is inexpensive, nontoxic, and
safe. Existing approaches in water without any co‐solvents
require considerable heating[3,4] and there are few exam-
ples of transition‐metal‐based cross‐coupling reactions
which run in pure water at room temperature involving
water‐insoluble substrates. Herein, we describe the use of
novel catalytic system that allow, for the first time, Heck
and Suzuki cross‐couplings to be run at room temperature
and in green solvent.
Palladium‐catalyzed Heck cross‐coupling reactions is
known as one of the most common and practical method
for the construction of new carbon–carbon bonds[5,6]
which have widely applications for the synthesis of a large
variety of organic substances, bioactive compounds and
natural products.[7,8]
and synthetic polymers have been developed.[9–11] Most
reported heterogeneous catalysts have higher reusability
but stability and environmental properties is their most
important weakness. For example, carbon nanotubes as
one of the most interested solid support have been found
as a serious health hazard materials.[12] In addition to,
mesoporous silica is instable in aqueous and basic
conditions.[13,14]
One of the excellent candidate as a support for cata-
lysts is chitosan, it is produced from a key constituent of
the exoskeletons of crustaceans.[15,16] Chitosan has been
exhibited biopesticidal, antifungal and anticancer proper-
ties and can be used as absorbents for metals in medicine
and drug delivery.[17,18]
Functionalization of chitosan with various ligands can
provide coordination sites that make it sufficient for metal
catalysts.[19–21] Therefore, several catalytic systems using
chitosan as a support are reported and their applications
in some reaction such as oxidation, cyclopropanation of
Appl Organometal Chem. 2017;e4112.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4112

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HAJIPOUR ET AL.
olefins, Suzuki and Heck cross coupling reactions were
investigated,[22–25]
The original catalytic system for Suzuki reaction con-
tain palladium due to its excellent catalytic activity and
stability. In recent years, extensive studies have been done
to designing new catalytic system with the unique ability
to provide excellent catalytic generality and activity.[36,37]
In this regard, palladium catalysts employed electron rich
phosphine ligands,[38,39] nitrogen containing ligands,[40,41]
heterocyclic carbenes,[42] oximes,[43] and imines[44,45] has
In recent year, MNPs, due to their unique properties
including good stability, easy preparation process and
functionalization, low toxicity and cost have emerged as
attractive as a core magnetic support. More importantly,
it can be separated from the reaction mixture facilely with
an external magnet.[26,27]
For the Heck reactions, in spite of rarity of using
chitosan palladium catalyst, a few reports are avail-
able.[28–30] For example, in 2011, Smith et al. used 6‐
deoxy‐6‐aminochitosan‐supported Pd (II) catalysts in
Suzuki and Heck cross‐coupling reactions in xylene
and aqueous ethanol solvents during long reaction time
at extremely high temperature (130 °C).[28] Application
of 2‐pyridinecarboxaldehyde as ligand to prepared
another chitosan palladium as catalyst in carbon–carbon
coupling reaction was also described by Naghipour and
his co‐workers in 2016 (at 120 °C using DMF as solvent
and organic base).[31] These reported catalysts have var-
ious advantages such as ease of preparation, stability,
reusability, versatility (organic or aqueous solvent catal-
ysis) and no measurable Pd leaching. In contrast, they
spent high temperature and long reaction time in these
reactions and show little or no activity with aryl chlo-
ride substrates. Therefore, to overcome these problems,
more convenient methods using a novel catalyst are
required.
One of the most powerful carbon–carbon bond
forming reaction for constructing biaryl compounds is
Suzuki[32,33] which have found mainly in pharmaceuti-
cals, agrochemicals and biologically active natural
compounds.[34,35]
FIGURE
1
FT‐IR spectra: (a)chitosan; (b) MNPs/Cs (c)
imine@MNPs/Cs; (d)Pd‐imine@MNPs/Cs
OH
NH2
O
HO
HO
O
Fe3O4=
O
O
O
O
O
O
H2N
H2N
OH
OH
Br
n
n
2
1
HO
N
HO
O
HO
Pd(OAc)2
O
O
O
O
O
O
O
N
NH
N
OAC
O
OH
OH
Pd
n
n
HO
N
3
4
SCHEME 1 Synthesis of the catalyst

HAJIPOUR ET AL.
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simple, highly economical, commercially feasible as well
as environmentally sustainable approaches for the synthe-
sis of biaryls are required.
In continuous of our interest in developing of prepara-
tion various heterogonous catalyst and studying their
applications in cross coupling reaction,[49–56] now the
work on the synthesis and characterization of chitosan‐
supported palladium complexes and its catalytic behavior
in Heck and Suzuki cross coupling reactions was
presented.
2 | RESULTS AND DISCUSSION
FIGURE 2 TGA thermogram: MNPs@Cs and Pd‐imine@
MNPs/Cs
The magnetic Schiff base palladium catalyst, shown as Pd‐
imine@MNPs/Cs, was prepared using multistep synthesis
process which demonstrated in Scheme 1. Detailed proce-
dures was given in experimental section.
The NH2 functional group in chitosan (CS) was
reacted with imine, synthesized through facile and com-
mon method for this type reactions, yielding imine‐func-
been reported, these catalysts suffer from air and moisture
sensitivity. However, recent efforts have been devoted
toward of development in reduction of chemical waste,
safer and more efficient reaction conditions. So, one way
to achieve these aims is application of environmentally
friendly solvents such as ethanol, water or ionic‐liquids.
Nevertheless, reported methods for Suzuki cross‐coupling
reactions in such green medium[46–48] have been applied
large amounts of catalyst, high reaction temperatures,
additives and time‐consuming workup procedures. There-
fore, to overcome these problems, more convenient very
tionalized chitosan via
a
carbon‐nitrogen bond
formation. Then, the resulting imine‐functionalized chito-
san was treated with palladium salt to form the complex
as shown in Scheme 1. These processes were checked by
FT‐IR spectra, thermogravimetric analysis (TGA) and ele-
mental analysis.
TABLE 1 Thermogravimetric analysis (TGA) and elemental analysis results
Sample
Organic [Wt. %]
Organic [mmolg−1 MNPs] (TGA)
Organic [mmolg−1 MNPs] (elemental analysis)
MNPs/CS
65.8
0.21
0.26
Pd‐imine@MNPs/Cs
66.9
0.13
0.15
FIGURE 3 XRD pattern: Pd‐imine@MNPs/Cs

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HAJIPOUR ET AL.
As can be seen in the FT‐IR spectrum of pure chitosan
(1) (Figure 1 (a)), the broad bands which appeared at 300–
3600 cm−1 are related to N‐H and O‐H bending vibration
and the presence of a bands at 1382 cm−1 was related to
its aliphatic C‐H. In spectra of 2, the 1383 cm−1 band is
related to the C‐O stretching of primary alcoholic group
of chitosan in MNPs@Cs and the band around 611 cm−1
ascribe to Fe‐O groups vibrations that indicate supposed
structure (Figure 1 (b)). In spectrum of final catalyst, the
absorption bands which appear at 1633 cm−1 correspond
to C = N, it show presentation of ligand in final catalyst
(Figure 1).
The TGA plots of MNPs@Cs and Pd‐imine@MNPs/
Cs (Figure 2) was given in supplemental data. The ther-
mal decomposition temperature of magnetic chitosan is
more than the final catalyst due to the deformation of
hydrogen bonds of chitosan.[57,58] In general, the ther-
mally stable of catalyst at high temperature was
observed and little reduction in the thermal stability of
the catalyst in compared with magnetic chitosan is
related to existence of ligands and their coordination
with metal ions. The amount of organic functions in
the catalyst was determined by TGA and elemental anal-
ysis. The TGA diagram was determined the weight loss
of MNPs/Cs, Pd‐imine@MNPs/Cs between 30–800 °C
as a function of temperature. Removal of physically
adsorbed water causes the first step of weight loss in
the cases, whereas, the removal of organic moieties cre-
ated the main weight loss. The TGA and elemental anal-
ysis results are summarized in Table 1. A good
agreement between elemental analysis and TGA data
for these conversions was observed. The total amount
of organic moieties on Pd‐imine@MNPs/Cs was about
0.13 mmolg‐1.
The XRD spectrum (Figure 3) provided more evidence
for the presence of iron and some palladium impurity in
the catalyst. The characteristic diffraction peaks
2θ = 20.1°, 43.1°, 53.5°, 57.0° and 62.6° can be clearly con-
sidered for cubic phase of Fe3O4 nanoparticles, in addi-
tion, characteristic diffraction peaks at 2θ = 53.1°, and
74.7° shows some impurity of crystalline palladium.
The field emission scanning electron microscopy (FE‐
SEM) images of Pd‐imine@MNPs/Cs exhibited the sur-
face morphologies of the catalysts (Figure 4). Addition-
ally, to confirm the presence of the metal ions, EDAX
spectra of the catalysts were recorded. The spectra proved
the presence of the palladium and iron ions (Figure 5).
These observations demonstrated that palladium ions
coordinated with the ligands.
Further characterization of catalyst was completed by
transmission electron microscopy (TEM). The TEM
images exhibit well‐defined spherical Pd particles dis-
persed in MNPs/CS (Figure 6). The size distribution of
FIGURE 4 FE‐SEM images of catalyst

HAJIPOUR ET AL.
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FIGURE 5 SEM–EDX spectra of catalyst
FIGURE 6 (a) TEM images and (b) particle size distribution for catalyst

6 of 11
HAJIPOUR ET AL.
8.1 emu/g, its curves was shown in Figure 7. This investi-
gation proved that coating of magnetic nanoparticles with
chitosan reduce the paramagnetic behaviour of catalyst in
compared with bulk magnetite.
In the palladium catalyzed Heck coupling reactions,
the type and amount of the catalyst, reaction time,
base system and temperature are main factors. To opti-
mize the reaction conditions the reaction of
bromobenzene with methyl acrylate was preferred as
a model reaction and the results are summarized in
Table 2. The model reaction was first performed in
the presence of different amounts of catalyst, the best
result was obtained using 3 mg of catalyst. Then, the
reaction was carried out in different solvents, according
to aims of green chemistry, although the results was so
near to each other, water was chosen as ideal solvent
and best reaction medium.
FIGURE 7 Room temperature magnetization curves of catalyst
Pd nanoparticles was about 20.5 nm. All these observa-
tions indicate that the magnetic chitosan functionalized
with imine is a good host and ligand for palladium nano-
particles. The metal content of the complexes (% mass)
were determined with ICP‐OES, showed a value 1.17
TABLE 3 Scope of heck cross coupling reactiona
mmolg−1
.
The magnetization value for pure magnetic nanoparti-
cles is equal to 69.4 emu/g and for catalyst is equal to
Entry
X
R
Olefin
Yieldb (%)
TOF (h−1
)
TABLE 2 Optimization of reaction conditions on heck reaction of
1
I
H
MA
94
7.1 × 104
bromobenzene with methyl acrylate in the presence of catalysta
2
I
4‐OMe
H
MA
92
90
87
79
73
41
53
71
65
45
75
79
69
71
63
49
57
51
40
7.0 × 104
6.8 × 104
6.4 × 104
6.0 × 104
5.5 × 104
3.1 × 104
4.0 × 104
5.4 × 104
4.9 × 104
3.4 × 104
5.7 × 104
6.0 × 104
5.2 × 104
5.4 × 104
4.8 × 104
3.7 × 104
4.3 × 104
3.9 × 104
3.0 × 104
3
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
I
MA
4
4‐OMe
4‐NO2
2‐me
4‐Cho
2‐NO2
H
MA
5
MA
Yieldb
(%)
6
MA
Cat (mg/mol%
Entry Pd)
Tem
Solvent (°C)
Base
7
MA
1
‐
DMSO 100
DMSO 100
DMSO 100
DMSO 100
K2CO3
‐
8
MA
2
5/0.006
2/0.002
3/0.004
3/0.004
3/0.004
3/0.004
3/0.004
3/0.004
3/0.004
3/0.004
3/0.004
3/0.004
3/0.004
K2CO3 92
K2CO3 63
K2CO3 91
K2CO3 92
K2CO3 90
K2CO3 92
K2CO3 92
9
MA
3
10
11
12
13
14
15
16
17
18
19
20
4‐Cn
3‐NO2
H
MA
4
MA
5
PEG
NMP
DMF
H2O
H2O
H2O
H2O
H2O
H2O
H2O
100
100
100
100
100
100
100
80
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
6
I
4‐OMe
H
7
I
8
Br
Br
Br
Cl
Cl
Cl
4‐OMe
4‐NO2
2‐me
H
9
KOH
87
84
10
11
12
13
14
K3PO4
NaHSO4 80
K2CO3 91
K2CO3 90
K2CO3 90
4‐Cn
3‐NO2
50
r.t.
aThe reaction was carried out with aryl halide (1.0 mmol), alkene (1.1 mmol),
K2CO3 (2.0 equiv.) in 2.0 ml H2O, 3 mg of catalyst (0.004 mol % of Pd) at room
temperature for 20 min
aThe reaction was carried out with bromobenzene (1.0 mmol), methyl acry-
late (1.1 mmol), base (2 eq.) solvent (2.0 ml) for 20 min
bGC yield
bIsolated yield

HAJIPOUR ET AL.
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Among various tested bases such as K2CO3, KOH,
functional groups and phenylboronic acid was used to
cover the scope of catalytic effectiveness of Pd‐
imine@MNPs/Cs in Suzuki reaction (Table 5). Aryl
NaHSO4 and K3PO4; K2CO3 was found as most effective
base. In continues, we encouraged to observe that Pd‐
imine@MNPs/Cs is significantly active to permits the
coupling reaction occurrence at room temperature. Con-
sistent with the optimization results and the important
goals of green chemistry and saving energy, the optimum
reaction conditions using K2CO3 (2 mmol), 3 mg of Pd‐
imine@MNPs/Cs and water as solvent at room tempera-
ture was selected.
TABLE 4 Optimization of reaction conditions on Suzuki reaction
of phenylboronic acid with bromobenzene in the presence of
catalysta
Encouraged by our initial results, the generality and
versatility of our catalyst in Mizoroki–Heck cross‐cou-
pling of aryl halides with olefins was examined. As can
be seen in Table 3, using optimized conditions, a diver-
sity of aryl iodides, bromides and chloride containing
electron‐donating and electron‐withdrawing substituents
reacted efficiently with methyl acrylate and styrene
under air atmosphere at exceedingly mild and green
conditions, the desired cross‐coupling products was
achieved in high yields and extremely short reaction
time. The experimental results indicated that the elec-
tronic properties of the starting materials had no signif-
icant effect on the reaction; nevertheless, aryl iodides
was found to be more reactive than aryl bromides.
Among aryl halides, aryl chlorides are more interesting
substrate for coupling reactions due to their cost and
availability comparison to their bromide or iodide coun-
terparts. The most reported methods required high load-
ings palladium catalyst and harsh reaction conditions for
aryl chloride substrates, even though they show little or
no activity. For more explore of the efficiency and appli-
cability of our method, the cross‐coupling of aryl chlo-
rides with olefins was also investigated under the same
conditions. The obtained results reveal that the catalyst
is efficient in Heck coupling of less reactive aryl chloride
derivatives with olefins.
The excellent results obtained in the Heck cross‐cou-
pling persuaded us to investigate potential activity of Pd‐
imine@MNPs/Cs in Suzuki reaction. In order to obtain
the optimum experimental conditions, the reaction of
phenylboronic acid with bromobenzene was considered
as a model reaction in the presence of catalyst. Various
reaction conditions such as the type of base and solvent
and different temperature was examined and a summary
of the optimization experiments is given in Table 4. As
can be seen, the best result was obtained using KOH
(2 eq) and 3 mg of Pd‐imine@MNPs/Cs (0.004 mol% Pd)
in ethanol as green solvent and at much desired room
temperature conditions (Table 4, entry 14). Interestingly,
the reaction was carried on significantly short reaction
time (20 minutes).
Entry
Solvent
Tem (°C)
Base
Yieldb (%)
1
DMSO
80
K2CO3
95
2
3
4
5
6
7
8
DMSO
DMSO
EtOH
50
K2CO3
K2CO3
KOH
93
91
93
91
89
86
71
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
EtOH
NaOH
K3PO4
KOH
EtOH
EtOH/H2O
H2O
KOH
aThe reaction was carried out with phenylboronic acid (1.0 mmol),
bromobenzene (1.1 mmol), base (2 eq.) solvent (2.0 ml) for 20 min
bGC yield.
TABLE 5 Suzuki cross‐coupling of various aryl halides in the
presence of catalysta
Entry
1
X
R
Yieldb (%)
97
TOF (h−1
)
I
H
7.4 × 104
2
I
4‐COCH3
4‐OMe
H
95
96
93
82
86
81
81
83
79
43
57
34
7.2 × 104
7.3 × 104
7.1 × 104
6.2 × 104
6.5 × 104
6.1 × 104
6.1 × 104
6.1 × 104
7.0 × 104
3.3 × 104
4.3 × 104
3.3 × 104
3
I
4
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
5
2‐COCH3
4‐Cn
6
7
Naphthalene
4‐Br
8
9
4‐OMe
2‐NO2
H
10
11
12
13
4‐NO2
NH2
aThe reaction was carried out with aryl halide (1.0 mmol), phenylboronic acid
(1.1 mmol), KOH (2.0 equiv.) in 2.0 ml EtOH, 3 mg of catalyst (0.004 mol % of
Pd) at room temperature for 20 min.
With the optimized reaction conditions in hand, var-
ious aryl iodides, bromides and chlorides with different
bIsolated yield.

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HAJIPOUR ET AL.
TABLE 6 Reusability of the catalyst in the heck reaction of
iodobenzene and methyl acrylate
The reactivity of aryl chlorides was lower than that of
aryl bromides.
One of the serious problem for supported metal cat-
alysts especially for palladium catalyst is leaching of
metal ions. To investigate of leaching, the reaction
between iodobenzene and methyl acrylate was carried
out in two different vessels under the exactly same
conditions.
Entry
Yielda (%)
Entry
Yielda (%)
1
94
5
91
2
3
4
94
92
90
6
7
8
90
89
87
aIsolated yield.
After 10 min the catalyst was separated from one of
these vessels by magnetic bar and the other was
remained unchanged. Then, both of the reactions was
continued, after another 10 min, the reactions stopped
and their development was tested using GC. The results
displayed that the reaction without catalyst was not
proceeded any more, while the other reaction was
improved, this experimental indicated that the leaching
does not present here and this novel catalyst was het-
erogeneous in nature.
iodides regardless of electronic nature of functional
groups was given excellent yield in the reactions. The
catalyst displayed high activity toward aryl bromides, as
can be seen, electronic properties of the substituents on
aromatic rings had no attractive effect on the reaction.
Due to steric hindrance, the substituents in the ortho
position gave rise to the corresponding biphenyls in
lower yield than the substituents in the other position.
FIGURE 8 XRD pattern of Pd‐imine@MNPs/Cs after eighth run
TABLE 7 Comparison of catalytic activities of our catalyst with literature examples for heck and Suzuki reactions
Entry
Catalystref
Chitosan ligand
Reaction conditions
Time
Yield(%)
Heck reaction between iodobenzene and methyl acrylate
1
2
Fe3O4@CS‐Schiff base Pd29
Fe3O4–CS–meth‐Pd31
2‐pyridinecarboxaldehyde
Pd (9.4 mol%) in DMF at 120 °C
10 (min)
2 (h)
98
90
Methionine
Pd (0.28 mol%), TBAB (0.25 mmol), in
H2O at 100 °C
3
6‐deoxy‐6‐amino/Cs/
6‐deoxy‐6‐amino
Pd (0.09 mol%) in DMF at 130 °C
4 (h)
98
Pd(II)30
4
5
Pd@MNPs/Cs61
‐
Pd (0.004 mol%) in H2O at r.t.
Pd (0.004 mol%) in H2O at r.t.
20 (min)
20 (min)
31
88
Present catalyst
2‐(2‐bromophenylimino)
Methyl)phenol
Suzuki reaction between phenylboronic acid and bromobenzene
6
7
8
Fe3O4@CS‐Schiff base Pd29
CS‐proline‐Pd(II)61
OCMCS‐Pd62
2‐pyridinecarboxaldehyde
Pd (9.4 mol%) in PEG at 80 °C
20 (min)
8 (min)
48 (h)
98
Proline
Pd (0.4 mol%) in H2O:EtOH at 70 °C
Pd (0.04 mol%) in toluene at 100 °C
100
97
O‐carboxymethylchitosan
Schiff bases
9
6‐deoxy‐6‐amino/Cs/Pd(II)30
Pd@MNPs/Cs61
6‐deoxy‐6‐amino
Pd (0.09 mol%) in xylene at 130 °C
Pd (0.004 mol%) in H2O at r.t.
Pd (0.004 mol%) in H2O at r.t.
6 (h)
34
43
97
10
11
‐
20 (min)
20 (min)
Present catalyst
2‐(2‐bromophenylimino)
Methyl)phenol

HAJIPOUR ET AL.
9 of 11
The achievability of recycling the catalyst was also
moderate to high yields of products in extremely short
reaction times (20 min). The catalyst loading is consider-
ably lower in most cases than previously reported car-
bon–carbon coupling reactions. Easy purification,
recyclability and very low Pd leaching are other main
characteristic of the procedure.
studied (Table 6). After the reaction, the catalyst was eas-
ily recovered by magnetic bar and washed with acetone,
then dried at room temperature and used in the next cat-
alytic cycle under the optimized conditions. However, no
significant reduction in activity was observed until the
eighth reuse. The XRD pattern of Pd‐imine@MNPs/Cs
after eighth run was given in Figure 8.
4 | EXPERIMENTAL
Even though some chitosan/palladium catalytic sys-
tems described previously, one of the main problem of
using them in cross coupling reactions is leaching of palla-
dium from the support to the reaction mixture that reduce
reusability capability. As mentioned in induction, various
ligands was used in designing this type catalyst, we chosen
2‐((E)‐(2‐bromophenylimino)methyl)phenol as ligand to
make more branching and more coordinate location.
Indeed, our ligand make cage like position to trapping
metal nanoparticles which make it very stable in reaction
conditions even after using in multiples run. In other
hand, according to previous studies,[59–61] special structure
of hosting ligands with multiple internal and external
functional groups, such as dendritic and highly branched
polymers, can be a very suitable hosts for a wide range of
ions, molecules and metal nanoparticle that minimizes
the leaching of the particles and increases catalyst recycla-
bility. Most importantly, the Pd‐imine@MNPs/Cs exhib-
ited high activities which may be related to good
dispersion and small size of metal nanoparticles and good
synergistic effects of selected ligand. Herein, to investigate
the effect of ligand on efficiency of catalyst, the present cat-
alytic system was compared with some published proce-
dures for the Heck and Suzuki reaction using chitosan/
palladium with various ligands, the results are shown in
Table 7. Moreover, the efficiency of Pd@MNPs/Cs in Heck
and Suzuki cross‐coupling reaction was investigated and
compared with our catalyst Pd‐imine@MNPs/Cs
(Table 7, entry 4 vs 5 and 10 vs 11). The results confirmed
the good effective of ligand in in this catalyst.
4.1 | General procedure for the catalyst
preparation
The magnetic nanoparticles (MNPs) was prepared
according to the literature.[62] based on precipitation of
magnetite nanoparticles from the mixture of iron(II)
sulfate and iron (III) chloride by ammonia (25% solu-
tion in water). Subsequent, a mixture of magnetic nano-
particles and sodium sulfate (20%, W⁄V) was added to a
solution of chitosan (1%, W⁄V) in acetic acid (2%, W⁄V)
in a round‐bottom flask equipped with mechanical stir-
rer and condenser and the mixture stirred for 1 h from
the reaction mixture by an external permanent magnet,
washed with ethanol and methanol and dried under
vacuum at 70 °C. In continuous, a solution of ethanol
suspension of MNPs@Cs (1.0 g/10 ml) was added to
ligand (2‐(2‐bromophenylimino) methyl)phenol which
synthesized and purified previously) (10 mmol) and
the mixture was refluxed for 24 h in presented copper
catalyst and C‐N standard conditions. The brown solid
of final catalyst Pd‐imine@MNPs/Cs was obtained by
addition of Pd(OAc)2 (3.2 mmol) solved in 10 ml etha-
nol to dispersed mixture of imine@MNPs/Cs (0.9 g) in
acetone (5 ml) and stirred at 60 °C for 18 h. The
resulting product was collected by an external perma-
nent magnet and washed with methanol (3 × 10 ml)
to remove the unreacted materials and finally dried
under air.
As can be seen in Table 7, the methods that reached to
desired products in high yield and significantly short time
(entry 1, 6 and 7) applied moderate to high temperature
conditions; moreover, in some cases high loading of
palladium and unsafe organic solvent (toluene and
xylene) was used.
4.2 | General procedure for the heck
reaction
To a mixture of K2CO3 (2 eq), olefin (1.1 mmol) and aryl
halide (1 mmol) in water (2 ml), in a round‐bottom flask
equipped with a mechanical stirring, 3 mg of catalyst
(0.004 mol% of Pd) was added. The mixture was stirred
at room temperature for 20 minutes under air atmo-
sphere. For monitoring of reaction's progress TLC (hex-
ane/EtOAc, 80:20) and gas chromatography (GC) we
used. After completion of the reaction the mixture was
diluted with ethyl acetate and water. The organic layer
was washed with brine, dried, concentrated under
3 | CONCLUSIONS
We have successfully developed a green and low con-
sumption energy method (using water or ethanol as sol-
vent & room temperature conditions) for the Heck and
Suzuki reactions, in the absence of organic co‐solvents
as well as other additives and promoter, providing
reduced
pressure
and
purified
by
column

10 of 11
HAJIPOUR ET AL.
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In a round‐bottomed flask equipped with a mechanical
stirring, aryl halide (1.0 mmol), phenylboronic acid
(1.1 mmol), KOH (2.0 equiv.) and 3 mg of catalyst
(0.004 mol % of Pd) in 2.0 ml EtOH was stirred for
20 minutes under air atmosphere at room temperature.
The progress of the reaction was monitored by TLC and
GC. After end of reaction, the mixture was diluted with
dichloromethane and water. The organic layer was
washed with brine, dried, concentrated and was isolated
by column chromatography to afford the corresponding
products. The products were characterized by m.p., IR,
1H, 13C NMR spectra.
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port from the Center of Excellence in Sensor and Green
Chemistry Research (IUT) is gratefully acknowledged.
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Abdol R. Hajipour http://orcid.org/0000-0002-7737-0558
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How to cite this article: Hajipour AR, Sadeghi
AR, Khorsandi Z. Pd nanoparticles immobilized on
magnetic chitosan as a novel reusable catalyst for
green Heck and Suzuki cross‐coupling reaction: In
water at room temperature. Appl Organometal
Chem. 2017;e4112. https://doi.org/10.1002/aoc.4112
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