CNC pincer palladium complex supported on magnetic chitosan as highly efficient and recyclable nanocatalyst in C─C coupling reactions

Article abstract of DOI:10.1002/aoc.4519

A stable and durable magnetic chitosan-supported triazine-bridged bisimidazolium pincer palladium catalyst (Fe₃O₄@ChC@CNC-Pd^II) was synthesized and characterized using various techniques. The Fe₃O₄@ChC@CNC-Pd^II complex displayed high activity in the production of substituted biaryls via the cross-coupling reactions of aryl halides with arylboronic acids. Also, this catalyst could be simply recovered from the reaction mixture and reused in 13 consecutive runs with no loss of its catalytic activity.

Full text of DOI:10.1002/aoc.4519

Received: 16 April 2018
DOI: 10.1002/aoc.4519
Revised: 18 June 2018
Accepted: 29 June 2018
F U L L P A P E R
CNC pincer palladium complex supported on magnetic
chitosan as highly efficient and recyclable nanocatalyst in
C─C coupling reactions
Fatemeh Rafiee
| S. Azam Hosseini
Department of Chemistry, Faculty of
Physic‐Chemistry, Alzahra University,
Vanak, Tehran, Iran
A
stable and durable magnetic chitosan‐supported triazine‐bridged
bisimidazolium pincer palladium catalyst (Fe3O4@ChC@CNC‐PdII) was synthe-
sized and characterized using various techniques. The Fe3O4@ChC@CNC‐PdII
complex displayed high activity in the production of substituted biaryls via the
cross‐coupling reactions of aryl halides with arylboronic acids. Also, this catalyst
could be simply recovered from the reaction mixture and reused in 13 consecu-
tive runs with no loss of its catalytic activity.
Correspondence
Fatemeh Rafiee, Department of
Chemistry, Faculty of Physic‐Chemistry,
Alzahra University, Vanak, Tehran, Iran.
Email: f.rafiee@alzahra.ac.ir
Funding information
Council of Alzahra University
KEYWORDS
chitosan, heterogeneous catalysts, magnetic nanoparticles, nanocatalyst, pincer palladium complex
1 | INTRODUCTION
biocatalyst supports in the synthesis of fine chemicals
due to their excellent properties such as availability, non‐
A number of effective catalytic methods have been devel-
oped for the palladium‐catalysed Suzuki–Miyaura cross‐
coupling reaction as one of the most popular ways for
the construction of biaryls.[1] Biaryl scaffolds have found
numerous applications in the synthesis of natural prod-
ucts, bioactive products, receptor macrocyclic molecules,
liquid crystal materials and asymmetric catalysts.[2–6]
Homogeneous and heterogeneous N‐heterocyclic
carbene (NHC)–metal complexes have attracted signifi-
cant attention in a wide variety of cross‐coupling reac-
tions. Compared with classical ligands, NHCs have
strong σ‐donor and weak π‐acceptor properties that lead
to stronger bonds with metal centres.[7–10] Among them,
pincer pyridine‐based NHCs have attracted much atten-
tion because the tridentate rigidity gives metal complexes
high stability against air, moisture and heat.[11–13] CNC
pincer homogeneous and heterogeneous complexes con-
taining pyridine‐bridged bisimidazolium coordinated
ligands with palladium coordinated to them as a
tridentate ligand were reported as highly active catalysts
for cross‐coupling reactions.[14–17]
toxicity, biodegradability, renewability and biocompatibil-
ity.[18–20] Chitosan represents an attractive alternative to
other biomaterials for the immobilization of catalytic
metals because of the presence of available amine and
hydroxyl chelating functional groups, stability of metal
anions such as Pt and Pd, and physical and chemical versa-
tility of the biopolymer.[21–26] The use of chitosan–metal
complexes has been researched as heterogeneous catalysts
in the reactions of hydrogenation and acetalization,[27] oxi-
dation.[28] cycloaddition,[29] oxidative carboxylation of ole-
fins[30] and cross‐coupling reactions.[31–34]
The low cost and eco‐friendliness, high hydrophilicity,
non‐toxicity, insolubility in organic solvents and multi-
functional properties of chitosan make it a valuable solid
support in the field of catalysis, but there are some limiting
factors in the use of this biopolymer, such as chemical
instability, lower surface area, dissolution and lower
dispersability.[22,35] Along this line, magnetic‐functional-
ized chitosan catalysts display many advantageous proper-
ties such as enhancement of the stability of chitosan in
solution, improvement of the adsorption capacity and
dispersability of chitosan due to high surface area and sur-
face functional groups and facile magnetic separation
Polysaccharides like starch, chitin, chitosan and cellu-
lose are widely used as suitable architectures for
Appl Organometal Chem. 2018;e4519.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4519

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RAFIEE AND HOSSEINI
without the need for filtration, centrifugation or other
tedious workup processes.[36–38]
Palladium nanoparticles immobilized on ligand‐free
chitosan[39] or modified chitosan, e.g. thiourea‐modified
chitosan,[31] silica–chitosan[32] and chitosan‐g‐mPEG
hybrid,[40] chitosan/cellulose–Pd(II) catalyst,[33] function-
alized chitosan–Pd(II) complexes such as Schiff bases[41,42]
and amino acid derivatives[43] and magnetic‐functional-
ized chitosan‐supported palladium catalyst[44] have been
used as efficient catalyst sources for Suzuki coupling.
2 | EXPERIMENTAL
FIGURE 1 FT‐IR spectra of (a) Fe3O4, (b) chitosan, (c) cyanuric
chloride, (d) ChC, (e) ChC@Me‐Im and (f) Fe3O4@ChC@CNC‐PdII
2.1 | Materials and Instrumentation
All reagents and solvents used in this study were com-
mercially available and were purchased from commercial
suppliers (Acros, Merck and Aldrich) and used without
any additional purification. Chitosan with degree of
deacetylation of 85% was purchased from Exire and its
400
350
300
250
200
150
100
50
molecular weight was 100 000–300 000 g mol−1
.
Fourier transform infrared (FT‐IR) spectra were
recorded using a Bruker Tensor 27 spectrometer within
1
the 400–4000 cm−1 range using KBr discs. H NMR and
13C NMR spectra were recorded with a Bruker Avance
400 and 100 MHz machine using CDCl3 as solvent and
tetramethylsilane as standard sample. X‐ray diffraction
(XRD) patterns were recorded with a PW 3710 X‐ray
0
10
20
30
40
50
60
70
Position (2 Theta)
FIGURE 2 XRD pattern of Fe3O4@ChC@CNC‐PdII catalyst
SCHEME 1 Procedure for preparation
of Fe3O4@ChC@CNC‐PdII catalyst

RAFIEE AND HOSSEINI
3 of 10
diffractometer (Philips) at room temperature using mono-
chromatic Cu Kαradiation with a wavelength of λ=
0.15418 nm. The peak positions and intensities were
X‐ray spectrometry (EDS) was conducted using a
TESCAN VEGA 3 LMU instrument. Magnetic susceptibility
measurements were carried out using a vibrating sample
magnetometer (MDK Co. Ltd, Iran) with the magnetic field
range between +10 000 and − 10 000 Oe at room tempera-
ture. Elemental analysis was performed with an Eager 300
for EA1112 CHNS instrument. X‐ray photoelectron spec-
troscopy (XPS) measurements were performed using a
Thermo Scientific ESCALAB 250 Xi with Mg X‐ray source.
obtained between 5° and 80° with a rate of 0.04° s−1
.
The morphology of the catalyst was observed using a
filed‐emission scanning electron microscopy (FE‐SEM)
instrument (Hitachi S4160, Japan) and transmission elec-
tron microscopy (TEM; Philips CM30). Energy‐dispersive
30
20
10
0
-15000
-10000
-5000
0
5000
10000
15000
-10
-20
-30
Applied field (Oe)
FIGURE
5
Room temperature magnetization curve of
FIGURE 3 EDS spectrum of Fe3O4@ChC@CNC‐PdII catalyst
Fe3O4@ChC@CNC‐PdII catalyst
FIGURE 4 XPS spectra of Fe3O4@ChC@CNC‐PdII catalyst

4 of 10
RAFIEE AND HOSSEINI
Thermogravimetric (TG) analysis of the new catalyst was
conducted using a Mettler Toledo TG analyser under nitro-
gen purge with a heating rate of 20 °C min−1.
added the Fe3O4@ChC@CNC‐PdII catalyst (0.003 g,
0.021 mmol% Pd) and stirred at 70 °C for the required
time. After completion of the reaction (monitored by
TLC (n‐hexane–EtOAc, 9:1) or GC), the reaction mix-
ture was cooled to room temperature and the catalyst
was separated by applying an external magnet. Then,
the reaction mixture was diluted with water and the
resultant mixture extracted with n‐hexane to isolate
the products. The combined organic layers were dried
over Na2SO4, and the solvent was evaporated under
reduced pressure.
2.2 | Chemical Modification of Chitosan
Biopolymer
An amount of 0.5 g of chitosan was suspended in 5 ml
of dry toluene, followed by the slow addition of 0.69 g
of cyanuric chloride under stirring. The mixture was
stirred at 100 °C for 24 h. The chitosan–cyanuric chlo-
ride (ChC) obtained was washed exhaustively with etha-
nol, then separated by filtration and dried under
vacuum at 60 °C for 12 h.[45] In the second step, N‐
methylimidazole (5 ml) and diisopropylethylamine
(1.3 ml) were added to the ChC mixture and refluxed
in dry toluene (5 ml) for 24 h. The new biopolymer
(ChC@Me‐Im) obtained from this reaction was washed
with dry CH2Cl2, separated by filtration and dried under
vacuum at 60 °C for 12 h.
3 | RESULTS AND DISCUSSION
3.1 | Preparation of Fe3O4@ChC@CNC‐
PdII Catalyst
The primary amines of chitosan offer a convenient han-
dle for grafting functional polymers. In the work reported
here, the chosen agent to fulfil the new biopolymer
design was the linking triazine agent cyanuric chloride
(2,4,6‐trichlo‐1,3,5‐triazine) that can act as a bridge
2.3 | Synthesis of Fe3O4@ChC@CNC‐PdII
Catalyst
For the preparation of Fe3O4@ChC@Me‐Im, Fe3O4 nano-
particles were firstly prepared via the conventional co‐
precipitation of iron(III) chloride (FeCl3⋅6H2O) and
iron(II) chloride (FeCl2⋅4H2O) according to a reported
procedure.[46] Fe3O4 nanoparticles (2 g) were treated with
0.5 g of ChC@Me‐Im biopolymer in 2 wt% acetic acid
solution. The resulting mixture was sonicated for
20 min and then stirred for 1 h at room temperature.
The magnetic modified chitosan was separated from the
mixture using an external permanent magnet, washed
with ethanol and deionized water several times and
finally dried under vacuum at 60 °C overnight.
The final nanocatalyst (Fe3O4@ChC@CNC‐PdII) was
obtained by addition of 0.2 g of Pd(OAc)2 to a dispersed
mixture of Fe3O4@ChC@Me‐Im in
5
ml of
dimethylsulfoxide (DMSO) under ultrasonication. Next,
the mixture was stirred at room temperature for 3 h and
then for 12 h at 50 °C and for an additional 1 h at 100 °C.
The resulting complex was collected using an external per-
manent magnet, washed with ethanol to remove the
unreacted Pd(OAc)2 and finally dried in an oven at 60 °C.
2.4 | General Procedure for Suzuki
Coupling Reaction of Aryl Halides with
Arylboronic Acids
To a round‐bottomed flask containing a mixture of aryl
halide (1 mmol), arylboronic acid (1 mmol) and
NaHCO3 (2 mmol) in 3 ml of water–ethanol (1:1) was
FIGURE
6
FE‐SEM (top) and TEM (bottom) images of
Fe3O4@ChC@CNC‐PdII catalyst

RAFIEE AND HOSSEINI
5 of 10
between chitosan and the other desired molecules. Highly
reactive cyanuric chloride was covalently bound to the
surface of the chitosan biopolymer. The reaction of ChC
with methylimidazole yielded the new biopolymer with
NHC carbene moiety. The CNC pincer palladium com-
plex was formed due to the magnetization of functional-
ized chitosan with Fe3O4 nanoparticles and then
treatment with palladium acetate in DMSO (Scheme 1).
associated with the ─OH groups. In the spectrum of pure
chitosan (Figure 1b), the characteristic absorption bands
appear at 3422 cm−1 (O─H stretching vibration which
overlaps the amino stretching band in the same region),
2922 cm−1 (C─H stretching vibration), 1653 cm−1 (N─H
bending vibration), 1423 cm−1 (C─N stretching vibration),
1383 cm−1 (CH3 symmetric angular deformation) and
1100–1150 cm−1 (C─O─C and C─O stretching vibrations).
A comparison of the spectrum of ChC@Me‐Im
(Figure 1e) with those of cyanuric chloride, unmodified
chitosan and ChC indicates amine condensation of chito-
san with cyanuric chloride and then reaction of ChC with
methylimidazole. Bands in the region 1500–1600 cm−1
are attributed to the triazine ring and melamine‐type
structures on the chitosan. Peaks that appeared in the
range 1430–1580 cm−1 correspond to C═C in imidazole
ring. Figure 1(f) shows successful immobilization of
ChC@CNC on the surface of Fe3O4 nanoparticles.
In the powder XRD pattern of the catalyst (Figure 2),
the diffraction peaks observed at 2θ = 30.14°, 35.58°,
43.14°, 53.44°, 57.12° and 62.69° correspond to crystalline
planes (220), (311), (400), (422), (511) and (440), respec-
tively, of Fe3O4 nanoparticles with a cubic spinel struc-
ture. The sharp and strong peaks confirm that the
products are well crystallized.
3.2 | Characterization of
Fe3O4@ChC@CNC‐PdII
The exact amount of palladium in the catalyst as deter-
mined using inductively coupled plasma atomic emission
spectroscopy (ICP‐AES) was 0.74 wt% (0.07 mmol g−1).
Also the content of carbon, nitrogen and hydrogen was
found by CHN analysis to be 30.34, 3.24 and 5.87%,
respectively.
Figure 1 shows the FT‐IR spectra of Fe3O4, unmodified
chitosan, cyanuric chloride, ChC, ChC@Me‐Im and
Fe3O4@ChC@Me‐Im catalyst with immobilized palla-
dium (Fe3O4@ChC@CNC‐PdII). In Figure 1(a), the
absorption bands at 582–634 cm−1 were related to the
vibration of the Fe─O bonds and the peak at 3423 cm−1
FIGURE 7 TG and DTG analyses of
Fe3O4@ChC@CNC‐PdII catalyst

6 of 10
RAFIEE AND HOSSEINI
The
elemental
composition
of
the
from Table 1, among the screened solvents, H2O–EtOH
(1:1) at 70 °C gave the best results for this reaction. The
influences of base and amount of catalyst were then
studied. NaHCO3 was found to be the best base and
0.003 g of catalyst (0.021 mmol% Pd) to be the optimum
amount. Under these conditions 4‐chlorobiphenyl was
obtained as the desired product, and biphenyl was not
formed as a by‐product via the homocoupling of
phenylboronic acid.
Fe3O4@ChC@CNC‐PdII nanocatalyst was determined
using EDS and XPS. The EDS spectrum shown in
Figure 3 reveals the presence of Fe, C, N, O, Cl and Pd
in the prepared catalyst.
The XPS elemental survey scan of the surface of the
nanocatalyst revealed the presence of Fe (Fe 2p at bind-
ing energies of 711.08 and 725.08 eV), O (O 1 s at binding
energy of 530.58 eV), N (N 1 s at binding energy of
399.78 eV) and C (C 1 s at binding energy of 285.08 eV)
elements. The XPS Pd 3d spectrum of the catalyst reveals
that Pd is present in the +2 oxidation state, correspond-
ing to binding energies of 338.08 and 342.98 eV for PdII
3d5/2 and 3d3/2 levels (Figure 4).
The optimized conditions were applied for the synthe-
sis of various biphenyl derivatives under air atmosphere
TABLE 1 Optimization of reaction conditions for Suzuki cross‐
coupling reactiona
Magnetic measurements of the magnetic nanocatalyst
were conducted with a vibrating sample magnetometer at
room temperature with the applied magnetic field sweep-
ing from −10 to 10 kOe (Figure 5).The saturation magneti-
zation (Ms) value for the Fe3O4@ChC@CNC‐PdII catalyst
(23.35 emu g−1) is determined to be lower than that of bare
Fe3O4 due to the successful coating of functionalized chito-
san layer on the surface of the Fe3O4 nanoparticles.
The FE‐SEM image (Figure 6) demonstrates that the
prepared catalyst particles are narrowly distributed, and
well dispersed, with average size of less than 40 nm in
diameter. The TEM image (Figure 6) shows that the mag-
netic nanoparticles are spherical, narrowly distributed,
and well dispersed with average size of less than 10 nm
in diameter.
TG and differential TG (DTG) analyses were carried
out to study the thermal stability of the
Fe3O4@ChC@CNC‐PdII catalyst (Figure 7). The results
showed a weight loss in three stages. The first stage (below
200 °C) shows a weight loss of about 4% corresponding to
the loss of adsorbed water (30.14–107.38 °C) and bound
water (107.38–179.52 °C). The second stage of weight loss
started at 223 °C and continued up to 470 °C with a 19%
weight loss due to the degradation of chitosan chains and
loss of other organic components. The weight loss of about
8.6% in the third stage between 470 and 800 °C was attrib-
uted to further degradation of the biopolymer. In the DTG
curve of the nanocatalyst, the main peaks were observed at
71.33, 162.53, 222.97 and 776.37 °C. The results of these
analyses indicate that the catalyst is stable at over 200 °C.
Catalyst Temp. Conversion
Entry Solvent
Base
(g)
(°C)
(%)
1
2
3
4
5
H2O
K2CO3
K2CO3
K2CO3
K2CO3
0.003
0.003
0.003
0.003
0.003
r.t.
100
r.t.
70
—
—
—
90
90
H2O
EtOH
EtOH
H2O–EtOH K2CO3
70
(1:1)
6
DMSO
DMF
K2CO3
K2CO3
K2CO3
K2CO3
0.003
0.003
0.003
0.003
Reflux
—
7
Reflux 100
Reflux 90
8
Toluene
MeCN
9
80
70
60
10
H2O–EtOH NaHCO3 0.003
100
(1:1)
11
12
13
14
15
16
17
18
H2O–EtOH NaOAc 0.003
70
70
70
70
70
70
70
70
20
25
25
—
—
30
70
100
(1:1)
H2O–EtOH KOH
(1:1)
0.003
0.003
—
H2O–EtOH N(Et)3
(1:1)
H2O–EtOH NaHCO3
(1:1)
H2O–EtOH —
(1:1)
0.003
H2O–EtOH NaHCO3 0.001
3.3 | Catalytic Activity of
Fe3O4@ChC@CNC‐PdII Complex in
Biphenyl Synthesis
(1:1)
H2O–EtOH NaHCO3 0.002
(1:1)
H2O–EtOH NaHCO3 0.004
To investigate the applicability of the CNC pincer palla-
dium complex for the synthesis of biaryls, we studied
the Suzuki coupling of p‐chlorobromobenzene with
phenylboronic acid under various conditions. As evident
(1:1)
aReactions conditions: p‐ClPhBr (1 mmol), PhB(OH)2 (1 mmol), base
(2 mmol), nanocatalyst, solvent (3.0 ml), 15 min.

RAFIEE AND HOSSEINI
7 of 10
TABLE 2 Suzuki cross‐coupling reaction of various aryl halidesa
Entry
ArX
Ar′B(OH)2
Time (min)
Yield (%)b
TON
TOF
1
PhBr
PhB(OH)2
10
98
97
92
96
91
97
98
91
97
90
97
96
95
92
98
90
93
92
40
490 ×104
485×104
460×104
480×104
455×104
485×104
490×104
455×104
485×104
450×104
485×104
480×104
475×104
460×104
490×104
450×104
465×104
460×104
200×104
2940×104
1940×104
613×104
823×104
455×104
647×104
980×104
607×104
970×104
900×104
970×104
640×104
475×104
153×104
245×104
225×104
116×104
92×104
2
p‐Cl‐PhBr
PhB(OH)2
15
3
p‐MeO‐PhI
p‐Me‐PhI
PhB(OH)2
45
4
PhB(OH)2
35
5
p‐MeOC‐PhBr
p‐NC‐PhBr
p‐Cl‐PhBr
PhB(OH)2
60
6
PhB(OH)2
45
7
p‐Me‐PhB(OH)2
p‐Me‐PhB(OH)2
p‐Me‐PhB(OH)2
p‐Me‐PhB(OH)2
p‐Me‐PhB(OH)2
p‐MeOC‐PhB(OH)2
p‐MeOC‐PhB(OH)2
p‐MeOC‐PhB(OH)2
m‐MeO‐PhB(OH)2
m‐MeO‐PhB(OH)2
3,4,5‐F‐PhB(OH)2
3,4,5‐F‐PhB(OH)2
PhB(OH)2
30
8
p‐MeOC‐PhBr
p‐NC‐PhBr
p‐MeO‐PhI
p‐Me‐PhI
45
9
30
10
11
12
13
14
15
16
17
18
19
30
30
p‐MeO‐PhI
p‐MeOC‐PhBr
p‐NC‐PhBr
p‐MeO‐PhI
p‐MeOC‐PhBr
p‐OHC‐PhBr
p‐MeOC‐PhBr
p‐NC‐PhCl
45
60
180
120
120
240
300
9 h
22×104
aReaction conditions: aryl halide (1 mmol), phenylboronic acid (1 mmol), NaHCO3 (2 mmol), Fe3O4@ChC@CNC‐PdII (0.003 g, 2 × 10−5 mol%), H2O–EtOH
(1:1) (3 ml), 70 °C.
bIsolated yields. Full conversions (100%) were achieved in all cases except aryl chlorides (entry 18).
(Table 2). A wide range of substrates with electron‐donat-
ing and electron‐withdrawing groups were used that
contained CN, CHO, COMe, Cl, OMe and Me groups on
the various aryl halides (iodide, bromide and chloride)
and F, COMe, OMe and Me groups on the arylboronic
acid. As is evident from the results, this catalytic system
is compatible with a wide range of functional groups.
All reactions except those involving aryl chlorides
afforded the corresponding biphenyls in excellent yields.
Also, in the investigation of the chemoselectivity of the
method, 4‐chlorobiphenyl was produced as the only
desired product using p‐chlorobromobenzene (Table 2,
entries 2 and 7) due to the lower reactivity of Cl as leaving
group.
To investigate the recyclability and reusability of the
catalyst, we carried out a set of catalytic recycling experi-
ments using the Suzuki coupling reaction of 1‐bromo‐4‐
chlorobenzene and phenylboronic acid under similar
conditions. After the completion of each cycle, the cata-
lyst was separated from the reaction mixture using an
external magnet and washed with ethanol to remove
residual product. Finally, it was dried and used in the
next run using fresh substrates. The examination of
Fe3O4@ChC@CNC‐PdII was repeated 13 times to evalu-
ate the catalyst recyclability and stability (Figure 8). The
results illustrate the excellent stability of the catalyst
under the reaction conditions. As shown in Figure 8,
the catalyst was reused ten times without observing any
loss of its catalytic activity. In this type of CNC pincer
complex the metal atom is even more tightly bound to
the ligand than in traditional pincer complexes with het-
eroatoms in the side arms, which imparts a particularly
high stability and durability for this type of complex.
100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10 11 12 13
Run number
Suzuki
cross‐coupling
reactions
using
FIGURE 8 Reusability of Fe3O4@ChC@CNC‐PdII catalyst

8 of 10
RAFIEE AND HOSSEINI
To determine the chemical structure of the reused
palladium leached from the catalyst to the filtrate and
also in the reaction mixture after the reusability experi-
ments was studied using ICP‐AES analysis. The results
showed that no palladium content was leached from the
surface into the filtrate. The robustness of this magnetic
CNC pincer complex prevents undesired leaching
processes.
To determine the nature of the catalytic species, we
performed a mercury poisoning test according to a
reported procedure for a chitosan‐supported heteroge-
neous Pd(II) catalyst.[47] The catalytic activity was sup-
pressed when excess amount of mercury (Hg:
nanocatalyst, XRD analysis was done after recyclability
experiments (Figure 9). The results confirm that the cata-
lyst retains its main structure during C─C coupling
reactions.
We also carried out a hot filtration test to investigate
the absence of the homogeneous palladium species which
is produced via leaching during the cross‐coupling reac-
tion. In a typical reaction, a mixture of 0.003 g of the
Fe3O4@ChC@CNC‐PdII catalyst in 3 ml of water–ethanol
(1:1) was prepared and left to stir at 70 °C for 15 min, and
then the catalyst was magnetically removed from the hot
reaction mixture. We found that the filtrate showed no
catalytic activity in the Suzuki cross‐coupling reaction of
1‐bromo‐4‐chlorobenzene and phenylboronic acid under
the optimal reaction conditions. The amount of
Pd
=
300:1) was added to
a
mixture of p‐
chlorobromobenzene and phenylboronic acid as a model
reaction. Also, addition of mercury during this cross‐cou-
pling reaction led to a loss of catalytic activity. Therefore,
mercury poisoned the catalyst, showing that the catalyst
had a heterogeneous nature.
Finally, a comparison of this protocol was performed
with recent reports describing the use of modified chito-
san, cellulose biopolymer‐supported palladium catalysts
and also magnetic and pincer‐type catalysts (Table 3,
entries 5 and 6). The reactions of 4‐iodotoluene (Table 3,
entries 1–7) or 4‐bromobenzonitrile (Table 3, entries
8–14) with phenylboronic acid were used for compari-
son as model reactions. This catalytic system was found
to be more active and efficient than the other reported
catalysts.
500
400
300
200
100
0
0
10
20
30
40
50
60
70
80
FIGURE 9 XRD patterns of reused catalyst (blue) and fresh
catalyst (red)
TABLE 3 Comparison of catalytic activity of Fe3O4@ChC@CNC‐PdII with that of other biopolymer‐supported catalysts in Suzuki cross‐
couplinga
Yield
Entry Catalyst (mol%)
Conditions
Time (%)
TON
TOF
Ref.
[48]
1
PdNPs@chitosan (0.1)
TBAB, 90 °C
H2O, 100 °C
5 h
3 h
95
66
950
190
[40]
[49]
[50]
[51]
[15]
2
Ch‐g‐mPEG350Pd(0) (0.5)
132
44
3
OCMCS‐SBL supported Pd catalyst (0.01) Solvent‐free, 50 °C, microwave
CS‐NNSB‐Pd(II) (6×10−3
4 min 54
5 min 38
5400
6333
180
81 818
79 162
90
4
)
Solvent‐free, 50 °C, microwave
5
Pd‐BIP‐γ‐Fe2O3@SiO2 (0.5)
DMF, 100 °C
2 h
90
6
SPIONs‐bis(NHC)‐Pd(OAc)2 (0.002)
Fe3O4@ChC@CNC‐PdII (2×10−5
DMF–H2O (1:2), 70 °C, microwave 4 min 92
46 000
48×105
94
660×103
7
)
H2O–EtOH (1:1), 70 °C
EtOH (95%), 80 °C
35 min 96
8220×103 This work
[32]
8
Pd‐Ch@SiO2 (1)
2 h
94
96
91
47
[52]
9
Cell‐Pd(0) (0.3)
TBAB, H2O, 100 °C
5.5 h
3.5 h
320
58.2
[53]
10
11
Cell‐AMP‐Pd (0.75)
EtOH (50%), 50 °C
121.3
18 000
34.7
[54]
Chitosan‐based pincer‐type Pd(II)
(OCS‐NS‐Pd(II)) (5×10−3
Solvent‐free, 50 °C, microwave
4 min 90
300×103
)
[55]
12
13
Chitosan‐pyridyl‐based Pd(II) (5×10−3
)
Solvent‐free, 50 °C, microwave
Solvent‐free, 50 °C, microwave
5 min 84
6 min 80
168 000 210×103
16 000
160×103
[56]
Cellulose Schiff base supported Pd(II)
(CL‐Sc‐Pd) (5×10−3
)
14
Fe3O4@ChC@CNC‐PdII (2×10−5
)
H2O–EtOH (1:1), 70 °C
45 min 97
4850×103 6467×103 This work
aReaction of 4‐iodotoluene with phenylboronic acid (entries 1–7) and reaction of 4‐bromobenzonitrile with phenylboronic acid (entries 8–14).

RAFIEE AND HOSSEINI
9 of 10
[15] M. Ghotbinejad, A. R. Khosropour, I. Mohammadpoor‐Baltork,
M. Moghadam, S. Tangestaninejad, V. Mirkhani, J. Mol. Catal.
A 2014, 385, 78.
4 | CONCLUSIONS
In summary, the synthesis and characterization of a sta-
ble and magnetic chitosan‐supported palladium CNC‐
type pincer complex have been reported. This well‐
defined complex showed excellent catalytic activity, recy-
clability, and air and moisture stability for the Suzuki
coupling reactions of a wide range of aryl halides and
arylboronic acids using a very low catalyst loading
(0.00002 mol% Pd). Due to the true heterogeneous nature,
high efficiency, good reusability and other unique proper-
ties of this nanocatalyst, we expect new prospects for its
application in other coupling reactions.
[16] V. M. Zende, C. Schulzke, A. R. Kapdi, Org. Chem. Front. 2015,
2, 1397.
[17] F. Churruca, R. SanMartin, B. Inés, I. Tellitu, E. Domínguez,
Adv. Synth. Catal. 2006, 348, 1836.
[18] A. Molnár, A. Papp, Sci. Technol. 2014, 4, 295.
[19] A. Dewan, P. Bharali, U. Bora, A. J. Thakur, RSC Adv. 2016, 6,
11758.
[20] S. Keshipour, N. Kalam Khalteh, Appl. Organometal. Chem.
2016, 30, 653.
[21] E. Guibal, Sep. Purif. Technol. 2004, 38, 43.
[22] E. Guibal, Prog. Polym. Sci. 2005, 30, 71.
ACKNOWLEDGEMENTS
[23] M. Lee, B. Y. Chen, W. Den, Appl. Sci. 2015, 5, 1272.
[24] G. Z. Kyzas, D. N. Bikiaris, Mar. Drugs 2015, 13, 312.
[25] A. E. I. Kadib, ChemSusChem 2015, 8, 217.
[26] A. Pestov, S. Bratskaya, Molecules 2016, 21, 330.
We gratefully acknowledge the partial financial support
received from the Research Council of Alzahra
University.
[27] J. Zhou, Z. Dong, H. Yang, Z. Shi, X. Zhou, R. Li, Appl. Surf.
Sci. 2013, 279, 360.
ORCID
[28] S. Keshipour, F. Ahmadi, B. Seyyedi, Cellulose 2017, 24, 1455.
Fatemeh Rafiee http://orcid.org/0000-0002-7987-600X
[29] M. Chtchigrovsky, A. Primo, P. Gonzalez, K. Molvinger, M.
Robitzer, F. Quignard, F. Taran, Angew. Chem. 2009, 121, 6030.
REFERENCES
[30] S. Kumar, N. Singhal, R. K. Singh, P. Gupta, R. Singh, S. L.
Jain, Dalton Trans. 2015, 44, 11860.
[1] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457.
[31] A. Affrose, P. Suresh, I. Abulkalam Azath, K. Pitchumani, RSC
Adv. 2015, 5, 27533.
[2] J. Wencel‐Delord, A. Panossian, F. R. Leroux, F. Colobert,
Chem. Soc. Rev. 2015, 44, 3418.
[32] S. Jadhav, A. Kumbhar, R. Salunkhe, Appl. Organometal.
Chem. 2015, 29, 339.
[3] G. Bringmann, T. Gulder, T. A. M. Gulder, M. Breuning, Chem.
Rev. 2011, 111, 563.
[33] T. Baran, I. Sargin, M. Kaya, A. Menteş, Carbohydr. Polym.
2016, 152, 181.
[4] F. M. Meyer, J. C. Collins, B. Borin, J. Bradow, S. Liras, C.
Limberakis, A. M. Mathiowetz, L. Philippe, D. Price, K. Song,
K. James, J. Org. Chem. 2012, (7), 3099.
[34] D. Lv, M. Zhang, Molecules 2017, 22, 150.
[5] S. Kappaun, C. Slugovc, E. J. W. List, Int. J. Mol. Sci. 2008, 9,
[35] Y. N. Gavhane, A. S. Gurav, A. V. Yadav, Biomed. Sci. 2013, 4,
1527.
312.
[6] J. Bao, W. D. Wulff, A. L. Rheingold, J. Am. Chem. Soc. 1993,
115, 3814.
[36] G. Li, Y. Jiang, K. Huang, P. Ding, J. Chen, J. Alloys Compd.
2008, 466, 451.
[7] W. A. Herrmann, C. P. Reisinger, M. Spiegler, J. Organometal.
Chem. 1998, 557, 93.
[37] L. Fan, C. N. Luo, M. Sun, X. J. Li, Colloids Surf., B 2012, 95, 42.
[38] L. Li, L. Fan, C. Luo, H. Duan, X. Wang, RSC Adv. 2014, 4,
[8] W. A. Herrmann, Angew. Chem. Int. Ed. 2002, 41, 1290.
24679.
[9] S. Díez‐González, N. Marion, S. P. Nolan, Chem. Rev. 2009, 109,
[39] S. S. Yi, D. H. Lee, E. Sin, Y. S. Lee, Tetrahedron Lett. 2007, 48,
3612.
6771.
[10] R. Zhong, A. C. Lindhorst, F. J. Groche, F. E. Kühn, Chem. Rev.
2017, 117, 1970.
[40] E. Sin, S. S. Yi, Y. S. Lee, J. Mol. Catal. A 2010, 315, 99.
[41] J. J. E. Hardy, S. Hubert, D. J. Macquarrie, A. J. Wilson, Green
Chem. 2004, 6, 53.
[11] D. Domyati, S. L. Hope, R. Latifi, M. D. Hearns, L. Tahsini,
Inorg. Chem. 2016, 55, 11685.
[42] T. Baran, Hacettepe J. Biol. Chem. 2016, 44, 307.
[12] A. R. Naziruddin, C. S. Lee, W. J. Lin, B. J. Sun, K. H. Chao, A.
[43] A. R. Hajipour, E. Boostani, F. Mohammadsaleh, RSC Adv.
2015, 5, 24742.
H. H. Chang, W. S. Hwang, Dalton Trans. 2016, 45, 5848.
[13] X. Y. Liu, H. B. Zhu, Y. J. Shen, J. Jiang, T. Tu, Chin. Chem.
Lett. 2017, 28, 350.
[44] A. Naghipour, A. Fakhri, Catal. Commun. 2016, 73, 39.
[14] C. Gao, H. Zhou, S. Wei, Y. Zhao, J. You, G. Gao, Chem.
Commun. 2013, 49, 1127.
[45] E. C. N. Lopes, K. S. Sousa, C. Airoldi, Thermochim. Acta 2009,
483, 21.

10 of 10
RAFIEE AND HOSSEINI
[46] X. Liu, Z. Ma, J. Xing, H. Liu, J. Magn. Magn. Mater. 2004, 270,
[54] T. Baran, A. Menteş, J. Mol. Struct. 2017, 1134, 591.
1.
[55] T. Baran, I. Sargin, A. Menteş, M. Kaya, Appl. Catal. A 2016,
523, 12.
[47] T. Baran, E. Açıksöz, A. Menteş, J. Mol. Catal. A 2015, 407, 47.
[48] P. Cotugno, M. Casiello, A. Nacci, P. Mastrorilli, M. M.
[56] N. Y. Baran, T. Baran, A. Menteş, Appl. Catal. A. 2017, 531, 36.
Dell'Anna, A. Monopoli, J. Organometal. Chem. 2014, 752, 1.
[49] T. Baran, T. Inanan, A. Menteş, Carbohydr. Polym. 2016, 145,
How to cite this article: Rafiee F, Hosseini SA.
CNC pincer palladium complex supported on
magnetic chitosan as highly efficient and recyclable
nanocatalyst in C─C coupling reactions. Appl
Organometal Chem. 2018;e4519. https://doi.org/
10.1002/aoc.4519
20.
[50] T. Baran, J. Mol. Struct. 2017, 1141, 535.
[51] S. Sobhani, Z. Zeraatkar, F. Zarifi, New J. Chem. 2015, 39, 7076.
[52] N. Jamwal, R. K. Sodhi, P. Gupta, S. Paul, Int. J. Biol.
Macromol. 2011, 49, 930.
[53] P. Hu, Y. Dong, X. Wu, Y. Wei, Front. Chem. Sci. Eng. 2016, 10,
389.