Assembly immobilized palladium(0) on carboxymethylcellulose/Fe3O4 hybrid: An efficient tailor-made magnetically catalyst for the Suzuki–Miyaura couplings

Article abstract of DOI:10.1002/aoc.3912

The Pd nanoparticles (Pd NPs) embedded on magnetically retrievable carboxymethylcellulose/Fe₃O₄ (Pd⁰@CMC/Fe₃O₄) organic/inorganic hybrid were prepared via the conventional simple process. The presence of the hydroxyl and carboxyl groups within the framework of the magnetic hybrid enables the facile preparation and stabilization of Pd NPs in this organic/inorganic hybrid. This hybrid catalyst was very effective in the Suzuki–Miyaura reaction of a variety of aryl halides with arylboronic acid to afford excellent product yields. The catalyst showed good stability and could be easily recovered with an external magnetic field and reused for several times without a significant loss in its catalytic activity. Furthermore, the Pd⁰@CMC/Fe₃O₄ hybrid catalyst was fully characterized by UV–Vis, FT–IR, XRD, SEM, EDX, TEM, XPS and TGA techniques. The hot filtration test suggests that a homogeneous mechanism is operative in Suzuki–Miyaura reaction.

Full text of DOI:10.1002/aoc.3912

Received: 13 January 2017
DOI: 10.1002/aoc.3912
Revised: 2 May 2017
Accepted: 10 May 2017
F U L L PA P E R
Assembly immobilized palladium(0) on carboxymethylcellulose/
Fe3O4 hybrid: An efficient tailor‐made magnetically catalyst for
the Suzuki–Miyaura couplings
Zhuan Zhang | Yizong Zhang | Xiaoping Liu | Binbin Shen | Tianzhu Zhang | Yiqun Li
Department of Chemistry, Jinan University,
Guangzhou 510632, China
The Pd nanoparticles (Pd NPs) embedded on magnetically retrievable carboxymeth-
ylcellulose/Fe3O4 (Pd0@CMC/Fe3O4) organic/inorganic hybrid were prepared via
the conventional simple process. The presence of the hydroxyl and carboxyl groups
within the framework of the magnetic hybrid enables the facile preparation and sta-
bilization of Pd NPs in this organic/inorganic hybrid. This hybrid catalyst was very
effective in the Suzuki–Miyaura reaction of a variety of aryl halides with arylboronic
acid to afford excellent product yields. The catalyst showed good stability and could
be easily recovered with an external magnetic field and reused for several times
without a significant loss in its catalytic activity. Furthermore, the Pd0@CMC/
Fe3O4 hybrid catalyst was fully characterized by UV–Vis, FT–IR, XRD, SEM,
EDX, TEM, XPS and TGA techniques. The hot filtration test suggests that a homo-
geneous mechanism is operative in Suzuki–Miyaura reaction.
Correspondence
Yiqun Li, Department of Chemistry, Jinan
University, Guangzhou 510632, China
Email: tlyq@jnu.edu.cn
Funding information
National Natural Science Foundation of
China, Grant/Award Number: 21372099 and
21072077; Natural Science Foundation of
Guangdong Province, Grant/Award Number:
10151063201000051 and
8151063201000016
KEYWORDS
carboxymethylcellulose, catalyst, magnetic nanohybrid, palladium nanoparticles, Suzuki–Miyaura reaction
1 | INTRODUCTION
reasonable and feasible to immobilize a catalytic Pd(II) com-
plex on the heterogeneous bed to mitigate these problems.
The Suzuki–Miyaura reactions[1–3] provide an attractive and
efficient route to construct Csp2–Csp2 bond for the synthesis
of a variety of important chemicals or structural motif for
their applications in pharmaceuticals and advanced materials.
Traditionally, palladium is one of the most commonly
employed catalysts which can be performed under both
homogeneous and heterogeneous conditions.[4] In general,
the wide use of homogeneous Pd catalysts is based on Pd(II)
complexes[5,6] such as phosphanes, N–heterocyclic carbenes,
oxime carbapalladacycle and imidazolium, and so on. They
display high catalytic activity and selectivity, excellent versa-
tility, rapid reaction rates, and large turnover numbers. The
major disadvantages of such catalytic systems are the recov-
ery of the catalyst as well as the instability and toxicity of
ligands. Moreover, aggregation and precipitation of palla-
dium metal in the homogeneous systems always lead to lost
activity of the catalysts. This fact rationalizes that it is
However, the catalytic sites in heterogeneous catalysts are
not as accessible as in a homogeneous system, and thus the
activity of the catalyst is usually reduced.[6,7] Consequently,
a semi‐heterogeneous catalysis[8] combining the characteris-
tics of heterogeneous catalysis (ease of catalyst separation
and recovery) with those of homogeneous catalysis (high
activity and selectivity) is the goal that may be achieved by
Pd NPs. Pd NPs, which possess several advantages such as
excellent activity, greater selectivity, and high stability over
conventional catalyst systems, partially due to their
large surface‐tovolume ratios,[8–10] are widely used for C–C
cross coupling reactions.[11–13] Unfortunately, Pd NPs are
unstable and easily aggregate and precipitate to bulk metal
and,
therefore,
decrease
the
catalytic
activity.
Moreover, isolation and recovery of these tiny nanocatalysts
from the reaction mixture are tedious. Generally, the aggrega-
tion of Pd NPs can be avoided by using suitable stabilizers or
Appl Organometal Chem. 2017;e3912.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3912

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ZHANG ET AL.
supporting materials.[14] In fact, stability, reactivity, and reus-
ability of Pd NPs are highly depended on the type of selected
materials using immobilized matrix. Some Pd NPs catalysts
which are immobilized onto inorganic supports (such as car-
bon, carbon nanotubes, different metal oxides, silica gel and
modified silica gel, hydroxyapatite, molecular sieves, etc.)
and organic supports (such as polystyrene, polyaniline, poly-
vinylpyrrolidone, hydrogel, biopolymer, and so forth) have
been reviewed.[15–17] The design and preparation of novel
hybrid catalyst[18–20] with superior activities and unique
potential application in catalysis have attracted extensive
attention in the academic and industrial community in recent
years. Although there has been some tremendous progress in
this area in recent years, a number of problems still remain to
be addressed. One of the biggest challenges is catalyst recov-
ering and reuse when the size of support is decreased to the
nanometer scale. The separation of nanocatalysts from the
reaction mixture is almost impossible merely dependent on
the use of the filter, high‐speed centrifugation, or precipita-
tion. This is the major reason why magnetic nanoparticles
(MNPs) are used as viable alternatives to conventional
supporting materials for immobilization of catalyst. The
unique paramagnetic character of MNPs is that the catalyst
based on them can be easily recovered from the reaction mix-
ture simply by using an external magnet, thus eliminating the
necessity of traditional separation steps. Another big chal-
lenge is to develop efficiently immobilized systems that
could simultaneously fulfill the demand of achieving high
catalytic activity.
Fe3O4 MNPs have emerged as smart materials for hetero-
geneous catalyst due to their intrinsic properties such as para-
magnetic character, high surface area, good chemo‐stability,
and low toxicity and biocompatible. Bare Fe3O4 MNPs mate-
rials can be directly used for immobilization of Pd nanoparti-
cles,[21–23] but in most cases, leaching of active species is
unavoidable for this material, so the reactivity of catalyst is
decreased. The surface of Fe3O4 MNPs can be post‐function-
alized by organic moieties using a chemical process to
improve its applicability as support in preparation of Pd
NPs catalysts. Recently, more effort has been focused on
the surface post‐modification of MNPs with suitable ligands
to anchor the catalytic active species.[24] However, this proto-
col has some defects such as multistep synthetic processes
using expensive reagents and solvents, and relatively low
loading of catalysts. In order to overcome these drawbacks,
magnetic organic/inorganic hybrid materials may be an effec-
tive alternative for the post‐functionalization of Fe3O4. One
of the most abundant polyhydroxyl materials, which have
been widely employed for immobilization and stabilization
of Pd NPs via the chelation with transition metals and
SCHEME 1 Schematic pathway for the preparation of the magnetic palladium hybrid catalyst

ZHANG ET AL.
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hydroxyl groups or carboxyl groups[25] is natural hydroxyl
biopolymer and its derivatives such as cellulose, carboxy-
methylcellulose, chitosan, starch. When ligated moieties such
as polyhydroxyl or carboxyl groups are hybridized with
Fe3O4 MNPs, most of these problems can be settled. In light
of this, we have reported highly efficient catalysts for
Suzuki–Miyaura couplings based on immobilization of Pd
NPs on cellulose or carboxymethylcellulose in our previous
work. Sodium carboxymethylcellulose (CMC–Na) carrying
a tremendous number of carboxymethyl groups (−CH2–
COO−Na+) has excellent cation exchange capacity.[26,27]
Considering this characteristic, CMC–Na has been reported
to serve as a template for the preparation of magnetic Fe3O4
organic/inorganic hybrid.
FIGURE 1 FT‐IR spectra of CMC–Na (a), Na–CMC/Fe3O4 (b), and
Pd0@CMC/Fe3O4 (c)
2 | RESULTS AND DISCUSSION
2.1 | Preparation and characterization of
Pd0@CMC/Fe3O4 catalysts
The magnetic nanocatalyst consisting of Pd NPs on a CMC/
Fe3O4 hybrid was prepared in two easy steps. In the first step,
the Na–CMC/Fe3O4 NPs hybrid was prepared via two‐step
metathesis and one‐step oxidation procedures according to
our previous work.[28] In the second step, the as‐prepared
Na–CMC/Fe3O4 hybrid was treated with Pd (II) aqueous
solution for overnight based on the property of CMC–Na
being capable of exchanging with Pd(II). The obtained
PdII@CMC/Fe3O4 hybrid catalyst was filtered off and
washed thoroughly with water and excessive ethanol. The
Pd0@CMC/Fe3O4 organic/inorganic hybrid catalyst thus
obtained via the reduction of Pd2+ ions with EtOH to form
the Pd(0) element, which assembled and nucleated on the
CMC/Fe3O4 hybrid supports. Scheme 1 displays the sche-
matic illustration of the formation of the Pd0@CMC/Fe3O4
NPs hybrid consisting of superparamagnetic Fe3O4 nanopar-
ticles, CMC and Pd(0) species.
FIGURE 2 XRD patterns of bare Fe3O4 (a), Pd0@CMC/Fe3O4 (b)
Then, the as‐prepared hybrid catalyst was fully character-
ized by FT‐IR, ICP‐AES, XRD, SEM, EDX, TEM, and TGA
techniques.
Figure 1 shows the FT‐IR spectra for CMC–Na, Na–
CMC/Fe3O4, and Pd0@CMC/Fe3O4 hybrid. A strong and
broad absorption band at 3000–3750 cm−1 is related to the
−OH group stretching vibrations. In curve b and c, the strong
vibration of Fe–O bonds at 580 cm−1 or 588 cm−1 indicate
the presence of Fe3O4.[29] In curve a, the characteristic peaks
at 1615 cm−1 and 1423 cm−1 are assigned to the carboxylate
(−COO−Na+) asymmetric and symmetric stretching
vibration.[30,31] The absorption peaks at 1593 cm−1 and
1410 cm−1 shifted to lower wavenumbers in curve b confirms
the hybridization of CMC and Fe3O4. Furthermore, these car-
boxylate characteristic peaks in curve c shift to 1628 cm−1
FIGURE 3 UV/Vis spectra of PdCl2 (a), Pd0@CMC/Fe3O4 (b)

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ZHANG ET AL.
FIGURE 4 FESEM images of fresh catalyst (a), (b) and recovered catalyst (c), (d) at the same magnifications
and 1409 cm−1, which indicated the coordination of palla-
dium with carboxylate groups.
peaks are in perfect agreement with the standard structure
of Fe3O4 nanoparticles (curve a). The peaks at 2θ of 40.1,
46.7° and 68.1° correspond to the diffraction of (111),
(200) and (220) of the Pd nanoparticles.[29] The XRD pattern
suggests that Pd0 is successfully immobilized on the hybrid.
The UV–Vis spectrum of Pd0@CMC/Fe3O4 hybrid was
also studied. According to the literature results, the UV–Vis
spectrum of PdCl2 revealing a peak at 280 nm refers to the
The crystallinity of the resulting products was investi-
gated by X‐ray diffraction (XRD). Figure 2 shows the XRD
pattern of the Pd0@CMC/Fe3O4. The diffraction peaks at
2θ of 30.1°, 35.4°, 43.1°, 53.4°, 57°, and 62.6° are assigned
to the diffraction of (220), (311), (400), (422), (511) and
(440) of the Fe3O4 (JCPDS 89–3854).[29] All diffraction
FIGURE 5 EDS data for the fresh catalyst

ZHANG ET AL.
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FIGURE 6 SEM images of Pd0@CMC/Fe3O4 shows the presence of C, O, Fe, Pd atoms in the catalyst
existence of Pd(II) (Figure 3a).[32] However, there was not
any obvious peak at 280 nm in the UV–Vis spectrum of
Pd0@CMC/Fe3O4 hybrid, which indicated a major reduction
of Pd(II) to Pd nanoparticles in the catalyst.
The morphology of the fresh catalyst and reused catalyst
was characterized by Field Emission Scanning Electron
Microscope (FE‐SEM). FE‐SEM images in Figure 4 are pre-
sented at two different magnifications (10 μm and 2 μm). FE‐
FIGURE 7 TEM images of fresh catalyst (a), nanoparticle diameter histogram (b), and recovered catalyst (c)

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ZHANG ET AL.
FIGURE 8 XPS images of fresh catalyst (images of a, b, c) and recovered catalyst (images of d, e, f)
SEM images clearly show a flocculated morphology with
porous nature, which facilitates the better mass transfer and
enlarges its contact area. Hence porous support increases cat-
alytic activity and also avoids Pd leaching. Furthermore, the
morphology of recovered catalyst remained intact after three
recoveries.
Figure 6 shows a representative FE‐SEM image and cor-
responding elemental maps for the synthesized catalyst. It
clearly exhibited that metallic Pd nanoparticles are well dis-
persed in the catalyst. At the same time, the selected‐area ele-
mental analysis indicates the existence of C, O, Fe and Pd
throughout hybrid in a homogeneous manner.
The presence of Pd species in the catalyst can be also con-
firmed by energy‐dispersive X‐ray spectroscopy (EDS)
coupled with SEM analysis (Figure 5). The EDS of fresh cat-
alyst clearly indicates the presence of C, O, Fe and Pd in the
organic/inorganic hybrid. Obviously, the presence of these
elements implies the existing of Pd, CMC, and Fe3O4 in the
hybrid catalyst.
In order to get insight into the morphology of the hybrid,
the field emission transmission electron microscopy (FE‐
TEM) images of the fresh and used Pd0@CMC/Fe3O4 were
recorded (Figure 7) showing the formation of quasi‐spherical
nanoparticles (Figure 7a). The size distribution plot (Figure 7
b) obtained from TEM measurements show the average parti-
cle size is located around 62 nm. (Figure 7b). Furthermore,

ZHANG ET AL.
7 of 11
284.78 eV, which indicates the existence of CMC. The
binding energies of O1s in the fresh catalyst and reused
catalyst are about 530.08 eV and 531.18 eV respectively,
which proves the interaction between Pd NPs and CMC.
It could also be found that the existence of two intense
doublets at 335.38 and 340.58 eV related to Pd(0) and
peaks at 337.78 and 342.98 eV related to Pd(II) corre-
sponding to Pd 3d5/2 and Pd 3d3/2 in the fresh catalyst
respectively, which indicates that about 64% of palladium
particles exist in the form of Pd(0). Nevertheless, only
strong peaks at 335.28 eV and 340.68 eV corresponding
to Pd 3d5/2 and Pd 3d3/2 can be seen in the reused cata-
lyst, which shows the main existence of Pd NPs after
the reaction.[33,34]
FIGURE 9 TGA diagram of catalyst and CMC–Na
Thermogravimetric analysis (TGA) was used to evaluate
the thermal stability of the catalyst, which was conducted in
nitrogen atmosphere varying from 25 to 700 °C. As can be
seen from the TGA plot in Figure 9, there are two‐step ther-
mal decomposition. The first weight loss occurred around
100 °C is attributed to the removal of loosely physically
adsorbed water. Then the main weight loss began near
200 °C due to the decomposition of CMC. By comparison
with the TGA of CMC–Na, the stability of Pd0@CMC/
Fe3O4 is less than that of CMC–Na.
the preserve of the morphology and the size of the reused cat-
alyst after the third run are observed (Figure 7c) by compar-
ison with the fresh catalyst.
XPS was used to investigate the valence state of the
fresh catalyst and reused catalyst. As shown in Figure 8,
it can be seen that the binding energies of C1s in the fresh
catalyst are the same as the reused catalyst around
TABLE 1 Optimization of the Suzuki‐Miyaura Reactions Conditiona
Entry
1
Solvent (v/v)
EtOH/H2O (75/25)
EtOH
Base
K2CO3
Catalyst (mol%)
Temp (°C)
Time [min]
Yield [%]
92
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.3
0.6
1.2
1.5
0.9
0.9
0.9
78
78
78
78
78
78
78
78
78
78
78
78
78
78
78
78
78
60
40
rt
15
20
30
30
30
30
30
50
30
20
20
30
30
30
15
15
15
30
120
480
2
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
87
3
MeOH
78
4
DMF
77
5
H2O
65
6
CH3CN
70
7
DMSO
76
8
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
EtOH/H2O (75/25)
75
.
9
Na3PO4 12H2O
Cs2CO3
84
10
11
12
13
14
15
16
17
18
19
20
82
.
K3PO4 3H2O
84
CH3ONa
NaOH
80
80
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
79
90
92
91
80
60
45
aReaction conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), base (2 mmol), catalyst (0.9 mol% of Pd), solvent (5 mL) at specific temperature.

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ZHANG ET AL.
2.2 | Catalytic performance of Pd0@CMC/
Fe3O4 hybrid in Suzuki–Miyaura reaction
The effects of the catalyst amount are also investigated.
As can be seen from Table 1, the yield of the cross‐cou-
pling product increased with the increase of catalyst. The
highest yield of 92% was obtained in the presence of
0.9 mol% of Pd (Table 1, entry 1). It is observed that
increasing the amount of catalyst from 0.9 to 1.2, even to
1.5 mol%, the yield of desired product does not change sig-
nificantly. Besides, upon decreasing quantity of catalyst
from 0.9 to 0.6, and even to 0.3 mol%, the yield of the
product decreases from 92 to 90, and 79% in prolonging
reaction time, respectively. The effect of reaction tempera-
ture on the model reaction was also explored. It is clearly
showed that the yields of the product significantly
decreased with the decrease of temperature. We have
concluded that the best result was obtained when the model
To evaluate the effect of base, catalyst loading, solvent, and
temperature, the cross‐coupling of p‐iodoanisole and phenyl
boronic acid was conducted as a model reaction.
Initially, the influence of different bases was investi-
gated on the model reaction in the aqueous ethanol
(EtOH/H2O, v/v = 75/25) at reflux. Among the explored
bases, K2CO3 was found to be the top one to afford the
highest yields of 92%, respectively (Table 1, entry 1). Sol-
vents play a crucial role in the Suzuki–Miyaura coupling
reaction. Screening of solvents indicated that the mixed sol-
vent of EtOH/H2O (v/v = 75/25) is the best choice for this
catalytic system, which makes this reaction quite efficient.
TABLE 2 The Suzuki–Miyaura Coupling of Aryl Halide with Arylboronic Acida
Entry
1
R1
4‐MeO
4‐MeO
4‐MeO
4‐MeO
4‐MeO
4‐Me
4‐NO2
4‐NO2
4‐NO2
4‐NO2
4‐NO2
H
R2
X
I
Time [h]
0.25
0.25
0.25
0.25
0.25
0.50
0.25
0.25
0.25
0.25
0.25
0.5
Yield [%]
92
Product
H
a
b
c
d
e
f
2
4‐MeO
4‐Me
4‐F
4‐CHO
H
I
93
3
I
90
4
I
92
5
I
91
6
I
83
7
H
I
95
g
h
i
8
4‐MeO
4‐Me
4‐F
4‐CHO
H
I
96
9
I
85
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
I
96
j
I
92
k
l
I
80
H
4‐MeO
4‐Me
4‐F
4‐CHO
H
I
0.5
92
a
f
H
I
0.5
85
H
I
0.5
87
m
n
o
p
q
r
H
I
0.5
85
3‐NO2
3‐NO2
4‐NH2
4‐NH2
4‐NO2
4‐NO2
4‐NO2
4‐NO2
4‐NO2
4‐MeO
4‐MeO
4‐Me
I
0.5
94
4‐MeO
H
I
0.25
0.5
96
I
90
4‐MeO
H
I
0.5
92
Br
Br
Br
Br
Br
Br
Br
Br
1.0
93
g
h
i
4‐MeO
4‐Me
4‐F
4‐CHO
H
1.0
92
1.0
90
1.0
92
j
1.0
89
k
a
b
c
1.0
88
4‐MeO
4‐MeO
1.0
90
1.0
80
aReaction conditions: aryl halide (1 mmol), phenylboronic acid (1.2 mmol), K2CO3 (2 mmol), catalyst (0.9 mol % of Pd), EtOH/H2O (v/v = 75/25, 5 mL) at 78 °C.
bIsolated yields

ZHANG ET AL.
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reaction was carried out with 0.9 mol % of the catalyst
using K2CO3 as a base in the aqueous ethanol (EtOH/
H2O, v/v = 75/25) at reflux.
To explore the scope and generality of the catalyst, the
optimized protocol was applied for reactions of a variety of
substituted aryl halides with arylboronic acids. The results
are presented in Table 2. In all cases, both activated and
deactivated aryl iodides and aryl bromides were completely
converted into the corresponding biaryls in 80–96% yields
within 15 min–1 h. Aryl iodides possessing either electron‐
withdrawing or electron‐donating group produced
the corresponding biaryls in good yields, whereas aryl bro-
mide required prolonging time in order to obtain excellent
yields. Notably, the electronic effects (electron donating or
electron withdrawing) of the substituents of the arylboronic
acids had a negligible influence on reactivity.
FIGURE 11 Recycling and reuse of Pd0@CMC/Fe3O4 in the
Suzuki‐Miyaura reaction
three runs with slightly agglomerate, which implies the
soluble and active Pd(0) species redeposited onto the catalyst
to form slight larger Pd(0) nanoparticls at the end of the
catalytic reaction.
2.3 | Recyclability of the catalyst and
characterization of the used catalyst
One crucial for practical application of magnetic catalyst is
convenient recovery, reusability, stability, and leaching. For
this propose, the reusability of the catalyst was investigated
using the model reaction. The catalyst was separated by exter-
nal magnet after each run (Figure 10), washed adequately
with ethyl acetate, dried, and applied in subsequent runs. It
is found that the catalyst can be reused at least six consecutive
runs without significant loss of its activity (Figure 11). This
catalyst demonstrated great thermal stability with high activ-
ity at reflux temperatures. The FE‐SEM (Figure 4b) image of
the used catalyst after the reaction under thermal conditions
indicated that the surface morphology of the magnetic hybrid
nanocatalyst was not changed. The FE‐TEM (Figure 7c)
image showed the morphology and size of the catalyst after
2.4 | Homogenous mechanism for Suzuki–
Miyaura reaction
To determine the homogeneous/heterogeneous nature of the
catalytic system, we have also performed the hot filtration
test[6] using model reaction. During this test, the catalyt was
removed from the reaction mixture by external magnet after
5 min, and the reaction was then allowed to further react till
the completion in 83% product yield, indicating that catalyti-
cally active Pd species remained in the filtrate. To further
confirm the homogeneity of the catalytic system, potential
Pd leaching into the reaction mixture was also measured with
ICP‐AES analysis. The analysis result showed that the Pd
concentration in the reaction solution after one run was
9.4 × 10−4 mmol/l, which corresponds to around 0.20% of
the starting Pd‐amount. Both findings suggest that the cata-
lyst is characteristic homogeneous in nature, and the soluble
Pd(0) species or soluble Pd(0) nanoparticle clusters are the
true catalytic species.
Based on the above‐mentioned hot filtrate test, ICP anal-
ysis, and the previous reports, we propose a tentative pathway
for this transformation (Scheme 2). The mechanism by which
this occurs involves the generation of a soluble, catalytically
active Pd(0) species that is released from and redeposited
onto the catalyst to form slight larger Pd(0) nanoparticles
after the reaction (Figure 7). The first step is an oxidative
addition, which the leaching active Pd(0) species inserts into
the aryl halide bond. The last step in all coupling reactions is
the regeneration and redeposition of Pd(0) species on the sur-
face of the magnetic hybrid by reductive elimination of the
Pd(II) compound in the presence of a base.[35]
FIGURE 10 Pd0@CMC/Fe3O4 dispersed in the reaction mixture (a),
the magnetic isolation of the catalyst by a magnet (b)

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ZHANG ET AL.
SCHEME 2 Plausible mechanism for the Suzuki‐Miyaura coupling
Melting points were measured by an Electrothermal X6
microscopic digital melting point apparatus. Flourier
transform infared spectra (FT‐IR) were recorded on a Nicolet
6700 FT‐IR spectrometer using KBr pellet. X‐Ray Powder
Diffraction (XRD) data were collected on an MSALXRD2
diffractometer using Cu Ka radiation in a range of Bragg's
angles (10–80°). Scanning electron microscopy (SEM) was
conducted with a Philips XL 30ESEM instrument. Transmis-
sion electron microscopy (TEM) was obtained with a Philips
Tecnai instrument. Thermogravimetric analysis (TGA) was
operated on a Netzsch STA449F3 in the range of 25–700 °
C under nitrogen atmosphere. 1H NMR spectra were
recorded on a Bruker‐300 Avance Spectrometer with CDCl3
as solvent and TMS as internal standard. The elemental Pd
content of the catalyst was determined by inductively
coupled plasma‐atomic emission spectrometry (ICP‐AES)
using Perkin Elmer Optima 2000 DV.
3 | CONCLUSION
In summary, a novel magnetic organic/inorganic hybrid
materials (CMC/Fe3O4) supported Pd nanoparticles
(Pd0@CMC/Fe3O4) was prepared by a simple and low‐cost
approach without using any expensive organosilane. The as‐
synthesized Pd0@CMC/Fe3O4 hybrid exhibited excellent
catalytic activities for Suzuki–Miyaura cross‐coupling reac-
tions in excellent yields under aerobic conditions. The high
catalytic activity of the catalyst can be attributed to the coor-
dination with both carboxyl groups and free hydroxyl groups
within the magnetic CMC/Fe3O4 hybrid, which prevents the
agglomeration of Pd NPs. The magnetic hybrid catalyst was
easily separated by application of an external magnetic field
and could be recycled at least six times without significant
loss of its reactivity, which makes it an attractive catalytic
system for the coupling reaction under mild condition. There-
fore, it is believed that this synthetic protocol described here
would greatly contribute to an environmentally greener and
safer process.
4.2 | Preparation of Pd0@CMC/Fe3O4
magnetic catalyst
PdCl2 aqueous solution (0.60 mmol PdCl2) was added into
100 ml aqueous solution dispersed Na–CMC/Fe3O4 (1 g)
with constantly stirring at room temperature for 24 h. The
resulting solid was separated from the mixture with external
magnetic field and washed successively with deionized
water and anhydrous ethanol thoroughly, then dried in
vacuum to constant weight to provide Pd0@CMC/Fe3O4 as
4 | EXPERIMENTAL
4.1 | Chemicals and characterization
Sodium carboxymethylcellulose (CMC–Na, Mw 250,000)
and other chemicals were purchased from commercial
sources and used as received without further purification.
Na–CMC/Fe3O4 hybrid was prepared with a slight modifica-
tion according to our previous work.[28]
a
powder. The Pd content was determined to be
0.46 mmol/g by ICP‐AES.

ZHANG ET AL.
11 of 11
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4.3 | General procedure for the catalytic
Suzuki–Miyaura reaction
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The aryl halide (1 mmol), arylboronic acid (1.2 mmol),
K2CO3 (2 mmol), and a catalytic amount of Pd0@CMC/
Fe3O4 catalyst (0.9 mol% of Pd) were added to 5.0 ml aque-
ous ethanol (EtOH/H2O, v/v = 75/25). The reaction mixture
was stirred under reflux condition for a specific time. The
progress was tracked by TLC. After completion of the reac-
tion, ethyl acetate was added to the flask and the magnetic
catalyst was collected by an external magnet, washed with
ethyl acetate thoroughly, and dried in air for the next run.
The organic phase was washed with brine and dried over
anhydrous Na2SO4. The product was obtained after removal
of the organic solution using a rotary evaporator. The desired
pure products were further purified by recrystallization with
ethanol/H2O mixed solvent. All the products are known and
1H NMR data were found to be identical to those reported
in the literature.
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ACKNOWLEDGEMENTS
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We are grateful to the National Natural Science Foundation of
China (Nos. 21372099 and 21072077), Natural Science Foun-
dation of Guangdong Province (Nos. 10151063201000051
and 8151063201000016) for financial support.
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SUPPORTING INFORMATION
Additional Supporting Information may be found online in
the supporting information tab for this article.
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How to cite this article: Zhang Z, Zhang Y, Liu X,
Shen B, Zhang T, Li Y. Assembly immobilized
palladium(0) on carboxymethylcellulose/Fe3O4
hybrid: An efficient tailor‐made magnetically catalyst
for the Suzuki–Miyaura couplings. Appl Organometal
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