Nano-Fe3O4@SiO2 supported Pd(0) as a magnetically recoverable nanocatalyst for Suzuki coupling reaction in the presence of waste eggshell as low-cost natural base

Article abstract of DOI:10.1016/j.tet.2017.05.054

In this study, a simple and efficient protocol was used for the synthesis of the nano-Fe₃O₄@SiO₂ supported Pd(0) (Fe₃O₄@SiO₂-Pd). SiO₂ nanoparticles were prepared by the simple method from rice husk biomass as the source of biosilica. The Fe₃O₄@SiO₂-Pd was characterized by a series of techniques such as SEM, EDS, XRD, TEM, ICP-AES, FT-IR and VSM. The Fe₃O₄@SiO₂-Pd was used as a magnetically recoverable nanocatalyst for Suzuki coupling reaction in the presence of waste eggshell as low-cost solid base. The present method has significant advantages, such as use of natural and waste materials, use of an inexpensive catalyst, simple experimental procedure and low catalyst loading. In addition, the magnetically recoverable nanocatalyst can easily be recovered from the reaction system by using an external magnet and reused several times with insignificant loss of catalytic activity.

Full text of DOI:10.1016/j.tet.2017.05.054

Accepted Manuscript
Nano-Fe O @SiO supported Pd(0) as a magnetically recoverable nanocatalyst for
3
4
2
Suzuki coupling reaction in the presence of waste eggshell as low-cost natural base
Ardeshir Khazaei, Marzieh Khazaei, Mahmoud Nasrollahzadeh
PII:
S0040-4020(17)30540-9
10.1016/j.tet.2017.05.054
TET 28720
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 8 October 2016
Revised Date: 11 May 2017
Accepted Date: 12 May 2017
Please cite this article as: Khazaei A, Khazaei M, Nasrollahzadeh M, Nano-Fe O @SiO supported
3
4
2
Pd(0) as a magnetically recoverable nanocatalyst for Suzuki coupling reaction in the presence of waste
eggshell as low-cost natural base, Tetrahedron (2017), doi: 10.1016/j.tet.2017.05.054.
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Nano-Fe O @SiO supported Pd(0) as a
3
4
2
magnetically recoverable nanocatalyst for
Suzuki cross-coupling reaction in the
presence of waste eggshell as low-cost
natural base
Ardeshir Khazaei*, Marzieh Khazaei and Mahmoud Nasrollahzadeh

ACCEPTED MANUSCRIPT
Tetrahedron
1
TETRAHEDRON
Pergamon
Nano-Fe O @SiO supported Pd(0) as a magnetically recoverable
3
4
2
nanocatalyst for Suzuki coupling reaction in the presence of
waste eggshell as low-cost natural base
*,a
a
b,c
Ardeshir Khazaei , Marzieh Khazaei and Mahmoud Nasrollahzadeh
a
Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
b
Department of Chemistry, Faculty of Science, University of Qom, Qom 3716146611, Iran
c
Center of Environmental Researches, University of Qom, Qom, Iran
Abstract—In this study, a simple and efficient protocol was used for the synthesis of the nano-Fe O @SiO supported Pd(0)
3
4
2
(
Fe O @SiO -Pd). SiO nanoparticles were prepared by the simple method from rice husk biomass as the source of biosilica. The
3 4 2 2
Fe O @SiO -Pd was characterized by a series of techniques such as SEM, EDS, XRD, TEM, ICP-AES, FT-IR and VSM. The
3
4
2
Fe O @SiO -Pd was used as a magnetically recoverable nanocatalyst for Suzuki coupling reaction in the presence of waste eggshell as
3
4
2
low-cost solid base. The present method has significant advantages, such as use of natural and waste materials, use of an inexpensive
catalyst, simple experimental procedure and low catalyst loading. In addition, the magnetically recoverable nanocatalyst can easily be
recovered from the reaction system by using an external magnet and reused several times with insignificant loss of catalytic activity.
show high activity in addition to being easily recovered,
1
. Introduction
separated, and reused in reactions are the ideal catalyst
11
from a “green chemist's” point of view. Especially Fe O
3
4
Palladium-catalyzed Suzuki coupling reaction of aryl
halides with arylboronic acids is one of the most valuable
synthetic methods for preparation of symmetric and
nanoparticles have attracted many attentions because of
their unique properties.
12
1
nonsymmetric biaryls, which has been extensively used in
In this study, in order to develop the use of an
environmentally friendly catalyst, we decided to introduce
Rice-husk as a suitable and naturally support for
stabilization of palladium magnetic nano-particles
2
3
4
the synthesis of pharmaceuticals, ligands, polymers, and
5
advanced materials. Many of the palladium catalysts have
been used as homogeneous catalysts for Suzuki coupling
6
reaction. Beside the advantages of homogeneous catalytic
1
3
systems, they could not be used for the large-scale
applications in liquid phase reactions. It causes greater
difficulties such as purification of the final product,
recycling of the catalyst and deactivation by aggregation
into palladium particles. Activity and recovery in catalysis
science are two important parameters. Hence, homogenous
catalysts are not acceptable from a “green chemist's” point
Rice-husk is considered as an agriculture waste material.
It has become a source for preparation of elementary
1
4
15
silicon and a number of silicon compounds, especially
1
6
17
17b
silica , silicon carbide and silicon nitride. So we used
Rice-husk as a source of silica (Scheme 1). SiO2
nanoparticles were prepared and used for synthesis of nano-
Fe O @SiO -Pd (Scheme 2). Eggshell, a plentiful natural
3
4
2
7
of view. Some heterogeneous palladium catalysts show
food source, is consumed worldwide because it contain
essential amino acids and minerals. Most of the eggshell
waste is commonly disposed without any pretreatment.
Eggshell is totally biodegradable, recyclable and
lower reactivity than homogeneous ones because of
8
leaching of palladium from the supports but can be
recycled and recovered. Thus, there is a need to design of
new heterogeneous catalysts that can retain the activities
and selectivities of homogeneous catalysts. Nano science
enables us to scale down the size of particles and make
18
biocompatible. Eggshells are included of a network of
protein fibers, associated with crystals of calcium
carbonate, calcium phosphate and magnesium carbonate
and also organic substances and water. They are comprised
9
nanoparticles with unique properties. Many types of
19
nanoparticles have been synthesized for use as catalysts in
of more than 90% CaCO3. In this study, CaO derived
1
0
reactions. The synthesis of magnetic nanoparticles that
from eggshell was used as natural solid base for Suzuki
—
——
*
Corresponding author. Tel.: +98 81 38257407; Fax: +98 81 38257407.
E-mail address: Khazaei_1326@yahoo.com (A. Khazaei).

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Tetrahedron
coupling reaction in the presence of Rice-husk supported
Fe O stabilized palladium magnetic nanoparticles (Scheme
3).
3
4
Scheme 1. The synthesis of silica from Rice-husk as a naturally support for stabilization of palladium magnetic nanoparticles.
Scheme 2. The synthesis of palladium magnetic nanoparticles as a green catalyst for Suzuki coupling reactions.
2
. Result and discussion
The catalyst was prepared using a simple and effective
method and characterized by SEM, EDS, XRD, TEM, FT-
IR and VSM.
Through this study we used the N H as a reducing agent
2
4
for the reduction of Pd(II) to Pd(0) and its application for
the preparation of the Fe O @SiO -Pd. Figure 1 shows the
3
4
2
UV-vis analysis of Pd(II) and Pd(0). After the addition of
II
N H , the yellow color of the Pd solution immediately
2
4
changed into dark brown which indicated that Pd(II) was
converted to Pd(0).
Figure 1. The UV-vis analysis of Pd(II) (a) and Pd(0) (b).
The XRD pattern of the CaO, SiO , Fe O , Fe O @SiO
2
2
3
4
3
4
and Fe O @SiO -Pd are given in Figure 2. The powder
3
4
2
diffraction pattern of the Fe O @SiO -Pd is analyzed. No
3
4
2
characteristic peak for Pd NPs was observed in the pattern
of the Fe O @SiO -Pd, indicating that the amount of Pd is
3
4
2
too low or the Pd NPs were highly dispersed on the
Fe O @SiO support.
3
4
2

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4
FT-IR spectra of the CaO, SiO , Fe O , Fe O @SiO ,
2
3
4
3
4
2
Fe O @SiO @NH and Fe O @SiO -Pd are given in
3
4
2
2
3
4
2
Figure 3. The FT-IR analysis of the Fe O @SiO ,
3
4
2
Fe O @SiO @NH and Fe O @SiO -Pd confirm that there
3
4
2
2
3
4
2
was no change in functional groups after the
immobilization of Pd NPs on the Fe O @SiO surface.
3
4
2
Figure 2. XRD patterns of the CaO (a), SiO
d) and Fe @SiO -Pd (e).
2
3 4 3 4 2
(b), Fe O (c), Fe O @SiO
(
3
O
4
2
2 3 4 3 4 2
Figure 3. FT-IR spectra of the CaO (a), SiO (b), Fe O (c), Fe O @SiO
(
d), Fe @SiO @NH (e) and Fe @SiO -Pd (f).
3
O
4
2
2
3
O
4
2
The morphology of the CaO, Fe O , Fe O @SiO ,
3
4
3
4
2
Fe O @SiO @NH and Fe O @SiO -Pd are characterized
3
4
2
2
3
4
2
by SEM (Figure 4 and 5). For additional study on
determinations of particle size of nanocatalyst, we used
SEM analysis. The shapes and dimensions of the particles
can be seen in Figure 4 and 5. The particles were found to
be in spherical shape. The particles size in Fe O @SiO -Pd
3
4
2
is estimated to be 31-73 nm.
The elemental composition of the CaO and Fe O @SiO -
3
4
2
Pd was also analyzed by Energy Dispersive X-ray
Spectroscopy (EDS) spectrum (Figure 6). It further
confirmed the presence of Fe, C, Si and O elements in the
Fe O @SiO -Pd.
3
4
2

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Tetrahedron
The magnetic properties of the Fe O and Fe O @SiO -Pd
have been investigated by VSM system at room
temperature, with the field sweeping from -10000 to
nanoparticles substance. Even with this reduction in the
saturation magnetization, the solid could still be capably
separated from solution with a permanent magnet.
3
4
3
4
2
+
10000 Oe (Figure 7). Fe O nanoparticles, shown super
3 4
paramagnetic properties with saturation magnetization
According to the Transmission Electron Microscopy
(TEM) images (Figure 8), the Pd NPs are well dispersed
through the catalyst surface with an average diameter of
-1
-1
about 60 emug and Fe O @SiO -Pd were 37 emug .
3
4
2
Compared with the Fe O nanoparticles, the saturation
3
4
magnetization of the magnetic nanoparticles catalyst clearly
decreased because the diamagnetic contribution of the thick
1
0-30 nm.
organic matter resulted in a low mass fraction of the Fe O4
3
3 4 3 4 2 3 4 2 2
Figure 4. SEM images of the CaO (a), Fe O (b), Fe O @SiO (c) and Fe O @SiO @NH (d).

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Tetrahedron
4
3 4 2
Figure 5. SEM images of the Fe O @SiO -Pd.
Figure 6. The EDX of the CaO (a) and Fe
3
O
4
@SiO
2
-Pd (b).

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5
Tetrahedron
b
3 4 3 4 2
Figure 7. The vibrating sample magnetometer (VSM) analysis of the Fe O (a) and Fe O @SiO -Pd (b).
3 4 2
Figure 8. TEM images of the Fe O @SiO -Pd.
The coupling reaction of iodobenzene with phenyl boronic
acid was carried out using Fe O @SiO -Pd under different
The palladium content in the Fe O @SiO -Pd determined
3
4
2
3
4
2
−1
by ICP-AES was 0.17 mmol g .
The catalytic activity of the Fe O @SiO -Pd in the Suzuki
conditions as a model reaction (Table 1). A preliminary
survey of reaction conditions was conducted including the
effects of the different solvents, temperatures, bases, and
amount of catalyst. As shown in Table 1, no target product
could be detected in the absence of Fe O @SiO -Pd even
3
4
2
coupling reaction of different aryl boronic acids with aryl
halides was investigated (Scheme 4).
3
4
2
after 120 min (Entry 10). The best results were achieved
with CaO as base in the presence of 0.03 mol%
o
Fe O @SiO -Pd in H O/EtOH (1:1) at 85 C (Table 1,
3
4
2
2
entry 4). As the catalyst loading decreased from 0.03 to

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4
0
8
.01 mol%, yield was found to be decrease from 96% to
4%, respectively.
Table 1. Optimization of the Suzuki coupling reaction.
o
Entry
Solvent
Base
CaO
CaO
CaO
CaO
Catalyst (mol%)
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.01
Temp. ( C)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
H
2
O
90
80
130
85
85
85
85
85
85
85
25
30
45
20
30
40
85
40
30
120
92
90
86
96
92
86
65
84
92
0
EtOH
DMF
H
2
O/EtOH (1:1)
O/EtOH (1:1)
O/EtOH (1:1)
O/EtOH (1:1)
O/EtOH (1:1)
O/EtOH (1:1)
O/EtOH (1:1)
H
2
H
2
H
2
H
2
H
2
H
2
K
2
CO
3
Na
2
CO
3
NEt
3
CaO
CaO
CaO
0.02
0.00
1
0
After the optimization study, the effect of electron
withdrawing and electron donating functional groups in
aryl iodides and bromides on the catalytic activity was
examined in the Suzuki coupling reaction in the presence of
Fe O @SiO -Pd as catalyst and CaO as base in H O/EtOH
3
4
2
2
mixture. Various aryl halides were reacted with aryl
boronic acids and converted into the corresponding
coupling products. As shown in Table 2, the reaction of
aryl halides bearing electron-withdrawing groups went to
completion in longer reaction times than those with
electron donating groups. In all the cases, aryl halides
afforded excellent yields of the products. However, this
method was not applicable for aryl chlorides (Table 2, entry 14).
In another study, recyclability and reusability of the
catalyst was confirmed on the reaction of between
iodobenzene with phenyl boronic acid. At the end of the
reaction, catalyst was separated by an external magnetic
field, washed with water and then and then reused. The
catalyst was used without further cleansing after isolation.
Afterwards the recycled catalyst was applied for alternative
reaction. The catalyst was used over 5 runs without
significant loss of activity (Table 3). To check the
heterogeneity of catalyst, which is an important factor, the
phenomenon of leaching was studied by Inductively
Coupled Plasma Atomic Emission Spectroscopy (ICP-
AES) analysis of the resulting reaction solution mixture. It
was shown that palladium content of the used Fe O @SiO -
3
4
2
-
1
Pd was the same as that of the fresh one (0.17 mmol g ).
As shown in TEM images of the recycled catalyst after 5th
recycle (Figure 9), no obvious change in morphology and
size of Pd NPs were observed.

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Tetrahedron
Table 2. Suzuki coupling of different aryl halides with aryl boronic acids in H
2
O/EtOH in the presence of the Fe
3
O
4
@SiO
2
-Pd using CaO as a base.
Yield (%)
Entry
1
Aryl halide
ArB(OH)
2
Reaction time (min)
20
96
92
93
89
2
3
4
30
26
50
5
25
35
91
90
6
7
24
38
93
90
8
9
30
45
40
65
90
88
90
85
1
1
1
1
0
1
2
3
70
87
1
4
100
No reaction

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3
Table 3. Reusability of the Fe
iodobenzene with phenyl boronic acid.
3 4 2
O @SiO -Pd in the Suzuki coupling of
a
Run
1
2
3
4
Yield (%)
Recovery of catalyst (%)
96
96
96
95
94
99
99
99
98
98
5
a
Reaction conditions: Iodobenzene = 1.0 mmol, phenyl boronic acid = 1.1
o
2
mmol, catalyst = 0.03 mol%, CaO (2.0 mmol), H O/EtOH (1:1) 85 C.
Figure 9. TEM images of the recycled catalyst after 5th recycle.
1
.5406 A˚). The scanning rate was 2º/min in the 2θ range
from 10 to 80˚. Scanning electron microscopy (SEM) was
performed on a Cam scan MV2300. The shape and size of
the catalyst was identified by transmission electron
microscope (TEM) using a Philips EM208 microscope
operating at an accelerating voltage of 90 kV. EDS
3
. Conclusions
Here we demonstrated the feasibility to generate
Fe O @SiO -Pd using a simple and efficient protocol.
SEM, EDS, XRD, TEM, FT-IR and VSM techniques
confirmed the formation of the Fe O @SiO -Pd. The Pd
NPs were characterized via UV-vis spectroscopy. It was
demonstrated that the prepared nanocatalyst was found
very effective catalyst for Suzuki coupling reaction in the
presence of waste eggshell as low-cost solid base. The
nanocatalyst was readily recovered by using an external
magnet and reused several times without significant loss of
activity.
3
4
2
(
S3700N) was utilized for chemical analysis of prepared
3
4
2
nanostructures. Vibrating sample magnetometer (VSM)
measurements were performed by using a SQUID
magnetometer at 298 K (Quantum Design MPMS XL). The
content of Pd in the catalyst was determined by ICP-AES
(
PROFILE SPEC, Leeman).
.2. Preparation of CaO from eggshell waste
4
CaO as natural solid base was prepared by calcination
method. Eggshells were collected, washed and dried. The
dried eggshell was calcined at 700-900 ºC in air atmosphere
for 4h. CaO was obtained as white powder. All calcined
samples were kept in the close vessel to avoid the reaction
with carbon dioxide and humidity in air before using.
4
. Experimental
4
.1. Instruments and reagents
High-purity chemical reagents were purchased from the
Merck and Aldrich chemical companies. All materials were
of commercial reagent grade. H NMR spectra were
4
.3. Preparation of the magnetic Fe O nanoparticles
3 4
1
Magnetic Fe O nanoparticles were prepared using simple
chemical coprecipitation described in the literature.
Typically, 11.3 g of FeCl .6H O and 4.6 g of FeCl .4H O
were dissolved in 250 mL of deionized water in a round-
bottom flask (500 mL) which was heated to 80 ºC until the
solution was clear. Thereafter, under rapid mechanical
stirring, 30 mL ammonia 25% in the mixture was stirred
until a black homogeneous phase was formed, after being
rapidly stirred for 2 h. The black precipitate form was
3
4
recorded on a Bruker Avance DRX-400 spectrometer at
20
4
00. FT-IR spectra were recorded on a Nicolet 370 FT/IR
3
2
2
2
spectrometer (Thermo Nicolet, USA) using pressed KBr
pellets. UV-visible spectral analysis was recorded on a
double‐beam spectrophotometer (Hitachi, U‐2900) to
ensure the formation of nanoparticles. X-ray diffraction
(
XRD) measurements were carried out using a Philips
powder diffractometer type PW 1373 goniometer (Cu Kα =

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Tetrahedron
isolated by magnetic decantation, and carefully washed
with deionized water and then washed twice with acetone
and dried at 60 ºC in vacuum.
stirred for the required period of time at 85 °C until
completion of the reaction, as monitored by TLC. After
completion of the reaction, the mixture was cooled to room
temperature and the catalyst separated from the reaction
mixture with an external magnet. The resultant solution
was extracted with n-hexane. The combined organic phase
4
.4. Preparation of SiO from Rice-husk
2
Rice-husk obtained from a local Industry in the north of
Iran and washed several times with distilled water to
remove any sticking materials and dried at 100 °C for 24 h.
The Rice-husk (5.0 g) was acid-leached with 10% HCl and
afterwards 30 wt.% sulfuric acid solution at 100°C for 3 h
in a pyrex round-bottom flask equipped with a reflux
condenser. Then, the resulting brown powder was filtered
and washed repeatedly three times using deionized water to
make it acid free and dried at 80 °C for 5 h. The resulted
powder was calcinated at 650 °C for 3 h to obtain SiO2.
was dried with CaCl , solvent was removed, and the
product was recrystallized with ethanol.
2
Acknowledgements
We gratefully acknowledge the Iranian Nano Council and
Bu-Ali Sina University for the support of this work.
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2546; (b) Baeza, A.; Guillena, G.; Ramón, D. J.
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Yuan, H.; Du, Z.; Wu, Y. Chem. Eng. J. 2015, 278, 129; (d)
2
4
added and stirred for 2 h. The reaction color changed to
black, due to conversion of Pd(II) into Pd(0). The black
nanoparticles were separated with an external magnet,
washed with distilled water several times and then dried at
6
5 ºC for 6 h.
.8. General procedure for the Suzuki coupling reaction
To a flask, a mixture of aryl halide (1.0 mmol [molar mass
4
1
-3
-3
×
10 g]), aryl boronic acids (1.1×10 × molar mass g),
CaO (0.112 g), H O (1.0 mL), ethanol (1.0 mL) and
2
catalyst (0.117 g) were added. The reaction mixture was

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