Pd–Schiff base complex supported on Fe3O4 magnetic nanoparticles: A new and highly efficient reusable catalyst for C–C bond formation in water

Article abstract of DOI:10.1002/aoc.5158

A protocol is introduced for the preparation of a new cage-like Pd–Schiff base organometallic complex supported on Fe₃O₄ nanoparticles (Fe₃O₄@Schiff-base-Pd). The structure of the nanomagnetic catalyst was comprehensively characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy (SEM), transmission electron microscopy, X-ray mapping, thermogravimetric analysis, vibrating sample magnetometry and inductively coupled plasma atomic emission spectroscopy. In the second stage, the catalytic activity of this catalyst was studied in the Suzuki and Heck cross-coupling reactions in water as a green solvent. In this sense, simple preparation of the catalyst from commercially available materials, high catalytic activity, simple operation, short reaction times, high yields and use of green solvent are some advantages of this protocol. Finally, the nanocatalyst was easily recovered, using an external magnet, and reused several times without significant loss of its catalytic efficiency. In addition, the stability of the catalyst after recycling was confirmed using SEM, XRD and FT-IR techniques.

Full text of DOI:10.1002/aoc.5158

Received: 11 June 2019
DOI: 10.1002/aoc.5158
Revised: 11 July 2019
Accepted: 15 July 2019
F U L L P A P E R
Pd–Schiff base complex supported on Fe3O4 magnetic
nanoparticles: A new and highly efficient reusable catalyst
for C–C bond formation in water
Lei Lei
School of Civil Engineering, Xuzhou
A protocol is introduced for the preparation of a new cage‐like Pd–Schiff base
University of Technology, Xuzhou 221000,
China
organometallic complex supported on Fe3O4 nanoparticles (Fe3O4@Schiff‐
base‐Pd). The structure of the nanomagnetic catalyst was comprehensively
Correspondence
characterized using Fourier transform infrared (FT‐IR) spectroscopy, X‐ray
Lei Lei, School of Civil Engineering,
Xuzhou University of Technology,
diffraction (XRD), energy‐dispersive X‐ray spectroscopy, Brunauer–Emmett–
Xuzhou, 221000, China.
Teller measurements, scanning electron microscopy (SEM), transmission elec-
Email: leilei7670@gmail.com;
LLPPMM222@163.com
tron microscopy, X‐ray mapping, thermogravimetric analysis, vibrating sample
magnetometry and inductively coupled plasma atomic emission spectroscopy.
In the second stage, the catalytic activity of this catalyst was studied in the Suzuki
and Heck cross‐coupling reactions in water as a green solvent. In this sense, sim-
ple preparation of the catalyst from commercially available materials, high cata-
lytic activity, simple operation, short reaction times, high yields and use of green
solvent are some advantages of this protocol. Finally, the nanocatalyst was easily
recovered, using an external magnet, and reused several times without signifi-
cant loss of its catalytic efficiency. In addition, the stability of the catalyst after
recycling was confirmed using SEM, XRD and FT‐IR techniques.
Funding information
Scientific Research Project of Xuzhou
University of Technology ‐ Cultivation,
Grant/Award Number: XKY2018133
KEYWORDS
C–C coupling, Fe3O4@Schiff‐base‐Pd, Heck, reusable catalyst, Suzuki
1 | INTRODUCTION
representative Pd catalysts are homogeneous Pd complexes
coordinated with various phosphine ligands and providing
The Suzuki and Heck cross‐coupling reactions play an
important role in natural product synthesis, biological,
medicinal and supramolecular chemistry, and also in
catalysis, coordination chemistry and polymer synthe-
sis.[1–5] Metal catalysts are powerful tools for C─C bond
formation and can also be widely used in organic chemis-
try. Such cross‐coupling reactions can be regarded as effi-
cient and direct techniques in the synthesis of important
products.[1–3,5] The use of Pd catalysts for these transforma-
tions is still interesting from an industrial perspective
because of the fact that palladium is less toxic and of lower
cost than other transition metals.[2–4] The most
excellent yields.[6] However, the homogeneous Pd com-
plexes suffer from significant drawbacks; including the dif-
ficulty of separation and recovery of Pd complexes from the
reaction system, high costs and potential environmental
pollution.[7] To circumvent these issues and with the rapid
advancement of nanotechnology, heterogeneous Pd cata-
lysts have been proposed by supporting Pd nanoparticles
on the surface of insoluble hosts.[8–12] Microporous and
mesoporous materials[13–15] and metal oxides[1,10,16–23]
have been widely used as supporting materials because of
their significant advantages, including high surface area,
low cost and good chemical stability. In this sense, Fe3O4
Appl Organometal Chem. 2019;e5158.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5158

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magnetic nanoparticles (MNPs) have attracted great
attention due to their intrinsic magnetic property, facile
synthesis and being environmentally friendly.[24–31] Dur-
Fe3O4@Schiff‐base‐Pd organometallic complex, the
obtained Fe3O4@Schiff‐base (0.5 g) was dispersed in
25 ml of ethanol by sonication for 30 min, and then pal-
ladium acetate (0.25 g) was added to the reaction mixture.
The reaction mixture was stirred under nitrogen atmo-
sphere at 80°C for 24 h. Afterwards, 3 mmol of NaBH4
was added to the reaction and stirred for a further 2 h.
Then, the final product (Fe3O4@Schiff‐base‐Pd) was sep-
arated using an external magnet, washed with water
and ethanol and dried at 80°C in an oven for 4 h.
ing past decades,
a few studies of monometallic
nanocrystals, supported on magnetic Fe3O4, have been
reported offering promising results in the catalysis of
C─C cross‐coupling
reactions.[29,32–37] Moreover,
there are many reports of Pd complexes supported on the
surface of MNPs, such as Pd@Fe3O4‐NH2/starch,[38]
Pd@g‐C3N4‐Fe‐GO,[39] PdAu/Fe3O4,[40] Fe3O4@SiO2/
isoniazide/Pd,[41] Fe3O4/bentonite‐Pd,[42] Pd(0/II)/CS‐
bigua@Fe3O4,[43] Fe2O3@FLG@Pd0,[44] Fe3O4@CA‐
Pd,[45] Fe3O4@SiO2‐Pd,[46] etc. These catalytic systems
benefit from the low toxicity, commercial availability and
recyclability of Fe3O4 MNPs.[47–54]
2.2 | General procedure for Suzuki
reaction
A mixture of aryl halide (1 mmol), phenylboronic acid
(1 mmol) and Cs2CO3 (3 mmol) was dissolved in 5 ml
of water in the presence of Fe3O4@Schiff‐base‐Pd catalyst
(0.30 mol%), and then stirred at 100°C (reflux conditions).
The progress of the reaction was monitored by TLC. After
completion of the reaction and magnetic separation of the
catalyst, the reaction mixture was treated with ethyl ace-
tate (10 ml) and water (3 ml). The organic layer was sep-
arated and the aqueous layer was extracted with ethyl
acetate (3 × 5 ml). The organic layer was dried over
Na2SO4. Then, the solvent was evaporated, and the corre-
sponding pure biphenyls were consequently obtained.
Now, in this report, a Pd complex supported on
surface‐modified Fe3O4 nanoparticles (Fe3O4@Schiff‐
base‐Pd) is introduced as a new and efficient reusable cat-
alyst for the Suzuki and Heck reactions.
2 | EXPERIMENTAL
2.1 | Preparation of cage‐like Schiff base
organometallic complex of Pd supported on
the surface of Fe3O4 MNPs (Fe3O4@Schiff‐
base‐Pd)
Fe3O4 MNPs were prepared by the coprecipitation tech-
nique as was previously reported.[43] For the synthesis
of the supported Fe3O4@Schiff‐base‐Pd complex, 1 g of
the prepared Fe3O4 nanoparticles was dispersed in
50 ml of ethanol–water (1:1) by sonication for 15 min,
and then 1.5 ml of 3‐chloropropyltrimethoxysilane
(CPTMS) was added to the reaction mixture. The reaction
mixture was stirred under nitrogen atmosphere at 40°C
for 24 h. Then, the obtained Fe3O4@CPTMS MNPs prod-
uct was separated by magnetic decantation, washed with
ethanol and dried at 90°C in an oven for 4 h. Afterwards,
diethylenetriamine (DETA) was grafted on 1 g of the
obtained Fe3O4@CPTMS MNPs in ethanol under nitro-
gen atmosphere at reflux conditions for 24 h. Then, the
reaction mixture was cooled, and Fe3O4@PTMS‐DETA
MNPs were separated by magnetic decantation,
Then, the Schiff base ligand supported on heterogeneous
Fe3O4 was obtained by the reaction of 2.5 mmol of
2.3 | General procedure for Heck reaction
A mixture of aryl halide (1 mmol), methyl acrylate
(1.2 mmol) and Cs2CO3 (3 mmol) was dissolved in 5 ml
of water in the presence of Fe3O4@Schiff‐base‐Pd catalyst
(0.30 mol%), and then the mixture was stirred at 100°C
(reflux conditions). The progress of the reaction was mon-
itored by TLC. After completion of the reaction and mag-
netic separation of the catalyst, the reaction mixture was
treated with ethyl acetate (10 ml) and water (3 ml). The
organic layer was separated and the aqueous layer was
extracted with ethyl acetate (3 × 5 ml). The organic layer
was dried over Na2SO4. Then, the solvent was evaporated
and the corresponding pure products were consequently
obtained.
2.4 | Selected spectral data
O‐bisMe‐furaldehyde
(5,5′‐oxybis(5‐methylene‐2‐
furaldehyde)) with the amine groups on the surface of
Fe3O4@PTMS‐DETA (1 g) in ethanol (20 ml) overnight
and under nitrogen atmosphere and reflux conditions.
The target Fe3O4@Schiff‐base was obtained by magnetic
separation, washed with ethanol and dried at 80°C in
2.4.1 | (4‐Methoxyphenyl)(p‐tolyl)sulfane
(Table 2, entry 2)
1,1′‐Biphenyl (Table 2, entry 2)
1H NMR (400 MHz, CDCl3, δ, ppm): 7.27–7.31 (m, 2H),
7.40 (t, J = 7.6 Hz, 4H), 7.56 (d, J = 8.1 Hz, 4H). 13C
an oven for
4 h. Finally, in order to prepare

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NMR (125 MHz, CDCl3, δ, ppm): 127.17, 127.24, 128.75,
141.25.
J = 7.24 Hz, 2H), 7.54 (d, J = 8.03 Hz, 2H), 7.64 (d,
J = 8.03 Hz, 2H). 13C NMR (125 MHz, CDCl3, δ, ppm):
21.65, 127.52, 127.54, 127.71, 129.26, 130.02, 137.56,
138.89, 141.69.
4‐Nitro‐1,1′‐biphenyl (Table 3, entry 1)
1H NMR (400 MHz, CDCl3, δ, ppm): 7.46–7.55 (m, 3H),
7.76–7.78 (d, J = 8.81 Hz, 2H), 7.65–7.67 (d, J = 8.3 Hz,
2H), 8.32–8.35 (d, J = 8.82 Hz, 2H). 13C NMR
(125 MHz, CDCl3, δ, ppm): 123.66, 126.95, 127.35,
128.49, 128.72, 138.32, 146.65, 147.18.
4‐Cyano‐1,1′‐biphenyl (Table 3, entry 1)
1H NMR (400 MHz, CDCl3, δ, ppm): 7.46–7.54 (m, 3H),
7.62 (d, 2H, J = 7.22 Hz), 7.70–7.77 (q, 4H). 13C NMR
(125 MHz, CDCl3, δ, ppm): 110.93, 118.94, 127.23,
127.74, 128.66, 129.11, 132.60, 139.19, 145.68.
4‐Methoxy‐1,1′‐biphenyl (Table 3, entry 1)
1H NMR (400 MHz, CDCl3, δ, ppm): 3.75 (s, 3H), 6.89 (d,
J = 8.73 Hz, 2H), 7.21 (t, J = 6.81 Hz, 1H), 7.34 (t,
J = 7.61 Hz, 2H), 7.45 (t, J = 8.43 Hz, 4H). 13C NMR
(125 MHz, CDCl3, δ, ppm): 55.36, 114.23, 126.75, 128.16,
128.72, 133.82, 140.88, 159.17.
4‐Phenylbenzaldehyde (Table 3, entry 1)
1H NMR (400 MHz, CDCl3, δ, ppm): 7.34 (t, J = 7.2 Hz, 1H),
7.39 (t, J = 7.23 Hz, 2H), 7.55 (d, J = 8.41 Hz, 2H), 7.66 (d,
J = 8.04 Hz, 2H), 7.86 (d, J = 8.04 Hz, 2H), 9.96 (s, 1H).
(E)‐Methyl cinnamate (Table 3, entry 1)
4‐Methyl‐1,1′‐biphenyl (Table 3, entry 1)
1H NMR (CDCl3, 400 MHz, δ, ppm): 3.71 (s, 3H), 6.35 (d,
J = 16.0 Hz, 1H), 7.27–7.29 (m, 3H), 7.41–7.44 (m, 2H),
7.60 (d, J = 16.01 Hz, 1H) . 13C NMR (CDCl3, 100 MHz,
1H NMR (400 MHz, CDCl3, δ, ppm): 2.44 (s, 3H), 7.28 (d,
J = 8.03 Hz, 2H), 7.37 (t, J = 7.22 Hz, 1H), 7.47 (t,
SCHEME 1 Stepwise preparation of Fe3O4@Schiff‐base‐Pd

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δ, ppm): 51.2, 117.4, 127.6, 128.4, 129.8, 133.96, 144.4,
166.9.
(E)‐Methyl 3‐(4‐nitrophenyl)acrylate (Table 3, entry 1)
1H NMR (CDCl3, 300 MHz, δ, ppm): 3.84 (s, 3H), 6.57 (d,
1H, J = 16.11 Hz), 7.68 (d, 2H, J = 8.73 Hz), 7.71 (s, 1H,
J = 16.14 Hz), 8.25 (d, 2H, J = 8.82 Hz). 13C NMR (CDCl3,
75 MHz, δ, ppm): 52.3, 122.3, 124.4, 128.8, 140.7, 142.1,
148.7, 166.6.
(E)‐Methyl 3‐(4‐chlorophenyl)acrylate (Table 3, entry 1)
1H NMR (300 MHz, CDCl3, δ, ppm): 3.80 (s, 3H), 6.40 (d,
J = 16.01, 1H), 7.35 (d, J = 8.62, 2H), 7.44 (d, J = 8.5, 2H),
FIGURE 1 FT‐IR spectra of Fe3O4 MNPs (a), Fe3O4@CPTMS
MNPs (b), Fe3O4@PTMS‐DETA MNPs (c), Fe3O4@Schiff‐base (d)
and Fe3O4@Schiff‐base‐Pd (e)
FIGURE 4 EDS spectrum of Fe3O4@Schiff‐base‐Pd
FIGURE 2 XRD pattern of Fe3O4@Schiff‐base‐Pd catalyst
FIGURE
5
Nitrogen adsorption/desorption isotherm of
FIGURE 3 XPS spectrum of Fe3O4@Schiff‐base‐Pd catalyst
Fe3O4@Schiff‐base‐Pd

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7.63 (d, J = 16.01, 1H). 13C NMR (75 MHz, CDCl3, δ,
ppm): 51.8, 118.5, 129.30, 129.33, 133.0, 136.3, 143.4,
167.2.
3 | RESULTS AND DISCUSSION
3.1 | Catalyst preparation
(E)‐Methyl 3‐(4‐methoxyphenyl)acrylate (Table 3,
entry 1)
A novel cage‐like Pd–Schiff base complex immobilized on
Fe3O4 as a reusable magnetic nanocatalyst is described.
Initially, Fe3O4 nanoparticles modified with CPTMS
(Fe3O4@CPTMS MNPs) were prepared according to a
1H NMR (CDCl3, 400 MHz, δ, ppm): 3.81 (s, 3H), 3.86 (s,
3H), 6.33 (d, J = 16.01 Hz, 1H), 6.90–6.94 (m, 2H), 7.50–
7.47 (m, 2H), 7.67 (d, J = 16.01 Hz, 1H). 13C NMR
(CDCl3, 100 MHz, δ, ppm): 51.6, 55.5, 114.4, 115.5,
127.2, 129.8, 144.6, 161.5, 167.8.
reported
procedure.[32]
In
order
to
prepare
Fe3O4@PTMS‐DETA MNPs, DETA was grafted on
Fe3O4@CPTMS MNPs via substitution reaction of NH2
with terminal Cl groups. Then, the Schiff base cage was
synthesized via the reaction of NH2 with O‐bisMe‐
furaldehyde. Finally, the catalyst was synthesized by the
reaction of Fe3O4@Schiff‐base with Pd(OAc)2 (Scheme 1).
This catalyst was characterized using various techniques.
(E)‐Methyl 3‐(p‐tolyl)acrylate (Table 3, entry 1)
1H NMR (CDCl3, 400 MHz, δ, ppm): 2.39 (s, 3H), 3.81 (s,
3H), 6.42 (d, J = 16.01 Hz, 1H), 7.19–7.21 (m, 2H), 7.42–
7.44 (m, 2H), 7.69 (d, J = 16.0 Hz, 1H). 13C NMR (CDCl3,
100 MHz, δ, ppm): 21.5, 51.6, 116.7, 128.0, 129.6, 131.7,
140.7, 144.9, 167.6.
3.2 | Catalyst characterization
(E)‐Methyl 3‐(4‐cyanophenyl)acrylate (Table 3, entry 1)
1H NMR (300 MHz, CDCl3, δ, ppm): 3.82 (s, 3H), 6.51 (d,
J = 16.01, 1H), 7.60 (d, J = 8.32, 2H), 7.66 (d, J = 16.1,
1H), 7.67 (d, J = 8.43, 2H). 13C NMR (75 MHz, CDCl3,
δ, ppm): 52.0, 113.6, 118.4, 121.5, 128.5, 132.7, 138.8,
142.5, 166.6.
The as‐prepared Fe3O4@Schiff‐base‐Pd catalyst was char-
acterized using Fourier transform infrared (FT‐IR) spec-
troscopy, X‐ray diffraction (XRD), energy‐dispersive X‐
ray spectroscopy (EDS), Brunauer–Emmett–Teller (BET)
measurements, scanning electron microscopy (SEM),
FIGURE 6 SEM images of Fe3O4 MNPs (a), Fe3O4@CPTMS MNPs (b), Fe3O4@PTMS‐DETA MNPs (c), Fe3O4@Schiff‐base (d),
Fe3O4@Schiff‐base‐Pd complex (e) and recovered Fe3O4@Schiff‐base‐Pd complex (f)

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transmission electron microscopy (TEM), X‐ray mapping,
thermogravimetric analysis (TGA), vibrating sample mag-
netometry (VSM) and inductively coupled plasma atomic
emission spectroscopy (ICP).
group on the Fe3O4 support.[57] Peaks at 1012 and
1117 cm−1 (C─N stretching vibration) in the spectrum of
Fe3O4@PTMS‐DETA MNPs provide evidence confirming
the formation of the desired ligand. The shift in the absorp-
tion peak at approximately 1624 cm−1 (C═N stretching
vibration) in the spectrum of Fe3O4@Schiff‐base‐Pd is
due to the complexion of Pd ions with Fe3O4@Schiff‐base.
The XRD pattern of Fe3O4@Schiff‐base‐Pd is shown in
Figure 2 in which the peak positions of 2θ at 30.17°, 35.5,
43.2°, 53.7°, 57.1° and 62.9° are in agreement with the
standard XRD pattern of Fe3O4 nanoparticles.[58] Other
peaks at 2θ values of 39.3°, 45.1° and 66.1° correspond
to Pd(0) in Fe3O4@Schiff‐base‐Pd.[59]
X‐ray photoelectron spectroscopy (XPS) measurements
were carried out to confirm that the Pd ions formed a com-
plex with the functional groups of Fe3O4@Schiff‐base. The
XPS data show Pd 3d3/2 and Pd 3d5/2 binding energies at
341.5 and 336.4 eV, respectively. Based on a previous
report,[60] the binding energy of Pd 3d5/2 for Pd(0) is
335.1 eV. In addition, we found that the Pd 3d5/2 peak
shifted to higher values as a result of the presence of the
surrounding positively charged ammonium groups of the
The FT‐IR spectra for the Fe3O4 MNPs, Fe3O4@CPTMS
MNPs, Fe3O4@PTMS‐DETA MNPs, Fe3O4@Schiff‐base
and Fe3O4@Schiff‐base‐Pd are shown in Figure 1. Strong
peaks at 590 and 628 cm−1 in the spectra of Fe3O4 MNPs,
Fe3O4@CPTMS MNPs, Fe3O4@PTMS‐DETA MNPs,
Fe3O4@Schiff‐base and Fe3O4@Schiff‐base‐Pd complex
were observed, attributed to the presence of Fe─O
stretching vibration.[55] In addition, the peak appearing at
1624 cm−1 was attributed to bending vibration of OH or
stretching vibrational mode of an adsorbed water layer.[16]
Moreover, the broad band at around 3392 cm−1 is attrib-
uted to asymmetric and symmetric stretching vibrations
of ─OH of the surface of the Fe3O4 nanoparticles.[56] In
the spectrum of Fe3O4@CPTMS MNPs, two peaks at 2853
and 2925 cm−1 can be attributed to the C─H stretching
vibrations of chloropropyl group. Also, the peak at
892 cm−1 attributed to Fe─O─Si stretching vibration con-
firmed the immobilization of the anchored chloropropyl
FIGURE 7 TEM images of Fe3O4@Schiff‐base‐Pd

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Fe3O4@Schiff‐base nanoparticles. This indicates that there
is a good interaction to make Pd more stable on the surface
of the Fe3O4@Schiff‐base nanoparticles.[61] It is also well
recognized that the designed cage‐like Fe3O4@Schiff‐base
can suppress the agglomeration of Pd nanoclusters, and
enhance the catalytic efficiency of Pd nanoparticles
(Figure 3).
The elemental composition of the Fe3O4@Schiff‐base‐
Pd organometallic complex was determined using EDS
(Figure 4). The presence of Fe, O, Si, C, N, and Pd in
the EDS pattern provides evidence confirming the forma-
tion of the organometallic complex. In addition, the exact
amount of Pd, which was immobilized on Fe3O4@Schiff‐
base, was obtained using ICP as 1.34 × 10−3 mol g−1
.
The surface area of the Fe3O4@Schiff‐base‐Pd
nanomaterial was analyzed using a fully automated BET
surface area analyzer (Belsorp MiniII) by nitrogen multi-
layer desorption measured as a function of relative
pressure (Ps/P0). As can be seen from Figure 5, the
BET surface area of the prepared nanostructure is
109.8 m2 g−1. The high surface may endow the material
with improved catalytic properties.
Figure 6 illustrates the morphology of Fe3O4 MNPs,
Fe3O4@CPTMS MNPs, Fe3O4@PTMS‐DETA MNPs,
FIGURE 8 X‐ray mapping images of Fe3O4@Schiff‐base‐Pd
FIGURE 9 TGA curves of
Fe3O4@CPTMS MNPs (a), Fe3O4@PTMS‐
DETA MNPs (b) and Fe3O4@Schiff‐base‐
Pd complex (c)

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Fe3O4@Schiff‐base, Fe3O4@Schiff‐base‐Pd complex and
recovered Fe3O4@Schiff‐base‐Pd complex as probed by
the SEM technique. As shown in Figure 6, the SEM
image of Fe3O4@Schiff‐base‐Pd complex depicts a spheri-
cal morphology for most particles.
compared to the saturation magnetization of Fe3O4 which
was found to be 78 emu g−1. This decrease in the saturation
magnetization of Fe3O4@Schiff‐base‐Pd complex is due to
the successful grafting of Schiff‐base‐Pd complex on the
surface of Fe3O4 nanoparticles.
The size and morphology of the Fe3O4@Schiff‐base‐Pd
complex were investigated using TEM. As shown in
Figure 7, the magnetic cores of the nanoparticles were
uniform in both size and shape. Moreover, the particle
size was measured to be about 15–25 nm and, conse-
quently, the spherical morphology was confirmed. The
results of TEM and SEM were in agreement.
All together, these analyses are indicative of the suc-
cessful immobilization of Pd(0) complex onto the
Fe3O4@Schiff‐base.
3.3 | Catalytic studies
The X‐ray mapping of the Fe3O4@Schiff‐base‐Pd
nanocatalyst is shown in Figure 8. The good dispersion
of Pd on the surface of the catalyst was confirmed using
the elemental mapping images.
After the successful characterization of the prepared
nanomaterial, the catalytic activities in the synthesis of
diaryl sulfides and ethers were evaluated. Suzuki and
Heck cross‐coupling reactions were chosen to evaluate
the catalytic efficiency of the prepared organometallic
Schiff base complex.
Figure 9 illustrates the TGA curves of Fe3O4@CPTMS
MNPs, Fe3O4@PTMS‐DETA MNPs and Fe3O4@Schiff‐
base‐Pd complex (c). The small weight loss of between 2
and 5% below 200°C in the curves of Fe3O4@CPTMS
MNPs, Fe3O4@PTMS‐DETA MNPs and Fe3O4@Schiff‐
base‐Pd complex was attributed to the evaporation of
the physically adsorbed solvents and surface hydroxyl
groups. Also, the next weight loss of about 9, 22.5 and
32%, respectively, occurred between 200 and 600°C which
is related to the decomposition of the functional groups
chemisorbed onto the surface of the catalyst support.
The obtained results show that, in each step, the amount
of weight loss has increased which confirmed the forma-
tion of the desired organometallic complex.
In order to optimize the reaction conditions, the cou-
pling of iodobenzene with phenylboronic acid was chosen
as a model reaction to evaluate the optimized catalytic
activity. The effect of various experimental parameters,
including the amount of catalyst, nature of base, solvent
and reaction temperature, on the selected model reaction
were screened to achieve high catalytic efficiency and
yield. The results are summarized in Table 1. The influ-
ence of the catalyst loading on the reaction efficiency
was studied by varying the amount of catalyst. A compar-
ison of the results related to the effect of various amounts
of catalyst revealed that the highest activity was observed
in the presence of 0.30 mol% of the catalyst (Table 1,
entry 6). Then, the effects of base, solvent and reaction
temperature on the model reaction were evaluated. Con-
sidering reaction time and product yield, Cs2CO3 and
water under reflux conditions proved to be the best
Magnetic measurements of the catalyst were conducted
using VSM at room temperature. Figure 10 exhibits the
magnetization curves of the Fe3O4@Schiff‐base‐Pd com-
plex. The value of the saturation magnetic moment of the
Fe3O4@Schiff‐base‐Pd complex is 51.3 emu g−1 as
FIGURE 10 VSM curves of Fe3O4 (red)
and @Schiff‐base‐Pd (blue)

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TABLE 1 Optimization of reaction conditions for cross‐coupling of iodobenzene with phenylboronic acid
Entry
Solvent
Catalyst (mol%)
Base
Temperature (°C)
Time (min)
Yield (%)a
1
H2O
—
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
NaOH
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
100
2400
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
NR
Trace
27
2
H2O
0.05
0.10
0.15
0.25
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
0.30
3
H2O
4
H2O
48
5
H2O
83
6
H2O
97
7
EtOH
PEG
43
8
67
9
Dioxane
DMF
DMSO
Solvent‐free
H2O–EtOH (1:1)
H2O
83
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
45
Reflux
100
53
Trace
49
100
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Rt.
50
H2O
Et3N
23
H2O
K2CO3
Na2CO3
KOH
71
H2O
69
H2O
57
H2O
K3PO4
Trace
Trace
NR
35
H2O
KF/Al2O3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
H2O
H2O
60
H2O
80
63
H2O
90
80
H2O
95
84
aIsolated yield. NR, no reaction.
choice for the base, solvent and temperature, respectively.
After an extensive screening of the reaction parameters,
as presented in Table 1, the best yield of C─C coupling
product was obtained when the reaction was performed
using 0.30 mol% of Fe3O4@Schiff‐base‐Pd in the presence
of Cs2CO3 in water at 100°C (Table 1, entry 6). In
addition, the influence of the Pd loading on the catalytic
performance was investigated. For this purpose, different
amounts of palladium acetate (0.25, 0.20, 0.15, 0.10 g)
were grafted on the Fe3O4@Schiff‐base support in etha-
nol. Then, the catalytic performance in the Suzuki reac-
tion was investigated under the same reaction
SCHEME 2 Fe3O4@Schiff‐base‐Pd
catalyzed the coupling of aryl halides and
phenylboronic acid
SCHEME 3 Fe3O4@Schiff‐base‐Pd
catalyzed the coupling of aryl halides and
methyl acrylate

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TABLE 2 Catalytic C&bond;C coupling reaction of aryl halides with phenylboronic acid in the presence of catalytic amounts of
Fe3O4@Schiff‐base‐Pda
Entry
Aryl halide
Product
Time (min)
Yield (%)b
TOF (s−1
)
1
30
97
2 328 000
2
25
96
4 800 000
3
4
5
6
25
70
65
50
96
94
96
91
4 800 000
972 413
1 066 666
1 310 924
7
120
99
594 000
8
9
35
40
96
96
592 795
1 729 729
10
11
40
91
86
1 639 639
34 838
160
12
13
35
90
94
96
1 934 819
768 000
14
15
160
180
85
91
382 595
32 760
16
240
60
180 000
17
18
180
240
46
51
184 000
153 000
(Continues)

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11 of 15
TABLE 2 (Continued)
Entry
Aryl halide
Product
Time (min)
Yield (%)b
TOF (s−1
)
19
100
91
655 462
20
21
420
240
20
66
34 285
198 000
aReaction conditions: aryl halide (1 mmol), Fe3O4@Schiff‐base‐Pd (0.30 mol%), phenylboronic acid (1 mmol) and Cs2CO3 (3 mmol) in H2O at reflux conditions.
bIsolated yield.
TABLE 3 Coupling of aryl halides with methyl acrylate in the presence of catalytic amounts of Fe3O4@Schiff‐base‐Pda
Entry
Aryl halide
Product
Time (min)
Yield (%)b
TOF (s−1
)
1
45
95
152 000
2
3
4
5
6
7
25
35
96
93
81
86
99
26
2 769 230
1 914 236
972 000
60
55
1 126 637
594 000
120
180
104 000
8
100
90
85
91
87
612 244
728 000
696 000
9
10
90
(Continues)

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TABLE 3 (Continued)
Entry
Aryl halide
Product
Time (min)
Yield (%)b
TOF (s−1
)
11
70
91
936 535
304 000
210 000
62 400
12
13
14
180
240
300
76
70
26
15
16
240
180
25
40
75 000
160 000
17
360
26
52 000
aReaction conditions: aryl halide (1 mmol), methyl acrylate (1.2 mmol), Fe3O4@Schiff‐base‐Pd (0.30 mol%) and Cs2CO3 (3 mmol) in H2O at reflux conditions.
bIsolated yield.
conditions. The results showed that a decrease in Pd load-
ing led to an increase in the reaction time and a decrease
the performance of the reaction.
Then, the catalytic effectiveness of the prepared
Fe3O4@Schiff‐base‐Pd catalyst was investigated in the
Suzuki–Miyaura and Heck cross‐coupling reactions of
various aryl halides (I, Br and Cl) with phenylboronic
acid (Scheme 2) and methyl acrylate (Scheme 3) as phe-
nyl and alkene sources, respectively. The results are listed
in Tables 2 and 3). Various aryl halides bearing different
FIGURE 11 Reusability of Fe3O4@Schiff‐base‐Pd in synthesis of 1,1′‐biphenyl (a) and methyl cinnamate (b)

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electron‐withdrawing group or electron‐donating groups,
such as OCH3, NO2, NH2 and CH3, produced excellent
reaction yields in the presence of the Fe3O4@Schiff‐
base‐Pd catalyst. Also, good reaction yields for aryl bro-
mides and chlorides were afforded in the presence of
the designed Fe3O4@Schiff‐base‐Pd catalyst, while the
catalytic activity of the Fe3O4@Schiff‐base‐Pd catalyst
was studied with less reactive aryl chlorides as compared
to aryl iodides and bromides.
3.4 | Recyclability of catalyst
FIGURE 13 FT‐IR spectrum of recycled Fe3O4@Schiff‐base‐Pd
catalyst
Recyclability of catalysts provides an important advan-
tage in industrial applications because it reduces produc-
tion costs. Therefore, the recovery and recyclability of the
Fe3O4@Schiff‐base‐Pd catalyst were explored in the syn-
thesis of 1,1′‐biphenyl and methyl cinnamate. After com-
pletion of the reaction, the reaction system was cooled to
room temperature and the catalyst was magnetically sep-
arated from the solution, washed with EtOH, air‐dried
and finally reused for the next reaction run. As shown in
Figure 11, the recycling process was repeated for five
cycles with a slight decrease in the activity of the catalyst.
Moreover, SEM analysis, after five runs, shows that its
chemical structure was retained.
The SEM image of the recycled catalyst is shown in
Figure 6f. The morphology of the recovered
Fe3O4@Schiff‐base‐Pd catalyst is similar to the particle
form of fresh catalyst. Moreover, Figure 12 shows the
XRD pattern of the recovered catalyst and the peak inten-
sities indicate the structural stability of the catalyst after
five consecutive cycles. Figure 13 shows the FT‐IR spec-
trum of the recycled Fe3O4@Schiff‐base‐Pd that points
to the catalyst being stable during the oxidation reaction.
Also, in order to examine the stability of the catalyst
after recycling, the recycled catalyst was characterized
using the XRD, SEM and FT‐IR techniques. These char-
acterizations confirmed that the results for the recovered
catalyst are in good agreement with those for the fresh
catalyst. These characterizations are strong evidence for
the high stability of Fe3O4@Schiff‐base‐Pd organometal-
lic complex after recycling.
3.5 | Leaching study
In order to consider the leaching of Pd into the reaction
media, ICP analysis was performed. In this sense, the
Pd content in the reaction media in the synthesis of
1,1′‐biphenyl and methyl cinnamate was found to be
0.59 and 2.32%, respectively. The results show that the
leaching of Pd during the reaction process is negligible.
4 | CONCLUSIONS
We have described a simple strategy for the immobiliza-
tion of a novel Pd–Schiff base complex on the modified
surface of magnetite nanoparticles. The prepared mag-
netic nanocatalyst was characterized using FT‐IR spec-
troscopy, XRD, EDS, BET measurements, SEM, TEM, X‐
ray mapping, TGA, VSM and ICP analysis. The activity
of the catalyst was investigated in Suzuki and Heck
cross‐coupling reactions of aryl halides with
phenylboronic acid and methyl acrylate. This method
offers several advantages, including green conditions,
high yield, short reaction times, simple work‐up proce-
dure and ease of separation and recyclability of the mag-
netic catalyst.
FIGURE 12 XRD pattern of recovered catalyst

14 of 15
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[22] U. U. Shaikh, Q. Y. Tamboli, S. M. Pathange, Z. A. Dahan, Z.
ACKNOWLEDGMENTS
Pudukulathan, Chem. Methodol. 2018, 2, 73.
This work was supported by the Scientific Research Pro-
ject of Xuzhou University of Technology ‐ Cultivation
project (No. XKY2018133).
[23] Q. Pu, M. Kazemi, M. Mohammadi, Mini. Rev. Org. Chem. 2019,
16, 5775.
[24] M. Nasr‐Esfahani, S. J. Hoseini, M. Montazerozohori, R.
Mehrabi, H. Nasrabadi, J. Mol. Catal. A 2014, 382, 99.
[25] M. Kazemi, M. Ghobadi, Nanotechnol. Rev. 2017, 6, 549.
ORCID
[26] M. Kazemi, H. Kohzadi, O. Abdi, J. Mater. Environ. Sci. 2015, 6,
Lei Lei https://orcid.org/0000-0003-4904-9983
1451.
[27] L. Shiri, S. Zarei, M. Kazemi, D. Sheikh, Appl. Organometal.
Chem. 2018, 32, e3938.
REFERENCES
[28] Q. An, M. Yu, Y. Zhang, W. Ma, J. Guo, C. Wang, J. Phys.
Chem. C 2012, 116, 22432.
[1] A. Ghorbani‐Choghamarani, M. Mohammadi, Z. Taherinia,
J. Iran. Chem. Soc. 2019, 16, 411.
[29] L. Kong, X. Lu, X. Bian, W. Zhang, C. Wang, ACS Appl. Mater.
Interfaces 2010, 3, 35.
[2] M. M. Heravi, R. Moradi, M. Malmir, Curr. Org. Chem. 2018,
22, 165.
[30] J. Mondal, T. Sen, A. Bhaumik, Dalton Trans. 2012, 41, 6173.
[3] A. Taheri Kal Koshvandi, M. M. Heravi, T. Momeni, Appl.
Organometal. Chem. 2018, 32, e4210.
[31] S. Rostamnia, B. Gholipour, X. Liu, Y. Wang, H. Arandiyan,
J. Colloid Interface Sci. 2018, 511, 447.
[4] M. M. Heravi, L. Mohammadkhani, J. Organometal. Chem.
2018, 869, 106.
[32] A. Ghorbani‐Choghamarani, H. Rabiei, F. Arghand, Appl.
Organometal. Chem. 2017, 31, 1.
[5] L. Chen, A. Noory Fajer, Z. Yessimbekov, M. Kazemi, M.
[33] A. Ghorbani‐Choghamarani, M. Norouzi, Appl. Organometal.
Chem. 2016, 30, 140.
Mohammadi, J. Sulfur Chem. 2019, 40, 451.
[34] X. Moreau, J. M. Campagne, G. Meyer, A. Jutand, Eur. J. Org.
Chem. 2005, 2005, 3749.
[6] H.
Khojasteh,
V.
Mirkhani,
M.
Moghadam,
S.
Tangestaninejad, I. Mohammadpoor‐Baltork, J. Iran. Chem.
Soc. 2017, 14, 1139.
[35] M. M. Mojtahedi, M. S. Abaee, A. Rajabi, P. Mahmoodi, S.
Bagherpoor, J. Mol. Catal. A 2012, 361, 68.
[7] A. V. Vorogushin, X. Huang, S. L. Buchwald, J. Am. Chem. Soc.
2005, 127, 8146.
[36] H. A. Elazab, A. R. Siamaki, S. Moussa, B. F. Gupton, M. S. El‐
Shall, Appl. Catal. A 2015, 491, 58.
[8] M. Khanmoradi, M. Nikoorazm, A. Ghorbani‐Choghamarani,
Catal. Lett. 2017, 147, 1114.
[37] T. Tamoradi, A. Ghorbani‐Choghamarani, M. Ghadermazi,
Polyhedron 2018, 145, 120.
[9] H. Filian, A. Ghorbani‐Choghamarani, E. Tahanpesar,
J. Porous Mater. 2018, 26, 1091. https://doi.org/10.1007/
s10934‐018‐0698‐9
[38] H. Sharma, M. Bhardwaj, M. Kour, S. Paul, Mol. Catal. 2017,
435, 58.
[39] S. Sadjadi, M. Malmir, M. M. Heravi, F. Ghoreyshi Kahangi,
[10] M. Kazemi, M. Ghobadi, A. Mirzaie, Nanotechnol. Rev. 2018, 7,
Inorg. Chim. Acta 2019, 488, 62.
43.
[40] X. Chen, D. Qian, G. Xu, H. Xu, J. Dai, Y. Du, Colloids Surf. A
2019, 573, 67.
[11] A. Ghorbani‐Choghamarani, R. Sahraei, Z. Taherinia, Res.
Chem. Intermed. 2019, 45, 3199.
[41] F. Heidari, M. Hekmati, H. Veisi, J. Colloid Interface Sci. 2017,
501, 175.
[12] S. Molaei, T. Tamoradi, M. Ghadermazi, A. Ghorbani‐
Choghamarani, Catal. Lett. 2018, 148, 1834.
[42] B. Bananezhad, M. R. Islami, E. Ghonchepour, H. Mostafavi,
[13] A. Ghorbani‐Choghamarani, M. Mohammadi, T. Tamoradi, M.
Ghadermazi, Polyhedron 2019, 158, 25.
A. M. Tikdari, H. R. Rafiei, Polyhedron 2019, 162, 192.
[43] H. Veisi, S. Najafi, S. Hemmati, Int. J. Biol. Macromol. 2018,
113, 186.
[14] Y. S. Feng, X. Y. Lin, J. Hao, H. J. Xu, Tetrahedron 2014, 70,
5249.
[44] F. Rafiee, P. Khavari, Z. Payami, N. Ansari, J. Organometal.
Chem. 2019, 883, 78.
[15] T. Tamoradi, A. Ghorbani‐Choghamarani, M. Ghadermazi,
Appl. Organometal. Chem. 2018, 32, e4340.
[45] E. Ghonchepour, M. R. Islami, A. M. Tikdari, J. Organometal.
Chem. 2019, 883, 1.
[16] N. Taheri, F. Heidarizadeh, A. Kiasat, J. Magn. Magn. Mater.
2017, 428, 481.
[46] A. Khazaei, M. Khazaei, M. Nasrollahzadeh, Tetrahedron 2017,
73, 5624.
[17] R. Kardooni, A. R. Kiasat, H. Motamedi, J. Taiwan Inst. Chem.
Eng. 2017, 81, 373.
[47] E. Pourian, S. Javanshir, Z. Dolatkhah, S. Molaei, A. Maleki,
[18] S. Gupta, M. Lakshman, J. Med. Chem. Sci. 2019, 2, 51.
ACS Omega 2018, 3, 5012.
[19] B. Maleki, A. V. Mofrad, R. Tayebee, A. Khojastehnezhad,
[48] L. Levy, Y. Sahoo, K.‐S. Kim, E. J. Bergey, P. N. Prasad, Chem.
Mater. 2002, 14, 3715.
H. Alinezhad, S. E. Rezaei, Russ. J. Gen. Chem. 2017, 87, 2922.
[20] B. Atashkar, A. Rostami, A. Rostami, M. A. Zolfigol, Appl.
Organometal. Chem. 2019, 33, e4691.
[49] P. B. Bhat, F. Inam, B. R. Bhat, ACS Comb. Sci. 2014, 16, 397.
[50] L. Nguyen, F. F. Tao, Y. Tang, J. Dou, X.‐J. Bao, Chem. Rev.
2019, 119, 6822.
[21] H. Hasani, M. Irizeh, Asian J. Green Chem. 2018, 2, 85.

LEI
15 of 15
[51] W. Adam, C. R. Saha‐Möller, P. A. Ganeshpure, Chem. Rev.
2001, 101, 3499.
[59] A. Ghorbani‐Choghamarani, M. Mohammadi, R. H. E. Hud-
son, T. Tamoradi, Appl. Organometal. Chem. 2019, 33, e4977.
[52] M. A. P. Martins, C. P. Frizzo, D. N. Moreira, L. Buriol, P.
[60] A. J. Amali, R. K. Rana, Chem. Commun. 2008, 35, 4165.
[61] D. K. Yi, S. S. Lee, J. Y. Ying, Chem. Mater. 2006, 18, 2459.
Machado, Chem. Rev. 2009, 109, 4140.
[53] M. A. P. Martins, C. P. Frizzo, A. Z. Tier, D. N. Moreira, N.
Zanatta, H. G. Bonacorso, Chem. Rev. 2014, 114, PR1.
[54] A. Domling, W. Wang, K. Wang, Chem. Rev. 2012, 112, 3083.
How to cite this article: Lei L. Pd–Schiff base
complex supported on Fe3O4 magnetic
nanoparticles: A new and highly efficient reusable
catalyst for C–C bond formation in water. Appl
Organometal Chem. 2019;e5158. https://doi.org/
10.1002/aoc.5158
[55] L. Shiri, A. Ghorbani‐Choghamarani, M. Kazemi, Appl.
Organometal. Chem. 2017, 31, 1.
[56] L. Shiri, S. Rahmati, Z. Ramezani Nejad, M. Kazemi, Appl.
Organometal. Chem. 2017, 31, 1.
[57] S. Hejazi, A. Shojaei, K. Tabatabaeian, F. Shirini, J. Serb. Chem.
Soc. 2015, 80, 971.
[58] M. Mirzaee, B. Bahramian, P. Gholampour, S. Teymouri, T.
Khorsand, Appl. Organometal. Chem. 2019, 33, e4792.