Highly Dispersed Palladium Nanoparticle-Loaded Magnetic Catalyst (FeS@EP–AG–Pd) for Suzuki Reaction in Water

Article abstract of DOI:10.1007/s10562-017-2009-5

Abstract: In this work, an efficient epichlorohydrin–aminoguanidine-modified Fe₃O₄@SiO₂ magnetic nanoparticles (FeS@EP–AG–Pd) with highly dispersed Palladium nanoparticles (Pd NPs) was reported for Suzuki reaction in water. After preparation of Fe₃O₄@SiO₂ (FeS), special epichlorohydrin–aminoguanidine linker as a ligand with high content of heteroatoms was covalently bonded onto the FeS MNPs to increase their electron density. Pd^II ions were then loaded on surface of FeS@EP–AG MNPs and reduced for achieving the uniformly dispersed Pd NPs. FeS@EP–AG–Pd MNPs were performed in Suzuki reaction as an efficient catalyst in water as a green non-toxic solvent. Magnetically separable and recyclable FeS@EP–AG–Pd MNPs were then fully characterized by FTIR, SEM, TEM, TGA, VSM, XRD, and ICP–OES. The heterogeneous catalyst could also easily be recovered and reused with no loss of activity over 6 cycles. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-017-2009-5

Catal Lett
DOI 10.1007/s10562-017-2009-5
Highly Dispersed Palladium Nanoparticle-Loaded Magnetic
Catalyst (FeS@EP–AG–Pd) for Suzuki Reaction in Water
Iraj Sarvi1 · Mostafa Gholizadeh1 · Mohammad Izadyar1
Received: 10 January 2017 / Accepted: 17 February 2017
© Springer Science+Business Media New York 2017
Abstract In this work, an efficient epichlorohydrin–ami-
noguanidine-modified Fe3O4@SiO2 magnetic nanoparti-
cles (FeS@EP–AG–Pd) with highly dispersed Palladium
nanoparticles (Pd NPs) was reported for Suzuki reaction
in water. After preparation of Fe3O4@SiO2 (FeS), special
epichlorohydrin–aminoguanidine linker as a ligand with
high content of heteroatoms was covalently bonded onto
the FeS MNPs to increase their electron density. PdII ions
were then loaded on surface of FeS@EP–AG MNPs and
reduced for achieving the uniformly dispersed Pd NPs.
FeS@EP–AG–Pd MNPs were performed in Suzuki reac-
tion as an efficient catalyst in water as a green non-toxic
solvent. Magnetically separable and recyclable FeS@
EP–AG–Pd MNPs were then fully characterized by FTIR,
SEM, TEM, TGA, VSM, XRD, and ICP–OES. The hetero-
geneous catalyst could also easily be recovered and reused
with no loss of activity over 6 cycles.
Graphical Abstract
B(OH)2
R'
OH
NH
H
N
O
N
H
NH2
R
Fe3O4
R'
Pd NPs
SiO2
X
H
2O
R
atalyst
Keywords Magnetic catalyst · Suzuki reaction · Biaryls ·
Epichlorohydrin · Aminoguanidine
1 Introduction
It is well-known that palladium-catalyzed coupling reac-
tions are very important and powerful methodologies in
the synthetic organic chemistry [1, 2]. Among them, the
Suzuki reaction is one of the most versatile methods for the
synthesis of a variety of biaryls and alkenes via C–C bond
formation [3–5]. These are structural constituents which
were presented in numerous agrochemicals, drugs, natural
products, pharmaceuticals, conjugate polymers, and other
valuable materials [6–11]. Suzuki reaction is generally car-
ried out using homogeneous palladium–ligand complexes
which are generally toxic and unrecoverable [3–5, 12]. The
Suzuki reaction have been reviewed in the literature, pre-
viously [13–19]. Heterogeneous Pd-based catalysts due to
ease of recovery and reuse of the precious metal have been
investigated [20–23]. Recently, the environmental impact
of chemical processes have been considered based on green
chemistry awareness [2, 24]. Most of the chemical waste
corresponds to the solvent. Therefore, the use of non-toxic
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-017-2009-5) contains supplementary
material, which is available to authorized users.
* Mostafa Gholizadeh
m_gholizadeh@um.ac.ir
1
Department of Chemistry, Ferdowsi University of Mashhad,
Mashhad 91775-1436, Islamic Republic of Iran
Vol.:(0123456789)
1 3

I. Sarvi et al.
solvents such as water as a benign solvent with abundant
natural occurrence are common choice for green organic
transformations. It is commonly considered that the use of
water will have the least impact to the environment [25].
The Suzuki reaction in water has been reviewed recently
[26]. The supported catalytic systems require toxic organic
solvents and high temperature due to the rate limiting steps
resulting from the high activation barriers of the substrates.
To improve the catalyst activity and lowering of the reac-
tion temperature many efforts are focused on producing
of the electron-rich homogeneous catalysts with special
expensive ligands but only a few approaches have been
reported for improving heterogeneous catalysts, because the
electron density of the metal sites in heterogeneous scale
could not be easily modified [27–31]. Although, these cata-
lytic systems can be carried out under mild reaction con-
ditions and within only several minutes, but still reaction
temperature, effective and activated metal–ligand systems
and green solvents are challenging. Several approaches
were reported for Suzuki reaction in water with different
ligands. Also, the previously reported studies showed that
increased length of the ligand and the incorporation of an
additional nitrogen atom in the structure of the catalyst lead
to higher activity in Suzuki reaction [32]. The tridentate
ligand Phenylphosphinacalix [3] trifuran in the presence of
palladium acetate was studied for Suzuki reaction in water
[33]. This catalyst leads to a facilitated oxidative addition
step which proved extremely active. The complex of pal-
ladium chloride and TPPTS (TPPTS=tris(3-sulfonato-
phenyl)phosphine hydrate, sodium salt) was prepared for
Suzuki reaction in aqueous medium at room temperature
[34, 35]. Palladium supported on triazolyl-functionalized
polysiloxane was studied as a recyclable catalyst for the
Suzuki coupling of aryl bromides and phenylboronic acid
in a 2-propanol–water mixture [36]. The application of the
modified Montmorillonite clay supported Pd(0)-nanoparti-
cles as an efficient catalyst for the Suzuki reaction in water
was explored [37]. Also, magnetic nanoparticles have been
received considerable attention in terms of a large surface
area, free of particle diffusion resistance, easy separation
and low cost [38, 39]. Waghmode and co-worker have
developed a protocol for the immobilization of Pd NPs on
NiFe2O4 as a separable catalyst for the Suzuki reaction [40].
Zhu and Diao have prepared a Fe3O4@Carbon composite
to be used in the immobilization of Pd NPs through a pre-
cipitation–deposition method [41]. Yu and co-workers have
synthesized a heterogeneous Pd catalyst by anchoring Pd
(II) onto poly (undecylenic acid-co-N-isopropylacrylamide-
bearing a phosphine-Pd(II) complex for Suzuki reaction
[44, 45]. Phan and co-workers have demonstrated that
increased length of the ligand and the incorporation of an
additional nitrogen atom in the structure of the catalyst
leading to higher activity in Suzuki reaction [46]. Those
studies indicated that the linkers or ligands between NPs
and core–shell structure had important effects on cata-
lytic activity. Based on this knowledge that introduction
of special ligands leading to activation of homogeneous
catalysts we are interested in enhancing the activity of het-
erogeneous Pd-based catalysts by increasing their electron
density via special epichlorohydrin and aminoguanidine
as ligands with high content of heteroatoms in water as a
solvent. Aminoguanidine is an investigational drug for the
treatment of diabetic nephropathy [47]. Our aim has been
to investigate designing of the efficient catalytic system
with high activity for Suzuki cross-coupling reaction with
minimum by-products in green media. Herein, we report
our work on impregnating Pd nanoparticles into epichlo-
rohydrin and aminoguanidine-functionalized Silica coated
Fe3O4 magnetic nanoparticles as an efficient catalyst for
Suzuki reaction in water. Magnetic nanoparticles coated by
aminoguanidine were used for selective adsorption of acid
dyes from aqueous solution which was reported previously
[48]. Heterogeneous palladium–aminoguanidine func-
tionalized graphene oxide was also reported for reduction
of 4-nitrophenol to 4-aminophenol. However, to the best
of our knowledge, there has been no report about the het-
erogeneous magnetic Pd/epichlorohydrin–aminoguanidine
(EP–AG) catalyst for Suzuki cross coupling reaction. A
schematic pathway of FeS@EP–AG–Pd catalyzed Suzuki
cross-coupling reaction is shown in Scheme 1.
2 Experimental
2.1 Materials and Apparatus
All chemical compounds were obtained from Sigma-
Aldrich in analytical grade and used without further puri-
fication. For morphology and size study of the as-prepared
samples TEM and SEM experiments were conducted on a
Leo 912AB microscope (Germany) operated at 120 kV and
Leo 1450VP (Germany), respectively. Wide-angle X-ray
diffraction (WAXRD) patterns were recorded on a Bruker
D4 X-ray diffractometer (Germany) with Ni-filtered Cu KR
radiation (40 kV, 40 mA). The percentage weight loss of
shell and arginine was studied using TGA, (Mettler Toledo
LF, Switzerland). FT-IR spectra were collected on a Nico-
let Fourier spectrophotometer, using KBr pellets (USA). To
exhibit the magnetic behavior of the catalyst, VSM (7400
co-potassium
4-acryloxyoylpyridine-2,6-dicarboxylate)-
coated Fe3O4 [42]. Alper’s group reported that the Pd/
(SiO2/Fe3O4) catalyzed the Heck reactions [43]. Heuze
and co-workers have reported the core–shell γ-Fe2O3/poly-
mer magnetic nanoparticles functionalized with a dendron
1
Lake Shore, USA) was used. H and 13C NMR spectra
were measured (CDCl3) with a Bruker DRX-300 AVANCE
1 3

Highly Dispersed Palladium Nanoparticle-Loaded Magnetic Catalyst (FeS@EP–AG–Pd) for Suzuki…
Scheme 1 Studied pathways of Suzuki coupling
Scheme 2 Schematic representation of catalyst preparation
spectrometer at 300 and 75 MHz, respectively. The con-
tents of palladium on the prepared solid catalysts and Pd
leaching were measured by Avio 200 ICP Optical Emission
Spectrometer (ICP–OES).
autoclave with a capacity of 100 ml, then sealed and
heated to 200 °C. After reaction for 12 h, the autoclave
was cooled to room temperature. The obtained black
Fe3O4 MNPs were collected with a magnet and washed
several times with water and ethanol. Finally, the product
was then dried under vacuum at 50 °C for 12 h. An aque-
ous dispersion of Fe3O4 nanoparticles (6 ml, 0.05 g) were
dissolved into a mixture of absolute ethanol (560 ml),
deionized water (140 ml). Ammonia solution (28 wt%,
10 ml) was then added to the mixture under ultrasound
for 20 min. Then, 8.0 ml tetraethyl orthosilicate (TEOS)
was dropped into the mixture under stirring for 12 h. The
acquired silica coated Fe3O4 nanoparticles were sepa-
rated by using a magnet, consequently washed with etha-
nol several times and dried under vacuum.
2.2 Synthesis of Fe3O4 and Fe3O4@SiO2 Magnetic
Nanoparticles (MNPs)
Fe3O4 Magnetic nanoparticles were prepared by a hydro-
thermal technique as previously reported [49]. Briefly,
1.6 g (6 mmol) FeCl3·6H2O, 4.0 g (48.8 mmol) sodium
acetate (NaOAc) and 1.5 g (5.8 mmol) trisodium citrate
(Na3Cit) were dissolved in 75 ml of ethylene glycol (EG),
after vigorous stirring for 1 h, the obtained yellow solu-
tion was transferred into a Teflon-lined stainless-steel
Fe3O4 MNPs
FeS@EP-AG-Pd
Fe-O
a
b
a
b
Si-O-Si
c
20
30
40
50
60
70
3900
3400
2900
2400
1900
1400
900
400
Wavenumber cm-1
2θ (degree)
Fig. 1 FTIR spectra of a Fe3O4 MNPs, b FeS@EP–AG MNPs, c
Fig. 2 XRD patterns of a Fe3O4 MNPs and b FeS@EP–AG–Pd
aminoguanidine
MNPs
1 3

I. Sarvi et al.
Fig. 3 a TEM image of Fe3O4 MNPs. b TEM, and d SEM images of FS MNPs. c1, c2 TEM and e EDS images of FS@EP–AG–A–Pd MNPs
1 3

Highly Dispersed Palladium Nanoparticle-Loaded Magnetic Catalyst (FeS@EP–AG–Pd) for Suzuki…
80
2-Methyl-4-nitro-1,1′-biphenyl 3d: white solid, mp:
1
217 °C. H-NMR (CDCl3, 300 MHz): δ = 2.29 (s, 1H),
60
40
7.18–7.42 (m, 5H), 8.01 (dd, J = 2.4 Hz, 2H), 8.03–8.08
(m, 1H). 13C-NMR (CDCl3, 75 MHz): δ = 20.64, 120.91,
125.16, 127.99, 128.47, 128.70, 130.65, 137.29, 139.77,
147.02, 148.57.
20
0
-20
-40
-60
-80
b
a
3 Results and Discussion
-20000
-10000
0
10000
20000
Applied field (Oe)
The FeS–EP–AG–Pd nanocatalyst was prepared in 4
steps: in the first step the Fe3O4@SiO2 magnetic nanopar-
ticles was prepared by Stöber method, in step 2, EP–AG
linker as novel designed ligand bonded on the surface of
FeS nanoparticles. In step 3, Pd(OAc)2 was complexed
to this ligand. Finally, Pd nanoparticles were gener-
ated via NaBH4 reduction procedure. Fe3O4@SiO2@
EP–AG–Pd (FeS–EP–AG–Pd) nanocatalyst was char-
acterized by transmission electron microscopy (TEM),
scanning electron microscopy (SEM), X-ray diffractom-
etry (XRD), thermal gravimetric analysis (TGA), vibra-
tion sampling magnetometer (VSM), and Fourier trans-
form infrared spectroscopy (FTIR). The preparation of
the nanocatalyst is schematically described in Scheme 2.
As shown in Fig. 1a the strong characteristic peak
at 565 cm−1 attributed to the stretching vibration of the
Fe–O bond of Fe3O4 magnetic nanoparticles (MNPs).
Intensity of Fe–O bond significantly was decreased and
a strong absorption peak at 1100 cm−1 and weak absorp-
tion peak at 950 cm−1 was appeared in Fig. 1b in compar-
ison with Fig. 1a, which assigned to asymmetric vibra-
tion of the Si–O–Si bond and the symmetric stretching of
the Si–OH bond, respectively. These characteristic peaks
confirm the silica coating of the surface of Fe3O4 MNPs.
Also, the C–H stretching and C–O–C vibration stretching
located at 3055 and 1260–1240 cm−1 respectively, which
were covered by the broad band of stretching vibration
Fig. 4 Magnetization hysteresis loops: a Fe3O4, b FeS@EP–AG–Pd
MNPS
2.3 Synthesis of FeS@EP–AG–Pd MNPs
Fe3O4@SiO2 (1 g) added to the solution of epichlorohy-
drin (1 ml) in ethanol (3 ml) and the mixture was stirred at
60°C. After 5 h, the solvent was removed and the resulting
solid was washed with ethanol and dried at 80°C. Finally,
0.1 g of FeS–EP MNPs and 0.2 g aminoguanidine in 20 ml
EtOH was mixed and sonicated for 30 min. the mixture was
then stirred for 2 h. The magnetic FeS–EP–AG MNPs were
collected with a magnet and washed several times with
water and ethanol and dried at 50°C. 0.2 g of FeS@EP–AG
were sonicated in 10 ml deionized water for 5 min and then
stirred with 5 ml of 1 M aqueous solution of Pd(OAc)2 for
6 h. Finally, the catalyst was separated from the solution.
For our main goal, PdII ions of catalyst was treated with
NaBH4 to produce the dispersed Pd NPs based catalyst.
2.4 Synthesis of Biaryls 3
In a test tube equipped with a magnetic stirrer bar, the
aryl halide 1 (1 mmol) was mixed with phenyl boric
acid 2 (1.2 mmol), K2CO3 (2 mmol), and the Pd-catalyst
(0.1 mol% Pd) in 2 ml of H2O in air. The reaction mixture
was then stirred at 50°C for appropriate time. After com-
pletion of the reaction, the catalyst was removed by magnet
and washed with ethanol and water (3×5 ml). The aque-
ous layer was extracted with chloroform, then organic layer
dried over anhydrous MgSO4. The solvent was evaporated
under reduced pressure to give the corresponding biaryl
compounds. All the products were previously reported [5,
8–12] and were confirmed by the spectroscopic method
DrTGA
mg/min
TGA
%
0.01
100
0.005
0
80
60
40
20
0
58.25
592.58
600
477.48
-0.005
-0.01
378.85
400
using H and 13C NMR (see supporting information). The
1
spectral data for selected product:
0
200
800
Biphenyl 3a: white solid, mp: 70–71°C. 1H-NMR
(CDCl3, 300 MHz): δ=7.37–7.40 (m, 2H), 7.43–7.53 (m,
4H), 7.63–7.68 (m, 4H). 13C-NMR (CDCl3, 75 MHz):
δ=122.45, 123.73, 124.03, 136.54.
Temp [oC]
Fig. 5 Thermogravimetric (TG) analysis curve of FeS@EP–AG–Pd
MNPs
1 3

I. Sarvi et al.
Yielda (%)
Table 1 Optimization of model
reaction over the FeS@EP–AG–
Pd MNPs
Entry
1
Base
Solvent
Mol% Pd
Time (h)
Temp (°C)
K2CO3
H2O
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.05
0.2
1.5
2
2
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
r.t./50
15/99
30/98
20/85
10/75
5/99
20/99
15/60
25/80
5/40
10/50
5/40
10/30
30/60b
25/65b
20/60b
5/55
H2O/EtOH
H2O/DMF
Toluene
H2O
H2O/EtOH
Toluene
DMF
DMF
H2O
DMF
H2O
2
2
CsCO3
1.5
1.5
2
2
3
3.5
3.5
5
5
5
3
4
Triethylamine
K3PO4
5
6
7
8
9
NaOH
H2O
H2O
H2O
H2O
Ba(OH)2
Ca(OH)2
K2CO3
K2CO3
4
4
2
20/93
Reaction conditions: 1 mmol of 4-bromoacetophenone, 1.2 mmol of phenylboronic acid, 2 mmol base, 2
ml solvent
aIsolated yield
bPd-black was also observed
O–H and Si–O–Si bonds. As shown in Fig. 1c broad
absorption band around 2900–3500 cm−1 are ascribed to
the stretching vibration of O–H and –NH2 groups. The
bands at 2950 and 2870 cm−1 are due to the stretching
vibration of aliphatic CH2 groups of epichlorohydrin, and
the band at 1470 cm−1 assigned to the C–N stretching of
aminoguanidine Fig. 1b, c). The band at 1660 cm−1 cor-
responds to the C=N stretching vibration of aminoguani-
dine [48].
by TEM and SEM (Fig. 3). The Fe3O4 MNPs are approxi-
mately round-shaped particles (Fig. 3a). After coating
of Fe3O4 MNPs surface with silica, the FeS nanoparti-
cles with typical core/shell morphology were obtained
(Fig. 3b). After reduction of immobilized PdII ions the uni-
formly dispersed Pd NPs on FeS MNPs were observed with
particles size below 5 nm (Fig. 3c1, c2). The EDS result
(Fig. 3e) shows that the elemental composition of the nano-
catalyst are Fe, Si, O, and Pd, and the catalyst is composed
of Fe3O4, silica, and Pd which agrees well with the XRD
analysis (Fig. 2). Based on SEM image of catalyst (Fig. 3d)
spherical morphology of nanocatalyst is clearly observed.
Also, aggregation of nanoparticles were observed due
to the magnetic nature of the catalyst. The content of Pd
NPs in the sample was confirmed by inductively cou-
pled plasma/optical electron microscopy (ICP–OES). The
amount of Pd NPs loaded onto the FeS@EP–AG–Pd MNPs
were 8.721 wt%.
As shown in Fig. 2, the X-ray diffraction patterns of
FeS MNPs and FeS@EP–AG–Pd NPs revealed diffrac-
tion peaks located at 30.35° (220), 35.44° (311), 43.31°
(400), 53.14° (422), 56.87° (511), and 62.51° (440), which
assigned to diffraction of the Fe3O4 crystal, according to
the JCPDS card no. 19-0629. No other peak can be found
in Fig. 2a, confirming the purity of Fe3O4 crystalline phase.
The Fe3O4 core exhibits a cluster-like nanostructure with
the average crystalline size of 13.4 nm calculated by the
Debye–Scherrer equation from the broadness of the (311)
peak. The intensity of Fe3O4 peaks were decreased due to
the heavy atom effect of Pd (Fig. 2b), with diffraction peaks
located at 39.79° (111), 46.10° (200), 67.15° (220) and a
face-centered cubic structure of Pd (JCPDS no. 46-1043).
Based on Debye–Scherrer equation the average size of the
Pd NPs is estimated to be 4.3 nm from the broadness of the
(111) peak.
To demonstrate the magnetic properties of synthesized
samples, VSM analyzes are illustrated in Fig. 4. The mag-
netic hysteresis loops of FeS@EP–AG–Pd MNPs (Fig. 4b)
indicate a superparamagnetic characteristic, which is inher-
ited from the Fe3O4 core. The magnetic saturation (Ms)
value of the Fe3O4 (Fig. 4a) and FeS@EP–AG–Pd MNPs
are 62.87 and 36.21 emu/g, respectively, this decrease in
the Ms values of FeS@EP–AG–Pd MNPs in comparison to
Fe3O4 MNPs related to the silica shell for the disordered
structure at interfaces.
The physical appearances of Fe3O4 and Fe3O4@SiO2
and FeS@EP–AG–Pd nanoparticles were characterized
1 3

Highly Dispersed Palladium Nanoparticle-Loaded Magnetic Catalyst (FeS@EP–AG–Pd) for Suzuki…
Table 2 Scope of the FeS@EP–AG–Pd MNPs-promoted Suzuki coupling of various aryl halides and phenylboronic acids
FeS@EP-AG-Pd
0.1
X
B(OH)2
mol%
+
CO 50 o
K
H
2O
,
3
C,
2
R
R'
R
R'
3
1
2
Entry
1
X
Time (h)
2/2
Yieldb (%)
R
R′
3
H
H
H
H
I/Br
99/98
98/98
96/97
3a
3b
3c
H
3C
2
3
4-CH3
4-NO2
I/Br
I/Br
2/2.5
1/1.5
N
O2
O2
CH3
4
5
6
2-Me/4-NO2
4-OMe
H
H
H
I
1
99
N
3d
H
3CO
I/Br
I/Br
2/2
99/96
97/98
3e
COOH
2-CO2H
1/1.5
3f
F
3C
7
8
9
3-CF3
4-I
H
H
H
I
1
96
99
3g
3h
Br
1.5
H2N
3-NH2
I/Br
2/2.5
94/96
3i
O
10
11
4-COCH3
4-CHO
H
H
Br
Br
1
99
99
H
3C
3j
O
1.5
H
3k
1 3

I. Sarvi et al.
Table 2 (continued)
Entry
X
Time (h)
Yieldb (%)
R
R′
3
12
2-I/Pyridine
H
Br
2.5/2.5
95
N
3l
13
H
3-NO2 I/Br
3-NO2 I/Br
3-NO2 I/Br
2.5/3
2/3
93/90
95/90
92/94
NO2
NO2
3m
3n
3o
14
15
4-Me
4-NO2
H
3C
NO2
2/2.5
N
O2
O2
CH3
N
16
17
2-Me/4-NO2 3-NO2
I
1.5
96
NO2
3p
H
3CO
4-OMe
3-NO2 I/Br
2/2.5
98/97
NO2
3q
3a
3c
18
19
H
H
H
Cl
Cl
10
8
35c
45c
N
O2
4-NO2
H
3CO
20
4-OMe
H
Cl
12
7
40c
45c
3e
3j
O
21
22
4-COCH3
H
H
Cl
Cl
H
3C
O
4-CHO
8
45c
H
3k
aConditions: 1 (0.1 mmol), 2 (0.12 mmol), K2CO3 (2 equiv.), FS@EP-AG-Pd MNPs 0.1
b
c
mol%, H2O (2 ml), 50 oC. Isolated yield. 0.15 mol% catalyst.
1 3

Highly Dispersed Palladium Nanoparticle-Loaded Magnetic Catalyst (FeS@EP–AG–Pd) for Suzuki…
studied. The highest yield were achieved with K2CO3 as a
a
Fe3O4MNPs
base (99%). Triethylamine and K3PO4 revealed low yield of
product (Table 1, entries 3, 4). With stronger alkalis such as
NaOH, Ba(OH)2, and Ca(OH)2 the yields were decreased
(Table 1, entries 5–7). Also, CsCO3 was employed which
gave 99% of yield (Table 1, entry 2), but due to high
price of this base, K2CO3 was selected as reaction base.
Extremely high alkalinity might decrease the catalytic effi-
ciency of FeS@EP–AG–Pd MNPs. Therefore, based on the
above experiments, water (2 ml), K2CO3 (2 mmol), and Pd
(0.1 mol%) were employed in following experiments.
The adaptability of FeS@EP–AG–Pd MNPs was also
investigated by coupling of phenylboronic acid (2) with
different iodo, bromo, and chloro benzenes (1) under the
optimized conditions to produce biaryl compounds (3),
as shown in Table 2. Various aryl halides with electron-
donating or electron-withdrawing groups were employed.
Electron withdrawing substituted halobenzene derivatives
such as 4-nitroiodo/bromobenzene (1c, entry 3), 2-iodo/
bromobenzoicacid (1f, entry 6), 3-CF3-iodobenzene (1g,
entry 7), 3-aminoiodo/bromobenzene (1i, entry 9), 4-bro-
moacetophenone (1j, entry 10), and 4-bromobenzaldehyde
(1k, entry 11) were converted in excellent yields to the cor-
responding biphenyl products 3c (96/97%), 3f (97/98%), 3g
(96%), 3i (94/96%), 3j (99%), and 3k (99%). The simulta-
neous double-coupling of phenylboronic acid on 1-iodo-
4-bromobenzene (1h, entry 8) and 2-iodo-5-bromopyri-
dine (1l, entry 12) provided triaryl compounds 3h and 3l
in 99 and 95% yield respectively, after only 1.5 h (Table 2,
entries 8, 12). Electron withdrawing and electron donating
substituted halobenzene derivatives with 3-nitrophenylbo-
ronic acid in Suzuki cross-coupling were also converted in
high yields to the corresponding biaryl products 3 (Table 2,
entries 13–17). More challenging Suzuki coupling of chlo-
rinated substrates was investigated in our optimized pro-
cedure (Table 2). These results showed slightly higher
catalyst loading (0.15 mol%) and reaction time (7–12 h)
were required. The reaction led to products 3 in good
yield (35–45%) with electron deficient and electron rich
substrates (Table 2, entries 18–22). There was no signifi-
cant change in cross-coupling of chlorinated substrates by
increasing of the reaction temperature up to 80°C, but the
yield of homocoupling products were increased (monitored
by TLC).
FS@EP-AG-Pd
20
30
40
50
60
70
2θ (degree)
99%
97%
98% 95%
93%
94%
93%
b
100%
80%
60%
40%
20%
0%
1
2
3
4
5
6
7
Number of runs
Fig. 6 a XRD analyze of recycled catalyst and b recyclability study
of catalyst for model reaction
To demonstrate the thermal stability of the nanocata-
lyst, thermal gravimetric (TG) were carried out in a static
atmosphere of nitrogen (Fig. 5). The FeS@EP–AG–Pd
MNPs revealed four-step weight loss in the temperature
region of 30–800°C which the initial weight loss up to
200°C was probably due to the removal of surface hydrox-
yls and surface adsorbed water, while the weight loss at
200–600°C could be attributed mainly to the decomposi-
tion of epichlorohydrin–aminoguanidine bound from the
silica shell. Probably, due to oxidation of Pd nanoparticles
or Fe3O4 MNPs the weight will increase in the temperature
region of 308–360°C.
The catalytic activity of FeS@EP–AG–Pd MNPs was
examined in the Suzuki cross-coupling reaction of 4-bro-
moacetophenone (1 mmol) with phenylboronic acid
(1.2 mmol). For optimization of the reaction conditions dif-
ferent bases, solvents, and Pd loading were used as shown
in Table 1. Water (2 ml) gave an excellent yield (99%) at
50°C with 0.1 mol% of catalyst loading (Table 1, entry
1). Also, the mixture of water/ethanol (2 ml, 1:1) at entry
2 showed high product yield (98%). The aprotic solvents
resulted in lower yields. With 0.05 mol% of catalyst only
65% of the product yield was observed, by increasing the
catalyst loading up to 0.2 mol% 93% of product yield was
achieved (Table 1, entries 8, 9). Different bases were also
Reusability study of FeS@EP–AG–Pd MNPs as the
main advantages of heterogeneous catalysts showed that
the prepared nanocatalyst has recyclability in addition to its
easy and simple recovery in model Suzuki reaction. FeS@
EP–AG–Pd MNPs has ability to be recycled at least for 6
runs (Fig. 6c). The catalyst was recovered after each run
and extensively washed with EtOH and dried at 50°C for
2 h. As shown in Fig. 6b the powder XRD data of recy-
cled catalyst after 6 cycle, clearly illustrate that the catalyst
1 3

I. Sarvi et al.
16. Maluenda I, Navarro O (2015) Molecules 20:7528
still remains as crystalline, and the average crystallite size
estimated using Scherrer’s equation is 4.2 nm. The amount
of Pd NPs loaded onto the FeS@EP–AG–Pd MNPs were
8.213 wt% after 6 recycle base on ICP–OES.
17. Li H, Seechurn CCCJ, Colacot TJ (2012) ACS Catal 2:1147
18. Kumar A, Rao GK, Kumar S, Singh AK (2013) Dalton Trans
42:5200
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4 Conclusion
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In summary, highly dispersed Pd-loaded nanocatalysts
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using
epichlorohydrin/aminoguanidine-functionalized
Fe3O4@SiO2 as a support were synthesized. The FeS@
EP–AG–Pd MNPs were used for Suzuki cross-coupling of
various iodo/bromo/chloro halo benzenes with phenylbo-
ronic acids. Our designed epichlorohydrin/aminoguanidine
linker as ligand with high content of heteroatoms lead to
the well dispersed Pd NPs onto the surface of catalyst with
high catalytic activity. This catalyst promotes the Suzuki
coupling in water as a green non-toxic solvent. The FeS@
EP–AG–Pd MNPs after easy separation from the reaction
mixture by an external magnet were reused 6 times with
high product yields.
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Acknowledgements The authors gratefully acknowledged for par-
tially financial support of this study (Grant No. 3/41258) by Research
Council of Ferdowsi University of Mashhad.
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1 3