Y. Dong et al.
Journal of Physics and Chemistry of Solids 153 (2021) 110007
Scheme. 1. Preparation of 1-methyl-3-(triethoxy silicon propyl) imidazole chloride salt.
including noble metals [39], carbon materials [40], polymer [41] and
metal oxide [42], thus preventing the aggregation of metal nano-
Technology Co., Ltd. Chloropropyl triethoxysilane was obtained from
Heowns Biochem Technologies LLC. N-Methylimidazole was acquired
from Sinopharm Chemical Reagent Beijing Co., Ltd and used as received.
2
particles. Amongst various coating materials, silica (SiO ) can solve
these limitations of pure magnetic particles through providing better
protection under weak acid conditions and presenting inertness to redox
reactions in aqueous systems, and numerous favorable properties,
including large pore volume, high surface area, excellent biocompati-
bility, tunable pore size as well as low cytotoxicity, which are suitable
2
Dichloromethane and toluene were dried with CaH overnight, distilled
and stored in brown bottles. Other reagents were used as provided for
the reaction without further treatment. Deionized water was used in
these experiments.
for specific desired applications [43,44]. Moreover, the SiO
the versatility for covalent attachment via various desirable functional
groups [45]. For instance, Sun et al. developed a Fe @SiO core-shell
2
exhibited
2.2. Characterization
3
O
4
2
Thermogravimetric analysis (TGA) was carried out on a STA 409 PC
thermal analysis apparatus (NETZSCH, Germany) with a heating rate of
structure supported Pd catalyst in an environmental benign way, which
showed high catalytic activity and good reusability for the catalytic
nitrite reduction in aqueous solution [46].
◦
ꢀ 1
10 C min under aerobic condition. The X-ray photoelectron spec-
troscopy (XPS) data were recorded with a PHI1600 instrument (Perki-
nElmer) using a monochromatic Al KR X-ray. Powder X-ray diffraction
As of late, as a vital kind of nitrogen-based ligands, N-heterocyclic
carbenes (NHCs) have been introduced as efficient ligands to fabricate
the novel catalyst for organic synthesis [47,48]. Dependent on the
properties including non-toxicity, air or moisture insensitivity, and easy
handle, NHCs have more advantages over than phosphine ligands for
acting as the quite flexible ligands in working effectively under mild and
green conditions [49,50]. In addition, these ligands could coordinate
numerous metals with its strong p-electrondonating nitrogen atoms,
displaying better resistance to metal leaching in catalysis process
involving high temperature [51,52]. However, only few studies con-
(XRD) were performed on a BDX3300 diffractometer using Cu/K
α
ra-
◦
diation with a wavelength of 1.54 Å in the 2θ range of 10–80 . The
scanning electron microscopic (SEM) images were collected on an FEI
Quanta 200SEM microscope. Transmission electron microscopy (TEM)
was performed with a Tecnai G2 F20 instrument. The elemental contents
of palladium were determined with Thermo Jarrell-Ash corporation,
ICP-9000 (N + M) inductively coupled plasma (ICP) atomic emission
spectrometer (AES). FT-IR spectra of samples were investigated on a
BIO-RAD FTS3000 IR spectrophotometer with pressed KBr pellets.
Elemental analysis was carried out using an Vario EL CUBE CHN
elemental analyzer. The purity of the products and the progress of the
reactions were analyzed by TLC on silica-gel 60 F254 (eluent: petroleum
sisting of SiO
reported and the resultant palladium complex was used in the Suzuki
reactions [53]. Gholinejad et al. reported that
2
as protecting shell to coat MNPs with NHCs have been
1
phosphinite-functionalized magnetic nanoparticles containing an imi-
dazolium ionic liquid moiety acted as the stabilizer for palladium
complex, and that utilized the catalyst on the synthesis of biaryls [54].
ether/ethyl acetate, 30/1). H NMR spectra were recorded on a Bruker
3
Avance 400 MHz spectrometer in CDCl with TMS as the standard.
Sedghi and co-workers prepared
a
magnetic carbon nano-
2.3. Synthesis of 1-methyl-3-(triethoxy silicon propyl) imidazole chloride
salt
tubes@chitosan N-heterocyclic carbene-palladium catalyst, which was
used as a green nanocatalyst in Suzuki cross-coupling reaction [55].
Nevertheless, these protocols have some defects such as the utilization of
toxic and air-sensitive phosphine ligands or relatively low loading of
catalysts. Encouraged by the existing progress, an assumption concern-
1-methyl-3-(triethoxy silicon propyl) imidazole chloride salt was
prepared according to the previous literature as depicted in Scheme 1
[56,57]. Briefly, a mixture of N-Methylimidazole (4.106 g, 50 mmol)
and (3-chloropropyl) triethoxysilane (12.412 g, 50 mmol) was refluxed
for three days in 40 mL toluene under inert atmosphere. After comple-
tion, the yellow phase was separated and washed with toluene (6 × 20
mL). The yellow oil product was obtained after drying under vacuum at
2
ing the incorporation of SiO coating MNPs with NHCs would be an ideal
approach for the purpose of anchoring palladium species on the sup-
porting material towards the afore-mentioned process.
3 4
As a promising and versatile matrix for the metal catalysts, Fe O
◦
MNPs are prone to be modified through binding to diverse kinds of
catalytic active species like transition metal complexes. Hence, we have
60 C for 24 h.
1-methyl-3-(triethoxy silicon propyl) imidazole chloride salt, yellow
1
designed a green responsive composite (Fe
3
O
4
@SiO
2
-NMIM-Pd). The
liquid [57], H NMR (400 MHz, CDCl ) δ = 10.18 (s, 1H), 7.64 (s, 1H),
3
green N-Methylimidazole modified Fe @SiO
3
O
4
2
nanoparticles sup-
7.27 (s, 1H), 4.14 (t, J = 7.2 Hz, 2H), 3.94 (s, 3H), 3.62 (q, J = 7.0 Hz,
6H), 1.81 (dt, J = 15.3, 7.5 Hz, 2H), 1.02 (t, J = 7.0 Hz, 9H), 0.43–0.38
(m, 2H).
ported Pd catalyst was prepared, and catalytic applicability in the pro-
duction of biaryls was evaluated. The Pd complex showed excellent
catalytic performance in Suzuki-Miyaura reactions with separation only
using an external magnet in several cycles. In brief, this study presented
that Pd complex was immobilized on the MNPs, which was exploited as
a heterogeneous catalyst for the preparation of biaryls.
1
3
C NMR (100 MHz, CDCl ) δ = 137.44, 123.86, 121.74, 58.42,
3
51.56, 36.39, 24.23, 18.11, 7.01.
2.4. Synthesis of Fe O4 magnetic nanoparticles (Fe O4 MNPs)
3
3
2
. Materials and methods
The Fe
58]. Briefly, a mixture of FeCl
(7.953 g, 0.04 mol) and sodium citrate dehydrate (C
.510 g) was dissolved in deionized water (100 mL) with vigorous me-
3
O
4
MNPs were synthesized according to our previous work
-6H O (21.624 g, 0.08 mol), FeCl -4H
Na -2H
[
3
2
2
2
O
2
.1. Chemicals
6
H
5
3
O
7
2
O,
0
Ferric chloride hexahydrate (FeCl
3
⋅6H
2
O), ferrous chloride tetrahy-
chanical stirring in a 500 mL three-necked flask. The resulting solution
◦
drate (FeCl
2
⋅4H
2
O) and trisodium citrate were analytical grade (AR) and
was stirred at 60 C under N
2
atmosphere for 0.5 h. Then 100 mL of
supplied by Tianjin Guangfu Fine Chemical Research Institute (Tianjin,
P. R. China). Toluene was delivered by Tianjin Jiangtian Chemical
NH
4
OH (25 wt%) was added to the above solution drop by drop and the
color became black immediately. The reaction was continued for
2