Y. Huo, J. Hu, Y. Tu et al.
Journal of Organometallic Chemistry 936 (2021) 121714
2
.3.2. Preparation of Fe O @SiO
3 4 2
The Fe O4 nanoparticles (1.920 g) were dispersed in 150 mL of
3
deionized water,then 1 mL of concentrated aqueous ammonia (25
wt%) and 3.012 g of TEOS were added into the suspension under
stirring.The mixture was stirred for another 30 min at room tem-
perature and then filtered before it was sequentially washed with
deionized water.The product was then dried in a vacuum drying
oven at 40°C for 6 h, and 2.556 g of the Fe O @SiO was obtained
3
4
2
as a brown powder.
2
.3.3. Preparation of Fe O @SiO -biIMI
3
4
2
Fe O @SiO (0.409 g) was suspended in 80 mL of anhydrous
3
4
2
ethanol under magnetic stirring.Subsequently, 1.60 mL of γ -
aminopropyltriethoxysilane was added dropwise into the suspen-
sion.The mixture was stirred at 80 °C for 4 h and cooled, then
ꢀ
an ethanol solution containing 0.200 g 1,1 -methylenebis (1H-
imidazole-4-carbaldehyde) was addedto this mixture.Themixture
was further refluxed for 6 h.The product was filtrated and washed
in ethanol before it was dried in a vacuum drying oven at 40 °C
for 6 h, thus yielding 0.435 g of the product Fe O @SiO -biIMI.
3 4 3 4 2 3 4 2 2
Fig. 1. The FTIR spectra of Fe O , Fe O @SiO , and Fe O @SiO -biIMI-PtCl .
3
4
2
2
.3.4. Preparation of Fe O @SiO -biIMI-PtCl
3 4 2 2
−1
in the spectrum of Fe O @SiO -
moderate bands at 2950 cm
biIMI-PtCl2 corresponded to the C-H vibrationsof the-(CH ) - moi-
3
4
2
Fe O @SiO -biIMI(0.355 g) was suspended in 80 mL of an-
3
4
2
2
3
hydrous ethanol under magnetic stirring. Sodium tert-butoxide
0.0760 g) and Pt(COD)Cl2 (0.102 g) were added into the suspen-
eties of APS [27]. The band at 1624 cm 1 that was exhibited by all
three materials can be attributed to the physical adsorption of CO2
onto the surface, and it overlapped the C=N vibration bands in the
−
(
sion under N2 protection. The mixture was stirred at 80 °C for 6
h and then filtered. The product was subsequently washed with
ethanol before it was dried in a vacuum drying oven at 40 °C for 6
spectra of Fe O @SiO -biIMI and Fe O @SiO -biIMI-PtCl . Yet the
3
4
2
3
4
2
2
band at 1560 cm 1 revealed the existence of C=C (bending) on the
−
h, thus yielding 0.396 g of the product Fe O @SiO -biIMI-PtCl .
3
4
2
2
imidazole ring of these two materials [28]. The characteristic Fe-O
stretching bands at 612 cm 1 were also identified in all materials
−
2
.4. Hydrosilylation reactions
The catalytic activity of Fe O @SiO -biIMI-PtCl was evaluated
[
29].
EDS analysis of Fe O @SiO -biIMI-PtCl (see Figure S4) showed
3
4
2
2
3
4
2
2
that the amount of Platinum in the catalyst was ~4.69wt% (Table
S1), which was less than the results from ICP (5.32 wt%). The pres-
based on its ability to catalyze the hydrosilylation reaction be-
tween 1-octene and triethoxylsilane.The reaction was performed in
a capped 25 mL round-bottom flask with magnetic stirring. Most
commonly, 780 μL (5mmol) of 1-octene and Fe O @SiO -biIMI-
−
ence of Cl is validated by EDS (Table S1), and the atom percentage
ratio between Cl and Pt was close to 2:1.The molar ratio of Fe:Si
in the catalyst was calculated to be 9:7, which meant that only
a thin SiO2 layer could have been formed on the surface of the
3
4
2
PtCl were added into the flask and stirred at 60 °Cfor 0.5 h, and
2
then 925 μL(5 mmol) of triethoxylsilane was added and the mix-
ture was further stirred for 2 h.
Fe O nano particles. The coordination between platinum and the
3
4
ligands of Fe O @SiO -biIMI-PtCl was investigatedby XPS (Fig. 2).
3
4
2
2
The recyclability of Fe O @SiO -biIMI-PtCl was evaluated in
3
4
2
2
The peaks at 76.18 (4f5/2) and 72.88 eV (4f7/2) in the spectra of
Pt4f (Fig. 2b) indicate thatthe platinum in the catalyst exists in the
terms of the conversion performance by repeated use for several
cycles. Briefly, 20.3 mg of the catalystthat had been suspended
in 1.60 mL (10.0 mmol) of 1-octene was first preheated at 60 °C
for 30 min, and then1.95 mL (10.0 mmol) of triethoxylsilane was
addedbefore the reaction was allowed to proceed for another 2
h. The catalyst was then collected via an extra magnet.The super-
natant was poured out and then theremaining catalyst was mixed
with fresh 1-octene beforea second reaction cycle was conducted
via the same procedureas mentioned above.The productsthat had
2+
form of Pt [30]. In the N1s spectrum (Fig. 2c), the peak at 399.78
eV is referred to the N atoms bonded with the methylene (-CH-)
bridge, while the peak at 400.98 eV, can be identified as the N
atoms in the imidazole imine which are coordinated with Pt [14].
The XPS analysis of O1s (Fig. 2d) shows two independent bind-
ing modes of oxygen atoms, one corresponds to Fe-O (529.68eV)
[
31] and the other to Si-O (532.08eV).
The morphology of Fe O @SiO -biIMI-PtCl
2
was studied
through N2 adsorption/desorption tests.The type II N2 ad-
sorption/desorption curves [13] of Fe O , Fe O @SiO , and
3
4
2
been obtainedfrom each cycle were subsequently analyzed via 1
H
NMRspectroscopy.
3
4
3
4
2
Fe O @SiO -biIMI-PtCl are shown in Fig. 3a, and the BET surface
3
4
2
2
2
3
. Results and discussion
.1. Characterization of Fe O @SiO -biIMI-PtCl
2
area of Fe O4 decreased from 98.8 to 71.2 m /g after it had been
3
coated by SiO . The BET surface area of Fe O @SiO -biIMI-PtCl
2
2
3
4
2
2
3
was 62.9 m /g, which is mainly a result of the trenches that had
formed across the surface of the material according to its SEM
images (Figure S 3 in the Supplementary Information).
3
4
2
The chemical composition of Fe O @SiO -biIMI-PtCl was firstly
3
4
2
2
analyzed by FT-IR and XPS techniques.The FT-IR spectra (Fig. 1) re-
The Fe O @SiO -biIMI-PtCl particles shown in the SEM (Fig-
3 4 2 2
−
1
vealedthat the intensity of the broad band at 3420 cm increased
significantly after Fe O nanoparticles had been coated by SiO2,
ure S2 in the SI) and TEM images (Fig. 4a) were spherical with-
rough surfaces, and they had a diameter of ~15-20 nm (Fig. 4b).
3
4
which was due to the increasing amount of OH moieties on the
In the HRTEM image (Fig. 4d) of Fe O @SiO -biIMI-PtCl , thelat-
3 4 2 2
−
1
surface of the silica shell. The strong band at 1087 cm
inthe
tice fringe of Fe O4 crystals could be identified, indicating that
3
spectra of Fe O @SiO -biIMI and Fe O @SiO -biIMI-PtCl also con-
the crystal structure of the Fe O4 core remained unchanged in
3
4
2
3
4
2
2
3
firmed the successful coating of the silica outer shell [26]. The
the final products.This observation can further be verified based
3