E. Hu et al.
Inorganic Chemistry Communications 130 (2021) 108718
2. Experiment
was refluxed under nitrogen for 12 h. The product was centrifuged and
separated, rinsed three times with deionized water and three times with
ethanol, and dried in an oven at 60 ◦C for 12 h. The dried catalyst was
dispersed in 10.0 mL of 30% hydrogen bromide in acetic acid, stirred at
room temperature for 12 h, centrifuged and washed three times with
water and three times with ethanol, and dried in an oven at 60 ◦C for 12
h to remove the protective groups and obtain the CSPro catalyst [20].
Elemental analysis of the catalyst shows that the elemental N content is
8.82% (0.63 mmol/g), so it can be determined that the L-proline content
is 0.63 mmol/g. A flow chart of the preparation is shown in Fig. 1.
2.1. Materials and instruments
Copper chloride dihydrate (CuCl2⋅H2O, AR, Tianjin Windship
Chemical Reagent Technology Co., Ltd.), cetyltrimethylammonium
bromide (CTAB, AR, Tianjin Comio Chemical Reagent Co., Ltd.), thio-
acetamide (TAA, 99%, Rhawn), ethyl orthosilicate (TEOS, AR, Rohn
Reagent), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (kh560, 97%,
Myriad), N-Boc-trans-4-hydroxy-L-proline methyl ester (98%, Guang-
dong Wengjiang Chemical Reagent), hydrogen bromide acetic acid so-
lution (30%, Micrel), p-nitrobenzaldehyde (Shanghai Xian-Dinn Biotech
Co., Ltd.), and acetone (Tianjin Kemiou Chemical Reagent Co., Ltd.)
were used without further purification.
2.3. Catalytic asymmetric hydroxyl aldol condensation reactions
We dissolved 0.15 g of p-nitrobenzaldehyde in 5 mL of acetone,
added 20 mol% catalyst, and held the reaction mixture at 50 ◦C in an oil
bath for 3 h. The catalyst was separated by centrifugation and spin-
Infrared (IR) absorbance spectra were measured using a Bruker
Tensor 27 FT-IR with a scan range of 4000–400 cmꢀ 1. Proton nuclear
magnetic resonance (1H NMR) absorbance spectra of the reaction
products were measured using a Bruker Biospin AVANCE 400 NMR. The
crystal structure of the catalyst was determined using a Bruker AVANCE
400 NMR with a scan speed of 12◦ minꢀ 1 and a scan range of 5◦–80◦
(2θ). The UV–Vis absorbance spectra of the catalysts were measured
with a Shimadzu UV2700 spectrophotometer. The L-proline loading was
determined using a fully automated Thermoelectric Flash EA1112
elemental analyzer. The morphology of the catalyst was detected with
an FEI Nova Nano SEM450 scanning electron microscope, and the
catalyst distribution was viewed with an EDAX Octane series energy
dispersive spectroscopy (EDS) system. The surface properties of the
catalyst were tested by Micromeritics’ ASAP 2460 surface area and
porosimetry system. The solid-state nuclear magnetic field was tested by
Bruker’s 400 M NMR spectrometer. A 2 W 808 nm NIR LED laser was
used as the NIR light source, and a Hikvision H10 infrared thermal
imager was used to measure temperature.
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dried, and HNMR was used to measure the reaction conversion of p-
nitrobenzaldehyde in the crude product. Subsequently, the products
were separated by column chromatography (PE:EA = 4:1), and the
product ee values were calculated by high-performance liquid chroma-
tography (Chiralpak OX-H, n-hexane:isopropanol = 90:10, λ = 273 nm,
1.0 mL/min, 25 ◦C).
The catalyst was stirred in the reaction system for 72 h and then
centrifuged. The solution was subjected to rotary evaporation and dry-
ing, and then the XRD test was performed. No diffraction peak of CuS
was detected in the spectrum, so it was determined that CuS was not
leached during the reaction.
3. Results and discussion
3.1. Characterization of the catalyst
The morphology of a material has a great influence on the catalytic
effect of a catalyst, as demonstrated through the characterization of the
morphology and microstructure of CuS and CSPro. Fig. 2(a) and (c)
show the SEM images of CuS and CSPro, respectively. As shown in Fig. 2
(a), CuS has hexagonal flakes with a smooth surface and good dispersion
without agglomeration, and the nanosheet thickness distribution is
about 13 nm. From the statistical chart in Fig. 2(b), it can be seen that
the diameters of the CuS nanoparticles are mainly distributed between
40 and 70 nm. As shown in Fig. 2(c), mSiO2 is coated on the CuS surface,
and the thickness increases to 25 nm.
2.2. Preparation of the catalysts
To prepare the CuS nanosheets, 0.34 g of copper (II) chloride)
dihydrate (CuCl2⋅2H2O) and 0.10 g of cetyltrimethylammonium bro-
mide (CTAB) were dissolved in 200 mL of deionized water, and 0.90 g of
Triamcinolone Acetonide Acetate (TAA) was dissolved in 100 mL of
deionized water. The two solutions were combined, magnetically stirred
for 30 min, and placed in an oil bath at 100 ◦C for 4 h to complete the
reaction. Then the mixture was cooled to room temperature and
centrifuged to collect the solid product, which was washed three times
with deionized water and dried in an oven at 60 ◦C for 12 h.
The catalyst was tested by SEM-EDS, and the results are shown in
Fig. 3, which shows that elemental Si and Cu are extremely overlapped,
indicating that the combination of copper sulfide and silica is very
effective. In addition, some elemental N is evenly distributed on the
surface of the catalyst, indicating that L-proline is successfully loaded
The CuS@mSiO2-kh560 nanosheets were prepared with mesoporous
silica using a modified published approach [20]. First, 0.30 g of CuS was
added to a solution consisting of 11.0 mL of ethanol, 64 mL of deionized
water, 0.20 g of diethanolamine, and 10.0 mL of CTAB (25 wt%) and
sonicated for 30 min to disperse the copper sulfide nanoparticles. The
mixture was stirred for an additional 30 min in an oil bath at 60 ◦C. Next,
0.7 mL of tetraethyl orthosilicate (TEOS) was added, and the reaction
mixture was kept in the oil bath at 60 ◦C for 3 h. Then the filtrate was
washed three times with deionized water and then with ethanol. The
resulting cyan solid was refluxed three times for 12 h in 120 mL of
ethanol using fresh ethanol for each reflux to remove excess CTAB, and
the intermediate product, CuS@mSiO2, was dried in an oven at 60 ◦C for
12 h. In the next step, 0.3 g of the CuS@mSiO2 and 0.5 mL of the silane
coupling agent kh560 were ultrasonically dispersed in 25 mL of anhy-
drous toluene and refluxed for 12 h. After the reaction, the mixture was
cooled to room temperature, and the solid product was filtered, washed
three times with deionized water and three times with ethanol, and
dried in an oven at 60 ◦C for 12 h to obtain CuS@SiO2-kh560.
To prepare the CuS@mSiO2@L-proline (CSPro) catalyst, 0.3 g of the
CuS@mSiO2-kh560 was ultrasonically dispersed in 25 mL of chloro-
form, 0.13 g N-Boc-trans-4-hydroxy-L-proline methyl ester and 0.02 g of
triethylamine were added for catalyzed ring opening, and the mixture
Fig. 1. Flow chart of CuS@mSiO2@L-proline catalyst preparation.
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