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experiment was performed with acetophenone as a model
substrate over SSBA-AEC(10)/Ir. At the end of each cycle, the
catalyst was separated from the reaction mixture by simple fil-
tration, dried, and then subjected to a new run without any
other treatment. As shown in Figure 9, the catalytic activity in
tivity and product enantioselectivity. Moreover, the MPTMS
dosage was found to have a considerable effect on the catalyt-
ic performance of the immobilized catalysts, and SSBA-AEC(5)/
Ir exhibited the highest catalytic activity and enantioselectivity.
Furthermore, these immobilized catalysts were very stable in
the reaction system and could be recovered for reuse.
4. Experimental Section
4.1. General
Triblock organic copolymer Pluronic P123 (EO -PO -EO ) was pur-
20
70
20
chased from Aldrich. MPTMS was supplied by Alfa Aesar. TEOS
AR), zirconium oxychloride octahydrate (ZrOCl ·8H O, AR), and
(
2
2
azodiisobutyronitrile (AIBN, AR) were provided by Jiangtian Chemi-
cal Technology Co., Ltd. in Tianjin. Acetophenone and its deriva-
tives (AR) were obtained from Aladdin Chemistry Co., Ltd. [Ir-
(
cod)Cl] (98%) was purchased from Suzhou Sinocompound Tech-
2
nology Co., Ltd. Cinchonine was supplied by Shanghai Ruji Bio-
technology Co., Ltd. AEC was synthesized from cinchonine follow-
[12]
ing the method in literature.
Figure 9. Recycling studies of the heterogeneous catalyst SSBA-AEC(10)/Ir in
the asymmetric transfer hydrogenation of acetophenone.
Powder XRD patterns were recorded on a Bruker D8 FOUCS diffrac-
tometer with CuKa radiation (40 kV and 40 mA) and a step size of
0
.018. N -adsorption–desorption analysis was carried out at 77 K on
2
a Micromeritics TriStar 3000 apparatus. The surface area was deter-
mined by using the BET equation, and the pore diameter was cal-
culated from the adsorption branch of the isotherm by using the
BJH model. FT-IR spectra were obtained on a Bruker Vector 22
spectrometer using self-supporting wafers. DRUV/Vis spectra were
collected on a Shimadzu UV-2550 UV/Vis spectrophotometer. N
and Ir elemental analyses were conducted with a PerkinElmer 240C
analyzer and an ICP-9000 (N+M) spectrometer (TJA Co.), respec-
the second run was as high as in the first run (97% versus
9
6% conversion), along with a comparable ee value of 75%.
However, in the third run, both the conversion and ee value
decreased. The inductively coupled plasma-atomic emission
spectroscopy (ICP-AES) analysis of the reaction filtrate showed
that a rather slight iridium leaching of about 0.1% occurred
I
after each run, indicating that the chiral Ir complex was
13
tively. Solid-state C CP-MAS NMR experiments were performed on
strongly anchored on the mesoporous supports. Moreover, no
further increase in the conversion was detected when fresh re-
actants were added to the filtrates. Accordingly, the catalyst,
used three times, was washed thoroughly with isopropanol,
acetone, ether, and hexane. Excitingly, almost full regeneration
of the catalyst was achieved with 95% conversion and 79% ee
for the fourth run, which is comparable to those of the first
run. Thus, the reason for the reduction in catalytic activity and
enantioselectivity was possibly that some catalytic active sites
in the immobilized catalyst were covered by the entrapped im-
purities during the reaction.
13
a Varian InfinityPlus-300 spectrometer operating at a C frequency
1
of 75.4 MHz and H frequency of 299.8 MHz with a spin rate of
1
0.0 KHz. SEM measurements were recorded on a Shimadu SS-550
operating at 15 kV. TEM experiments were performed on a Philips
2
Tecnai G F20 operating with an acceleration voltage of 120 kV. The
catalytic activity and ee values were measured on a FL9790II gas
chromatograph equipped with a chiral b-DEX 325 column (30 m
0
.25 mm0.25 mm) and a flame-ionization detector.
4.2. Synthesis of thiol-functionalized SBA-15 with short
mesochannels [SSBA-SH(x)]
The thiol-functionalized SBA-15 materials with short mesochannels
were synthesized by a co-condensation method as described pre-
3
. Conclusions
[7e]
viously. In a typical synthesis, Pluronic P123 (4.0 g) was dissolved
in 2m HCl solution (160 g) at 308 K under stirring, followed by the
addition of ZrOCl ·8H O (0.66 g). The required quantity of TEOS
Chiral AEC covalently immobilized onto thiol-functionalized
SBA-15 with short mesochannels were prepared and evaluated
as catalysts for the asymmetric transfer hydrogenation of aro-
2
2
was then added dropwise into the solution and prehydrolyzed for
1–2 h, after that, MPTMS was added dropwise. The resulting mix-
ture was stirred for additional 24 h, and a gel with a molar compo-
matic ketones after complexation with [Ir(cod)Cl] . High catalyt-
2
ic activities comparable to, or even higher than, those of the
homogeneous system were observed over the heterogeneous
catalysts. Notable enhancement of enantioselectivity was ob-
tained for all the ketone substrates investigated as compared
with the free catalyst. Also, the thiol-functionalized SBA-15 ma-
terial with short mesochannels synthesized by means of co-
condensation were found to be far superior to the propylthiol
grafting-modified SBA-15 materials with conventional or short
mesochannels when used as supports, in terms of catalytic ac-
sition of (1–0.01x)TEOS/0.01xMPTMS/0.017P123/0.051ZrOCl
·8H O/
2
2
7
.94HCl/206H O was obtained, where x(%) represents the molar
2
ratio of MPTMS to total Si. Then the gel was transferred into
a Teflon-lined autoclave for static crystallization at 363 K for 24 h.
The solid product was recovered by filtration, washed with deion-
ized water, and air-dried. The template was removed by Soxhlet ex-
traction with ethanol for 72 h, and the thiol-functionalized short-
mesochannel materials SSBA-SH(x) (x=2.5, 5, 10, and 15) were ob-
tained.
ChemCatChem 2016, 8, 1199 – 1207
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