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for 6 h. After cooling down to ambient temperature, the mixture
was filtered through filter paper and rinsed with excess ethanol
and CH2Cl2. The collected white solids were suspended in 20.0 mL
distilled water again and Ag2O (229.0 mg, 1.0 mmol) was added at
ambient temperature. The resulting mixture was heated at 908C
for 6 h. After cooling down to ambient temperature, a solution of
2.0 NH2SO4 (10 mL) was added and stirred overnight. The solids
were collected by centrifugation, washing repeatedly with excess
distilled water. The collected light grey solids were suspended in
the mixture solution (10.0 mL of methanol and 10.0 mL distilled
water) again and 199.0 mg (0.25 mmol) of [(Cp*IrCl2)2] was added
at ambient temperature. The resulting mixture was stirred for 12 h.
Finally, 221.0 mg (0.50 mmol) of (S,S)-pentafluorophenylsulfonyl-
1,2-diphenylethylenediamine was added and the reaction was fur-
ther stirred for another 6 h at ambient temperature. The mixture
was then filtered through filter paper and rinsed with excess water
and CH2Cl2. After Soxhlet extraction in CH2Cl2 solvent to remove
homogeneous and unreacted starting materials for 24 h, the solid
was dried at ambient temperature under vacuum overnight to
afford the catalyst 3 (1.35 g) as a light yellow powder. ICP analysis
showed that the Ir loading-amount was 14.80 mg (0.0778 mmol)
per gram catalyst. IR (KBr): n˜ =3416.2 (s), 2928.4 (w), 2857.6 (w),
1630.1 (m), 1496.5 (w), 1457.9 (w), 1082.0 (s), 947.6 (m), 801.8 (m),
699.4 (w), 568.1 (w), 462.2 cmÀ1 (m); 29Si MAS/NMR (79.4 MHz): d=
À67.2 (T3), À91.3 (Q2), À101.5(Q3), À110.4 ppm (Q4); 13C CP/MAS
(100.5 MHz): d=10.1 (CpCH3, SiCH2 and CH3 of CTAB), 17.7
(SiCH2CH2), 27.1 (CH2 of CTAB), 53.1 (CH2SO3), 59.2, 63.7 (NCH2 or
NCH3 of CTAB), 70.2, (NCH), 86.6 (C5 of Cp), 128.0, 130.4, 139.2 ppm
(C of Ph); SBET: 229.4 m2 gÀ1, dpore: 3.60 nm, Vpore: 0.62 cm3 gÀ1.; Ele-
mental analysis (%): C 8.59, H 1.97, N 0.69, S 0.49.
tries 11–16). Again, short reaction times, excellent conversions,
and enhanced enantioselectivities were obtained all cases.
These results demonstrate that catalyst 3 can serve as a general
catalyst in the asymmetric transfer hydrogenation of different
substrates.
An important feature for design of any heterogeneous cata-
lyst is easy to separate via simple centrifuge and the recovered
catalyst can retain its catalytic activity and enantioselectivity
after multiple cycles. Remarkably, the catalyst 3 was recovered
easily and reused repeatedly when benzoylacetonitrile was
chosen as a substrate. In ten consecutive reactions, the reused
catalyst 3 still afforded 99% conversion and 94% ee (Figure 3,
Figure 3. Reusability of 3 using benzoylacetonitrile as a substrate.
Table S1, and Figure S9 in the SI). The high recyclability can be
attributed to the unique mesoporous morphology, which sig-
nificantly decreases the leaching of Ir. An evidence to support
the view came from the ICP analysis, in which the amount of Ir
after tenth recycle was 13.89 mg per gram catalyst and only
6.1% of Ir was lost.
Catalytic experiments
A typical procedure was as follows: The catalyst 3 (26.1 mg,
2.0 mmol of Ir based on the ICP analysis), benzoylacetonitrile
(116.0 mg, 0.80 mmol) and the aqueous solution of formic acid
(5.0 equiv 1.0m formate solution, 0.2m overall concentration, for
X=CN, pH 3.5; for X=NO2, pH 2.0,) were added in a 10.0 mL
round-bottom flask in turn. The mixture was then stirred at room
temperature for 10–20 h. During that time, the reaction was moni-
tored constantly by TLC. After completion of the reaction, the cata-
lyst was separated via centrifuge (10000 rminÀ1) for the recycle ex-
periment. The aqueous solution was extracted by ethyl ether (3ꢁ
3.0 mL). The combined ethyl ether was washed with brine twice
and dehydrated with Na2SO4. After the evaporation of ethyl ether,
the residue was purified by silica gel flash column chromatography
to afford the desired product. The conversion was calculated by
the external standard method and the ee value could be deter-
mined by a HPLC analysis with a UV-Vis detector using a Daicel OJ-
H chiralcel column (F 0.46ꢁ25 cm).
In conclusion, we have developed a new strategy for the im-
mobilization of chiral organoiridium complexes onto the meso-
porous silica, which displays higher catalytic activity and enan-
tioselectivity than its homogeneous counterpart for the asym-
metric transfer hydrogenation of a-cyano and a-cyanoaceto-
phenones in aqueous medium. More importantly, cetyltrime-
thylammonium bromide acted as a phase transfer catalyst
within its mesoporous silicate network can increase greatly cat-
alytic performance, while the unique mesostructure of meso-
porous silica can boost the enantioselectivity. Furthermore, the
heterogeneous catalyst can be recovered conveniently and
subsequently reused at least 10 times without affecting its cat-
alytic activity. More importantly, this strategy described here
might expand to other chiral complexes for asymmetric organ-
ic transformations, which represents our future effort.
Acknowledgements
We are grateful to the China National Natural Science Founda-
tion (20673072), Shanghai Sciences and Technologies Develop-
ment Fund (10J1400103, 10JC1412300 and 12nm0500500), CSIRT
(IRT1269), and Shanghai Municipal Education Commission
(12ZZ135) for financial support.
Experimental Section
Preparation of Cp*IrPFPSDPEN-functionalized FMS (3)
To a suspension of Mercapto-functionalized FMS (2) (1.00 g) in
10.0 mL acetic acid was added a solution of 30% H2O2 (20.0 mL) at
room temperature and the resulting mixture was stirred at 1008C
Keywords: asymmetric catalysis
heterogeneous catalyst · immobilization · mesoporous material
· bifunctional catalysis ·
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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