Table 2 Asymmetric transfer hydrogenation of ketones using catalyst 6
Ketone
Product (R)
Solvent/temperature
CH2Cl2/rt
94–100
97–98
CH2Cl2/rt
97–99
90–92
CH2Cl2/rt
88–94
97
iPrOH/45 uC
90–95
96–97
iPrOH/rt
95–98
71–73
Yield (%)a
ee (%)b
a
Yields were based on GC analysis and isolated material. Configuration was determined from the sign of rotation of the product.
Enantiomeric excess was determined by HPLC analysis.
b
J. Y. Ying, Langmuir, 2000, 16, 8291; J. S. Lettow, T. M. Lancaster,
C. J. Glinka and J. Y. Ying, Langmuir, 2005, 21, 5738.
In summary, TsDPEN has been successfully anchored onto
silica supports. Siliceous MCF was shown to be a superior support
to conventional silica gel. The Ru complex immobilized on MCF
demonstrated excellent reactivity, enantioselectivity and reusability
in the asymmetric transfer hydrogenation of an imine and ketones.
This work was sponsored by the Singapore-MIT Alliance. The
authors thank Timothy McClure (MIT Center for Materials
Science and Engineering) for his assistance in Raman spectro-
scopy. This work made use of the National Science Foundation
MRSEC Shared Experimental Facilities (DMR-02-13282) and
Laser Facilities (CHE-01-11370) at MIT.
7 P. Schmidt-Winkel, W. W. Lukens, Jr., D. Zhao, P. Yang,
B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc., 1999, 121, 254.
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Tetrahedron: Asymmetry, 2001, 12, 2931; Y. Han, S. S. Lee and
J. Y. Ying, Chem. Mater., 2006, 18, 643.
9 T. M. Lancaster, S. S. Lee and J. Y. Ying, Chem. Commun., 2005, 3577;
S. S. Lee, S. Hadinoto and J. Y. Ying, Adv. Synth. Catal., 2006, 348,
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10 P. N. Liu, P. M. Gu, F. Wang and Y. Q. Tu, Org. Lett., 2004, 6, 169;
P.-N. Liu, P.-M. Gu, J.-G. Deng, Y.-Q. Tu and Y.-P. Ma, Eur. J. Org.
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Chem. Commun., 2004, 2070. Mesoporous MCM-41 and SBA-15 were
reported to be worse supports for the Ru–TsDPEN catalyst than silica
gel in the asymmetric transfer hydrogenation.
Notes and references
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14 The N/S molar ratio for N-sulfonylated-1,2-diamine should be 2, but the
elemental analysis of ligand 3 showed a N/S molar ratio of 1.8 (see
ESI{). The slight reduction in the N/S molar ratio could be due to the
formation of small amounts of the N,N9-disulfonylated-1,2-diamine
compound (which has a N/S molar ratio of 1) on MCF. Although an
excess of 1,2-diphenylethylenediamine was used to react with 4-ethyl
benzenesulfonyl chloride immobilized on MCF to suppress the
formation of N,N9-disulfonylated-1,2-diamine, the latter was still found
in small quantities on the high surface area MCF support.
Consequently, catalyst 6 likely involved Ru supported by a mixture of
N-sulfonylated-1,2-diphenylethylenediamine and N,N9-disulfonylated-
1,2-diphenylethylenediamine ligands, giving a similar enantioselectivity
but lower reactivity compared to the homogeneous Ru–TsDPEN
catalyst.
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