Ruthenium-Catalyzed Asymmetric Hydrosilylation of
Ketones and Imine
Yoshiaki Nishibayashi,
²
Izuru Takei,
²
Sakae Uemura,*
,‡
and Masanobu Hidai*
,²
Department of Chemistry and Biotechnology, Graduate School of Engineering,
The University of Tokyo, Hongo, Tokyo 113-8656, Japan, and Department of Energy and
Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University,
Sakyo-ku, Kyoto 606-8501, Japan
Received May 19, 1998
Summary: Ruthenium complexes with (oxazolinylferro-
cenyl)phosphines, RuCl
2
(PPh
3
)((oxazolinylferrocenyl)-
phosphine), have been prepared and characterized by
spectroscopy. These ruthenium complexes are very ef-
fective catalysts for asymmetric hydrosilylation of not
only ketones but also an imine to give the corresponding
sec-alcohols (up to 97% ee) and a sec-amine (88% ee) after
acid hydrolysis, respectively.
Intensive studies have recently been focused on the
asymmetric hydrosilylation of ketones to obtain chiral
alcohols, owing to the exceedingly mild reaction condi-
tions and technical simplicity as compared to the
asymmetric hydrogenation of ketones.
1-3
A variety of
transition-metal complexes are now known to show
catalytic activity in the hydrosilylation of ketones, but
effective catalysts for asymmetric hydrosilylation are
strictly limited to rhodium complexes with various kinds
of chiral ligands.
1-4
In contrast, asymmetric hydro-
silylation of imines remains undeveloped. Only a few
examples of rhodium-chiral diphosphine catalysts have
been reported, but none of these reactions afforded
amines with high enantioselectivity.
5
Quite recently,
the highly enantioselective titanocene-catalyzed hy-
drosilylation of ketones and imines has been reported
by Buchwald et al.
6,7
These findings prompted us to
develop an alternative transition-metal-catalyzed asym-
metric hydrosilylation of ketones and imines, although
the highly efficient asymmetric hydrogenation and
transfer hydrogenation of alkyl aryl ketones and imines
have been realized by using ruthenium complexes.
8
We
wish here to describe a quite efficient ruthenium-
catalyzed asymmetric hydrosilylation of ketones and an
imine by employing chiral (oxazolinylferrocenyl)phos-
phines.
9
Various ruthenium complexes having chiral ligands
were prepared from RuCl
2
(PPh
3
)
3
and the chiral chelate
compound L (Scheme 1; L ) 1-6). When an equimolar
mixture of RuCl
2
(PPh
3
)
3
and 1 was reacted in toluene
at room temperature for 20 h, the ruthenium complex
[RuCl
2
(PPh
3
)(1)] was obtained in 86% yield. Recrystal-
lization from dichloromethane-diethyl ether afforded
single crystals of [RuCl
2
(PPh
3
)(1)], and the formation
of its diastereoisomer was not observed by NMR in
CDCl
3
. The molecular structure of [RuCl
2
(PPh
3
)(1)] was
unambiguously clarified by X-ray analysis, and an
ORTEP drawing is shown in Figure 1.
10
The ruthenium
atom has a distorted-trigonal-bipyramidal geometry
²
The University of Tokyo.
‡
Kyoto University.
(1) For reviews, see: (a) Catalytic Asymmetric Synthesis; Ojima, I.,
Ed.; VCH: New York, 1993. (b) Brunner, H.; Zettimeier, W. Handbook
of Enantioselective Catalysis with Transition Metal Compounds;
VCH: Weinheim, Germany, 1993. (c) Noyori, R. Asymmetric Catalysis
in Organic Synthesis; Wiley: New York, 1994.
(2) For recent examples, see: (a) Nishiyama, H.; Kondo, M.; Naka-
mura, T.; Itoh, K. Organometallics 1991, 10, 500-508. (b) Sawamura,
M.; Kuwano, R.; Ito, Y. Angew. Chem., Int. Ed. Engl. 1994, 33, 111-
113. (c) Hayashi, T.; Hayashi, C.; Uozumi, Y. Tetrahedron: Asymmetry
1995, 6, 2503-2506. (d) Newman, L. M.; Williams, J. M. J.; McCague,
R.; Potter, G. A. Tetrahedron: Asymmetry 1996, 7, 1597-1598. (e)
Langer, T.; Janssen, J.; Helmchen, G. Tetrahedron: Asymmetry 1996,
7, 1599-1602. (f) Herrmann, W. A.; Goossen, L. J.; Ku¨ cher, C.; Artus,
G. R. Angew. Chem., Int. Ed. Engl. 1996, 35, 2805-2807. (g) Haag,
D.; Runsink, J.; Scharf, H.-D. Organometallics 1998, 17, 398-409.
(3) (a) Nishibayashi, Y.; Segawa, K.; Ohe, K.; Uemura, S. Organo-
metallics 1995, 14, 5486-5488. (b) Nishibayashi, Y.; Segawa, K.;
Takada, H.; Ohe, K.; Uemura, S. Chem. Commun. 1996, 847-848. (c)
Nishibayashi, Y.; Segawa, K.; Arikawa, Y.; Ohe, K.; Hidai, M.; Uemura,
S. Unpublished results.
(4) (a) Nishibayashi, Y.; Singh, J. D.; Segawa, K.; Fukuzawa, S.;
Uemura, S. J. Chem. Soc., Chem. Commun. 1994, 1375-1376. (b)
Nishibayashi, Y.; Singh, J. D.; Segawa, K.; Fukuzawa, S.; Ohe, K.;
Uemura, S. Organometallics 1996, 15, 370-379. (c) Nishibayashi, Y.;
Singh, J. D.; Arikawa, Y.; Uemura, S.; Hidai, M. J. Organomet. Chem.
1997, 531, 13-18.
(5) (a) Kagan, H. B.; Langlois, N.; Dang, T.-P. J. Organomet. Chem.
1975, 90, 353-365. (b) Becker, R.; Brunner, H.; Mahboobi, S.;
Wiegrebe, W. Angew. Chem., Int. Ed. Engl. 1985, 24, 995-996.
(6) Ketones: Carter, M. B.; Schiott, B.; Gutierrez, A.; Buchwald, S.
L. J. Am. Chem. Soc. 1994, 116, 11667-11670.
(7) Imines: (a) Verdaguer, X.; Lange, U. E. W.; Reding, M. T.;
Buchwald, S. L. J. Am. Chem. Soc. 1996, 118, 6784-6785. (b)
Verdaguer, X.; Lange, U. E. W.; Buchwald, S. L. Angew. Chem., Int.
Ed. Engl. 1998, 37, 1103-1106.
(8) (a) Ohkuma, T.; Ooka, H.; Hashiguchi, S.; Ikariya, T.; Noyori,
R. J. Am. Chem. Soc. 1995, 117, 2675-2676. (b) Ohkuma, T.; Doucet,
H.; Pham, T.; Mikami, K.; Korenaga, T.; Terada, M.; Noyori, R. J. Am.
Chem. Soc. 1998, 120, 1086-1087. (c) Noyori, R.; Hashiguchi, S. Acc.
Chem. Res. 1997, 30, 97-102 and references therein.
(9) (a) Nishibayashi, Y.; Uemura, S. Synlett 1995, 79-81. (b)
Nishibayashi, Y.; Segawa, K.; Arikawa, Y.; Ohe, K.; Hidai, M.; Uemura,
S. J. Organomet. Chem. 1997, 545-546, 381-398 and references
therein.
(10) Crystal data for [RuCl
2(PPh3)(1)]‚CH2Cl2 are as follows: mono-
clinic, space group P21 (No. 4); a ) 11.370(8) Å, b ) 17.914(8) Å, c )
12.210(4) Å, ) 114.63(3)°; V ) 2260(1) Å
3
; Z ) 2; Dcalcd ) 1.520 g
cm
-3
; μ(Mo KR) ) 10.01 cm
-1
. The final R value was 0.040 (Rw ) 0.043)
for 4264 unique reflections with I > 3σ(I).
Scheme 1
3420 Organometallics 1998, 17, 3420-3422
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Publication on Web 07/09/1998