Asymmetric hydrosilane reduction of ketones catalyzed by an iridium complex bearing a hydroxyamide-functionalized NHC ligand

Article abstract of DOI:10.1002/adsc.201100897

An enantioselective hydrosilylation of prochiral ketones was achieved by using a catalytic amount of the readily accessible and air- and moisture-stable iridium complex [IrCl(cod)(NHC)] at room temperature. Copyright

Full text of DOI:10.1002/adsc.201100897

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DOI: 10.1002/adsc.201100897
Asymmetric Hydrosilane Reduction of Ketones Catalyzed by an
Iridium Complex Bearing a Hydroxyamide-Functionalized NHC
Ligand
a
a
a
a
Shun Kawabata, Hiromu Tokura, Hiroyuki Chiyojima, Masaki Okamoto,
a,
and Satoshi Sakaguchi *
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai
University, Suita, Osaka 564-8680, Japan
a
Fax : (+81)-6-6339-4026; phone: (+81)-6-6368-0867; e-mail: satoshi@kansai-u.ac.jp
Received: November 18, 2011; Published online: March 13, 2012
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201100897.
Abstract: An enantioselective hydrosilylation of
prochiral ketones was achieved by using a catalytic
amount of the readily accessible and air- and mois-
hydrogenation because the silylated product can be
easily hydrolyzed under mild conditions to produce
a reduced final product such as an alcohol. However,
to the best of our knowledge, there are only three re-
ports on the highly enantioselective hydrosilylation of
ketones catalyzed by a chiral NHC complex. Shi de-
ture-stable iridium complex [IrCl
room temperature.
ACTHUNGTNERNUNG( cod) CAHTUNGTRNEUNNG( NHC)] at
Keywords: asymmetric catalysis; carbene ligands;
hydrosilylation; iridium; ketones
veloped an axially chiral bis
asymmetric hydrosilane reduction with Ph SiH . Rh
ACHTUNGTRENNUNG( NHC)-Rh complex for
[6]
2
2
complexes with chiral bidentate oxazoline/NHC li-
gands have been designed by Gade and Bellemin-La-
[
7]
ponnaz. Andrus demonstrated that a Ru complex
with a bis-paracyclophane-NHC ligand catalyzes the
[
8]
Catalytic asymmetric synthesis provides one of the asymmetric reduction of ketones. However, these
most powerful and economical approaches for the reactions have been achieved only by using reactive
preparation of a variety of optically active organic and expensive silylating reagents such as Ph SiH , and
2
2
compounds that are key compounds for the pharma- some of these reactions require severe reaction condi-
ceutical and materials industries. Despite the enor- tions (À608C). Moreover, there are no reports on
mous progress in the field of catalytic asymmetric syn- chiral NHC-Ir-catalyzed hydrosilylation with high
[
9]
thesis, the development of asymmetric methods that enantioselectivity under mild conditions.
lead to both enantioenriched products by using Recently, we designed and synthesized easily acces-
a single chiral source remains a significant chal- sible NHC ligands such as hydroxyamide-functional-
[1,2]
[10]
lenge.
This concept of asymmetric catalysis pro- ized azoliums from chiral a-amino acids. Polyden-
vides a highly attractive synthetic tool using readily tate anionic amidate/NHC-Pd(II) complexes derived
available single natural organic compounds such as from the functionalized azolium salts catalyze the
amino acids.
asymmetric oxidative Heck-type reaction with excel-
During the last decade, N-heterocyclic carbenes lent enantioselectivity. The chiral NHC ligand precur-
NHC) have emerged as an important family of li- sor could also be employed in the Cu-catalyzed conju-
(
[
3,4]
gands with strong s-donor electronic properties.
In gate addition reaction. Surprisingly, a reversal of
2
001, Burgess et al. reported an efficient chiral iridi- enantioselectivity with the same ligand was achieved
[11]
um catalyst containing an oxazoline/NHC ligand for by changing the Cu precatalyst. In addition, we in-
the asymmetric hydrogenation of alkenes. Interest- vestigated the versatility of the chiral NHC ligand for
ingly, an unexpected inversion of enantioselectivity the Ir-catalyzed asymmetric transfer hydrogenation
[
5]
was observed in hydrogenation of 2-(4’-methoxyphen- reaction. Thus, a new monodentate [IrCp*Cl ACHTUNGETRNN(UNG NHC)]
2
yl)-but-1-ene using the same NHC-Ir complex. On complex was synthesized and fully characterized, and
the other hand, hydrosilylations of carbon-oxygen acetophenone (1) was reduced with isopropyl alcohol
double bonds are useful alternatives to asymmetric even at room temperature to afford (R)-1-phenyletha-
Adv. Synth. Catal. 2012, 354, 807 – 812
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
807

Shun Kawabata et al.
COMMUNICATIONS
mation of the desired NHC complexes. However, the
1
13
H and C NMR spectra showed very complicated
sets of signals that were difficult to assign accurate-
[
13]
ly.
In contrast to the iridium complex, a fully assigna-
ble NMR spectrum was obtained for complex 7,
RhCl(cod)(NHC)], which was prepared from [RhCl-
(cod)] by the same procedure as described for the
[
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
2
synthesis of 4 and 6 (Figure 1). The observation of the
complicated sets of signals of [IrCl(cod)(NHC)] may
be due to the rotation around the IrÀC
axis
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
carbene
[
13]
being hindered and slow.
The two signals of the
Scheme 1. Dual enantioselective control in the NHC-Ir-cata-
lyzed reduction of ketones.
methyl group protons at around d=4.3 ppm in
Figure 1 indicate that 7 exists as a mixture of two
NHC-Rh compounds. The presence of a mixture of
[
12]
nol (2) with 60% ee (Scheme 1). During the course two compounds was supported by the integral of the
1
of this study, we found that an NHC-Ir complex, signals in the H NMR spectra. The ratio was 77:23.
which was prepared from [IrCl ACHTUNGTERNNUN(G cod)] and the chiral These compounds were not separable by column
2
azolium compound, catalyzes the asymmetric hydrosi- chromatography. This may be due to the existence of
lane reduction of 1 to form (S)-2 as the major prod- two atropisomers owing to the restricted RhÀC
carbene
uct. These facts suggested the possibility of achieving bond reported in a similar [RhX ACHUTNGRENNU(G cod) ACHTUNGERTNNUNG( NHC)] com-
[14]
the formal reversal of stereoselectivity by the two re- plex having a stereocenter on the NHC ligand. The
duction systems with the same ligand (Scheme 1). appearance of the two signals (a’) corresponding to
Here, we focus on the asymmetric hydrosilylation of the tert-butyl group of the minor isomer might be ex-
ketones catalyzed by the NHC-Ir complex. We pres- plained by agostic interactions between the CÀH
ent the development of an efficient catalytic reduction bond and the metal center, although we do not have
system at room temperature.
The preparation of the NHC-Ir complex was car- consideration was also reported by Nagel et al. In
ried out according to the Ag O method (Scheme 2). the C NMR spectra, we observed a characteristic
any data to corroborate this hypothesis. A similar
[15]
1
3
2
The NHC precursors used in this study are benzimi- doublet at d=196.7 ppm with a typical C-Rh coupling
dazolium salts 3 and 5 derived from phenylalaninol constant of 49.7 Hz for the carbene carbon atom.
and leucinol, respectively. The reaction of 3 with
Catalytic asymmetric hydrosilylation was examined
Ag O in dichloromethane at room temperature for using acetophenone (1) and (EtO) MeSiH in the pres-
2
2
1
h gave the corresponding NHC-Ag complex. After ence of 4 (4 mol%) in THF at room temperature.
removing the solvent, [IrCl(cod)] in THF was added, After the reaction, a small amount of K CO3 in
and then, the resulting mixture was stirred at room CH OH was added to give (S)-1-phenylethanol (2).
AHCTUNGTRENNUNG
2
2
3
temperature for 16 h, affording [IrCl
ACTHUNGTNERNUNG( cod) CAHTUNGTRNEUNNG( NHC)] 4 in Representative results are summarized in Table 1.
88% yield. Similarly, 5 was converted into the NHC- The reaction with 4 alone resulted in low yield and
Ir complex 6 in 89% yield. Complexes 4 and 6 are air- poor enantioselectivity (entry 1). The addition of
and moisture-stable and reproducible, and they were AgBF (1 equiv. with respect to 4) led to a remarkable
4
purified by column chromatography on silica gel. The increase in the stereoselectivity of the reaction (74%
absence of the signals of the C-2 proton of the azoli- ee) (entry 2). Other silver salts, including AgPF6,
1
um salts 3 and 5 in H NMR and the observation of AgClO , and AgOTf, were tested with catalyst 4, and
4
13
carbene carbons in
C NMR (d=191.7 and AgBF was found to be the best choice of additive
4
191.9 ppm for 4 and 6, respectively) suggested the for- (entries 3–7). In the literature, a decrease in enantio-
Scheme 2. Preparation of [MCl ACHUNTGRENNUG( cod) ACHTUNGERTNNUNG( NHC)] (M=Ir or Rh) complexes.
808
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 807 – 812

Asymmetric Hydrosilane Reduction of Ketones Catalyzed by an Iridium Complex
1
Figure 1. H NMR spectrum of 7.
Table 1. Asymmetric hydrosilane reduction of 1 by 4 to pro- 1 with Ph SiH under the influence of the NHC-Ir cat-
2
2
[a]
duce (S)-2.
alyst 4 furnished a racemic mixture of 2 (entry 11).
This contrasts with the cases of NHC-Rh and NHC-
Ru-catalyzed asymmetric hydrosilylation, where the
Entry Silane
Additive Yield [%]
AHCTUNGTERNNUNG[ mol%] (recovered 1 [%]) [%]
ee
[b]
[
6–8]
use of Ph SiH is essential.
Increasing the amount
2
2
1
2
3
4
5
6
7
8
9
1
1
1
1
1
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO) MeSiH none
5 (77)
12
74
53
48
7
25
–
58
17
À3
1
2
of silylating reagent facilitated the reaction rate (en-
tries 12–14). Substrate 1 was reduced to (S)-2 in satis-
factory yield (80%) with a slightly better enantiose-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO) MeSiH
AgBF4
34 (58)
2
ACHTUNGTRENNUNG( EtO) MeSiH AgOAc 17 (78)
ACHTUNGTRENNUNG( EtO) MeSiH AgNO3 17 (76)
2
2
lectivity (78% ee) by using 3.5 equiv. of (EtO) MeSiH
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO) MeSiH AgPF6
7 (84)
2
with respect to 1 (entry 14)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO) MeSiH AgClO4 5 (72)
2
It was found that replacement of the benzyl group
by the isobutyl group as the stereodirecting group of
the NHC ligand resulted in a slight improvement in
the enantioselectivity (Table 2). When the reaction of
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO) MeSiH AgOTf
<1 (>99)
31 (56)
7 (83)
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(MeO) MeSiH AgBF4
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO) SiH
AgBF4
AgBF4
AgBF4
3
0
1
2
3
4
Et SiH
Ph SiH2
6 (86)
3
36 (50)
44 (52)
78 (18)
80 (18)
1 with 3 equiv. of (EtO) MeSiH was carried out in the
2
2
[
[
[
c]
d]
e]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO) MeSiH
AgBF4
70
76
78
2
presence of 6 combined with AgBF , (S)-2 was ob-
4
ACHTUNGTRENNUNG( EtO) MeSiH
ACHTUNGTRENNUNG( EtO) MeSiH AgBF4
2
AgBF4
2
tained in 74% yield and 85% ee (entry 1). In contrast
to the 4/AgBF catalytic system, very small amounts
4
[
a]
of several unidentified products were also formed in
Reaction conditions: 1 (0.5 mmol), silane (0.6 mmol), 4
(
4 mol%), additive (4 mol%), THF (0.5 mL), room tem- the 6/AgBF4 system (Table 1 entry 13 vs. Table 2
perature, 20 h, then MeOH and K CO .
Determined by GLC analysis. Average of two runs.
entry 1). To optimize the reaction, the solvent effect
was investigated. The first promising result was
2
3
[
[
[
[
b]
c]
d]
e]
(
(
(
EtO) MeSiH (1.0 mmol).
2
achieved
with
2-methyltetrahydrofuran
(2-
EtO) MeSiH (1.5 mmol).
[16]
2
MeTHF), which gave 92% ee (entry 2). To the best
of our knowledge, this is the first example of the
NHC-Ir-catalyzed hydrosilane reduction of a ketone
EtO) MeSiH (1.75 mmol).
2
À
selectivity was observed in the series of BF > with high stereoselectivity at room temperature. It
4
À
À
À
6
À
OTs >BPh >PF >OTf in the asymmetric hydro- should be noted that the excellent enantioselectivity
4
silylation of 1 with Ph SiH catalyzed by an NHC-Rh was obtained by employing a monodentate NHC-Ir
2
2
[7c]
complex. The type of the silylating reagent is also complex such as 6, in which the stereodirecting func-
an important factor for achieving a stereoselective re- tionalized group on the ligand is far from the metal
action. Slightly lower enantioselectivity was observed center. It seems that the addition of AgBF to the cat-
4
in the case of (MeO) MeSiH, although the product alytic reaction mixture serves to remove a chloride
2
yield was comparable to that of the reaction with ligand from 6. Then, the formation of a polydentate
(
EtO) MeSiH (entry 8). Most of the substrate was re- ligand via chelation with the amide oxygen could lock
2
covered unchanged in the reaction with (EtO) SiH or the stereodirecting functionalized group in a fixed
3
Et SiH (entries 9 and 10). Notably, the treatment of conformation.
3
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809

Shun Kawabata et al.
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Table 2. Asymmetric reduction of 1 with (EtO) MeSiH cata-
lyzed by iridium complex/AgBF4.
Table 3. Asymmetric
reduction
of
ketones
[a]
with
2
[a]
(EtO) MeSiH catalyzed by iridium complex/AgBF .
2
4
Entry
Cat.
Solvent
Yield [%]
recovered 1 [%])
ee
[%]
[b]
(
1
2
3
4
5
6
7
8
9
6
6
6
6
6
6
6
6
6
THF
2-MeTHF
74 (10)
71 (5)
70 (7)
68 (2)
69 (6)
56 (15)
59 (14)
67 (8)
62 (12)
9 (90)
85
92
89
90
88
84
87
90
83
–
[
c]
Entry
Cat.
Ar
Yield
[%]
ee
[c]
[b]
Et O
R
[%]
2
t-BuOMe
1
2
3
4
5
6
7
8
9
4-MeO H
3-MeO H
4-n-BuC H
4-ClC H
2-ClC H
4-Me NC H
Ph
Ph
Ph
Me
Me
Me
Me
Me
Me
Et
c-C H
i-Pr
Me
8
9
75
54
72
60
49
25
85
53
61
29
90
86
89
84
68[
6
4
4
i-Pr O
2
6
CH Cl
2
2
10
11
12
13
14
15
16
17
6
4
CHCl3
6
4
4
C H Me
6
5
6
n-C H
6
14
d]
[d]
[c]
79
89
85
91
89
2
6
4
10
–
2-MeTHF
[
a]
[d]
Reaction conditions:
1.5 mmol), iridium catalyst (4 mol%), AgBF (4 mol%),
1
(0.5 mmol), (EtO) MeSiH
2
6
11
(
4
solvent (0.5 mL), room temperature, 20 h, then MeOH
and K CO .
10
2-thienyl
2
3
[a]
[
[
[
b]
Reaction conditions: ketone (0.5 mmol), (EtO) MeSiH
2
Determined by GLC analysis. Average of two runs.
-MeTHF=2-methyltetrahydrofuran.
IrCl(cod)] (4 mol%) instead of 6 was used.
c]
(1.5 mmol), 6 (4 mol%), AgBF (4 mol%), 2-methyltetra-
hydrofuran (0.5 mL), room tempertaure, 20 h, then
4
2
[
d]
ACHTUNGTRENNUNG
2
MeOH and K CO .
Isolated yield.
Determined by GLC analysis.
Determined by HPLC analysis; see Supporting Informa-
tion for details.
2
3
[
[
b]
c]
The yield and enantioselectivity of the reduction of
using other ethereal solvents such as Et O, tert-butyl
[d]
1
2
methyl ether, and diisopropyl ether were found to be
comparable to or slightly lower than that obtained
using 2-MeTHF (entries 3–5). In addition, the use of piophenone (14) at ambient temperature, furnishing
halogenated solvents as well as hydrocarbons was also the corresponding alcohols in 85% yield with 89% ee
effective, yielding (S)-2 with satisfactory enantioselec- (entry 7). Cyclohexyl phenyl ketone (15) was reduced
tivity (83–90% ee) (entries 6–9). It is important to to the corresponding alcohol with 85% ee, whereas
note that the hydrosilylation reaction catalyzed by 91% ee was also recorded in the reaction of iso-
[
IrCl
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(cod)] in combination with AgBF at room tem-
ACHTUNGTRENNGNUb utyrophenone (16) (entries 8 and 9). Despite the
2
4
perature occurred with difficulty and most of the sub- achievement of good enantioselectivity (89% ee) in
strate was recovered (entry 10). This fact strongly sug- the reduction of 2-acetylthiopehene (17), a very slow
gested that the coordination of the NHC ligand to the reaction was observed probably due to the presence
metal center not only induces the stereoselectivity of of sulfur as a catalyst poison (entry 10).
the reaction but also enhances the reaction rate.
Based on these results, the reduction of other ke- enantioselective hydrosilylation of ketones catalyzed
tones was performed by the 6/AgBF catalytic system by the [IrCl(cod)(NHC)] complex. The hydroxy-
amide-functionalized azolium compound derived
In conclusion, we have described the first efficient
A
H
U
G
R
N
N
ACHTUNGTRENNUNG
4
in 2-MeTHF at room temperature (Table 3). 4-Me-
ACHTUNGTRENNUNG
thoxyacetophenone (8) was readily reduced to afford from isoleucinol serves as a versatile chiral NHC
the corresponding alcohol in 75% yield and 90% ee, ligand for achieving a highly stereoselective reduction
while 3-methoxyacetophenone (9) produced a some- without controlling the reaction temperature.
what lower yield probably owing to steric hindrance
(
entries 1 and 2). Although the reaction of the 4-
alkyl-substitued acetophenone derivatives such as 10
took place effortlessly (entry 3), reactions of the aryl
methyl ketone bearing an electron-withdrawing group
such as 4-chloro- and 2-chloroacetophenone (11 and
Experimental Section
Procedure for the Preparation of 7
A suspension of the corresponding benzimidazolium salt 7’
1
2) proceeded slowly (entries 4 and 5). In these reac-
(
36 mg, 0.1 mmol) and silver(I) oxide (24 mg, 0.05 mmol) in
tions, most of the substrates were recovered un-
changed. The reduction of 4-(dimethylamino)aceto-
phenone (13) resulted in low yield of the product be-
cause of the formation of several unidentified prod-
CH Cl (5 mL) was stirred in the dark for 1 h at room tem-
2
2
perature. After evaporation of the solvent, a solution of
RhCl(cod)] (25 mg, 0.05 mmol) in THF (5 mL) was added
in the dark at room temperature. The resulting suspension
[
ACHTUNGTRENNUNG
2
ucts (entry 6). The present catalytic system is suitable was stirred for 16 h, filtered through a membrane filter
for the enantioselective hydrosilane reduction of pro- (pore size: 0.2 mm), and evaporated to dryness under
810
asc.wiley-vch.de
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 807 – 812

Asymmetric Hydrosilane Reduction of Ketones Catalyzed by an Iridium Complex
vacuum. The desired [RhCl
fied by column chromatography on silica gel (CH Cl /
A
H
U
G
R
N
U
G
A
H
U
G
R
N
N
(NHC)] complex was puri-
e) W.-Q. Wu, Q. Peng, D.-X. Dong, X.-L. Hou, Y.-D.
Wu, J. Am. Chem. Soc. 2008, 130, 9717.
2
2
CH OH=19:1) to give 7 as a yellow solid; yield: 53 mg
[3] For selected recent reviews: a) N-Heterocyclic Car-
benes, (Ed.: S. Dꢂez-Gonzꢃlez), RSC Publishing, Cam-
bridge, 2011; b) L. Benhamou, E. Chardon, G. Lavigne,
S. Bellemin-Laponnaz, V. Cꢄsar, Chem. Rev. 2011, 111,
2705; c) O. Kꢅhl, Functionalised N-Heterocyclic Car-
bene Complexes, Wiley-VCH, Weinheim, 2010; d) S.
Dꢂez-Gonzꢃlez, N. Marion, S. P. Nolan, Chem. Rev.
2009, 109, 3612; e) F. E. Hahn, M. C. Jahnke, Angew.
Chem. 2008, 120, 3166; Angew. Chem. Int. Ed. 2008, 47,
3122; f) N-Heterocyclic Carbenes in Transition Metal
Catalysis, in: Topics in Organometallic Chemistry, Vol.
21, (Ed.: F. Glorius), Springer-Verlag, Berlin, Heidel-
berg, 2007; g) N-Heterocyclic Carbenes in Synthesis
(Ed.: S. P. Nolan), Wiley-VCH, Weinheim, 2006; h) V.
Cꢄsar, S. Bellemin-Laponnaz, L. H. Gade, Chem. Soc.
Rev. 2004, 33, 619.
3
(
96%).
1
7
(major): H NMR (CDCl ): d=7.53–7.28 (m, 4H,
3
CHbenzimid.), 6.46 (d, J=16.1 Hz, 1H, NCH CO), 5.15–5.12
2
(
br, 2H, CHcod), 4.90 (d, J=16.1 Hz, 1H, NCH CO), 4.34 (s,
2
3
H, NCH ), 3.90–3.85 (br, 1H, NHCH), 3.67–3.67 (br, 1H,
3
CH OH), 3.65–3.48 (br, 2H, CHcod), 3.43–3.29 (br, 1H,
2
CH OH), 3.05 (t, J=8.0 Hz, 1H, OH), 2.51–2.44 (br, 4H,
2
CH2cod), 2.29–2.27 (br, 1H, NH), 2.07–2.02 (br, 4H, CH2cod),
1
3
0
1
.55 (s, 9H, CCH ); C NMR: d=196.7 (J=49.7 Hz, C-Rh),
3
67.4 (CO), 135.1 (Cbenzimid.), 133.8 (Cbenzimid.), 123.3
(
Cbenzimid.), 123.0 (Cbenzimid.), 110.0 (Cbenzimid.), 109.5 (Cbenzimid.),
1
1
5
3
01.5 (J=5.8 Hz, CHcod), 101.2 (J=6.6 Hz, CHcod), 69.5 (J=
4.9 Hz, CHcod), 69.3 (J=15.7 Hz, CHcod), 60.6 (CH OH),
2
9.5 (NHCH), 52.5 (CH CO), 34.5 (NCH ), 33.5 [C ACHTGNUTRNEUNG( CH ) ],
3 3
2
3
2.7 (CH2cod), 32.6 (CH2cod), 28.6 (CH2cod), 28.6 (CH2cod), 26.4
(CH ) ]; anal. calcd. for C H ClN O Rh·0.5H O: C
[C
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
3
24 35
3
2
2
[4] a) G. Erre, S. Enthaler, K. Junge, S. Gladiali, M. Beller,
Coord. Chem. Rev. 2008, 252, 471; b) Y.-M. Li, F.-Y.
Kwong, W.-Y. Yu, A. S. C. Chan, Coord. Chem. Rev.
2007, 251, 2119.
52.90, H 6.66, N 7.71; found: C 53.22, H 6.46, N 7.13%.
General Procedure for the Hydrosilylation Reaction
[
5] a) Y. Zhu, K. Burgess, J. Am. Chem. Soc. 2008, 130,
894; b) X. Cui, Y. Fan, M. B. Hall, K. Burgess, Chem.
A solution of 6 (14 mg, 0.02 mmol) in 2-methyltetrahydro-
furan (0.5 mL) was added to AgBF4 (4 mg, 0.02 mmol).
After the mixture had been stirred for 1 h at room tempera-
8
Eur. J. 2005, 11, 6859; c) Y. Fan, X. Cui, K. Burgess,
M. B. Hall, J. Am. Chem. Soc. 2004, 126, 16688;
d) M. C. Perry, X. Cui, M. T. Powell, D.-R. Hou, J. H.
Reibenspies, K. Burgess, J. Am. Chem. Soc. 2003, 125,
ture, ketone (0.5 mmol) and (EtO) MeSiH (201 mg,
2
1
2
.5 mmol) were added. The reaction mixure was stirred for
0 h at room temperature. K CO (2 mg) and MeOH (2 mL)
2
3
1
13; e) M. T. Powell, D.-R. Hou, M. C. Perry, X. Cui,
were then added and the resulting mixture was stirred for
h at room temperature. After evaporation of the solvents,
K. Burgess, J. Am. Chem. Soc. 2001, 123, 8878.
2
[
[
6] a) W.-L. Duan, M. Shi, G.-B. Rong, Chem. Commun.
the residue obtained was purified by column chromatogra-
phy on silica gel (AcOEt/n-hexane=1:10 to 1:4). The ee was
measured by chiral GLC or HPLC.
2
2
003, 2916; b) T. Chen, X.-G. Liu, M. Shi, Tetrahedron
007, 63, 4474; c) L. Liu, F. Wang, M. Shi, Organome-
tallics 2009, 28, 4416.
7] a) N. Schneider, M. Finger, C. Haferkemper, S. Belle-
min-Laponnaz, P. Hofmann, L. H. Gade, Angew. Chem.
2
009, 121, 1637; Angew. Chem. Int. Ed. 2009, 48, 1609;
Acknowledgements
b) N. Schneider, M. Kruck, S. Bellemin-Laponnaz, H.
Wadepohl, L. H. Gade, Eur. J. Inorg. Chem. 2009, 493;
c) V. Cꢄsar, S. Bellemin-Laponnaz, H. Wadepohl, L. H.
Gade, Chem. Eur. J. 2005, 11, 2862; d) L. H. Gade, V.
Cꢄsar, S. Bellemin-Laponnaz, Angew. Chem. 2004, 116,
This work was supported by a Grant-in-Aid for Scientific Re-
search (C) (23550128) from Japan Society for the Promotion
of Science (JSPS), A-STEP (AS231Z00460D) from Japan
Science and Technology Agency (JST) and the Kansai Uni-
versity Research Grants. Grant-in-Aid for Encouragement of
Scientists, 2011.
1
036; Angew. Chem. Int. Ed. 2004, 43, 1014.
[
8] C. Song, C. Ma, Y. Ma, W. Feng, S. Ma, Q. Chaia, M. B.
Andrus, Tetrahedron Lett. 2005, 46, 3241.
[
9] Selected publications on asymmetric hydrosilylation of
ketones: a) W. A. Herrmann, L. J. Goossen, C. Kçcher,
G. R. J. Artus, Angew. Chem. 1996, 108, 2980; Angew.
Chem. Int. Ed. Engl. 1996, 35, 2805; b) D. Enders, H.
Gielen, J. Runsink, K. Breuer, S. Brode, K. Boehn,
Eur. J. Inorg. Chem. 1998, 913; c) L. Ren, A. C. Chen,
A. Decken, C. M. Crudden, Can. J. Chem. 2004, 82,
1781; d) A. R. Chianese, R. H. Crabtree, Organometal-
lics 2005, 24, 4432.
References
[
1] a) M. Bartꢁk, Chem. Rev. 2010, 110, 1633; b) T.
Tanaka, M. Hayashi, Synthesis 2008, 3361; c) G.
Zanoni, F. Castronovo, M. Franzini, G. Vidari, E. Gian-
nini, Chem. Soc. Rev. 2003, 32, 115; d) M. P. Sibi, M.
Liu, Curr. Org. Chem. 2001, 5, 719.
[
2] For selected recent examples: a) T. Inagaki, A. Ito, J.
Ito, H. Nishiyama, Angew. Chem. 2010, 122, 9574;
Angew. Chem. Int. Ed. 2010, 49, 9384; b) Y. Liu, D.
Shang, X. Zhou, Y. Zhu, L. Lin, X. Liu, X. Feng, Org.
Lett. 2010, 12, 1803; c) A. Nojiri, N. Kumagai, M. Shi-
basaki, J. Am. Chem. Soc. 2009, 131, 3779; d) H. Y.
Kim, H. J. Shih, W. E. Knabe, K. Oh, Angew. Chem.
[10] a) S. Sakaguchi, K. S. Yoo, J. OꢆNeill, J. H. Lee, T.
Stewart, K. W. Jung, Angew. Chem. 2008, 120, 9466;
Angew. Chem. Int. Ed. 2008, 47, 9326; b) K. S. Yoo, J.
OꢆNeill, S. Sakaguchi, R. Giles, J. H. Lee, K. W. Jung, J.
Org. Chem. 2010, 75, 95; c) S. Sakaguchi, M. Kawaka-
mi, J. OꢆNeill, K. S. Yoo, K. W. Jung, J. Organomet.
Chem. 2010, 695, 195; d) R. Kamisue, S. Sakaguchi, J.
Organomet. Chem. 2011, 696, 1910.
2
009, 121, 7556; Angew. Chem. Int. Ed. 2009, 48, 7420;
Adv. Synth. Catal. 2012, 354, 807 – 812
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
811

Shun Kawabata et al.
COMMUNICATIONS
[
11] a) M. Okamoto, Y. Yamamoto, S. Sakaguchi, Chem.
Commun. 2009, 7363; b) N. Shibata, M. Okamoto, Y.
Yamamoto, S. Sakaguchi, J. Org. Chem. 2010, 75, 5707;
c) A. Harano, S. Sakaguchi, J. Organomet. Chem. 2011,
Kꢅndig, Angew. Chem. 2011, 123, 7576; Angew. Chem.
Int. Ed. 2011, 50, 7438; b) C. C. Scarborough, A. Ber-
gant, G. T. Sazama, I. A. Guzei, L. C. Spencer, S. S.
Stahl, Tetrahedron 2009, 65, 5084.
6
96, 61; d) M. Yoshimura, N. Shibata, M. Kawakami, S.
Sakaguchi, Tetrahedron 2011, DOI: 10.1016/
j.tet.2011.04.028.
12] H. Chiyojima, S. Sakaguchi, Tetrahedron Lett. 2011, 52,
788.
[14] a) A. Ros, M. Alcarazo, J. Iglesias-Sigꢅenza, E. Dꢂez,
E. ꢇlvarez, R. Fernꢃndez, J. M. Lassaletta, Organome-
tallics 2008, 27, 4555; b) H. Seo, B. Y. Kim, J. H. Lee,
H.-J. Park, S. U. Son, Y. K. Chung, Organometallics
2003, 22, 4783.
[
[
6
13] In the literature, it was reported that the NMR spectra
of some NHC-metal complexes were difficult to inter-
pret: a) M. Nakanishi, D. Katayev, C. Besnard, E. P.
[15] U. Nagel, C. Diez, Eur. J. Inorg. Chem. 2009, 1248.
[16] T. Robert, J. Velder, H.-G. Schmalz, Angew. Chem.
2008, 120, 7832; Angew. Chem. Int. Ed. 2008, 47, 7718.
812
asc.wiley-vch.de
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 807 – 812