Novel catalytic hydrogenolysis of silyl enol ethers by the use of acidic ruthenium dihydrogen complexes

Article abstract of DOI:10.1016/S0022-328X(03)00470-4

Treatment of 1-trimethylsilyloxy-1-cyclohexene (1a) in the presence of a catalytic amount of the acidic dihydrogen complex [RuCl(η²-H₂)(dppe)₂]OTf (4a) [dppe=1,2-bis(diphenylphosphino)ethane, OTf=OSO₂CF₃] (10 mol.%) under 1 atm of H₂ in anhydrous ClCD₂CD₂Cl at 50 °C for 8 h afforded cyclohexanone (3a) and Me₃SiH in quantitative NMR yields. Silyl enol ethers such as 1-triethylsilyloxy-1-cyclohexene (1b), 1-t-butyldimethylsilyloxy-1-cyclohexene (1c), and other trimethylsilylethers (1d, 1e, and 1f) reacted similarly with H₂ to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H₂ to the trimethylsilyl enol ethers (1a and 1d-1f) was confirmed by the experiments employing D₂ gas, where α-monodeuterated ketones (3a′ and 3d′-3f′) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H₂ by employing [RuCl(η²-H₂) ((S)-BINAP)₂]OTf (4e) [BINAP=2,2′-bis (diphenylphosphino)-1,1′-binaphthyl] and [RuCl(η²-H₂)((R, R)-CHIRAPHOS)₂]OTf (4f) [CHIRAPHOS=2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe)₂] (5a) with one equivalent of Me₃SiOTf under 1 atm of H₂ produced rapidly 4a, concurrent with the formation of Me₃SiH. Based on these studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the coordinated H₂ on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and Me₃SiOTf, and the subsequent reaction of the resultant complex 5a with Me₃SiOTf under 1 atm of H₂ to regenerate the original dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at -78 °C in CH₂Cl₂ under 1 atm of H₂ afforded 2-methyl-1-tetralone (3e) with 75% ee (S) in >95% yield, together with the formation of [RuHCl((S)-BINAP)₂] (5e).

Full text of DOI:10.1016/S0022-328X(03)00470-4

Journal of Organometallic Chemistry 679 (2003) 32ꢁ42
/
www.elsevier.com/locate/jorganchem
Novel catalytic hydrogenolysis of silyl enol ethers by the use of acidic
ruthenium dihydrogen complexes
Izuru Takei a,b, Yoshiaki Nishibayashi c, Youichi Ishii d,1, Yasushi Mizobe a,
Sakae Uemura c, Masanobu Hidai b,*
a Institute of Industrial Science, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8505, Japan
b Department of Materials Science and Technology, Faculty of Industrial Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510,
Japan
c Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
d Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Received 9 April 2003; received in revised form 20 May 2003; accepted 22 May 2003
Abstract
Treatment of 1-trimethylsilyloxy-1-cyclohexene (1a) in the presence of a catalytic amount of the acidic dihydrogen complex
[RuCl(h2-H2)(dppe)2]OTf (4a) [dppeꢀ
/
1,2-bis(diphenylphosphino)ethane, OTfꢀOSO2CF3] (10 mol.%) under 1 atm of H2 in
/
anhydrous ClCD2CD2Cl at 50 8C for 8 h afforded cyclohexanone (3a) and Me3SiH in quantitative NMR yields. Silyl enol ethers
such as 1-triethylsilyloxy-1-cyclohexene (1b), 1-t-butyldimethylsilyloxy-1-cyclohexene (1c), and other trimethylsilylethers (1d, 1e,
and 1f) reacted similarly with H2 to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H2 to the
trimethylsilyl enol ethers (1a and 1dꢁ
and 3d?ꢁ3f?) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H2 by
employing [RuCl(h2-H2)((S)-BINAP)2]OTf (4e) [BINAPꢀ2,2?-bis(diphenylphosphino)-1,1?-binaphthyl] and [RuCl(h2-H2)((R, R)-
CHIRAPHOS)2]OTf (4f) [CHIRAPHOSꢀ2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in
/
1f) was confirmed by the experiments employing D2 gas, where a-monodeuterated ketones (3a?
/
/
/
either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe)2] (5a) with
one equivalent of Me3SiOTf under 1 atm of H2 produced rapidly 4a, concurrent with the formation of Me3SiH. Based on these
studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the
coordinated H2 on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and
Me3SiOTf, and the subsequent reaction of the resultant complex 5a with Me3SiOTf under 1 atm of H2 to regenerate the original
dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at ꢂ
/
78 8C
in CH2Cl2 under 1 atm of H2 afforded 2-methyl-1-tetralone (3e) with 75% ee (S) in ꢀ95% yield, together with the formation of
/
[RuHCl((S)-BINAP)2] (5e).
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Hydrogenolysis; Dihydrogen complexes; Silyl enol ethers; Asymmetric protonation
1. Introduction
as their reactivities [1ꢁ4]. In the bonding between a
/
metal (M) and dihydrogen (H2), s donation from the s
bonding orbital of H2 to the d-orbital of metal depletes
the electron density on the H2, while back-bonding from
the metal to the antibonding s* orbital of H2 increases
the electron density on the H2. The contribution of the
former bonding is believed to be higher than the latter in
most of dihydrogen complexes, so that the coordinated
H2 is expected to be more acidic than free H2. Actually,
treatment of some dihydrogen complexes with a variety
of bases gives rise to the heterolytic cleavage of
Extensive studies on dihydrogen complexes have been
performed to reveal their bonding and structures as well
* Corresponding author. Tel.: ꢃ
1699.
E-mail address: hidai@rs.noda.tus.ac.jp (M. Hidai).
/
81-47-124-1501; fax: ꢃ81-47-124-
/
1
Present address: Department of Applied Chemistry, Faculty of
Science and Engineering, Chuo University, Kasuga, Bunkyo-ku,
Tokyo 112-8551, Japan.
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00470-4

I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ
/42
33
coordinated H2 [2]. The systematic research of ligand
effects on the reactivity of coordinated H2 has led to the
synthesis of a series of acidic dihydrogen complexes.
However, development of catalytic hydrogenation reac-
tions by using the unique properties of coordinated H2
temperature, complex 2a is known to be quantitatively
transformed into [RuCl(h2-H2)(dppe)2]OTf (4a) with
relatively high acidity (pKaꢀ6.0) [9,13,14]. In contrast,
/
the 1H and 31P{1H}-NMR analysis of the reaction
mixture of complex 2a with 1a or 3a in ClCD2CD2Cl
indicated that both 1a and 3a are not coordinated to the
metal at ambient temperature or even 50 8C, probably
due to the steric effect of the phosphine ligands around
the metal.
has been still limited [5ꢁ
During the long-standing studies on the reactivities of
dinitrogen complexes of the type M(N2)2(L)4 (MꢀMo
or W; Lꢀphosphine) [8], we have recently succeeded in
/7].
/
/
Several acidic Ru(h2-H2) complexes were employed as
catalyst for the hydrogenolysis of 1a. Typical results are
shown in Table 1. In all cases, the reaction of 1a (0.60
mmol) with 1 atm of H2 was carried out in the presence
of a catalytic amount of 2 (5 or 10 mol.%) in anhydrous
1,2-dichloroethane at 50 8C. Although the hydrogeno-
lysis of 1a took place smoothly at 50 8C with the aid of
complex 2a (10 mol.%), the reaction did not proceed in
the transformation of coordinated N2 on tungsten into
NH3 by treatment with H2 mediated by [RuCl(dipho-
sphine)2]X complexes or sulfido-bridged dinuclear mo-
lybdenum complexes [9]. In these reactions, only one of
the two hydrogen atoms of H2 activated by the
complexes is used for the NÃ/H bond formation, while
the other is not employed for the product formation.
Thus, the reactions are stoichiometric and the activated
H2 only behaves as a proton. However, this finding has
led us to find novel hydrogenolysis of silyl enol ethers to
form ketones and silanes by employing acidic h2-H2
complexes [RuCl(h2-H2)(diphosphine)2]X as catalysts
[10]. It is to be noted that treatment of silyl enol ethers
with H2 in the presence of the Wilkinson catalyst
the absence of either complex 2a or H2 (Table 1; runs 1ꢁ
/
3). The reaction of 1a with H2 proceeded in the presence
of 5 mol.% of 2a at 50 8C for 18 h to afford 3a in 88%
yield, and a longer reaction time (48 h) improved the
yield of 3a up to ꢀ
an analogous
/
95% (Table 1; runs 4 and 5). When
complex
Ru(h2-H2)
[RuCl(h2-
[RhCl(PPh3)3] results in the hydrogenation of the CÄ
/C
H2)(dppe)2]PF6 (4b) [13] was used in place of complex
4a, the yield of 3a did not significantly change (Table 1;
runs 4 and 6). Employment of a dihydrogen complex
[RuH(h2-H2)(dppe)2]OTf (4c) with much lower acidity
bond [11]. Preliminary results on the hydrogenolysis
have already been reported in a communication form
[12]. In the present contribution we describe the more
detailed results of a conceptually new type of the
hydrogenolysis reactions.
(pKaꢀ
effectively (Table 1; run 7). On the other hand, when
[RuCl(h2-H2)(dppp)2]OTf (4d) [dpppꢀ
1,3-bis(diphe-
nylphosphino)propane] with higher acidity (pKaꢀ4.3)
/15.0) [15] did not induce the hydrogenolysis
/
/
2. Results and discussion
[9b,16] derived from [RuCl(dppp)2]OTf (2d) and H2 was
used as catalyst, the yield of 3a was slightly lower
compared with that from 4a (Table 1; runs 4 and 8).
This is compatible with the previous findings that
treatment of 2d with 1 atm of H2 in solution at ambient
temperature gives a mixture of complexes 2d and 4d in a
ratio of about 9:1 [9b,16], whereas complex 2a is
completely transformed into complex 4a under the
same conditions [9b,13]. New dihydrogen complexes
[RuCl(h2-H2)(diphosphine)2]OTf containing typical
chiral diphosphine ligands such as BINAP [17] and
CHIRAPHOS [18] prepared here (vide infra) were also
found to be effective for this catalytic reaction (Table 1;
runs 9 and 10). Noteworthy is the remarkable catalytic
activity of the dihydrogen complex (4e) containing
BINAP (Table 1; run 9), although we could not
determine the pKa [19]. Hydrogenolysis of 1-triethylsi-
lyloxy-1-cyclohexene (1b) and 1-t-butyldimethylsily-
loxy-1-cyclohexene (1c) also occurred in the presence
of 4a or 4e under the same conditions, but the reactions
were slower than that of 1a probably due to the steric
2.1. Novel catalytic hydrogenolysis of trialkylsilyl enol
ethers by using acidic Ru(h2-H2) complexes
When 1-trimethylsilyloxy-1-cyclohexene (1a) was
treated with 1 atm of H2 in the presence of a catalytic
amount of [RuCl(dppe)2]OTf (2a) (10 mol.%) in anhy-
drous ClCD2CD2Cl at 50 8C for 8 h in an NMR tube,
1H and 29Si{1H}-NMR analysis of the reaction mixture
clearly showed the quantitative formation of cyclohex-
anone (3a) and Me3SiH (29Si{1H}-NMR d ꢂ
16.4)
/
(Scheme 1). However, the reaction was very slow at
room temperature. Under 1 atm of H2 at room
factors of the bulky substrates (Table 1; runs 11ꢁ
/16)
Scheme 1.
[20].

34
I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ42
/
Table 1
Hydrogenolysis of silyl enol ethers catalysed by Ru(h2-H2) complexes under 1 atm of H2
a
2.2. The hydrogenolysis of silyl enol ethers with D2 gas
the a-position of 3a? and 3d?ꢁ
/
3f? was fully characterized
MS analysis (see Section 3).
1
by H-NMR and GCꢁ
/
The experiment employing D2 gas in the hydrogeno-
lysis unequivocally demonstrated the proton transfer
from H2 to silyl enol ethers. Thus, treatment of 1a with 5
mol.% of 2a under 1 atm of D2 at 50 8C for 48 h in
anhydrous 1,2-dichloroethane resulted in the formation
of a-monodeuterated 3a? in very high GLC yield (Table
2; run 1). The same procedure was applied for other
trialkylsilyl enol ethers (1b and 1c), 1,1-disubstituted
trimethylsilyl enol ether (1d), and 1,1,2,2-tetrasubsti-
tuted trimethylsilyl enol ethers (1e and 1f). Reactions of
bulky trialkylsilyl enol ethers (1b and 1c) were sluggish
under the same conditions, but a-monodeuterated
ketone 3a? being obtained with high selectivities (Table
2; runs 2 and 3). Similar treatment of other trimethylsilyl
enol ethers (1d, 1e, and 1f) with D2 afforded the
corresponding a-monodeuterated ketones 3d?, 3e?, and
2.3. Synthesis of chiral dihydrogen complexes [RuCl(h2-
H2)((S)-BINAP)2]OTf (4e) and [RuCl(h2-H2)((R,
R)-CHIRAPHOS)2]OTf (4g) toward asymmetric
protonation of prochiral silyl enol ethers
We intended to extend the novel catalytic reaction to
the asymmetric protonation of prochiral silyl enol ethers
with H2 assisted by new acidic Ru(h2-H2) complexes
containing chiral diphosphines. Protonation of
[RuHCl((S)-BINAP)2] (5e) [21] with trifluoromethane-
sulfonic acid (HOTf) gave the dihydrogen complex
[RuCl(h2-H2)((S)-BINAP)2]OTf (4e) in high yield.
This complex was also prepared from the reaction of
[RuHCl((S)-BINAP)2] (5e) with a hydride acceptor
Me3SiOTf under 1 atm of H2 (Scheme 2). The existence
of the h2-H2 moiety in complex 4e was confirmed by
3f? (Table 2; runs 4ꢁ6). Incorporation of deuterium at
/

I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ
/42
35
Table 2
Hydrogenolysis of silyl enol ethers catalysed by [RuCl(h2-
H2)(dppe)2]OTf (4a) under 1 atm of D2
Scheme 2.
readily replaced by dihydrogen to form the dihydrogen
complex 4g. The existence of the h2-H2 moiety in
complex 4g was confirmed by variable-temperature T1
measurement. A minimum T1 value of 15 ms (400 MHz
in CD2Cl2) at 273 K was obtained for the broad signal
at ꢂ
12.6 ppm, assignable to the h2-H2 coordination [3].
/
Catalytic asymmetric protonation of silyl enol ethers
with 1 atm of H2 was investigated by using both 4e and
4g under various reaction conditions (Scheme 4). How-
ever, treatment of 1e (0.20 mmol) in the presence of a
catalytic amount of 4e or 4g (0.010 mmol, 5 mol.%) at
25 8C for 48 h in anhydrous dichloromethane under 1
atm of H2 afforded 3e in 41 or 13% GLC yield,
respectively, with no enantioselectivity. Change of the
solvent from dichloromethane to THF or toluene did
not induce any asymmetric reaction. The protonation of
tert-butyldimethylsilyl enol ethers with HCl is known to
occur at the sp2 carbon bearing the methyl group (C-
protonation) [23]. Thus, we expected that if 1g is used as
substrate in place of 1e, some asymmetric induction may
be realized. However, the reaction of 1g with H2 in the
presence of a catalytic amount of 4e (5 mol.%) under the
same reaction conditions proceeded quite slowly to give
3e in 20% GLC yield with no enantioselectivity.
Furthermore, the stoichiometric protonation of 1e
aAll the reactions were carried out in the presence of [RuCl(h2-
H2)(dppe)2]OTf (4a) (5 mol.%) and silyl enol ether (0.60 mmol) in
anhydrous 1,2-dichloroethane (5 ml) at 50 8C for 48 h under 1 atm of
D2. bDetermined by GLC.
variable-temperature T1 measurement and the observa-
1
tion of a large JHD for the corresponding isotopomer.
The broad signal at ꢂ9.11 ppm exhibited a minimum T1
/
value of 21 ms (400 MHz in CD2Cl2) at 243 K. The
deuterio derivative trans-[RuCl(h2-HD)((S)-BINA-
P)2]OTf (4e-d1) was prepared by the reaction of 5e
with a stoichiometric amount of trifluoromethanesulfo-
nic acid-d1 (DOTf) in CD2Cl2 at room temperature. A
1JHD coupling constant of 21.5 Hz in CD2Cl2 at 20 8C
was observed for complex (4e-d1). These values of the
1
minimum T1 and JHD are compatible with the h2-H2
bonding to the metal [3].
Dihydrogen and dinitrogen ruthenium complexes
containing CHIRAPHOS ligands [RuCl(h2-H2)((R,
R)-CHIRAPHOS)2]OTf (4g) and [RuCl(N2)((R, R)-
CHIRAPHOS)2]OTf (4f) were synthesized by the fol-
lowing procedures (Scheme 3). At first, [RuCl2((R, R)-
CHIRAPHOS)2] (2f) was prepared from the reaction of
[RuCl2(PPh3)3] with two equivalents of (R, R)-CHIR-
APHOS in toluene at reflux temperature [22]. Subse-
quent treatment of complex 2f with AgOTf in
dichloromethane under 1 atm of N2 afforded the
dinitrogen complex 4f in high yield. The dinitrogen
complex 4f was converted to [RuCl(N2)((R, R)-CHIR-
APHOS)2]PF6 (4h) by anion exchange with NaPF6. The
molecular structure of 4h was unambiguously deter-
mined by X-ray analysis (see Section 3). The N2
stretching absorption at 2155 cmꢂ1 for 4f indicates
that the back-bonding from the metal to the N2 ligand is
weak. In fact, the coordinated N2 on the Ru atom was
Scheme 3.

36
I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ42
/
with one equivalent of 4e at ꢂ
anhydrous dichloromethane under 1 atm of H2 afforded
95% yield, but no enantioselectivity was
observed. These results indicate that Hꢃ of activated
H2 on the ruthenium is transferred not to the sp2
carbon, but to the oxygen atom of silyl enol ethers (O-
protonation).
/
78 8C for 3 h in
[RhCl(PPh3)3] under 1 atm of H2 in anhydrous C6H6 at
50 8C for 24 h afforded (1-phenyl-1-trimethylsilylox-
3e in ꢀ
/
y)ethane in ꢀ95% GLC yield [25]. Furthermore, the
/
reaction of 2-cyclohexen-1-one in the presence of a
catalytic amount of 2a under 1 atm of H2 at 50 8C for 18
h did not produce 3a at all, indicating that the
hydrogenolysis of 1a does not proceed via 2-cyclo-
hexen-1-one, which might be formed from dehydrosily-
lation of 1a [26].
2.4. The reaction mechanism for the hydrogenolysis of 1a
catalysed by 4a
Based on the above results, we propose a mechanism
for the novel hydrogenolysis of a silyl enol ether 1a
catalysed by dihydrogen complex 4a as a typical
example (Scheme 7). The reaction is initiated by the
nucleophilic attack of the oxygen atom of the enol ether
on the coordinated H2 on the ruthenium atom. This
induces the heterolytic cleavage of the H2 and results in
the formation of 3a and Me3SiOTf together with 5a. The
following reaction of Me3SiOTf with 5a under 1 atm of
H2 regenerates the starting dihydrogen complex 4a via
2a, concurrent with theformation of Me3SiH. It is
presumed that a delicate balance of the acidity of
dihydrogen complex 4a and the nucleophilicity of the
hydride complex 5a might realize this novel catalytic
hydrogenolysis of silyl enol ethers. However, we cannot
exclude the possibility that the concerted transfer of a
proton and a hydride of the activated H2 to the oxygen
atom and the silicon atom of the enol ether, respectively,
gives rise to the formation of 3a and Me3SiH. It is to be
noted that this reaction mechanism is comparable to
that of the heterolytic cleavage of H2 catalysed by
In order to obtain further information about the
reaction mechanism, we investigated the following
stoichiometric or catalytic reactions. When dihydrogen
complex 4a was reacted with one equivalent of 1a under
1 atm of N2 in ClCD2CD2Cl at room temperature in an
NMR tube, 1H-, 29Si{1H}-, and 31P{1H}-NMR analysis
of the reaction mixture showed the almost quantitative
formation of Me3SiH, 2a (ꢀ
mol.%), and a small amount (B
dride complex [RuHCl(dppe)2] (5a; 1H-NMR
(ClCD2CD2Cl): d ꢂ
18.5 (s), 31P{1H}-NMR: d 61.6
/
95 mol.%), 3a (ꢀ
/95
/5 mol.%) of monohy-
/
(s)) [24]. Furthermore, treatment of lithium enolate 6a,
which was prepared in situ from 1a and MeLi, with one
equivalent of [RuCl(h2-D2)(dppe)2]OTf (4a?) under 1
atm of D2 in anhydrous THF at room temperature led
to the formation of a-monodeuterated 3a? in ꢀ
/
95%
GLC yield and monodeuteride complex
a
[RuDCl(dppe)2] (5a?) in 85% isolated yield (Scheme 5).
In this case, the nucleophilic reaction of 6a on the
coordinated D2 causes the heterolytic cleavage of the D2
to form 3a?, while Dꢂ remains at the ruthenium atom as
5a?. Noteworthy is that the reaction of [RuHCl(dppe)2]
(5a) [13] with equimolar Me3SiOTf (29Si{1H}-NMR d
46.0) under 1 atm of H2 in anhydrous C6D6 at room
temperature rapidly produced the dihydrogen complex
4a and Me3SiH in quantitative NMR yields (Scheme 6).
This finding indicates that the cationic complex 2a may
initially form from the reaction of complex 5a with
Me3SiOTf as a hydride acceptor, which is immediately
transformed into the dihydrogen complex 4a under H2.
In sharp contrast, the catalytic hydrogenation of
trimethylsilyl enol ethers by using typical homogeneous
catalysts such as Wilkinson complex [RhCl(PPh3)3]
under the same reaction conditions led to the formation
of the corresponding saturated trimethylsilyl ethers. For
example, treatment of 1d in the presence of 5 mol.% of
[Cp*RuH(dppm)]
(dppmꢀbis(diphenylphosphi-
/
no)methane), where tetramethylpiperidine and an acri-
dinium salt work as proton and hydride acceptors,
respectively [6a].
2.5. Stoichiometric asymmetric protonation of prochiral
lithium enolate 6e
Treatment of lithium enolate 6e, which was prepared
in situ from the reaction of 1e and MeLi, with one
Scheme 4.
Scheme 5.

I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ
/42
37
cleaved into Hꢃ and Hꢂ on the ruthenium centre and
transferred to the enol oxygen and the trialkylsilyl
silicon atom, respectively, to form a ketone and a silane.
Furthermore, employment of a stoichiometric amount
of a chiral dihydrogen complex 4e results in the
enantioselective protonation of a prochiral lithium
enolate with H2 to give a chiral ketone with high
enantioselectivity (up to 75% ee). This provides a new
approach to the enantioselective protonation of pro-
chiral enolates [27].
Scheme 6.
equivalent of complex 4e in anhydrous dichloromethane
under 1 atm of H2 at ꢂ
/
78 8C gave 3e in ꢀ95% GLC
/
yield with 75% ee (S), together with the formation of 5e
in 69% isolated yield (Scheme 8). In this stoichiometric
protonation, the enantiomeric excess of 3e critically
depended upon the nature of the solvent. When THF,
diethyl ether, or toluene was used in place of dichlor-
3. Experimental
3.1. General considerations
omethane, no or much lower enantioselectivities (B
ee, B1% ee, and 5% ee (S), respectively) were observed
under similar reaction conditions. On the other hand,
the stoichiometric protonation of 6e with 4g at ꢂ78 8C
under similar reaction conditions afforded 3e in ꢀ95%
GLC yield with lower enantioselectivity (B10% ee);
/
1%
Preparation of complexes was performed under 1 atm
of N2 or Ar dried by passage through CaCl2 and P2O5.
Reaction of trialkylsilyl enol ethers with dihydrogen was
carried out under 1 atm of H2 dried by passage through
CaCl2 and P2O5. D2 (99.9%) was obtained from
Takachiho Chemical Industrial Co. (Japan). Solvents
/
/
/
/
thus, 4g was less effective for the asymmetric protona-
tion of 6e compared with 4e. These results indicate that
the reaction mechanism is different between silyl enol
ethers (1e and 1g) and lithium enolate (6e). We believe
that the high enantioselectivity attained by the proto-
nation of lithium enolate (6e) with a stoichiometric
amount of 4e is realized by the protonation of the
coordinated H2 at the sp2 carbon bearing the methyl
group (C-protonation) in place of the O-protonation
(vide supra).
were dried by refluxing over Naꢁbenzophenone ketyl
/
(THF, toluene, benzene, and hexanes), P2O5 (dichlor-
omethane, 1,2-dichloroethane), and distilled just before
use. Unless otherwise noted, all manipulations were
done by use of Schlenk techniques. Schlenks and flasks
were dried thoroughly in an oven at 150 8C for 3 h just
before use.
NMR spectra were recorded on a JEOL JNM-LA-
400 spectrometer. IR spectra were recorded on a
Shimadzu FTIR-8100M spectrometer. Quantitative
GLC analyses were performed on a Shimadzu GC-
14A instrument equipped with a flame ionization
2.6. Conclusion
detector using a 25 mꢄ
propylphenylpolysiloxane in fused silica capillary col-
umn. GCꢁMS analyses were carried out on a Shimadzu
GCꢁMS QP-5000 spectrometer. Elemental analyses
were performed on a PerkinꢁElmer 2400 series II
/
0.25 mm CBP-10, 14% cyano-
Novel catalytic hydrogenolysis of trialkylsilyl enol
ethers with H2 has been found to be catalysed by acidic
dihydrogen complexes of ruthenium such as [RuCl(h2-
H2)(dppe)2]OTf (4a) and [RuCl(h2-H2)((S)-BINA-
P)2]OTf (4e). In this reaction, H2 is heterolytically
/
/
/
Scheme 7.
Scheme 8.

38
I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ42
/
CHN analyzer. Optical rotation was measured on a
JASCO DIP-360.
(20 mg) of HOTf and D2O (1/1, wt.%) at r.t. under 1 atm
of N2. 1H-NMR spectra of the reaction mixture showed
1
Trimethylsilyl enol ethers (1a, 1d, and 1h), triethylsilyl
chloride, t-butyldimethylsilyl chloride and Me3SiOTf
were purchased from Tokyo Chemical Industry Co.
(Japan) and distilled under reduced pressure. Other silyl
enol ethers (1b [28], 1c [29], 1e [30], 1f [31] and 1g [32])
were prepared by the method described in the litera-
tures. (S)-BINAP [17], n-BuLi and MeLi were pur-
chased from Kanto Chemical Co., Inc. (Japan). 2-
Methyl-1-tetralone (3e) and (R, R)-CHIRAPHOS [18]
were purchased from Aldrich Chemical Company, Inc.
Me3SiH was obtained from Trichemical Co. Ltd (Ja-
pan). Amounts of the solvent molecules in the crystals
the formation of 4e-d1. H-NMR (CD2Cl2): d ꢂ
/
9.01
2
(tq, JPH
1
7.2 Hz, JHD
ꢀ
/
ꢀ21.5 Hz).
/
3.4. Preparation of [RuCl2((R, R)-CHIRAPHOS)2]×
/
CH2Cl2 (2f×CH2Cl2)
/
A solution of [RuCl2(PPh3)3] (910 mg, 0.95 mmol)
and (R, R)-CHIRAPHOS (812 mg, 1.90 mmol) in
toluene (20 ml) was stirred at reflux temperature for 3
h under 1 atm of N2. After evaporation of the solvent,
the residue was washed with hexanes (20 mlꢄ
extracted with CH2Cl2. Addition of hexanes to the
concentrated CH2Cl2 solution afforded 2f×CH2Cl2 (821
mg, 0.74 mmol) in 78% yield as yellow crystals. 1H-
NMR (CDCl3): d 0.72 (br s, 12H), 2.81 (br s, 4H), 6.83ꢁ
7.51 (m, 40H). 31P{1H}-NMR (CDCl3): d 46.8 (s). Anal.
Calc. for C56H56Cl2P4Ru×CH2Cl2: C, 61.69; H, 5.27.
Found: C, 61.83; H, 5.31%.
/
3) and
1
were determined by both elemental analyses and H-
NMR spectroscopy.
/
3.2. Preparation of [RuCl(h2-H2)((S)-BINAP)2]OTf
(4e)
/
/
To a solution of [RuHCl((S)-BINAP)2] (5e) (1.152 g,
0.83 mmol) in dichloromethane (10 ml) and THF (10
ml) was added 80 ml of HOTf by syringe under 1 atm of
H2. The reaction mixture was stirred at room tempera-
ture (r.t.) for 30 min, during which the yellow solution
turned to a red solution. Addition of hexanes (50 ml) to
the reaction mixture afforded a pale red solid 4e, which
was collected by filtration, washed with hexanes (20
3.5. Preparation of [RuCl(N2)((R, R)-
CHIRAPHOS)2]OTf (4f)
A solution of 2f (821 mg, 0.74 mmol) and AgOTf (210
mg, 0.82 mmol) in CH2Cl2 (20 ml) was stirred at r.t. for
30 min under 1 atm of N2. After evaporation of the
solvent, the residue was extracted with CH2Cl2 (10 ml).
Addition of Et2O to the concentrated CH2Cl2 solution
of product under 1 atm of N2 afforded 4f (739 mg, 0.63
mmol) in 86% yield as pale yellow crystals. IR (KBr):
mlꢄ
(1.050 g, 0.68 mmol). H-NMR (CD2Cl2): d ꢂ
2H), 5.2ꢁ8.8 (m, 64H); a minimum T1 value of 21 ms
(400 MHz) at 243 K was obtained for the broad signal at
9.11 ppm upon changing the temperature from 233 to
303 K. 31P{1H}-NMR (CD2Cl2): d 2.5 (t, Jꢀ
27 Hz),
26.3 (t, Jꢀ27 Hz). Anal. Calc. for
/
3), and dried under reduced pressure. Yield: 82%
1
/9.11 (br,
/
1
n(N2), 2155 cmꢂ1. H-NMR (CDCl3): d 0.36 (q, 6H,
ꢂ
/
/
Jꢀ
(br m, 2H), 6.71ꢁ
(CDCl3): d 37.7 (t, Jꢀ
/
7 Hz), 0.65 (q, 6H, Jꢀ
7.48 (m, 40H). 31P{1H}-NMR
22 Hz) and 51.0 (t, Jꢀ22 Hz).
/
7 Hz), 2.37 (br m, 2H), 3.00
/
/
C89H66ClF3O3P4SRu: C, 69.73; H, 4.34. Found: C,
69.74; H, 4.38%.
/
/
Anal. Calc. for C57H56ClF3N2O3P4RuS: C, 58.69; H,
4.84; N, 2.40. Found: C, 58.91; H, 5.13; N, 2.51%.
Complex 4e was also prepared form the reaction of 5e
with Me3SiOTf under 1 atm of H2. To a solution of 5e
(138 mg, 0.10 mmol) in dichloromethane (10 ml) was
added Me3SiOTf (22 mg, 0.10 mmol) by syringe under 1
atm of H2. The reaction mixture was stirred at r.t. for 30
min under 1 atm of H2. The color of the solution turned
from yellow to red during the reaction. Addition of
hexanes (50 ml) to the reaction mixture afforded a pale
red powder, which was collected by filtration and
3.6. Conversion of 4f into [RuCl(h2-H2)((R, R)-
CHIRAPHOS)2]OTf (4g)
In an NMR tube was placed 4f (15.0 mg, 0.013 mmol)
under 1 atm of N2. Dry CD2Cl2 (0.60 ml) was then
added by syringe under 1 atm of N2. The reaction
mixture was stirred at r.t. for 5 min under 1 atm of H2.
1H and 31P{1H}-NMR spectra of the reaction mixture
showed the complete conversion of 4f into 4g. 1H-NMR
washed with hexanes (20 mlꢄ/3). The resultant powder
was recrystallized from THFꢁhexanes to give a pale red
/
solid of 4e (49 mg, 0.032 mmol) in 32% yield.
(CD2Cl2): d ꢂ
(q, 6H, Jꢀ6 Hz), 1.78 (br m, 2H), 3.16 (br m, 2H),
6.69ꢁ7.55 (m, 40H); a minimum T1 value of 15 ms (400
MHz) at 273 K was obtained for the broad signal at ꢂ
12.6 ppm upon changing the temperature from 233 to
303 K. 31P{1H}-NMR (CD2Cl2): d 36.1 (t, Jꢀ
24 Hz)
and 64.9 (t, Jꢀ24 Hz).
/
12.6 (br, 2H), 0.37 (q, 6H, Jꢀ
/
6 Hz), 0.80
3.3. Preparation of [RuCl(h2-HD)((S)-BINAP)2]OTf
(4e-d1)
/
/
/
The Ru(h2-HD) complex (4e-d1) was prepared in situ
by the following procedure. To a solution of 5e (28 mg,
0.020 mmol) in CD2Cl2 (0.75 ml) was added a mixture
/
/

I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ
/42
39
3.7. Reaction of 1a with H2 in the presence of 2a in an
NMR tube (Scheme 1)
position of 3a?. GCꢁ
20], 98 [Mꢃꢂ
1, 2].
The presence of D at the a-position of 3d? (ꢀ
/
MS m/z (relative intensity) 99 [Mꢃ,
/
/
95%
MS.
CH3,
2.4 Hz), 7.47 (t, 2H), 7.68 (t, 2H), 7.96 (d, 1H).
This result indicates the ꢀ99% deuterium content at the
a-position of 3d?. GCꢁMS m/z (relative intensity) 121
[Mꢃ, 30], 120 [Mꢃꢂ
1, 10].
The presence of D at the a-position of 3e? (ꢀ
1
In an NMR tube was placed 2a (16.3 mg, 0.015 mmol)
under 1 atm of H2. A solution of 1a (28 mg, 0.16 mmol)
in anhydrous ClCD2CD2Cl (0.8 ml) was then added by
syringe. The reaction mixture was kept at 50 8C for 8 h
under 1 atm of H2. The 1H-NMR analysis of the
GLC yield) was confirmed by H-NMR and GCꢁ
1H-NMR (CDCl3): d 2.62 (t, 2.00H; OÄ
CÃ
1JHD
/
/
/
ꢀ
/
/
/
mixture revealed that 3a was obtained in ꢀ95% yield.
/
/
The quantitative formation of Me3SiH was confirmed
by 1H and 29Si{1H}-NMR spectra of the reaction
/
95%
1
GLC yield) was also confirmed by H-NMR and GCꢁ
/
mixture. Me3SiH: 29Si{1H}-NMR (C6D6): d ꢂ
16.4.
/
1
MS. H-NMR (CDCl3): d 1.26 (s, 3H), 1.90 (m, 1H),
(1a: 29Si{1H}-NMR (C6D6): d 14.6).
2.20 (m, 1H), 2.63 (m, 0.07H; OÄCÃC(CH3)H ÃCH2Ã),
/
/
/
/
2.99 (m, 2H), 7.22 (d, 1H), 7.29 (t, 1H), 7.44 (t, 1H), 8.03
(d, 1H). This result indicates the 93% deuterium content
3.8. Reaction of 1a in the presence of a catalytic amount
of 4a under 1 atm of H2
at the a-position of 3e?. GCꢁ
161 [Mꢃ, 64], 160 [Mꢃꢂ
1, 9].
The presence of D at the a-position of 3f? (ꢀ
/MS m/z (relative intensity)
/
/
95%
GLC yield) was also confirmed by H-NMR and GCꢁ
MS. 1H-NMR (CDCl3): d 0.99 (s, 3H), 1.05 (s, 3H), 1.18
(s, 3H), 1.6ꢁ2.0 (m, 6H), 2.68 (m, 0.15H; OÄ
CCH(CH2)ÃCH2Ã). This result indicates the 85%
deuterium content at the a-position of 3f?. GCꢁMS m/
z (relative intensity) 141 [Mꢃ, 22], 140 [Mꢃꢂ
1, 1].
A typical experimental procedure for the reaction
described in Table 1 is as follows. In a 20 ml flask were
placed 2a (32.5 mg, 0.030 mmol) and naphthalene (30
mg) as an internal standard for GLC analysis under 1
atm of N2. Anhydrous 1,2-dichloroethane (5 ml) was
added, and then the mixture was magnetically stirred at
r.t. for 5 min. After the N2 atmosphere was replaced by
1 atm of H2, 1a (102 mg, 0.60 mmol) was added by
syringe. The reaction mixture was stirred at 50 8C for 18
h in the flask attached with a balloon (3 l) containing 1
atm of H2. The yield of 3a was determined by GLC.
1
/
/
/
/
/
/
/
3.10. Stoichiometric reaction of 4a? and 6a under D2
atmosphere (Scheme 5)
3.9. Reaction of trimethylsilyl enol ethers (1aꢁ1f and 1g)
in the presence of a catalytic amount of 4a under 1 atm of
D2
/
A solution of 6a was prepared by the lithiation of 1a
(17.5 mg, 0.10 mmol) with MeLi (0.10 ml of 1.02 N
diethyl ether solution, 0.10 mmol) in Et2O (1 ml) at r.t.
for 2 h under 1 atm of N2. A solution of complex 4a?,
which was prepared from 2a (110 mg, 0.10 mmol) in dry
THF (10 ml) under 1 atm of D2, was added to the above
solution at 0 8C under 1 atm of D2. The mixture was
warmed up to r.t. and stirred at r.t. for 1 h under 1 atm
of D2. The GLC analysis based on naphthalene (10 mg)
as an internal standard showed the formation of 3a? in
A typical experimental procedure for the reaction of
1a with D2 catalysed by 4a (Table 2; run 1) is described
below. In a 20 ml flask were placed 2a (32.5 mg, 0.030
mmol) and naphthalene as an internal standard for
GLC under 1 atm of N2. Anhydrous 1,2-dichloroethane
(5 ml) was added, and then the mixture was magnetically
stirred at r.t. for 5 min. After the N2 atmosphere of the
reaction mixture was replaced by 1 atm of D2, 1a (102
mg, 0.60 mmol) was added by syringe. The reaction
mixture was stirred at 50 8C for 48 h in the flask
attached with a balloon (3 l) containing 1 atm of D2.
ꢀ95% yield. For the isolation of 3a?, the solvent was
/
removed under reduced pressure and the residue was
extracted with Et2O (10 ml). The Et2O solution was
distilled at atmosphere pressure to give a colorless liquid
1
3a? (b.p. 155 8C). H-NMR (CDCl3): d 1.74 (m, 2H),
The formation of 3a? was observed by GLC (ꢀ
yield). No other products than 3a? and Me3SiD were
observed by NMR, GLC and GCꢁMS. For the isola-
/
95%
1.87 (m, 4H), 2.34 (br t, 3.04H; OÄ
result indicates the 96% deuterium content at the a-
position of 3a?. GCꢁ
MS m/z (relative intensity) 99 [Mꢃ,
22], 98 [Mꢃꢂ
1, 1]. On the other hand, the remained
residue was recrystallized from CH2Cl2ÃEt2O to give
/
CÃ
/
CH2Ã/CH2). This
/
/
tion of 3a?, the solvent was removed under reduced
pressure and the residue was extracted with Et2O (10
ml). The Et2O solution was distilled at atmosphere
pressure to give a colorless liquid 3a? (b.p. 155 8C). The
/
/
deuteride complex 5a? (79 mg, 0.085 mmol) in 85% yield.
1
31P{1H}-NMR (C6D6): d 62.7 (s); H-NMR (C6D6): d
presence of D at the a-position of 3a? was confirmed by
1
MS. H-NMR (CDCl3): d 1.74 (m,
1H-NMR and GCꢁ
/
ꢂ
/
17.6 (m, 0.12H; RuH), 2.04 (br, 4H), 2.65 (br, 4H),
6.87ꢁ
7.70 (m, 40H). The 1H-NMR spectrum of 5a?
indicates the 88% deuterium content as deuteride of 5a?.
/
2H), 1.87 (m, 4H), 2.34 (br t, 3.05H; OÄ
/
CCH2CH2).
This result indicates the 95% deuterium content at the a-

40
I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ42
/
3.11. Stoichiometric reaction of 5a with Me3SiOTf under
H2 atmosphere (Scheme 6)
Table 3
Crystallographic data of [RuCl(N2)((R, R)-CHIRAPHOS)2]PF6 (4h)
Formula
C56H56ClF6N2P5Ru
1162.45
Orthorhombic
P212121(#19)
Yellow
15 107(3)
23.838(4)
14.838(3)
5343(1)
4
In an NMR tube was dissolved 5a (28.0 mg, 0.03
mmol) in anhydrous C6D6 (1.0 ml) under 1 atm of H2.
Then, Me3SiOTf (9.0 mg, 0.04 mmol) was added by
syringe. The 31P{1H}-NMR spectrum of the reaction
Formula weight
Crystal system
Space group
Crystal color
˚
a (A)
mixture showed that 4a was formed in ꢀ
/
95% yield. 4a:
31P{1H}-NMR (C6D6): d 51.6 (s); H-NMR (C6D6): d
11.5 (br, 2H), 2.01 (br, 4H), 2.48 (br, 4H), 6.76ꢁ7.70
˚
b (A)
1
˚
c (A)
3
V (A )
˚
ꢂ
/
/
Z
(m, 40H). On the other hand, the complete consumption
of Me3SiOTf (29Si{1H}-NMR d 46.0) and the formation
Dcalc (g cmꢂ1
F(0 0 0)
)
1.445
2384
of Me3SiH (29Si{1H}-NMR d ꢂ
16.4) was confirmed by
/
mcalc (cmꢂ1
No. of unique data
)
5.53
6778
1H and 29Si{1H}-NMR spectra of the reaction mixture.
No. of data used (I ꢀ
No. of parameters refined
R
/
3s(I))
3251
427
3.12. Asymmetric protonation of 6e with 4e (Scheme 8)
0.057
0.058
Rw
A solution of 6e was prepared by lithiation of 1e (25.0
mg, 0.10 mmol) with MeLi (0.10 ml of 1.02 N diethyl
ether solution, 0.10 mmol) in anhydrous Et2O (3 ml) at
r.t. for 2 h under 1 atm of N2. A solution of complex 4e
(150 mg, 0.10 mmol) in anhydrous CH2Cl2 (5 ml) was
Goodness-of-fit indicator
˚
Maximum residuals (e A
1.45
0.64
ꢂ3
)
then added to the above solution of 6e at ꢂ
/
78 8C under
1 atm of H2. The mixture was stirred at ꢂ78 8C for 4 h
under 1 atm of H2. Then the reaction mixture was
gradually warmed up to r.t. and stirred at r.t. for 12 h.
/
corrected for Lorentz-polarization effects and for ab-
sorption (scans). Details of crystal and data collection
parameters are summarized in Table 3. Structures
solution and refinements were carried out by using the
TEXSAN program package [34]. The positions of heavy
atoms were determined by Patterson methods and
subsequent Fourier syntheses (DIRDIF PATTY) [35].
All non-hydrogen atoms except for carbon atoms of
phenyl rings of 4h were refined anisotropically by full-
matrix least-squares techniques (based on F). All
hydrogen atoms were placed at the calculated positions
and included in the final stage of refinement with fixed
parameters. The ORTEP drawing of 4h is shown in Fig. 1.
Selected bond lengths and angles are listed in Table 4.
The GLC analysis showed the formation of 3e in ꢀ
yield. The solvent was removed under reduced pressure
and the residue was extracted with Et2O (5 mlꢄ3). The
Et2O solution was purified by TLC (SiO2, hexaneꢁ
EtOAcꢀ7/3 as an eluent) to afford 3e as a pale yellow
/
95%
/
/
/
liquid (12 mg, 0.075 mmol) in 75% isolated yield. On the
other hand, the remained residue was recrystallized from
CH2Cl2Ã
/
Et2O to give 5e as a yellow solid (95 mg, 0.069
mmol) in 69% yield. The absolute configuration of (S)-
3e was determined by its optical rotation [33]. [a]18D 30
(c 0.40, dioxane). The 75% ee value of (S)-3e was
determined by GLC (carrier gas, helium; column
temperature, 120 8C; split ratio, 20:1) on a cyclodextrin
phase (Chiraldex GT-A, 30 m). The retention time of
(R)-3e, 22.87 min (12.6%); the retention time of (S)-3e,
24.01 min (87.4%).
3.13. An X-ray crystallographic study
A
single crystal of [RuCl(N2)((R, R)-CHIRA-
PHOS)2]PF6 (4h) obtained by anion exchange of 4f
with NaPF6 was sealed in Pyrex glass capillaries under
N2 atmosphere and used for data collection. Diffraction
data were collected on a Rigaku AFC-7R four-circle
automated diffractometer at 20 8C. Orientation matrixes
and unit cell parameters were determined by least-
squares treatment of 25 reflections with 27.0B
/
2u B
/
28.78 for 4h. No significant decay was observed for
three standard reflections monitored every 150 reflec-
tions during the data collection. Intensity data were
Fig. 1. ORTEP drawing of [RuCl(N2)((R, R)-CHIRAPHOS)2]PF6 (4h).
PF6ꢂ anion and hydrogen atoms are omitted for clarity.

I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ
/42
41
S.T. Lo, T.B. Wen, Z.Y. Zhou, C.-P. Lau, G. Jia, Organometallics
20 (2001) 667. (h) B.F.M. Kimmich, R.M. Bullock, Organome-
tallics 21 (2002) 1504.
Table 4
Selected bond lengths and angles in [RuCl(N2)((R, R)-CHIRA-
PHOS)2]PF6 (4h)
[3] For recent reviews, see, (a) P.G. Jessop, R.H. Morris, Coord.
Chem. Rev. 121 (1992) 155. (b) D.M. Heinekey, W.J. Oldham,
Chem. Rev. 93 (1993) 913. (c) R.H. Crabtree, Angew. Chem. Int.
Ed. Engl. 32 (1993) 789. (d) S. Sabo-Etienne, B. Chaudret, Chem.
Rev. 98 (1998) 2077. (e) S. Sabo-Etienne, B. Chaudret, Coord.
˚
Bond lengths (A)
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
/
Cl(1)
P(1)
P(2)
P(3)
2.399(3)
2.427(4)
2.421(4)
2.421(4)
Ru(1)Ã
Ru(1)Ã
N(1)Ã
/
P(4)
2.423(4)
1.96(1)
1.02(1)
/
/N(1)
/
/
N(2)
/
Chem. Rev. 178ꢁ
Chem. Rev. 98 (1998) 577. (g) G. Jia, C.-P. Lau, Coord. Chem.
Rev. 190ꢁ192 (1999) 83. (h) R. Custelcean, J.E. Jackson, Chem.
/180 (1998) 381. (f) M.A. Esteruelas, L.A. Oro,
Bond angles (8)
/
Cl(1)Ã
Cl(1)Ã
Cl(1)Ã
Cl(1)Ã
Cl(1)Ã
P(1)ÃRu(1)Ã
P(1)ÃRu(1)Ã
P(1)ÃRu(1)Ã
/
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
/
P(1)
P(2)
P(3)
P(4)
N(1)
94.0(1)
84.9(1)
92.4(1)
82.1(1)
178.6(4)
82.1(1)
173.6(1)
98.8(1)
P(2)Ã
P(2)Ã
P(3)Ã
P(1)Ã
P(2)Ã
P(3)Ã
P(4)Ã
Ru(1)Ã
/
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
Ru(1)Ã
N(1)Ã
/
P(3)
P(4)
P(4)
N(1)
N(1)
N(1)
N(1)
98.8(1)
167.0(1)
81.8(1)
86.1(4)
96.4(4)
87.4(4)
96.5(3)
178.0(1)
Rev. 101 (2001) 1963. (i) G.J. Kubas, J. Organomet. Chem. 635
/
/
/
/
(2001) 37.
[4] (a) It is well known that M(h2-H2) complexes serve as precursors
to homogeneous hydrogenation catalysts [3a,e,f]. (b) The first
/
/
/
/
/
/
/
/
/
/
/
/
well-documented examples of M(h2-H2) (Mꢀ
catalytic hydrogenation of carbonꢁcarbon triple bonds are found
/Fe or Ru)-assisted
/
/
P(2)
P(3)
P(4)
/
/
/
/
/
/
/
in the following literatures; C. Bianchini, A. Meli, M. Peruzzini, P.
Frediani, C. Bohanna, M.A. Esteruelas, L.A. Oro, Organome-
tallics 11 (1992) 138. (c) C. Bianchini, C. Bohanna, M.A.
Esteruelas, P. Frediani, A. Meli, L.A. Oro, M. Peruzzini,
Organometallics 11 (1992) 3837. (d) C. Bianchini, F. Laschi, D.
Masi, F.M. Ottaviani, A. Pastor, M. Peruzzini, P. Zanello, F.
Zanobini, J. Am. Chem. Soc. 115 (1993) 2723.
[5] (a) G. Jia, R.H. Morris, C.T. Schweitzer, Inorg. Chem. 30 (1991)
594;
/
/
/
/N(2)
4. Supplementary material
Crystallographic data for this structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 211323 (compound 4h). Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge,
(b) K. Abdur-Rashid, A.J. Lough, R.H. Morris, Organometallics
19 (2000) 2655;
(c) K. Abdur-Rashid, A.J. Lough, R.H. Morris, Organometallics
20 (2001) 1047;
CB2, 1EZ, UK (Fax: ꢃ44-1223-336-033, or e-mail:
/
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.
uk).
(d) K. Abdur-Rashid, A.J. Lough, R.H. Morris, J. Am. Chem.
Soc. 123 (2001) 7473.
[6] (a) R.T. Hembre, J.S. McQueen, J. Am. Chem. Soc. 116 (1994)
2141;
(b) R.T. Hembre, J.S. McQueen, V.W. Day, J. Am. Chem. Soc.
118 (1996) 798.
Acknowledgements
[7] (a) V.I. Bakhmutov, E.V. Vorontsov, D.Y. Antonov, Inorg.
Chim. Acta 278 (1998) 122;
This work was supported by
a Grant-in-Aid
(b) R.M. Bullock, M.H. Voges, J. Am. Chem. Soc. 122 (2000)
12594;
(09102004 and 12750747) from the Ministry of Educa-
tion, Science, Sports, and Culture of Japan. We thank
Dr Dai Masui and Dr Shin Takemoto for assistance
with 400 MHz NMR analyses.
(c) M.P. Magee, J.R. Norton, J. Am. Chem. Soc. 123 (2001) 1778.
[8] (a) M. Hidai, Y. Mizobe, Chem. Rev. 95 (1995) 1115;
(b) M. Hidai, Y. Ishii, Bull. Chem. Soc. Jpn 69 (1996) 819;
(c) H. Seino, Y. Mizobe, M. Hidai, Chem. Rec. 1 (2001) 362.
[9] (a) Y. Nishibayashi, S. Iwai, M. Hidai, Science 279 (1998) 540;
(b) Y. Nishibayashi, S. Takemoto, S. Iwai, M. Hidai, Inorg.
Chem. 39 (2000) 5946;
References
(c) Y. Nishibayashi, I. Wakiji, K. Hirata, M. Rakowski DuBois,
M. Hidai, Inorg. Chem. 40 (2001) 578.
[1] (a) G.J. Kubas, R.R. Ryan, B.I. Swanson, P.J. Vergamini, H.J.
Wasserman, J. Am. Chem. Soc. 106 (1984) 451;
(b) G.J. Kubas, Accounts Chem. Res. 21 (1988) 120;
[10] A short account of our recent work, see, M. Hidai, Y.
Nishibayashi, in: M. Peruzzini, R. Poli (Ed.), Recent Advances
in Hydride Chemistry, Elsevier, Amsterdam, 2001, p. 117.
[11] For an example, see: M. Tanaka, Y. Watanabe, T. Mitsudo, Y.
Yasunori, Y. Takegami, Chem. Lett. (1974) 137.
[12] Y. Nishibayashi, I. Takei, M. Hidai, Angew. Chem. Int. Ed. 38
(1999) 3047.
(c) G.J. Kubas, Metal Dihydrogen and s-Bond Complexes:
Structure, Theory, and Reactivity, Kluwer Academic/Plenum
Publishers, New York, 2001;
(d) M. Peruzzini, R. Poli (Eds.), Recent Advances in Hydride
Chemistry, Elsevier, Amsterdam, 2001.
[13] B. Chin, A.J. Lough, R.H. Morris, C.T. Schweitzer, C. D’Agos-
tino, Inorg. Chem. 33 (1994) 6278.
[14] The pseudo-aqueous pKa values are estimated by NMR analysis
[2] For recent examples, see; (a) D.H. Lee, B.P. Patel, E. Clot, O.
Eisenstein, R.H. Crabtree, Chem. Commun. (1999) 297. (b) S.E.
Landau, R.H. Morris, A.J. Lough, Inorg. Chem. 38 (1999) 6060.
(c) V.I. Bakhmutov, C. Bianchini, M. Peruzzini, F. Vizza, E.V.
Vorontsov, Inorg. Chem. 39 (2000) 1655. (d) N. Mathew, B.R.
Jagirdar, R.S. Gopalan, G.U. Kulkarni, Organometallics 19
(2000) 4506. (e) J.K. Law, H. Mellows, D.M. Heinekey, J. Am.
Chem. Soc. 123 (2001) 2085. (f) K. Abdur-Rashid, T.P. Fong, B.
Greaves, D.G. Gusev, J.G. Hinman, S.E. Landau, A.J. Lough,
R.H. Morris, J. Am. Chem. Soc. 122 (2000) 9155. (g) S.H. Liu,
of acidꢁbase reactions in organic solvents such as CD2Cl2 or
/
THF-d8 [13]. We shall simply use the term pKa in the text.
[15] E.P. Cappellani, S.D. Drouin, G. Jia, P.A. Maltby, R.H. Morris,
C.T. Schweitzer, J. Am. Chem. Soc. 116 (1994) 3375.
[16] E. Rocchini, A. Mezzetti, H. Ruegger, U. Burckhardt, V.
¨
Gramlich, A.D. Zotto, P. Martinuzzi, P. Rigo, Inorg. Chem. 36
(1997) 711.

42
I. Takei et al. / Journal of Organometallic Chemistry 679 (2003) 32ꢁ42
/
[17] Recent examples, see, (a) T. Ohkuma, H. Doucet, T. Pham, K.
Mikami, T. Korenaga, M. Terada, R. Noyori, J. Am. Chem. Soc.
120 (1998) 1086. (b) H. Doucet, T. Ohkuma, K. Murata, T.
Yokozawa, M. Kozawa, E. Katayama, A.F. England, T. Ikariya,
R. Noyori, Angew. Chem. Int. Ed. 37 (1998) 1703. (c) T.
Ohkuma, M. Koizumi, H. Doucet, T. Pham, M. Kozawa, K.
Murata, E. Katayama, T. Yokozawa, T. Ikariya, R. Noyori, J.
Am. Chem. Soc. 120 (1998) 13529. (d) J. Yin, S.L. Buchwald, J.
Am. Chem. Soc. 122 (2000) 12051. (e) K. Ueda, Y. Sato, M. Mori,
J. Am. Chem. Soc. 122 (2000) 10722. (f) M. Ogasawara, H. Ikeda,
T. Nagano, T. Hayashi, J. Am. Chem. Soc. 123 (2001) 2089.
[18] Recent examples, see, (a) B.F.M. Kimmich, E. Somsook, C.R.
Landis, J. Am. Chem. Soc. 120 (1998) 10115. (b) D.K. Wicht,
M.A. Zhuravel, R.V. Gregush, D.S. Glueck, I.A. Guzei, L.M.
Liable-Sands, A.L. Rheingold, Organometallics 17 (1998) 1412.
(c) M.A. Casado, J.J. Perez-Torrente, M.A. Ciriano, L.A. Oro, A.
Orejon, C. Claver, Organometallics 18 (1999) 3035. (d) H.S. Park,
E. Alberico, H. Alper, J. Am. Chem. Soc. 122 (2000) 11697. (e) R.
Kuwano, K. Sato, T. Kurokawa, D. Karube, Y. Ito, J. Am.
Chem. Soc. 122 (2000) 7614.
[23] M.H. Novice, H.R. Seikaly, A.D. Seiz, T.T. Tidwell, J. Am.
Chem. Soc. 102 (1980) 5835.
[24] No other products except for Me3SiH were not confirmed by the
29Si{1H}-NMR study of the reaction mixture.
[25] In the catalytic hydrogenation of trimethylsilyl enol ethers, the
corresponding ketones are sometimes observed as by-products.
This is considered to arise from the reaction of trimethylsilyl enol
ethers with adventitious water in a solvent. In fact, treatment of
1a with 10 equivalent of D2O in the presence of 5 mol.% of
[RhCl(PPh3)3] under H2 (1 atm) at 50 8C for 18 h afforded 3a? in
ꢀ95% GLC yield, together with Me3SiOSiMe3. However, no
/
reaction occurred upon treatment of 1a with 10 equivalent of D2O
in the absence of the catalyst at 50 8C for 18 h.
[26] The formation of 2-cyclohexen-1-one by the Pd(II)-catalysed
dehydrosilylation of 1a was reported. Y. Ito, T. Hirao, T.
Saegusa, J. Org. Chem. 43 (1978) 1011.
[27] (a) C. Fehr, Angew. Chem. Int. Ed. Engl. 35 (1996) 2566;
(b) A. Yanagisawa, K. Ishihara, H. Yamamoto, Synlett (1997)
411;
(c) M. Sugiura, T. Nakai, Angew. Chem. Int. Ed. 36 (1997) 2366;
(d) G. Asensio, P. Aleman, J. Gil, L.R. Domingo, M. Medio-
Simon, J. Org. Chem. 63 (1998) 9342;
[19] We attempted to determine the pKa value of 4e from reactions of
4e with PEtPh2 (HPEtPh2ꢃ, pKa:4.9), PCy2Ph (HPCy2Phꢃ
,
/
pKa:
/
6), or PCy3 (HPCy3ꢃ, pKa:
9.7) in either CD2Cl2 or THF-
/
(e) S. Nakahara, M. Kaneeda, K. Ishihara, H. Yamamoto, J. Am.
Chem. Soc. 122 (2000) 8120.
d8 at 20 8C by employing the NMR method [13]. Unfortunately, it
was unsuccessful because mixtures of unidentified products and 5e
were obtained from the reactions. However, the finding that 4e
was readily deprotonated by Et3N in CD2Cl2 at 20 8C indicates
[28] P.F. Hudrlik, J.M. Takacs, J. Org. Chem. 43 (1978) 3861.
[29] R.D. Clark, K.G. Untch, J. Org. Chem. 44 (1979) 248.
[30] Y. Watanabe, Y. Ishimura, J. Am. Chem. Soc. 111 (1989) 410.
[31] G.M. Rubottom, H.D. Juve, Jr., J. Org. Chem. 48 (1983) 422.
[32] K. Morikawa, J. Park, P.G. Andersson, T. Hashiyama, K.B.
Sharpless, J. Am. Chem. Soc. 115 (1993) 8463.
that the pKa value of 4e is far below 10.8, the pKa of Et3NHꢃ
.
[20] The formation of 3a and Et3SiH or t-BuMe2SiH was confirmed
by the 1H and 29Si{1H}-NMR study of the reaction mixture
performed
(ClCD2CD2Cl):
(ClCD2CD2Cl): d ꢂ
in
NMR
tubes
0.50, t-BuMe2SiH; 29Si{1H}-NMR
0.54).
(Et3SiH;
29Si{1H}-NMR
d
ꢂ/
[33] G. Jaouen, A. Meyer, J. Am. Chem. Soc. 97 (1975) 4667.
[34] TEXSAN: Crystal Structure Analysis Package, Molecular Structure
Corp., The Woodlands, TX, 1985 and 1992.
/
[21] H. Kawano, T. Ikariya, Y. Ishii, M. Saburi, S. Yoshikawa, Y.
Uchida, H. Kumobayashi, J. Chem. Soc. Perkin. Trans. 1 (1989)
1571.
[35] P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, S.
Garcia-Granda, R. Gould, J.M.M. Smits, C. Smykalla, PATTY:
The DIRDIF Program System, Technical Report of the Crystal-
lography Laboratory, University of Nijimegen, The Netherlands,
1992.
[22] Independently, Mezzetti and co-workers reported the preparation
of [RuCl2(CHIRAPHOS)2] and [RuCl(CHIRAPHOS)2]BF4;
R.M. Stoop, C. Bauer, P. Setz, M. Worle, T.Y.H. Wong, A.
¨
Mezzetti, Organometallics 18 (1999) 5691