J. Am. Chem. Soc. 2000, 122, 11019-11020
11019
key intermediate. Preliminary results on this catalytic reaction
are described here.
Novel Propargylic Substitution Reactions Catalyzed
by Thiolate-Bridged Diruthenium Complexes via
Allenylidene Intermediates
Yoshiaki Nishibayashi,† Issei Wakiji, and Masanobu Hidai*,‡
Treatment of 1-phenyl-2-propyn-1-ol (3a) in EtOH in the
presence of 1a (5 mol %) and NH4BF4 (10 mol %) at 60 °C for
15 min afforded the corresponding ethyl ether (4aa) in 88%
isolated (95% GLC) yield (Table 1; run 1).8 Interestingly, the
substitution occurred selectively at the propargylic ipso-carbon.
Neither allenic byproduct nor other regioisomer of 4aa was
observed by GLC and 1H NMR. The reaction at room temperature
was completed within 1 h to give 4aa in 90% GLC yield. Similar
thiolate-bridged diruthenium(III,III) complexes (1b-e) were also
effective in the reaction, however, a diruthenium(II,III) complex
29 was ineffective. Noteworthy is that conventional monoruthe-
nium complexes such as [CpRuCl(PPh3)2] (Cp ) η5-C5H5),
[RuCl2(dppe)2] (dppe ) 1,2-bis(diphenylphosphino)ethane), [RuCl2-
(PPh3)3], and [RuCl2(p-cymene)], which were known to react with
propargylic alcohols to produce the corresponding allenylidene
complexes (vide infra),3b,c did not work at all.8 When MeOH and
iPrOH were used in place of EtOH, the corresponding methyl
and isopropyl ethers (4ab and 4ac) were obtained in 84 and 91%
yields, respectively (Table 1; runs 2 and 3).
Reactions of various propargylic alcohols catalyzed by 1a have
been investigated. Propargylic substitution reactions of 1-monoalkyl-
and 1,1-dialkyl-substituted propargylic alcohols (3c-e) at 60 °C
occurred rapidly to afford the corresponding ethers (4c-e) in high
yields, respectively (Table 1; runs 5-7). In contrast, reactions of
1,1-diaryl-substituted propargylic alcohols (3f and 3g) were
sluggish under identical conditions, prolonged time being required
to produce the diaryl-substituted ethers (4f and 4g) in moderate
yields (Table 1; runs 8 and 9). On the other hand, when the
reactions of 3a with 5 equiv of chiral alcohols were carried out
in ClCH2CH2Cl at 60 °C for 1 h, a mixture of two diastereomeric
isomers was obtained in moderate to high yields with the isomer
ratio of ca. 1:1 (Table 1; runs 11-14).
Department of Chemistry and Biotechnology
Graduate School of Engineering, The UniVersity of Tokyo
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
ReceiVed June 13, 2000
We have long been interested in development of homogeneous
catalysis of polynuclear transition metal complexes since direct
and indirect cooperation of plural transition metals can be expected
for the activation of substrates to provide novel transformations
that are not attainable at conventional monometallic centers.
Toward this end, our studies have been focused on the synthesis
and reactivities of polynuclear noble metal complexes with
bridging sulfur ligands.1 In the course of our investigation, we
have synthesized a series of thiolate-bridged diruthenium com-
plexes such as [Cp*RuCl(µ2-SR)2RuCp*Cl] (Cp* ) η5-C5Me5;
i
R ) Me (1a), Et (1b), nPr (1c), Pr (1d)), [Cp*RuCl(µ2-Si-
Pr)2RuCp*(OH2)]OTf (1e; OTf ) OSO2CF3), and [Cp*Ru(µ2-Si-
Pr)3RuCp*] (2) and revealed that these complexes provide unique
reaction sites for various stoichiometric and catalytic transforma-
tions of terminal alkynes.2
Transition metal allenylidene (MdCdCdC<) complexes have
attracted a great deal of attention in recent years as a new type
of organometallic intermediate.3 Theoretical studies indicate that
the CR and Cγ carbon atoms of allenylidene ligands are electro-
philic centers, while the Câ carbon atom is nucleophilic.4 In fact,
stoichiometric reactions of allenylidene ruthenium complexes with
a variety of nucleophiles have been reported, where nucleophiles
attack either the CR or Cγ carbon atom in allenylidene ligands to
afford Fischer-type carbenes or alkynyl complexes, respectively.5
In sharp contrast, only a few examples of catalytic reactions via
allenylidene intermediates have been reported until now.6,7 As
an extension of our study on reactivities of terminal alkynes at
the thiolate-bridged diruthenium complexes,2 we have now found
propargylic substitution reactions of propargylic alcohols with a
variety of nucleophiles catalyzed by 1. This provides a new type
of catalytic reaction via an allenylidene ruthenium complex as a
To elucidate the mechanism of the propargylic ipso-substitution,
the following stoichiometric and catalytic reactions were inves-
tigated. Reaction of 1a with 1 equiv of 3g in the presence of
NH4BF4 in EtOH at room temperature for 1 h afforded the
allenylidene complex [Cp*RuCl(µ2-SMe)2RuCp*(CdCdC(Tol-
p)2)]BF4 (5a) in 84% yield, which was unambiguously character-
ized by X-ray crystallography (eq 1).10 The structure of 5a is
† Present address: Department of Energy and Hydrocarbon Chemistry,
Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-
8501, Japan.
‡ Present address: Department of Materials Science and Technology,
Faculty of Industrial Science and Technology, Science University of Tokyo,
Noda, Chiba 278-8510, Japan.
(1) Hidai, M.; Kuwata, S.; Mizobe, Y. Acc. Chem. Res. 2000, 33, 46 and
references therein.
(2) (a) Takagi, Y.; Matsuzaka, H.; Ishii, Y.; Hidai, M. Organometallics
1997, 16, 4445 and references therein. (b) Qu¨, J.-P.; Masui, D.; Ishii, Y.;
Hidai, M. Chem. Lett. 1998, 1003. (c) Nishibayashi, Y.; Yamanashi, M.;
Wakiji, I.; Hidai, M. Angew. Chem., Int. Ed. Engl. 2000, 39, 2909.
(3) For recent reviews, see: (a) Werner, H. Chem. Commun. 1997, 903.
(b) Touchard, D.; Dixneuf, P. H. Coord. Chem. ReV. 1998, 178-180, 409.
(c) Bruce, M. I. Chem. ReV. 1998, 98, 2797.
essentially the same as that of the previously reported allenylidene
complex [Cp*RuCl(µ2-SiPr)2RuCp*(CdCdC(Tol-p)2)]OTf11 (5b),
which is obtained from 1e and 3g. Treatment of 5a in EtOH at
60 °C for 20 h gave rise to the formation of 4g in 89% GLC
yield. Furthermore, reaction of 3g with EtOH in the presence of
5 mol % of 5a at 60 °C for 20 h afforded 4g in 69% GLC yield.
These results indicate that the propargylic substitution reactions
of propargylic alcohols with various alcohols proceed via alle-
nylidene complexes such as 5a.
(4) (a) Esteruelas, M. A.; Go´mez, A. V.; Lo´pez, A. M.; Modrego, J.; On˜ate,
E. Organometallics 1997, 16, 5826. (b) Berke, H.; Huttner, G.; Von Seyerl,
J. Z. Naturforsh. 1981, 36b, 1277.
(5) For a recent example, see: Esteruelas, M. A.; Go´mez, A. V.; Lo´pez,
A. M.; Oliva´n, M.; On˜ate, E.; Ruiz, N. Organometallics 2000, 19, 4 and
references therein.
(6) (a) Trost, B. M.; Flygare, J. A. J. Am. Chem. Soc. 1992, 114, 5476. (b)
Trost, B. M.; Flygare, J. A. Tetrahedron Lett. 1994, 35, 4059.
(7) Quite recently, some groups have reported the ring closing metathesis
catalyzed by allenylidene ruthenium complexes; however, the intermediates
are carbene complexes: (a) Fu¨rstner, A.; Picquet, M.; Bruneau, C.; Dixneuf,
P. H. Chem. Commun. 1998, 1315. (b) Picquet, M.; Bruneau, C.; Dixneuf, P.
H. Chem. Commun. 1998, 2249. (c) Fu¨rstner, A.; Hill, A. F.; Liebl, M.; Wilton-
Ely, J. D. E. T. Chem. Commun. 1999, 601. (d) Harlow, K. J.; Hill, A. F.;
Wilton-Ely, J. D. E. T. J. Chem. Soc., Dalton Trans. 1999, 285. (e) Jafarpour,
L.; Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics 1999, 18, 3760.
(8) See Supporting Information for experimental details.
(9) The unusual coupling reaction of propargylic alcohols by using 2 has
been reported already by our group; Matsuzaka, H.; Koizumi, H.; Takagi, Y.;
Nishio, M.; Hidai, M. J. Am. Chem. Soc. 1993, 115, 10396.
(10) Crystallographic data for 5a‚(EtOH)2: C43H62BClF4O2Ru2S2, fw )
999.48, black, orthorhombic, C2221 (No. 20), a ) 9.532(6) Å, b ) 24.712(8)
Å, c ) 38.47(1) Å, V ) 9062(7) Å3, Z ) 8, R ) 0.069, Rw ) 0.086, GOF )
2.43.
(11) Matsuzaka, H.; Takagi, Y.; Hidai, M. Organometallics 1994, 13, 13.
10.1021/ja0021161 CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/21/2000
Nishibayashi
