(Z)-Selective cross-dimerization of arylacetylenes with silylacetylenes catalyzed by vinylideneruthenium complexes

Article abstract of DOI:10.1039/b504436g

The vinylideneruthenium(II) complexes bearing bulky and basic tertiary phosphine ligands, RuCl₂(=C=CHPh)L₂ (L = PPr ⁱ₃, PCy₃), serves as a good catalyst precursor for (Z)-selective cross-dimerization between arylacetylenes and silylacetylenes in the presence of N-methylpyrrolidine. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b504436g

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(Z)-Selective cross-dimerization of arylacetylenes with silylacetylenes
catalyzed by vinylideneruthenium complexes{
Hiroyuki Katayama,* Hiroshi Yari, Masaki Tanaka and Fumiyuki Ozawa*
Received (in Cambridge, UK) 1st April 2005, Accepted 4th July 2005
First published as an Advance Article on the web 28th July 2005
DOI: 10.1039/b504436g
The vinylideneruthenium(II) complexes bearing bulky and basic
tertiary phosphine ligands, RuCl2(LCLCHPh)L2 (L 5 PPri3,
PCy3), serves as a good catalyst precursor for (Z)-selective
cross-dimerization between arylacetylenes and silylacetylenes in
the presence of N-methylpyrrolidine.
Catalytic dimerization of alkynes is one of the simplest methods
for synthesizing conjugated enynes, which are useful building
blocks in organic synthesis.1 Enyne structures are also present as
active components in conducting and light-emitting polymers.2
Accordingly, a number of studies have been carried out for
dimerization of alkynes, and some transition metal complexes
have proven to be highly selective catalysts.3 However, most
studies have been concerned with homo-dimerization, and cross-
dimerization of two different alkynes has remained almost
unexamined. Trost et al. showed that a variety of terminal
alkynes, RCMCH (R 5 alkyl, aryl, silyl), are selectively coupled
with electron-deficient internal alkynes, R9CMCEWG (R9 5 alkyl,
Scheme 1 Cross-dimerization of arylacetylenes with silylacetylenes
silyl; EWG 5 CO2Me, COMe, SO2Ph), in the presence of
catalyzed by vinylideneruthenium complexes.
Pd(OAc)2
and
tris(2,6-dimethoxyphenyl)phosphine.4
The
Cu/Pd-catalyzed version of this reaction was recently reported by
Li et al.5 As for the cross-dimerization between two kinds of
terminal alkynes, to the best of our knowledge, there have been
only two reports on gem-selective catalysis. Nakamura et al.
demonstrated that Cp*2TiCl2/PriMgBr efficiently catalyzes the
cross-dimerization between RCMCH (R 5 1-cyclohexenyl, Ph) and
R9CMCH (R9 5 alkyl, silyl) into RCMCHC(R9)LCH2 in 63–99%
selectivities.6 Eisen et al. reported the reaction catalyzed by a
cationic uranium complex [U(NEt2)3][BPh4].7 On the other hand,
in this study it was found that arylacetylenes (2) are coupled with
silylacetylenes (3) to form (Z)-1-aryl-4-silyl-1-buten-3-ynes ((Z)-4)
in high selectivities using RuCl2(LCLCHPh)(PPri3)2 (1-Pri) as a
catalyst precursor (Scheme 1).
Catalytic dimerization of terminal alkynes generally forms three
isomers of butenynes: i.e., (Z), (E), and geminal (gem) isomers
(Scheme 2). It is widely accepted that the (Z)-isomer is afforded by
intramolecular addition of an alkynyl ligand onto the a-carbon of
the vinylidene ligand (path A).8 On the other hand, (E)- and gem-
isomers are produced by insertion of an alkyne into the metal–
alkynyl bond in the opposite regiochemical course with each other
(paths B and C, respectively). Therefore it was considered that
International Research Center for Elements Science (IRCELS),
Institute for Chemical Research, Kyoto University, Uji, Kyoto,
611-0011, Japan. E-mail: hiroyuki@scl.kyoto-u.ac.jp;
ozawa@scl.kyoto-u.ac.jp; Fax: +81 774 38 3039; Tel: +81 774 38 3035
{ Electronic Supplementary Information (ESI) available: Experimental
procedures and spectroscopic data for all new compounds. See http://
dx.doi.org/10.1039/b504436g
Scheme 2 Alkyne-dimerization pathways.
4336 | Chem. Commun., 2005, 4336–4338
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(Z)-selective cross-dimerization may be possible by the combina-
tion of two types of alkynes that possess significantly different
properties, toward the tautomerization between alkyne and
vinylidene ligands. Thus, the nature of several types of alkynes
was examined in homo-dimerization systems.
rationalized by the effect of substituents on the formation of
vinylidene ligand: arylacetylenes, especially those bearing electron-
donating substituents, facilitate the alkyne-to-vinylidene tautomeri-
zation on ruthenium(II) coordinated with bulky and basic
phosphine ligands.10
The cross-dimerization between two strikingly different types of
acetylenes, aryl- and silyl-acetylenes, was next examined. The
optimal reaction conditions were investigated using 2a as a
substrate (Table 2). Treatment of a 1 : 1 mixture of 2a and 3m with
1-Pri (5 mol%) and N-methylpyrrolidine (20 mol%) in CH2Cl2 at
room temperature formed the cross-dimer 4am with 86%
(Z)-content in 38% yield, together with homo-dimers 5a [(Z) :
(E) : gem 5 92 : 0 : 8] and 6m [(Z) : (E) : gem 5 0 : 15 : 85] (run 1).
On the other hand, the cross-dimer 7, with the opposite
substitution pattern, was not detected in the system using GLC
analysis. Increasing the amount of 3m effectively reduced the
amount of 5a (run 2). Using a 10 molar excess of 3m, the cross-
dimer 4am [(Z) : (E) : gem 5 90 : 1 : 9] was obtained in 93% yield
(run 3). The homo-dimer 5a and 6m were successfully separated by
silica gel column chromatography, yielding (Z)-4am with 93%
isomeric purity in 78% yield after isolation.
The results are listed in Table 1. All reactions were performed in
CH2Cl2 at room temperature in the presence of catalytic amounts
of 1-Pri and N-methylpyrrolidine, the latter of which was added
to generate
a catalytically active alkynylruthenium species
[RuCl(CMCPh)(PPri3)2] by abstracting HCl from 1-Pri.9
Although alkylacetylenes and p-MeO2CC6H4CMCH, having an
electron-withdrawing substituent, were poorly reactive (runs 7–9),
electron-rich arylacetylenes (2a–f) underwent highly (Z)-selective
dimerization to yield (Z)-ArCHLCH–CMCAr (5) in 90–97%
selectivities. On the other hand, (trimethylsilyl)acetylene (3m)
yielded a 15 : 85 mixture of (E)- and gem-dimerization products
(6m); no trace of the (Z)-dimer was detected in the system using
GC-MS analysis. The product selectivity thus observed may be
Table 1 Homo-dimerization of terminal alkynes catalyzed by 1-Pria
Run Alkyne
1
Time/h Yield (%)b (Z) : (E) : gemb
N-Methylpyrrolidine was the base of choice, while DBU gave a
comparable result (run 4). On the other hand, the less basic
pyridine, bulky amines such as Pri2NH and proton sponge, and
potassium carbonate as an inorganic base were less effective (runs
5–7). PCy3-coordinated 1-Cy exhibited catalytic ability similar to
1-Pri (run 8). 1-Ph, having PPh3 ligands, was poorly reactive
(run 9). Although other dimerization catalysts such as
Cp*RuCl(PPh3)2,11 TpRuCl(PPh3)2,12 RhCl(PPh3)3,13 and
Pd(OAc)2/SIMes?HCl/Cs2CO3 (SIMes?HCl 5 1,3-dimesitylimida-
zolinium chloride)3b were also tested, complex mixtures of homo-
and cross-dimerization products were formed in all cases.
9
3
5
.99
.99
.99
92 : 0 : 8
96 : 1 : 3
93 : 0 : 7
2c
3
The cross-dimerization with 3m was also successful for non-
substituted and substituted phenylacetylenes (2b–d), and 2-thienyl-
and 2-fluorenyl-acetylenes (2e, 2f) (Table 3). All reactions afforded
(Z)-4 in over 90% selectivity (runs 1–5). (Phenyldimethylsilyl)- and
(triisopropylsilyl)-acetylenes (3n, 3o) also served as good coupling
partners with almost perfect (Z)-selectivities; however, their
4
5
6
2
96
82
99
91 : 1 : 8
97 : 0 : 3
90 : 0 : 10
5
Table 2 Cross-dimerization of 4-ethynyltoluene (2a) with (trimethyl-
silyl)acetylene (3m)a
6c
Cross-dimer 4am
Homo-dimer
Time/ Yield
h
Run 2a : 3mb Basec
(%)d (Z) : (E) : geme 5ad
6mf
7
8
9
24
24
24
0
0
0
1
2
3
1 : 1
1 : 5
1 : 10
C4H8NMe
C4H8NMe
C4H8NMe 16
3
5
38 86 : 0 : 14
86 91 : 0 : 9
93 90 : 1 : 9
(78) 93 : 0 : 7
82 88 : 4 : 8
40 89 : 0 : 11
12 88 : 0 : 12
,1
56
13
5
25
28
24
4
5
6
7
1 : 10
1 : 10
1 : 10
1 : 10
DBU 16
Pyridine 16
10
,1
0
20
8
1
Pri2NH
K2CO3
16
16
8g 1 : 10
9h 1 : 10
a
C4H8NMe 16
C4H8NMe 24
89 90 : 1 : 9
6
4
,1
20
4
82 : 17 : 1
10
48
54
0 : 15 : 85
Reaction conditions: 2a (1.0 mmol), 1-Pri (0.050 mmol), base
b
(0.20 mmol), CH2Cl2 (1.0 mL), room temperature. Molar ratio.
c
d
5 N-methylpyrrolidine. GLC yield based on the
C4H8NMe
amount of 2a employed. Isolated yield is in parentheses.
a
Reaction conditions: alkyne (1.0 mmol), 1-Pri (0.010 mmol (runs 1
and 2), 0.050 mmol (runs 3–10)), N-methylpyrrolidine (0.20 mmol),
e
f
Determined by GLC. GLC yield based on the amount of 3m
b
c
g
h
CH2Cl2 (1.0 mL), room temperature. Determined by GLC. The
data were taken from ref. 2a.
employed. 1-Cy was used in place of 1-Pri. 1-Ph was used in
place of 1-Pri.
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Table 3 Cross-dimerization of arylacetylene 2 with silylacetylene 3a
MeOH, so that the overall process provides a new entry for the
synthesis of terminal alkenylacetylenes (ArCHLCH–CMCH (7))
with (Z)-configurations.14
Alkynes
Run (molar ratio) Product
Yield (%)b
[(Z) : (E) : gem]c
In conclusion, it has been discovered that cross-dimerization
between arylacetylenes (2a–f) and (trimethylsilyl)acetylene (3m)
proceeds in high (Z)-selectivity using vinylideneruthenium 1-Pri as
a catalyst precursor. The reaction provides complementary regio-
and stereo-selectivities to Nakamura’s titanium-catalyzed system
yielding ArCMC–C(SiMe3)LCH2.
This work was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science
and Technology of Japan.
1
2b : 3m
(1 : 20)
83 (79)
[95 : 5 : 0]
2d
2c : 3m
(1 : 5)
72 (65)
[90 : 5 : 5]
3e
2d : 3m
(1 : 5)
85 (76)
[93 : 7 : 0]
Notes and references
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Chemistry, VCH, New York, 1995; (b) J. Henkelmann, in Applied
Homogeneous Catalysis with Organometallic Compounds, ed. B. Cornils
and W. A. Herrman, VCH, New York, 1996; (c) D. R. Kanis,
M. A. Ratner and T. J. Marks, Chem. Rev., 1994, 94, 195.
2 (a) H. Katayama, M. Nakayama, T. Nakano, C. Wada, K. Akamatsu
and F. Ozawa, Macromolecules, 2004, 37, 13; (b) M. Nishiura and
Z. Hou, J. Mol. Catal. A: Chem., 2004, 213, 101; (c) M. Ueda and
I. Tomita, Polym. Bull., 2004, 51, 359; (d) C.-K. Choi, I. Tomita
and T. Endo, Macromolecules, 2000, 33, 1487; (e) D. Venkatesan,
M. Yoneda and M. Ueda, React. Funct. Polym., 1996, 30, 341.
3 For recent examples, see: (a) M. Nishiura, Z. Hou, Y. Wakatsuki,
T. Yamaki and T. Miyamoto, J. Am. Chem. Soc., 2003, 125, 1184; (b)
C. Yang and S. P. Nolan, J. Org. Chem., 2002, 67, 591; (c) M. Rubina
and V. Gevorgyan, J. Am. Chem. Soc., 2001, 123, 11107; (d) T. Ohmura,
S.-I. Yorozuya, Y. Yamamoto and N. Miyaura, Organometallics, 2000,
19, 365; (e) Y. Nishibayashi, M. Yamanashi, I. Wakiji and M. Hidai,
Angew. Chem., Int. Ed., 2000, 39, 2909.
4
5
2e : 3m
(1 : 10)
81 (76)
[93 : 7 : 0]
2f : 3m
(1 : 10)
95 (90)
[93 : 0 : 7]
4 B. M. Trost, M. T. Sorum, C. Chan, A. E. Harms and G. Ru¨hter,
J. Am. Chem. Soc., 1997, 119, 698.
5 L. Chen and C.-J. Li, Tetrahedron Lett., 2004, 45, 2771.
6 M. Akita, H. Yasuda and A. Nakamura, Bull. Chem. Soc. Jpn., 1984,
57, 480.
6
7
a
2a : 3n
(1 : 10)
74
[100 : 0 : 0f]
7 J. Wang, M. Kapon, J. C. Berthet, M. Ephritikhine and M. S. Eisen,
Inorg. Chim. Acta, 2002, 334, 183.
8 (a) C. Bianchini, M. Peruzzini, F. Zanobini, P. Frediani and A. Albinati,
J. Am. Chem. Soc., 1991, 113, 5453; (b) C. Bianchini, P. Frediani,
D. Masi, M. Peruzzini and F. Zanobini, Organometallics, 1994, 13,
4616; (c) Y. Wakatsuki, H. Yamazaki, N. Kumegawa, T. Satoh and
J. Y. Satoh, J. Am. Chem. Soc., 1991, 113, 9604.
9 This type of transformation has already been documented: C. S. Yi,
N. Liu, A. L. Rheingold and L. M. Liable-Sands, Organometallics,
1997, 16, 3910.
10 H. Katayama, C. Wada, K. Taniguchi and F. Ozawa, Organometallics,
2000, 21, 3285.
11 C. S. Yi and N. Liu, Synlett, 1999, 281.
12 C. Slugovc, K. Mereiter, E. Zobetz, R. Schmid and K. Kirchner,
Oragnometallics, 1996, 15, 5275.
2a : 3o
(1 : 10)
45 (38)
[100 : 0 : 0]
Reaction conditions:
2
(1.0 mmol), 1-Pri (0.050 mmol),
N-methylpyrrolidine (0.20 mmol), CH2Cl2 (1.0 mL), room
temperature, 16–24 h. GLC yield based on the amount of 2
b
c
employed. Isolated yield is in parentheses. Isomer ratio of isolated
Reaction time 5 80 h.
product. Determined by 1H NMR.
Reaction time 5 5 h. Determined by GLC.
d
e
f
13 J. Ohshita, K. Furumori, A. Matsuguchi and M. Ishikawa, J. Org.
Chem., 1990, 55, 3277.
14 (a) M. Hoshi and K. Shirakawa, Synlett, 2002, 1101; (b) A. W. Gibson,
G. R. Humphrey, D. J. Kennedy and S. H. B. Wright, Synthesis, 1991,
414 and references cited therein.
reactivities were lower than that of 3m (runs 6 and 7). The
products (Z)-4 were easily desilylated by treatment with K2CO3 in
4338 | Chem. Commun., 2005, 4336–4338
This journal is ß The Royal Society of Chemistry 2005