Phosphine-dependent selective cross-dimerization between terminal alkylacetylene and silylacetylene by iridium(I) guanidinate complex-phosphine system

Article abstract of DOI:10.1055/s-0028-1083514

The new iridium(I)-guanidinate complex served as an efficient catalyst for phosphine-dependent selective cross-dimerization between silylacetylene and terminal alkyl- or arylacetylene. Especially, in case of cross-dimerization between silylacetylene and alkylacetylene, E/Z selectivity of resulting enynes could be controlled by changing phosphine.

Full text of DOI:10.1055/s-0028-1083514

LETTER
2663
Phosphine-Dependent Selective Cross-Dimerization between Terminal
Alkylacetylene and Silylacetylene by Iridium(I) Guanidinate Complex–
Phosphine System
C
ross-Dimerizatio
e
n
betweenT
n
erminal Alk
i
ylacety
c
lene and
S
i
lylacetylenei Ogata,*a Oji Oka,b Akinori Toyota,b Noriyuki Suzuki,c Shin-ichi Fukuzawa*a
a
Department of Applied Chemistry, Institute of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku,
Tokyo 112-8551, Japan
Fax +81(3)38171916; E-mail: kogata@chem.chuo-u.ac.jp
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology,
2-24-16 Naka-cho, Koganei-shi, Tokyo 184-8588, Japan
b
c
RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
Received 17 July 2008
dependent selective cross-dimerization between various
silylacetylenes and terminal alkylacetylenes as well as
arylacetylenes with high regio- and stereoselectivity.
Abstract: The new iridium(I)–guanidinate complex served as an
efficient catalyst for phosphine-dependent selective cross-dimeriza-
tion between silylacetylene and terminal alkyl- or arylacetylene. Es-
pecially, in case of cross-dimerization between silylacetylene and
alkylacetylene, E/Z selectivity of resulting enynes could be con-
trolled by changing phosphine.
We prepared an iridium(I)–guanidinate complex through
the reaction of [IrCl(cod)]2 with a lithium guanidinate
(Scheme 1). Iridium(I)–guanidinate complex 1 was isolat-
ed in good yield as an orange solid.6 Although many late-
transtion-metal guanidinate complex has been reported,7
the example of iridium complex bearing a guanidinate
ligand is scarce.8 Especially, a low valent iridium(I)–
guanidinate complex, which might be suitable for metal-
catalyzed reactions, has not been prepared. In the 1H NMR
spectrum of 1, two kinds of methyl protons were obserbed
as doublet at d = 0.96 and 1.23 ppm, respectively. The
structure of complex 1 was also confirmed by X-ray anal-
ysis.9 The complex have square planar geometry around
an iridium atom.
Key words: alkynes, enynes, coupling, dimerizations, iridium
The transition-metal-catalyzed regio- and stereoselective
dimerization of alkynes has been received much atten-
tions as a useful method for the synthesis of substituted
enynes.1 Not only homodimerization of terminal alkynes
but also cross-dimerization between terminal alkynes and
internal alkynes have been reported,2 while the cross-
dimerization between two different terminal alkynes is
scarce.3 A notable success of such a reaction is Ru-3c and
Rh-catalyzed3d head-to-head cross-dimerization between
terminal acetylene and silylacetylene, and Pd-catalyzed
head-to-tail cross-dimerization between terminal alkyl-
acetylene and triisopropylsilylacetylene.3e
To evaluate the catalytic efficiency of complex 1 for
dimerization of alkyne, we investigated homodimeriza-
tion of terminal alkylacetylene and arylacetylene by com-
plex 1 in the presence of phosphine. As shown in Table 1,
head-to-head dimerization of 1-octyne (2a) proceeded
with high E-selectivity by 1–Ph3P system (entry 1).10
Straight-chain alkylacetylenes such as 1-octyne (2a) hard-
ly dimerize by a previously reported [IrCl(cod)]2–phos-
phine catalytic system.1a In the case of the acetylacetonato
complex catalytic system {[Ir(acac)(cod)]–Ph3P} which
bears a less electron-donating anionic ligand than the
guanidinate ligand, the dimerization of 1-octyne (2a) re-
sulted in low yield (38%, E/Z = 80:20). From this result,
the catalytic reactivity for dimerization of 1-octyne by 1–
Ph3P system probably derived from electron-donating
Our research group has recently demonstrated that an iri-
dium(I)–pyridine-2-thiolate complex [Ir(SNC5H4)(PPh3)2]
catalyzes homodimerization of terminal alkynes in good
yield with high E-selectivity through activation of a termi-
nal C–H bond of an alkyne.4 We anticipated that an iridi-
um(I) complex bearing a highly electron-donating anionic
chelate ligand would show high catalytic activity toward
dimerization of terminal alkynes.
In this report, we describe the preparation of a new iridi-
um(I) complex with a highly electron-donating guanidi-
nate ligand5 and its application to the first phosphine-
N
N
Li
1/2
[IrCl(cod)]2
+
Ir
N
N
THF
–78 °C to r.t.
N
N
1
Scheme 1
SYNLETT 2008, No. 17, pp 2663–2666
x
x
.x
x
.2
0
0
8
Advanced online publication: 01.10.2008
DOI: 10.1055/s-0028-1083514; Art ID: U07608ST
© Georg Thieme Verlag Stuttgart · New York

2664
K. Ogata et al.
LETTER
ability of guanidinate ligand. The selectivity of resulting
enynes were highly dependent on using phosphine. After
screening various phosphines, we found that a Z-selective
dimerization of 2a was achieved by the use of diethylphe-
nylphosphine (Et2PhP) in good yield with high selectivity
(entry 2). The dimerization of 2a catalyzed by 1 with tri-
alkylphosphine such as a triethylphosphine (Et3P) or tri-n-
propylphosphine (n-Pr3P) resulted in low Z-selectivity.11
Not only alkylacetylene but also arylacetylene such as
phenylacetylene (2b) gave head-to-head dimers 3b in
high yields with excellent selectivities (entries 3 and 4).
Me3Si
3 mol%
H
1/Ph3P
6 h
H
SiMe3
(E)-3c 79% yield
3 mol%
1/Et2PhP
SiMe3
Me3Si
H
•
H
SiMe3
•
24 h
toluene
80 °C
H
2c
4c 61% yield
5 mol%
1/n-Pr3P
H
H
12 h
SiMe3
Table 1 Dimerization of Terminal Alkyne 2 Catalyzed by 1–Phos-
phine System
Me3Si
(Z)-3c 92% yield
R
3 mol%
Scheme 2
H
H
H
R
1/Phosphine
+
H
R
toluene
80 °C
H
R
tion of terminal alkyne. The reaction by 1–Et2PhP system
resulted in low Z-selectivity compared with that by 1–n-
Pr3P system.15 The cross-dimerization involving branch-
chain alkylacetylene 2d by 1–Ph3P or 1–n-Pr3P also pro-
ceeded in good yield with complete E- or Z-selectivity, re-
spectively (entries 3 and 4). The cross-dimer between 2c
and benzylacetylene (2e) also obtained in good yield with
excellent or high selectivity (entries 5 and 6). Cyclohexy-
lacetylene (2f) also reacted with 2c to give the corre-
sponding cross-dimer 5f in good yield with complete E-
and high Z-selectivity, respectively (entries 7 and 8). Not
only alkylacetylene but also arylacetylene such as pheny-
lacetylene (2b) could participate in the E-selective cross-
dimerization with good yield and good selectivity (entry
9), however, Z-selective dimerization by 1–i-Pr3P system
could not achieved (entry 10). Concerning E-selective
cross-dimerization between 2c and other terminal aryl-
acetylene, cross-dimerization between 2c and 4-tolyl-
acetylene (2g) or 4-methoxyphenylacetylene (2h) were
also achieved in good yield with good to high E-selectiv-
ity (entries 11 and 12).
R
2
(E)-3
(Z)-3
Entry 2 (R)
Phosphine Time (h) Yield of 3 (%)a E/Zb
1
2
3
4
2a (n-C6H13)
Ph3P
6
24
6
3a (71)
3a (77)
3b (94)
3b (92)
85:15
7:93
2a (n-C6H13)
2b (Ph)
Et2PhP
Ph3P
>99:1
0:100
2b (Ph)
Et2PhP
24
a Isolated yield.
b Determined by 1H NMR.
The catalyst system 1–Ph3P also catalyzed dimerization of
trimethylsilylacetylene (2c) leading to enyne in good
yield with complete E-selectivity (Scheme 2).10 On the
other hand, the reaction of 2c by 1–Et2PhP system afford-
ed a Z-butatriene 4c in a moderate yield. The Z-enyne was
obtained by 1–n-Pr3P system in a good yield with com-
plete Z-selectivity. Reaction mechanism for homodimer-
ization of alkyne have been demonstrated in various
research groups.1,12 It is known that phosphine ligand con-
taining high electron-donating property such as alky-
lphosphine favors the formation of Z-enyne and Z-
butatriene rather than that of E-enyne because of a forma-
tion of vinylidene intermediate.1f In our catalytic system,
the dimerization reaction probably proceeded with similar
reaction mechanism.
In the presence of the 1–Ph3P or 1–n-Pr3P, other silylacet-
ylenes such as triisopropylacetylene and tert-butyl-
dimethylsilylacetylene were also reacted with alkyl-
acetylene (Scheme 3).13 The cross-dimerization between
triisopropylsilylacetylene (2i) and 1-octyne (2a) proceed-
ed to give the corresponding cross-dimer (E)-5i or (Z)-5i
in high yield with complete stereoselectivity. tert-Bu-
tyldimethylsilylacetylene (2j) also reacted with 2a to give
the corresponding cross-dimer 5j though yields and selec-
tivities of resulting cross-dimers 5j are lower than that of
5i.
We next examined the cross-dimerization between trime-
thylsilylacetylene (2c) and 1-octyne (2a) in the presence
of a 1–Ph3P catalyst. After screening the reaction condi-
tions, we found that cross-dimerization between 2c and
excess 2a (2 equiv) proceeded to give the corresponding
cross-dimer 5a with complete E-selectivity (Table 2, en-
try 1).13 Although the homo-dimer (E)-3a also formed in
this reaction,14 the resulting cross-dimer 5a could be iso-
lated by silica gel column chromatography in high yield.
It should be noted that Z-type cross-dimerization between
2c and 2a proceeded by 1–n-Pr3P catalytic system in high
yield with complete selectivity (entry 2). It is the first ex-
ample for phosphine-controlled cross-dimerization reac-
In summary, we demonstrated that an iridium(I)–guanidi-
nate complex–phosphine system is a versatile new cata-
lyst for regio- and stereoselective cross-dimerization
between two different terminal alkynes. Especially, in the
case of cross-dimerization between silylacetylenes and
alkylacetylenes, the E/Z selectivity of resulting enynes
could be controlled by changing phosphines.
Synlett 2008, No. 17, 2663–2666 © Thieme Stuttgart · New York

LETTER
Cross-Dimerization between Terminal Alkylacetylene and Silylacetylene
2665
Yorozuya, S.; Yamamoto, Y.; Miyaura, N. Organometallics
2000, 19, 365. (b) Yang, C.; Nolan, S. P. J. Org. Chem.
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(g) Weng, W.; Guo, C.; Celenligil-Cetin, R.; Foxman, B. M.;
Ozerov, O. V. Chem. Commun. 2006, 197.
Table 2 Cross-Dimerization between Trimethylsilylacetylene (2c)
and Alkyl- or Arylacetylene 2a,b,d–h Catalyzed by 1–Phosphine Sys-
tem
H
SiMe3
Me3Si
2c (1.0 mmol)
5 mol%
H
H
H
R
1/Phosphine
+
+
toluene
80 °C, 6 h
H
R
H
R
(E)-5
(Z)-5
Me3Si
2a,b,d–h (2 mmol)
(2) (a) Trost, B. M.; McIntoshi, M. C. J. Am. Chem. Soc. 1995,
117, 7255. (b) Trost, B. M.; Sorum, M. T.; Chan, C.; Harms,
A. E.; Rhter, G. J. Am. Chem. Soc. 1997, 119, 698. (c) Yi,
C. S.; Liu, N. Organometallics 1998, 17, 3158. (d) Trost,
B. M.; Frontier, A. J. J. Am. Chem. Soc. 2000, 122, 11727.
(e) Chen, L.; Li, C. Tetrahedron Lett. 2004, 45, 2771.
(f) Hirabayashi, T.; Sakaguchi, S.; Ishii, Y. Adv. Synth.
Catal. 2005, 347, 872. (g) Nishimura, T.; Guo, X.-X.;
Ohnishi, K.; Hayashi, T. Adv. Synth. Catal. 2007, 349,
2669. (h) Katagiri, T.; Tsurugi, H.; Funayama, A.; Satoh, T.;
Miura, M. Chem. Lett. 2007, 36, 830.
(3) (a) Akita, M.; Yasuda, H.; Nakamura, A. Bull. Chem. Soc.
Jpn. 1984, 57, 480. (b) Wang, J.; Kapon, M.; Berthet, J. C.;
Ephritikhine, M.; Eisen, M. S. Inorg. Chim. Acta 2002, 334,
183. (c) Katayama, H.; Yari, H.; Tanaka, M.; Ozawa, F.
Chem. Commun. 2005, 4336. (d) Katagiri, T.; Tsurugi, H.;
Satoh, T.; Miura, M. Chem. Commun. 2008, 3405.
(e) Tsukada, N.; Ninomiya, S.; Aoyama, Y.; Inoue, Y. Org.
Lett. 2007, 9, 2919.
Entry 2 (R)
Phosphine
Ph3P
Yield of 5 (%)a E/Zb
1
2
2a (n-C6H13)
5a (80)
5a (90)
5d (78)
5d (87)
5e (72)
5e (70)
5f (72)
5f (92)
5b (72)
5b (60)
5g (76)
5h (81)
100:0
0:100
100:0
0:100
100:0
10:90
100:0
4:96
2a (n-C6H13)
2d [Me2CH(CH2)2]
2d [Me2CH(CH2)2]
2e (PhCH2)
2e (PhCH2)
2f (Cy)
n-Pr3P
Ph3P
3
4
n-Pr3P
Ph3P
5
6
n-Pr3P
Ph3P
7
8
2f (Cy)
n-Pr3P
Ph3P
9
2b (Ph)
88:12
87:13
91:9
10
11
12
2b (Ph)
n-Pr3P
Ph3P
(4) Ogata, K.; Toyota, A. J. Organomet. Chem. 2007, 692, 4139.
(5) Baiely, P. J.; Pace, S. Coord. Chem. Rev. 2001, 214, 91; and
references therein.
2g (4-MeC6H4)
2h (4-MeOC6H4)
Ph3P
91:9
(6) Synthesis of {Ir[(N2 (i-Pr)2CN(i-Pr)2](cod)} (1)
A solution of [IrCl(cod)]2 (281 mg, 0.42 mmol) in THF (5
mL) was cooled to –78 °C, and then a THF solution of
Li[(N2 (i-Pr)2CN(i-Pr)2], which was prepared by the reaction
of the DIC (0.13 mL, 0.84 mmol) with LDA solution (1.8 M
in heptane–THF–ethylbenzene solution, 0.48 mL, 0.86
mmol) at –78 °C, was added. The mixture was allowed to
warm to r.t. After 4 h, the volatiles were removed under
reduced pressure. The residual solid was extracted with
toluene and the filtrate was evaporated off under high
vacuum to give orange complex 1 (278 mg, 0.53 mmol,
63%). 1H NMR (400 MHz, C6D6): d = 0.96 (d, J = 6.4 Hz,
12 H, i-PrCH3), 1.23 (d, J = 6.9 Hz, 12 H, i-PrCH3), 1.39 (d,
J = 7.8 Hz, 4 H, cod), 2.20 (br, 4 H, cod), 3.43 (sept, J = 6.9
Hz, 2 H, i-PrCH), 3.80 (sept, J = 6.4 Hz, 2 H, i-PrCH), 4.09
(br, 4 H, cod). 13C{1H} NMR (100 MHz, CDCl3): d = 22.8,
25.0, 32.5, 47.1, 48.6, 58.9 (cod, i-Pr), 128.5 (cod), 179.7
(NCN). Anal. Calcd for C21H40IrN3: C, 47.88; H, 7.65; N,
7.98. Found: C, 47.82; H, 7.60; N, 8.00.
a Isolated yield.
b Determined by 1H NMR.
Si
H
Ph3P
H
Si
H
n-C6H13
2i, 2j (1.0 mmol)
5 mol% 1
(E)-5i (yield 90%, E/Z = 100:0)
(E)-5j (yield 71%, E/Z = 72:28)
+
toluene
80 °C, 6 h
H
n-C6H13
H
H
n-Pr3P
2a (2.0 mmol)
n-C6H13
2i (Si = i-Pr3Si)
2j (Si = Me2t-BuSi)
Si
(Z)-5i (yield 92%, E/Z = 0:100)
(Z)-5j (yield 78%, E/Z = 12:88)
Scheme 3
(7) (a) Jenke, T.; Stoeckli-Evans, H.; Bodensieck, U.; Suess-
Fink, G. J. Organomet. Chem. 1991, 401, 347. (b) Yip,
H.-K.; Che, C.-M.; Zhou, Z.-Y.; Mak, T. C. W. J. Chem.
Soc., Chem. Commun. 1992, 1369. (c) Bailey, P. J.;
Mitchell, L. A.; Parson, S. J. Chem. Soc., Dalton Trans.
1996, 2839. (d) Dinger, M. B.; Henderson, W. Chem.
Commun. 1996, 211. (e) Holman, K. T.; Robinson, S. D.;
Sahajpal, A.; Steed, J. W. J. Chem. Soc., Dalton Trans. 1999,
15. (f) Foley, S. R.; Yap, G. P. A.; Richeson, D. S. Chem.
Commun. 2000, 1515. (g) Bailey, P. J.; Grant, K. J.;
Mitchell, L. A.; Pace, S.; Parkin, A.; Parsons, S. J. Chem.
Soc., Dalton Trans. 2000, 1887. (h) Berry, J. F.; Cotton,
F. A.; Huang, P.; Murillo, C. A.; Wang, X. Dalton Trans.
2005, 3713.
Acknowledgment
The authors are grateful to Ms. Keiko Yamada (RIKEN) for the as-
sistance in elemental analyses. Dr. Yayoi Hongo (RIKEN) is ack-
nowledged for assistance in high-resolution mass spectrometry
analysis. We thank Dr. Daisuke Hashizume (RIKEN) for his help in
X-ray crystallographic analysis.
References and Notes
(1) For recent example of transition-metal-catalyzed
homodimerization of alkynes, see: (a) Ohmura, T.;
Synlett 2008, No. 17, 2663–2666 © Thieme Stuttgart · New York

2666
K. Ogata et al.
LETTER
(8) (a) Robinson, S. D.; Sahajal, A. J. Chem. Soc., Dalton Trans.
1997, 3349. (b) Robinson, S. D.; Sahajpal, A.; Steed, J.
Inorg. Chim. Acta 2000, 303, 265. (c) Holland, A. W.;
Bergman, R. G. J. Am. Chem. Soc. 2002, 124, 9010.
(9) Crystal Data for 1
1 H, CH=CH), 7.10–7.40 (m, 5 H, Ph). 13C{1H} NMR (100
MHz, CDCl3): d = –0.1 (s, SiMe3), 39.3 (s, CH2Ph), 93.5,
103.7 (s, C=C), 111.0, 126.4, 128.5, 128.7, 138.6, 144.2 (S,
C=C, Ph). HRMS (EI): m/z [M]+calcd for C14H18Si:
214.1178; found: 214.1169.
C21H40IrN3, MW = 526.79, monoclinic, P21/n, a = 20.5195
(4) Å, b = 15.5067 (4) Å, c = 27.6890 (4) Å, b = 102.4145
(16)°, V = 8604.4 (3) Å3, Z = 16, Dcalc = 1.626 g/cm3, m (Mo
Ka) = 62.328 cm–1, 84841 measured reflections, 24677
independent (Rint = 0.063), 13318 observed [I > 2s(I)].
R1 = 0.0353, wR2 = 0.0903 (all data). Atomic coordinates,
thermal parameters, bond distances, and angles have been
deposited at the Cambridge Crystallographic Data Center.
CCDC number: 668977.
Product (Z)-5e: 1H NMR (400 MHz, CDCl3): d = 0.22 (s,
9 H, SiMe3), 3.67 (d, J = 7.3 Hz, 2 H, CH2), 5.60 (d, J = 11.0
Hz, 1 H, CH=CH), 6.10 (dt, J = 10.6, 7.3 Hz, 1 H, CH=CH),
7.10–7.40 (m, 5 H, Ph). 13C{1H} NMR (100 MHz, CDCl3):
d = –0.02 (s, SiMe3), 36.5 (s, CH2Ph), 99.0, 101.8 (s, C=C),
109.9, 126.2, 128.5, 128.5, 139.7, 143.2 (S, C=C, Ph).
HRMS (EI): m/z [M]+ calcd for C14H18Si: 214.1178; found:
214.1158.
Product (E)-5g: 1H NMR (400 MHz, CDCl3): d = 0.22 (s,
9 H, SiMe3), 2.34 (s, 3 H, CH3), 6.12 (d, J = 16.5 Hz, 1 H,
CH=CH), 6.98 (d, J = 16.5 Hz, 1 H, CH=CH), 7.10–7.30 (m,
4 H, Ar). 13C{1H} NMR (100 MHz, CDCl3): d = 0.0 (s,
SiMe3), 21.5 (s, CH3), 96.4, 104.6 (s, C=C), 106.9, 126.2,
129.0, 129.4, 138.9, 142.4 (s, C=C, Ph). HRMS (EI): m/z
[M]+ calcd for C14H18Si: 214.1178; found: 214.1171.
Product (E)-5h: 1H NMR (400 MHz, CDCl3): d = 0.11 (s,
9 H, SiMe3), 3.81 (s, 3 H, CH3, 6.16 (d, J = 19.2 Hz, 1 H,
CH=CH), 6.48 (d, J = 19.2 Hz, 1 H, CH=CH), 6.84 (d,
J = 9.2 Hz, 2 H, Ar), 7.37 (d, J = 9.2 Hz, 2 H, Ar). 13C{1H}
NMR (100 MHz, CDCl3): d = –1.6 (s, SiMe3), 55.2 (s,
OCH3), 88.4, 89.9 (s, C=C), 113.9, 128.4, 132.1, 133.0,
144.7, 159.6 (s, C=C, Ph). HRMS (EI): m/z [M]+ calcd for
C14H18OSi: 230.1127; found: 230.1133.
(10) General Procedure for Homodimerization of Terminal
Alkynes (Table 1 and Scheme 2)
The mixture of 1 (16 mg, 0.03 mmol), toluene (3 mL),
phosphine (16 mg, 0.06 mmol), and terminal alkyne (1.0
mmol) was charged in a sealed tube under argon atmosphere.
After stirring for 6 h at 80 °C, the solvent was removed, and
the residue was chromatographed on SiO2, using hexane or
Et2O–hexane (1:3) as eluent. The solvent was removed to
give dimeric product 3 or 4.
(11) Results of dimerization of 1-octyne(2a) catalyzed by
1–trialkylphosphine system; 1–Et3P: yield 60%, E/Z =
42:58; 1–n-Pr3P: yield 79%, E/Z = 40:60
(12) (a) Bianchini, C.; Peruzzini, M.; Zanobini, F.; Frediani, P.;
Albinati, A. J. Am. Chem. Soc. 1991, 113, 5453.
(b) Wakatsuki, Y.; Yamazaki, H.; Kumegawa, N.; Satoh, T.;
Satoh, J. Y. J. Am. Chem. Soc. 1991, 113, 9604.
(c) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.;
Zanobini, F. Organometallics 1994, 13, 4616.
Product (E)-5i: 1H NMR (400 MHz, CDCl3): d = 0.80–2.20
(m, 16 H, C6H13, i-PrCH), 1.07 (br d, 18 H, i-PrCH3), 5.52
(dt, J = 16.0, 1.4 Hz, 1 H, CH=CH), 6.20 (dt, J = 16.0, 6.9
Hz, 1 H, CH=CH). 13C{1H} NMR (100 MHz, CDCl3): d =
11.3, 14.1, 22.6, 28.6, 28.9, 31.7, 33.1 (s, C6H13, i-PrCH),
18.6 (s, i-PrCH3), 88.5, 106.1 (s, C=C), 109.8, 145.8 (s,
CH=CH). HRMS (EI): m/z [M]+ calcd for C19H36Si:
292.2586; found: 292.2583.
(13) General Procedure for Cross-Dimerization of
Silylacetylene with Terminal Alkynes (Table 2 and
Scheme 3)
The mixture of 1 (25 mg, 0.05 mmol), toluene (3 mL),
phosphine (26 mg, 0.10 mmol), silylacetylene (1.0 mmol),
and terminal alkyne (2.0 mmol) was charged in sealed tube
under argon atmosphere. After stirring for 6 h at 80 °C, the
solvent was removed, and the residue was chromatographed
on SiO2, using hexane as eluent. Homo-dimer was eluted
first. Then the eluate containing cross-dimer 5 was obtained.
The solvent was removed to give cross-dimer 5 as colorless
or pale-yellow oil.
Product (Z)-5i: 1H NMR (400 MHz, CDCl3): d = 0.80–2.40
(m, 16 H, C6H13, i-PrCH), 1.09 (br d, 18 H, i-PrCH3), 5.50
(d, J = 10.5 Hz, 1 H, CH=CH), 6.0 (m, 1 H, CH=CH).
13C{1H} NMR (100 MHz, CDCl3): d = 11.3, 14.1, 22.6, 28.8,
29.0, 30.4, 31.7 (s, C6H13, i-PrCH), 18.6 (s, i-PrCH3), 94.6,
103.9 (s, C=C), 109.6, 145.2 (s, CH=CH). HRMS (EI): m/z
[M]+ calcd for C19H36Si: 292.2586; found: 292.2587.
Product (E)-5j: 1H NMR (400 MHz, CDCl3): d = 0.11 (s,
6 H, SiMe2), 0.80–2.20 (m, 13 H, C6H13), 0.94 (s, 9 H, t-Bu),
5.50 (d, J = 15.8 Hz, 1 H, CH=CH), 6.21 (dt, J = 15.8, 7.0
Hz, 1 H, CH=CH). 13C{1H} NMR (100 MHz, CDCl3): d =
–4.6 (s, SiMe2), 14.1, 16.6, 22.6, 28.6, 28.8, 31.6, 33.1 [s,
C6H13, C(CH3)3], 26.1 [s, C(CH3)3], 90.6, 104.8 (s, C=C),
109.6, 146.2 (s, CH=CH). HRMS (EI): m/z [M]+ calcd for
C16H30Si: 250.2117; found: 250.2116.
Spectral Data for New Compounds
Product (E)-5d: 1H NMR (400 MHz, CDCl3): d = 0.18 (s,
9 H, SiMe3), 0.87 (d, J = 7.0 Hz, 6 H, CH3), 1.20–1.30 (m,
2 H, CH2), 1.50–1.60 (m, 1 H, CH), 2.00–2.20 (m, 2 H, CH2),
5.50 (dt, J = 15.8, 1.8 Hz, 1 H, CH=CH), 6.21 (dt, J = 15.8,
7.0 Hz, 1 H, CH=CH). 13C{1H} NMR (100 MHz, CDCl3):
d = 0.0 (s, SiMe3), 22.4, 27.3, 30.9, 37.6 (s, C6H13), 92.4,
104.2 (s, C=C), 109.4, 146.5 (C=C). HRMS (EI): m/z [M –
Me]+ calcd for C11H19Si: 179.1256; found: 179.1259.
Product (Z)-5d: 1H NMR (400 MHz, CDCl3): d = 0.19 (s,
9 H, SiMe3), 0.90 (d, J = 6.4 Hz, 6 H, CH3), 1.20–1.30 (m,
2 H, CH2), 1.50–1.60 (m, 1 H, CH), 2.30–2.40 (m, 2 H, CH2),
5.46 (d, J = 10.5 Hz, 1 H, CH=CH), 5.95 (dt, J = 10.5, 7.6
Hz, 1 H, CH=CH). 13C{1H} NMR (100 MHz, CDCl3): d =
0.0 (s, SiMe3), 22.4, 27.3, 30.9, 37.6 (s, C6H13), 88.7, 92.4 (s,
C=C), 109.4, 146.5 (C=C). HRMS (EI): m/z [M – Me]+ calcd
for C11H19Si: 179.1256; found: 179.1213.
Product (Z)-5j: 1H NMR (400 MHz, CDCl3): d = 0.13 (s,
6 H, SiMe2), 0.80–2.40 (m, 13 H, C6H13), 0.96 (s, 9 H, t-Bu),
5.48 (d, J = 10.8 Hz, 1 H, CH=CH), 5.96 (dt, J = 10.8, 7.4
Hz, 1 H, CH=CH). 13C{1H} NMR (100 MHz, CDCl3): d =
–4.6 (s, SiMe2), 14.1, 16.6, 22.6, 28.7, 28.9, 30.3, 31.6 [s,
C6H13, C(CH3)3], 26.1 [s, C(CH3)3], 96.6, 102.8 (s, C=C),
109.2, 145.6 (s, CH=CH). HRMS (EI): m/z [M]+ calcd for
C16H30Si: 250.2117; found: 250.2108.
(14) Formation ratio of (E)-5a/(E)-3a = 77:23 (determined by 1H
NMR).
(15) Result of cross-dimerization between 2c and 2a catalyzed by
1–Et2PhP system: yield 88%, E/Z = 9:91.
Product (E)-5e: 1H NMR (400 MHz, CDCl3): d = 0.17 (s,
9 H, SiMe3), 3.43 (d, J = 6.9 Hz, 2 H, CH2), 5.53 (dt,
J = 15.6, 1.8 Hz, 1 H, CH=CH), 6.35 (dt, J = 15.6, 6.9 Hz,
Synlett 2008, No. 17, 2663–2666 © Thieme Stuttgart · New York

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