Formation of 1,4-Disilyl-2-butenes from Vinyl Grignard Reagent and Chlorosilanes Catalyzed by a Titanocene Complex

Article abstract of DOI:10.1021/ol015928q

(matrix presented) Symmetrical 1,4-disilyl-2-butenes 1 have been prepared by the reaction of vinyl Grignard reagent with chlorosilanes. This reaction proceeds efficiently in the presence of a catalytic amount of titanocene dichloride at 0 °C in THF. When dichlorodiphenylsilane was used, 1,1-diphenyl-1-silacyclo-3-pentene 2 was obtained in a good yield.

Full text of DOI:10.1021/ol015928q

ORGANIC
LETTERS
2001
Vol. 3, No. 11
1733-1735
Formation of 1,4-Disilyl-2-butenes from
Vinyl Grignard Reagent and
Chlorosilanes Catalyzed by a Titanocene
Complex
Hiroyasu Watabe, Jun Terao,* and Nobuaki Kambe*
Department of Applied Chemistry, Graduate School of Engineering, Osaka UniVersity,
Suita, Osaka 565-0871, Japan
terao@ap.chem.eng.osaka-u.ac.jp
Received April 3, 2001
ABSTRACT
Symmetrical 1,4-disilyl-2-butenes 1 have been prepared by the reaction of vinyl Grignard reagent with chlorosilanes. This reaction proceeds
efficiently in the presence of a catalytic amount of titanocene dichloride at 0 °C in THF. When dichlorodiphenylsilane was used, 1,1-diphenyl-
1-silacyclo-3-pentene 2 was obtained in a good yield.
Titanocene dichloride catalyzes the reduction of alkyl, aryl,
and vinyl bromides;1a,b aryl chlorides;1c alkoxy- and halo-
silanes;1d ketones;1e esters,1f and carboxylic acid1g by the aid
of alkyl Grignard reagents. This Cp2TiCl2/RMgX system can
also be applied to the hydromagnesation of alkynes, dienes,
and alkenes.1a,2 We have recently developed regioselective
introduction of alkyl and/or silyl functionalities to alkenes
and dienes by the use of Cp2TiCl2 as a catalyst in the
presence of nBuMgCl.3 In these reactions, however, Grignard
reagents have been used as the reducing reagent of titanocene
complexes or as the hydrogen source and their carbon
moieties have never been incorporated in the products.
Herein, we wish to disclose a new type of titanocene-
catalyzed transformation using vinyl Grignard reagents and
chlorosilanes giving rise to 1,4-disilyl-2-butenes as shown
in Scheme 1.
Scheme 1
For example, into a mixture of chlorodimethylphenylsilane
(2.85 mmol) and a catalytic amount of titanocene dichloride
(0.05 equiv) was added a THF solution of vinyl Grignard
reagent (0.95 M in THF, 3 mL, 1.0 equiv) at 0 °C, and the
solution was stirred for 10 min. The NMR analysis of the
crude mixture indicated the formation of 1,4-bis(dimethyl-
phenylsilyl)-2-butene4 (1a; R3Si ) PhMe2Si) in 94% yield
with an E/Z ratio of 74/26 (Table 1, run 1). The product
(1) (a) Colomer, E.; Corriu, R. J. Organomet. Chem. 1974, 82, 367-
373. (b) Rilatt, J. A.; Kitching, W. Organometallics 1982, 1, 1089-1093.
(c) Hara, R.; Sato, K.; Sun, W. H.; Takahashi, T. J. Chem. Soc., Chem.
Commun. 1999, 845-846. (d) Corriu, R. J. P.; Meunier, B. J. Organomet.
Chem. 1974, 65, 187-194. (e) Sato, F.; Jinbo, T.; Sato, M. Tetrahedron
Lett. 1980, 21, 2171-2174. (f) Sato, F.; Jinbo, T.; Sato, M. Tetrahedron
Lett. 1980, 21, 2175-2178. (g) Sato, F.; Jinbo, T.; Sato, M. Synthesis 1981,
871.
(2) Sato, F. J. Organomet. Chem. 1985, 285, 53-64. Gao, Y.; Sato, F.
J. Chem. Soc. Chem. Commun. 1995, 659-660 and references therein.
(3) (a) Terao, J.; Saito, K.; Nii, S.; Kambe, N.; Sonoda, N. J. Am. Chem.
Soc. 1998, 120, 11822-11823. (b) Terao, J.; Kambe, N.; Sonoda, N.
Tetrahedron Lett. 1998, 39, 9697-9698. (c) Nii, S.; Terao, J.; Kambe, N.
J. Org. Chem. 2000, 65, 5291-5297.
(4) The products 1a-c and 2 are known compounds, and their yields
and E/Z ratios were determined by NMR. Registry nos.: 1a, 60404-57-1;
1b, 3528-12-9; 1c, 58458-84-7, 84812-44-2; 2, 34106-93-9.
10.1021/ol015928q CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/04/2001

titanocene group on the other allylic position. Subsequent
transmetalation of 7 with CH2dCHMgBr followed by
trapping with a chlorosilane gives the corresponding product
along with regeneration of 3.
Table 1. Silylative Homocoupling of Vinylmagnesium
Bromide
run
catalyst
clorosilane
product yield (%)a
E/Z
We carried out the following control experiments to
examine the validity of this reaction pathway. Since a small
amount of the vinylsilane was formed as a byproduct (<5%)
in the present silylation reaction, we first examined whether
the double silylated product is formed via vinylsilanes as an
intermediate.10 When a reaction of chlorotripropylsilane (1.0
equiv) with vinyl Grignard reagent under identical conditions
as run 4 in Table 1 was carried out at 0 °C for 10 min in the
presence of CH2dCHSiEt3 (1.0 equiv), 1d was obtained as
the sole product in 49% yield and 92% of unreacted CH2d
CHSiEt3 was recovered. When the reaction was conducted
for 2 h, the yield of 1d was improved to 62%. This result
rules out the intermediacy of vinylsilanes.
It is known that Cp2TiCl2 reacts with CH2dCHLi at low
temperature in the presence of tetramethylethylenediamine
(TMEDA) to give butadiene and Cp2Ti(TMEDA).7a On the
other hand, it was also reported that titanocene alkenylidene
complexes were prepared from titanocene dichloride with 2
equiv of vinyl Grignard reagents.11 So, we tested whether
the reductive coupling of divinyltitanocene 3 giving rise to
1,3-butadiene does take place under the conditions employed.
Titanocene dichloride was treated with 2 equiv of vinyl-
magnesium bromide in THF at -78 °C. After stirring for 1
h, the solution was warmed to 0 °C over 5 min and stirred
for another 5 min at the same temperature. NMR analysis
1
2
3
4
5
6
7
8
9
Cp2TiCl2 PhMe2Si-Cl
Me3Si-Cl
1a
1b
1c
1d
1e
1a
1a
1a
1a
94 (86)
83
68 (61)
64
72, 86b
<1
8
6
74/26
72/28
76/24
82/18
64/36
Et3Si-Cl
Pr3Si-Cl
Me3SiMe2Si-Cl
Cp2ZrCl2 PhMe2Si-Cl
TiCl4
Ti(OiPr)4
Cp2HfCl2
0
a NMR yield. Isolated yield is in parentheses. b At -20 °C, 10 min.
was obtained in pure form in 86% yield by a recycling
preparative HPLC using CHCl3 as an eluent. In this reaction,
only a trace amount of CH2dCHSiMe2Ph (<1%) was formed
as a byproduct, probably via direct reaction of CH2dCHMgBr
with PhMe2SiCl. The elongation of the reaction time did not
lead to the change of E/Z ratio.
Table 1 summarizes the results of this silylative coupling
of vinyl Grignard reagent. Chlorotrialkylsilanes can also be
employed as the silylation reagents to give the desired
products4,5 (1b, R ) Me; 1c, R ) Et; 1d, R ) nPr) in good
yields (runs 2-4). Under similar conditions, chloropenta-
methyldisilane also gave the corresponding product6 (1e, R3-
Si ) Me3SiMe2Si) in 72% yield (run 5). The yield increased
to 86% when the reaction was conducted at -20 °C for 10
min. Substituted vinyl Grignard reagents, such as R-methyl
or â-methyl vinylmagnesium bromides, were sluggish under
the same conditions. When Cp2ZrCl2 was used as a catalyst,
only a trace amount of 1a was obtained under the identical
conditions (run 6). The use of TiCl4 and Ti(OiPr)4 in place
of Cp2TiCl2 afforded 8% and 6% yields of 1a, respectively
(runs 7 and 8), but no reaction took place with Cp2HfCl2
(run 9).
(5) Data for 1d: IR (neat) 2954, 2925, 2868, 1459, 1409, 1332, 1202,
1067, 1004, 815, 738 cm-1; 1H NMR (400 MHz, CDCl3) (trans isomer) δ
5.21-5.18 (m, 2 H), 1.41-1.40 (m, 4 H), 1.38-1.28 (m, 12 H), 0.97-
0.91 (t, J ) 7.2 Hz, 18 H), 0.54-0.49 (m, 12 H); (cis isomer) δ 5.28-5.15
(m, 2 H), 1.45-1.40 (m, 4 H), 1.38-1.28 (m, 12 H), 0.97-0.91 (t, J ) 7.2
Hz, 18 H), 0.54-0.49 (m, 12 H); 13C NMR (100 MHz, CDCl3) (trans
isomer) δ 124.1, 18.5, 18.4, 17.3, 15.0. (cis isomer) δ 122.8, 18.6, 18.5,
17.4, 15.1; MS (EI) m/z (relative intensity, %) 368 (M+, 10), 158 (15), 157
(100), 116 (12), 115 (90), 87 (17), 73 (27), 59 (9), 45 (10); HRMS calcd
for C22H48Si2 368.3295, found 368.3292. Anal. Calcd for C22H48Si2: C,
71.65; H, 13.12. Found: C, 71.84; H, 13.32.
(6) Data for 1e: IR (neat) 2950, 2893, 1244, 833, 809, 723, 690 cm-1
;
When dichlorodiphenylsilane (0.5 equiv) was treated with
vinyl Grignard reagent at -20 °C for 3 h, cyclization
predominated to afford 1,1-diphenyl-1-silacyclo-3-pentene4
(2) in 73% yield (Scheme 2).
1H NMR (400 MHz, CDCl3) (trans isomer) δ 5.23-5.19 (m, 2 H), 1.49-
1.47 (m, 4 H), 0.05 (s, 18 H), 0.02 (s, 12 H); (cis isomer) 5.31-5.28 (m,
2 H), 1.49-1.47 (m, 4 H), 0.06 (s, 18 H), 0.04 (s, 12 H); 13C NMR (100
MHz, CDCl3) (trans isomer) δ 124.2, 20.6, -2.0, -4.5. (cis isomer) δ 122.9,
15.8, -2.0, -4.5; MS (EI) m/z (relative intensity, %) 316 (M+, 10), 243
(14), 169 (8), 155 (40), 132 (21), 131 (100), 116(15), 73(50); HRMS calcd
for C14H36Si4 316.1894, found 316.1902. Anal. Calcd for C14H36Si4: C,
53.08; H, 11.45. Found: C, 53.07; H, 11.02
(7) (a) Beckhaus, R.; Thiele, K.-H. J. Organomet. Chem. 1986, 317, 23-
31. (b) Beckhaus, R.; Flatau, S.; Trojanov, S.; Hofmann, P. Chem. Ber.
1992, 125, 291-299. (c) Beckhaus, R. Angew. Chem., Int. Ed. Engl. 1997,
36, 686-713.
Scheme 2
(8) Similar reaction has also been reported for zirconocene, i.e., Cp2-
ZrCl2 reacts with CH2dCHLi to form Cp2Zr(CHdCH2)2, which undergoes
reductive coupling to afford butadiene. Beckhaus, R.; Thiele, K.-H. J.
Organomet. Chem. 1984, 268, C7-C8.
(9) It is known that isomerization of zircocene-butadiene complex to
zirconacyclopentene was suggested, see: (a) Erker, G.; Wicher, J.; Engel,
K.; Rosenfeldt, F.; Dietrich, W.; Kru¨ger, C. J. Am. Chem. Soc. 1980, 102,
6344-6346. (b) Yasuda, H.; Nakamura, A. Angew. Chem., Int. Ed. Engl.
1987, 26, 723-742.
A plausible reaction pathway is shown in Scheme 3.
Titanocene dichloride reacts with 2 equiv of CH2dCHMgBr
to generate divinyltitanocene complex 3, which readily forms
titanocene-butadiene complex 4 or its s-trans isomer via
reductive coupling.7,8 Then, 4 would isomerize to titanacyclo-
pentene 5.9 The successive transmetalation of 5 with vinyl
Grignard reagent affords allylmagnesium species 6, which
reacts with chlorosilane to give allylsilane 7 carrying a
(10) It is also reported that homodimerization of vinyl silane catalyzed
by transition metal gives 1,4-disilyl-butenes: (a) Yur’ev, V. P.; Gailyunas,
G. A.; Yusupova, F. G.; Nurtdinova, G. V.; Monakhova, E. S.; Tolstikov,
G. A. J. Organomet. Chem. 1979, 169, 19-24. (b) Kretschmer, W. P.;
Troyanov, S. I.; Meetsma, A.; Hessen, B.; Teuben. J. H. Organometallics
1998, 17, 284-286.
(11) Petasis, N. A.; Hu, Y.-H. J. Org. Chem. 1997, 62, 782-783.
1734
Org. Lett., Vol. 3, No. 11, 2001

Scheme 3. A Plausible Pathway of Ti-Catalyzed Double Silylative Vinyl Coupling
of this solution, after addition of THF-d8, indicated the
An alternative pathway from 5 to 7 was proposed by a
referee, i.e., reaction of 5 with R3SiCl to give Cp2TiClCH2-
CHdCHCH2SiR3 followed by the transmetalation with
CH2dCHMgBr leading to 7. However, this might be ruled
out by the evidence that a reaction of Cp2TiCl2 with 2 equiv
of CH2dCHMgBr in the presence of Me3SiCl followed by
protonolysis did not afford any silylated products.
In conclusion, a novel silylative coupling of vinylmagne-
sium bromides with chlorosilanes has been developed by the
aid of a titanocene catalyst. Many reactions catalyzed by
titanocene complexes using Grignard reagents have been
reported, in which Grignard reagents have been employed
as reducing reagents of titanocene complexes or as hydrogen
sources. This reaction is unique because organic moieties
of Grignard reagents are incorporated in the products, which
has never been achieved by the use of Cp2TiCl2 as a catalyst
before this. The present reaction would involve reductive
coupling of divinyltitanocene complex in the carbon-carbon
bond forming step and electrophilic trapping of allylmag-
nesium intermediates with chlorosilanes.
formation of 1, 3-butadiene in 64% yield. We have already
reported that 1,4-disilyl-2-butenes were formed by the
reaction of 1,3-butadiene with 2 equiv of chlorosilane and
nBuMgCl in the presence of a catalytic amount of Cp2TiCl2.3b
This result also supports the intermediary of butadiene.
To support the intermediary of allyl Grignard reagents,
we examined their reactivities toward chlorosilanes. To a
mixture of CH2dCHCH2MgBr (5 mmol) and CH2d
CHMgBr (5 mmol) in THF (10 mL) was added PhMe2SiCl
(1 mmol) at 0 °C, and the mixture was stirred for 10 min.
The NMR analysis of the crude mixture indicated the
formation of allylsilane (10) quantitatively, but vinylsilane
(11) was not detected at all (Scheme 4). This result suggests
Scheme 4
Acknowledgment. This work was supported, in part, by
a Grant-in-Aid from the Ministry of Education, Science,
Sports and Culture, Japan. Thanks are due to the Instrumental
Analysis Center, Faculty of Engineering, Osaka University.
that allyl Grignard reagents react with chlorosilanes much
faster than CH2dCHMgBr.
OL015928Q
Org. Lett., Vol. 3, No. 11, 2001
1735