Hydrosilylation-metathesis sequence leading to 1-silaindenes

Article abstract of DOI:10.1055/s-0030-1258816

1-Silaindenes are prepared starting from (2-vinylphenyl)hydrosilanes and alkynes through a ruthenium-catalyzed hydrosilylation-ring-closing-metathesis sequence. The method is successfully applied to the synthesis of molecules containing multiple silaindene units.

Full text of DOI:10.1055/s-0030-1258816

LETTER
2743
Hydrosilylation–Metathesis Sequence Leading to 1-Silaindenes
H
ydrosilylation
a
–Metathesi
k
s
Sequence
L
a
eading to 1
n
-Silaindenesori Matsuda,*,1 Yoshiyuki Yamaguchi, Naoki Ishida, Masahiro Murakami*
Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan
Fax +81(75)3832752; E-mail: murakami@sbchem.kyoto-u.ac.jp
Received 25 August 2010
catalyst for the preparation of the silicon-tethered dienes.
The trans-hydrosilylation of terminal alkynes with hy-
dro(2-styryl)silanes would construct the desired skeleton
of the siladienes for RCM. Initially, dimethyl(2-vinylphe-
nyl)silane (1a) as the hydrosilylating agent was prepared
from commercially available starting materials; 2-bro-
mostyrene was treated with n-butyllithium in THF at –78
°C to generate (2-vinylphenyl)lithium, which was directly
reacted with chlorodimethylsilane (1.5 equiv). The result-
ing dimethyl(2-vinylphenyl)silane (1a) was isolated in
91% yield by column chromatography (Scheme 2).
Abstract: 1-Silaindenes are prepared starting from (2-vinylphe-
nyl)hydrosilanes and alkynes through a ruthenium-catalyzed hy-
drosilylation–ring-closing-metathesis sequence. The method is
successfully applied to the synthesis of molecules containing multi-
ple silaindene units.
Key words: hydrosilylation, metathesis, ruthenium, homogeneous
catalysis, ring closure
Silole (silacyclopentadiene) derivatives2 are promising
candidates of electron-transporting materials for organic
light-emitting diodes (OLED)3 and chemosensory materi-
als for the detection of nitroaromatic explosives.4 There-
fore, extensive studies have been carried out for the
synthesis of siloles and their derivatives.5,6 We recently
reported that the silole skeleton of 1-silaindenes (ben-
zosiloles) was constructed by ring-closing metathesis
(RCM) of silicon-tethered dienes.6c,7 The silicon-tethered
dienes requisite for the RCM were prepared by stepwise
introduction of two alkene moieties into dichlorosilanes
by nucleophilic substitution with organometallic reagents
(Scheme 1). However, we often encountered difficulty in
stepwise introduction of two different organometallic spe-
cies, and thus, the range of structural variation possible
with the method was limited. For example, substrates pos-
sessing multiple siladiene units which would afford the si-
laindene derivatives with extended conjugation (vide
infra) were unavailable when the previous method was
employed. In addition, it was hardly possible to install a
base-labile functional group on a resulting silaindene
skeleton. Thus, a new procedure for the preparation of sil-
icon-tethered dienes was desired in order to expand struc-
tural variation of 1-silaindenes accessible through RCM.
In this paper, we report that trans-hydrosilylation of ter-
minal alkynes with hydro(2-vinylphenyl)silanes and that
the following RCM allow further structural elaboration of
1-silaindene skeletons.
M2
Cl
R2
M1
Cl
M1, M2 = Li, MgX
Si
R1
2
RCM
R2
Si
Si
R1
R1
R2
2
2
Scheme 1 Previous synthesis of 1-silaindene
1) n-BuLi, THF, –78 °C
2) Me2SiHCl
H
Br
Si
Me2
1a 91%
Scheme 2
Hydrosilane 1a (1.3 equiv) thus prepared was treated with
phenylacetylene (2a) in the presence of 20 mol% of
[Cp*Ru(CH3CN)3]PF6 in dichloromethane at room tem-
perature. The trans-hydrosilylation reaction occurred to
give alkenyl(2-vinylphenyl)silane 3a in 76% yield
(Scheme 3).9 Only the C–C triple bond of 2a underwent
the hydrosilylation, and the styrenic C–C double bond of
1a remained intact. Decreasing the catalyst loading to 5
mol% resulted in a lower yield (28%), which might be
ascribed to steric bulkiness of dimethyl(2-vinylphenyl)-
silane.10 As we previously reported,6c RCM of 2a was suc-
cessfully catalyzed by the Grubbs second-generation cat-
alyst to afford 2-phenyl-1-silaindene 4a in good yield.
Thus, a new preparative method for the silicon-tethered
dienes was developed by utilization of the ruthenium-
catalyzed trans-hydrosilylation reaction.
Trost et al. reported that the ruthenium complex
[Cp*Ru(CH3CN)3]PF6 catalyzes the trans-selective hy-
drosilylation reaction of terminal alkynes to give
branched silylalkenes in a regioselective manner.8 Their
results led us to develop a new method for the synthesis of
siloles6d and germoles6a by double trans-hydrometalation
of 1,3-diynes catalyzed by the ruthenium complex. We
next examined the use of the ruthenium complex as the
SYNLETT 2010, No. 18, pp 2743–2746
x
x
.x
x
.2
0
1
0
Advanced online publication: 08.10.2010
DOI: 10.1055/s-0030-1258816; Art ID: U07510ST
© Georg Thieme Verlag Stuttgart · New York

2744
T. Matsuda et al.
LETTER
20 mol%
[Cp*Ru(MeCN)3]PF6
Table 1 Ruthenium-Catalyzed trans-Hydrosilylation–RCM Se-
quencea
+
H
CH2Cl2, r.t., 1.5 h
Ph
Si
Me2
hydrosilylation
RCM
R
+
1a
2a
1a (1.3 equiv)
Si
Si
R
Me2
Me2
R
5 mol%
Grubbs II cat.
2
3
4
Ph
toluene
80 °C, 2 h
Ph
Si
Entry 2
R
Time 3
(h)
Yield
4
Yield
(%)b
Si
Me2
Me2
(%)b
3a 76%
4a 90%
1
2
3
4
5
6
7
2b
2-BrC6H4
12
2
3b
65
4b
4c
4d
4e
4f
75c
99
83
91
21e
56
82
Scheme 3 Ruthenium-catalyzed trans-hydrosilylation and RCM
2c
2d
2e
2f
4-BrC6H4
3c
3d
3e
3f
63
3,5-Br2C6H3
4-Me2NC6H4
3-pyridyl
18
2
60
The new trans-hydrosilylation method was applied to var-
ious combinations of substrates to obtain silicon-tethered
dienes which were difficult to prepare by the previous
method, and RCM of the silicon-tethered dienes thus ob-
tained was examined under conditions that were used in
our previous study (Table 1). Of note were the cases
where a bromophenyl group was contained in the sub-
strates, which could not be synthesized by our previous
method using strongly basic conditions (entries 1–3).
Silaindene 4e having a dimethylamino group was also
prepared (entry 4). However, 2-ethynylpyridine failed to
react with 1a under identical conditions. On the other
hand, 3-ethynylpyridine (2f) underwent the trans-hydro-
silylation at 40 °C to give 3f in 26% yield, and the corre-
sponding RCM product 4f was obtained in 21% yield by
using the Hoveyda–Grubbs second-generation catalyst
(entry 5). The hydrosilylation–RCM sequence also
worked with 1-ethynylcyclohexene (2g) to afford 4g (en-
try 6). Aliphatic alkyne 2h was more reactive than aryl-
substituted alkynes for the hydrosilylation, producing si-
ladiene 3h in good yield even with 5 mol% of the catalyst
(entry 7).
46
19
3
26d
68
2g
2h
cyclohexenyl
n-C6H13
3g
3h
4g
2
92 (85f) 4h
a Hydrosilylation: alkyne 2 was reacted with hydrosilane 1a (1.2–1.3
equiv) in the presence of [Cp*Ru(CH3CN)3]PF6 (20 mol%) in CH2Cl2
(0.5 M) at r.t. RCM: siladiene 3 was reacted in the presence of Grubbs
II catalyst (5 mol%) in toluene (0.1 M) at 80 °C for 2 h.
b Isolated yield by preparative TLC.
c Additional 5 mol% of catalyst was added after 21 h, and the reaction
mixture was reacted further for 5 h.
d Reacted at 40 °C.
e Reaction was carried out in the presence of 10 mol% of Hoveyda–
Grubbs II catalyst in toluene at 110 °C for 22 h.
f Result with 5 mol% of catalyst.
The hydrosilylation of 2a with hydrosilane 1b having a
trifluoromethyl group para to the silicon also yielded sila-
diene 3i in 55% yield, and RCM of 3i furnished 1-silain-
dene 4i in excellent yield (Scheme 4).
Substances containing two or more silaindene skeletons
are attractive in terms of organic optoelectronic materials.
In particular, the change in the photophysical properties
when silaindene skeletons are connected through unsatur-
ated linkers is of significant interest. The newly developed
preparative method of silicon-tethered dienes was applied
to the reaction using diynes and a triyne, leading to the
synthesis of molecules containing multiple silaindene
units.
20 mol%
F3C
[Cp*Ru(MeCN)3]PF6
+
2a
H
CH2Cl2, r.t., 2 h
Si
Me2
1b
5 mol%
Grubbs II cat.
F3C
F3C
Ph
toluene
80 °C, 2 h
Si
Si
Me2
Me2
Ph
1,4-Bis(1-silainden-2-yl)butane 4j in which two silain-
dene skeletons were connected through a tetramethylene
3i 55%
4i 92%
Scheme 4 Reaction of hydrosilane 1b and 2a
Me2
Si
Me2Si
10 mol%
Grubbs II cat.
12 mol%
[Cp*Ru(MeCN)3]PF6
1a
+
(2.5 equiv)
toluene, 80 °C, 2 h
CH2Cl2, r.t., 2 h
Si
SiMe2
Me2
2i
3j 63%
4j 83%
Scheme 5 Synthesis of 1,4-bis(silaindenyl)butane 4j
Synlett 2010, No. 18, 2743–2746 © Thieme Stuttgart · New York

LETTER
Hydrosilylation–Metathesis Sequence Leading to 1-Silaindenes
2745
linker was easily prepared from octa-1,7-diyne (2i) and 1a
(2.5 equiv) through the hydrosilylation–RCM sequence as
shown in Scheme 5.
Me2Si
Bissilaindenes 4k–m with their conjugation extended
through phenlyne linkers were also obtained from the se-
quence employing diethynylbenzenes 2j–l and 1a
(Scheme 6).
as above
+
1a
(3k 54%)
Me2Si
Even threefold incorporation of a silaindene unit into a
triyne is facilely achieved. 1,3,5-Triethynylbenzene (2m)
underwent the hydrosilylation with hydrosilanes 1a and
1b, and the following RCM furnished 1,3,5-tris(1-silain-
den-2-yl)benzenes 4n and 4o, respectively (Scheme 7).
2j
4k 99%
Me2Si
With the substances 4k–n in which silaindene units were
linked through various benzene spacers in hand, their flu-
orescence spectra were measured. As with the case of si-
laindene 4a which exhibited its emission maximum at 387
nm with quantum efficiency of 0.83 upon irradiation at
250 nm in hexane,6c bissilaindenes 4k–m and trissilain-
dene 4n also showed intense fluorescence with various
maximum wavelengths depending on the substitution pat-
terns. The maximum wavelength of m-phenylene-linked
bissilaindene 4k (lem = 401 nm, F = 0.56) is smaller than
that of p-phenylene derivative 4l (lem = 418 nm, F =
0.87). Interaction between two silaindene skeletons might
occur more effectively through the p-phenylene spacer,
albeit the exact reason of the wavelength shift is unclear.
Dibromophenylene linked bissilaindene 4m (lem = 431
nm, F = 0.22) has an even longer maximum wavelength
than nonsubstituted phenylene derivative 4l. Trissilain-
dene 4n (lem = 406 nm, F = 0.52) has a similar maximum
wavelength with m-phenylene-linked bissilaindene 4k.
as above
+
1a
X
X
R
R
(3l 39%)
(3m 61%a)
SiMe2
4l 95%
4m 83%
2k X = H
2l X = Br
Scheme 6 Synthesis of bis(silaindenyl)benzenes 4k–m. Reagents
and conditions: hydrosilylation: alkyne 2 was reacted with hydrosi-
lane 1a (2.2–2.5 equiv) in the presence of [Cp*Ru(MeCN)3]PF6 (20
mol%) in CH2Cl2 at r.t. RCM: siladiene 3 was reacted in the presence
of Grubbs II catalyst (5 mol% for 3l and 10 mol% for 3k and 3m) in
toluene at 80 °C. a [CpRu(MeCN)3]PF6 was used as catalyst.
R
1a,b
+
Further extension of the conjugation of bissilaindene 4m
having a dibromophenylene part was achieved by palladi-
um-catalyzed cross-coupling reaction with terminal
alkynes (Scheme 8). The reaction of 4m with trimethylsi-
lylacetylene (2n) afforded 1,4-dialkynyl-2,5-bis(1-silain-
den-2-yl)benzene 8a in 90% yield. The reaction of 4m
with aryl-substituted alkynes also gave the corresponding
coupling products 8b–d. Introduction of the arylethynyl
substituents on the p-phenylene unit of 4l caused a further
red shift of the fluorescence maxima (8b: 466 nm, 8c: 528
Me2Si
as above
(3n 38%)
(3o 35%)
Me2
Si
SiMe2
R
2m
4n 99%
4o 85%
R
Scheme 7 Synthesis of tris(silaindenyl)benzenes 4n and 4o.
Reagents and conditions: hydrosilylation: alkyne 2m was reacted
with hydrosilane
1
(3.3–5 equiv) in the presence of nm, and 8d: 479 nm) with a larger Stokes shift in compar-
[Cp*Ru(MeCN)3]PF6 (21 mol% for 1a and 30 mol% for 1b) in
CH2Cl2 at r.t. RCM: siladiene 3 was reacted in the presence of Grubbs
II catalyst (15 mol%) in toluene at 80 °C.
ison to 4l. Of note was that intense solid-state fluores-
cence was observed with 8c (yellow) and 8d (green).
Me2Si
Me2Si
10 mol% PdCl2(PPh3)2
6 mol% CuI
R
+
Br
Br
R
R
Et3N, reflux, 4–18 h
2n R = SiMe3
8a 90%
8b 61%
8c 36%
8d 46%
SiMe2
SiMe2
2a R = Ph
2e R = 4-(Me2N)C6H4
2o R = 4-CF3C6H4
4m
Scheme 8 Palladium-catalyzed cross-coupling of 4m with alkynes. Reagents and conditions: 4m reacted with alkyne (10 equiv for 2n and 5
equiv for the others) in refluxing Et3N in the presence of PdCl2(PPh3)2 (10 mol%) and CuI (6 mol%).
Synlett 2010, No. 18, 2743–2746 © Thieme Stuttgart · New York

2746
T. Matsuda et al.
LETTER
L.; Huby, N.; Van der Lee, A. Synth. Met. 2006, 156, 1262.
(k) Ilies, L.; Sato, Y.; Mitsui, C.; Tsuji, H.; Nakamura, E.
Chem. Asian J. 2010, 5, 1376.
In summary, a simple and efficient method for the synthe-
sis of 1-silaindenes has been developed, where two differ-
ent ruthenium-catalyzed reactions operated well in
sequence. The trans-hydrosilylation–RCM sequence fac-
ilely installs the 1-silaindene skeleton onto a terminal
alkyne moiety, allowing the synthesis of oligo(silaindene)
derivatives which are otherwise difficult to prepare
(Scheme 9).
(4) (a) Sohn, H.; Sailor, M. J.; Magde, D.; Trogler, W. C. J. Am.
Chem. Soc. 2003, 125, 3821. (b) Sanchez, J. C.; DiPasquale,
A. G.; Rheingold, A. L.; Trogler, W. C. Chem. Mater. 2007,
19, 6459. (c) Li, Z.; Dong, Y. Q.; Lam, J. W. Y.; Sun, J.;
Qin, A.; Häußler, M.; Dong, Y. P.; Sung, H. H. Y.; Williams,
I. D.; Kwok, H. S.; Tang, B. Z. Adv. Funct. Mater. 2009, 19,
905. (d) Liu, J.; Zhong, Y.; Lam, J. W. Y.; Lu, P.; Hong, Y.;
Yu, Y.; Yue, Y.; Faisal, M.; Sung, H. H. Y.; Williams, I. D.;
Wong, K. S.; Tang, B. Z. Macromolecules 2010, 43, 4921.
(5) (a) Gilman, H.; Gorsich, R. D. J. Am. Chem. Soc. 1958, 80,
1883. (b) Braye, E. H.; Caplier, W. H. J. Am. Chem. Soc.
1961, 83, 4406. (c) Curtis, M. D. J. Am. Chem. Soc. 1969,
91, 6011. (d) Okinoshima, H.; Yamamoto, K.; Kumada, M.
J. Am. Chem. Soc. 1972, 94, 9263. (e) Ishikawa, M.;
Sugisawa, H.; Haruta, O.; Kumada, M. J. Organomet. Chem.
1981, 217, 43. (f) Fagan, P. J.; Nugent, W. A. J. Am. Chem.
Soc. 1988, 110, 2312. (g) Tamao, K.; Yamaguchi, S.; Shiro,
M. J. Am. Chem. Soc. 1994, 116, 11715. (h) Palmer, W. S.
Organometallics 1997, 16, 1097. (i) Yamaguchi, S.; Jin,
R.-Z.; Itami, Y.; Goto, T.; Tamao, K. J. Am. Chem. Soc.
1999, 121, 10420. (j) Xu, C.; Wakamiya, A.; Yamaguchi, S.
Org. Lett. 2004, 6, 3707. (k) Wang, Z.; Fang, H.; Xi, Z.
Tetrahedron Lett. 2005, 46, 499. (l) Li, L.; Xiang, J.; Xu, C.
Org. Lett. 2007, 9, 4877. (m) Ohmura, T.; Masuda, K.;
Suginome, M. J. Am. Chem. Soc. 2008, 130, 1526.
(n) Tobisu, M.; Onoe, M.; Kita, Y.; Chatani, N. J. Am. Chem.
Soc. 2009, 131, 7506. (o) Mochida, K.; Shimuzu, M.;
Hiyama, T. J. Am. Chem. Soc. 2009, 131, 8350.
1) trans-hydrosilylation
2) ring-closing metathesis
R
R
Si
Me2
Scheme 9
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.
References and Notes
(1) Present address: Department of Applied Chemistry, Tokyo
University of Science, Shinjuku, Tokyo 162-8601, Japan.
(2) For reviews, see: (a) Dubac, J.; Laporterie, A.; Manuel, G.
Chem. Rev. 1990, 90, 215. (b) Yamaguchi, S.; Tamao, K.
J. Chem. Soc., Dalton Trans. 1998, 3693. (c) Hissler, M.;
Dyer, P. W.; Réau, R. Coord. Chem. Rev. 2003, 244, 1.
(d) Chen, J.; Cao, Y. Macromol. Rapid Commun. 2007, 28,
1714. (e) Zhan, X.; Barlow, S.; Marder, S. R. Chem.
Commun. 2009, 1948. (f) Liu, J.; Lam, J. W. Y.; Tang, B. Z.
J. Inorg. Organomet. Polym. 2009, 19, 249. (g) Ohshita, J.
Macromol Chem. Phys. 2009, 210, 1360.
(3) (a) Tamao, K.; Uchida, M.; Izumizawa, T.; Furukawa, K.;
Yamaguchi, S. J. Am. Chem. Soc. 1996, 118, 11974.
(b) Tang, B. Z.; Zhan, X.; Yu, G.; Lee, P. P. S.; Liu, Y.; Zhu,
D. J. Mater. Chem. 2001, 11, 2974. (c) Liu, M. S.; Luo, J.;
Jen, A. K.-Y. Chem. Mater. 2003, 15, 3496. (d) Lee, J.; Liu,
Q.-D.; Bai, D. R.; Kang, Y.; Tao, Y.; Wang, S.
(p) Dierker, G.; Ugolotti, J.; Kehr, G.; Fröhlich, R.; Erker, G.
Adv. Synth. Catal. 2009, 351, 1080.
(6) For our recent studies, see: (a) Matsuda, T.; Kadowaki, S.;
Yamaguchi, Y.; Murakami, M. Org. Lett. 2010, 12, 1056.
(b) Matsuda, T.; Kadowaki, S.; Yamaguchi, Y.; Murakami,
M. Chem. Commun. 2008, 2744. (c) Matsuda, T.;
Yamaguchi, Y.; Murakami, M. Synlett 2008, 561.
(d) Matsuda, T.; Kadowaki, S.; Murakami, M. Chem.
Commun. 2007, 2627. (e) Matsuda, T.; Kadowaki, S.; Goya,
T.; Murakami, M. Org. Lett. 2007, 9, 133.
(7) For a review on the synthesis of heteroles by RCM, see:
Donohoe, T. J.; Orr, A. J.; Bingham, M. Angew. Chem. Int.
Ed. 2006, 45, 2664.
(8) (a) Trost, B. M.; Ball, Z. T. J. Am. Chem. Soc. 2001, 123,
12726. (b) Trost, B. M.; Ball, Z. T. J. Am. Chem. Soc. 2005,
127, 17644; and references therein.
(9) The regioselectivity of the trans-hydrosilylation was so high
that other isomers were scarcely found in the crude reaction
mixtures.
(10) Replacement of the dimethylsilylene (-SiMe2-) moiety of 1a
with diethylsilylene (-SiEt2-) moiety significantly retarded
the hydrosilylation (6%) due to severe steric congestion
around the silicon.
Organometallics 2004, 23, 6205. (e) Kim, W.; Palilis, L. C.;
Uchida, M.; Kafafi, Z. H. Chem. Mater. 2004, 16, 4681.
(f) Li, Z.; Dong, Y.; Mi, B.; Tang, Y.; Häussler, M.; Tong,
H.; Dong, Y.; Lam, J. W. Y.; Ren, Y.; Sung, H. H. Y.; Wong,
K. S.; Gao, P.; Williams, I. D.; Kwok, H. S.; Tang, B. Z.
J. Phys. Chem. B 2005, 109, 10061. (g) Yu, G.; Yin, S.; Liu,
Y.; Chen, J.; Xu, X.; Sun, X.; Ma, D.; Zhan, X.; Peng, Q.;
Shuai, Z.; Tang, B.; Zhu, D.; Fang, W.; Luo, Y. J. Am. Chem.
Soc. 2005, 127, 6335. (h) Chan, K. L.; McKiernan, M. J.;
Towns, C. R.; Holmes, A. B. J. Am. Chem. Soc. 2005, 127,
7662. (i) Geramita, K.; McBee, J.; Shen, Y.; Radu, N.;
Tilley, T. D. Chem. Mater. 2006, 18, 3261. (j) Habrard, F.;
Ouisse, T.; Stéphan, O.; Aubouy, L.; Gerbier, Ph.; Hirsch,
Synlett 2010, No. 18, 2743–2746 © Thieme Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not
be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.