Ruthenium-catalysed double trans-hydrosilylation of 1,4-diarylbuta-1,3- diynes leading to 2,5-diarylsiloles

Article abstract of DOI:10.1039/b703397d

Dihydrosilanes undergo double trans-hydrosilylation with 1,4-diarylbuta-1,3-diynes in the presence of a cationic ruthenium catalyst to afford 2,5-diarylsiloles: in particular, 9-silafluorene is a good hydrosilylating agent to produce spiro-type siloles in good yield. The Royal Society of Chemistry.

Full text of DOI:10.1039/b703397d

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COMMUNICATION
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Ruthenium-catalysed double trans-hydrosilylation of 1,4-diarylbuta-
1,3-diynes leading to 2,5-diarylsiloles{{
Takanori Matsuda, Sho Kadowaki and Masahiro Murakami*
Received (in Cambridge, UK) 7th March 2007, Accepted 23rd March 2007
First published as an Advance Article on the web 5th April 2007
DOI: 10.1039/b703397d
Table 1 Reaction of 1,4-diphenylbuta-1,3-diyne (2a) with dihydrosi-
lanes 3a–d in the presence of [Cp*Ru(MeCN)3]PF6 (1)a
Dihydrosilanes undergo double trans-hydrosilylation with 1,4-
diarylbuta-1,3-diynes in the presence of a cationic ruthenium
catalyst to afford 2,5-diarylsiloles: in particular, 9-silafluorene is
a good hydrosilylating agent to produce spiro-type siloles in
good yield.
Studies on the synthesis of heteroles and metalloles continue to
be of great importance owing to their unique photophysical
and electronic properties.1 2,5-Disubstituted heteroles of group
14–16 elements can be synthesised by [4 + 1]-type annulation
reactions of 1,3-diynes with appropriate group 14–16 element
compounds (eqn (1)).2 For example, a thermal reaction of hexa-
2,4-diyne with dibutyltin dihydride affords the corresponding
stannole.2g However, no [4 + 1]-type annulation reaction of 1,3-
diynes producing siloles has been reported. Ever increasing interest
in silicon-based s- and p-conjugated molecules3 prompted us to
explore an efficient process for the preparation of siloles from 1,3-
diynes. We herein wish to report a new synthesis of 2,5-diarylsiloles
by means of catalytic double hydrosilylation.4
Dihydrosilane
Silole
Entry 3 (R2SiH2)
Equiv. mol% Ru
4
Yieldb
1
2
3
4
5
6
a
3a (Et2SiH2)
3b (PhMeSiH2)
3c (Ph2SiH2)
3d (9-silafluorene) 3.0
3d
3d
3.0
3.0
3.0
20
20
20
20
20
10
4aa 0%
4ab trace
4ac
4ad 79%
4ad 75%
4ad 58%
51%
1.5
3.0
Diyne 2a and silane 3 were reacted in 1,2-dichloroethane at rt for
b
10 h in the presence of 1. Isolated yield by preparative TLC.
ð1Þ
Hydrosilylation of alkynes is catalysed by various transition
metal complexes, and in most cases, cis adducts are formed.5
However, a synthesis of silole derivatives by hydrosilylation of 1,3-
diynes necessitates a trans addition process. Trost et al. reported
that ruthenium complex, [Cp*Ru(MeCN)3]PF6 (1), catalyses trans-
hydrosilylation of alkynes.6 We tried to apply this catalyst to the
reaction of 1,3-diynes and dihydrosilanes (Table 1). No reaction
occurred when 1,4-diphenylbuta-1,3-diyne (2a) was treated with
Et2SiH2 (3a, 3 equiv.) in the presence of 1 (20 mol%) in 1,2-
dichloroethane (entry 1). Only a trace amount of silole was
obtained when PhMeSiH2 (3b) was used (entry 2). Gratifyingly,
the desired double hydrosilylation of 2a occurred with Ph2SiH2
(3c) to afford 1,1,2,5-tetraphenylsilole (4ac) in 51% yield
(entry 3).7,8 9-Silafluorene (3d)9 was found to be a better
hydrosilylating agent to produce spiro-type silole 4ad in 79% yield
(entry 4).10 The reaction proceeded efficiently to give 4ad in 75%
yield even with 1.5 equiv. of 3d (entry 5). The yield of 4ad
decreased to 58% with 10 mol% of the catalyst (entry 6).
Chloro(phenyl)silane (3e) also successfully participated in the
reaction with 2a to produce 1-chlorosilole derivative 4ae
(Scheme 1). The following treatment with methyllithium afforded
1-methyl-1-phenylsilole 4ab in 61% yield, which was difficult to
obtain through a direct double hydrosilylation process using 3b.
Ethynylation of 4ae with HCMCMgBr gave ethynylsilole 5
(40%).11
Thus, the double hydrosilylation of 1,3-diynes provides a new
synthetic route to 2,5-diarylsiloles. Next, a wide variety of 1,3-
diynes were subjected to the double trans-hydrosilylation reaction
with 3d (Table 2).§ Some results obtained with 3c are included
therein.
Department of Synthetic Chemistry and Biological Chemistry, Kyoto
University, Katsura, Kyoto, 615-8510, Japan.
E-mail: murakami@sbchem.kyoto-u.ac.jp; Fax: +81 (75) 383-2748
{ Electronic supplementary information (ESI) available: Experimental
procedures and characterization data for new compounds. See DOI:
10.1039/b703397d
{ This paper is dedicated to the late Professor Yoshihiko Ito in
appreciation of his inspiring mentorship.
a
Scheme 1 Reagents and conditions:
b
HCMCMgBr, THF, 0 y 50 uC.
MeLi, Et2O, 278 uC y rt,
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Table 2 Ruthenium-catalysed double trans-hydrosilylation of 1,3-
diynes 2b–n with 9-silafluorene (3d)a
Entry 1,3-diyne 2 (R)
Silole 4 %yieldb,c
1
2
3
4
5
6
7
8
9
2b (2-naphthyl)
2c (4-MeC6H4)
2d (4-MeOC6H4)
2e (4-MeCOC6H4)
2f (4-FC6H4)
4bd
4cd
4dd
4ed
4fd
4gd
4hd
4id
59 (55)
77 (65)
78 (75)
25
65
71
62
73
76 (67)
50
63
Scheme 2
2g (3-BrC6H4)
2h (4-Me3SiC6H4)
materials. Thus, the present reaction was applied to the synthesis
of extended p-conjugated silole derivatives. m-Bis(diynyl)benzene 6
that possess two 1,3-diyne moieties reacted with two molecules of
silane 3d to provide m-phenylenebissilole 7 (Scheme 2).
d
2i (3-(pin)BC6H4
2j (3-thienyl)
2k (cyclohexenyl)
)
4jd
4kd
4ld
10
11
As another approach to extend silole-containg p-conjugation,
we carried out polymerization by a cross-coupling reaction.
Suzuki–Miyaura coupling of diborylsilole 4id with 1,4-dibromo-
benzene 8 in the presence of a palladium catalyst furnished
alternating copolymer 9 in 99% yield (Scheme 3).
12
13
a
4md
4nd
56
69
Selected photophysical and thermal data for the produced siloles
are shown in Table 3. Tetraphenylsilole 4ac exhibits its absorption
maximum at 382 nm and fluorescence maximum at 467 nm.
Substitution of the –SiPh2– moiety with silafluorenylene causes red
shifts of both the absorption and fluorescence maxima. Siloles 4ac
and 4gd have high quantum efficiencies (WF) of 0.64 and 0.65,
respectively. Introduction of the spiro linkage increases the glass
transition temperature (Tg) and melting point (Tm); 4hd has Tg of
90 uC and 4jd has Tm of 233 uC.
Reaction conditions: 2 (1 equiv.), 3d (3 equiv.), 1 (20 mol%), 1,2-
b
c
dichloroethane, rt, 10 h. Isolated yield. Yields in parentheses are
d
results with Ph2SiH2 (3c). pin = pinacolato (–OCMe2CMe2O–).
The production of 2,5-diarylsiloles from 1,3-diynes and
dihydrosilanes can be accounted for by assuming that the initial
ruthenium-catalysed trans-hydrosilylation is followed by the
2-Naphthyl-substituted 1,3-diyne 2b afforded the corresponding
silole 4bd in 59% yield (entry 1), whereas 1-naphthyl-substituted
1,3-diyne failed to react with 3d presumably due to steric reasons.
1,3-Diynes (2c and 2d) having electron-donating groups on the
para positions of the phenyl rings provided the siloles (4cd and 4dd)
in good yields (entries 2 and 3). In contrast, introduction of
electron-withdrawing acetyl groups significantly retarded the
reaction (entry 4). Various heteroatom functionalities including
halogens, silicon, and boron on the phenyl rings survived
unscathed under the reaction conditions (entries 5–8). Other sp2
carbon-substituted diynes like bis(3-thienyl)butadiyne 2j and
dicyclohexenylbutadiyne 2k worked well (entries 9 and 10). On
the other hand, hexa-2,4-diyne (R = Me) failed to react with 2d,
and 1,4-bis(trimethylsilyl)buta-1,3-diyne (R = SiMe3) afforded a
complex mixture of products. These results suggest that 1,3-diynes
with the 1- and 4-carbons being connected to sp2 carbons are
suitable substrates for the present silole forming reaction. The
reaction of unsymmetrical 1,3-diynes was also examined. 1-Phenyl-
4-(4-vinylphenyl)buta-1,3-diyne (2l) furnished silole 4ld with the
vinyl group remaining intact (entry 11). Siloles 4md (R = OMe)
and 4nd (R = CF3) having electronically biased aryl groups were
produced by hydrosilylation of the corresponding unsymmetrical
1,3-diynes 2m and 2n (entries 12 and 13).
second intramolecular hydrosilylation in
a trans fashion
(Scheme 4).12 In order to support this assumption, 2-alkynylphe-
nylsilane 10 was prepared and subjected to the reaction conditions.
Intramolecular hydrosilylation occurred in a trans fashion to give
1-silaindene 11 in 72% yield (eqn (2)).13 This experiment
corroborates the successive double hydrosilylation mechanism.
The incorporation of silole cores into a p-conjugated backbone
is of particular interest because silole-containing oligomers and
polymers have been regarded as promising electron-transporting
Scheme 3
2628 | Chem. Commun., 2007, 2627–2629
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under an argon atmosphere for 10 h at room temperature, the reaction
mixture was concentrated under reduced pressure. The residue was purified
by thin-layer chromatography (hexane:AcOEt = 10 : 1) to give
29,59-diphenylspiro[9-silafluorene-9,19-silole] (4ad, 91.4 mg, 79%).
Table 3 Photophysical and thermal properties of siloles
UV-visa
fluorescenceb
Silole
labs (nm)
log e
lem (nm)
WF
Tg (uC)
Tm (uC)
1 (a) U. Salzner, J. B. Lagowski, P. G. Pickup and R. A. Poirier, Synth.
Met., 1998, 96, 177; (b) D. Delaere, M. T. Nguyen and
L. G. Vanquickenborne, Phys. Chem. Chem. Phys., 2002, 4, 1522; (c)
Y. Narita, I. Hagiri, N. Takahashi and K. Takeda, Jpn. J. Appl. Phys.,
2004, 43, 4248.
2 For syntheses of heteroles from 1,3-diynes, see: (a) K. E. Schulte,
J. Reisch and L. Hoerner, Chem. Ber., 1962, 95, 1943; (b) R. F. Curtis,
S. N. Hasnain and J. A. Taylor, Chem. Commun., 1968, 365; (c)
V. A. Potapov, N. K. Gusarova, S. Amosova, A. S. Kashik and
B. A. Trofimov, Sulfur Lett., 1985, 4, 13; (d) J. Reisch and K. E. Schulte,
Angew. Chem., 1961, 73, 241; (e) G. Ma¨rkl and R. Potthast, Angew.
Chem., 1967, 79, 58; (f) G. Ma¨rkl, H. Hauptmann and A. Merz,
J. Organomet. Chem., 1983, 249, 335; (g) A. J. Ashe, III and
T. R. Diephouse, J. Organomet. Chem., 1980, 202, C95.
3 For a leading reference, see: S. Yamaguchi and K. Tamao, J. Chem.
Soc., Dalton Trans., 1998, 3693.
4ac
4ad
4gd
4hd
4jd
a
382
391
390
401
398
4.26
4.12
4.24
4.34
3.95
b
467
490
488
500
493
0.64
0.35
0.65
0.31
0.26
35
65
52
90
81
169
197
157
203
233
Measured in CHCl3. Measured in hexane. Determined with
reference to quinine sulfate in 0.1 N H2SO4 and anthracene in EtOH
(excited at 250 nm).
4 We recently reported an iridium-catalysed [2 + 2 + 2] cycloaddition
reaction en route to 9-silafluorene derivatives: T. Matsuda, S. Kadowaki,
T. Goya and M. Murakami, Org. Lett., 2007, 9, 133.
5 I. Ojima, Z. Li and J. Zhu, in The Chemistry of Organic Silicon
Compounds, ed. Z. Rappoport and Y. Apeloig, John Wiley & Sons,
New York, 1998, vol. 2, ch. 29.
Scheme 4
6 (a) B. M. Trost and Z. T. Ball, J. Am. Chem. Soc., 2001, 123, 12726; (b)
B. M. Trost and Z. T. Ball, J. Am. Chem. Soc., 2005, 127, 17644 and
references therein.
7 For other preparative methods of 2,5-diarylsiloles, see: (a) W. H. Atwell,
D. R. Weyenberg and H. Gilman, J. Org. Chem., 1971, 32, 885; (b)
T. J. Barton, W. D. Wulff, E. V. Arnold and J. Clardy, J. Am. Chem.
Soc., 1979, 101, 2733; (c) S. Yamaguchi, R.-Z. Jin, K. Tamao and
F. Sato, J. Org. Chem., 1998, 63, 10060; (d) M. Katkevics,
S. Yamaguchi, A. Toshimitsu and K. Tamao, Organometallics, 1998,
17, 5796.
ð2Þ
In summary, we have discovered a new double trans-
hydrosilylation reaction of 1,3-diynes catalysed by a cationic
ruthenium complex. The reaction enabled the rapid assembly of
2,5-diarylsiloles from readily available starting materials under
mild conditions.
8 When deuterated silane 3c-d2 was used, the deuterium atoms were
incorporated at the 3- and 4-positions of the silole in 93% D.
9 J. Y. Corey, C. S. John, M. C. Ohmsted and L. S. Chang, J. Organomet.
Chem., 1986, 304, 93.
10 Other related cationic ruthenium complexes afforded inferior results:
[CpRu(MeCN)3]PF6: 8%; [Cp*Ru(MeCN)3]OTf: 75%.
We thank the Japan Society for the Promotion of Science for
the fellowship support to S. K.
11 1,2,5-Triphenylsilole (30%) was also obtained as a byproduct.
12 For a DFT calculation of the ruthenium-catalysed trans-hydrosilylation,
see: L. W. Chung, Y.-D. Wu, B. M. Trost and Z. T. Ball, J. Am. Chem.
Soc., 2003, 125, 11578.
13 G. Ma¨rkl and K.-P. Berr, Tetrahedron Lett., 1992, 33,
1601.
Notes and references
§ General procedure: To a solution of [Cp*Ru(MeCN)3]PF6 (1, 30.3 mg,
0.060 mmol) in 1,2-dichloroethane (1.5 mL) was added a solution of 1,4-
diphenylbuta-1,3-diyne (2a, 60.7 mg, 0.30 mmol) and 9-silafluorene (3d,
164.1 mg, 0.90 mmol) in 1,2-dichloroethane (1.5 mL). After being stirred
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Chem. Commun., 2007, 2627–2629 | 2629