Triallyl(aryl)silanes serve as a convenient agent for silicon-based cross-coupling reaction of aryl halides

Article abstract of DOI:10.1016/j.jorganchem.2003.08.041

Triallyl(aryl)silanes, stable and easily accessible arylsilanes, were found to react with aryl bromides in the presence of a palladium catalyst (PdCl₂-PCy₃) and tetrabutylammonium fluoride (TBAF) in good yields. The scope of the reaction is broad, and a wide variety of functional groups are tolerant. Allyl groups on Si are readily cleaved upon treatment with TBAF to form fluorosilanes, silanepolyols, siloxanes and/or their mixed forms, which might be responsible for high efficiency of the reaction.

Full text of DOI:10.1016/j.jorganchem.2003.08.041

Journal of Organometallic Chemistry 687 (2003) 570Á573
/
www.elsevier.com/locate/jorganchem
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Triallyl(aryl)silanes serve as a convenient agent for silicon-based
cross-coupling reaction of aryl halides
Yoshiaki Nakao, Takuro Oda, Akhila K. Sahoo, Tamejiro Hiyama *
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8501, Japan
Received 23 June 2003; accepted 1 August 2003
Dedicated to Professor J.P. Gen eˆ t on the occasion of his 60th birthday
Abstract
Triallyl(aryl)silanes, stable and easily accessible arylsilanes, were found to react with aryl bromides in the presence of a palladium
catalyst (PdCl2ÁPCy ) and tetrabutylammonium fluoride (TBAF) in good yields. The scope of the reaction is broad, and a wide
variety of functional groups are tolerant. Allyl groups on Si are readily cleaved upon treatment with TBAF to form fluorosilanes,
/
3
silanepolyols, siloxanes and/or their mixed forms, which might be responsible for high efficiency of the reaction.
2003 Elsevier B.V. All rights reserved.
#
Keywords: Palladium; Cross-coupling; Triallyl(aryl)silane; Aryl iodide; Aryl bromide
Transition metal-catalyzed cross-coupling reaction of
arylmetals with aryl halides or pseudo halides is now a
straightforward way to construct biaryls that play
important roles in many functional organic molecules
such as electronic materials and pharmaceuticals [1]. Of
organometallic reagents employed for this reaction,
organosilicon compounds are attractive in view of
availability, stability and non-toxicity [2]. We and others
have demonstrated that aryl(halo)silanes [3], trialkox-
y(aryl)silanes [4], arylsilanols [5] and poly(phenylsilox-
ane) [6] can be employed for this reaction. However,
these arylsilanes require at least one heteroatom on
silicon to enhance the electrophilicity and thus are
generally sensitive to water, a base and an acid. Stable
all-carbon-substituted arylsilanes would overcome these
drawbacks. As for alkenylsilanes, we recently reported
that alkenyl(2-thienyl)silanes react with aryl- and alke-
nylhalides under very mild conditions [7]. This reaction
has recently been applied to the stereocontrolled synthe-
sis of poly(p-phenylenevinylene)s by Ozawa and
Katayama [8]. They also reported that alkenyl[3,5-
bis(trifluoromethyl)phenyl]silanes and alkenyl(4-tri-
fluoromethylphenyl)silanes are also effective [9]. Den-
mark demonstrated that alkneylsilacyclobutanes are
excellent coupling partners [10]. Yoshida and Itami
also reported that alkenyl(2-pyridyl)dimethylsilanes are
effective [11]. Very recently, Trost reported alkenyl(ben-
zyl)dimethylsilanes [12]. In these reactions, (hetero)aryl
or benzyl group acts as a good leaving group and
silacyclobutane undergoes ring-opening reaction upon
treatment with fluoride ion to form possibly alkenylsil-
anols and/or alkenylsiloxanes [13]. We also found that
allyl group on silicon atom worked in a manner similar
to 2-thienyl group [14]. However, these strategies have
been limited only to cross-coupling of alkenylsilanes.
Herein we report that triallyl(aryl)silanes (1) are stable
toward moisture, bases and acids [15], and react with
aryl bromides and an aryl iodide smoothly in good
yields in the presence of a palladium catalyst and TBAF
(
Eq. (1)).
ð1Þ
First, we examined the reaction of triallyl(phenyl)sil-
ane (1a) [16] with 4-iodobenzotrifluoride (2) under
* Corresponding author.
E-mail address: thiyama@npc05.kuic.kyoto-u.ac.jp (T. Hiyama).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.08.041

Y. Nakao et al. / Journal of Organometallic Chemistry 687 (2003) 570Á
/573
571
various conditions. After treatment of 1a (1.1 mmol)
with TBAF (4.4 mmol) in DMSOÁH O (10:1) at room
/
2
temperature, the mixture was treated with 2 and Pd
catalyst (5 mol%) (Scheme 1). Among various catalyst
systems examined, the one consisting of PdCl and PCy
2
3
Scheme 1.
(1:2) was found to be optimal, and the corresponding
biaryl was obtained in 97% yield (Table 1, entry 1) [17].
Other ligands (PPh , P(t-Bu) and 1,3-bis(diphenylphos-
3
Table 1
Cross-coupling reaction of triallyl(phenyl)silane with aryl bromides
3
a
phino)propane), silanes (diallyl(methyl)phenylsilane and
allyl(dimethyl)phenylsilane), and solvents (DMFÁH O,
dioxaneÁH O, tolueneÁH O, and DMSO) were inferior
18].
The scope of the present reaction is demonstrated in
Table 1. Since the reaction of 4-bromobenzotrifluoride
entry 1) proceeded similarly (95%), the study was
/
2
/
/
2
2
[
(
conducted using aryl bromides having either an elec-
tron-withdrawing or -donating group at 4- and/or 3-
position to give coupled product in good yields (entries
2
Á
/
11). In some cases (entries 6, 8, 9 and 11), a different
DMSOÁH O ratio led to a slight increase of yields,
/
2
though the effect of the amount of water is unclear at
present. Sterically demanding substrates also gave the
corresponding biaryls in high yields (entries 12Á15).
/
Heteroaryl bromides were also applicable to the present
reaction. Thus, 2-bromopyridine and 3-bromobenzo-
thiophene afforded the products in good yields (entries
1
6 and 17).
Next, variously substituted triallyl(aryl)silanes [19]
were examined as shown in Table 2. Although elec-
tron-rich 4-methoxyphenyl coupled with electron-rich
and poor aryl bromides in high yields (entries 1Á3), 4-
/
trifluoromethylphenyl- and 2-methylphenylsilane re-
acted in modest yields due presumably to their lower
nucleophilicity and steric hindrance (entries 4 and 5),
respectively. In these cases, volatile protonolysis prod-
ucts of coupling partners might be formed since GC
showed no starting materials and only a small amount
of homo-coupling of aryl bromide other than the desired
biaryls.
Although we could not identify the reactive inter-
mediate directly from 1a, treatment of allyldi-
methyl(phenyl)silane, instead of 1a, with TBAF in
DMSOÁ/H O led to the formation of silanol (3) and
2
siloxane (4) by GCÁ/MS (Scheme 2). Thus, three allyl
groups on Si would leave upon treatment with TBAF
and water to form possibly fluorosilanes, silanepolyols,
siloxanes and/or their mixed forms. Some evidence is
presented by Denmark [13], Yoshida [11] and us [5].
Three oxygen atoms make Si atom acidic enough to
accept fluoride ion to form reactive pentacoordinate
silicates. Since diallyl(methyl)arylsilane or allyl(dimeth-
yl)arylsilanes were not effective for the present reaction
as mentioned above, arylsilanediols or arylsilanols
would not be active under the present condition
presumably due to less acidity of Si, although we and

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Y. Nakao et al. / Journal of Organometallic Chemistry 687 (2003) 570Á573
/
Scheme 2.
Table 2
Cross-coupling reaction of substituted triallyl(aryl)silane with aryl
References
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(
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In conclusion, we have demonstrated that triallyl(ar-
yl)silanes are highly effective and convenient arylating
reagents for the cross-coupling reaction with aryl
bromides and iodides. The reaction tolerates a diverse
range of functional groups. Stability and accessibility of
the reagents compared with previous arylsilanes are
worthy of note. Efforts to expand the scope of the
present chemistry to aryl chlorides, other organic
halides, and other organosilanes are ongoing subjects
in our laboratory.
[
[
8] H. Katayama, M. Nagao, R. Moriguchi, F. Ozawa, J. Organo-
met. Chem. 676 (2003) 49.
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(
(
b) K. Itami, T. Nokami, J.-i. Yoshida, J. Am. Chem. Soc. 123
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[
[
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period and brief treatment with 1 M HCl aq. does not affect, slow
decomposition (ca. 20% conv.) was observed after 1 h treatment.
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Koten, Tetrahedron Lett. 39 (1998) 2397; (b) X. Deng, A.
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Acknowledgements
The authors thanks a Grant-in-Aid for Scientific
Research on Priority Areas ‘‘Reaction Control of
Dynamic Complex’’ and Grant-in-Aid for COE Re-
search on ‘‘Elements Science’’, No. 12CE2005 and on
[
/
3
16] Treatment of PhÁSiCl with 3.3 equivalents of allylmagnesium
‘
‘United Approach to New Material Science’’ from the
bromide gives 1a (89% yield).
17] General procedure: A mixture of triallyl(phenyl)silane (0.25 g,
Ministry of Education, Culture, Sports, Science and
Technology, Japan for financial supports. A.K.S. thanks
JSPS for the award of postdoctoral fellowship.
[
1
.10 mmol) TBAF×
(10:1, 5.0 ml) was degassed by three freezeÁ
/3H
2
O (1.40 g, 4.40 mmol) in DMSOÁ
/
2
H O
/
thaw cycles, and

Y. Nakao et al. / Journal of Organometallic Chemistry 687 (2003) 570Á
/573
573
stirred at room temperature for 1 h. To this were added PdCl
mg, 50 mmol), PCy (28 mg, 0.100 mmol) and 4-iodobenzotri-
fluoride (0.27 g, 1.00 mmol). The resulting mixture was stirred at
0 8C for 3 h before quenching with water, and the resulting
mixture was extracted with Et O. Drying over MgSO , evapora-
tion of the solvent, and purification by flash chromatography
2
(8.9
using silica gel afforded 4-trifluoromethylbiphenyl (0.22 g,
97%).
[18] Details of the results will be presented in a forthcoming full paper.
3
8
[19] Triallyl(aryl)silanes were prepared by sequential reaction of SiCl
4
2
4
with arylmagnesium bromide and allylmagnesium bromide. See,
also Ref. [15].