Efficient synthesis of substituted diarylsilanes

Article abstract of DOI:10.1055/s-0029-1218696

A highly efficient synthesis of substituted diarylsilanes is presented. The treatment of substituted arylbromides with tert-bu-tyllithium in diethyl ether at -78 °C, followed by the addition to dichlorodiethoxysilane at the same temperature, leads to the quantitative formation of diaryldiethoxysilane. Selective substitution of the chlorine atoms allows an aqueous work up in air. Subsequently, the diaryldiethoxysilane is reduced to the corresponding diarylsi-lane by stirring with lithium aluminum hydride in diethyl ether. The product is purified by bulb-to-bulb distillation. This method does not lead to any mono- or tri-substituted products and avoids handling gaseous and explosive dichlorosilane, which is a significant advantage over previously reported procedures. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0029-1218696

SHORT PAPER
1431
Efficient Synthesis of Substituted Diarylsilanes
S
ubstituted D
i
e
arylsilanester Gigler,a Wolfgang A. Herrmann,*a Fritz E. Kühn*a,b
a
Institut für Siliciumchemie, Lehrstuhl für Anorganische Chemie, Department Chemie, Technische Universität München,
Lichtenbergstr. 4, 85747 Garching b. München, Germany
Fax +49(89)28913473; E-mail: wolfgangherrmann@ch.tum.de
Molecular Catalysis, Catalysis Research Center, Technische Universität München, Lichtenbergstr. 4, 85747 Garching b. München,
b
Germany
Fax +49(89)28913473; E-mail: fritz.kuehn@ch.tum.de
Received 9 February 2010
warm to room temperature it was quenched with water,
and processed through a simple work-up (see experimen-
tal section) to yield the diaryldiethoxysilane in nearly
quantitative yield. In a second step, the ethoxy groups
Abstract: A highly efficient synthesis of substituted diarylsilanes is
presented. The treatment of substituted arylbromides with tert-bu-
tyllithium in diethyl ether at –78 °C, followed by the addition to
dichlorodiethoxysilane at the same temperature, leads to the quanti-
tative formation of diaryldiethoxysilane. Selective substitution of were reduced by lithium aluminum hydride in diethyl
ether.9
the chlorine atoms allows an aqueous work up in air. Subsequently,
the diaryldiethoxysilane is reduced to the corresponding diarylsi-
lane by stirring with lithium aluminum hydride in diethyl ether. The
Br
Li
product is purified by bulb-to-bulb distillation. This method does
not lead to any mono- or tri-substituted products and avoids hand-
ling gaseous and explosive dichlorosilane, which is a significant ad-
vantage over previously reported procedures.
t-BuLi
–78 °C
(Et2O)
R
R
Key words: arylation, hydrosilylation, lithiation, reduction, silicon
–78 °C
(Et2O)
(EtO)2SiCl2
Secondary silanes are useful synthetic precursors for the
preparation of silicon compounds such as chloro- and
alkoxysilanes1 or as precursors for dehydrocoupling reac-
tions leading to oligo- and polysilanes.2 Especially, diphe-
nylsilane plays an important role in the hydrosilylation of
ketones.3 The use of substituted diarylsilanes allows the
electronic and steric properties to be easily adjusted.4
However, facile synthetic procedures with which to obtain
diarylsilanes are still lacking.
SiH2
Si(OEt)2
LiAlH4
(Et2O)
2
2
R
R
Scheme 1 Synthesis of substituted diarylsilanes
After a straightforward work-up (see experimental sec-
tion), the crude diarylsilane was purified by bulb-to-bulb
distillation to afford the products in very good yields (see
Table 1). The product purity was confirmed by NMR and
infrared spectroscopy, and by elemental analysis.
One method involves handling gaseous and explosive
dichlorosilane, which is reacted with Grignard reagents.5
Others start from higher chloro- or ethoxysilanes, such as
tetrachlorosilane,6 trichlorosilane7 or tetraethoxysilane.8
The drawbacks of these methods are the concurrent for-
mation of mono- and trisubstituted byproducts – if no ster-
ically demanding substituent is used – and the resulting
difficulties for the separation of the products. Further-
more, the residual chlorine substituents require anhydrous
work-up.
This ease of access to substituted diaryldiethoxysilanes
without formation of any mono- or trisubstituted species
offers a number of further applications. Selected examples
are presented in Figure 1.
Ar2SiH2
Ar2SiD2
LiAlD4
BzCl
In this work, a new, straightforward and generally appli-
cable method with which to synthesize diarylsilanes, as
depicted in Scheme 1, is reported. Dichlorodiethoxysilane
was found to be the most appropriate precursor due to the
differing reactivity of the Si–Cl and Si–O bonds. At –78 °C
the chlorine atoms are selectively substituted by the aryl-
lithium reagent, which is generated in situ, to form the di-
aryldiethoxysilane. After allowing the reaction mixture to
Ar2Si(OEt)2
LiAlH4
RM
Ar2SiCl2
Ar2SiR2
Figure 1 Important reactions involving diaryldiethoxysilanes
As mentioned above, the reduction of diaryldiethoxy-
silane with lithium aluminum hydride leads to the diaryl-
silane species.9 The use of lithium aluminum deuteride
instead, makes the corresponding deuterated diarylsilanes
SYNTHESIS 2010, No. 9, pp 1431–1432
Advanced online publication: 09.03.2010
DOI: 10.1055/s-0029-1218696; Art ID: Z03110SS
© Georg Thieme Verlag Stuttgart · New York
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x
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x
x
.2
0
1
0

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P. Gigler et al.
SHORT PAPER
1H NMR (400 MHz, C6D6): d = 1.21 (t, 3J = 7.1 Hz, 6 H, CH3), 3.27
(s, 6 H, OCH3), 3.87 (q, 3J = 7.1 Hz, 4 H, CH2), 6.87 (d, 3J = 8.5 Hz,
4 H, ArH), 7.83 (d, 3J = 8.5 Hz, 4 H, ArH).
Table 1 Synthesized Diarylsilanes
Product
Yield (%)
13C NMR (100 MHz, C6D6): d = 18.6 (s, CH3), 54.5 (s, OCH3), 58.8
(s, CH2), 114.0 (s, Ar-C3/5), 125.2 (s, Ar-C1), 137.0 (s, Ar-C2/6),
161.9 (s, Ar-C4).
29Si NMR (79 MHz, C6D6): d = –30.4 (s).
R = OEt
R = H
81
99
MeO
SiR2
2
Di(4-methoxyphenyl)silane
98
99
78
82
SiR2
SiR2
Diethoxybis(4-methoxyphenyl)silane (869 mg, 2.61 mmol) was
dissolved in anhydrous Et2O (10 mL) and added dropwise to a sus-
pension of LAH (198 mg, 5.23 mmol) in Et2O (20 mL). The mixture
was stirred for 16 h and then added to HCl (1 M, 15 mL). The organ-
ic phase was extracted with brine (10 mL), dried with Na2SO4, and
filtered, before the solvent was removed in vacuo. The crude prod-
uct was purified by bulb-to-bulb distillation (250 °C, 14 mbar) to af-
ford the pure product.
2
F
2
SiR2
96
96
74
72
2
Yield: 516 mg (81%); white solid.
IR (CH2Cl2): 2139 (Si–H) cm–1.
OMe
1H NMR (400 MHz, CDCl3): d = 3.82 (s, 6 H, OCH3), 4.89 (s, 2 H,
SiR2
3
3
SiH), 6.93 (d, J = 8.5 Hz, 4 H, ArH), 7.52 (d, J = 8.5 Hz, 4 H,
2
ArH).
13C NMR (100 MHz, CDCl3): d = 55.0 (s, OCH3), 113.9 (s, Ar-C3/
accessable.10 Another possibility is to substitute the
ethoxy groups with further alkyl or aryl substituents (R) to
obtain quaternary silane species.11 The reaction with ben-
zoylchloride (Bz-Cl), yielding diaryldichloro species, of-
fers further possibilities such as subsequent conversion
into diarylalkoxysilanes or diaminodiarylsilanes.12
5), 122.6 (s, Ar-C1), 137.1 (s, Ar-C2/6), 161.1 (s, Ar-C4).
29Si NMR (79 MHz, CDCl3): d = –34.0 (s).
Anal. Calcd for C14H16O2Si: C, 68.81; H, 6.60; Si, 11.49. Found: C,
68.78; H, 6.84; Si, 11.21.
Acknowledgment
The presented method is a straightforward procedure with
which to synthesize diarylsilanes in high yields. It avoids
the use of gaseous dichlorosilane and prevents the forma-
tion of any byproducts, thus opening new and interesting
applications in organosilicon chemistry.
We are grateful for financial support from the Wacker Chemie AG.
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Diethoxybis(4-methoxyphenyl)silane
At –78 °C, 4-bromoanisole (0.66 mL, 0.99 g, 5.29 mmol) was added
dropwise to a solution of t-BuLi (1.9 M in pentane, 5.57 mL, 10.6
mmol) in anhydrous Et2O (5 mL). The solution was stirred at this
temperature for 2 h and then transferred to a pre-cooled solution of
dichlorodiethoxysilane (0.44 mL, 0.50 g, 2.64 mmol) in Et2O (5
mL) via cannula. The solution was stirred for 1 h at –78 °C and then
allowed to warm to r.t. (CARE: gas evolution!). After quenching
the reaction mixture with H2O (8 mL), the phases were separated
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Na2SO4, filtered and the solvent removed under vacuo.
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Yield: 869 mg (99%); colorless oil.
Synthesis 2010, No. 9, 1431–1432 © Thieme Stuttgart · New York