An efficient and simple method for the preparation of symmetrical disiloxanes from hydrosilanes by Lewis acid-catalyzed air oxidation

Article abstract of DOI:10.1016/j.tetlet.2009.10.020

Symmetrical disiloxanes were prepared in high yields by air oxidation of mono, di, and trihydrosilanes under Lewis acid catalysis.

Full text of DOI:10.1016/j.tetlet.2009.10.020

Tetrahedron Letters 50 (2009) 7166–7168
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An efficient and simple method for the preparation of symmetrical
disiloxanes from hydrosilanes by Lewis acid-catalyzed air oxidation
*
Madabhushi Sridhar , Beeram China Ramanaiah, Chinthala Narsaiah, Mudam Kumara Swamy,
Bellam Mahesh, Mallu Kishore Kumar Reddy
Fluoroorganics Division, Indian Institute of Chemical Technology, Hyderabad 500 607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Symmetrical disiloxanes were prepared in high yields by air oxidation of mono, di, and trihydrosilanes
under Lewis acid catalysis.
Received 4 September 2009
Revised 30 September 2009
Accepted 5 October 2009
Available online 8 October 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Symmetrical disiloxanes
Hydrosilanes
Air oxidation
Lewis acid catalyst
Symmetrical disiloxanes are important class of compounds in
in 97% yield. This reaction was found to proceed with equal effi-
ciency in solvents such as tetrahydrofuran (THF), dichloromethane,
chloroform and no reaction was observed in hexane and under sol-
vent-free conditions. We have studied aerobic oxidation of a vari-
1
silicon chemistry. Some of the symmetrical disiloxanes are known
2
to have important applications as liquid crystals and pharmaco-
logically active compounds3 (Fig. 1). Recently, they have drawn
more attention as useful intermediates in organic synthesis. For
3
ety of mono, di and trihydrosilanes in THF using InBr as a catalyst
4
5
9
example, the recent reports of Napier et al. and Sore et al. show
novel applications of aryl disiloxanes and vinyl disiloxanes, respec-
tively, as efficient coupling partners in Hiyama cross-coupling
reactions. Mézailles et al.6 have employed 1,3-bis(phenyleth-
ynyl)tetramethyldisiloxane as a building block in the synthesis of
novel macrocycles.
under similar conditions and obtained corresponding symmetrical
disiloxanes in high yields (85–99%). These results are shown in Ta-
2 2
ble 2. The compounds Me SiHCl and MeHSi(OEt) , which were
substituted with electronegative atom such as Cl and O have, how-
ever, remained unreactive under the reaction conditions.
InBr
3
forms a stable solid complex [InBr
3
Á(THF)
2
] with THF.10 In
The general methods available in literature for the preparation
of symmetrical disiloxanes are intermolecular condensation of sil-
the present study, THF was used as a solvent and the reaction mix-
ture separated into two liquid layers upon removal of the solvent
after completion of the reaction, in which, the upper layer was
7
8
anols, and reaction of polysiloxanes with Grignard reagents. Here
we report for the first time, a simple, mild, and non-aqueous meth-
od for the preparation of Symmetrical disiloxanes in high yields
from mono, di, and trihydrosilanes by Lewis acid-catalyzed air oxi-
dation, which proceeds with the evolution of hydrogen gas as
shown in Scheme 1.
found to be disiloxane and the bottom layer was InBr
plex. We have recovered 81% of InBr as THF complex (white pow-
der) from the bottom layer by removal of the solvent under
vacuum. The recovered InBr complex was also found to
3
–THF com-
3
3
Á(THF)
2
be highly active in catalyzing air oxidation of hydrosilane to disil-
In our preliminary study, we have investigated aerobic oxida-
tion of triethylsilane to 1,1,1,3,3,3-hexaethyl disiloxane using Le-
oxane. For example, oxidation of dimethyl-p-tolyl silane 1l using
InBr as catalyst and THF as solvent gave disiloxane 2l in 98% yield.
3
wis acids such as InCl
Bi(OTf) , TaCl , BF
ÁEt
K10 clay as catalysts. The results are shown in Table 1.
In this study, InBr was found to be an excellent catalyst in pro-
moting this reaction, which gave 1,1,1,3,3,3-hexaethyl disiloxane
3
, InBr
3
, SbCl
3
, Cu(OTf)
3
, CuCl
2
Á2H
2
O, NbCl
5
,
The recovered catalyst from the first cycle, that is, InBr
3
–THF com-
9
3
5
3
2
O, FeCl
3
, La(OTf)
3
, and montmorillonite
plex, gave 2l in 92% yield under similar conditions.
1
1
Recently, Berberova reported intensive evolution of hydrogen
when hydrosilanes were subjected to single electron electrochem-
ical oxidation, which was associated with the fragmentation of
radical cation of hydrosilane into silyl cation and hydrogen. In
the present reaction also, oxidation of hydrosilane was accompa-
nied with the evolution of hydrogen. Since Lewis acids (metal
3
*
Corresponding author. Tel.: +91 040 27191772; fax: +91 040 27160387.
E-mail address: smiict@gmail.com (M. Sridhar).
0
040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.10.020

M. Sridhar et al. / Tetrahedron Letters 50 (2009) 7166–7168
7167
CH3 CH3
F
OOC
O-(CH ) -Si-O-Si-(CH ) -O
COO
F
2
p
2 p
n
n
CH3 CH3
Liquid crystal
Si
N
Si
O
Muscle relaxant
Figure 1.
SET
Lewis Acid
air, THF, rt
R SiH + InBr
3
[R SiH] + [InBr3]
3
R4-nSiHn
n=1,2,3
R4-nHn-1Si-O-SiHn-1R4-n + H2
5-99% (with InBr3)
3
O /polar solvent
2
8
[
R SiH]
R Si +
H
3
R=alkyl, aryl, alkynyl
3
Scheme 1.
R Si + [InBr ]
R Si + InBr
3
3
3
3
H + H
H2
Table 1
Lewis acid-catalyzed air oxidation of triethylsilane to 1,1,1,3,3,3- hexaethyldisiloxane
R SiH + H
R
3
Si + H
2
3
2R
Si + O
R
3
Si-O-O-SiR
2R Si-O-SiR
3
3
3
2
S.No.
Lewis acid
AlCl
ZnCl
FeCl
CuCl
Cu(OTf)
NbCl
Bi(OTf)
BF
ÁEt
Reaction time (h)
Yielda (%)
2
R Si
3
1
2
3
4
5
6
7
8
9
3
6
6
6
6
6
6
6
6
6
6
6
6
6
3
N.R.
20
Trace
51
62
55
R Si-O-O-SiR
3
3
3
2
3
Scheme 2.
2
Á2H
2
O
3
5
3
70
halides) are known to induce single electron transfer (SET) reac-
tions, it appears that Lewis acid-catalyzed air oxidation of hyd-
12
3
2
O
N.R.
Trace
N.R.
90
N.R.
90
I
2
rosilane to disiloxane involves SET pathway as the initial step of
the process as shown in Scheme 2. Polar solvents are favorable to
SET reactions and the present reaction was found to proceed well
only in polar solvents.
In conclusion, this work describes the first observation of Lewis
acid-catalyzed efficient and selective aerobic oxidation of hydrosil-
anes to symmetrical disiloxanes. We have developed a mild, effi-
cient, and environmentally friendly method for selective
preparation of symmetrical disiloxanes from mono, di, and trihy-
10
11
12
13
14
K10 clay
SbCl
La(OTf)
InCl
InBr
3
3
3
3
97
a
Isolated yields; all the reactions were carried out using 5 mol % catalyst.
drosilanes by air oxidation using InBr
recoverable and recyclable.
3
as a catalyst, which is easily
Table 2
InBr
3
-catalyzed air oxidation of hydrosilanes to disiloxanes
InBr3
R4-nSiHn
n=1,2,3
R4-nHn-1Si-O-SiHn-1R4-n
Acknowledgment
air, THF, rt
Entry Disiloxane
Reaction time
h)
Yielda
(%)
B.C.R. is thankful to the Director, IICT, Hyderabad. C.N. is thank-
ful to UGC, New Delhi, M.K., B.M., and M.K.K.R. are thankful to CSIR,
New Delhi, for financial support in the form of Junior Research
Fellowship.
(
a
b
c
d
e
f
g
h
i
PhMe
2
Si–O–SiMe
MeSi–O–SiMePh
Si–O–SiPh
2
Ph
2
2
5
3(3 )
24
12
5
99
92
95
97(90 )
96
Ph
Ph
2
2
3
3
b
b
Et
(i-Pro)
PhC„C–Si(Me)
(n-C
PhMeHSi–O–SiHMePh
Ph HSi–O–SiHPh
Et HSi–O–SiHEt
(t-Bu) HSi–O–SiH(t-Bu)
(p-MeC )Me Si–O–Si (p-
MeC )Me
(n-C 13)H
3
Si–O–SiEt
3
References and notes
3
Si–O–Si(i-Pro)
3
2
–O–(Me)
2
Si–C„CPh
85
87
99
97
98
85
98
1
.
.
Chemistry and Technology; Koerner, G., Schulze, M., Weis, J., Eds.; Vulkan: Essen,
Germany, 1991.
(a) Engel, M.; Hisgen, B.; Keller, R.; Kreuder, W.; Reck, B.; Ringsdorf, H.;
Schmidt, H.-W.; Tschirnerp, P. Pure Appl. Chem. 1985, 57, 1009–1014; (b) Zhi-
qian, Z.; Yu-fei, L.; Dong, Z.; Xin-hua, W.; Qi-feng, Z. Chin. J. Poly. Sci. 2000, 18,
8
H
17
3
) Si–O–Si(n-C
8
H
)
17 3
4
4
3
24
4
2
2
2
j
k
l
2
2
2
2
101–107; (c) Yusuke, K.; Hirokuni, I.; Kishimoto, A. Polym. Bull. 1996, 36, 653–
H
6 4
2
658; (d) Matthias, R.; Alessandro, C.; Christophe, B.; Vladimir, L.; Yuri, P. P.;
6
H
4
2
Nils, O.; Jagdish, K. V.; Giancarlo, G. Ferroelectrics 2004, 309, 111–119; (e)
Mohammed, I.-E.; Antoine, S.; Daniel, G.; Joanna, N.; Philip, H.; Harry, J. C. J.
Phys. II France 1996, 6, 271–279; (f) Corrie, T. I.; Peter, A. H. Chem. Soc. Rev. 2007,
m
6
H
2
Si–O–SiH
2
(n-C
6
H
13
)
5
90
a
Isolated yields; all the products gave satisfactory 1H, 13C NMR, IR and Mass
spectral data.
Corresponds to air oxidation of neat hydrosilane with preformed InBr
complex.
3
6, 2096–2124.
3.
(a) Levier, R. R.; Chandler, M. L.; Wendel, S. R. The Pharmacology of Silanes and
Siloxanes. In The Biochemistry of Silicon and Related Problems; Bendz, G.,
Lindquist, I., Eds.; Plenum: New York, 1978; p 473; (a) Sander, B. The Value and
b
3
–THF

7
168
M. Sridhar et al. / Tetrahedron Letters 50 (2009) 7166–7168
NMR (CDCl
À1
New Directions of Silicon Chemistry for Obtaining Bioactive Compound In
Silicon Chemistry; Cory, J. Y., Corey, E. R., Eds.; Ellis Horwood Ltd: England, 1988;
pp 135–144. Chapter 13.
3
, 75 MHz) d = 139.7, 137.5, 132.6, 128.5, 21.8, 1.0; IR (Neat, cm+ ): m
3056, 2967, 1426, 1245, 1108, 1050, 837, 789; EIMS (m/z, %): 314 (M , 23),
299(65), 267(25), 225(20), 223(35), 207(84), 179(24), 149(32), 93(54), 77(23),
4
.
.
.
.
.
.
Napier, S.; Marcuccio, S. M.; Tye, H.; Whittaker, M. Tetrahedron Lett. 2008, 49,
57(27), 43(100). Exact mass observed for
314.1522).
18 2
C H26OSi : 314.1514 (calcd:
3
939–3942.
5
6
7
8
9
Sore, H. F.; Boehner, C. M.; MacDonald, S. J. F.; Norton, D.; Fox, D. J.; Spring, D. R.
Org. Biomol. Chem. 2009, 7, 1068–1071.
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Chem. 2001, 66, 1054–1056.
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J.; Buchner, W.; Degen, B. U.S. Patent 4,060,537, 1977.
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Study of the reusability of the catalyst: The recovered bottom layer obtained
above was InBr –THF complex, which was in the form of a viscous liquid. It was
thoroughly washed with hexane (3 Â 5 ml) and dried under vacuum to obtain
[InBr ] in the form of a white powder (135 mg). 50 mg of InBr
3
3
Á(THF)
2
3
Á(THF)
2
obtained as above was taken into a 25 ml r.b. flask and to this, dimethyl-p-tolyl
silane 1l (0.4 g, 2.6 mmol) and THF (5 ml) were added and stirred for 4 h at
room temperature keeping open to air. After the completion of the reaction,
0.38 g (92%) of disiloxane 2l was obtained upon purification and its spectral
data were identical to that obtained above.Study of the reusability of the catalyst:
1
975, 82, 4411.
Typical procedure for Lewis acid-catalyzed air oxidation of hydrosilane to
disiloxane: Dimethyl-p-tolyl silane 1l (1.0 g, 6.7 mmol), InBr (118 mg,
.33 mmol), and tetrahydrofuran (10 ml) were taken in 25 ml round-
3
The recovered bottom layer obtained above was InBr
was in the form of a viscous liquid. It was thoroughly washed with hexane
(3 Â 5 ml) and dried under vacuum to obtain [InBr Á(THF) ] in the form of a
white powder (135 mg). 50 mg of InBr obtained as above was taken
3
–THF complex, which
0
a
bottomed flask and stirred for 4 h at room temperature keeping the reaction
open to air. The reaction proceeded with the evolution of hydrogen gas bubbles
3
2
3
Á(THF)
2
(
The isolated gas gave a positive ‘pop’ test with lit splinter). After completion of
into a 25 ml r.b. flask and to this, dimethyl-p-tolyl silane 1l (0.4 g, 2.6 mmol)
and THF (5 ml) were added and stirred for 4 h at room temperature keeping
open to air. After completion of the reaction, 0.38 g (92%) of disiloxane 2l was
obtained upon purification and its spectral data were identical to that obtained
above.
the reaction (TLC), the solvent was removed under reduced pressure. The
resulting mixture was separated into two liquid layers. The upper layer was
found to be the desired disiloxane, which is miscible in hexane and the bottom
3
layer was InBr –THF complex, which is not miscible with hexane. Hence, the
crude product was extracted with hexane (4 Â 5 ml) from this bi-layer mixture
and concentrated under reduced pressure. Purification of the crude product by
column chromatography (silica gel 100–200 mesh, hexane) gave 1,3,3-
10. InBr
3
forms stable solid complex [InBr
3
Á(THF)
2
] upon treatment with THF. Ref.:
Willey, G. R.; Aris, D. R.; Haslop, J. V.; Errington, W. Polyhedron 2001, 20, 423–
429.
tetramethyl-1,3-di-p-tolyl-disiloxane 2l (1.02 g, 98%) as a colorless oil. The
11. Berberova, N. T. Russ. J. Electrochem. 2000, 36, 174–182.
12. (a) Haynes, R. K. Aust. J. Chem. 1978, 31, 121–129; (b) Haynes, R. K. Aust. J. Chem.
1978, 31, 131–138.
1
spectral data obtained for 2l is as follows: H NMR (CDCl
3
, 300 MHz): d = 7.3–
13
7
.4 (d, J = 7.6 Hz, 4H), 7.1–7.1(d, J = 7.6 Hz, 4H), 2.3 (s, 6H), 0.3 (br s, 12H);
C