A simple one-pot synthesis of methyltribromosilane

Article abstract of DOI:10.1080/10426500701323382

A simple one-pot synthesis of methyltribromosilane has been developed. The straightforward reaction of a slight excess of silicon tetrabromide with one equivalent of powdered methyllithium in refluxing pentane produces methyltribromosilane in high yields.

Full text of DOI:10.1080/10426500701323382

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Phosphorus, Sulfur, and Silicon
and the Related Elements
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A Simple One-Pot Synthesis of
Methyltribromosilane
Michael W. Pitcher a & Patricia A. Bianconi b
a Department of Chemistry , Middle Eastern
Technical University , Ankara, Turkey
b Department of Chemistry , The University of
Massachusetts at Amherst. , Amherst, MA, USA
Published online: 15 Jun 2007.
To cite this article: Michael W. Pitcher & Patricia A. Bianconi (2007) A Simple One-
Pot Synthesis of Methyltribromosilane, Phosphorus, Sulfur, and Silicon and the Related
Elements, 182:8, 1819-1822, DOI: 10.1080/10426500701323382
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Phosphorus, Sulfur, and Silicon, 182:1819–1822, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701323382
A Simple One-Pot Synthesis of Methyltribromosilane
Michael W. Pitcher
Department of Chemistry, Middle Eastern Technical University,
Ankara, Turkey
Patricia A. Bianconi
Department of Chemistry, The University of Massachusetts at Amherst.
Amherst, MA, USA
A simple one-pot synthesis of methyltribromosilane has been developed. The
straightforward reaction of a slight excess of silicon tetrabromide with one equiv-
alent of powdered methyllithium in refluxing pentane produces methyltribromosi-
lane in high yields.
Keywords Halogenated organosilanes; methyltribromosilane; Rochow synthesis; silicon
carbide
INTRODUCTION
Halogenated organosilanes are today used in an enormous variety of
industries and in a diverse array of applications. Methyltribromosilane
and other halogenated organosilanes are of interest as precursors
for the Chemical Vapor Deposition (CVD) of β-SiC films,1,2 and in
the synthesis of novel polysilyne network polymers.3−5 Methyltribro-
mosilane and other halogenated organosilanes are usually prepared
by the Rochow synthesis,6 or by a method involving dropwise ad-
dition of a Grignard reagent to an ether solution containing silicon
tetrabromide.7 The former method requires high temperatures and the
use of hydrogen bromide gas, and the later synthesis is complicated by
difficult separation of the products. In this article, we report a simple,
alternative route to the production of methyltribromosilane.
Received December 8, 2006; accepted February 6, 2007.
Address correspondence to Michael Pitcher, Department of Chemistry, Middle Eastern
Technical University, 06531 Ankara, Turkey. E-mail: pitcher@metu.edu.fr
1819

1820
M. W. Pitcher and P. A. Bianconi
RESULTS AND DISCUSSION
The simple addition of powdered methyllithium to a refluxing mixture
of silicon tetrabromide and pentane produces white crystalline bro-
mosilane products which are easily isolated. NMR studies of the crys-
talline material confirm the major product to be methyltribromosilane
(1—Scheme 1), along with smaller quantities of dimethyldibromosilane
SCHEME 1

Methyltribromosilane
1821
((CH3)2SiBr2) (2) and trimethylbromosilane ((CH3)3SiBr) (3).8 1H NMR
(200 MHz, d6-benzene) shows the methyl resonance of 1 at δ = 1.00,
that of 2 at δ = 0.67, and that of 3 at δ =.31, in a ratio of 4.1:1.9:0.5
by integration. 13C NMR (75.5 MHz) shows a methyl resonance at
δ = 126.6 (triplet, JC−H = 96.4 Hz) corresponding to methyltribromosi-
lane (1). The other resonances at δ = 124.2 (triplet) and δ = 121.4
(triplet), corresponding to the methyl groups of the di-and tri-methyl-
substituted products are not seen. Elemental analyses: Found (C 5.03%,
H 0.91%); Calculated for (CH3SiBr3) (C 4.24%, H 1.06%). Based on the
1H NMR, the reaction product therefore consists of 79% CH3SiBr3,
18% (CH3)2SiBr2 and 3% (CH3)3SiBr. The purity is acceptable, for
the intended use as a reagent in the synthesis of poly(methlysilyne).3
Fractional distillation of the mixture, would enable isolation of pure
methyltribromosilane.6,7 Although this process has not been used to
produce any other halogenated organosilanes, it is presumed that this
facile synthesis method could be used as a route for the preparation of
these compounds, too.
EXPERIMENTAL
Silicon tetrabromide (99+%) was purchased from Aldrich and used as
received. Methyllithium in diethylether (1.4 M) was purchased from
Aldrich; the ether was removed by vacuum and the methyllithium
used in powder form. Anhydrous pentane (99+%) was purchased from
Aldrich and dried over sodium and benzophenone. All work was per-
formed under an argon atmosphere, using either a glove box or schlenk
line techniques.
Using a two-necked 300 ml round bottom flask equipped with a stir-
rer, reflux condenser and powder addition funnel, addition of powdered
methyllithium (3 g, 0.1367 mol) to a 5% excess of silicon tetrabromide
(50 g, 0.1438 mol) in 250 ml of pentane, was done at a rate sufficient to
maintain reflux (about a one-hour addition time, Scheme 1). The reac-
tion mixture was then refluxed for an additional hour in order to ensure
complete reaction.
After reflux, the apparatus and products of the synthesis were
allowed to cool to room temperature, and the lithium bromide side
product was removed by filtration. The bromosilane reaction products
can then be isolated from the remaining pentane by crystallization in
a dry-ice/acetone bath. After immersion for approximately two hours,
the pentane can be cannulaed off, leaving white crystals (28.1 g, 69.1%
yield based on methlytribromosilane) behind.

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M. W. Pitcher and P. A. Bianconi
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