.alpha., .omega.-chlorosilazanes, and a process for their preparation

The invention 1204 to a process for the preparation of .alpha., .omega.-chlorosilazanes which comprises reacting an oligohydridoorganylsilazane of the formula [--RSiH--NH--].sub.n in which n is from about 3 to about 12 with at least one of the chlorosilanes R.sup.1 HSiCl.sub.2, R.sup.2 R.sup.3 SiCl.sub.2, R.sup.4 SiCl.sub.3, Cl.sub.2 R.sup.5 SiCl.sub.2 CH.sub.2 SiR.sup.5 Cl.sub.2 and Cl.sub.3 SiCH.sub.2 CH.sub.2 SiR.sup.6 Cl.sub.2 where R is C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl and,independently of one another, R.sup.1 -R.sup.6 are H, C.sub.1 -C.sub.6 alkyl, or C.sub.2 -C.sub.6 -alkenyl, at from -20.degree. C. to +50.degree. C. In addition, the invention relates to the novel .alpha., .omega.-chlorosilazanes obtainable by this process.

DESCRIPTION 
The invention relates to novel chlorine-containing silazanes and to a 
process for their preparation. The chlorine-containing silazanes according 
to the invention, also abbreviated to .alpha.,.omega.-chlorosilazanes 
below, can be converted into polymeric chlorosilazanes by heating. The 
latter can themselves be converted first into chlorine-free polysilazanes 
and then into silicon nitride-containing ceramic materials. 
The preparation of polysilazanes from other silazanes has already been 
described (U.S. Pat. No. 4,482,669, U.S. Pat. No. 4,720,532 and PCT-WO 
88/01260), as has the pyrolysis of polysilazanes to give silicon 
nitride-containing ceramic materials (R. R. Wills et al., Ceramic 
Bulletin, Vol. 62 (1983) 904-915). 
To prepare oligomeric or low-molecular-weight silazanes as intermediates 
for polysilazanes, chlorosilanes have generally been employed hitherto as 
starting materials and have been reacted with ammonia, or primary or 
secondary amines (U.S. Pat. No. 4,540,803, U.S. Pat. No. 4,543,344, U.S. 
Pat. No. 4,595,775 and U.S. Pat. No. 4,397,828). 
The present invention now provides novel starting materials for 
polysilazanes, namely .alpha.,.omega.-chlorosilazanes. 
The present invention relates to a process for the preparation of 
.alpha.,.omega.-chlorosilazanes, which comprises reacting an 
oligohydridoorganylsilazane of the formula [--RSiH--NH--].sub.n in which n 
is from about 3 to about 12, with at least one of the chlorosilanes 
R.sup.1 HSiCl.sub.2, R.sup.2 R.sup.3 SiCl.sub.2, R.sup.4 SiCl.sub.3, 
Cl.sub.2 R.sup.5 SiCH.sub.2 CH.sub.2 SiR.sup.5 Cl.sub.2 and Cl.sub.3 
SiCH.sub.2 CH.sub.2 SiR.sup.6 Cl.sub.2 where R is C.sub.1 -C.sub.6 -alkyl 
or C.sub.2 -C.sub.6 -alkenyl and, independently of one another, R.sup.1 
-R.sup.6 are H, C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl, at 
from -20.degree. C. to +50.degree. C. 
R is preferably CH.sub.3 and, independently of one another, R.sup.1 
-R.sup.6 are preferably H, C.sub.1 -C.sub.3 -alkyl or C.sub.2 -C.sub.3 
-alkenyl. R is particularly preferably CH.sub.3 and, independently of one 
another, R.sup.1 -R.sup.6 are particularly preferably H, CH.sub.3 or 
vinyl. 
The chlorosilanes R.sup.1 HSiCl.sub.2, R.sup.2 R.sup.3 SiCl.sub.2 and 
R.sup.4 SiCl.sub.3 employed as starting materials are commercially 
available, and the ethylene-bridged chlorosilanes Cl.sub.2 R.sup.5 
SiCH.sub.2 CH.sub.2 SiR.sup.5 Cl.sub.2 and Cl.sub.3 SiCH.sub.2 CH.sub.2 
SiR.sup.6 Cl.sub.2 are accessible by hydrosilylation of R.sup.1 
HSiCl.sub.2 and ethyne or by hydrosilylation of vinyl trichlorosilane and 
R.sup.1 HSiCl.sub.2. The oligohydridoorganylsilazanes also used as 
starting material are prepared by reacting dichlorohydridoorganylsilane 
RSiHCl.sub.2 where R is as defined above with NH.sub.3 in a solvent, as 
described in U.S. Pat. No. 4,482,669 (see, in particular, columns 4, 5, 7 
and 8 therein). This generally gives a mixture of linear and cyclic 
oligohydridoorganylsilazanes [--RSiH--NH--].sub.n where n is from about 3 
to about 12. For reaction with said chlorosilanes, the 
oligohydridoorganylsilazanes [--RSiH--NH--].sub.n are preferably treated 
carefully, without solvents, with the chlorosilanes. The reaction 
temperature is from -20.degree. C. to + 50.degree. C., preferably 
-10.degree. C. to 0.degree. C. It is also possible to carry out the 
reaction in a solvent which does not react with the reactants. Thus, the 
chlorosilane can be added in pure form or as a solution to the 
oligosilazane in a solvent or as the pure substance. Examples of solvents 
which are suitable for the reaction are saturated aliphatic or aromatic 
hydrocarbons, such as n-pentane, cyclohexane or toluene, or chlorinated 
hydrocarbons, such as chloroform or chlorobenzene, or ethers, such as 
diethyl ether or THF. 
The process may also, if desired, be carried out under reduced pressure. 
The process may also be carried out continuously. The novel 
.alpha.,.omega.-chlorosilazanes prepared have a linear molecular structure 
which may be reproduced by the formula (I) 
##STR1## 
In this formula, m has a value between 1 and 12, and -(Si) is, depending on 
the chlorosilane employed: 
##STR2## 
Accordingly, the invention furthermore relates to 
.alpha.,.omega.-chlorosilazanes of the formula (I) 
##STR3## 
where --(Si) may be the above radicals 
In this formula, R is C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl 
and, independently of one another, R.sup.1 -R.sup.6 are H, C.sub.1 
-C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl. The values for m are between 
1 and 12. 
The .alpha.,.omega.-chlorosilazanes of the formula (I) according to the 
invention may be converted into silicon-nitride containing ceramic 
material as follows: 
They are heated without a solvent to temperatures between 100.degree. C. 
and 300.degree. C., whereupon a rearrangement of the linear 
.alpha.,.omega.-chlorosilazanes into polymeric hydridochlorosilazanes 
occurs. Heating is preferably effected to temperatures between 150.degree. 
C. and 250.degree. C. 
These polymeric hydridochlorosilazanes can be converted into silicon 
nitride-containing ceramic material by further heating to up to 
1600.degree. C. in an inert-gas atmosphere or in an ammonia atmosphere 
(see, for example, German Offenlegungsschrift 3 733 727). 
EXPERIMENTAL REPORT 
Preparation of oligohydridomethylsilazane [--CH.sub.3 SiH--NH--].sub.n 
100 ml (0.97 mol) of methyldichlorosilane were dissolved in 800 ml of 
absolute THF, and ammonia was passed in for 3 hours (inlet rate: 0.5 
l/min). The reaction temperature was kept in the range from 10.degree. to 
15.degree. C. by cooling using an ice bath. In order to complete the 
reaction, the mixture was stirred at room temperature for 1 hour, and the 
ammonium chloride was subsequently separated off under argon. The 
precipitate was washed twice with 350 ml of THF in each case, and the 
combined THF solutions were evaporated under reduced pressure, to give a 
clear, readily mobile oil of [--CH.sub.3 SiH--NH--].sub.n where n=3-12 in 
a yield of 44.5 g=78% of theory.

EXAMPLE 1 
Reaction of [--CH.sub.3 SiH--NH--].sub.n with CH.sub.3 SiHCl.sub.2 
100 g (1.7 mol, based on n=1) of [--CH.sub.3 SiH--NH--].sub.n (n=3-12) were 
cooled to -5.degree. C. 48.9 g (0.425 mol) of CH.sub.3 SiHCl.sub.2 were 
then slowly added dropwise with stirring, and the abovementioned 
temperature was maintained for a further 60 minutes. 
200 ml of THF were subsequently added, and dimethylamine was passed in to 
saturation without the temperature of the reaction mixture exceeding 
0.degree. C. The precipitated dimethylamine hydrochloride was filtered 
off, and the filtrate was freed from solvent and volatile constituents. 
The resultant oily product was separated by gas chromatography, and the 
individual fractions were analyzed by mass spectrometry. 
The following molecules, inter alia, were detected: 
##STR4## 
These dimethylamino derivatives arise from the reactive 
.alpha.,.omega.-dichlorosilazanes: 
##STR5## 
EXAMPLE 2 
Reaction of [--CH.sub.3 SiH--NH--].sub.n with CH.sub.3 SiHCl.sub.2 and 
Subsequent Preparation of a Polymeric Hydridochlorosilazane 
100 g (1.0 mol, based on n=1) of [--CH.sub.3 SiH--NH--].sub.n (n=3-12) were 
cooled to -5.degree. C. 48.9 g (0.425 mol) of CH.sub.3 SiHCl.sub.2 were 
then slowly added dropwise with stirring, and the abovementioned 
temperature was maintained for a further 60 minutes. 
The mixture was subsequently heated to an oil-bath temperature of 
220.degree. C. over the course of 4 hours. The internal temperature was 
190.degree. C. After 2 hours at this temperature, the mixture was allowed 
to cool. 
At 20.degree. C., 110 g of a hard, brittle substance remained, which was 
dissolved in THF and filtered to remove insoluble constituents The 
filtrate was freed from the solvent, leaving a clear material which was 
glassy-brittle at 20.degree. C. and had a reproducible softening point at 
about 120.degree. C. (95 g). 
Analytical data (in % by weight): Si 44.7%; C 19.2%; N 17.9%; H 6.9%; Cl 
11.3%. 
Ceramic yield on pyrolysis in N.sub.2 up to 1100.degree. C.: 68.5%. Ceramic 
yield on pyrolysis in NH.sub.3 up to 1100.degree. C.: 58.9%. 
EXAMPLE 3 
Reaction of [--CH.sub.3 SiH--NH--].sub.n with Vinylmethyldichlorosilane 
100 g (1.7 mol, based on n=1) of [--CH.sub.3 SiH--NH--].sub.n (n=3-12) were 
cooled to -5.degree. C. 70.5 g (0.5 mol) of vinylmethyldichlorosilane were 
then slowly added dropwise with stirring, and the abovementioned 
temperature was maintained for a further 60 minutes. 
200 ml of THF was subsequently added, and dimethylamine was passed in to 
saturation without the temperature of the reaction mixture exceeding 
0.degree. C. 
The precipitated dimethylamine hydrochloride was filtered off, and the 
filtrate was freed from the solvent. 
The resultant oily product was separated by gas chromatography, and the 
individual fractions were analyzed by mass spectrometry. 
The following molecules, inter alia, were detected: 
##STR6## 
having the following values for the variables: 
______________________________________ 
1. a = 1 b = 0 R = vinyl 
2. a = 2 b = 0 R = vinyl 
3. a = 3 b = 0 R = vinyl 
4. a = 1 b = 1 R = vinyl 
5. a = 2 b = 1 R = vinyl 
6. a = 3 b = 1 R = H 
______________________________________ 
These dimethylamino derivatives arise from the corresponding 
.alpha.,.omega.-dichlorosilazanes. 
EXAMPLE 4 
Reaction of [--CH.sub.3 SiH--NH--].sub.n with Vinylmethyldichlorosilane and 
Subsequent Preparation of a Polymeric Hydridochlorosilazane 
100 g (1.7 mol, based on n=1) of [--CH.sub.3 SiH--NH--].sub.n (n=3-12) were 
cooled to -5.degree. C. 70.5 g (0.5 mol) of vinylmethyldichlorosilane were 
then slowly added dropwise with stirring, and the abovementioned 
temperature was maintained for a further 60 minutes. 
The mixture was subsequently heated to an oil-bath temperature of 
220.degree. C. over the course of 4 hours. The internal temperature was 
205.degree. C. After 2 hours, the mixture was allowed to cool. 
At 20.degree. C., 114 g of a mixture of a very viscous oil and solid 
constituents remained. THF was added, and the mixture was filtered. The 
clear filtrate was freed from the solvent, leaving a clear, slightly 
yellowish, very viscous oil which had a viscosity of about 5 Poise. 
Analytical data (in % by weight): Si 38.2%; C31.1%; N 16.2%; H 7.2%; Cl 
7.3% . 
Ceramic yield on pyrolysis of N.sub.2 up to 1100.degree. C.: 54.2%. 
Ceramic yield on pyrolysis of NH.sub.2 up to 1100.degree. C.: 42.1%.