DE4320786A1 - Prodn. of boron-contg. poly:silane(s), useful for prodn. of ceramics - by reacting tris-chloro:silyl:ethyl-borane(s) with alkali metal(s) - Google Patents

Abstract

B-contg. polysilanes (II) are produed by reacting tris-silyl-borane(s) of formula B-(C2H4-SiCl2X)3 (I) with metallic Li, Na and/or K. In (I), -C2H4- is -CH2-CH2- or -CHMe-; and X is Cl or 1-4C aliphatic residue. In (II), R = 1-4C aliphatic residue; and a + b is 1. At least equimolar amts. of alkali metal are useed, and the reaction is carried out in organic solvent, by adding the other reactants at 50-120 deg. C and then heating at 60-200 deg. C, pref. with exposure to ultrasound. Pref. (I) are prepd., e.g. by reaction of corresp. vinylsilanes of formula CH2=CH-SiCl2X with BH3.THF as described in J. Organomet. Chem. 34 (1972) C9 and 135 (1977) 249, and in Zhur. Obshchei. Thim. 30 (1960) 3615. Suitable solvents are, e.g. heptane, toluene, THF etc. USE/ADVANTAGE - (II) are new B-contg. polysilanes, useful for the prodn. of B- and Si- contg. ceramics with good adhesion, hardness and surface quality, which are useful for coating steel etc., esp. for the surface coating of machine components which are subjected to mechanical and chemical stress. (II) can also be shaped before pyrolysis, e.g. to give ceramic fibres which are useful for reinforcement of Al, Al alloys and ceramic components. In an example, tris-((dichloromethylsilyl) ethyl)-borane (I) was prepd. by reacting 216g dichloromethylvinylsilane in 255 ml toluen with 255 ml 2M soln. of BH3.SM32 in toluene, followed by evapn. of solvent to give 233g (I). Refluxing suspension of Na/K alloy (obtd. by melting 2.83g Na with 10.05g K) in THF was treated slowly with 27.5g (I), under the action of ultrasound. Mixt. was then worked up by filtration and evapn. to give polymer (II), contg. (apporx.) 42.8 wt.% C, 8.4 wt.% H, 11.8 wt.% B, 32.1 wt.% Si, below 0.2 wt.% Cl. 2.5g (II) was pressed-moulded to form a cylinder which was pyrolysed by heating under N2 to 1200 deg. C at 1 deg./min. and maintaining this temp. for a further 3 hrs. Black ceramic prod. obtd. showed slight shrinkage but no evidence of melting; X-ray diffraction analysis showed no crystalline phases.

Description

The invention relates to new boron-containing polysilanes, their preparation, their Further processing to ceramic materials containing boron and silicon, as well as these materials themselves. The ceramic materials mentioned are obtained by pyrolysis from the boron-containing polysilanes.

The production of certain organosilicon polymers and their pyrolysis to ceramic and boron-containing ceramic materials is already known. RR Wills et al. (Cer. Bulletin 62 (1983) 905) describe the preparation of boron-containing polysiloxanes by mixing alkoxysilanes with boralkoxides B (OR) ₃ and then using the sol-gel process. However, sol-gel processes are known to be very lengthy; In addition, inhomogeneities can occur because mechanical mixing does not produce an ideally homogeneous solution with an ideal distribution of siloxanes and boralkoxide.

According to EP-A 0 325 483, boroxines, cyclic boron-oxygen molecules, implemented with silazanes. The boroxines and silazanes must be separate synthesized and then implemented together. This multi-step synthesis is complicated and yet there are inhomogeneities possible.

According to EP-A-0 337 843, BCl ₃ is reacted with bis (trimethylsilyl) alkali amide. However, alkali amides are highly flammable compounds that are difficult to handle.

According to US Pat. No. 4,906,763, silicon-containing borazines are used in SiBN ceramics transferred. One starts from chloroborazine and leaves it with  React hexamethyldisilazane.

According to US Pat. No. 4,780,337, SiH-containing polymers, u. a. Silane, with Boralkene oxides in a hydrosilylation reaction (with platinum compounds as Catalysts) implemented. This leads u. a. also to boron-containing polysilanes. Difficulties arise in the recovery of the catalyst and in the Manufacture of boralkene oxides.

It has now been found that new organosilicon polymers, namely polysilanes containing boron, in a simple manner from tris-silylboranes of the formula (I)

B [-C₂H₄-SiCl₂X] ₃ (I)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical with 1-4 C atoms, by reaction with at least one of the Alkali metals Li, Na or K can produce. Ceramic materials containing boron and silicon can then be produced in a simple manner from these boron-containing polysilanes by pyrolysis.

The invention therefore relates to a method for producing boron-containing polysilanes, characterized in that at least one tris silylborane of formula (I)

B [-C₂H₄-SiCl₂X] ₃ (I)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical with 1-4 C atoms, with at least one of the alkali metals Li , Na or K implemented.

The tris-silylboranes of the formula B [-C ₂ H ₄ -SiCl ₂ X] ₃ used as starting products can, according to PR Jones et al. (J. Organomet. Chem. 34 (1972) C9), TFO Lim et al. (J. Organomet. Chem. 135 (1977) 249) and BM Mikailev et al. (Zhur. Obshchei. Khim. 30 (1960) 3615; CA (55) 20920) can be prepared by reacting corresponding vinylsilanes of the formula CH ₂ = CH-SiCl ₂ X with BH ₃ .THF (tetrahydrofuran). This generally results in a mixture of 1- and 2-substitution products (with -CH (CH ₃ ) - or -CH ₂ -CH ₂ groups). These can be separated and then reacted individually according to the invention, but it is also easily possible to use the mixture as it is in the reaction as such. But you can also from different vinyl silanes by reaction with BH ₃ · THF first produce different tris-silylborane mixtures, then separate these mixtures into their two 1- and 2-substitution products and new mixtures, z. B. only from 1 substitution products or only from 2 substitution products and then implement according to the invention. This mixing of previously isolated pure components leads to mixtures which cannot be obtained directly by the vinylsilane reaction with BH ₃ · THF.

At least one is preferably used to produce the boron-containing polysilanes of the alkali metals mentioned in a solvent which is inert towards the reactants - tris-silylborane and alkali metal - and their behavior Boiling point at least equal to the melting point of the alkali metal used is. Are suitable for. B. saturated aliphatic or aromatic Hydrocarbons such as heptane, decalin, xylene, toluene or ethers such as Dibenzyl ether, dibutyl ether or tetrahydrofuran (THF). To the submitted The tris-silylborane is added dropwise to alkali metal. In general it will Alkali metal used in at least an equimolar amount, preferably in slight excess of about 0.1 to 1 mol%, particularly preferably 0.1 to 0.5 mol%. An equimolar amount means that on a chlorine atom in Tris-silylborane, or the tris-silylboranes, an alkali metal atom is omitted. Preferably, in order to accelerate the dehalogenation, the reaction is performed under the influence of ultrasound.

The reaction temperature is increased during the dropping of the tris-silylborane preferably first kept at 50 ° C to 120 ° C, and then heated to temperatures from 60 ° C to 200 ° C, preferably to 60 ° C to 100 ° C.  

The reaction produces akali chloride, which is extracted by extraction with an inert organic solvent can be separated from the boron-containing polysilane. The same solvents are suitable for this as for dissolving the tris silylboranes.

If desired, the process can also be carried out under reduced pressure be performed. Even at pressures in the range of 1 to 10 bar be worked.

The process can also be designed continuously.

The new boron-containing polysilanes produced in this way have one molecular structure represented by formula (II)

can be reproduced in which the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) -, R is an aliphatic radical with 1-4 C atoms and a, b the mole fractions of the two structural units mean. Where a + b = 1.

If only B [-C ₂ H ₄ -SiCl ₃ ] _{3 is} used, then a = 1 and b = 0.

If only B [-C ₂ H ₄ -SiCl ₂ CH ₃ ] _{3 is} used, then a = 0 and b = 1 and R = CH ₃ .

Is z. B. a mixture of 40 mol% B [-C ₂ H ₄ -SiCl ₃ ] ₃ and 60 mol% B [-C ₂ H ₄ -SiCl ₂ CH ₃ ] _{3 is} used, then a = 0, 4 and b = 0.6 and R = CH ₃ .

In order to differentiate the 1- and 2-borane units in the polymer, the mol fraction a of the alkyl-free structural unit is divided into a ₁ for the proportion of the 1-borane unit (-CH (CH ₃ ) -) and a ₂ for the proportion of the 2-borane unit (-CH ₂ -CH ₂ -) and analogously the mol fraction b of the structural unit containing the alkyl radical R in b ₁ (1-borane unit) and b ₂ (2-borane unit).

If only a B [-C ₂ H ₄ -SiCl ₃ ] ₃ mixture of 10 mol% B [-CH ₂ -CH ₂ -SiCl ₃ ] ₃ and 90 mol% B [-CH (CH ₃ ) -SiCl ₃ ] ₃ , then a = 1, with a ₁ = 0.9 and a ₂ = 0.1, while b = 0.

In a similar manner, the proportion of different alkyl radicals R of different lengths can be given by the mole fractions b ₁ (1-borane unit) and b ₂ (2-borane unit) in b ₁ ¹ , b ₁ ² , b ₁ ³ , b ₁ ⁴ and b ₂ ¹ , b ₂ ² , b ₂ ³ , b ₂ ^{4 can be} divided, the upper index representing the number of C atoms in the radical R, B. b ₁ ² and b ₂ ² as mole fractions for the 1- or 2-borane unit with R = C ₂ H ₅ .

The present invention accordingly furthermore relates to boron-containing Polysilanes of the general formula (II)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) -, R is an aliphatic radical with 1-4 C atoms and a, b are the mole fractions of the respective structural units , where a + b = 1 applies.

The present invention furthermore relates to boron-containing polysilanes, obtainable by at least one tris-silylborane of the formula (I)

B [-C₂H₄-SiCl₂X] ₃ (I)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical with 1-4 C atoms, with at least one of the alkali metals Li , Na or K implemented.

The preferred embodiments of this implementation are already above have been specified.

The boron-containing polysilanes according to the invention are very homogeneous with respect to the element distribution of B, Si and C. You can by pyrolysis in inert Nitrogen or argon atmosphere at temperatures from 500 to 2000 ° C, preferably 800 to 1400 ° C, pyrolyzed to amorphous, dense materials be, which consist essentially of Si, C and B and in traces also H and can contain O.

A particular advantage is that the boron-containing polysilanes before pyrolysis have three-dimensional moldings formed using various processes.

An important method of shaping is pulling fibers. Let it go fibers from highly viscous solutions of boron-containing polysilane Draw solvents such as toluene, THF or hexane. The fiber drawing happens advantageously by means of spinnerets of 80 to 350 microns in diameter. By subsequent stretching, the thread is tapered so that after pyrolysis very strong thread of 2 to 20 µm, especially 5 to 15 µm in diameter arises. Find the fibers produced by subsequent pyrolysis Use as mechanical reinforcement inclusions in fiber reinforced Aluminum, aluminum alloys and ceramic components.

Another important processing option for the boron-containing polysilanes is Production of dense, well adhering, amorphous ceramic coatings Metals, especially steels. The coating is done with the help of a solution  of the polysilane in organic solvents such as toluene, THF or hexane. The Pyrolytic conversion into an amorphous layer takes place in the same Temperature range from 500 to 2000 ° C, preferably 800 to 1400 ° C below Inert gas as described above for the three-dimensional shaped bodies.

The ceramic coatings are suitable because of their excellent Adhesion, high hardness and surface quality especially for surface finishing of mechanically and chemically stressed machine components.

Furthermore, the boron-containing polysilanes described above can be pyrolyzed with an equally high ceramic yield of 70 to 90% in an NH ₃ atmosphere instead of in inert gas. The result is a practically carbon-free, crystal-clear, colorless material. When pyrolysis in NH ₃ at 1000 ° C or higher, the C content is below 0.5 wt .-%. The pyrolysis product consists of practically pure amorphous SiBN. The pyrolysis in NH ₃ can be applied to all shaped bodies produced by the shaping processes described above, that is to say bodies, fibers, and coatings formed from powders.

The invention therefore also relates to the production of Si, B and C. containing ceramic material, characterized in that the mentioned above, by their formula or their manufacturing process characterized boron-containing polysilanes in inert nitrogen or Argon atmosphere at 500 to 2000 ° C, preferably 800 to 1400 ° C, pyrolyzed, as well as the ceramic material itself.

The invention also relates to the production of Si, B and N. containing ceramic material, characterized in that the mentioned above, by their formula or their manufacturing process characterized boron-containing polysilanes in an atmosphere containing ammonia pyrolyzed at 500 to 2000 ° C, preferably 800 to 1400 ° C, and that thereby obtainable ceramic material itself.  

Before their pyrolysis, either in an inert nitrogen or argon atmosphere or in an atmosphere containing ammonia, the boron-containing polysilanes are preferably heated to 400-500 ° C. (if desired, under pressure), so that a radical insertion of CH ₂ units into the Si -Si binding takes place, analogously to boron-free polysilanes (K. Shiina, M. Kumada, J. Org. Chem. 23 (1958) 139; MT Davidson, C. Eaborn, J. Chem. Soc., Faraday Trans. 70 ( 1974) 249). The boron-containing polysilanes treated in this way are generally more soluble than the untreated ones.

The following examples illustrate the invention.

Test report Production of tris [(dichloromethylsilyl) ethyl] borane

To a solution of 200 ml (216 g, 1.53 mol) of dichloromethylvinylsilane in 255 ml of toluene, cooled to 0 ° C., 255 ml of a 2-molar solution of dimethyl sulfide borane (0.51 mol of BH ₃ ) in toluene were slowly added dropwise with vigorous stirring . The temperature was kept below 10 ° C. After the dropping, the reaction mixture was stirred for a further 5 hours at 0 ° C. and then for a further 36 hours at room temperature. After the solvent had been removed in vacuo, 223 g of tris [(dichloromethylsilyl) ethyl] borane were isolated.

The tris-silylborane produced was a colorless, oily liquid that adhered to the air ignites by itself if you have a large surface available is placed (e.g. on pulp).  

example 1 Reaction of tris [(dichloromethylsilyl) ethyl] borane with potassium

To 6.8 g (0.17 mol) of potassium in 50 ml of THF were at 68 ° C under Ultrasound influence 10 ml (12.5 g; 0.029 mol) of tris [(dichloromethylsilyl) ethyl] borane slowly added dropwise. The mixture was kept at this temperature for 24 hours stirred and then the liquid phase in the absence of air from Potassium chloride separated.

The resulting soluble boron-containing polysilanes were removed from the solvent and volatile components. 4.6 g of a colorless powder were obtained. The elementary analysis showed the following values:

C 42.8% by weight
H 8.4% by weight
B 11.8% by weight
Si 32.1% by weight
Cl <0.2% by weight

Example 2 Reaction of tris [(dichloromethylsilyl) ethyl] borane with Na / K alloy

A Na / K alloy was made in a reaction flask by melting Na and K made without solvent. 2.83 g (0.123 mol) Sodium and 10.05 g (0.257 mol) of potassium are used. After formation of the Alloy at 20 ° C was added as a solvent THF and stirred very violently on.

Then, under the influence of ultrasound, 27.5 g (0.063 mol) Tris [(dichloromethylsilyl) ethyl] borane was slowly added dropwise with reflux of the THF. The work-up was carried out as in Example 1. The elementary analysis also indicated slight deviations the same values as in example 1.  

Example 3 Pyrolysis in a nitrogen atmosphere

2.5 g of the boron-containing polysilane from Example 2 were ground in a mill and then pressed into a cylinder. Then this cylinder was under Nitrogen heated to 1200 ° C at a rate of 1 degree per minute and then held that temperature for 3 hours. After cooling, the Oven opened and the jet black cylinder could be removed. Of the The cylinder had shrunk somewhat, but not when it heated up melted.

X-ray diffraction analysis of the ceramic material did not reveal any crystalline ones Recognize phases.

Example 4 Pyrolysis in an ammonia atmosphere

The procedure was as in Example 3, except that 3.2 g of the boron-containing polysilane were used and the heating was carried out in an NH ₃ atmosphere instead of an N ₂ atmosphere.

After cooling, the colorless and translucent cylinder was out of the oven taken. The X-ray diffraction analysis showed that this was a amorphous material traded.

Claims (11)

1. A process for the preparation of boron-containing polysilanes, characterized in that at least one tris-silylborane of the formula (I) B [-C₂H₄-SiCl₂X] ₃ (I) wherein the group -C ₂ H ₄ - the structure -CH ₂ - CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical with 1-4 C atoms, with at least one of the alkali metals Li, Na or K. 2. The method according to claim 1, characterized in that one Alkali metal is used in at least an equimolar amount. 3. The method according to claim 1 or 2, characterized in that the Alkali metal placed in an organic solvent and then reacted becomes. 4. The method according to any one of claims 1 to 3, characterized in that a temperature of 50 ° C to Maintains 120 ° C and then heated to 60 to 200 ° C. 5. The method according to any one of claims 1 to 4, characterized in that the reaction is carried out under ultrasound. 6. Boron-containing polysilanes of the general formula (II) wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) -, R is an aliphatic radical with 1-4 C atoms and a, b are the mole fractions of the two structural units , where a + b = 1 applies. 7. Boron-containing polysilanes, obtainable by the process according to one of the Claims 1 to 5. 8. Process for the production of ceramic containing Si, B and C. Material, characterized in that boron-containing polysilanes according to Claim 6 or 7 in an inert nitrogen or argon atmosphere at 500 ° C to Pyrolyzed at 2000 ° C. 9. Ceramic material containing Si, B and C, available after A method according to claim 8. 10. A process for producing Si, B and N containing ceramic Material, characterized in that boron-containing polysilanes according to Claim 6 or 7 in an atmosphere containing ammonia at 500 ° C to Pyrolyzed at 2000 ° C. 11. Si, B and N containing ceramic material, available after A method according to claim 10.