DE102016104442A1 - Process for the preparation of halogenated oligosilanes and use of a Lewis base as a catalyst for the preparation of halogenated oligosilanes - Google Patents

Abstract

The invention relates to a process for the preparation of halogenated oligosilanes which comprises a disproportionation of hexahalogendisilane, the disproportionation being carried out with the aid of a catalyst. In this case, the catalyst is selected from Lewis bases of the following general formulas: R 1 -O-R 2 and R 1 -Y, where R 1 is in each case an aryl, R 2 is an alkyl or an aryl, and Y is a halogen selected from F, Cl, Br and I is. Furthermore, the use of a Lewis base is given as a catalyst for the preparation of halogenated oligosilanes.

Description

The invention relates to a process for the preparation of halogenated oligosilanes comprising a disproportionation of hexahalogendisilane, wherein the disproportionation is carried out with the aid of a catalyst.

From the prior art, the production of silicon layers of oligosilanes or mixtures of various oligosilanes is known. Silanes are compounds that consist only of silicon and hydrogen atoms. In the following, oligosilanes are silanes which have more than two Si atoms. In detail, among other things, thermolysis, chemical vapor deposition (English: Chemical Vapor Deposition, short: CVD), the vapor-liquid-solid method (English: Vapor-Liquid-Solid-Method, short: VLS) or laser ablation for deposition suitable for silicon layers.

It has been found that, in particular, oligosilanes which have a high number of silicon atoms per molecule, in general at least three, preferably at least five, silicon atoms are well suited for the production of silicon layers. For example, e.g. the deposition rate in the production of the silicon layer - ie the layer thickness obtained per unit time - the higher, the more Si atoms have the oligosilanes used.

Oligosilanes in turn are accessible by the hydrogenation of halogenated oligosilanes.

In order to obtain oligosilanes having the highest possible number of Si atoms per molecule, it is necessary to use halogenated oligosilanes as starting materials in the hydrogenation, which themselves have a high number of Si atoms per molecule.

For this reason, there is a need for halogenated oligosilanes having the highest possible number of Si atoms. Therefore, preparatively simple and efficient processes for the preparation of halogenated oligosilanes are needed.

It is therefore an object of the present invention to provide a process for the preparation of halogenated oligosilanes, wherein the halogenated oligosilanes are to be obtained from an easily accessible starting material.

This object is achieved by a method according to claim 1.

• – R¹-O-R²,
• – R¹-Y,

wobei R¹ jeweils ein Aryl ist,
R² ein Alkyl oder ein Aryl ist, und
wobei Y ein Halogen ausgewählt aus F, Cl, Br und I ist.Accordingly, the present invention relates to a process for the preparation of halogenated oligosilanes comprising a disproportionation of hexahalogendisilane, wherein the disproportionation is carried out using a catalyst which is selected from Lewis bases of the following general formulas:

• R ¹ -OR ² ,
• - R ¹ -Y,

where R ^{1 is in} each case an aryl,
R ^{2 is} an alkyl or an aryl, and
wherein Y is a halogen selected from F, Cl, Br and I.

First of all, some terms will be discussed in more detail.

Halogenated oligosilanes are to be understood as meaning molecular compounds which comprise silicon atoms and halogen atoms, in particular compounds which consist exclusively of silicon atoms and halogen atoms. Suitable halogens are fluorine, chlorine, bromine and iodine. The halogen atoms are preferably chlorine atoms. Halogenated oligosilanes according to the invention have at least three silicon atoms.

For example, halogenated oligosilanes, as prepared by the process according to the invention, can have at least four, preferably at least five, and more preferably at least six, silicon atoms. The higher the number of Si atoms per molecule, the easier it is to produce from the corresponding halogenated oligosilanes, oligosilanes having a high number of Si atoms by means of hydrogenation. For example, the halogenated oligosilanes may be selected from a group of halogenated oligosilanes comprising three, four, five and six Si atoms. For example, halogenated oligosilanes within the meaning of the invention may comprise at most 12 Si atoms, preferably at most 8 Si atoms, and further preferably have at most six Si atoms. In general, however, as many Si atoms per halogenated oligosilane are desirable.

The halogenated oligosilanes according to the invention may be, for example, linear, branched or even cyclic.

By disproportionation is meant a chemical reaction whereby as part of a redox reaction, an element simultaneously appears as an oxidant and as a reducing agent, so that it is previously in a middle oxidation state, while later present in an elevated and partly in a lower oxidation state , In the case of the present invention, the silicon of hexahalogendisilane is present in a middle oxidation state, while silicon also assumes higher and lower oxidation states within the reaction products obtained in the context of the process according to the invention.

The disproportionation of hexahalogendisilane is catalyzed by compounds of the general formulas R ¹ -OR ² and R ¹ -Y described. These catalysts are distinguished by the fact that they each have at least one radical R ¹ , which is an aryl radical and that both compounds are each Lewis bases.

Lewis bases are electron pair donors. They have at least one free electron pair. The at least one free electron pair of the catalyst R ¹ -OR ² is located at the oxygen atom of the ether function, while the at least one free electron pair of the catalyst R ¹ -Y is located on the halogen (Y).

The Lewis bases R ¹ -OR ² and R ¹ -Y, which can each be used independently of one another as catalysts for the process according to the invention, each have a radical R ¹ which is an aryl radical.

Preferably, this is a C ₅ -C ₂₀ aryl, more preferably a C ₆ -C ₁₂ aryl, most preferably a phenyl. It may be a substituted or unsubstituted aryl.

Aryles are usually characterized by a + M effect. This allows them to enhance the Lewis base properties in the Lewis base catalyst.

The general formula R ¹ -OR ² also has a substituent R ² , which may be both an alkyl substituent and an aryl substituent.

In the latter case, the aryl is again preferably a C ₅ -C ₂₀ -aryl. More preferably, the aryl is a C ₆ -C ₁₂ aryl, in particular a phenyl. The aryl may be substituted or unsubstituted.

If R ² is an alkyl substituent, then alkyl is preferably a C ₁ -C ₁₀ -alkyl, more preferably a C ₁ -C ₆ -alkyl, especially a methyl. The alkyl substituent may in principle be linear, branched and cyclic.

The inventors of the present invention have found that ethers having at least one aryl substituent (of the general formula R ¹ -OR ² ) and haloaryls (of the general formula R ¹ -Y) are good catalysts for the preparation of halogenated oligosilanes from hexahalogendisilane. In contrast, so far only amines have been known as catalysts for the preparation of halogenated oligosilanes from hexahalogendisilane.

Catalysts based on amines often require a complex synthesis and are therefore relatively expensive. In addition, the most common and thus somewhat cheaper representatives such as trimethylamine (NMe ₃ ) have low boiling temperatures and therefore allow a simple reaction only at low reaction temperatures.

In contrast, the catalysts of the process according to the invention are generally easier to prepare and for this reason significantly cheaper. They also show a low vapor pressure and therefore have higher boiling points than the commonly used catalysts based on amines. For this reason, the catalysts according to the invention allow the reaction to be carried out at considerably higher temperatures without the expense of equipment.

The inventors of the present invention have also recognized that the catalysts of the process according to the invention show a significantly lower tendency to react with halogenated oligosilanes than is the case with the amine-based catalysts used hitherto. The hitherto known catalysts based on amines react especially at elevated reaction temperatures often with the reaction products and can be much more difficult to separate from the product mixture for this reason. In contrast, the catalysts used in the process according to the invention can be more easily separated from the halogenated oligosilanes, which facilitates the work-up and purification of the product mixture.

The cited catalysts of the method according to the invention are preferably liquid at room temperature, generally have high boiling points, preferably above 100 ° C. or more preferably above 130 ° C., and thus can be used at relatively high reaction temperatures without much effort. In addition, they are usually stable in air. These properties also facilitate handling and lead to a further reduction of the technical complexity of the method according to the invention over conventional methods.

Hexahalogendisilane can be described by the general formula Si ₂ X ₆ , wherein X is a halogen selected from fluorine, chlorine, bromine and iodine. Hexahalogendisilane is compared to other starting materials for the production of higher halogenated oligosilanes comparatively easily accessible and therefore also relatively inexpensive. The hexahalkenedisilane is preferably hexachlorodisilane (Si ₂ Cl ₆ )

In addition, the inventors have found that the said catalysts of the general formulas R ¹ -OR ² and R ¹ -Y of the process according to the invention show a good selectivity for the preparation of halogenated oligosilanes with a high number of Si atoms per molecule.

The halogenated oligosilanes obtained by the process according to the invention are preferably linear and branched halonated oligosilanes. These can be described by the general formula Si _n X _m , where n ≥ 3. Here X is a halogen selected from F, Cl, Br and I and m is 2n + 2.

• – X₃SiSiX₂SiX₃,
• – XSi(SiX₃)₃,
• – Si(SiX₃)₄,
• – X₃SiSiX₂Si(SiX₃)₃.

The process according to the invention makes it possible, for example, to prepare halogenated oligosilanes of the following general formula:

• X ₃ SiSiX ₂ SiX ₃ ,
• XSi (SiX ₃ ) ₃ ,
• Si (SiX ₃ ) ₄ ,
• - X ₃ SiSiX ₂ Si (SiX ₃ ) ₃ .

In this case, X is again a halogen selected from F, Cl, Br and I. It is possible in each case to obtain individual of the halogenated oligosilanes mentioned or else mixtures thereof. A common by-product of the process according to the invention is tetrahalosilane (SiX ₄ ).

So far, the preparation of halogenated oligosilanes was known only with the aid of amines as catalysts. In contrast, the inventors of the process of the present invention have discovered that amines or generally nitrogen-containing compounds need not be present in the reaction mixture to permit production of halogenated oligosilanes. Thus, the process according to the invention also works in the absence of amines and can consequently be carried out in the absence of amines. It can also be carried out, for example, in the absence of nitrogen-containing organic or organometallic compounds. In addition to the mentioned catalysts of the process according to the invention therefore no further catalysts for the functioning of the disproportionation must be present. In the absence of amines, this means a fraction of less than 1 percent by weight, preferably less than 0.5 percent by weight, more preferably less than 0.1 percent by weight and most preferably less than 0.01 percent by weight of the reaction mixture. In particular, no amines can be present in the reaction mixture at all.

The inventors have surprisingly found that high yields can also be achieved for halogenated oligosilanes with n ≥ 5 by the process according to the invention.

For n = 5 z.T. a selectivity of ≥ 90% and in some cases from ≥ 95% up to approximately 100% based on the proportion of halogenated oligosilanes obtained can be achieved.

With the method according to the invention, it is also possible for the first time to achieve appreciable yields and selectivities for halogenated oligosilanes having six Si atoms per molecule.

In the following, further preferred embodiments of the present invention will be described.

In a preferred embodiment, the hexahalogendisilane is hexachlorodisilane (Si ₂ Cl ₆ ). Hexachlorodisilane is an easily accessible and relatively inexpensive starting material, which is characterized by good handling. Hexachlorodisilane can be used to prepare chlorinated oligosilanes, which can be converted into corresponding oligosilanes in a particularly simple manner by hydrogenation and therefore represent highly suitable starting materials.

In a preferred embodiment, the particular catalyst (R ¹ -OR ² , R ¹ -Y) as radical R ^{1 has} a C ₆ -C ₁₂ -aryl radical. An aryl radical having at least six carbon atoms generally leads to catalysts having a significantly lower vapor pressure and thus a higher boiling point. Catalysts having an aryl radical having at least six carbon atoms are thus also particularly suitable for higher reaction temperatures. On the other hand, excessively large aryl systems may make steric access to the lone pair less difficult. Therefore, it is preferable that the aryl group has not more than twelve carbon atoms. For example, the aryl system may be a homocyclic aryl system, that is, an aryl radical containing only C and H atoms and no heteroatoms. For example, the aryl radical may be naphthyl or phenyl, but preferably the aryl radical is a phenyl.

In a preferred embodiment, the radical R ^{1 is} a substituted aryl radical, it being possible for the substituents to be, for example, alkyl substituents, preferably short-chain C ₁ -C ₃ -alkyl substituents. A positive effect for catalysis by substituents with donor properties, ie a + M effect, is also conceivable.

In a preferred embodiment of the process according to the invention, the radical R ¹ is unsubstituted. This facilitates the steric accessibility of the Lewis base.

• – Ph-O-R²
• – Ph-Y,

wobei Ph- jeweils für einen Phenyl-Rest steht.In a preferred embodiment, the radical R ^{1 is} a phenyl radical. Both the catalysts according to the invention which are ethers and the catalysts according to the invention which are haloaryls preferably have a phenyl radical as the aryl radical. The catalysts can then be expressed by the following general formulas:

• - Ph-OR ²
• Ph-Y,

wherein each Ph- represents a phenyl radical.

Ethers having at least one phenyl radical (Ph-OR ² ) and halobenzenes (Ph-Y) are comparatively easy to prepare and therefore commercially available at low cost. They are generally much cheaper than comparable catalysts with more complex aryl radicals. Also, they are generally much cheaper than comparable amine catalysts. At the same time they usually have higher boiling points. The phenyl radical also shows a good + M effect, which may be a starting point for explaining the good catalytic activity of the described Lewis bases.

The phenyl radical may in principle be substituted or unsubstituted. For example, the phenyl radical may have substituents with donor properties or alkyl substituents, for example C ₁ -C ₃ alkyl substituents. The phenyl radical may preferably be free of amino groups or other groups as substituents. These are not required for catalysis in the process of the invention.

It is preferred for catalysis for steric reasons if the phenyl substituent itself is not further substituted. Thus, a good steric accessibility of the Lewis base can be facilitated.

In a preferred embodiment, the radical R ² of R ¹ -OR ^{2 is} a C ₆ -C ₁₂ aryl radical, more preferably a phenyl radical. In this case, the ether has two aryl radicals, for example two phenyl radicals (Ph-O-Ph). In these cases, the ether has two + M-effect radicals.

In a preferred embodiment of the process according to the invention, the radical R ^{2 is} a C ₁ -C ₁₀ -alkyl radical, preferably a C ₁ -C ₆ -alkyl, more preferably a C ₁ -C ₄ -alkyl. Although the alkyl radical can in principle be linear, branched and cyclic, but is preferably linear in order not to complicate the steric accessibility.

In a preferred embodiment of the process according to the invention, R ^{2 is} selected from the group consisting of phenyl, methyl, ethyl, propyl and butyl. Among these embodiments, it is particularly preferred when R ^{2 is} phenyl, methyl or ethyl. Most preferred is when R ^{2 is} a methyl radical. The phenyl radical has a + M effect. The short-chain alkyl radicals allow, in addition to a + I effect, good steric accessibility. For the latter reason, methyl is the most preferred steric least demanding substituent.

In a preferred embodiment, the catalyst R ¹ -Y with Y is bromine or iodine. Br and I are characterized by lone pairs of electrons that are particularly high in energy. This leads to particularly favorable Lewis base properties.

In a preferred embodiment, Y is chlorine. Chloro-aryls of the general formula R ¹ -Cl are particularly easy to produce by means of chlorination processes and therefore inexpensive with at the same time good catalytic properties. Also, they are usually stable in air and easy to store.

In a preferred embodiment, the catalyst is anisole. This is the most preferred catalyst with particularly good catalytic activity and high selectivities. Anisole, also referred to as methoxybenzene, has a boiling point of 154 ° C, is liquid and is also air stable. Due to its high boiling point, it can be easily handled even at high temperatures, which allows a good reaction without great experimental effort. Anisole shows a low reactivity with halogenated oligosilanes and in particular does not react with chlorinated oligosilanes. Finally, anisole is easy to prepare and commercially available at moderate prices.

In a preferred embodiment of the process according to the invention, the catalyst is chlorobenzene. Chlorobenzene is a liquid with a boiling point of 132 ° C. Chlorobenzene is a very common chemical that is much cheaper than anisole. Overall, both anisole and chlorobenzene are significantly cheaper and more readily available than most conventional amine catalysts. Like anisole, chlorobenzene, in contrast to amines, generally does not react with the halogenated oligosilanes of the product mixture of the process according to the invention.

In a preferred embodiment, the disproportionation is promoted by thermal energy or by microwave radiation.

A promotion of disproportionation with microwave radiation is particularly preferred. If the process is carried out by introducing microwave radiation instead of conventional heating, the reaction time is drastically shortened.

In a preferred embodiment, the disproportionation is promoted by the supply of thermal energy. The preferred temperatures for the process are in the range between -78 ° C and 300 ° C, more preferably between 0 ° C and 250 ° C. Especially preferred are temperatures between 20 ° C and 210 ° C. This temperature range allows high metabolic rates in conjunction with a high yield of halogenated oligosilanes having more than three silicon atoms, in particular halogenated oligosilanes having five or even six silicon atoms.

In a preferred embodiment, the inventive method is carried out at temperatures between -78 ° C and 70 ° C, preferably at a temperature between 0 ° C and 70 ° C and more preferably between a temperature of 20 ° C and 55 ° C.

The inventors of the present invention have found that the product distribution in the process of the present invention correlates strongly with the reaction temperature. The lower the reaction temperature, the higher the selectivity for halogenated oligosilanes having six Si atoms. Accordingly, the reaction temperature is preferably less than 100 ° C, more preferably less than or equal to 70 ° C, and most preferably less than or equal to 55 ° C.

However, too low reaction temperatures slow the reaction so that the reaction is preferably carried out at at least 0 ° C, more preferably at least 20 ° C or at least at room temperature.

In a preferred embodiment, the inventive method at a temperature between 50 ° C and 300 ° C, more preferably between 50 ° C and 250 ° C, more preferably between 60 ° C and 210 ° C and most preferably between 80 ° C and 180 ° C performed. The higher reaction temperatures according to this embodiment allow a faster reaction than with the lower temperature ranges mentioned above. At the same time they allow a very high conversion of material in this temperature range usually over 90 to 100% with otherwise suitable conditions. Although the inventors of the present invention have observed that in this temperature range, usually no or hardly halogenated oligosilanes are formed with six silicon atoms, but they could find that halogenated oligosilanes are formed with five Si atoms with very high selectivities. The selectivity for halogenated oligosilanes with five Si atoms based on the halogenated oligosilanes formed may be more than 90%. Especially in the temperature range between 80 ° C and 180 ° C, the proportion of Pentasiliziumdodekahalogenid (Si (SiX ₃ ) ₄ ) is almost 100% of the obtained halogenated oligosilanes. This calculation refers exclusively to the halogenated oligosilanes obtained, ie by-products which have a proportion of silicon atoms below three are not included in the calculation of the proportion. The major byproduct is usually tetrahalosilane (SiX ₄ ).

In a preferred embodiment, the inventive method is carried out in a protective gas atmosphere. Suitable inert gas is in principle any gas which does not react with the reaction mixture, in particular the haloated oligosilanes obtained. Most suitable are nitrogen (N ₂ ) and argon (Ar). If the reaction is carried out in a protective gas atmosphere, undesirable side reactions with atmospheric oxygen or moisture can be better avoided.

In a preferred embodiment, the process is carried out without the presence of a solvent. Since both the catalysts and hexahalogendisilane are usually liquid, a reaction mixture can also be formed without further solvent and the reaction can also be carried out without further solvent. The catalysts according to the invention can even be used in excess because of their low price. In this case, the catalysts of the invention may even take the place of the solvent. This leads to particularly good selectivities for halogenated oligosilanes having five or more Si atoms.

In a preferred embodiment, the process according to the invention or the disproportionation is carried out in a solvent, preferably in a nonpolar solvent. Further preferred solvents are benzene and toluene or mixtures thereof. Both solvents have comparatively high boiling points and can therefore be used even at elevated temperatures.

In a preferred embodiment, the ratio of the amount (mol: mol) of Si ₂ X ₆ to the solvent is between 1: 0.01 and 1: 1000, preferably between 1: 0.1 and 1: 100, more preferably between 1: 0.1 and 1:10 , These areas have proven themselves. For example, it is advantageous if the ratio of Si ₂ X ₆ to the solvent is as large as possible, ie not too much solvent dilutes the reaction mixture. Preferably, the ratio (Si ₂ X ₆ : solvent) may be less than 1:10, more preferably equal to or less than 1: 4, most preferably equal to or less than 1: 2, most preferably equal to or less than 1: 1.

Also advantageous is the use of dried solvents, for example, solvents which have previously been freed of conventional drying agent such as sodium or by distillation of moisture.

In a preferred embodiment, the molar ratio (mol: mol) of Si ₂ X ₆ to the catalyst (R ¹ -OR ² , R ¹ -Y) is between 1: 1000 and 1: 0.001. The ratio is to be understood here and below as the substance volume ratios. The inventors of the present invention have recognized that disproportionation is possible in a surprisingly wide range of mixing ratios. Preferably, the ratio of Si ₂ X ₆ to the catalyst is in the range between 1: 100 and 1: 0.01.

In a preferred embodiment, the ratio of Si ₂ X ₆ to the catalyst is greater than 1: 0.001, preferably greater than 1: 0.01, more preferably greater than 1: 0.1, and most preferably greater than 1: 1. In addition, the Lewis base R ¹ -OR ² or R ¹ -Y can be present in excess. A high proportion of Lewis base in the reaction mixture favors high yields of halogenated oligosilanes with a high number of Si atoms and also accelerates the disproportionation reaction.

In a preferred embodiment, the ratio of Si ₂ X ₆ to the catalyst is less than 1: 1000, preferably less than 1: 100, more preferably less than 1:10 and particularly preferably 1: 1 or less than 1: 1. It is also possible according to an embodiment that the ratio is less than 1: 0.1. Even if the Lewis base is added in the same or smaller amount, good yields of halogenated oligosilanes in the context of the invention can be achieved.

• – R¹-O-R²,
• – R¹-Y

ausgewählt ist,
wobei R¹ jeweils ein Aryl ist,
R² ein Alkyl oder ein Aryl ist, und
wobei Y ein Halogen ausgewählt aus F, Cl, Br und I ist. In addition to a method, the present invention also relates to the use of a Lewis base as a catalyst for the preparation of halogenated oligosilanes, wherein the Lewis base of Lewis bases of the general formulas

• R ¹ -OR ² ,
• - R ¹ -Y

is selected,
where R ^{1 is in} each case an aryl,
R ^{2 is} an alkyl or an aryl, and
wherein Y is a halogen selected from F, Cl, Br and I.

All definitions and preferred embodiments for the radicals R ¹ , R ² , Y, the catalysts as a whole, as well as for the starting material and the halogenated oligosilanes obtained and other reaction parameters are to be selected here as well as in the method according to the invention already described above.

Surprisingly, the inventors of the present invention were able to establish that the Lewis basicity of said catalysts is sufficient to catalyze the disproportionation of hexahalogisilane to halogenated oligosilanes having at least three silicon atoms. The use of these compounds as catalysts allows in particular a high selectivity for halogenated oligosilanes having at least five or even six Si atoms.

In a preferred embodiment, the catalysts used are anisole or chlorobenzene. As already mentioned, both substances are not only inexpensive, but also have sufficient Lewis basicity to catalyze the reactions given efficiently. Since they are much easier to separate from the products, processes that use these catalysts can be made possible with less equipment.

The invention is explained below with reference to figures:

1 shows a simplified, schematic representation of the disproportionation of the inventive method.

2 shows a table summarizing experimental data for a number of embodiments (Examples I to VI).

3 shows the ²⁹ Si NMR spectra to the product mixtures of Examples I to VI.

• – R¹-O-R^2,
• – R¹-Y,

wobei R¹ jeweils ein Aryl ist,
R² ein Alkyl oder ein Aryl ist, und
wobei Y ein Halogen ausgewählt aus F, Cl, Br und I ist. 1 shows an embodiment of the method according to the invention comprising a disproportionation of hexahalogendisilane (Si ₂ X ₆ ) as starting material. The disproportionation is carried out in the presence of a catalyst, which is at least one of the Lewis bases of the following general formulas:

• R ¹ -OR ^2,
• - R ¹ -Y,

where R ^{1 is in} each case an aryl,
R ^{2 is} an alkyl or an aryl, and
wherein Y is a halogen selected from F, Cl, Br and I.

The product obtained halogenated oligosilanes with more than two Si atoms per molecule. The halogenated oligosilanes are preferably halogenated oligosilanes of the general formula Si _n X _m , where n ≥ 3. Surprisingly, halogenated oligosilanes are accessible in good yields with the process according to the invention, for which n = 5 or even n = 6 the halogenated oligosienes obtained are branched or linear halogenated oligosilanes for which m = 2n + 2 selected reaction conditions, individual or mixtures of different halogenated oligosilanes can be obtained. In particular, SiX ₄ can be formed as a by-product.

2 summarizes the selected reaction conditions for a number of embodiments (Examples I to VI) and compares what proportion each of the halogenated oligosilanes quantified by means of ²⁹ Si NMR spectroscopy to the total amount of halogenated oligosilanes obtained. The data demonstrate that the process according to the invention provides reliably halogenated oligosilanes for a wide range of possible reaction temperatures. Neo-Si ₆ Cl ₁₄ could only be obtained for temperatures below 80 ° C, preferably temperatures below 60 ° C (Examples I and II). For this purpose, very good selectivities for neo-Si ₅ Cl ₁₂ could be achieved up to about 200 ° C. (Examples III, IV, V). The data further demonstrate that the reaction, even for a wide range of possible ratios of the starting material Si ₂ X ₆ to the Lewis base, reliably shows high selectivities for halogenated oligosilanes with a high number of Si atoms per molecule. The reaction can be carried out both with a high excess of Lewis base, as well as with small amounts of Lewis base. Because of the low price of the Lewis bases which can be used as catalysts in the case of the present invention, it is also possible, for example, to carry out the reaction in the Lewis base without further solvent. High amounts of Lewis base in the reaction mixture have an equally favorable effect on the reaction rate and the selectivity towards high Si numbers per molecule.

3 shows the measured in C ₆ D ₆ ²⁹ Si NMR spectra, which were obtained for the respective product mixtures for Examples I to VI. The chemical shift allows an unambiguous assignment of the respective ²⁹ Si nuclei of the various compounds obtained.

The signals were assigned as follows: By-product: 1: SiCl ₄ at approx. -19 ppm Starting material: 2: Si ₂ Cl ₆ at approx. -6.5 ppm Products: 3: Si ₃ Cl ₈ at about -7.8 ppm and about -4 ppm 4: i-Si ₄ Cl ₁₀ at about -0.2 ppm 5: neo-Si ₅ Cl ₁₂ at about 3.5 ppm 6: neo-Si ₆ Cl ₁₄ at about 3.8 ppm and about 5.8 ppm

Example I shows a product mixture with various halogenated oligosilanes with NMR signals at -7.8 ppm and -4 ppm (3: Si ₃ Cl ₈ ), at -0.2 ppm (4: i-Si ₄ Cl ₁₀ ) 3.5 ppm (5: neo-Si ₅ Cl ₁₂ ) and at 3.8 ppm and 5.8 ppm (6: neo-Si ₆ Cl ₁₄ ).

Example II has signals with the same chemical shifts and thus the same halogenated oligosilanes as Example I but with different quantitative proportions.

Examples III, IV and V each show a signal in the NMR spectrum at 3.5 ppm and thus each have as halogenated oligosilane neo-Si ₅ Cl ₁₂ (5).

Examples VI has NMR signals at -7.8 ppm and -4 ppm (3: Si ₃ Cl ₈ ) and at 3.5 ppm (5: neo-Si ₅ Cl ₁₂ ).

In the following, a number of examples (Examples I to VI) are given with concrete reaction conditions, which further illustrate the inventive method.

The process of the invention is shown below using the example of the anisole-catalyzed disproportionation of hexachlorodisilane Si ₂ Cl ₆ . The influence of the reaction temperature and the Composition of the reaction mixture (ratio Si ₂ X ₆ to the catalyst and the solvent) explained on the composition of the resulting product mixture.

The experiments (Example I to Example VI) were carried out in each case in benzene (deuterated benzene C ₆ D ₆ for NMR analysis). The experiments were carried out in the absence of air and water in a nitrogen (99.996%) or argon (99.996%) inert gas atmosphere. The solvents were pre-dried with sodium in the presence of benzophenes and distilled from these materials before use. For NMR spectra, the Bruker AM 250, Bruker DPX 250, Bruker Avance 300, and Bruker Avance 400 nuclear magnetic resonance spectrometers were used. Reactions were performed in melted NMR tubes. An assignment of the reaction products as well as the evaluation of substance conversion and product distribution was carried out in each case by means of ²⁹ Si NMR spectroscopy on the normalized Edukt- and product signal surfaces. In each case tetrachlorosilane (SiCl ₄ ) was formed as a by-product.

With regard to the evaluation of the NMR spectra, it should be pointed out that due to the existence of isotopomers (further signals mostly undetectable) the signal surfaces are only proportionally proportional to the concentration, ie the signal surfaces of higher halogenated oligosilanes are on the one hand too small, on the other hand those of simple halosilanes like tetrachlorosilane too big. In addition, the presence of SiCl ₄ in the reaction mixture inhibits the progress of the reaction regardless of the amount of Lewis base used (electron pair donor). Example I: Room temperature, ratio Si ₂ Cl ₆ : anisole = 1: 1

Example I shows the anisole-catalyzed disproportionation of hexachlorodisilane (Si ₂ Cl ₆ ) at room temperature (25 ° C). 0.95 g (3.3 mmol) of hexachlorodisilane, 0.36 g of anisole (3.3 mmol) and 0.1 mL of benzene were used. After 2800 hours at a conversion of 72%, a mixture comprising tetrachlorosilane (SiCl ₄ ), unreacted hexachlorodisilane (Si ₂ Cl ₆ ) and four different halogenated oligosilanes containing three, four, five and six Si atoms was obtained. The proportion of the three Si atoms comprising octachlorotrisilane (Cl ₃ SiSiCl ₂ SiCl ₃ or Si ₃ Cl ₈ ) in the totality of the resulting halogenated oligosilanes was 32%. Decachloroisotetrasilane (ClSi (SiCl ₃ ) ₃ or i-Si ₄ Cl ₁₀ ) was obtained in a proportion of 12%.

Dodecachloroneopentasilane (Si (SiCl ₃ ) ₄ ) or neo-Si ₅ Cl ₁₂ ) was obtained in a proportion of 36% based on the total of halogenated oligosilanes. Surprisingly, it was possible to obtain the tetradecaneohexasilane (Cl ₃ SiSiCl ₂ Si (SiCl ₃ ) ₃ or neo-Si ₆ Cl ₁₄ ), which is difficult to prepare, with a proportion of 20%. Example II: 50 ° C, ratio Si ₂ Cl ₆ : anisole = 1: 1

Example II shows the same reaction as in Example I, but with 2.73 g (9.3 mmol) of hexachlorodisilane, 1 g of anisole (9.3 mmol) and 0.1 mL of benzene. The reaction was carried out at 50 ° C. The higher reaction temperature resulted in lower selectivity for neo-Si ₅ Cl ₁₂ and especially for neo-Si ₆ Cl ₁₄ . It is noteworthy that at only 50 ° C a substance conversion of more than 46% could be observed after just 3.5 hours. Example III: 80 ° C, Ratio Si ₂ Cl ₆ : Anisole = 1: 9.3

Example III shows an anisole-catalyzed disproportionation of hexahalogenedisilane at 80 ° C with anisole added in excess. 0.17 g (0.6 mmol) hexachlorodisilane, 0.6 g anisole (5.6 mmol) and 0.1 mL benzene were used. neo-Si ₅ Cl ₁₂ could be obtained in very good yield. After 48 hours, an approximately 100% conversion was observed. Example IV: 120 ° C, ratio Si ₂ Cl ₆ : anisole = 1: 0.6

Example IV shows an anisole-catalyzed disproportionation of hexahalogendisilane at 120 ° C, wherein the proportion of hexahalogendisilane prevails over the reaction mixture. 0.89 g (3.1 mmol) hexachlorodisilane, 0.20 g anisole (1.9 mmol) and 0.15 mL benzene were used. neo-Si ₅ Cl ₁₂ could be obtained in very good yield. After 50 hours, an approximately 90% conversion was observed. A comparison of Example III and IV shows that a high anisole content of the reaction mixture favors a higher metabolic rate. Example V: 180 ° C, ratio Si ₂ Cl ₆ : anisole = 1: 10.8

Example V shows an anisole-catalyzed disproportionation of hexahalogenedisilane at 180 ° C with anisole added in excess. 0.15 g (0.5 mmol) of hexachlorodisilane, 0.60 g of anisole (5.4 mmol) and 0.15 ml of benzene were used. Again, neo-Si ₅ Cl ₁₂ could be obtained in very good yield. After only 24 hours, an approximately 94% conversion was observed. The experiment emphasizes that a high anisole content in the starting mixture is advantageous for a rapid reaction with high yields of halogenated oligosilanes with a high number of Si atoms. Example VI: 210 ° C, Ratio Si ₂ Cl ₆ : Anisole = 1: 0.04

Example VI shows an anisole-catalyzed disproportionation of hexahalogenedisilane at 210 ° C, with only small amounts of anisole added in relation to Si ₂ Cl ₆ . 0.6 g (2.1 mmol) of hexachlorodisilane, 0.01 g (0.09 mmol) of anisole and 0.1 ml of benzene were used. Under these conditions, neo-Si ₅ Cl ₁₂ could only be obtained with a proportion of 12% of the total of the halogenated oligosilanes obtained. The remaining 88% was accounted for by Si ₃ Cl ₈ . The reaction shows that even at temperatures of 210 ° C and only a small proportion of anisole on the reaction mixture halogenated oligosilanes are accessible.

In summary, the selectivity for halogenated oligosilanes with the highest possible number of Si atoms of low temperatures and of a high proportion of Lewis base on the reaction mixture is favored, as well as surprising over a surprisingly wide range of mixing ratios and temperatures high substance conversions and yields based on the halogenated oligosilanes were achieved.

The invention is not limited by the description with reference to the embodiments. Rather, the invention encompasses any novel feature as well as any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments.

Claims (15)

A process for the preparation of halogenated oligosilanes comprising disproportionation of hexahalogendisilane, wherein the disproportionation is carried out with the aid of a catalyst selected from Lewis bases of the following general formulas: - R ¹ -OR ^2, - R ¹ -Y, wherein R ¹ each is an aryl, R ^{2 is} an alkyl or an aryl, and wherein Y is a halogen selected from F, Cl, Br and I. A process according to the preceding claim, wherein the hexahalkenedisilane is hexachlorodisilane. A process according to any one of the preceding claims, wherein R ^{1 is} a phenyl radical. A process according to any one of the preceding claims, wherein R ^{2 is} selected from the group consisting of phenyl, methyl, ethyl, propyl and butyl. A process according to any one of the preceding claims, wherein Y is chlorine. A process according to any one of the preceding claims, wherein the catalyst is anisole. A process according to any one of the preceding claims, wherein the catalyst is chlorobenzene. Method according to one of the preceding claims, wherein the disproportionation is promoted by thermal energy or microwave radiation. Method according to one of the preceding claims, carried out at a temperature between -78 ° C and 300 ° C, preferably between 0 ° C and 250 ° C. Method according to one of the preceding claims, carried out at a temperature between 0 ° C and 70 ° C, preferably between 20 and 55 ° C. Method according to one of the preceding claims, carried out at a temperature between 60 ° C and 210 ° C, preferably between 80 ° C and 180 ° C. Method according to one of the preceding claims, carried out in a protective gas atmosphere. Method according to one of the preceding claims, wherein the disproportionation is carried out in a non-polar solvent, preferably in benzene, toluene or mixtures thereof. Use of a Lewis base as a catalyst for the preparation of halogenated oligosilanes, wherein the Lewis base is selected from Lewis bases of the general formulas - R ¹ -OR ² , - R ¹ -Y, wherein R ^{1 is in} each case an aryl, R ^{2 is} an alkyl or an aryl, and wherein Y is a halogen selected from F, Cl, Br and I. Use according to the preceding claim, wherein the Lewis base is anisole or chlorobenzene.

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