GB2244993A - Method of transsilylation - Google Patents

Abstract

A transsilylation method comprises reacting a compound of the general formula <IMAGE> with an organosilicon compound of the general formula <IMAGE> in the presence of a rhodium or palladium based catalyst. A, A', A'', X, X', X'', Y, Y' and Y'' denote H, halogen, aliphatic or aromatic hydrocarbon or hydrocarbonoxy or an organosilicon group consisting of C, H and Si atoms and optionally O atoms. By selecting the substituents to increase volatility of the reaction products transsilylation is encouraged.

Description

METHOD OF TRANSSILYLATION This invention relates to a method of transsilylation. The invention also relates to the materials obtained by such method.

It has been known for a long time that olefinic unsaturated compounds, or acetylenic unsaturated compounds, may be reacted with silicon compounds having silicon-bonded hydrogen atoms in the presence of Group VIII catalyst.

This reaction is called hydrosilylation reaction and can be summarised by the following reaction scheme

or

wherein R may be hydrogen or an organic compound, preferably a hydrocarbon group. In each of these reactions the unsaturation is changed either from olefinic unsaturation to complete saturation or from acetylenic unsaturation to olefinic unsaturation. The most favoured catalyst for the hydrosilylation reaction is a Pt compound or complex.

Thiere such hydrosilylation reaction is carried out with compounds having acetylenic unsaturation and R being an organosilicon group in the presence of a Pt compound or complex the reaction follows the general scheme set out above, although some side reactions tend to occur as well.

We have now found that if, in the latter reaction, a Pd or Rh based catalyst is used tie transsilylation reaction is preferred.

According to the invention there is provided a method of transsilylation which comprises reacting a compound (1) of the general formula

with an organosilicon compound (2) of the general formula

in the presence of (3) a rhodium or palladium based catalyst wherein each of A, A', A", X, X', X", Y, Y' and Y" denote independently hydrogen, halogen, an aliphatic or aromatic hydrocarbon group, an aliphatic or aromatic hydro- carbonoxy group or an organosilicon group linked to the silicon atom of compound (1) or (2) directly or via an oxygen atom or a bivalent carbon or hydrocarbon group and consisting of C, H and Si atoms and, optionally 0 atoms, wherein the silicon-bonded groups may be hydrogen, halogen, aliphatic or aromatic hydrocarbon or hydrocarbonoxy groups.

Compound (1) for use in the method of the inventIon may be any compound in which the silicon-bonded substituents are hydrogen, aliphatic or aromatic hydrocarbon or organosilicon groups. SuItable hydrocarbon substituents include alkyl, aryl, arylalkyl and alkylaryl groups, e.g.

methyl, ethyl, propyl, isobutyl, phenyl, phenylethyl and styryl. Suitable organosllicon groups include triorganosilyl groups, siloxanyl groups and polysilyl groups, e.g.

trimethylsilyl groups, trimethylsilyl endblocked polydi methylsiloxanyl groups and trimethylsilyl endblocked polydimethylsilyl groups. It is preferred, however, that in compound (1) A, A', A", X, X' and X" are all alkyl groups, most preferably lower alkyl, particularly methyl groups. Accordingly the most preferred compound is bis (trimediylsilyl) acetylene.

Compound (2) for use in the method of the invention may be any organosilicon compound which has at least one silicon-bonded hydrogen atom. The Y, Y' and Y" groups may be any of those discussed for A, A', A", , X, Xl and X" above. It is, however, preferred that Y' and Y1, are both alkyl groups, most preferably lower alkyl, particularly methyl. Y may be the same or different from Y' and Y".

This will vary according to the type of reaction product one is planning to make. A particularly useful type of Y substituent is the one which provides compound (2) with a second silicon-bonded hydrogen atom, e.g. a dimethylhydrosilyl endblocked polydiorganosiloxanyl group or a dimethylhydrosilyl endblocked polydiorganosilyl group.

This type of substituent would result in the production of copolymers having silethynyl groups and either polysiloxane groups or polysilyl groups. The former of these have been described for example in G.B. patent application 2 234 517.

In general it is preferred that the substituents Y, Y' and Y" are chosen thtls ttiat the compound (2) is less volatile than the reaction product of the general formulae

This would encourage the transsilylation reaction by removal of one of the reaction products during the reaction.

It is possible that compound (1) and compound (2) are identical. This would occur e.g. where the group X would be a hydrogen atom and the group Y a group A3SiC~C-.

The catalyst (3) may be any rhodium or palladium catalyst which is suitable for standard fiydrosilylation reactions. Many of these catalysts are well known in die art and have been described in numerous publications. They include phosphine palladium complexes, phosphine rhodium complexes, silylrhodium complexes and rhodium carbene complexes, to name but a few.Examples of suitable catalyst wherein Ph denotes a phenyl group, Et an ethyl group and Me a methyl group are PdCl2, PdC, (Ph3P)2Pd, PdCl2(PPh3)2, PdCl2(PhCN)2, Pd(PPh)4, PdCl2(PhCK)2, (Ph3P)3RhCl, RhCl(CO)(PPh3)2, RhH(CO)(PPh3)3, (PhCh2MePhP)2RhCl, (PhCH2PPhMe)Rh(S)Cl, RhCl2H(CHNMe2)(PPh3)2, ((C8H14)2RhCl)2, (NMe3)2(Rh2Cl9), (NME3)(Rh(Me2SO)2Cl4), (NMe3)(Rh(Et2SO)2Cl4), reaction product of oxidative addition of hydrosilanes with hydridotetrakis(triphenylphosphine)Rh, RhH2(SiPhMe2)(PPh3)2, RhH2(SiPhMe2)(PPh3), RhH2(SiPh(OMe)2)(PPh3), Et3SiEliH. (PPh3)2Cl, tris(pentanedionato! Rhodium(III), RhCl(SbPh3)3, Rh(Acetylacetonate) (CO)2, 3,3-(PPh3)2-4-C5H5N-3,1,2-RhC2B8H10, RhCl2(P(o-C6H4Me)3)2, RbCl2(P(C6H11)3)2, Rh4(CO)12, (RhCl(1,Scyclooctadiene))2, RhCl(Et)2)2, Rh(acetylacetonate) 3' (RhCl(norbornadiene))2, Rh-1,4-diphosphinobutane, (bicyclo(2.2.1)hepta-2,5-diene) rhodium complexes, (Rh(1,5cyclooctadiene)Cl)2-n-menthylsalicylaldimine, (Rh(1,5cyclooctadiene)Cl)2-N,N'-bis(menthyl)butyane2,3-diimine, (Rh(1,5cyclooctadiene)Cl)2-4-N-menthylpentanimin-2-one, (RhCl(P(OMe)3)2)2, (RhH(P(O-o-tolyl)3)2, RhH2(Si(MeO)3)(PPh3)2, (Rh(dimethylglyoxime)2PPh3)2, reaction product of (Rh(1,5hexadiene)Cl)2 or (Rh(1,5hexadiene)Cl)2 with benzyl-methylphenylphosphine, Rh(I)-(2,3-O-isopropylidene-2,3-dihydroxy-1, 4-bis(diphenylphosphino)butane) and (RhI2H2S2)+ ClO4-.

Preferred are the the triphenylphosphine complexes of palladium and rhodium, most preferred the rhodium complexes.

The reaction may be carried out at any convenient temperature but preferred are higher temperatures, e.g. 100 to 2500C. Most preferred are temperatures at which the product of the general formulae

are easily removed, e.g. by use of an air flow or a nitrogen blanket possibly assisted by the use of reduced pressure. Most preferably the temperature is chosen to be at least at or above the boiling point of said reaction products at atmospheric pressure. In order to obtain transsilylation at both silicon atoms which are adjacent to die acetylenic unsaturation in compound (1), a stoichiometric excess of the organosilicon compound (2) is required.The reaction may be carried out under normal atmospheric conditions but it is preferred to carry out the invention under a nitrogen an argon or a dried air blanket, most preferably air.

The transsilylation reaction is useful e.g. for forming substituted disilylacetylene from bis(trimethyl silyl)acetylere which is itself readily available. The method of the invention is also useful to form poly(silylethynylene) or copolymers with polysiloxane materials.

Such copolymers are useful as precursors for ceramic silicon-based materials.

There now follow a number of examples in which the invention is illustrated. All percentages and ratios are given by weight. Ph denots a phenyl group, He a hexyl group, Bu a butyl group and Me a methyl group.

Example 1 ig of bis(trimethylsilyl)acetylene and 0.85g of dimethylliexylsilane (HSiMe2He) were mixed together and reacted in the presence of 6mg of Rh(PPh3)3C1 at 1300C for 30 minutes under a nitrogen blanket. Of the reaction product 17% by weight was unreacted bis(trimetE1ylsilyl) acetylene, 52t had the formula MeSiC#CSiMe2He and 22% was the di-transsilylated product HeMe2SiC-CSiMe2He. The products were characterised by gas chromatography, mass spectroscopy and Si29 nuclear magnetic resonance.

Example 2 The procedure of Example 1 was followed except that 1.1g of HSiMe2OSiMe2Bu was used instead of dimethylhexylsilane. The resulting reaction mixture contained 15% of the unreacted bis(trimethylsilyl)acetylene, 61% was the mono-transsilylated Me3SiCECSiMe2OSiMe2Bu and 20% the ditranssilylated BuMe2SiOme2OSiMe2Bu. The products were characterised by gas chromatography, mass spectroscopy and Si29 nuclear magnetic resonance.

Example 3 Ig of bis(trimethylsilyl)acetylene and 2.lg of dimethylsilyl-endblocked dimethyltrisiloxane (HSiMe2(OSiMe2)4H) were mixed together and reacted in the presence of 30mg of Rh(PPh3)3Cl at 1300C for 3C minutes under a nitrogen blanket. The resulting product had the average formula -[(Me2SiO)4-Me2Si-C#C-]. The compound was analysed by Gel Permeation Chromatography and C13 nuclear magnetic resonance.

Example 4 lg of bis(trimethylsilyl)acetylene and 0.85g of HeSiMeqH were mixed together and reacted in the presence of 5mg of Pd(PPh3)2Cl2 at 130 C for 7 hours under dry air.

The resulting reaction mixture contained 38% of die unreacted bis(trimethylsilyl)acetylene, 12X was die monotranssilylated Me3SiCSCSiMe2OSiMe2Bu and 7% the ditranssilylated BuMe2SiOMe2SiC#CSiMe2Bu. The compound was analysed by Gel Permeation Chromatography and Si29 nuclear magnetic resonance.

Example 5 0.7g of Me3SiC#CSiMe2H was reacted with 5mg of Rh(PPh3)3C1 under dry air at 130 C for l hour. The resulting reaction product included 30% of Me3SiCECSiMe2CECSiMe3. The compound was characterised by gas chromatography mass spectroscopy.

Claims (10)

1. A method of transsilylation comprising reacting a compound (1) having the general formula

with an organosilicon compound (2) of the general formula

in the presence of (3) a rhodium or palladium based catalyst wherein each of A, A', A", X, X', X", Y, S" and Y" denote independently hydrogen, halogen, an aliphatic or aromatic hydrocarbon group, an aliphatic or aromatic hydrocarbonoxy group or an organosilicon group linked to the silicon atom of compound (1) or (2) directly or via an oxygen atom or a divalent carbon or hydrocarbon group said organosilicon group consisting of C, H and Si atoms and, optionally 0 atoms, wherein the silicon-bonded groups may be hydrogen, halogen, aliphatic or aromatic hydrocarbon or hydrocarbonoxy groups.

2. A method according to Claim 1 wherein all A, A', A", X, X' and X" groups are alkyl groups.

3. A method according to Claim 1 or Claim 2 wherein all A, A', A", X, X' and X" groups are methyl groups.

4. A method according to any one of the preceding claims wherein Y' and Y" are alkyl groups.

5. A method according to any one of the preceding claims wherein Y' and Y" are methyl.

6. A method according to any one of the preceding claims wherein Y is a hydrogen atom.

7. A method according to any one of the preceding claims wherein compound (2) is less volatile than compounds

and/or

8. A method according to any one of the preceding claims wherein compound (3) is a triphenylphosphine complex of palladium or rhodium.

9. A method according to any one of the preceding claims wherein the reaction is carried out at a temperature which is at least equal to the boiling point at atmospheric pressure of compounds

10. Transsilylated products formed by a method according to any one of the preceding claims.