Methylchlorosilanes disproportionation

At higher temperatures the methylchlorosilanes themselves appear to react with aluminum, furnishing methyl groups for the further alkylation of some molecules at the expense of others which are reduced to free silicon. This actually is a form of disproportionation, in which organic groups are stripped from some silicon atoms and attached to others. In this and the similar reactions zinc or aluminum acts as halogen acceptor. 

The disadvantages of the synthesis routes 1-4 are the application of highly reactive and expensive metals (Li, Na, K, Mg) and the enormous quantity of solvents. Particularly, as result of the dehalocoupling reactions, the polymers are unreactive at room temperature. To overcome these problems we synthesized spinnable reactive poly(silanes/-carbosilanes) via heterogeneous catalytic disproportionation of methylchlorodisilanes which have been wasted as a byproduct of the "Direct synthesis" of methylchlorosilanes so far. 

Scheme 1. Disproportionation of 1,1,2,2-tetrachlorodimethyldisilane (1) into methyltrichlorosilane (2) and oligo-(methylchlorosilane) (3)...

The polymers were melt spun under inert conditions into polymer filaments with diameters of about 25 pm. Spectroscopic investigations of these polymers are described in [5]. As shown in Scheme 2 the disproportionation of methylchlorodisilanes (1) in presence of olefins like styrene (4) gives poly(methylchlorosilanes-co-styrene) (5) with excellent spiimability. 

Poly(methylchlorosilanes) which have been prepared by Lewis-base catalyzed disproportionation of 1,1,2,2-tetrachlorodimethyldisilane give rise to a complex pyrolytic conversion into silicon carbide. In the temperature region 180-450 °C under dry argon, the polymer samples are cross-linked. Characterization of the pyrolysis intermediates and final products by and Si MAS in both CP and IRCP techniques as well as TG/MS studies strongly suggest the loss of methylchlorosilanes as well as oligosilanes during pyrolysis (c.f. Scheme 21). 

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