SILYL AND SILYLMETHYL RADICALS, SILYLENES, SILA-ALKENES, AND SMALL RING SILACYCLES IN REACTIONS OF ORGANOCHLOROSILANES WITH ALKALI METAL VAPOURS

Article abstract of DOI:10.1016/0022-328X(85)87334-4

Dehalogenation of the organochlorosilanes Me3SiCl (I), Me2PrSiCl (II), Me3SiSiMe2Cl (III), Me3SiCH2SiMe2Cl (IV), ClCH2SiMe3 (V), ClCH2SiMe2SiMe3 (VI), ClCH2Me2SiSiMe2CH2Cl (VII), Me2SiCl2 (VIII), MePrSiCl2 (IX), Me3SiCH2SiMeCl2 (X), Me3SiCH2CH2SiMeCl2 (XI), Me3SiCH2CH2CH2SiMeCl2 (XII), ClCH2Si(H)MeCl (XIII), ClCH2SiMe2Cl (XIV), ClMe2SiSiMe2Cl (XV), ClCH2CH2CH2Si(H)MeCl (XVI), ClCH2CH2CH2SiMe2Cl (XVII), ClCH2CH2OSiMe2Cl (XVIII), ClMe2SiCH2SiMe2Cl (XIX), ClMe2SiCH2CH2SiMe2Cl (XX), and ClMe2SiCH2CH2CH2SiMe2Cl (XXI) with K/Na alloy vapours at 0.1-1 Torr and 300-320 deg C yields products derived from the reactions of short-lived intermediates, such as silyl and silylmethyl radicals, silylenes, and sila-alkenes.In addition, small-ring silacycles of low stability are formed as the intermediates in some of the dehalogenation reactions.Combination and H-atom abstraction are the main reactions of silyl and silyl-methyl radicals.These radicals are not prone to decomposition reactions when C-H, C-C, or Si-C bonds are at the β(Si-Si) bond with the formation of Me2Si=CH2 and the trimethylsilyl radical.The generation of alkylmethylsilylenes is accompanied by their decomposition processes, which involves intramolecular β(C-H) insertion of alkylmethylsilylenes and <3->2+1>-thermocyclodecomposition of intermediate silacyclopropanes.The contribution of δ(C-H) and ε(C-H) insertion reactions is much less pronounced, and in the formation of five- or six-membered silacycles.We did not succeed in obtaining monosilacyclobutanes, as the intramolecular γ(C-H) insertion is not typical for silylenes with alkyl substituents.Dehalogenation of chloromethylchlorosilanes with alkali metal vapours yields sila-alkenes, and that of 1,2-dichlorodisilanes gives disilenes. 1-Methyl-1-silaethylene, obtained by this method, does not rearrange into dimethylsilene, but dimerizes to give 1,3-dimethyl-1,3-disilacyclobutane.The formation of 1,3,5-trisilacyclohexanes takes place due to subsequent radical addition at the silicon-carbon double bond and cyclization of 1,6-biradicals.Dehalogenation of organochlorosilanes XVI, XVII, and XX opens up possibilities for the gas-phase synthesis of small organosilicon heterocycles: monosilecyclobutanes and 1,2-disilacyclobutanes.A new, low-stability heterocycle, i.e. 1,1,2,2-tetramethyl-1,2-disilacyclobutane, has been obtained, which enables a new, high polymer, polyethylenetetramethyldisilene, to be obtained.In the case of organochlorosilanes XVIII and XIX, cyclization is accompanied by secondary reactions of silacycles, rearrangements, dimerization, or decomposition.