Silicon–nitrogen compounds. Part X. Dehydrofluorination of tetrafluorosilane–amine adducts with anionic hydrides and related compounds

Abstract

Adducts of tetrafluorosilane and secondary amines NHR₂(R = Me or Et) react, especially when an excess of tetrafluorosilane is present, with the following dehydrofluorinating agents: LiAlH₄(200°); NaBH₄(200°); B₂H₆(190–200°); electropositive metals (350°). The products are corresponding substituted aminofluoro-silanes SiF_4–n(NR₂)_n, (R = Me, n= 1 or 2; R= Et, n= 1). Tetrafluorosilane slowly reacts at 25° with alkali metals in liquid NHMe₂ to give SiF₂(NMe₂)₂. Similarly, SiF₄ and primary amines, on heating with LiAlH₄(or in some cases NaBH₄), produce corresponding N-substituted hexafluorodisilazanes (SiF₃)₂NR (R = H, Me, Et, Ph, or NMe₂). In some cases, evidence for partly-substituted SiF₃NHR or condensed SiF₃NR(SiF₂NR)_n SiF₃ derivatives was obtained. The chief or sole product from SiF₄–NH₂R–B₂H₆ reactions is a borazole B₃H₃N₃R₃: also the diamine NHMe[CH₂]₂NHMe gives rise to H[graphic omitted]Me. The adduct SiF₄,2NH₂Me is not dehydrofluorinated when heated alone or with added NEt₃, NH₂Ph, zinc, or Fe(CO)₅; above 300° some disproportionation of the amine occurs. Physical properties of the products, including the mass spectrum of (SiF₃)₂NH and i.r. spectra are reported; also possible intermediates in dehydrofluorination are discussed.