NEW AZASILATRANE CATIONS - QUATERNIZATION OF AN EQUATORIAL NITROGEN IN AZASILATRANES

Azasilatranes (RSi(R'N(eq)CH2CH2)3N(ax)) possessing strong SiN(ax) transannular interactions are regioselectively quaternized by Me+ or Me3Si+ at an equatorial nitrogen, giving stable isolable salts. For the reaction of Me3SiO3SCF3 with the azasilatrane in which R = R' = Me, mixtures of the triflate salts of the cations MeSi[Me3SiN+(Me)CH2CH2]-(MeNCH2CH2)2N and MeSi(MeNCH2CH2)3N+SiMe3 are present in solution and in the solid state. The stability of the latter cation is suggested to arise from delocalization of electron density and the N(ax) positive charge in an elongated four-center four-electron MO system oriented along the molecular axis. The reaction of MeSi(Me3SiNCH2CH2)3N with Me3SiO3SCF3 is also unusual, giving the novel cation MeSi(Me3SiNCH2CH2)2N+CH2CH2N(SiMe3)2, which may be in equilibrium with a dimer containing five-coordinate silicon. The H-1 C-13, Si-29, and N-15 NMR spectra of these compounds are discussed.