Anionic 1,2-(O -> N) and neutral 1,2-(N -> O, O -> N) silyl group migration - Synthesis of isomeric tris(silyl)hydroxylamines and a silylaminodisiloxane

The lithium derivative of N,O-bis(tert-butyldimethylsilyl)hydroxyl Me3CSiMe 2NH-OSiMe2CMe3 (1), is isolated as the first dimeric O-lithium-N,N-bis(sily l)hydroxylamide, [(THF)Li-O-N(SiMe2CMe2)(2)](2) (2). The tendency of the ha rd Lewis-acid lithium to bind the hard Lewis-base oxygen explains the O --> N-silyl group migration. 2 reacts with tert-butyltrifluorosilane to give t he tris(silyl)hydroxylamine Me3CSiF2-O-N(SiMe2CMe3)(2) (3). An irreversible rearrangement involving positional exchange between the fluorosilicon grou p on oxygen and one organosilicon group on nitrogen in 3 leads to the forma tion of the isomeric tris(silyl)hydroxylamine Me3CSiMe2-O-N(SiMe2CMe3)-SiF2 CMe3 (4). The rearrangement proceeds via a dyotropic transition state. 4 un dergoes an intramolecular thermal rearrangement involving the insertion of a silyl moiety into the N-O bond and the transfer of a methyl group from si licon to nitrogen. The silylaminodisiloxane Me3CSiMe2-O-SiMe(CMe3)-NMe-SiF2 CMe3 (5) is obtained. The influence of the effects of the substituents of t he product formation is discussed and the crystal structure of 2 is reporte d.