METHYLSILYLHYDROXYLAMINES - PREPARATIVE, SPECTROSCOPIC AND AB-INITIO STUDIES

Methylsilylhydroxylamines [(MeH2Si)2NOMe, (MeH2Si)MeNOMe, Me2NOSiH2Me] have been prepared from bromo(methyl)silane and the corresponding met hylhydroxylamines in the presence of an auxiliary base (triethylamine or N,N,N',N'-tetramethylethylenediamine). The compounds were studied b y NMR spectroscopy of all elements present (H-1, C-13, N-15, O-17, Si- 29). The magnitude of the one-bond coupling constants (J(NSi))-J-1-N-1 5-Si-29 is interpreted in terms of the hybridization associated with t he pyramidal co-ordination of nitrogen, a unique structural feature in Si/N chemistry. Ab initio studies confirmed these structural predicti ons. Singly silylated hydroxylamines have been shown to be more strong ly pyramidal than doubly silylated ones. Calculations on the model com pound (H3Si)2NOMe gave a barrier to inversion at nitrogen of 9.7 kcal mol-1. This inversion is accompanied by a partial rotation around the N-O bond. The NMR chemical shifts of the compounds have been calculate d and the results are in good agreement with the experimental data. Th e unusually low chemical shifts delta(O-17) of hydroxylamines have thu s been confirmed by theory. A comparison of the calculated normal mode s of vibration with experimental data leads to a complete assignment o f the IR spectra.