METHYLSILYLHYDROXYLAMINES - PREPARATIVE, SPECTROSCOPIC AND AB-INITIO STUDIES

Methylsilylhydroxylamines [(MeH2Si)2NOMe, (MeH2Si)MeNOMe, Me2NOSiH2Me] have been prepared from bromo(methyl)silane and the corresponding methylhydroxylamines in the presence of an auxiliary base (triethylamine or N,N,N',N'-tetramethylethylenediamine). The compounds were studied by 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-15-Si-29 is interpreted in terms of the hybridization associated with the pyramidal co-ordination of nitrogen, a unique structural feature in Si/N chemistry. Ab initio studies confirmed these structural predictions. Singly silylated hydroxylamines have been shown to be more strongly pyramidal than doubly silylated ones. Calculations on the model compound (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 calculated and the results are in good agreement with the experimental data. The unusually low chemical shifts delta(O-17) of hydroxylamines have thus been confirmed by theory. A comparison of the calculated normal modes of vibration with experimental data leads to a complete assignment of the IR spectra.