Methylsilylhydroxylamines: preparative, spectroscopic and ab initio studies

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Abstract
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 (1H, 13C, 15N, 17O, 29Si). The magnitude of the one-bond coupling constants 1J(15N29Si) 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 δ(17O) 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.