A Steeply Pyramidal Silylamine: N,O-Dimethyl-N-silylhydroxylamine.

Abstract

N,O-Dimethyl-N-silylhydroxylamine (H(3)SiMeNOMe) has been prepared by reaction of HMeNOMe with H(3)SiBr and 2,6-lutidine as an auxiliary base. Its identity has been proved by gas-phase IR and solution NMR spectroscopy of the nuclei (1)H, (13)C, (15)N, (17)O, and (29)Si and by mass spectrometry. The solution NMR data indicate aggregation of the compound in solution. H(3)SiMeNOMe decomposes within weeks at ambient temperature, and an extrusion of methylnitrene is probably the mechanistic pathway involved. The final products of this decomposition are an insoluble precipitate and SiH(4). The energy of H(3)SiMeNOMe relative to its potential rearrangement isomer MeHN-H(2)Si-OMe has been estimated by ab initio calculations to be 289 kJ mol(-)(1). The molecular structure of H(3)SiMeNOMe has been determined by gas-phase electron diffraction and by ab initio calculations. The results show H(3)SiMeNOMe to possess a steeply pyramidal nitrogen atom and to adopt a trans conformation. It is thus the first silyl nitrogen compound that adopts a typically pyramidal nitrogen coordination for purely electronic reasons. The Si-N bond is found to be only slightly elongated with respect to those of comparable compounds with planar nitrogen coordination. Important bond length and angles are Si-N 1.742(1), N-O 1.449(4), N-C 1.460(3), and O-C 1.425(4) Å and Si-N-C 121.8(5), Si-N-O 104.3(4), C-N-O 106.2(12), and N-O-C 103.2(12) degrees. Results of an NBO analysis show the silyl group to be bound by a nitrogen sp(2) hybrid, the d-orbital contribution at silicon to be less than 2%, and the N-O bond to comprise mainly p-orbital contribution. The presence of a marked p(lp-N)-sigma(Si-H) hyperconjugation in the NBO description shows that this effect cannot be solely responsible for the generally observed flattening of the nitrogen coordination in silylamines.