A STEEPLY PYRAMIDAL SILYLAMINE - N,O-DIMETHYL-N-SILYLHYDROXYLAMINE

N,O-Dimethyl-N-silylhydroxylamine (H3SiMeNOMe) has been prepared by re action of HMeNOMe with H3SiBr and 2,6-lutidine as an auxiliary base. I ts identity has been proved by gas-phase IR and solution NMR spectrosc opy of the nuclei H-1, C-13, N-15, O-17, and Si-29 and by mass spectro metry. The solution NMR data indicate aggregation of the compound in s olution. H3SiMeNOMe decomposes within weeks at ambient temperature, an d an extrusion of methylnitrene is probably the mechanistic pathway in volved. The final products of this decomposition are an insoluble prec ipitate and SiH4. The energy of H3SiMeNOMe relative to its potential r earrangement isomer MeHN-H2Si-OMe has been estimated by ab initio calc ulations to be 289 kJ mol(-1). The molecular structure of H-3-SiMeNOMe has been determined by gas-phase electron diffraction and by ab initi o calculations. The results show H3SiMeNOMe to possess a steeply pyram idal nitrogen atom and to adopt a trans conformation. It is thus the f irst silyl nitrogen compound that adopts a typically pyramidal nitroge n coordination for purely electronic reasons. The Si-N bond is found t o be only slightly elongated with respect to those of comparable compo unds with planar nitrogen coordination. Important bond length and angl es are Si-N 1.742(1), N-O 1.449(4), N-C 1.460(3), and O-C 1.425(4) Ang strom 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 sil icon 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) hyperconj ugation in the NBO description shows that this effect cannot be solely responsible for the generally observed flattening of the nitrogen coo rdination in silylamines.