Molecular structure of N-trimethylsilylaziridine in the gas phase

N-Trimethylsilylaziridine, Me3SiNC2H4 1, prepared by a literature procedure has been studied by gas-phase IR and NMR spectroscopy of the nuclei H-1, C -13, N-15, Si-29. The molecular structure of 1 has been determined in the g as phase by analysis of electron diffraction (GED) data augmented by geomet ric and vibrational amplitude restraints derived from ab initio calculation s employing the second order Moller-Plesset (MP2) level of theory and the 6 -311G(d,p) basis set. The molecule was found to adopt C-s symmetry and has a pyramidal arrangement around the nitrogen atom with a slightly elongated Si-N bond [1.770(4) Angstrom], relative to those in other Si-N species havi ng a planar nitrogen co-ordination. The results for the principal distances (r(a)) and angles from the combined GED/ab initio study of Me3SiNC2H4 are (uncertainties: one sigma): r(Si-N) = 1.770(4), r(Si-Cin-plane) = 1.868(4), r(Si-Cout-of-plane) = 1.881(2), r(C-N) = 1.459(3) Angstrom, C-N-C 61.1(5), N-Si-Cin-plane 109.7(7), N-Si-Cout-of-plane 107.8(10), Si-N-C 121.9(4)degr ees. The structure data are complemented by natural bond orbital analyses, and calculation of the barrier to inversion at the nitrogen centre, which i s predicted to be 21.4 kJ mol(-1). Calculations on the simpler model compou nd H3SiNC2H4 [up to QCISD/6-311G(d,p)] gave geometrical and energetic resul ts similar to those of 1. The steeply pyramidal nitrogen co-ordination is a ttributed to the strain of the aziridine ring, as was found by comparison w ith the results of other calculations on acyclic systems and those with lar ger rings.