1,3-Dimethyl-3-silapiperidine: synthesis, molecular structure, and conformational analysis by gas-phase electron diffraction, low temperature NMR, IR and Raman spectroscopy, and quantum chemical calculations

Bagrat A Shainyan; Svetlana V Kirpichenko; Erich Kleinpeter; Sergey A Shlykov; Dmitriy Yu Osadchiy; Nina N Chipanina; Larisa P Oznobikhina

doi:10.1021/jo400289g

1,3-Dimethyl-3-silapiperidine: synthesis, molecular structure, and conformational analysis by gas-phase electron diffraction, low temperature NMR, IR and Raman spectroscopy, and quantum chemical calculations

J Org Chem. 2013 Apr 19;78(8):3939-47. doi: 10.1021/jo400289g. Epub 2013 Mar 22.

Authors

Bagrat A Shainyan¹, Svetlana V Kirpichenko, Erich Kleinpeter, Sergey A Shlykov, Dmitriy Yu Osadchiy, Nina N Chipanina, Larisa P Oznobikhina

Affiliation

¹ A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Science, 1 Favorsky Street, 664033, Irkutsk, Russian Federation. bagrat@irioch.irk.ru

PMID: 23477596
DOI: 10.1021/jo400289g

Abstract

The first Si-H-containing azasilaheterocycle, 1,3-dimethyl-3-silapiperidine 1, was synthesized, and its molecular structure and conformational properties were studied by gas-phase electron diffraction (GED), low temperature NMR, IR and Raman spectroscopy and quantum chemical calculations. The compound exists as a mixture of two conformers possessing the chair conformation with the equatorial NMe group and differing by axial or equatorial position of the SiMe group. In the gas phase, the SiMe(ax) conformer predominates (GED: ax/eq = 65(7):35(7)%, ΔG = 0.36(18) kcal/mol; IR: ax/eq = 62(5):38(5)%, ΔG = 0.16(7) kcal/mol). In solution, at 143 K the SiMe(eq) conformer predominates in the frozen equilibrium (NMR: ax/eq = 31.5(1.5):68.5(1.5)%, ΔG = -0.22(2) kcal/mol). Thermodynamic parameters of the ring inversion are determined (ΔG(‡) = 8.9-9.0 kcal/mol, ΔH(‡) = 9.6 kcal/mol, ΔS(‡) = 2.1 eu). High-level quantum chemical calculations (MP2, G2, CCSD(T)) nicely reproduce the experimental geometry and the predominance of the axial conformer in the gas phase.