title: Molecular structure and conformations of 2,2-di-tert-butyl-1,3-diaza-2-silacyclopentane: gas electron diffraction and quantum chemical calculations.
abstract: The geometric structure and conformational properties of the saturated five-membered-ring compound 2,2-di-tert-butyl-1,3-diaza-2-silacyclopentane, (t-Bu)(2)Si(NH)(2)(CH(2))(2), was investigated by gas electron diffraction and quantum chemical methods (B3LYP and MP2 with 6-31G basis sets). The compound exists as a mixture of two conformers, both possessing a twist conformation and C(2) symmetry. In the prevailing form (76(6) % at 305 K) the N-H bonds stagger the adjacent CH(2) groups, and in the minor form the N-H bonds eclipse the CH(2) groups. This conformational mixture corresponds to a free energy difference of DeltaG degrees = 0.69(19) kcal/mol. The B3LYP method predicts a preference for the eclipsed conformer. The largest torsion occurs around the C-C bond with tau(NCCN) = 29.2(24) degrees. The degree of puckering in the title compound is considerably smaller than that in silacyclopentane with tau(CCCC) = 49.7(14) degrees. This has been rationalized by larger angle strain in the title compound.
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Tübingen, 72076 Tübingen, Germany. heinz.oberhammer@uni-tuebingen.de
authors.forename: Heinz
authors.initials: H
authors.lastname: Oberhammer
authors.forename: Georgiy V
authors.initials: GV
authors.lastname: Girichev
authors.forename: Nina I
authors.initials: NI
authors.lastname: Giricheva
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Krasnov
authors.forename: Uwe
authors.initials: U
authors.lastname: Klingebiel