Molecular Structure and Conformations of 2,2-Di-tert-butyl-1,3-diaza-2-silacyclopentane:  Gas Electron Diffraction and Quantum Chemical Calculations

• Published in: Inorganic chemistry 2004-05, Vol.43 (11), p.3537-3542
• Main Authors: Oberhammer, Heinz, Girichev, Georgiy V, Giricheva, Nina I, Krasnov, Alexander V, Klingebiel, Uwe
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic0497836

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)2Si(NH)2(CH2)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 CH2 groups, and in the minor form the N−H bonds eclipse the CH2 groups. This conformational mixture corresponds to a free energy difference of ΔG° = 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 τ(NCCN) = 29.2(24)°. The degree of puckering in the title compound is considerably smaller than that in silacyclopentane with τ(CCCC) = 49.7(14)°. This has been rationalized by larger angle strain in the title compound.