Crytal and molecular structures of γ-1-phenylsilatrane: some structural features of silatranes

Abstract

γ-1-phenylsilatrane crystallizes in the monoclinic space group P2 1/ n, with a 8.475, b12.949, c 11.122 » and β 90.86°. The structure was determined by direct methods and was refined to R 0.078 for 1687 observed reflexions and 0.081 for all 1813 reflexions. The →Si bond length is 2.132(4), SiC is 1.894(5) ». The mean SiO bond distance is 1.656 Å, angle NSiC is 179.0(2)°. The average NSiO, CSiO and OSiO angles are 83.6, 96.4 and 123.5°. By use of published data for six other silatrane molecules, some structural features were established. Thus, the length of the N→Si bond is affected by the other apical substituents of the silicon atom, the number of oxygen atoms attached to it and steric effects. Increase in the length of the dative N→Si bond is accompanied by further distortion of the trigonal bipyramidal configuration and of the tetrahedron around the nitrogen atom. The relatively long SiC( sp 2) bond may be due to decrased d π  p π interaction. The crystalline modifications (α, β, ψ) of the 1-phenyl-derivative possibly result from rapid ring-inversion in solution.