Five-co-ordinated silicon compounds: geometry of formation by intramolecular co-ordination. Crystal structure of 2-(dimethylaminomethyl)phenyl-1-naphthylsilane

Abstract

Studies of a wide range of intramolecularly five-co-ordinated silicon compounds with chelating nitrogen donors have been made, with a view to obtaining further information on the details of nucleophilic substitution reactions at silicon. The crystal structure of 2-(dimethylaminomethyl)-phenyl-1 -naphthylsilane has been determined by single-crystal X-ray diffraction (R= 0.074 for 564 observed reflections). Crystals are tetragonal, space group I, with Z= 8 in a unit cell of dimensions a= 21.845(5) and c= 7.119(2)Å. The central silicon atom shows essentially trigonal-bipyramidal co-ordination, with the axial positions occupied by the naphthyl group and the donor nitrogen atom, and the two hydrogen atoms occupying equatorial positions. Comparison with other structures reported in the literature shows that this geometry, always with axial disposition of the donor atom, is generally adopted by molecules of this type. Silicon-29, ¹⁹F, and ¹H n.m.r. spectroscopic data for similar compounds with varying substituents on the silicon atom show that the same geometry is adopted by these intramolecularly co-ordinated species in solution.