The Physical Chemistry of Silatranes

Silatranes and Their Tricyclic Analogs

“…Their dipole moments ( ) lie in the range 5 11 D, while the influence of the Si and C substituents and the medium on the values has been discussed in detail in previous reviews 1,5,6,12,13,28 .…”

“…Despite the extensive experimental evidence for the silicon pentacoordination in silatranes, for a long time there were doubts concerning the true reasons of the endo configuration of these molecules (see literature cited elsewhere 12,13 ). In particular, it was suggested that this geometry is not realized due to a transannular Si N bonding, but primarily owing to steric factors typical for medium-ring bicyclic nitrogen compounds 175 which push the nitrogen atom inside the molecular cage.…”

“…Previous semiempirical computations of silatranes and some other pentacoordinated organosilicon species found either increase or decrease in the negative silicon charge under pentacoordination, depending on the method and the basis set used 12 . However, the view of a higher positive charge on the pentacoordinate silicon as compared with the tetracoordinate state is widely accepted 184 .…”

“…The energetic preference of the endo form was demonstrated by the first quantum chemical calculations of silatranes performed on 1-hydro-and 1-fluorosilatranes 12,181 . These calculations employed the CNDO/2 semiempirical method with spd basis set and geometries of the endo and exo forms corresponding to those obtained for 1-methylsilatrane by modified molecular mechanics method.…”

“…Moreover, many experimental and quantum chemical data ruled out the valence role of d orbitals in molecules of main group elements 171,172 . In 1977 the Musher model of hypervalency 173 was modified with reference to the Group 14 elements and used for a qualitative analysis of the structural trends in silatranes 12,13,174 .…”