Modelling nucleophilic substitution at silicon using hypervalent silicon compounds based on di and tri halosilanes

The 29Si- and 13C-NMR spectral parameters of a range of N-(amidomethyl)-polyhalosilanes have been measured in solution and the extent of SiO bond formation and pentacoordination determined. The larger the number of electronegative groups attached to the silicon the greater the extent of pentacoordination achievable by the silicon. Thus with trichlorosilanes a ‘tight’ pentacoordinate silicon is observed where the SiO bond is almost fully formed.