NUCLEOPHILIC SUBSTITUTIONS AT SILICON AND PHOSPHORUS. A COMPARISON OF CONTROLLING FACTORS

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Abstract
The stereochemical behavior of functional organosilanes is explained considering electronic factors. The reactivity depends on the stereochemistry. Retention and/or inversion are controlled by a frontier orbital process. The same conclusions can be extended to the mechanism of nucleophilic substitution of halogenophosphorus compounds. The kinetic data show that the electronic interaction between the incoming nucleophile and the leaving group is very deep when they are both in the apical position of a tbp intermediate. By contrast, the influence of the nucleophile is minimized when the approach of the nucleophile affords a 90° angle, i.e. overall retention at phosphorus. The hydrolysis of silicates should be certainly more connected to the process of hydrolysis of phosphates through a mechanism involving pseudorotation of the pentacoordinated intermediates.

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