Structural Relationships in Silatrane Molecules

An updated compendium of silatrane structural data is presented. The relationships between nonplanarity at silicon (Delta Si) and d(N-Si), the length of the dative bond, and nonplanarity at nitrogen Delta N and d(N-Si) are examined. Excluding a platinum-substituted derivative: the Delta Si relationship is strong and predicts the limiting length of a strong N -> Si bond, while the Delta N relationship is weak. A good relationship between Sigma sigma(1) for the four (non-N) exo- and endocyclic substituents attached to Si holds for silatranes, methyl, keto, and diketo derivatives as well as for 2-carbasilatranes. The relationship fails for strong pi-donor exocyclic substituents, implicating resonance, and for benzo-and tribenzosilatranes, where steric effects dominate.