Proton Affinities of the Silatranes and Their Analogues

Abstract

Ab initio calculations with full geometry optimization have been used to investigate the O and N atom proton affinities and the molecular structures of silatranes (RSi(OCH2CH2)3N), as well as the related compounds RSi(OCH3)3, RSi(OCH2)3CH, and RSi(OCH2CH2)3CH, where R = F, Cl, CH3, SiH3, utilizing the 6-31G(d) basis set. It is found that larger electron donor substituents R induce large proton affinities. The silatranes have stronger proton affinities than the other compounds because of the transannular Si−N interaction. For silatranes, only a small difference between the O and N atom proton affinities is found. The silatrane Si−R bond distances are apparently determined by the degree of the anomeric effect in the R−Si−O fragment and transannular Si−N interactions.