Aminopropylsilanes versus silatranes: an experimental and theoretical study

The 1H-, 13C-, 15N- and 29Si-NMR spectra of 3-aminopropyltrimethoxysilane and N,N-dimethylamino-propyltrimethoxysilane have been recorded. An analysis of the spectra together with GIAO calculations leads to the conclusion that these compounds exist as open-chain structures and not as ring-closed silatranes. The N→Si interaction is important only when there is at least one cycle in the structure, although two or three cycles (silatranes) are a more favorable disposition.