Formation of 1-aza-2-silacyclopentanes and unexpected products from the insertion of phenylisocyanate into 2,2-dimethyl-1-(trimethylsilyl)-1-aza-2-silacyclopentane

Substances like 3-aminopropyltriethoxysilane are often used as adhesive promoters in various formulations for coatings or to adjust the properties of siloxanes and other polymers. Cyclisation of similar substances is also interesting because of the formation of the Si-N bond. 1-Aza-2-silacyclopentanes were synthesised from 3-aminopropylalkoxysilanes by intramolecular condensation reactions and substitution reactions at the silicon atom. The products tend to undergo ring-opening polymerisation. In contrast to literature reports, they can only be isolated as N-substituted derivatives. Phenylisocyanate inserts into the Si-N bonds of cyclic aminosilanes to form seven-membered heterocycles. Furthermore, phenylisocyanate reacts with N-H bonds in the same molecule. Two insertion products were isolated, and their crystal structures were determined.