Synthesis and Reactivity of Three New N-Heterocyclic Silylenes

Three new stable silylenes, rac-1,3,4-tri-tert-butyl-1,3-diaza-2-silacyclopentane-2-ylide (5), 1,3-di-tert-butyl-4,4-dimethyl-1,3-diaza-2-silacyclopentane-2-ylide (6), and rac-1,3-di-tert-butyl-4-methyl-1,3-diaza-2-silacyclopentane-2-ylide (7), have been synthesized by the reaction of their corresponding dibromides with KC8. Unlike the analogous silylene 2, which lacks any backbone substitution and tetramerizes in concentrated solution or as a solid, silylenes 5, 6, and 7 show no tendency to oligomerize. The reactions of 5 with tert-butanol and chloroalkanes give only 1:1 O−H or C−Cl insertion products; with adamantyl azide 5 yields the spirosilatetrazoline 8, while with mesityl azide it gives the azadisilacyclopropane 9.