Structures and Properties of Phenylene‐Bridged 1,3‐Diaza‐2‐silole and Related 2H‐Azasilirenes Obtained by the Reactions of a Dialkylsilylene with Arylnitriles

Abstract

Cycloadditions of silylenes (silicon analogues of carbene) have been extensively explored as convenient and efficient routes to silacycles. Among these, reactions of silylenes with nitriles are still limited and the electronic properties of the resulting azasilacycles such as 2H‐azasilirene and 1,3‐diaza‐2‐siloles are less examined. We report herein synthesis of a phenylene‐bridged 1,3‐diaza‐2‐silole and C‐aryl 2H‐azasilirenes using cycloaddition reactions of a silylene as well as their structures and UV/Vis absorption spectra. Treatment of an isolable dialkylsilylene with o‐phthalonitrile afforded a phenylene‐bridged 1,3‐diazasilole and an isomeric dearomatized product. Similar reactions with p‐substituted benzonitriles gave new 2H‐azasilirenes. UV/Vis absorption spectra and theoretical calculations showed that high‐lying n(C=N) orbitals in 1,3‐diaza‐2‐siloles and 2H‐azasilirenes and low‐lying π*(1,3‐diaza‐2‐silole) orbitals are important for their electronic characters. Computational studies revealed that 1,3‐dipolar cycloaddition of silylene nitrile complexes (nitrile silaylides) with the second nitrile and an aromatic C=C bond of 2‐cyanopheyl group are key steps for the cycloaddition.