A Curtius-type rearrangement in the silicon series; an ab initio study of the model silylnitrene–silanimine isomerization

Abstract

The model silylnitrene–silanimine rearrangement (H₃SiN: → H₂SiNH) has been examined in four electronic states, namely the closed- and open-shell singlet, triplet, and cationic states. Ab initio calculations have demonstrated that the silylnitrene has a triplet ground state (³A₂), while its closed-shell singlet (¹A′) and cationic (²A″) states correspond to saddle points. The 1,2-hydrogen migration connecting ³H₃SiN to ³H₂SiNH has an energy barrier of 83 kcal mol^–1. Hence both species can exist in the lowest triplet state, where they are energetically equivalent. Silanimine (H₂SiNH) exhibits a triplet–singlet separation of 39 kcal mol^–1 and a first adiabatic ionization energy of 8.8 eV. Calculations indicate that the Curtius-type rearrangement occurring during the thermolysis or direct photolysis of silyl azide does not involve silylnitrene as an intermediate. However, preliminary data suggest that the excited ¹(n→π*) state of silylnitrene might play a role in a photochemically sensitized decomposition of silyl azide.