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.