Mechanism of the Thermal Z⇌E Isomerization of a Stable Silene; Experiment and Theory

The E and Z geometric isomers of a stable silene (tBu2MeSi)(tBuMe2Si)Si=CH(1‐Ad) (1) were synthesized and characterized spectroscopically. The thermal Z to E isomerization of 1 was studied both experimentally and computationally using DFT methods. The measured activation parameters for the 1Z⇌1E isomerization are: Ea=24.4 kcal mol−1, ΔH≠=23.7 kcal mol−1, ΔS≠=−13.2 e.u. Based on comparison of the experimental and DFT calculated (at BP86‐D3BJ/def2‐TZVP(‐f)//BP86‐D3BJ/def2‐TZVP(‐f)) activation parameters, the Z⇌E isomerization of 1 proceeds through an unusual (unprecedented for alkenes) migration–rotation–migration mechanism (via a silylene intermediate), rather than through the classic rotation mechanism common for alkenes. Drehen und Wandern: Die E‐ und Z‐Isomere eines stabilen Silens, (tBu2MeSi)(tBuMe2Si)Si=CH(1‐Ad) (1), wurden synthetisiert und charakterisiert. Kinetischen Studien und DFT‐Rechnungen zufolge verläuft die thermische Z⇌E‐Isomerisierung von 1 über einen Silylmigrations‐Rotations‐Migrations‐Mechanismuns (über Silylenintermediate) statt über den klassischen Rotationsmechanismus, der für Alkene üblich ist.