Mechanism of the Thermal ZE Isomerization of a Stable Silene; Experiment and Theory

摘要

The E and Z geometric isomers of a stable silene (tBu(2)MeSi)(tBuMe(2)Si)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 1Z1E isomerization are: E-a=24.4 kcal mol(-1), Delta H-not equal=23.7 kcal mol(-1), Delta S-not equal=-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 ZE 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.