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

Abstract

The Ea nd Zg eometric isomers of as table silene (tBu 2 MeSi)(tBuMe 2 Si)Si=CH(1-Ad) (1)were synthesized and characterized spectroscopically.T he thermal Zt oEisomerization of 1 was studied both experimentally and computationally using DFT methods.The measured activation parameters for the 1ZÐ1E isomerization are:E a = 24.4 kcal mol À1 , DH°= 23.7 kcal mol À1 , DS°= À13.2 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 ZÐEisomerization of 1 proceeds through an unusual (unprecedented for alkenes) migration-rotation-migration mechanism (via as ilylene intermediate), rather than through the classic rotation mechanism common for alkenes.

Heavier Carbonyl Olefination: The Sila-Wittig Reaction

“…Very recently, Apeloig et al reported on the synthesis and isomerization of ( E )/( Z )-( t Bu 2 MeSi)­( t BuMe 2 Si)­SiCH­(1-Ad), the first-ever isolable silene stereoisomers . Thus, we conducted further DFT calculations to support the formation of the silenes and especially the assignment of the ( E )/( Z )-isomers.…”

Room temperature stable E,Z-diphosphenes: their isomerization, coordination, and cycloaddition chemistry

“…Consequently, cis -folded isomers of R 2 EER 2 or Z -isomers of REER with heavy main group elements are rare due to increased steric repulsion caused by these substituents. 3 a , b , d ,4…”