Synthesis and Unusual Reactivity of Acyl-Substituted 1,4-Disilacyclohexa-2,5-dienes

Abstract

In continuation of our recent studies on group 14 rings with exocyclic silicon−carbon double bonds, we report here on the synthesis and reactivity of previously unknown acyl-substituted 1,4-disilacyclohexa-2,5dienes. 1,1,4,4-Tetrakistrimethylsilyl-1,4-disilacyclohexa-2,5-diene 1 cleanly afforded the silyl anion 1-K after addition of 1 equiv of KO t Bu. 1-K subsequently could be reacted with various electrophiles to the expected substitution products including compounds 4 and 5. When photolyzed with λ > 300 nm radiation, 4 and 5 undergo Brook-type 1,3-Si → O migration reactions to generate the corresponding 1,4-disilacyclohexadienes with exocyclic Si�C bonds as the primary products. These metastable silenes only could be characterized in form of appropriate quenching products. The reaction of compound 4 with KO t Bu followed by the addition of 1 equiv of PhMe 2 SiCl surprisingly gave the silylated 1,4-disilanorbornadiene cages 8 and 9 instead of the expected exocyclic silene. The responsible sila-Peterson-type mechanism could be elucidated by density functional theory calculations at the conductor-like polarizable continuum model (THF) B3LYP-GD3/6-31 + G(d) level and by the isolation and characterization of unstable intermediate products after proper derivatization.

Synthesis and Properties of Backbone Silylated Imidazol‐2‐thiones

“…Recently, strong cyclic cross‐hyperconjugational type interactions have been detected in properly substituted 1,4‐disilacyclohexa‐2,5‐dienes VIII (Scheme 3), conferring quite unique electronic properties to this class of compounds [18] . In our laboratories, we have recently explored possible synthetic approaches towards 1,4‐disilacyclohexadienes with exocyclic Si=C double bonds of type IX [19] . However, the obtained silanes were only metastable, which prevented detailed studies of their characteristics.…”

“…[18] In our laboratories, we have recently explored possible synthetic approaches towards 1,4-disilacyclohexadienes with exocyclic Si=C double bonds of type IX. [19] However, the obtained silanes were only metastable, which prevented detailed studies of their characteristics. In this context, the imidazole-2-thione fused species of type X are of interest because the donor properties of the imidazole-2-thione ring could be beneficial for the stabilization of adjacent low-valent silicon centers formed in follow-up reactions of X.…”