Photoinduced Brook-Type Rearrangement of Acylcyclopolysilanes

Abstract

Previously unknown 1,1,4-tris­(trimethylsilyl)-4-acyldodecamethylcyclohexasilanes (Me₃Si)₂Si₆Me₁₂(Me₃Si)­COR (<b>16a</b>, R = <i>tert</i>-butyl; <b>16b</b>, R = 1-adamantyl) have been synthesized by the reaction of the potassium silanides (Me₃Si)₂Si₆Me₁₂(Me₃Si)K with acid chlorides ClCOR, and their photochemical rearrangement reactions have been studied. The molecular structures of <b>16a</b>,<b>b</b> as determined by single-crystal X-ray diffraction analysis exhibit an unusual twist-boat conformation of the cyclohexasilane ring. When <b>16a</b>,<b>b</b> were photolyzed with λ >300 nm radiation, they underwent Brook type 1,3-Si → O migration reactions to generate the cyclohexasilanes <b>17a</b>,<b>b</b> with exocyclic SiC bonds along with smaller amounts of the ring-enlarged species <b>19a</b>,<b>b</b> with endocyclic SiC double bonds. While <b>17a</b>,<b>b</b> were stable enough to allow characterization by NMR and UV absorption spectroscopy, the less stable products <b>19a</b>,<b>b</b> could only be observed in the form of their methanol adducts