Photoinduced Brook-Type Rearrangement of Acylcyclopolysilanes

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