Stable cyclic and acyclic persilyldisilenes

Synthesis, structure, and reactions of persilylated cyclic and acyclic disilenes that we have synthesized are described in detail. Due to the remarkable electronic and steric effects of trialkylsilyl substituents, tetrakis(trialkylsilyl)disilenes (RR′Si=SiRR′: R, R′ = i-Pr₂MeSi (1a), t-BuMe₂Si (1b), i-Pr₃Si (1c); R = i-Pr₂MeSi, R′ = t-BuMe₂Si (1d)) showed interesting features in the geometry around Si=Si bond, electronic spectra, ²⁹Si-NMR resonances of the unsaturated silicon nuclei, E,Z-isomerization, reduction by alkali metals, and various bimolecular reactions with alcohols, alkyl lithium, alkenes, alkynes, and haloalkanes. As the first cyclooligosilenes, 1-tris(t-butyldimethylsilyl)silyl-2,3,3-tris(t-butyldimethylsilyl)cyclotrisilene (2) and hexakis(t-butyldimethylsilyl)cyclotetrasilene (3) were synthesized typically by the reduction of the corresponding tris(trialkylsilyl)silyltrihalosilane with potassium graphite in THF and with sodium in toluene, respectively. Photochemical conversion of 3 to the corresponding bicyclo[1.1.0]butane (9) and its thermal reversion to 3, as well as photochemical isomerization of 2 to 9 were observed.