Structure and oxidation of octakis(tert-butyldimethylsilyl)octasilacubane

The molecular structure of the silyl-substituted octasilacubane [(t-BuMe2Si)Si]8 (1) was analyzed by X-ray crystallography, and the structural parameters (bond length and angles) were compared with those of the alkyl- and aryl-substituted octasilacubanes. A thermogravimetric analysis revealed that 1 remained stable under argon up to 300 °C, indicating that 1 is much more thermally stable than alkyl-substituted (ThexSi)8 (Thex=1,1,2-trimethylpropyl) (2), which decomposed at 200 °C. Although compound 1 is stable in the air, 1 reacted with m-chloroperoxybenzoic acid (mCPBA). Thus, treatment of 1 with fourteen equivalents of mCPBA led to the formation of octakis(tert-butyldimethylsilylsilsesquioxane) (3) in 98% yield. The structure of 3 was also established by X-ray crystallography, indicating that all the oxygen atoms inserted into the SiSi bonds of the Si8 framework and the exocyclic SiSi bonds remained intact under the conditions employed. Compound 3 is the first example of silsesquioxane with bulky silyl substituents, and shows relatively intense absorptions in the UV region.