Silanetriols as Powerful Starting Materials for Selective Condensation to Bulky POSS Cages

Controlled condensation reactions of tertiary silanetriols CH<sub>3</sub>(CH<sub>2</sub>)<sub><i>n</i></sub>(CH<sub>3</sub>)<sub>2</sub>CSi­(OH)<sub>3</sub> (<b>1b</b>–<b>f</b>; <i>n</i> = 1–5) in the presence of trifluoroacetic acid and the hydrolysis of CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>(CH<sub>3</sub>)<sub>2</sub>CSiCl<sub>3</sub> (<b>3</b>) lead to the selective formation of the corresponding disiloxane tetrols [CH<sub>3</sub>(CH<sub>2</sub>)<sub><i>n</i></sub>(CH<sub>3</sub>)<sub>2</sub>CSi­(OH)<sub>2</sub>]<sub>2</sub>O (<b>2b</b>–<b>g</b>; <i>n</i> = 1–6) in good yields. The TBAF-driven condensation reactions of the silanetriols CH<sub>3</sub>(CH<sub>2</sub>)<sub><i>n</i></sub>(CH<sub>3</sub>)<sub>2</sub>CSi­(OH)<sub>3</sub> (<b>1a</b>–<b>c</b>; <i>n</i> = 0–2) as well as of the disiloxane-1,1,3,3-tetrol <b>2d</b> (<i>n</i> = 3) yield in the selective formation of the first T<sub>8</sub> cages bearing tertiary carbon substituents, CH<sub>3</sub>(CH<sub>2</sub>)<sub><i>n</i></sub>(CH<sub>3</sub>)<sub>2</sub>C (<b>4a</b>–<b>d</b>; <i>n</i> = 0–3), which was not possible via the condensation of their alkoxysilane counterparts so far. The resulting compounds <b>2b</b>–<b>g</b> and <b>4a</b>–<b>d</b> have been characterized by multinuclear NMR, MS, and single-crystal X-ray diffraction.