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

Controlled condensation reactions of tertiary silanetriols CH₃(CH₂)_<i>n</i>(CH₃)₂CSi­(OH)₃ (<b>1b</b>–<b>f</b>; <i>n</i> = 1–5) in the presence of trifluoroacetic acid and the hydrolysis of CH₃(CH₂)₆(CH₃)₂CSiCl₃ (<b>3</b>) lead to the selective formation of the corresponding disiloxane tetrols [CH₃(CH₂)_<i>n</i>(CH₃)₂CSi­(OH)₂]₂O (<b>2b</b>–<b>g</b>; <i>n</i> = 1–6) in good yields. The TBAF-driven condensation reactions of the silanetriols CH₃(CH₂)_<i>n</i>(CH₃)₂CSi­(OH)₃ (<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 T₈ cages bearing tertiary carbon substituents, CH₃(CH₂)_<i>n</i>(CH₃)₂C (<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