cis-trans-cis-Tetrabromotetramethylcyclotetrasiloxane:: A versatile precursor of ladder silsesquioxanes

The title compound was isolated for the first time by a novel procedure including dephenylbromination of cyclotetrasiloxane. The stereostructure of the tetrabromide was confirmed by condensation with diphenylsilanediol, affording anti-tricyclo[7.3.1.1(3.7)]hexasiloxane. This tetrabromide spontaneously decomposed in air to afford a white powder insoluble in organic solvents. Measurements of the TG, IR, and solid-state NMR spectra of the product revealed that a ladder polysilsesquioxane with high thermal stability and stereoregularity was obtained.