Synthesis and structure of ladder oligosilsesquioxanes: Tricyclic ladder oligomethylsilsesquioxanes

Novel tricyclic ladder oligomethylsilsesquioxanes were prepared by heterofunctional condensation of cis-trans-cis- 1,3,5,7- tetraisocyanato- 1,3,5,7- tetramethylcyclotetrasiloxane with 1,3- di- tert- butoxy- 1,3dimethyldisiloxane- 1,3- diol in the presence of triethylamine in THF. A mixture of stereoisomers of the tricyclic oligomethylsilsesquioxanes was obtained. Two of the isomers were separated as white solids by recycle- type high- performance liquid- phase chromatography. They were determined by X- ray crystallography to be tricyclic ladder oligomethylsilsesquioxanes consisting of three eight- membered rings arranged in syn- and anti- configurations.