Synthesis and characterization of cage and bicyclic silsesquioxanes via dehydration of silanols

Abstract

Synthesis of cage and ladder silsesquioxanes by the dehydration of silanols using dicyclohexylcarbodiimide (DCC) is described. The reaction of 1,3-dicyclohexyldisiloxane-1,1,3,3-tetraol with DCC gave octa(cyclohexylsilsesquioxane) in 13% yield. The bicyclic ladder siloxane 3 (Ph 8 Thex 2 Si 6 O 7 ) was prepared from 1,1,3,3-tetraphenyldisiloxane-1,3-diol and 1,3-dithexyldisiloxane-1,1,3,3-tetraol (Thex or thexyl denotes 1,1,2-trimethylpropy) at 80 °C. In this reaction, the propellane-type cage siloxane 2 (Ph 6 Thex 2 Si 5 O 6 ) was generated also. Upon reaction completion at 120 °C, only 2 was obtained. The reaction from the same starting compounds with diisopropylcarbodiimide at 80 °C resulted in another caged siloxane, Ph 4 Thex 4 Si 6 O 8 (5). The structures of 2, 3 and 5 were determined by X-ray crystallography. Copyright © 1999 John Wiley & Sons, Ltd.