The hexasilsesquioxanes (RSiO1.5)6
(1, R =
1,1,2-trimethylpropyl; 2, R = tert-butyl) were
synthesized
by a new method: condensation of the corresponding
silanetriol, RSi(OH)3, or
1,1,3,3-tetrahydroxydisiloxane,
(HO)2RSiOSiR(OH)2, using
dicyclohexylcarbodiimide
(DCC) as a dehydrating reagent in DMSO or DMF.
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 1,1,3,3tetraphenyldisiloxane-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.
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