| Abstract
| - The incompletely condensed monosilylated silsesquioxanes (c-C5H9)7Si7O9(OSiRR‘2)(OH)2 (SiRR‘2= SiMe3, SiMe2C(H)CH2, SiMePh2) were reacted with SiCl4 in the presence of an amine which yielded thedichloro compounds (c-C5H9)7Si7O9(OSiRR‘2)O2SiCl2 (1−3). These compounds could be hydrolyzed intothe corresponding silsesquioxanes containing geminal silanols, (c-C5H9)7Si7O9(OSiRR‘2)O2Si(OH)2 (4−6).At elevated temperatures, the geminal silsesquioxanes 4 and 5 undergo condensation reactions and formthe closed-cage silsesquioxane monosilanol, (c-C5H9)7Si8O12(OH). The more sterically hindered geminalsilsesquioxane 6 undergoes in solution intermolecular dehydroxylation, yielding the thermodynamically stabledimeric disilanol, [(c-C5H9)7Si7O9(OSiMePh2)(O2Si(OH)-)]2-(μ-O) (7). NMR and FT-IR studies show that thetwo silanols of the geminal silsesquioxanes 4−6 are different from each other with respect to hydrogenbonding, both in solution and in the solid state. Hydrogen bonding of the geminal silanol-containingsilsesquioxanes was examined and compared to hydrogen bonding in silsesquioxanes possessing vicinalor isolated silanol groups. The relative Brønsted acidity of the geminal silanols was determined using pKip(ion-pair acidity) measurements in THF with UV−vis. These acidities were compared with those of othersilsesquioxanes containing silanol groups. Acidities of 4−6 were found to be among the lowest known forsilsesquioxanes.
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