Fluoride catalyzed rearrangements of polysilsesquioxanes, mixed Me, vinyl T₈, Me, vinyl T₁₀ and T₁₂ cages

Abstract

Abstract Insoluble mixtures of polyvinylsilsesquioxane, ‐(vinylSiO 1.5 ) n ‐ PVS, and polymethylsilsesquioxanes, ‐(MeSiO 1.5 ) n ‐ PMS, in THF at ambient when treated with catalytic amounts (1–5 mol%) of fluoride ion introduced as t Bu 4 NF will depolymerize and dissolve. The resulting soluble species consist of [vinyl x Me 8− x (SiO 1.5 )] 8 , [vinyl x Me 8− x (SiO 1.5 )] 10 and [vinyl x Me 8− x (SiO 1.5 )] 12 . Ratios of 1:1 of PVS:PMS greatly favor formation of vinyl rich cages. Only at ratios of 1:5 are the proportions of vinyl:Me in the cages approximately equal. Of the T 8 , T 10 and T 12 species produced, all conditions tried, including changing the solvent to EtOH or toluene or at reflux (THF), favor the formation of the larger cages sometimes completely excluding formation of the T 8 materials. Efforts to isolate the cage compounds by removal of solvent regenerates polysilsesquioxanes, albeit those containing mixtures of Me and vinyl groups. Introduction of CaCl 2 sufficient to form CaF 2 prior to workup prevents repolymerization, allowing recovery of the mixed cage systems. The approach developed here provides a novel way to form mixed functional group silsesquioxane cages. The fact that T 10 and T 12 cage formation is favored appears to suggest that these cages are more stable than the traditionally produced T 8 cages. Copyright © 2009 John Wiley & Sons, Ltd.