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

• Published in: Applied organometallic chemistry 2010-08, Vol.24 (8), p.551-557
• Main Authors: Ronchi, M., Sulaiman, S., Boston, N. R., Laine, R. M.
• Format: Article
• Language: English
• Subjects: Cage compounds; Cages; Calcium fluoride; Catalytic reformation of Si-O bonds; fluoride activation of T resins; Fluorides; Metalorganic compounds; mixed functional T10 and T12 silsesquioxanes; Polysilsesquioxanes; Solvents; Toluene
• ISSN: 0268-2605; 1099-0739; 1099-0739
• DOI: 10.1002/aoc.1579

Insoluble mixtures of polyvinylsilsesquioxane, ‐(vinylSiO1.5)n‐ PVS, and polymethylsilsesquioxanes, ‐(MeSiO1.5)n‐ PMS, in THF at ambient when treated with catalytic amounts (1–5 mol%) of fluoride ion introduced as tBu4 NF will depolymerize and dissolve. The resulting soluble species consist of [vinylxMe8−x(SiO1.5)]8, [vinylxMe8−x(SiO1.5)]10 and [vinylxMe8−x(SiO1.5)]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 T8, T10 and T12 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 T8 materials. Efforts to isolate the cage compounds by removal of solvent regenerates polysilsesquioxanes, albeit those containing mixtures of Me and vinyl groups. Introduction of CaCl2 sufficient to form CaF2 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 T10 and T12 cage formation is favored appears to suggest that these cages are more stable than the traditionally produced T8 cages. Copyright © 2009 John Wiley & Sons, Ltd. Catalytic amounts of tButyl4NF cleave and reform Si‐O bonds in methyl and vinylsilsesquioxane resins transforming them at ambient (THF) into mixed functional Viny,Methyl T10/T12 cages with Methyl:Vinyl ratio controlled by the initial ratio of insoluble resins. If F− is not removed, solvent evaporation led to THF soluble mixed‐functional resins. However, if F− is removed using CaCl2 then the cages could be recovered. The evidence suggests that T10 and T12 cage are more stable than T8 cages contrary to current expectations.