Post-synthesis modification of functionalised polyhedral oligomeric silsesquioxanes with encapsulated fluoride – enhancing reactivity of T8-F POSS for materials synthesis

Abstract

Previous studies have demonstrated that functionalised T₈ polyhedral oligomeric silsesquioxanes with fluoride anions encapsulated within the T₈ cage (T₈-F) have very low reactivity, with no reports of successful modification of the organic moieties. Herein, we report the successful modification of a styryl functionalised T₈-F compound with mercaptopropyltriethoxysilane using a thiol–ene click reaction. This strategy enables the vinyl moiety to be modified while maintaining the influence of the electron-withdrawing phenylene group, which stabilises the fluoride within the cage. The triethoxysilylated T₈-F cages were subsequently converted into nanohybrids by sol–gel processing. Multinuclear NMR experiments (²⁹Si, ¹⁹F, ¹³C) demonstrated that the POSS cage remained intact during both post functionalisation of T₈-F and subsequent sol-gel processing. Furthermore, ²⁹Si cross polarisation solid state NMR experiments using ¹⁹F as a cross polarisation agent demonstrated that the fluoride anions remain localised within the cages in the nanohybrids. The functionalisation of the styryl bearing T₈-F POSS cage is the first example of both the successful modification of the poorly reactive T₈-F family and the formation of a nanohybrid material incorporating fluoride ions immobilised within covalently bound T₈ cages.