Novel materials based on functionalised silsesquioxanes

Hardy, Julie (2001). Novel materials based on functionalised silsesquioxanes. PhD thesis The Open University.



The functionalisation of silsesquioxanes results in materials with novel physical properties. A series of compounds has been coupled with silsesquioxanes [HSiO3/2]8 and [SiO3/2]8 [OSi(CH3)2H]8 and the properties of the products investigated. Typically, coupling reactions involved hydrosilylation with H2PtCl6 or [Pt{(η-ViMe2Si)2O}(PtBu3)].

Mesogenic compounds have been shown to undergo a change in the liquid crystalline phase produced, once attached to the silsesquioxane core. A more ordered phase was observed due to the tethering of the mesogen to the cage. The silsesquioxanes core was considered to have been deformed in the production of this phase.

Silsesquioxanes capable of complexing metal atoms have also been studied. Polyether derivatised cages were prepared and preliminary studies indicate potential for potassium complexation. Vinyl functionalised silsesquioxanes have also been shown to complex platinum, in an exchange reaction with [Pt{(η-ViMe2Si)2O}(PtBu3)].

Investigations into the hydrosilylation reaction have involved coupling triethylsilane, triethoxysilane and the silsesquioxanes with a variety of vinyl, allyl and alkenic compounds. The proportions of α and β adducts were considered. Particular substituents were found to encourage α addition, with species having an oxygen or phenyl group at the allylic position producing the α-regioisomer as well as the typical β product. It is suggested that such substitution affects the mode of cis ligand insertion in the Chalk Harrod mechanism. A preference for the α-regioisomer was also observed for the hydrosilylations of vinyl silsesquioxane compounds.

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