Amanda Sylvester, Appalachian State University, Boone, NC and Michael Ramey, Appalachian State University, Boone, NC.
The long term objective of this research is to synthesize and develop a set of functionalized hexaphenylbenzene polyelectrolytes. Catalytic amounts of cobalt octacarbonyl are used in a catalytic cyclization reaction with appropriately substituted 4,4'-diphenylacetylenes (tolanes) to form hexaphenylbenzene molecules. Efforts have focused on optimizing the conditions and yields for production of two tolane molecules, a) Bis[4-(ethoxycarbonyl)phenyl]acetylene [an ester tolane] and b) 4,4'-(3-[N,N-diethylamino]-1-oxapropyl)diphenylacetylene [an alkoxyamine tolane]. Synthesis of the ester tolane was first explored using a series of Sonogashira coupling reactions with purification of each intermediate then compared to a one step approach recently described in the literature. The ester tolane can subsequently be cyclized using a cobalt catalyst into a hexaphenylbenzene which can be treated with strong base to form single molecules with six carboxylate salt sites. Alternatively, the ester tolane can be converted into a dicarboxylic acid from which a variety of tolane derivatives are accessible. Based on the results of the ester tolane experiments, the alkoxyamine tolane was synthesized using the one step approach. Post cyclization, the amine groups can be reacted with acid (HCl) or alkylhalides (methyl/ethyl bromide) to provide a single molecule with six positively charged quaternized amine sites. Synthetic progress towards these materials is offered in this presentation.