SYNTHESIS AND SELF-ASSOCIATION OF FIRST-GENERATION 1,3,4-OXADIAZOLE-CONTAINING DENDRIMERS

Two 1,3,4-oxadiazole-containing dendrimers, 14 and 15, have been prepa red employing a palladium-catalyzed carbonylation reaction as the key step of the synthesis. In order to shorten the reaction sequence, a ne w oxadiazole synthesis has been developed based on the coupling of ary l iodides with aryl tetrazoles in the presence of a Pd(0) catalyst and carbon monoxide, and has been applied to the preparation of dendrimer 14. Both new dendrimers are highly soluble in chlorinated solvents, b ut 14, with fewer solubilizing tert-butyl groups at its periphery, sel f-associates in solution by pi-pi interactions and possibly due to sol vophobic effects. Considerable upfield shifts of the H-1-NMR signals o f the protons in the centre of the molecule indicate the formation of pi-stacks in solution. Vapour-pressure osmometry studies allow a degre e of association of greater than or equal to 3 to be estimated.