Synthesis and Structural Analysis of Substituted Tripod-Shaped Tri- and Tetra(p-phenylene)s

We report here the synthesis of several tripod-shaped oligo(p-phenylene)s with legs composed of three or four phenylene units. Each leg is end-capped with an iodine atom or a TMS or carboxyl group, and an ethoxy group is present on the functional arm. The tripod containing methyl tri(ethylene glycol) side chains was designed for biological applications. The key step in the synthesis is the Pd-catalyzed Suzuki cross-coupling reaction of the silicon-derived core molecule with the appropriately substituted p-biphenyl moiety. This synthesis should be considered a new strategy for these compounds, as iterative coupling of the substituted p-biphenyl building blocks with the first-generation tripods will allow the homologation of the tripod legs to obtain giant tripod-shaped oligo(p-phenylene)s. Also, the iodine end-capped leg with the ethoxy group on the functional arm permits modular design of the tripod for further functionalization, which will define the applications of the tripod-nanostructured surfaces. The structure of some of the synthesized tripods was studied through both experimental (Raman spectra) and theoretical (DFT calculation) methods.