Synthesis and characterization of pyridinophane- and pincer-based monomers for polymer formation

Abstract

The work herein investigates the synthesis of vinyl-decorated pyridinophane and pincer monomers for future incorporation into polymer backbones. Synthetic pathways for chloro- and iodo-decorated pyridinophanes were developed, and each precursor molecule was characterized by 1H and 13C NMR spectroscopy. ESI-HRMS was utilized for each novel compound. Connectivity of various intermediate molecules, as well as the final target molecules, were further supported through XRD studies. Hiyama coupling reaction conditions were used to synthesize the target pyridinophane and pincer monomers. It was determined that chloro-substituted pyridinophanes are unsuitable precursor molecules for the installation of vinyl-moieties under the conditions described herein. Contrastingly, the iodo congeners are successful reagents that afford the target vinylated pyridinophane. In a similar fashion, the iodo NNN pincer congener was used to install the vinyl moiety. Binding capabilities of both the pyridinophane and pincer monomers were supported through XRD studies. The vinylated NNN pincer monomer was subjected to radical polymerization reactions. Although attempts to synthesize the homopolymer were unsuccessful, a copolymer with styrene produced a gel matrix. The incorporation of the pincer monomer into the polymer backbone was qualitatively proven through incubation with CuCl2, to produce an insoluble green solid. Both the vinylated pyridinophane and pincer monomers will be the subjects of future polymerization reactions performed by colleagues in the Green Research Group and collaborators in the Long Research Group at the University of Tennessee.