Synthesis of conjugated helical acetylene-bridged polymers and cyclophanes

Pd(0)-catalyzed reactions of 2,15-diethynyl[6]helicene with derivatives of p- and o-diiodobenzene give, respectively, polymers 4 and cyclophanes 5, in which helicenes are linked by diethynylbenzenes. Both are very soluble in many common solvents. The molar rotation of polymer 4 is greater than that of monomeric analogue 12, and peaks in its UV and CD spectra at wavelengths greater than 350 nm are shifted to the red of those in 12. Cyclophane 5a, which contains two helicene rings, could be isolated from the reaction mixture in pure form. Its maxima in the UV and CD spectra are not shifted to the red of those of 12, most likely because the two helicene rings in 5a are twisted with respect to one another.