One-Pot Synthesis of Large Macrocycles via McMurry Couplings

Significance

Iyoda and co-workers synthesize π-extended oligo(thiophene) macrocycles using a modified McMurry coupling with low-valent titanium in a remarkably efficient one-pot procedure. Dimers, trimers, tetramers, pentamers and hexa­mers were isolated from the reaction mixture in varying yields. These macrocycles showed a persistent red-shift in the absorption maxima from 10-mer (447 nm) through 20-mer (479 nm) to 30-mer (488 nm), indicating full conjugation throughout the macrocycle. As expected, these molecules form stable cationic species on oxidation; exposure to iodine vapor produced moderately conductive materials (σ_rt ˜ 10^-3 S/cm). Interestingly, the X-ray crystal structure for the 10-mer revealed a molecule of solvent (heptane) threaded through the macrocycle. The larger macrocycles self-­assembled to form nanofibers and nanoparticles.