Tuning of Heterocyclic Ring in Para -Benzi Heterosapphyrins.

Three examples of moderately aromatic p -benzi dithiasapphyrin and p -benzi tellurathiasapphyrins have been synthesized by condensing p -benzithiophene diol with 16-thia/telluratripyrrane under acid-catalyzed reaction conditions. The X-ray structural analysis showed that the thiophene ring in p -benzi dithiasapphyrin was inverted, whereas the tellurophene ring in p -benzi tellurathiasapphyrins was normal conformation with respect to the macrocyclic core. However, NMR studies revealed that the thiophene ring in protonated p -benzi dithiasapphyrin flips to normal, whereas the tellurophene ring in p -benzi tellurathiasapphyrins flips to inverted orientation.