The Lewis acid catalyzed self-condensation of hybrid diheterole (furan-pyrrole and thiophene-pyrrole) precursors has afforded novel Hückel antiaromatic 24π hexaphyrin(188.8.131.52.1.0) and 32π octaphyrin(184.108.40.206.220.127.116.11) structures without β-annulated bridges. Single-crystal X-ray diffraction analysis of the hybrid porphyrinoids (S 3 N 3 -ox and O 4 N 4 -ox) revealed a nearly planar conformation and the 1 H NMR spectra suggest the presence of paratropic ring currents. These antiaromatic macrocycles show characteristic optical features and underwent reversible two-electron reduction to Hückel aromatic 26π- and 34π-electron species, respectively, as is evident from the results of spectroscopic and theoretical studies (nucleus-independent chemical shift (NICS) and anisotropy of the current-induced density (ACID) calculations). The incorporation of hybrid diheteroles alternately into expanded porphyrin skeletons provides a novel approach to the fine-tuning of the electronic structures of planar antiaromatic macrocycles.
All Science Journal Classification (ASJC) codes
- Organic Chemistry