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Planar Antiaromatic Core-Modified 24π Hexaphyrin(1.0.1.0.1.0) and 32π Octaphyrin(1.0.1.0.1.0.1.0) Bearing Alternate Hybrid Diheterole Units |
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| Authors: | Jayaprakash Ajay Sriram Shirisha Dr Masatoshi Ishida Kosuke Ito Dr Shigeki Mori Prof Dr Hiroyuki Furuta Dr Sabapathi Gokulnath |
| Institution: | 1. Indian Institute of Science Education and Research, Thiruvananthapuram, Kerala, 695016 India;2. Inorganic & Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology (IICT), Tarnaka, Hyderabad, 500007 Telangana, India;3. Department of Chemistry and Biochemistry, Graduate School of Engineering and Center for Molecular Systems, Kyushu University, Fukuoka, 819-0395 Japan;4. Advanced Research Support Center, Ehime University, Matsuyama, 790-8577 Japan |
| Abstract: | The Lewis acid catalyzed self-condensation of hybrid diheterole (furan-pyrrole and thiophene-pyrrole) precursors has afforded novel Hückel antiaromatic 24π hexaphyrin(1.0.1.0.1.0) and 32π octaphyrin(1.0.1.0.1.0.1.0) structures without β-annulated bridges. Single-crystal X-ray diffraction analysis of the hybrid porphyrinoids ( S3N3-ox and O4N4-ox ) revealed a nearly planar conformation and the 1H 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. |
| Keywords: | antiaromaticity conformation analysis cyclization porphyrinoids redox chemistry |