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- Title
Cross-Conjugated Hexaphyrins and Their Bis-Rhodium Complexes.
- Authors
Naoda, Koji; Sung, Young Mo; Lim, Jong Min; Kim, Dongho; Osuka, Atsuhiro
- Abstract
A cross-conjugated hexaphyrin that carries two meso-oxacyclohexadienylidenyl (OCH) groups 9 was synthesized from the condensation of 5,10-bis(pentafluorophenyl)tripyrrane with 3,5-di- tert-butyl-4-hydroxybenzaldehyde. The reduction of 9 with NaBH4 afforded the Möbius aromatic [28]hexaphyrin 10. Bis-rhodium complex 11, prepared from the reaction of 10 with [{RhCl(CO)2}2], displays strong Hückel antiaromatic character because of the 28 π electrons that occupy the conjugated circuit on the enforced planar structure. The oxidation of 11 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) yielded complexes 12 and 13 depending upon the reaction conditions. Both 12 and 13 are planar owing to bis-rhodium metalation. Although complex 12 bears two meso-OCH groups at the long sides and is quinonoidal and nonaromatic in nature, complex 13 bears 3,5-di- tert-butyl-4-hydroxyphenyl and OCH groups and exhibits a moderate diatropic ring current despite its cross-conjugated electronic circuit. The diatropic ring current increases upon increasing the solvent polarity, most likely due to an increased contribution of an aromatic zwitterionic resonance hybrid.
- Subjects
HEXAPHYRIN; RHODIUM; HUCKEL molecular orbitals; BENZOQUINONES; METALATION; ZWITTERIONS
- Publication
Chemistry - A European Journal, 2014, Vol 20, Issue 25, p7698
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201402328