5,20-Di(pyridin-2-yl)-[28]hexaphyrin(1.1.1.1.1.1): A Stable Hückel Antiaromatic Hexaphyrin Stabilized by Intramolecular Hydrogen Bonding and Protonation-Induced Conformational Twist to Gain Möbius Aromaticity

Koji Naoda, Hirotaka Mori, Juwon Oh, Kyu Hyung Park, Dongho Kim, Atsuhiro Osuka

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

5,20-Di(pyridin-2-yl)-[28]hexaphyrin(1.1.1.1.1.1) 7 was prepared and characterized as a stable Hückel antiaromatic molecule with a dumbbell-like structure stabilized by effective intramolecular hydrogen bonding interactions involving the 2-pyridyl nitrogen atoms. Pd(II) metalation of 7 afforded two bis-Pd(II) complexes, 9-syn and 9-anti, whose structures are rigidly held by Pd(II) coordination, rendering 9-syn to be nonaromatic because of its highly distorted structure and 9-anti to be Hückel antiaromatic because of its enforced planar dumbbell structure. In contrast, protonation of 7 with methanesulfonic acid (MSA) led to the formation of its triprotonated species 7H3, which has been shown to take on twisted conformations with Möbius aromaticity in CH2Cl2, while the structure was held to be a planar rectangular conformation in the crystal. Excited-state dynamics were measured for 7, 7H3, 9-syn, and 9-anti, which indicated their electronic nature to be antiaromatic, aromatic, nonaromatic, and antiaromatic, respectively.

Original languageEnglish
Pages (from-to)11726-11733
Number of pages8
JournalJournal of Organic Chemistry
Volume80
Issue number23
DOIs
Publication statusPublished - 2015 Jul 28

All Science Journal Classification (ASJC) codes

  • Organic Chemistry

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