The Kim and Osuka groups have reported another Möbius aromatic porphyrin, 1, a 28 π-electron system.1 This hexaporphyrin is produced without the need for low temperature, complexation with a metal or protonation (see this post for a discussion of their earlier work). The x-ray crystal structure shows the Möbius twist, and the 1H NMR shifts of the interior protons at 2.22 and 1.03 ppm. B3LYP/6-31G** computations indicate a NICS value at the center of the molecule of -11.8 ppm. These are consistent with aromatic behavior.
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References
(1) Tokuji, S.; Shin, J.-Y.; Kim, K. S.; Lim, J. M.; Youfu, K.; Saito, S.; Kim, D.; Osuka, A., "Facile Formation of a Benzopyrane-Fused [28]Hexaphyrin That Exhibits Distinct Möbius Aromaticity," J. Am. Chem. Soc. 2009, 131, 7240-7241, DOI: 10.1021/ja902836x.
InChIs
1: InChIKey=YGJLOPZWRVMFIJ-XFAHNSIYBC
