Siamese-Twin Porphyrin Origami: Oxidative Fusing and Folding.

Abstract

Oxidation of a nonaromatic Siamese-twin porphyrin, a pyrazole-containing expanded porphyrin with two porphyrinlike binding pockets, with a stoichiometric amount of the two-electron, two-proton oxidizing agent 2,3-dichloro-5,6-dicyano-1,4-benzochinone led to the formation of a single N(pz) -C(o-Ph) linkage between the pyrazole unit with a neighboring meso-phenyl group, forming a pyrazolo- [1,5-a]indole moiety. Repeated treatment with a second equivalent of the oxidant yielded a doubly N-fused species, involving the second pyrazole moiety. The conversion products were characterized by variable-temperature and multinuclear 1D and 2D NMR spectroscopy. The fusions strongly alter the conformation of the macrocycles, as shown by X-ray diffraction analyses of all three compounds, eventually leading to a folded structure. UV/Vis and NMR-spectroscopic investigations indicated the presence of highly delocalized but nonmacrocycle-aromatic π systems. This behavior of the Siamese-twin porphyrin in response to oxidation is in contrast to the behavior of related all-pyrrole-based expanded macrocycles that switch, by redox processes and protonation, between Hückel and Möbius aromatic states.

• Authors: Anastasia Vogel, Sebastian Dechert, Michael John, Christian Brückner, Franc Meyer
• Journal: Chemistry (Weinheim an der Bergstrasse, Germany) (Chemistry) Vol. 22 Issue 7 Pg. 2307-16 (Feb 12 2016) ISSN: 1521-3765 [Electronic] Germany
• PMID: 26670580 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.