Vogel Anastasia, Dechert Sebastian, John Michael, Brückner Christian, Meyer Franc
Institute of Inorganic Chemistry, Georg-August-University Göttingen, Tammannstr. 4, D-37077, Göttingen, Germany.
Department of Chemistry, Unit 3060, University of Connecticut, Storrs, CT, 06269-3060, USA.
Chemistry. 2016 Feb 12;22(7):2307-16. doi: 10.1002/chem.201503699. Epub 2015 Dec 16.
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.
