Octulene. A Hyperbolic Molecular Belt that Binds Chloride Anions

Majewski, M.A.; Hong, Y.; Lis, T.; Gregoliński, J.; Chmielewski, P. J.; Cybińska, J.; Kim, D.; Stępień, M.
Angew. Chem. Int. Ed. 2016, 55, 14072–14076 | view at publisher's site

Octulene, the higher homologue of kekulene and septulene, was synthesized using the fold-in method. This new hydrocarbon macrocycle contains a large 24-membered inner circuit, which is peripherally fused to 24 benzene rings. Such an arrangement produces considerable hyperbolic distortion of the π-conjugated surface. The consequences of distortion in octulene were explored using photophysical methods, which revealed a reduced electronic bandgap, and greater flexibility of the π system. Octulene contains a functional cavity with a diameter larger than 5.5 Å that is capable of efficiently binding the chloride anion in a non-polar solvent (Ka = 2.2(4)·104 M–1, 1% dichloromethane in benzene). The octulene–chloride interaction is stabilized by eight weak C(sp2)H···Cl bonds,providing the first example of a hydrocarbon-based anion receptor.