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Cyclo[6]pyridine[6]pyrrole: a dynamic, twisted macrocycle with no meso bridges.

Journal of the American Chemical Society (2014-05-13)
Zhan Zhang, Won-Young Cha, Neil J Williams, Elise L Rush, Masatoshi Ishida, Vincent M Lynch, Dongho Kim, Jonathan L Sessler
ABSTRACT

A large porphyrin analogue, cyclo[6]pyridine[6]pyrrole, containing no meso bridging atoms, has been synthesized through Suzuki coupling. In its neutral form, this macrocycle exists as a mixture of two figure-eight conformers that undergo fast exchange in less polar solvents. Upon protonation, the dynamic twist can be transformed into species that adopt a ruffled planar structure or a figure-eight shape depending on the extent of protonation and counteranions. Conversion to a bisboron difluoride complex via deprotonation with NaH and treatment with BF3 acts to lock the macrocycle into a figure-eight conformation. The various forms of cyclo[6]pyridine[6]pyrrole are characterized by distinct NMR, X-ray crystallographic, and spectroscopic features.

MATERIALS
Product Number
Brand
Product Description

Supelco
Methanesulfonic acid concentrate, 0.1 M CH3SO3H in water (0.1N), eluent concentrate for IC
Sigma-Aldrich
Methanesulfonic acid solution, 4 M (with 0.2% (w/v) tryptamine)
Sigma-Aldrich
Methanesulfonic acid solution, 70 wt. % in H2O
Sigma-Aldrich
Methanesulfonic acid, ≥99.0%
Supelco
Methanesulfonic acid, suitable for HPLC, LiChropur, ≥99.5% (T)