A Hybrid Macrocycle with a Pyridine Subunit Displays Aromatic Character upon Uranyl Cation Complexation

Reported
here is a new hybrid macrocycle, cyclo[1]­furan[1]­pyridine[4]­pyrrole
(1), that bears analogy to the previously reported mixed
heterocycle system cyclo[2]­pyridine[4]­pyrrole (2) and
cyclo[6]­pyrrole 3, an all-pyrrole 22 π-electron
aromatic expanded porphyrin. The oxidized, dianionic form of 1, [1 – 4H]2–, has been
characterized as its uranyl complex. In contrast to 2 and 3 and in spite of the presence of a 2,6-disubstituted
pyridine subunit, the uranyl complex of [1 – 4H]2– displays solid-state structural and solution-phase
spectroscopic features consistent with contributions to the overall
electronic structure that involve a conjugated, (4n + 2) π-electron aromatic periphery.