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Global Aromaticity in Macrocyclic Cyclopenta‐Fused Tetraphenanthrenylene Tetraradicaloid and Its Charged Species

2018; Wiley; Volume: 57; Issue: 40 Linguagem: Inglês

10.1002/anie.201807185

1521-3773

Xuefeng Lu, Tullimilli Y. Gopalakrishna, Hoa Phan, Tun Seng Herng, Qing Jiang, Chunchen Liu, Guangwu Li, Jun Ding, Jishan Wu,

Organic Chemistry Cycloaddition Reactions

A stable cyclopenta-fused tetraphenanthrenylene macrocycle, CPTP-M, was synthesized, and the structure was confirmed by X-ray crystallographic analysis. It exhibits a large radical character (number of unpaired electron, NU =3.52) and a small singlet-triplet energy gap (ΔES-T =-2.8 kcal mol-1 by SQUID). Its backbone contains 60 ([4n]) conjugated π electrons and is globally antiaromatic. NMR measurements and theoretical calculations revealed that its dication/dianion is globally aromatic owing to the existence of [4n-2]/[4n+2] π-conjugated electrons. Remarkably, the ring-current map of the tetraanion shows a unique ring-in-ring structure, with a diamagnetic outer ring and a paramagnetic inner ring. Accordingly, both the inner-rim and outer-rim protons are deshielded in its 1 H NMR spectrum. The tetraanion can be regarded as an isoelectronic structure of the known octulene, which shows similar electronic properties.