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

• Published in: Angewandte Chemie International Edition Vol. 57; no. 40; pp. 13052 - 13056
• Main Authors: Lu, Xuefeng, Gopalakrishna, Tullimilli Y., Phan, Hoa, Herng, Tun Seng, Jiang, Qing, Liu, Chunchen, Li, Guangwu, Ding, Jun, Wu, Jishan
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 01.10.2018; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Anions; Aromaticity; Chemistry; Chemistry, Multidisciplinary; Crystallography; Diamagnetism; Electronic properties; Electrons; Energy gap; global aromaticity; macrocycles; NMR; Nuclear magnetic resonance; phenanthrene; Physical Sciences; polycyclic hydrocarbons; Protons; Ring structures; Science & Technology; tetraradicaloids; LOWEST; HYDROCARBONS; macrocycles; CYCLOARENES; tetraradicaloids; STATE; SUPERAROMATICITY; MODEL; ANISOTROPY; global aromaticity; phenanthrene; polycyclic hydrocarbons
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201807185

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 1H NMR spectrum. The tetraanion can be regarded as an isoelectronic structure of the known octulene, which shows similar electronic properties. A global trend: A fully fused cyclic tetraphenanthrenylene tetraradicaloid showing substantial radical character and a small singlet–triplet energy gap was prepared in crystalline form (see structure). The neutral and corresponding charged species exhibited unusual global (anti‐)aromaticity. The tetraanion can be regarded as an isoelectronic structure of octulene, with a unique ring‐in‐ring ring‐current‐density map.