Global Aromaticity in Macrocyclic Cyclopenta‐Fused Tetraphenanthrenylene Tetraradicaloid and Its Charged Species |
| |
| Authors: | Dr Xuefeng Lu Dr Tullimilli Y Gopalakrishna Dr Hoa Phan Dr Tun Seng Herng Dr Qing Jiang Chunchen Liu Dr Guangwu Li Prof Jun Ding Prof Jishan Wu |
| |
| Institution: | 1. Department of Chemistry, National University of Singapore, Singapore, Singapore;2. Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore |
| |
| Abstract: | 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. |
| |
| Keywords: | global aromaticity macrocycles phenanthrene polycyclic hydrocarbons tetraradicaloids |
|
|
