美国纽约州立大学Anderson, Harry L.团队报道了[18]环烯的反芳香二阴离子和芳香四阴离子。相关研究成果发表在2024年3月6日出版的《自然—化学》。

π-共轭大环的行为与类似的线性链不同，因为它们的电子波函数类似于环上的量子粒子，导致芳香性或反芳香性。[18] 环烯，（CH）18，是典型的非苯类芳烃。具有4n+2π电子回路的分子，如[18]环烯（n=4），是芳香的，具有增强的稳定性和全向性环电流（环内的磁屏蔽），而具有4nπ电子的分子，例如[18]环二烯的二价离子，预计是反芳香的，并表现出相反的行为。

该文中，研究人员使用¹H NMR光谱来重新评估[18]环烯二胺离子的结构。研究表明，它可以进一步还原为芳香四阴离子，其形状与二阴离子相同。四阴离子锂盐的晶体结构证实了其几何形状，并揭示了类茂金属夹层，五个Li⁺阳离子插在两个[18]环烯四阴离子之间。研究人员还报道了一种具有[18]环烯和珊瑚烯四阴离子甲板的异质夹层。

附：英文原文

Title: The anti-aromatic dianion and aromatic tetraanion of [18]annulene

Author: Stawski, Wojciech, Zhu, Yikun, Ronevi, Igor, Wei, Zheng, Petrukhina, Marina A., Anderson, Harry L.

Issue&Volume: 2024-03-06

Abstract: π-Conjugated macrocycles behave differently from analogous linear chains because their electronic wavefunctions resemble a quantum particle on a ring, leading to aromaticity or anti-aromaticity. [18]Annulene, (CH)18, is the archetypal non-benzenoid aromatic hydrocarbon. Molecules with circuits of 4n+2 π electrons, such as [18]annulene (n=4), are aromatic, with enhanced stability and diatropic ring currents (magnetic shielding inside the ring), whereas those with 4n π electrons, such as the dianion of [18]annulene, are expected to be anti-aromatic and exhibit the opposite behaviour. Here we use 1H NMR spectroscopy to re-evaluate the structure of the [18]annulene dianion. We also show that it can be reduced further to an aromatic tetraanion, which has the same shape as the dianion. The crystal structure of the tetraanion lithium salt confirms its geometry and reveals a metallocene-like sandwich, with five Li+ cations intercalated between two [18]annulene tetraanions. We also report a heteroleptic sandwich, with [18]annulene and corannulene tetraanion decks.

DOI: 10.1038/s41557-024-01469-1

Source: https://www.nature.com/articles/s41557-024-01469-1