Adaptive σ aromaticity in the rhenacyclopropene rings

• Published in: Journal of computational chemistry Vol. 44; no. 29; pp. 2294 - 2301
• Main Authors: Deng, Qianqian, Zhu, Jun
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 05.11.2023
• Subjects: Aromaticity; Atomic energy levels; Density functional theory; DFT calculations; adaptive σ aromaticity; rhenacyclopropene
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.27192

Species generally exhibit one-state aromaticity either in the lowest singlet state (S ) or the lowest triplet state (T ) according to the Hückel's and Baird's rules. Hence, it is rare for species exhibit two-state aromaticity in both the S and T states (termed as adaptive aromaticity), let alone adaptive σ aromaticity. Here, we report adaptive σ aromaticity in unsaturated rhenacyclopropene rings via density functional theory (DFT) calculations. Various aromaticity indices including NICS, ACID, EDDB together with isodesmic reactions support the adaptive σ aromaticity in these rhenacyclopropene rings. As the T state of these species is formed by the ππ* excitation, the σ-aromaticity of these three-membered rings in the S state could hold in the T state. In addition, the aromaticity effect of the fused rings is also examined. Our findings expand the family of adaptive σ aromaticity, enriching the metallaaromatic chemistry.