Tricyclic 1,4‐Diphosphinines: Local vs. Global Aromaticity

• Published in: Chemphyschem 2024-10, Vol.25 (19), p.e202400417-n/a
• Main Authors: Kalisch, Tim, Brehm, Philipp C., Streubel, Rainer
• Format: Article
• Language: English
• Subjects: Aromaticity; Benzene; Diphosphinine; Functional groups; Heterocyclic carbenes; Heterocyclic compounds; Hydrocarbons; NICS; Pyrazines; Ring currents; Sulfur content; TTF
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.202400417

1D and 2D NICSπ.zzSOM ${{{\rm { NICS}}}_{{\rm { {\rm \pi}{}}}{\rm { .zz}}}^{{\rm { SOM}}}$ (Sigma only model) calculations were performed on recently established tricyclic 1,4‐diphosphinines as well as related benzene and pyrazine derivatives. The study was extended to evaluate the effect of the fused rings on the overall aromatic properties with a special focus on functional groups such as carbenes. The effect of non‐aromatic heterocycles on the local ring current of the central ring is small, while aromatic heterocycles (e. g. NHC, imidazolium) lead to a global aromaticity. A higher sulfur content of the adjacent five‐membered rings reduces the central ring current. The comparison to related tricyclic benzene and pyrazine derivatives showed that the 1,4‐diphosphinine systems resemble more closely the situation in the benzene derivatives than the pyrazines. The effect of charged systems was studied using bis(TTF)‐fused 1,4‐diphosphinines and, according to NICSπ.zzSOM ${{{\rm { NICS}}}_{{\rm { {\rm \pi}{}}}{\rm { .zz}}}^{{\rm { SOM}}}$ values, the neutral form doesn't possess significant aromaticity but the tetracation resembles the global aromatic situation observed for other heterocycles in this study. Aromatic, tricyclic 1,4‐diphosphinines as well as related benzene and pyrazine derivatives and their individual monocycles were investigated using 1D and 2D NICSSOMπ.zz calculations to understand the distribution of aromaticity therein.