Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins. Issue 6 (28th November 2022)

• Record Type: Journal Article
• Authors: Casademont‐Reig, Irene; Woller, Tatiana; García, Victor; Contreras‐García, Julia; Tiznado, William; Torrent‐Sucarrat, Miquel; Matito, Eduard; Alonso, Mercedes
• Is Part Of: Chemistry. Volume 29:Issue 6(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-11-28
• Subjects: annulene model -- aromaticity -- charged macrocycles -- porphyrinoids -- ring currents; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202202264
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π ‐conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine‐type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins. Abstract : Choosing the right path : We show that the search for the most aromatic pathway in charged expanded porphyrins is a more puzzling quest than for their neutral analogue structures. Among the most popular aromatic indices, AVmin turns out to be the most useful tool for seeking the most aromatic path.