TY - JOUR
T1 - Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins
AU - Casademont-Reig, Irene
AU - Woller, Tatiana
AU - García, Victor
AU - Contreras-García, Julia
AU - Tiznado, William
AU - Torrent-Sucarrat, Miquel
AU - Matito, Eduard
AU - Alonso, Mercedes
N1 - © 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.
PY - 2023/1/27
Y1 - 2023/1/27
N2 - 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.
AB - 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.
KW - annulene model
KW - aromaticity
KW - charged macrocycles
KW - porphyrinoids
KW - ring currents
UR - http://www.scopus.com/inward/record.url?scp=85143222765&partnerID=8YFLogxK
U2 - 10.1002/chem.202202264
DO - 10.1002/chem.202202264
M3 - Article
C2 - 36194440
AN - SCOPUS:85143222765
SN - 0947-6539
VL - 29
SP - e202202264
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 6
M1 - e202202264
ER -