The Effect of Hydrogenation on the Contest between Aromaticity and Antiaromaticity in Norcorrole

Peter B Karadakov; Tom Riley

doi:10.1002/chem.202203400

The Effect of Hydrogenation on the Contest between Aromaticity and Antiaromaticity in Norcorrole

Chemistry. 2023 Feb 24;29(12):e202203400. doi: 10.1002/chem.202203400. Epub 2023 Jan 18.

Authors

Peter B Karadakov¹, Tom Riley¹

Affiliation

¹ Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.

PMID: 36436122
DOI: 10.1002/chem.202203400

Abstract

Magnetic shielding studies demonstrate that successive hydrogenation of Ni^II norcorrole (NiNc), a stable molecule combining aromatic and antiaromatic features, first weakens and then eliminates the central antiaromatic region, even though the NiNc antiaromatic "core", a 14-membered conjugated cycle with 16 π electrons, is formally preserved throughout the H₂ NiNc-H₈ NiNc series. The differences between aromatic and non-aromatic isotropic shielding distributions and nucleus-independent chemical shift (NICS) values in these hydrogenated porphyrin analogues are highlighted by comparing the results for the members of the H₂ NiNc-H₈ NiNc series to those for the aromatic Ni^II porphyrin complex. The results strongly support the unexpected and counterintuitive conclusion that H₈ NiNc will be nonaromatic, without even a trace of antiaromaticity. Based on these findings, H₈ NiNc is predicted to be the most stable member of the H₂ NiNc-H₈ NiNc series.

Keywords: Aromaticity; hydrogenated norcorrole; magnetic shielding; norcorrole; nucleus independent chemical shifts.