Evidence that π‐ligand exchange reactions of chalcogen iranium ions proceed via Hückel pseudocoarctate transition states

• Published in: Journal of physical organic chemistry Vol. 33; no. 12
• Main Authors: Brydon, Samuel C., Silva, Gabriel, White, Jonathan M.
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.12.2020
• Subjects: anisotropy of the induced current density; Aromaticity; chalcogen iranium ions; density functional theory; Ligands; Magnetic properties; natural bond orbital analysis; pseudocoarctate transition states
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.4111

Despite numerous computational and experimental studies on the π‐ligand exchange reactions of chalcogen iranium ions, a classification of the reaction class has yet to be made. The characteristics of the transition states presented thus far suggested a coarctate nature with two bonds breaking and forming simultaneously at the chalcogen centre. The change in barrier height, depending on the nature of the chalcogen and the alkene, was initially attributed as a shift in the degree of aromaticity moving from pseudocoarctate to coarctate reactions. However, this paper suggests that all 12 reactions under consideration are pseudocoarctate with a Hückel number of delocalised π electrons based on comprehensive studies of the orbital interactions and magnetic properties both at the transition state and along the reaction path. The change in barrier height was largely driven by the electrophilicity of the chalcogen and the strain present in the three‐membered ring rather than a shift in the degree of aromaticity. The nature of π‐ligand exchange reactions of chalcogen iranium ions has been explored by examining the magnetic properties and change in orbitals both at the transition state and along the reaction coordinate. This density functional theory study has found evidence for a pseudocoarctate transition state with the reaction being driven by both the electrophilicity and the strain present in the three‐membered rings rather than a shift in aromaticity.