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

Abstract

AbstractDespite 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.