Experimental and DFT Studies on the Identity Exchange Reactions between Phenyl Chalcogen Iranium Ions and Alkenes

The gas-phase ion-molecule identity exchange reactions of phenyl chalcogen iranium ions with alkenes have been examined experimentally in a linear ion trap mass spectrometer by isotope labeling experiments. The nature of both the alkene and the chalcogen play crucial roles, with the bimolecular rates for π-ligand exchange following the order: [PhTe(c-C₆H₁₀)]⁺ + c-C₆D₁₀ > [PhTe(C₂D₄)]⁺ + C₂H₄ > [PhSe(c-C₆H₁₀)]⁺ + c-C₆D₁₀, with no reaction being observed for [PhSe(C₂D₄)]⁺ + C₂H₄, [PhS(C₂D₄)]⁺ + C₂H₄, and [PhS(c-C₆H₁₀)]⁺ + c-C₆D₁₀. The experimental results correlate with RRKM modeling and density functional theory (DFT) calculations, which also demonstrates that these reactions proceed via associative mechanisms. Natural bond orbital (NBO) analysis reveals a shift in the association complexes from a σ-hole interaction to ones mirroring the π-p⁺ and n-π* at the transition state in accordance with the rates of reaction.