Ylidic radical reactivity towards ethylene and acetylene

Abstract

A detailed computational study at the Gaussian-3//B3LYP/6-31G(d) level is performed on the PH 3CH + C 2H 4/C 2H 2 reactions to unravel the chemical reactivity of the ylidic radical PH 3CH towards π-bonded species. Both reactions are associated with the addition–elimination mechanism, eventually leading to PH 3 + cCH 2CHCH 2, PH 2CHCH 2 + CH 3 and PHCH 2 + C 2H 5 for the PH 3CH + C 2H 4 reaction, and most favorably to PHCHCHCH 2 + H for the PH 3CH + C 2H 2 reaction. The four-membered ring species (cPH 3CHCH 2CH 2 and cPH 3CHCHCH, respectively) are important entrance intermediates for both reactions, whereas they are of negligible importance for normal unsaturated radical reactions with alkenes and alkynes. For both the PH 3CH + C 2H 4/C 2H 2 reactions, the λ 5-P bonding within PH 3CH is effectively transformed into the λ 3-P bonding within the products, also in contrast to normal reactions of unsaturated radicals, where the π-bonding within the radical is well kept throughout the reactions. The distinct feature of the ylidic reactions can be explained by the fact that the ylidic radical PH 3CH has a P–C π-bonding LUMO, whereas normal unsaturated radicals have σ-bonding LUMO localized on one atom. Finally, the solvent effects of benzene, methanol and water on the title reactions are considered. The present study should be useful for understanding the ylidic radical chemistry.