Computational study of the substitution effect on the mechanism for phospha-Wittig reaction

The phospha-Wittig reaction HP=PH3 + O=CHX → HP=CHX + O=PH3 (X = H, F, Cl, Me, OMe, NMe2, CMe3) was examined using the density functional theory calculations. All of the structures were completely optimized at the B3LYP/6-311++G** level of theory. The reactivities of various O=CHX were examined by estimating their activation energies. The main finding of this work is that the configuration mixing model can successfully predict the relative ordering of the activation energy and reaction enthalpies of the phospha-Wittig reaction. It was demonstrated that O=CHX with more electro-releasing substituents will possess a smaller singlet–triplet splitting. This will facilitate the phospha-Wittig reaction and will result in a larger exothermicity.