Computational Study of the Substitution Effect on the Mechanism for the Aza‐ and Arsa‐Wittig Reactions

The aza‐ and arsa‐Wittig reactions HM=PH₃ + O=CHX → HM=CHX + O=PH₃ (M = N, As; X = H, F, Cl, Me, OMe, NMe₂, CMe₃) were examined using the density functional theory calculations. All of the structures were completely optimized at the B3LYP/6‐311++G** level of theory. The main finding of this work is that the difference between singlet‐triplet splitting of O=CHX and HM=PH₃ play an important role in determining the kinetic and thermodynamic stability of the aza‐ and arsa‐Wittig reactions. When HM=PH₃ with more ylidic character is utilized, the reaction has a smaller activation energy and a larger exothermicity.