Computational study of the bonding structure in ylide compounds

Abstract

The ylide compounds H_mDAH_n (DH_m = NH₃, PH₃, OH₂, SH₂; AH_n = CH₂, NH, NH₂⁺, SiH₂, PH, PH₂⁺) were examined using ab initio calculations. The main finding is that the geometrical planarity and bond strength of the DA double bond vary significantly for different carbenoid AH_n adducts. Some rationalization of this interesting observation was provided by the ΣΔE_ST (CGMT model) and the HOMO–LUMO gap of the two bonding fragments. In addition, this study demonstrated that protonated pnictenes behave much like heavy carbenes, with respect to their weak π-bonding character. In contrast, nitrene (HN) and nitrenium (H₂N⁺) are predicted to have triplet ground states. Thus, both of these species have strong π-bonding character similar to that in carbene.