Computational study of the bonding structure in ylide compounds

Abstract

The ylide compounds HmDAHn (DHm = NH3, PH3, OH2, SH2; AHn = 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 AHn adducts. Some rationalization of this interesting observation was provided by the ΣΔEST (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.