Enhancing effects of hydrogen/halogen bonds on σ-hole interactions involving ylide.

Cooperativity between the H/Cl···C bonds of XH/XCl···CH2PH3 and the P···N interaction of CH2PH3···NH3 in XH/XCl···CH2PH3···NH3 (X = F, N3, CN, CCCN, CCF) was investigated by performing second-order Møller-Plesset perturbation theory (MP2) calculations and quantum theory of atoms in molecules (QTAIM) studies. The formation of a hydrogen/halogen bond greatly extends the scope and increases the most positive electrostatic potential of the σ-hole on the outer surface of the phosphorus atom. This increases the P···N interaction energy, the electron density at the P···N bond critical point, the electrostatic character of the P···N interaction, and it decreases the P···N interaction distance. The net result is that the formation of a hydrogen/halogen bond enhances the P···N interaction, and vice versa. However, the P···N interaction is enhanced by the presence of the hydrogen or halogen bond to a much greater degree than the hydrogen or halogen bond is enhanced by the P···N interaction.