Study on the aromaticity and reactivity of chlorophosphinines

Aromaticity of phosphinine derivatives, such as 2‐, 3‐, and 4‐chlorophosphinines and 4‐chloro‐3‐methyl‐and 3,5‐dimethylphosphinine, has been investigated by means of quantum‐chemical calculations and photoelectron spectroscopy. The position of the π‐bands in the photoelectron spectra of 4‐chloro‐3‐methyl‐ and 3,5‐dimethylphosphinine indicated that the aromaticity of these species is similar to that of the corresponding benzene derivatives. The MP2/6‐31G* and the HF/3‐21G(*) geometries of the chlorophosphinines, together with the isodesmic reaction energies and Mulliken charge distributions, showed that the electronic system of phosphinine is not significantly perturbed by the chloro‐substitution. 3‐methyl‐4‐chlorophosphinine, similarly to 2‐chlorophosphinine, was inert toward nucleophiles even under forced conditions. This unreactivity can more likely be rationalized by kinetic considerations than by thermodynamic arguments (such as increased aromatic stabilization of the chlorophosphinines).