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 pi-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 kv thermodynamic arguments (such as increased aromatic stabilization of the chlorophosphinines).