Density functional studies on the reagents Me3PX2 (where X=F, Cl, Br and I) in the gas phase and in solution

The solvents cyclohexane, dichloromethane and water were modelled using the polarised continuum model. The trigonal structure is the most stable for X=F, whatever the solvent, just as the CT complex is the most stable for X=I whatever the solvent. The X=Cl and Br reagents show intermediate behaviour, depending on the nature of the solvent. Their behaviour is in accord with the common wisdom that polar solvents favour the more ionic species. We suggest that there is no stable CT complex for X=F whatever the solvent, and we agree with the experimental finding that the X=Cl reagent is ionic in dichloromethane, with the possibility that a covalent complex (TR) might also be observed at room temperature.