Exchange of Cl⁺ between lone-pair donors and π-donors: A computational study

The chemistry of mono-adducts ([Cl-X]⁺) between Cl⁺ and a Lewis base (X = NH₃, H₂O, HF, PH₃, H₂S or HCl) has been investigated using ab initio molecular orbital calculations at the G2 level. The reactions of such mono-adducts with additional Lewis bases (Y) are found to give [Y-Cl]⁺ plus X, generally without an intermediate barrier, via a bis-adduct [Y-Cl-X]⁺. The binding energies of the bis-adduct and the reaction energies are related to the donor properties of the Lewis bases. The reactions between the mono-adducts [Cl-X]⁺ and the π-donors ethylene and acetylene yield chloriranium and chlorirenium ions, respectively. These reactions proceed via complexes that resemble either the reactants or products depending on the sign of the reaction energy, the latter in turn being determined by the donor ability of the Lewis base. Results for the chlorine systems are compared with those for the corresponding phosphorus systems investigated previously.