Palladium superoxido complexes. In what way (σ or π) is O2– co-ordinated? A quantum chemical approach

Abstract

The relative stability of palladium superoxido complexes, formed viaσ- or π-type co-ordination of a superoxide ion in monomeric and trimeric palladium species, has been investigated by CNDO-S², a semi-empirical quantum chemical SCF-m.o. method. The CNDO-S² method has been adapted to calculate the energetic and geometric properties of transition-metal compounds. A π-type co-ordination for O₂^– is calculated to be most stable for monomeric palladium species, while σ-type co-ordination is favoured for trimeric species. Experimental data on the reactivity of palladium superoxido complexes towards the epoxidation of simple alkenes are in agreement with the results of CNDO-S² calculations.