Oxygenation reactions of saturated and unsaturated substrates by molecular O₂ catalyzed by the versatile catalyst K[Ru(EDTA---H)Cl]·2H₂O: rate and activation studies

Abstract

Oxygenation of olefinic and saturated substrates, including triphenylphosphine, with molecular oxygen is catalyzed by (ethylene-diaminetetraacetato)aquoruthenate(III) ion, [Ru^III(EDTA)(H₂O)]⁻1, in a mixed solvent medium to yield a variety of products. The wide range of products formed includes oxides, epoxides, alcohols, ketones and aldehydes. The kinetics of these oxidation reactions have been investigated by oxygen absorption methods and product analysis at pH 3.0 (μ=0.1 M NaClO₄) in the temperature range 288-318 K in water-dioxane medium (1:1). In order to eliminate any radical chemical pathway with dioxane:H₂O, the oxygenation of a few selected substrates, cyclohexane and 1-hexane was conducted in water-DMF (1:1) medium. General mechanisms are proposed for both saturated and unsaturated substrates on the basis of the kinetic data and are discussed in terms of reactivity. In all cases, a μ-peroxoruthenium(IV)-substrate complex was suggested as the active intermediate. The activation parameters corresponding to rate constants at different temperatures were computed. The activation enthalpies are much more favourable for the oxidation of PPh₃ and olefins, as compared to saturated substrates