Simple soluble Bi(iii) salts as efficient catalysts for the oxidation of alkanes with H2O2

Abstract

A simple catalytic system based on a soluble bismuth(III) salt, Bi(NO₃)₃/H₂O₂/HNO₃/CH₃CN + H₂O, exhibits pronounced activity towards the homogeneous oxidation of inert alkanes with the yield of oxygenate products up to 32% and TON up to 112. The experimental selectivity parameters and kinetic data together with theoretical DFT calculations indicate that the reaction occurs via a free radical mechanism involving the formation of the HO˙ radicals which directly react with alkane molecules. The mechanism of the HO˙ generation (which is the rate limiting step of the whole process) includes the substitution of a water ligand for H₂O₂ in the initial aqua complex [Bi(H₂O)₈]³⁺, hydrolysis of the coordinated H₂O₂, second H₂O-for-H₂O₂ substitution and the homolytic HO–OH bond cleavage in complex [Bi(H₂O)₄(H₂O₂)(OOH)]²⁺ (6). The relatively low overall activation energy for this process (ca. 20 kcal mol⁻¹) is accounted for by the high lability and acidity of the Bi aqua complexes and tremendous activation of coordinated H₂O₂ in 6 towards homolysis.