Oxidation of Hydrocarbons with Tetrabutylammonium Oxone Catalyzed by β-Tribrominated meso-Tetraphenylporphyrinatomanganese(III) Acetate in the Presence of N-Bases

Abstract

Different manganese porphyrins and related systems such as Schiff bases have been used extensively in chemical modeling of biological monooxygenation reactions. The biomimetic oxidation of hydrocarbons and nitrogenand sulfur-containing compounds with different oxygen donors such as PhIO, NaOCl, H2O2, periodate, amine N-oxides and Bu4NHSO5 (TBAO) have been extensively studied. [1-20] Iron and manganese porphyrins bearing halogen substituents on the periphery of the porphyrin ring have been shown to be particularly efficient for epoxidation and hydroxylation reactions.[21-23] Such porphyrins are also more resistant to degradation via free-radical attack or direct oxidation of porphyrin ring than those containing electron-donating substituents.[1,24-25] The employment of nitrogenous donors in metalloporphyrin systems for mimicking the oxygenation function of P-450 has led to marked improvement in selectivities and turnover rates in the epoxidation of alkenes.[18,26-27] Despite the favorable employment of Oxone® (2KHSO5·KHSO4·K2SO4) in the Mn porphyrin catalyzed oxygenation of hydrocarbons,[28-29] attempts at using TBAO as an oxygen source in association with porphyrin catalysts has been unsuccessful until 2002.[18] Oxidation of hydrocarbons with TBAO in the presence of different electron-rich and electron-deficient MnIII meso-tetra(halogensubstituted aryl)porphyrins have been reported. The present work is the first report on using electron deficient Mn porphyrins bearing halogen atoms at β-positions (β-tri-brominated meso-tetraphenylporphyrinato-manganese(III) acetate, Mn(TPPBr3) OAc, as catalyst for oxidation of hydrocarbons with TBAO in the presence of different nitrogen donors as co-catalyst.