Catalytic activity of manganese(III)-oxazoline complexes in urea hydrogen peroxide epoxidation of olefins: The effect of axial ligands

Abstract

The catalytic activity of two manganese(III)-oxazoline complexes [Mn(phox) 2(CH 3OH) 2]ClO 4 and Mn(phox) 3 (Hphox = 2-(2′-hydroxylphenyl)oxazoline), was studied in the epoxidation of various olefins. All of epoxidation reactions were carried out in (1:1) mixture of methanol:dichloromethane at room temperature using urea hydrogen peroxide (UHP) as oxidant and imidazole as co-catalyst. The epoxide yields clearly demonstrate the influence of steric and electronic properties of olefins, the catalysts and nitrogenous bases as axial ligand. [Mn(phox) 2(CH 3OH) 2]ClO 4 catalyst with low steric properties has higher catalytic activity than Mn(phox) 3. The highest epoxide yield (95%) was achieved for indene at the presence of [Mn(phox) 2(CH 3OH) 2]ClO 4 within 5 min. The proximal and distal interactions of strong π-donor axial ligands such as imidazole with the active intermediate are efficiently increased activity of the catalytic system.