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

The catalytic activity of two manganese(III)-oxazoline complexes [Mn(phox)2(CH3OH)2]ClO4 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(CH3OH)2]ClO4 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(CH3OH)2]ClO4 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.

Two manganese-oxazoline complexes [Mn(phox)2(CH3OH)2]ClO4 and Mn(phox)3, have been used as catalyst in efficient epoxidation of olefins with urea hydrogen peroxide (UHP) in the presence of a nitrogenous base such as imidazole as co-catalyst in a mixture 1:1 of CH2Cl2/CH3OH solvent system at room temperature. The best co-catalytic effect is observed in the presence of imidazole with strong π-donating ability resulting in effective proximal and hydrogen bonding interactions of this axial ligand with the intermediate catalyst–H2O2 complex. The epoxide yields are depended on the steric and electronic effects of the catalyst, olefin, and axial ligand. Figure optionsDownload as PowerPoint slide