Selective oxidation of alcohols with hydrogen peroxide catalyzed by hexadentate binding 8-quinolinolato manganese(III) complexes

A series of hexadentate 8-quinolinolato manganese(III) complexes were synthesized and proven to own a distorted octahedral geometry via elemental analysis, solid UV–vis spectroscopy and Hartree–Fock/3-21G+ calculation. These Mn(III) complexes were found to be more efficient than their corresponding tetradentate 8-quinolinolato manganese(II) and salen-MnIIIOAc for the oxidation of alcohols in acetone medium, being due to their special hexadentate binding structures that could open an axial MnO bond to form the more active pentadentate structures in the presence of aqueous hydrogen peroxide, as supported by UV–vis spectra. The halogen substituents in ligand's aryl ring could significantly enhance the catalytic activities and 5-chloro-7-iodo-8-quinolinolato manganese(III) gave the highest turnover number (TON). A reasonable mechanism for the present catalytic system was proposed.

Graphical abstractHexadentate 8-quinolinolato MnII complexes are highly efficient catalysts for alcohol oxidation with aqueous H2O2 in acetone medium. A reasonable mechanism for the present catalytic system was proposed.Figure optionsDownload full-size imageDownload high-quality image (31 K)Download as PowerPoint slide