New manganese catalysts for alcohol oxidation

The in situ prepared manganese complexes based on ligands 1–6 have been used in the catalytic oxidation of alcohols to aldehydes or ketones. Highly active and selective catalysts were found with excellent turnover numbers (up to 900) using aqueous hydrogen peroxide as oxidant at ambient temperatures. EPR spectroscopy and electrospray mass spectrometry has indicated that dinuclear species may be involved in the catalytic oxidations. Comparing the rate of oxidation of benzyl-d7 alcohol with that of benzyl alcohol by the different catalysts yielded isotope effects (kH/kD) of 2.2–4.3. Although the exact nature of the oxidising species has not been elucidated, these results indicate that hydroxyl radicals are not involved in these processes.