Highly Efficient NaOCl Olefin Epoxidations Catalyzed by Imidazole or Pyridine "Tailed" Manganese Porphyrins under Two-Phase Conditions. Influence of pH and of the Anchored Axial Ligand

Article abstract of DOI:10.1021/jo00224a048

Mn(III) tetraarylporphyrins 2 and 3, bearing a pyridine or an N-alkyl-substituted imidazole function anchored by an aliphatic chain, are extremely efficient catalysts for olefin epoxidations carried out with NaOCl under aqueous-organic two-phase conditions.Reaction rates are strongly increased by lowering the pH of the aqueous phase, and at pH 9.5 catalyst turnovers are in the range of 0.8-3.3 per s at 0 deg C.At the lower pH values rates are only slightly affected by the presence of a phase-transfer catalyst, whereas the latter becomes important at the pH of commercial bleach (12.5-13.0).A similar behavior has been found for epoxidations catalyzed by Mn(III) tetraphenylporphyrin 1, carried out in the presence of a molar excess of 3-pycoline or N-hexylimidazole.The latter is a particularly effcient axial ligand.