Toward a Catalytic Cycle for the Mn-Salen Mediated Alkene Epoxidation: A Computational Approach

BP86 density functional calculations for the title reaction are presented, where a model catalyst with hypochlorite as oxygen-containing counter ligand, (ClO)(O)Mn(acacen′) (acacen′ = ^-O(CH)₃N-C ₂H₄-N(CH)₃O^-), is employed. The epoxidation reaction on potential energy surfaces corresponding to an overall spin-density of two and four unpaired electrons is investigated. The presence of the hypochlorite ligand is found to cause the reaction to proceed under conservation of spin. Further, the oxygen-containing counter ligand causes reoxidation of the Mn-center, thus closing the catalytic cycle. A catalytic scheme is therefore proposed, which includes a step of regeneration of the catalytically active species. Energetic estimates including corrections for solvent effects are presented for the relevant steps constituting the proposed catalytic scheme.