Mechanism of one oxygen atom transfer from oxo (salen)manganese(V) complex to olefins

In the Mn-salen catalyzed asymmetric epoxidation of some olefins, non-linear relationship between reaction temperature and enantioselectivity was observed. For example, me epoxidation of 1,3-cycloalkadiene with complex 3a as a catalyst showed the maximum enantioselectivity at 0 degrees C. It was also found that the electronic nature of the aromatic substituent in the salen ligand affects enantioselectivity but its effect does not necessarily correspond to the Hammet's sigma-values. Based on these new experimental results, we propose a reaction mechanism which proceeds through metallaoxetane intermediate, for one oxygen atom transfer reaction from oxo (salen)manganese(V) complex to olefins.