Theoretical and experimental investigations of the enantioselective epoxidation of olefins catalyzed by manganese complexes

The enantioselective epoxidation of olefin by Mn^(II)(R,R-PMCP)(OTf)2, H_(2)O_(2) and H_(2)SO_(4) was explored by DFT calculations and experiments. Theoretical results suggest that [Mn^(V)(O)(R,R-PMCP)(SO_(4))]^(+) species with a triplet ground spin state serves as the active species for the olefin epoxidation. It can be generated by the H_(2)SO_(4) assisted O-O heterolysis of Mn^(III)(OOH) species. Mn^(III)-persulfate is also involved in this system, but it cannot promote the olefin epoxidation directly, preferring instead to transform into Mn^(V)(O). Actually, the asymmetric epoxidation reactions with H_(2)O_(2)/H_(2)SO_(4) or Oxone provide similar enantioselectivity in the presence of manganese catalyst. These observations further support the transformation of Mn^(III)-persulfate to Mn^(V)(O) species.