Experimental Support for a Chiral Pentacoordinate, Axially Symmetric Cationic Mn(V)-Oxo Complex as the Key Reactant in the Highly Enantioselective Catalytic Epoxidation of Olefins

Reported herein are new results on the mechanism of action and scope of a recently discovered process for enantio- and position-selective epoxidation of C═C using a novel chiral Mn(II) catalyst at 3 mol %. A novel axially symmetric cationic Mn(V)-oxo complex has been found to deliver oxygen to a double bond with a strong and predictable enantiofacial preference. The method has been demonstrated for a variety of mono- and trisubstituted olefins. The rate-limiting step is not formation of the Mn(V)-oxo intermediate but transfer of oxygen from it to the olefin operating under the Curtin-Hammett principle.