Manganese(II)/(III) glycolates: preparation, X-ray crystallographic study, and application in radical cycloaddition reactions

Alternative methods for stereoselective synthesis of the chiral racemic manganese(II) glycolate have been developed. Its geometry is proven to be independent of the nature of the starting material (Mn(Gly)3 and Mn(OAc)3) and reaction conditions (temperature, solvent). The single-crystal X-ray analysis shows that a chiral environment around the manganese atom is created by glycolate units lying in the perpendicular planes and water molecules disposed cis to each other. By its thermodynamic stability, the isolated complex ranks as second most unstable among five alternative isomeric structures. Manganese(III) glycolate has been suggested as a novel mediator for radical cycloadditions of β-dicarbonyl compounds to alkenes. It is the first time that an α-hydroxycarboxylic acid is used as a spectator ligand thus providing a possibility for using this class of compounds in asymmetric manganese(III)-mediated radical processes.