Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle

The present paper details the first application of a fully reduced meso-octamethylporphyrinogen macrocycle as an effective ligand for simple operative manganese-catalyzed alkene epoxidation. The efficiency of the novel catalyst was determined in the presence of various oxidants, apical ligands and acidic/basic additives. Higher reactivity was found in favour of electron-rich alkenes, whereas an electron-deficient conjugated alkene appeared as a poor substrate in the screening. Sulfur additives were active as apical ligands, whereas nitrogen-containing additives influenced the reactivity only moderately. cis-Stilbene and 3β-acetoxy-5-cholestene were epoxidized in a stereoselective manner. The X-ray structures of the new manganese complexes were determined and showed a rigid planar coordination geometry of the saturated macrocyclic ligand to the metal centre.