C₂ and C₁‐Symmetric Camphopyrazole Dioxomolybdenum(VI) Complexes catalyze the Epoxidation of Cyclic Olefins

Abstract

Dioxomolybdenum(VI) complexes (1‐6) were prepared in good yields (≥79 %) using enantiopure C2 and C1‐symmetric bidentate N,N‐ligands (L1‐L6) derived from (+)‐camphor. The ligands and complexes were characterized by NMR spectroscopy, IR, and elemental analysis. Single crystal X‐ray diffraction analyses of complexes 3, 4 and 6 confirmed the bidentate coordination modes of ligands L3, L4, and L6 and revealed distorted octahedral coordination geometries around the metal center. Complexes 3 and 6 form conformational isomers depending on the orientation of the substituents of the ligand aryl groups. Preliminary evaluation of the complexes as catalysts for the epoxidation of cyclohexene (81–93 % conversion) and cis‐cyclooctene (66–94 % conversion) with cumyl hydroperoxide and 35 % w/w aqueous hydrogen peroxide (39–73 %) demonstrated their activity for oxygen atom transfer reactions, opening the way for asymmetric epoxidations.