Novel chiral (salen)MnIII complexes containing a calix[4]arene unit as catalysts for enantioselective epoxidation reactions of (Z)-aryl alkenes

New asymmetric (salen)Mn-III and UO2 complexes containing a calix[4]arene unit in the ligand framework were synthesized. The UO2 complexes were characterized by H-1-, C-13-, 2D TOCSY and T-ROESY NMR spectroscopy. Furthermore, the structure of one UO2 complex was determined by single-crystal X-ray analysis. The data showed that UO2 complexes, which can be considered in first approximation models of the Mn = O oxidant active species, possess a chiral pocket and adopt relevant conformations for the selectivity of the oxygen transfer process. Epoxidation data of model alkenes with the Mn-III complexes showod moderdate ee values and were not conclusive in indicating that the calix[4]arene unit might be able to influence the solectivity by a molecular recognition mechanism. ((c) Wiley-VCH Verlag GmbH & Co, KGaA, 69451 Weinheim, Germany, 2005).