Building biomimetic model compounds of dinuclear and trinuclear copper clusters for stereoselective oxidations

The biomimetic model chemistry of copper enzymes containing dinuclear and trinuclear clusters that was developed during several years in our group has been reviewed. The emphasis was on the stereoselectivity aspects of the oxidation reactions, because a large number of our biomimetic complexes were derived from polydentate N6 (for dinuclear complexes) or N8 (for trinuclear complexes) chiral ligands. Various synthetic strategies were followed to obtain such ligands and different types of stereocenters were introduced in the ligand skeletons. The chiral discrimination properties of the biomimetic complexes were routinely assayed in the catalytic oxidation of a group of enantiomeric biogenic catechols. In several instances, the chiral recognition of L vs. D substrates reached satisfactory values above 70% of the chiral discrimination R parameter. However, the goal of performing hydroxylation of the aromatic phenol ring of l/d-tyrosine derivatives could not be achieved so far, as only radical coupling products were systematically obtained. In any case, the most recently synthesized dinuclear complexes were capable of performing the asymmetric sulfoxidation of alkyl aryl sulfides with the promising e.e. of about 40%.