Dinuclear Copper(I) Complexes Supported by Bis‐Tridentate N‐Donor‐Ligands: Turning‐On Tyrosinase Activity
Four structurally related bis-tridentate N-donor ligands with either two secondary amine or two imine functions were synthesized, and the corresponding dicopper(I) complexes were investigated as catalysts for the tyrosinase-like conversion of 2,4-di-tert-butylphenol (DTBP-H) to 3,5-di-tert-butylquinone (DTBQ). Notably, the imine systems show evidence for both a μ-η2 : η2-peroxo-dicopper(II) species and catalytic conversion of DTBP-H to DTBQ. Moreover, kinetic studies indicate that a dinuclear copper-oxygen species is involved in the monooxygenation of DTBP-H. In contrast, the amine systems do not show monooxygenase activity. Comparison of the experimentally determined catalytic activities with DFT-optimized geometries of μ-η2 : η2-peroxo-dicopper(II) intermediates suggests that the ligand rigidity of the imine systems allows equatorial attack of the substrate and, thus, subsequent monooxygenation whereas this is not possible in the amine systems due to the fact that no free equatorial positions are available in the μ-peroxo intermediate.