Catalytic Conversion of Monophenols to Ortho‐Quinones in a Tyrosinase‐Like Fashion: Towards More Biomimetic and More Efficient Model Systems

A new tyrosinase model based on the mononuclear copper(I) complex CuLbzm1 is synthesized and characterized. The ligand Lbzm1 of this system contains a combination of an imine and a benzimidazole function which renders the system more biomimetic in comparison to the recently published Lpy1 model of tyrosinase (M. Rolff, J. Schottenheim, G. Peters, F. Tuczek, Angew. Chem. Int. Ed. 2010, 122, 6583). As shown by UV/Vis and NMR spectroscopy, the CuLbzm1 complex catalytically mediates the conversion of the monophenol DTBP-H to the o-quinone DTBQ with a TON of 31. This reaction was also conducted in a stoichiometric fashion to get information about the involved intermediates and identify possible reasons for the observed increase in catalytic performance with respect to the Lpy1 system. DFT calculations were performed for the μ-catecholato dicopper intermediate, compound 4bzm. These calculations indicate a mixed valent CuI-semiquinone-CuII structure, indicating that one-electron transfer from the monohydroxylated substrate to the copper centers has already occurred at this stage.