Dinuclear Copper Complex with a Pyridazine-Bridged Octadentate Ligand: Monooxygenase Activity and Characterization of Copper-Oxygen Intermediates
Copper-containing enzymes catalyze the mono-oxygenation of aromatic and aliphatic substrates in nature. Herein, we report on the synthesis of a new dinuclear copper complex supported by an octadentate ligand with a pyridazine backbone. Low-temperature oxygenation leads to a μ-1,1-hydroperoxo dicopper(II) (Cu2OOH) complex, which in turn stoichiometrically converts anthrone (AT) to anthraquinone (AQ). Oxygenation at room temperature, by contrast, leads to a new species that mediates the conversion of AT to AQ in a catalytic fashion, but neither corresponds to a μ-peroxo nor a mono μ-oxo dicopper complex. For further analysis, a μ-hydroxo dicopper(II) (Cu2OH) complex is synthesized by oxidation of the copper(I) complex with AgOTf. The electronic and geometric structures of the Cu2OOH and Cu2OH intermediates, as well as the structure of the room-temperature oxygenation product are elucidated by UV/Vis, Raman, X-ray absorption spectroscopy (XAS), and mass spectrometry, coupled to DFT.
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