Fine Tuning of Structure and Reactivity of Dicopper-Dioxygen Complexes

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Reaction of copper(I) complexes with molecular oxygen have been examined using a series of N-alkyl-bis[2-(2-pyridyl)ethyl]amine tridentate ligands and N, N-dialkyl-2-(2-pyridyl)ethylamine didentate ligands at low temperature. The tridentate ligands predominantly provide (μ-η^2 : η^2-peroxo)dicopper(II) complexes (side-on type peroxo complex), while the didentate ligands enhance O-O bond homolysis of the peroxo species to produce bis(μ-oxo)dicopper(III) complexes. With the (μ-η^2 : η^2-peroxo)dicopper(II) complexes supported by the tridentate ligand, efficient oxygenation of phenolates to the corresponding catechols has been accomplished to provide a good model reaction of tyrosinase. The bis(μ-oxo)dicopper(III) complexes, on the other hand, undergo aliphatic ligand hydroxylation as well as oxygen atom transfer to sulfides to give the corresponding sulfoxides. In the reaction of bis(μ-oxo)dicopper(III) complex with 10-methyl-9, 10-dihydroacridine (AcrH_2) and 1, 4-cyclohexadiene (CHD), a new active oxygen intermediate such as a (μ-oxo)(μ-oxyl radical)dicopper(III) or a tetranuclear copper-oxygen complex has been suggested to be involved as the real active oxygen species for the C-H bond activation of the external substrates. A mixed valence bis(μ_3-oxo) trinuclear copper(II, II, III) complex has also been assessed using the didentate ligand with the smallest N-alkyl substituent (methyl). Mechanistic details of the above reactions as well as ligand effects on the copper(I)-dioxygen reactivity are discussed systematically. In addition to the copper-dioxygen complexes, a similar type of nickel-dioxygen complexes as well as copper-disulfide complexes have been developed in order to provide further insights into the redox functions of metalloproteins