Fine Tuning of Structure and Reactivity of Dinuclear Transition Metal Active Oxygen Complexes

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In this research project, structure, physicochemical property, and reactivity of dinuclear transition metal-active oxygen complexes have been systematically investigated in order to shed light on the dioxygen activation mechanism in not only biological systems but also catalytic oxygenation reactions. Followings are summary of the results.(1) Reactions of Cu (I) complexes supported by a series of bidentate, tridentate, and tetradentate amine ligands with molecular oxygen have been investigated to explore the ligand effects on the structure and physicochemical properties of the active oxygen intermediates.(2) Quantitative oxygenation of phenols to catechols by a (μ-η^2 : η^2-peroxo) dicopper (II) complex have been found for the first time. Detailed mechanistic studies including kinetics and product analysis implicated that the oxygenation of phenolates to catechols by the (μ-η^2 : η^2-peroxo) dicopper (II) complex proceeds via an electrophilic attack of the peroxo species to the phenola … More te ring in a binary complex between the peroxo intermediate and the substrate, providing valuable insight into phenolase activity of tyrosinase.(3) Formation mechanism and reactivity of a bis (μ-oxo) dicopper (III) complex that could be derived from a (μ-η^2 : η^2-peroxo) dicopper (II) complex via the O-O bond homolysis have been investigated in detail. It has been found that the bis (μ-oxo) dicopper (III) complex decomposes leading to intramolecular aliphatic ligand hydroxylation reaction. In the C-H bond activation of external substrates such as 10-methyl-9, 10-dihydroacridine (AcrH_2) and 1, 4-cyclohexadiene (CHD) with the bis (μ-oxo) dicopper (III) complex supported by a pyridylethylamine bidentate ligand, formation of a new copper-active oxygen intermediate, such as (μ-oxo)(μ-oxyl radical) dicopper (III), has been implicated as an actual reactive species for hydrogen atom abstraction from the substrates.(4) The first systematic studies on spectroscopic features and the formation mechanism as well as the reactivity of the bis (μ-oxo) dinickel (III) complexes supported by a series of bis [2-(2-pyridyl) ethyl] amine ligands have been carried out in order to shed light further on the dioxygen activation mechanism by non-heme transition-metal complexes.(5) Three different types of dinuclear copper complexes have been obtained in the reactions of cuprous ions and structurally related three dinucleating ligands containing a disulfide group in it. The crystal structures of the complexes reveal that two of the three complexes are dicopper (I) retaining the disulfide group of the parent ligands, but that the coordination mode of the disulfide group to the two cuprous ions are significantly different. In contrast to those complexes, the third one has a bis (μ-thiolato) dicopper (II) core in it which is regarded as a good model of the Cu_A electron-transfer site of cytochrome c oxidase (CcO) and nitrous oxide reductase (NOR). Less