Copper-dioxygen compound dinuclear

A typical example of the more complex reactions that may occur when aromatic compounds react with dioxygen in the presence of copper salts is seen in Fig. 9-30. When solutions of the hexadentate ligand 9.14 react with copper salts and dioxygen, a complex of a new ligand is obtained. The new phenolic compound that is formed acts as a dinucleating ligand and its dinuclear copper(n) complexes turn out to be effective oxygenation catalysts for other substrates. 

Ascorbate oxidase is a tetramer each subunit has 552 amino acids and contains 4 copper ions, the type-I blue copper center and the adjacent trinuclear center (arranged as a type-n center and a type-in dinuclear center) separated by /S-sheets (Figure 20) °. Ascorbate is oxidized to dehydroascorbate by dioxygen however, it is not bound directly to the metal center to be oxidized, but is proposed to bind near the type-I Cu site which may facihtate electron transfer to oxygen, presumably in the tri-Cu cluster site. Since humans cannot synthesize ascorbic acid, conservation of this important compound is highly regulated. For example, the oxidized ascorbate can be transported into red blood... 

Usually the stable nitroxyl radicals alone cannot directly catalyze the oxidation of alcohols with dioxygen or peroxide, so they rely on the assistance of various cocatalysts that play an important role in activating the oxidation agent. The most used cocatalysts are first row transition-metal complexes where Cu compounds with various N-donor ligands account for the prime ones. In many instances this combination serves as some kind of model to compare catalytic properties of copper compounds. For example, the performances of two asymmetric tetranuclear (with the Cu4(p—0)2(p — 0)2 404 core) and dinuclear (with the Cu2(p-0)2N202 core) copper(II) complexes were compared in the catalytic TEMPO-mediated aerobic oxidation ofbenzylic alcohols. In spite of their similarity, the complexes perform differently the tetranuclear copper(II) (R) complex is highly active leading to yields up to 99% and TONs up to 770, while the (S,R)-2 dinuclear complex is not so efficient under the same conditions. However, no solid explanation of the activity differences was proposed. 

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