Dioxygen Activation by Copper Complexes. Mechanistic Insights into Copper Monooxygenases and Copper Oxidases

摘要

Reactions of copper (I) complexes with molecular oxygen have been examined using a series of N-alkyl-bis [2-(2-pyridyl) ethyl] amine tridentate ligands (~(R')Py2~R) and N,N-dialkyl-2-(2-pyridyl) ethylamine didentate ligands (~(R')Py l~(R1,R2)) at low temperature. The tridentate ligands predominantly provide (mu-eta~2:eta~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 (mu-oxo) dicopper (III) complexes. With the (mu-eta~1:eta~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 (mu-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 (mu-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 (mu-oxo)(mu-oxyl radical) dicopper (III) or a tetranulcear 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 (mu_3-oxo) trinuclear copper (II,II,III) complex has also been assessed using the didentate ligand with the smallest N-alkyl substitutent (methyl). Mechanistic details details of the above reactions as well as ligand effects on the copper (I) -dioxygen reactivity are discussed systematically.