Intramolecular Phenolic H-Atom Abstraction by a N₃ArOH Ligand-Supported (μ-η²:η²-Peroxo)dicopper(II) Species Relevant to the Active Site Function of oxy-Tyrosinase

Abstract

Synthetic side-on peroxide-bound dicopper(II) ( S P) complexes are important for understanding the active site structure/function of many copper-containing enzymes. This work highlights the formation of new {CuII(μ-η2:η2-O2 2–)CuII} complexes (with electronic absorption and resonance Raman (rR) spectroscopic characterization) using tripodal N3ArOH ligands at −135 °C, which spontaneously participate in intramolecular phenolic H-atom abstraction (HAA). This results in the generation of bis(phenoxyl radical)bis(μ-OH)dicopper(II) intermediates, substantiated by their EPR/UV–vis/rR spectroscopic signatures and crystal structural determination of a diphenoquinone dicopper(I) complex derived from ligand para-CC coupling. The newly observed chemistry in these ligand–Cu systems is discussed with respect to (a) our Cu-MeAN (tridentate N,N,N′,N′,N″-pentamethyl­dipropylenetriamine)-derived model S P species, which was unreactive toward exogenous monophenol addition (J. Am. Chem. Soc. 2012, 134, 8513–8524), emphasizing the impact of intramolecularly tethered ArOH groups, and (b) recent advances in understanding the mechanism of action of the tyrosinase (Ty) enzyme.