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) (SP) complexes are important for understanding the active site structure/function of many copper-containing enzymes. This work highlights the formation of new {CuII(µ-η2η2-O22-)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 SP 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.