The phenol ortho-oxygenation by mononuclear copper(I) complexes requires a dinuclear mu-eta2:eta2-peroxodicopper(II) complex rather than mononuclear CuO2 species.

The mononuclear complex [Cu(L)]+ performs the ortho-oxygenation of an exogeneous phenol through the formation of a dinuclear mu-eta2:eta2-peroxodicopper(II) intermediate, which is so far the only type of copper-dioxygen complex that mediates the tyrosinase monophenolase reaction.