Modeling Tyrosinase Monooxygenase Activity. Spectroscopic and Magnetic Investigations of Products Due to Reactions between Copper(I) Complexes of Xylyl-Based Dinucleating Ligands and Dioxygen: Aromatic Ring Hydroxylations and Irreversible Oxidation Products.

Abstract

A full account of a chemical system possessing features that mimic the reactivity aspects of tyrosinase is presented. Using dinucleating ligands with a m-xylyl spacer three new dicopper(I) complexes have been synthesized and their reactivity with dioxygen investigated. The six-membered chelate ring forming ligands provide only two nitrogen coordinations to each copper. The complexes [CuI2L(CH3CN)2]X2 (X = ClO4- (1a), SbF6- (1b)) and [CuI2(L-NO2)(CH3CN)2][SbF6]2 (1c) [L = α,α‘-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; L-NO2 = para-nitro derivative of L] have been characterized by IR and 1H NMR spectroscopy. The reaction of O2 with 1a−c in CH2Cl2 or THF is instantaneous and causes stoichiometric xylyl hydroxylation reactions producing phenol products. Thus 1a produces phenoxo-/hydroxo-bridged product [CuII2(L-O)(OH)][ClO4]2 (2a). The existence of putative peroxo−dicopper(II) species could not be detected even at −80 °C. A trend is observed for the extent of aromatic ring hydroxylation (298 K): CH3CN ...