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) complex:es 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 [(Cu2L)-L-I(CH3CN)(2)]X-2 (X = ClO4-(1a), SbF6- (1b)) and [Cu-2(I)(L-NO2)(CH3CN)(2)][SbF6](2) (1c) [L = alpha,alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; L-NO2 = para-nitro derivative of L] have been characterized by LR and H-1 NMR spectroscopy. The reaction of O-2 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 [Cu-2(II)(L-O)(OH)][ClO4](2) (2a). The existence of putative peroxo-dicopper(II) species could not be detected even at -80 degrees C. A trend is observed for the extent of aromatic ring hydroxylation (298 K): CH3CN similar to DMF > CH3OH much greater than CH2Cl2. Cyclic voltammetric experiment of 1a in DMF reveals an appreciably low redox potential (E-1/2 = -0.26 V vs SCE) for the Cu-2(II)/Cu-2(I) redox process. Variable-temperature (25-300 K) magnetic susceptibility measurements establish that the copper(II) centers in 2a and the dihydroxo-bridged complex [(Cu2L)-L-II'(OH)(2)][ClO4](2) (2b) [formed due to an impurity (L') present during the synthesis of L following Method A; L' = bis[alpha,alpha'-bis(N-methyl-N-(2-pyridylethyl)amino)-m-xylene]methylamine] are antiferromagnetically coupled, with 2a considerably more coupled than 2b. Reaction of 1a with O-2 in CH2Cl2 (298 K) produces an additional unhydroxylated product of composition [(Cu2L)-L-II(OH)(OH2)][ClO4](3). 2H(2)O . 0.5HCl (3a). In agreement with its proposed hydroxo-/aquo-bridged structure, 3a is weakly antiferromagnetically coupled. In CH3CN solution, 3a rearranges to generate a doubly hydroxo-bridged species [(Cu2L)-L-II(OH)(2)](2+). Using a solution-generated dicopper(I) complex of a closely similar ligand (L ") providing five-membered chelate ring, the reactivity toward dioxygen was also investigated. It produces only an irreversibly oxidized product of composition (Cu2L)-L-II "(OH)(ClO4)(3)(H2O)(2) (3b) (L " = alpha,alpha'-bis[N-methyl-N-(2-pyridylmethyl)-amino]-m-xylene). For 3b the copper(II) centers are almost uncoupled.