Chemical model systems possessing the reactivity aspects of both tyrosinase and catechol oxidase are presented. Using two m-xylyl-based ligands providing bidentate alkylamine terminal coordination, 1,3-bis[(N,N-dimethylaminoethyl)aminomethyl]benzene (L-H,L-H) and 1,3-bis[(N,N,N'-trimethylaminoethyl)aminomethyl]benzene (L-Me'Me), four new dicopper(I) complexes, [Cu-2(I)(L-H,L-H)-(MeCN)(4)][ClO4](2) (1), [Cu-2(I)(L-H,L-H)(PPh3)(2)(MeCN)(2)][ClO4], (2), [Cu-2(I)(L-Me,L-Me)(MeCN)(2)][ClO4], (3), and [Cu-2(I)(L-Me,L-Me)(PPh3),][ClO4](2) (4), have been synthesized and characterized. Complex 2 has been structurally characterized. Reaction of the dicopper(I) complex 3(2+) with dioxygen at 183 K generates putative bis(mu-oxo)dicopper(III) intermediate (absorption spectroscopy). Oxygenation of 1 and 3 brings about m-xylyl-ring hydroxylation (monooxygenase-like activity), with a noticeable color change from pale-yellow to dark green. The presence of phenoxo- and hydroxo-bridges in the end products [Cu-2(II)(L-H,L-H-O)(OH)(MeCN)(2)][ClO4](2) (5) and [Cu-2(II)(L-Me,L-Me-O)(OH)(OClO3)][ClO4].MeCN(6) has been authenticated by structural characterization. Oxygenation of 3 afforded not only the green complex 6 isolation but also a blue complex [Cu-2(II)(L-Me,L-Me)(OH)(2)][ClO4](2) (7). Variable temperature magnetic susceptibility measurements on 5 and 6 establish that the Cu-II centers are strongly antiferromagnetically coupled [singlet-triplet energy gap (J) = -528 cm(-1) (5) and -505 cm(-1) (6)]. The abilities of phenoxo- and hydroxo-bridged dicopper(II) complexes 5 and 6, the previously reported complex [Cu-2(II)(L-2-O)(OH)-(OClO3)(2)]center dot 1.5H(2)O (8) (L-1-OH = 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol), and [Cu-2(II)(L-2-O)(OH)-(OClO3)][ClO4] (9) (L-2-OH = 1,3-[(2-dimethylaminoethyl)iminomethyl][(N,N,N'-trimethyl)aminoethyl]-4-methylphenol) have been examined to catalyze the oxidation of catechol to quinone (catecholase activity of tyrosinase and catechol oxidase-like activity) by employing the model substrate 3,5-di-tert-butylcatechol. Saturation kinetic studies have been performed on these systems to arrive at the following reactivity order [k(cat)/K-M (catalytic efficiency) X 10(-3) (M-1 h(-1))]: 470 (6) > 367 (5) > 128 (9) > 90 (8).