The reactivity of dicopper(I) complexes of the. ligands alpha,alpha'-bis(4,7-diisopropyl-1,4,7-triazacyclononan-1-yl)-p- and m-xylene (p- and m-XYLiPr4) with dioxygen was examined by spectroscopic and rapid stopped-flow kinetics methods. Only bis(mu-oxo)dicopper(III) core formation was observed with p-XYLiPr4, but both (mu-eta(2):eta(2)-peroxo)dicopper(II) and bis(mu-oxo)dicopper(III) species were generated in the m-XYLiPr4 case, their relative proportions being dependent on the solvent, concentration of the dicopper(I) precursor, and temperature. Subsequent decomposition under conditions that favored bis(mu-oxo) core formation resulted in oxidative N-dealkylation of isopropyl groups, whereas mu-eta(2):eta(2)-peroxo decay led to the product resulting from hydroxylation of the bridging arene, [(m-XYLiPr4-O)Cu-2(mu-OH)](SbF6)(2). Evidence from kinetics studies, decomposition product analyses, and comparison to the chemistry exhibited by complexes of other substituted 1,4,7-triazacyclonane ligands support a model for the oxygenation of the m-XYLiPr4 compound involving initial, essentially rate-limiting:1:1 Cu:O-2 adduct formation followed by partitioning between intra-and intermolecular pathways. At low temperature and high starting material concentrations, the latter route that yields tetranuclear "dimer-of-dimer" species and/or higher order oligomers with bis(mu-oxo) cores is favored, while at higher temperatures and dilution, intramolecular reaction predominates to afford a (peroxo)dicopper(II) species. The course of the subsequent decompositions of these oxygenated products correlates with their proposed formulations. Thus, analysis of final products and kinetics data, including with selectively deuterated compounds, showed that N-dealkylation arises from the high-nuclearity bis(mu-oxo) species and arene hydroxylation occurs upon decay of the intramolecular peroxo complex. Geometric rationales for the divergent oxygenation and decomposition reactions supported by p-and m-XYLiPr4 are proposed.