BINUCLEATING LIGAND STRUCTURAL EFFECTS ON (MU-PEROXO)-DICOPPER AND BIS(MU-OXO)DICOPPER COMPLEX-FORMATION AND DECAY - COMPETITION BETWEEN ARENE HYDROXYLATION AND ALIPHATIC C-H BOND ACTIVATION

The reactivity of dicopper(I) complexes of the. ligands is(4,7-diisopr opyl-1,4,7-triazacyclononan-1-yl)-p- and m-xylene (p- and m-XYLiPr4) w ith dioxygen was examined by spectroscopic and rapid stopped-flow kine tics methods. Only bis(mu-oxo)dicopper(III) core formation was observe d with p-XYLiPr4, but both (mu-eta(2):eta(2)-peroxo)dicopper(II) and b is(mu-oxo)dicopper(III) species were generated in the m-XYLiPr4 case, their relative proportions being dependent on the solvent, concentrati on of the dicopper(I) precursor, and temperature. Subsequent decomposi tion under conditions that favored bis(mu-oxo) core formation resulted in oxidative N-dealkylation of isopropyl groups, whereas mu-eta(2):et a(2)-peroxo decay led to the product resulting from hydroxylation of t he bridging arene, [(m-XYLiPr4-O)Cu-2(mu-OH)](SbF6)(2). Evidence from kinetics studies, decomposition product analyses, and comparison to th e chemistry exhibited by complexes of other substituted 1,4,7-triazacy clonane ligands support a model for the oxygenation of the m-XYLiPr4 c ompound involving initial, essentially rate-limiting:1:1 Cu:O-2 adduct formation followed by partitioning between intra-and intermolecular p athways. 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 predomin ates to afford a (peroxo)dicopper(II) species. The course of the subse quent decompositions of these oxygenated products correlates with thei r 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 a rene hydroxylation occurs upon decay of the intramolecular peroxo comp lex. Geometric rationales for the divergent oxygenation and decomposit ion reactions supported by p-and m-XYLiPr4 are proposed.