Reversible dioxygen binding and arene hydroxylation reactions: Kinetic and thermodynamic studies involving ligand electronic and structural variations

Copper–dioxygen interactions are of intrinsic importance in a wide range of biological and industrial processes. Here, we present detailed kinetic/thermodynamic studies on the O2-binding and arene hydroxylation reactions of a series of xylyl-bridged binuclear copper(I) complexes, where the effects of ligand electronic and structural elements on these reactions are investigated. Ligand 4-pyridyl substituents influence the reversible formation of side-on bound μ-η2:η2-peroxodicopper(II) complexes, with stronger donors leading to more rapid formation and greater thermodynamic stability of product complexes [CuII2(RXYL)(O22−)]2+. An interaction of the latter with the xylyl π-system is indicated. Subsequent peroxo electrophilic attack on the arene leads to C–H activation and oxygenation with hydroxylated products [CuII2(RXYLO–)(−OH)]2+ being formed. A related unsymmetrical binucleating ligand was also employed. Its corresponding O2-adduct [CuII2(UN)(O22−)]2+ is more stable, but primarily because the subsequent decay by hydroxylation is in a relative sense slower. The study emphasizes how ligand electronic effects can and do influence and tune copper(I)–dioxygen complex formation and subsequent reactivity.

Binuclear copper(I) complexes react with dioxygen to give adducts, which effect arene hydroxylation reactions. The kinetics and thermodynamics are studied and presented.Figure optionsDownload as PowerPoint slideHighlights
► Low-temperature stopped-flow kinetics provide insights into copper(I)–O2 chemistry.
► Dicopper(I)–O2 reactions leads to Cu2O2 formation and arene substrate hydroxylation.
► Ligand 4-pyridyl substituents tune copper(I)–O2 kinetics–thermodynamics.
► An unsymmetrical binucleating ligand generates altered CuI2–O2 reactivity behavior.