Reduction of Oxygen to H2O2 Coupled to Phenol Oxidation at Copper: Metal-Ligand Cooperativity in Hydrogen Atom Relay

Though a wide array of copper-oxygen intermediates arising from the dioxygen reactions of copper(I) sites have been investigated over the decades, examples of copper-catalyzed oxygen reduction processes remain rare and poorly understood. Xray diffraction, UV-vis, FTIR, and NMR/EPR provide unambiguous characterizations of a new family of copper(I/II)–halide complexes ( PyPz ArOH )CuX n ( 1 X /2 X ; X = Cl,Br; n= 1,2), supported by a bidentate ligand PyPz ArOH with an appended phenol. Incorporation of the phenol moiety in the second coordination sphere of the low-coordinate copper(I) complex ( PyPz ArOH )CuX ( 1 X ; X= Cl/Br) enables O 2 -to-H 2 O 2 transformation, wherein the phenol moiety serves as a proton donor, resulting in the formation of phenolate-bound copper(II) species ( PyPz ArO )CuX ( 3 X ). Furthermore, this report shows that the copper(II)–phenolate species 3 X participates in H-atom transfer (HAT) reactivity, in the presence of exogenous substituted phenols as the sacrificial H•(/H + +e – ) donors, thereby regenerating ( PyPz ArOH )CuX ( 1 X ). Analyses of kinetic isotope effect (KIE) and activation parameters (ΔH ‡ , ΔS ‡ , E a ) disclose mechanistic insights into the reactions of copper(II)–phenolate and substituted phenols. Finally, this mechanism-driven study allows the demonstration of catalytic reduction of dioxygen coupled to phenol oxidation mediated by 1 X . Collectively, these findings illustrate the dual role of the phenol(ate) moiety in the coordination sphere of copper in promoting proton and H-atom transfer during the catalytic reduction of oxygen, thereby providing insights into the possible functional role of the tyrosine residue in the active sites of metalloenzymes like lytic polysaccharide monooxygenases (LPMOs).