Dioxygen Reactivity of a Copper(I) Complex with a N₃S Thioether Chelate; Peroxo−Dicopper(II) Formation Including Sulfur-Ligation

Employing a tetradentate N₃S_(thioether) ligand, L^N3S, dioxygen reactivity of a copper(I) complex, [(L^N3S)Cu^I]⁺ (1) was examined. In CH₂Cl₂, acetone (at −80 °C), or 2-methyltetrahydrofuran (at −128 °C), 1 reacts with O₂ producing the end-on bound peroxodicopper(II) complex [{(L^N3S)Cu^II}₂(μ-1,2-O₂^2-)]²⁺ (2), the first reported copper−dioxygen adduct with sulfur (thioether) ligation. Its absorption spectrum contains an additional low-energy feature (but not a Cu−S CT band) compared to the previously well-characterized N₄ ligand complex, [{(TMPA)Cu^II}₂(μ-1,2-O₂^2-)]²⁺ (3) (TMPA = tris(2-pyridylmethyl)amine). Resonance Raman spectroscopy confirms the peroxo formulation {ν_(O-O) = 817 cm^-1 (^16-18O₂ Δ = 46 cm^-1) and ν_(Cu-O) = 545 cm^-1 (^16-18O₂ Δ = 26 cm^-1), in close analogy to that known for 3 {ν_(O-O) = 827 cm^-1 and ν_(Cu-O) = 561 cm^-1}. Direct evidence for thioether ligation comes from EXAFS spectroscopy {Cu K-edge; Cu−S = 2.4 Å}