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 CH ₂Cl₂, 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}