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, LN3S, dioxygen reactivity of a copper(I) complex, (LN3S)CuI]+ (1) was examined. In CH2Cl2, acetone (at -80 degrees C), or 2-methyltetrahydrofuran (at -128 degrees C), 1 reacts with O2 producing the end-on bound peroxodicopper(II) complex {(LN3S)CuII}2(mu-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)CuII}2(mu-1,2-O2(2-))]2+ (3) (TMPA = tris(2-pyridylmethyl)amine). Resonance Raman spectroscopy confirms the peroxo formulation {nu(O-O) = 817 cm-1 (16-18O2 Delta = 46 cm-1) and nu(Cu-O) = 545 cm-1 (16-18O2 Delta = 26 cm-1), in close analogy to that known for 3 {nu(O-O) = 827 cm-1 and nu(Cu-O) = 561 cm-1}. Direct evidence for thioether ligation comes from EXAFS spectroscopy {Cu K-edge; Cu-S = 2.4 A}.