Thioether Sulfur Oxygenation from O<sub>2</sub> or H<sub>2</sub>O<sub>2</sub> Reactivity of Copper Complexes with Tridentate N<sub>2</sub>S<sub>t</sub><sub>hioether</sub> Ligands
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To model thioether−copper coordination chemistry including oxidative reactivity, such as occurs in the copper monooxygenases peptidylglycine α-hydroxylating monooxygenase (PHM) and dopamine β-hydroxylase (DβH), we have synthesized new tridentate N2S ligands LSEP and LSBz [LSEP = methyl(2-phenethylsulfanylpropyl)(2-pyridin-2-ylethyl)amine; LSBz = (2-benzylsulfanylpropyl)methyl(2-pyridin-2-ylethyl)amine)]. Both copper(I) and copper(II) complexes have been prepared, and their respective O2 and H2O2 chemistry has been studied. Under mild conditions, oxygenation of [(LSEP)CuI]+ (1a) and [(LSBz)CuI]+ (2a) leads to ligand sulfoxidation, thus exhibiting copper monooxygenase activity. A copper(II) complex of this sulfoxide ligand product, [(LSOEP)CuII(CH3OH)(OClO3)2], has been structurally characterized, demonstrating Cu−Osulfoxide ligation. The X-ray structure of [(LSEP)CuII(H2O)(OClO3)]+ (1b) and its solution UV−visible spectral properties [S−CuII LMCT band at 365 nm (MeCN solvent); ε = 4285 M-1 cm-1] indicate the thioether sulfur atom is bound to the cupric ion in both the solid (CuII−S distance: 2.31 Å) and solution states. Reaction of 1b with H2O2 leads to sulfonation via the sulfoxide; excess hydrogen peroxide gives mostly sulfone product. These results may provide some insight into recent reports concerning protein methionine oxidation, showing the potential importance of copper-mediated oxidation processes in certain biological settings.
