Thioether Sulfur Oxygenation from O2 or H2O2 Reactivity of Copper Complexes with Tridentate N2St hioether Ligands

• Published in: Inorganic chemistry 2006-12, Vol.45 (25), p.10098-10107
• Main Authors: Lee, Yunho, Lee, Dong-Heon, Narducci Sarjeant, Amy A, Zakharov, Lev N, Rheingold, Arnold L, Karlin, Kenneth D
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic060730t

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.