Thioether Sulfur Oxygenation from O_2 or H_2O_2 Reactivity of Copper Complexes with Tridentate N_2S_(thioether) Ligands

摘要

To model thioether-copper coordination chemistry including oxidative reactivity,such as occurs in the copper monooxygenases peptidylglycine a-hydroxylating monooxygenase (PHM) and dopamine beta-hydroxylase (DbetaH),we have synthesized new tridentate N_2S ligands L~(SEP) and L~(SBz) [L~(SEP) = methyl(2-phenethylsulfanylpropyl)(2-pyridin-2-ylethyl)amine;L~(SBz) = (2-benzylsulfanylpropyl)methyl(2-pyridin-2-ylethyl)amine)].Both copper(l) and copper(ll) complexes have been prepared,and their respective O_2 and H_2O_2 chemistry has been studied.Under mild conditions,oxygenation of [(L~(SEP))Cu~I]~+ (1a) and [(L~(SBz))Cu~I]~+ (2a) leads to ligand sulfoxidation,thus exhibiting copper monooxygenase activity.A copper(ll) complex of this sulfoxide ligand product,[(L~(SOEP))Cu~(II)(CH_3OH)(OCIO_3)_2],has been structurally characterized,demonstrating Cu-O_(sulfoxide) ligation.The X-ray structure of [(L~(SEP))Cu~(II)(H_2O)(OCIO_3)]~+ (1b) and its solution UV-visible spectral properties [S-Cu~(II) LMCT band at 365 nm (MeCN solvent);epsilon = 4285 M~(-1) cm~(-1)] indicate the thioether sulfur atom is bound to the cupric ion in both the solid (Cu~(II)-S distance:2.31 A) and solution states.Reaction of 1b with H_2O_2 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.