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Lee DH, Hatcher LQ, Vance MA, Sarangi R, Milligan AE, Sarjeant AA, Incarvito CD, Rheingold AL, Hodgson KO, Hedman B, Solomon EI, Karlin KD: Copper (I) complex O (2)-reactivity with a N (3) S thioether ligand: a copper-dioxygen adduct including sulfur ligation, ligand oxygenation, and comparisons with all nitrogen ligand analogues. Inorg Chem. 2007 Jul 23;46(15):6056-68. Epub 2007 Jun 20.
In order to contribute to an understanding of the effects of thioether sulfur ligation in copper-O (2) reactivity, the tetradentate ligands L (N3S) (2-ethylthio-N,N-bis (pyridin-2-yl) methylethanamine) and L (N3S')(2-ethylthio-N,N-bis (pyridin-2-yl) ethylethanamine) have been synthesized. Corresponding copper (I) complexes, [CuI (L (N3S))] ClO (4) (1-ClO (4)), [CuI (L (N3S))] B (C (6) F (5))(4) (1-B (C (6) F (5))(4)), and [CuI (L (N3S'))] ClO (4) (2), were generated, and their redox properties, CO binding, and O (2)-reactivity were compared to the situation with analogous compounds having all nitrogen donor ligands, [CuI (TMPA)(MeCN)](+) and [Cu (I)(PMAP)](+) (TMPA = tris (2-pyridylmethyl) amine; PMAP = bis [2-(2-pyridyl) ethyl]-(2-pyridyl) methylamine). X-ray structures of 1-B (C (6) F (5))(4), a dimer, and copper (II) complex [Cu (II)(L (N3S))(MeOH)](ClO (4))(2) (3) were obtained; the latter possesses axial thioether coordination. At low temperature in CH (2) Cl (2), acetone, or 2-methyltetrahydrofuran (MeTHF), 1 reacts with O (2) and generates an adduct formulated as an end-on peroxodicopper (II) complex [{Cu (II)(L (N3S))}(2)(mu-1,2-O (2)(2-))](2+) (4)){lambda (max) = 530 (epsilon approximately 9200 M (-1) cm (-1)) and 605 nm (epsilon approximately 11,800 M (-1) cm (-1))}; the number and relative intensity of LMCT UV-vis bands vary from those for [{Cu (II)(TMPA)}(2)(O (2)(2-))](2+) {lambda (max) = 524 nm (epsilon = 11,300 M (-1) cm (-1)) and 615 nm (epsilon = 5800 M (-1) cm (-1))} and are ascribed to electronic structure variation due to coordination geometry changes with the L (N3S) ligand. Resonance Raman spectroscopy confirms the end-on peroxo-formulation {nu (O-O) = 817 cm (-1) (16-18O (2) Delta = 46 cm (-1)) and nu (Cu-O) = 545 cm (-1) (16-18O (2) Delta = 26 cm (-1)); these values are lower in energy than those for [{Cu (II)(TMPA)}(2)(O (2)(2-))](2+) {nu (Cu-O) = 561 cm (-1) and nu (O-O) = 827 cm (-1)} and can be attributed to less electron density donation from the peroxide pi* orbitals to the Cu (II) ion. Complex 4 is the first copper-dioxygen adduct with thioether ligation; direct evidence comes from EXAFS spectroscopy {Cu K-edge; Cu-S = 2.4 Angstrom}. Following a [Cu (I)(L (N3S))](+)/O (2) reaction and warming, the L (N3S) thioether ligand is oxidized to the sulfoxide in a reaction modeling copper monooxygenase activity. By contrast, 2 is unreactive toward dioxygen probably due to its significantly increased Cu (II)/Cu (I) redox potential, an effect of ligand chelate ring size (in comparison to 1). Discussion of the relevance of the chemistry to copper enzyme O (2)-activation, and situations of biological stress involving methionine oxidation, is provided. |
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