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Characterization of Imidazolate-Bridged Dinuclear and Mononuclear Hydroperoxo Complexes

2001; American Chemical Society; Volume: 40; Issue: 13 Linguagem: Inglês

10.1021/ic001036v

1520-510X

Hideki Ohtsu, Shinobu Itoh, Shigenori Nagatomo, Teizo Kitagawa, Seiji Ogo, Yoshihito Watanabe, Shunichi Fukuzumi,

Magnetism in coordination complexes

Dinucleating ligands having two metal-binding sites bridged by an imidazolate moiety, Hbdpi, HMe2bdpi, and HMe4bdpi (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole, HMe2bdpi = 4,5-bis((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)aminomethyl)imidazole, HMe4bdpi = 4,5-bis(di(6-methyl-2-pyridylmethyl)aminomethyl)imidazole), have been designed and synthesized as model ligands for copper−zinc superoxide dismutase (Cu,Zn−SOD). The corresponding mononucleating ligands, MeIm(Py)2, MeIm(Me)1, and MeIm(Me)2 (MeIm(Py)2 = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)1 = (1-methyl-4-imidazolylmethyl)(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine, MeIm(Me)2 = (1-methyl-4-imidazolyl-methyl)bis(6-methyl-2-pyridylmethyl)amine), have also been synthesized for comparison. The imidazolate-bridged Cu(II)−Cu(II) homodinuclear complexes represented as [Cu2(bdpi)(CH3CN)2](ClO4)3·CH3CN·3H2O (1), [Cu2(Me2bdpi)(CH3CN)2](ClO4)3 (2), [Cu2(Me4bdpi)(H2O)2](ClO4)3·4H2O (3), a Cu(II)−Zn(II) heterodinuclear complex of the type of [CuZn(bdpi)(CH3CN)2](ClO4)3·2CH3CN (4), Cu(II) mononuclear complexes of [Cu(MeIm(Py)2)(CH3CN)](ClO4)2·CH3CN (5), [Cu(MeIm(Me)1)(CH3CN)](ClO4)2 (6), and [Cu(MeIm(Me)2)(CH3CN)](ClO4)2 (7) have been synthesized and the structures of complexes 5−7 determined by X-ray crystallography. The complexes 1−7 have a pentacoordinate structure at each metal ion with the imidazolate or 1-methylimidazole nitrogen, two pyridine nitrogens, the tertiary amine nitrogen, and a solvent (CH3CN or H2O) which can be readily replaced by a substrate. The reactions between complexes 1−7 and hydrogen peroxide (H2O2) in the presence of a base at −80 °C yield green solutions which exhibit intense bands at 360−380 nm, consistent with the generation of hydroperoxo Cu(II) species in all cases. The resonance Raman spectra of all hydroperoxo intermediates at −80 °C exhibit a strong resonance-enhanced Raman band at 834−851 cm-1, which shifts to 788−803 cm-1 (Δν = 46 cm-1) when 18O-labeled H2O2 was used, which are assigned to the O−O stretching frequency of a hydroperoxo ion. The resonance Raman spectra of hydroperoxo adducts of complexes 2 and 6 show two Raman bands at 848 (802) and 834 (788), 851 (805), and 835 (789) cm-1 (in the case of H218O2, Δν = 46 cm-1), respectively. The ESR spectra of all hydroperoxo complexes are quite close to those of the parent Cu(II) complexes except 6. The spectrum of 6 exhibits a mixture signal of trigonal-bipyramid and square-pyramid which is consistent with the results of resonance Raman spectrum.