Naoyasu Oishi

Bioinorganic approach to the type-I and type-II copper proteins. Synthesis and properties of copper(II) complexes with tripod-like ligands containing three or four door species

Abstract Copper(II) complexes with new tripod-like quadridentate ligands containing three or four donor species, such as benzimidazole, thioether and phenol, were prepared. The ESR and electronic spectral studies have revealed that these complexes are classified into three types, that is, four-coordinated, five-coordinated trigonal bipyramindal and five-coordinated tetragonal pyramidal complexes, and that some of them are good models for blue(Type-I) and non-blue(Type-II) copper proteins.

Importance of structural factor in the catalytic activity of copper(II) complexes for the oxidation of TMPD by dioxygen

Abstract Binuclear copper(II) complexes with appropriate CuCu distance (3.0 ∼ 3.5 A) exhibited high catalytic activity, except for some binuclear complexes with non-equivalent coordination sites, whereas planar mononuclear copper(II) complexes have practically no catalytic activity for the oxidation of TMPD (N,N,N′,N′-tetramethyl-p-phenylenediamine) by dioxygen. Measurements of polarographic halfwave potentials of copper(II) complexes have revealed that the catalytic activity of binuclear complexes largely depends on molecular structure as well as reduction potential. An intermediate complex formed by O2, two molecules of TMPD and a binuclear complex were proposed at which two-electron transfer proceeds easily as a ‘concerted reaction’ of the three reaction components.

Effect of substituents in the chelate ring on the electronic state of tetraazamacrocyclic complexes of cobalt(II), nickel(II) and copper(II)

Abstract The ESR and electronic spectral studies were performed for the square planar copper(II), nickel(II) and cobalt(II) complexes with Jagers N 4 -macrocyclic ligands ( cf. Fig. 1). From the results, it was shown that the introduction of the electron withdrawing group (COCH 3 , COOC 2 H 5 ) in the N 4 -macrocycles causes a significant change in the π-systems of the ligands, that is, the lowering of the energies of π-orbitals and/or the decreasing of the π-electron delocalization.

Effect of coordination structure on the redox reactions of mononuclear copper(II) complexes

Abstract Catalytic activities of mononuclear copper(II) complexes were studied for the reactions, 1) O2 oxidation of N, N, N′,N′-tetramethyl-1,4-diaminobenzene, and 2) decomposition of hydrogen peroxide. For both reactions, distorted tetrahedral complexes showed much higher reactivities than the complexes of other coordination geometries such as plane, square pyramid and trigonal bipyramid. This could not be explained in terms of the reduction potentials of the complexes only, but the governing factor for this fact was attributed to the ease of the fifth coordination of tetrahedral complexes caused by the spacial distribution of the electron hole of copper(II) ion.

Catalytic activity of copper(II) complexes with a flexible polyatomic bridging group for the oxidation of TMPD by O2

Abstract The catalytic activities of copper(II) complexes with a flexible polyatomic bridging group were investigated on the oxidation of N , N ,′ N ,′ N -tetramethyl- p -phenylenediamine by dioxygen. The general trends revealed are: 1) the longer and more flexible the bridging chain, the higher the catalytic activity, and 2), flexibility is also required for chelating groups to manifest a high catalytic activity; complexes composed of chelating groups which form stable, rigid, square-planar coordination units would not be good catalysts.

Catalytic activity of binuclear planar copper(II) complexes for the decomposition of hydrogen peroxide

Abstract Planar binuclear copper(II) complexes generally showed high catalytic activities for the decomposition of hydrogen peroxide compared with the relevant planar mononuclear copper(II) complexes. This result was explained on the assumption that the two-electron transfer occurs between H 2 O 2 molecules via an intervening binuclear copper(II) complex.

Synthesis and properties of copper(II), zinc(II), nickel(II) and cobalt(II) complexes with N,N′-diaryl-β-iminoamines

Abstract New zinc(II), copper(II), nickel(II) and cobalt(II) complexes with N,N′-diaryl-β-iminoamines were prepared, the ligands being obtained from 4-phenyl-1,2-dithiolium salt and aromatic monoamines, such as aniline, p -toluidine and p -chloroaniline. Judging from the steric consideration, the coordination geometry of the copper(II) complexes may be in between the square plane and the tetrahedron. In the absorption spectra of the copper(II) complexes, two distinct bands were observed in the ranges 6000–7000 and 13000–15000 cm −1 . These bands were assigned to the d-d and charge-transfer bands, respectively, on the basis of their intensities and in view of the results of other copper(II) complexes with distorted tetrahedral structures. The intensities of the bands of the copper(II) complexes are highly dependent on the ring substituents ( cf. Fig. 1 in the text), however the ESR parameters suffer little effect by the ring substituents. It was concluded that the effect due to the mixing of 3d and 4p orbitals is not so important as has been claimed in distorted tetrahedral copper(II) complexes.