Hiroshi Sakiyama

A functional model of manganese catalase. Mass spectrometric and visible spectral evidence for {MnIV(O)}2 and MnIIMnIV(O) intermediates

A dinuclear manganese(II) complex [Mn2(L)(PhCO2)2(NCS)][L = 2,6-bis{N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenolate(1–)] decomposes H2O2 catalytically indimethylformamidesolution; two oxomanganese(IV) species {MnIV(O)}2 and MnIIMnIV(O) are detected for the first time as intermediates in the H2O2 disproportionation reaction based on mass spectrometric and visible spectral studies.

Dimanganese(II) complexes of a new phenol-based dinucleating ligand with two amino chelating arms: synthesis, structure and catalase-like activity

A new phenol-based dinucleating ligand with two amino chelating arms, 2,6-bis{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-methylphenolate (L–), formed dinuclear manganese(II) complexes [Mn2L(p-XC6H4CO2)2(NCS)(MeOH)](X = H 1, Cl 2, Me 3 or NO24). X-Ray analysis revealed that complex 1 crystallizes in the monoclinic space group P21/c, a= 12.607(3), b= 19.566(6), c= 16.743(5)A and β= 107.56(2)°. The two magnese ions are bridged by the phenolic oxygen and two benzoate groups. The NCS– ion is co-ordinated to one of the maganese ions through its nitrogen and the methonal molecule to the other, providing distorted-octahedral geometries around each maganese. Magnetic susceptibility measurements over the temperature range 4.2–300 K indicated a weak antiferromagnetic interaction (J=–3 to –5 cm–1 based on Ĥ=–2JŜ1·Ŝ2). The complexes show a catalase-like activity in disproportionating H2O2 in dimethylformamide. The rate of dioxygen evolution was proportional to the concentration of H2O2 and the rate constant decreased in the order 1(X = H) > 2(Cl) > 3(Me) > 4(NO2).

A tetrahedral zinc(II) complex of N-(R)-1-phenylethylsalicylideneimine. Structural and circular dichroism spectral investigations on stereoselectivity

The stereoselectivity of bis[N-(R)-1-phenylethylsalicylideneiminato]zinc(II) has been studied by means of single-crystal X-ray analysis and circular dichroism (c.d.) spectra. The complex crystallizes in space group P212121 with a= 17.738(4), b= 29.632(9), c= 9.968(2)A, and Z= 4. The unit cell is comprised of four units each containing two complex molecules (A and B). Each molecule adopts a nearly tetrahedral structure with two bidentate ligands; the dihedral angle defined by the two chelate rings is 81.7° for molecule A and 84.9° for molecule B. The absolute configuration along the pseudo-C2 axis is Λ for both molecules. Based on the X-ray analysis it is suggested that intramolecular non-covalent interactions between the chiral N-substituent and the adjacent chelate ring give rise to stereoselectivity and the Λ configuration around the metal ion. The c.d. couplet (+and – signs) induced at the azomethine π–π* transition at around 27 000 cm–1 is discussed with respect to the absolute configuration and in comparison with the spectra of related Schiff-base complexes.

Dinuclear Mn complexes as functional models of Mn catalase

p-Phenoxo-bis(p-carboxy1ato)dimanganese complexes with a core structure of Cs symmetry show a high catalytic activity to disproportionate H202 (2H202 + 2H20 + 02), whereas complexes with a core structure of C2 symmetry and mononuclear Mn complexes show only a low activity. For the Cs symmetric complexes, a dinuclear cis-{ MnIV(=O))2 intermediate has been detected in the H202 disproportionation reaction and a mechanistic scheme to catalyze the H202 disproportionation through the interconversion cis-{ MnIV(=O))~cis-{ MnIII(OH))2 is proposed. It is shown that the equivalence of two Mn ions in electronic nature is essential to show a CAT-like activity.

Dinuclear nickel(II) complexes of a series of dinucleating macrocycles with similar or dissimilar coordination sites: synthesis, structure and physicochemical property

Abstract The dinucleating macrocycles H 2 (L m,n ) containing two 2, 6-di(aminomethyl)-4-methylphenol entities combined through two alkane chains, -(CH 2 ) m - ( m =2, 3) and -(CH 2 ) n - ( n =2, 3, 4, 5), at the amine nitrogens, form nickel(II) complexes of the general formula [Ni 2 (L m,n )(OAc) 2 ] (( m, n )=(2,2), (2,4), (2,5), (3,3)) and [Ni 2 (L 2,3 )(OAc)(NCS)(CH 3 OH)]. [Ni 2 (L 2.2 )(OAc) 2 ]·10H 2 O crystallizes in the triclinic system of space group P 1 with a =9.983(2), b =12.832(2), c =7.932(1) A, α=101.29(1), β=101.08(2), γ=106.57(2)°, V =921.1(3) A 3 and Z =1. The refinement converges with R =5.65 and R w =5.89% based on 2308 reflections with ¦F 0 ¦ > 3σ(¦F 0 ¦). The macrocycle adopts a folded conformation and each nickel has a cis -β octahedral geometry with the N 2 O 2 donor set of the macrocycle and two oxygens of a bidentate acetate group. The Ni-Ni separation bridged by two phenolic oxygens is 3.004 A and the Ni-O-Ni angle is 95.6°. Cryomagnetic properties (4.2-300 K) of the complexes are well reproduced based on the spin Hamiltonian H =-2 JS 1 · S 2 - D ( S z1 2 - S z2 2 ) with a positive exchange integral ( J =+10.1 to +2.1 cm −1 ) and a negative zero-field splitting parameter ( D =−0.53 to −2.40 cm -1 ). Each complex shows two reduction waves and two oxidation waves attributable to the metal centers.

Template synthesis of copper(II)lead(II) complexes of new binucleating macrocycles with dissimilar co-ordination sites

New binucleating macrocycles comprised of two molecules of 2,6-diformyl-4-methylphenol, a diamine (ethylenediamine or 1,3-propanediamine), and a diaminoalcohol (1,3-diaminopropan-2-ol or 1,5-diaminopentan-3-ol) have been synthesised as copper(II)lead(II) complexes by ‘stepwise’ template reactions. The macrocycles possess two dissimilar co-ordination sites, a four-co-ordination N2O2 donor set and a five-co-ordination N2O3 set, sharing two bridging phenolic oxygens. The CuPb complex of the macrocycle with ethylenediamine and 1,3-diaminopropan-2-ol as the amine components has been structurally characterized by single-crystal X-ray analysis. The CuII is bound to the four-co-ordination site and has a planar configuration. The PbII is bound to the five-co-ordination site and assumes a seven-co-ordinate geometry with a unidentate perchlorate ion and a dimethylformamide molecule. In the macrocycles derived from 1,3-diaminopropan-2-ol the alcoholic oxygen can co-ordinate to PbII in both protonated and deprotonated forms, whereas in the macrocycles derived from 1,5-diaminopentan-3-ol the alcoholic oxygen co-ordinates to PbII in only the deprotonated form. Template synthesis of the macrocycle of 1,3-propanediamine and 1,5-diaminopentan-3-ol, using CuII and BaII as template ions, afforded a mononuclear copper(II) complex in which the five-co-ordination site of the macrocycle is occupied by a proton instead of BaII.

µ-Pyrazolato-µ-carboxylato- and di(µ-pyrazolato)dimanganese(II) complexes: synthesis, characterization and catalase-like function

3,5-Bis[N,N-di(2-pyridylmethyl)aminomethyl]pyrazole (HL1) and 3,5-bis[N,N-bis(2-diethylaminoethyl)aminomethyl]pyrazole (HL2) formed µ-pyrazolato-µ-carboxylato-dimanganese(II) complexes [Mn2L(O2CR)][BPh4]2(L = L1, R = Ph; 1; L = L2, R = Me 2) and 3,5-bis[N-(2-pyridylmethyl)aminomethyl]pyrazole (HL3) gave a di(µ-pyrazolato)-dimanganese(II) complex [Mn2L32][BPh4]23. The ditoluene adduct of 3 crystallizes in the triclinic space group P with a= 14.452(3), b= 15.573(5), c= 10.988(4)A, α= 108.78(3), β= 93.31(2) and γ= 115.10(2)°. X-Ray diffraction analysis revealed a di(µ-pyrazolato)-dimanganese(II) core with Mn ⋯ Mn separation 4.181(2)A. All the complexes showed catalytic activity towards disproportionation of H2O2 in dimethylformamide at 0 °C. The initial rate of dioxygen evolution in the presence of 1 is first order in both the complex concentration and that of H2O2; v=k[Mn2][H2O2], k= 1.45 dm3 mol–1 s–1. Together with the observation of a ligand-to-metal charge-transfer band characteristic of MnIVO in the catalysis by 2, a mechanistic scheme involving a cycle from {MnIII(OH)}2 to {MnIV(O)}2 is inferred. In the disproportionation by 3 the initial rate of evolution is first order in complex concentration and second order in that of H2O2; v=k[Mn2][H2O2]2, k= 29 dm6 mol–2 s–1).

Dinuclear manganese(II) complexes of 2,6-Bis[2-(dialkylamino)ethyliminomethyl]-4-methylphenolate(1–): synthesis, structure, and magnetism

2,6-Bis[2-(dialkylamino)ethyliminomethyl]-4-methylphenolate(1–)[alkyl = methyl (L1) or ethyl (L2)] forms two types of dinuclear manganese(II) complexes [Mn2L(RCO2)2(NCS)](L = L1 or L2, R = CH3 or C6H5) and [Mn2LCl3](L = L1 or L2). The crystal structure of [Mn2L1(CH3CO2)2(NCS)]·H2O·CH3OH has been determined: monoclinic, space group P21/n, a= 17.700(3), b= 12.516(2), c= 15.263(3)A, β= 107.16(1)° and Z= 4. The X-ray analysis reveals a dinuclear structure bridged by the phenolic oxygen of L1 and two acetate groups. The thiocyanate group co-ordinates to one Mn, resulting in different co-ordination geometries about the two manganese ions, i.e. trigonal bipyramidal and pseudo-octahedral. Magnetic susceptibility measurements over the temperature range 4.2–300 K indicate weak antiferromagnetic interaction (J=–2 to –5 cm–1) for [Mn2L(RCO2)2(NCS)] and no appreciable interaction for [Mn2LCl3].

Two typical cases of magnetism for dinuclear high-spin cobalt(II) complexes in trigonal-bipyramidal fields

Abstract Previously, an acyclic ligand 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene (baib) was found to form some dinuclear metal complexes [metal=manganese(II), cobalt(II), and zinc(II)], and crystal structures of the two cobalt(II) complexes [Co2(baib)(MeCO2)3]BPh4 (1) and [Co2(baib)(PhCO2)3]BPh4 (2) were determined. Magnetic measurement was also carried out, but the magnetic analysis was not made. In this study, the cryomagnetic data for 1 were analyzed well by using isotropic Heisenberg model with the parameters g=2.30, J=−13.3 cm−1, and Nα=70×10−6 cm−1, indicating that a ground term does not possess an orbital angular momentum. On the other hand, however, the data for 2 could be interpreted using the so-called Lines’ theory with the parameters λ=−175 cm−1, κ=0.63 and J=−1.0 cm−1, indicating that a ground term possesses an orbital angular momentum. This difference was explained by the fact that the complex cation [Co2(baib)(PhCO2)3]+ in 2 was much distorted than [Co2(baib)(MeCO2)3]+ in 1, as found by the X-ray analysis.

Different interpenetrated coordination polymers based on flexible dicarboxylate ligands: topological diversity and magnetism

Through tuning the nature of the secondary ligands, the ligand-to-metal molar ratio and the metal ions, four coordination polymers, namely {[Ni2(bcp)2(4,4′-bipy)2(H2O)4]·3.5H2O}n (1), {[Co2(bcp)2(bpt)2]·2.29H2O·bpt}n (2), [Co2(bcp)2(bib)]n (3) and {[Co(bcp)(2,2′-bipy)(H2O)]·H2O}n (4), have been synthesized and characterized. The structural feature of 1 shows a 3D three-fold parallel interpenetrating framework with CdSO4 topology. 2 exhibits a 2D→3D interpenetrating motif with pseudorotaxane. Compound 3 shows two identical 2D layers with 22·48·65 topology that are interpenetrated in a parallel fashion, resulting in a twofold interpenetrating motif containing polyrotaxane and polycatenane character. However, a 1D zipper-like double-stranded chain is observed in polymer 4. This work evidently indicates that the effect of the secondary ligands and geometric preferences of the metal centers are critical in the construction of the resulting networks. In addition, the magnetic properties of compounds 2 and 3 were also discussed.