Masahito Kodera

An Iron(III)–Monoamidate Complex Catalyst for Selective Hydroxylation of Alkane CH Bonds with Hydrogen Peroxide

Selective oxidation: the success of the title reaction is caused by the strong electron donation from the amidate moiety of the dpaq ligand to the iron center (dpaq=2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate). This process facilitates the O-O bond heterolysis of the intermediate Fe(III)OOH species to generate a selective oxidant without forming highly reactive hydroxyl radicals.

First example of a rigid (µ-oxo-di-µ-acetato) diiron(III) complex with 1,2-bis[2-di(2-pyridyl)methyl-6-pyridyl]ethane; its efficient catalysis for functionalization of alkanes

The µ-oxo-di-µ-acetatodiiron(III) complex [Fe2(hexpy)(O)-(OCOMe)2][ClO4]2{hexpy = 1,2-bis[2-di(2-pyridyl)-methyl-6-pyridyl]ethane} efficiently catalyses the oxygenation of cyclohexane, methylcyclohexane and adamantane in the presence of m-choloroperbenzoic acid.

Detection of enzymatically generated hydrogen peroxide by metal-based fluorescent probe.

We developed a metal-based fluorescent probe for H(2)O(2) called MBFh1, which has an iron complex as a reaction site for H(2)O(2) and a 3,7-dihydroxyphenoxazine derivative as the fluorescent reporter unit. The iron complex reacts quickly with H(2)O(2) to form oxidants, and then the oxidants convert the closely appended nonfluorescent 3,7-dihydroxyphenoxazine moiety to resorufin in an intramolecular fashion. The quick response to H(2)O(2) allows us to plot the enzymatic evolution of H(2)O(2). A combination of N-acetyl-3,7-dihydroxyphenoxazine and horseradish peroxidase has been frequently used to detect enzymatically generated H(2)O(2), but this method has interference with phenol derivatives. The use of MBFh1 overcomes this drawback.

Reversible O–O Bond Scission of Peroxodiiron(III) to High-Spin Oxodiiron(IV) in Dioxygen Activation of a Diiron Center with a Bis-tpa Dinucleating Ligand as a Soluble Methane Monooxygenase Model

The conversion of peroxodiiron(III) to high-spin S = 2 oxodiiron(IV) via reversible O-O bond scission in a diiron complex with a bis-tpa dinucleating ligand, 6-hpa, has been characterized by elemental analysis; kinetic measurements for alkene epoxidation; cold-spray ionization mass spectrometry; and electronic absorption, Mössbauer, and resonance Raman spectroscopy to gain insight into the O(2) activation mechanism of soluble methane monooxygenases. This is the first synthetic example of a high-spin S = 2 oxodiiron(IV) species that oxidizes alkenes to epoxides efficiently. The bistability of the peroxodiiron(III) and high-spin S = 2 oxodiiron(IV) moieties is the key feature for the reversible O-O bond scission.

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.

Spectroscopic and computational studies of (μ-Oxo)(μ-1, 2-peroxo)diiron(III) complexes of relevance to nonheme diiron oxygenase intermediates

With the goal of gaining insight into the structures of peroxo intermediates observed for oxygen-activating nonheme diiron enzymes, a series of metastable synthetic diiron(III)-peroxo complexes with [Fe(III)(2)(mu-O)(mu-1,2-O(2))] cores has been characterized by X-ray absorption and resonance Raman spectroscopies, EXAFS analysis shows that this basic core structure gives rise to an Fe-Fe distance of approximately 3.15 A; the distance is decreased by 0.1 A upon introduction of an additional carboxylate bridge. In corresponding resonance Raman studies, vibrations arising from both the Fe-O-Fe and the Fe-O-O-Fe units can be observed. Importantly a linear correlation can be discerned between the nu(O-O) frequency of a complex and its Fe-Fe distance among the subset of complexes with [Fe(III)(2)(mu-OR)(mu-1,2-O(2))] cores (R = H, alkyl, aryl, or no substituent). These experimental studies are complemented by a normal coordinate analysis and DFT calculations.

Mechanisms for (porphyrinato)iron(III)-catalyzed oxygenation of styrenes by O2 in presence of BH−4

Abstract Mechanisms have been proposed for the (porphyrinato)iron(III)-catalyzed oxidation of styrene and α-methylstyrene by O2 in benzene-ethanol containing NaBH4. The product analysis and the deuterium incorporation using NaBD4 suggest that the (σ-alkyl)FeIIIPor complex, [C6H5CH(CH3)]FeIIIPor, is formed as an intermediate in the reaction of styrene. Insertion of O2 to the (σ-alkyl)FeIIIPor complex having a radical character yields a (peroxy)iron(III) complex, [C6H5CH(CH3)OO]FeIIIPor. The homolytic fission of the OO bond followed by the hydrogen abstraction within the radical pair affords acetophenone and (HO)FeIIIPor. Acetophenone is readily reduced with NaBH4 to give l-phenylethanol. Meanwhile, the reaction of α-methylstyrene with BH−4 in the presence of PorFeIIICl may also yield the (σ-alkyl)FeIIIPor complex, which takes up O2 to form a (peroxy)iron(III) complex, (C6H5C(CH3)2OO)FeIIIPor. The (peroxy)iron(III) complex is directly reduced by BH−4 to give 2-phenyl-2-propanol and (HO)FeIIIPor. In the reaction of styrene, such direct reduction of the (peroxy)iron(III) complex as a minor pathway competes with the homolytic fission of its OO bond.

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].

Electronic Tuning of Iron–Oxo-Mediated CH Activation: Effect of Electron-Donating Ligand on Selectivity

We have reported previously that an iron(III) complex supported by an anionic pentadentate monoamido ligand, dpaq(H) (dpaq(H) =2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamido), promotes selective CH hydroxylation with H2 O2 with high regioselectivity. Herein, we report on the preparation of Fe(III) -dpaq derivatives that have a series of substituent groups at the 5-position of a quinoline moiety in the parent ligand dpaq(H) (dpaq(R) , R: OMe, H, Cl, and NO2 ), and examine them with respect to their catalytic activity in CH hydroxylation with H2 O2 . As the substituent group becomes more electron-withdrawing, both the selectivity and the turnover number increase, but the selectivity of epoxidation shows the opposite trend.

Synthesis, structure, and magnetic properties of di-μ-pyrazolatodicopper(II) complexes of 3,5-bis(aminomethyl)pyrazole

Abstract 3,5-Bis(aminomethyl)pyrazole (Hbampz) forms binuclear copper(II) complexes of the formula [Cu2(bampz)2X2] (X = CI, Br). The crystal structure of [Cu2(bampz)2Br2] has been determined by the X-ray method: formula = CuBrN4C5H9, monoclinic, space group P21/n, a = 9.214(1), b = 10.078(1), c = 8.775(1) A, β = 97.33(1)°, V = 808.1 A3. Two bampz− molecules combine with two copper(II) ions via the pyrazolate nitrogen and aminonitrogen atoms in the side chains affording an essentially planar N4 environment for each metal ion. The Cu-Cu separation is 3.947(5)A. The axial site of each copper is weakly coordinated by a bromide ion with a Cu-Br distance of 2.895(4) A. Cryomagnetic investigations over the temperature range 80-300 K revealed a significant antiferromagnetic interaction through the pyrazolate bridges. The exchange integrals (J) based on the Heisenberg model (H =—2JŜ1.Ŝ2) was estimated at—200.8 and—192.0 cm−1 for [Cu2(bampz)2Cl2] and [Cu2(bampz)2Br2], respectively.