Showing papers by "Jean-Jacques Girerd published in 2001"

The electronic structure of non-heme iron(III)-hydroperoxo and iron(III)-peroxo model complexes studied by Mössbauer and electron paramagnetic resonance spectroscopies.

Abstract: Ferric peroxo complexes are currently extensively studied due to their proposed occurrence as reactive intermediates in the catalytic oxygenation reactions of enzymes. An electronic structure investigation is presented for the synthetic mononuclear nonheme Fe(III)−hydroperoxo complex and the related Fe(III)−peroxo compound which is based on complementary EPR and applied-field Mossbauer spectroscopy. The data provide detailed insight into the properties of the iron(III) site in the low-spin Fe−OOH compound and the high-spin Fe−OO complex.

Biomimetic Catalysis of Catechol Cleavage by O2 in Organic Solvents − Role of Accessibility of O2 to FeIII in 2,11‐Diaza[3,3](2,6)pyridinophane‐Type Catalysts

Abstract: Three new complexes, [Fe(LN4H2)Cl2]+, [Fe(LN4H2)(Cat)]+, and [Fe(LN4H2)(DBC)]+, were synthesized by using the tetradentate macrocyclic ligand LN4H2 (where LN4H2, Cat, and DBC stand for 2,11-diaza[3,3](2,6) pyridinophane, catecholate, and 3,5-di-tert-butylcatecholate, respectively). The structure of [Fe(LN4H2)Cl2]+ was determined by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with a = 9.613(1), b = 11.589(1), c = 14.063(2) A, β=110.20(2)°, V = 1541.9(3) A3, and Z = 4. These complexes were found to catalyze the oxidation of catechol groups using O2. This was performed in various organic solvents at 20 °C. The reaction rates were measured for the stoichiometric complexes [Fe(LN4H2)(Cat)]+ and [Fe(LN4H2)(DBC)]+. It was found that despite the relatively high energy of the ligand-to-metal charge transfer O(DBC or Cat)FeIII, their activity was comparable to that of the fast TPA systems [TPA indicates tris(2-pyridylmethyl)amine]. The oxidation products of DBCH2 have been studied. It has then been shown that the LN4H2 systems catalyse by means of both intra- and extradiol cleavage of catechol groups. The existence of multiple reactive pathways can account for the fast reactivity observed.

Synthesis, Structure and Characterization of the New Complex [L1(H2O)Fe(μ‐O)Fe(OH2)L1]4+ [L1 = N,N′‐Bis(1‐methylimidazolyl‐2‐methyl)‐N,N′‐Bismethyl‐1,2‐ethanediamine] − Formation of the (μ‐O)(μ‐H3O2) Complex upon Deprotonation

Abstract: The compound [L1(H2O)Fe(μ-O)Fe(OH2)L1](ClO4)4·2H2O [1(ClO4)4·2H2O] [L1 = N,N′-bis(1-methylimidazolyl-2-methyl)-N,N′-bismethyl-1,2-ethanediamine] was synthesized. It is characterized by a linear Fe−(μ-O)−Fe motif with an Fe···Fe distance of 3.584(1) A. The measurement of the magnetic susceptibility as a function of temperature indicated a strong antiferromagnetic coupling between the two high-spin FeIII ions (J = −223 cm−1 with H = −J·S1·S2). In the solid state, the symmetric stretching vibration mode of the Fe−(μ-O)−Fe core unit was detected at 347 cm−1, in agreement with a straight Fe−(μ-O)−Fe angle. Upon addition of up to one equivalent of triethylamine to an acetonitrile solution of 1, conversion to the [L1(H2O)Fe(μ-O)Fe(OH)L1]3+ complex 2 was observed. This last species was isolated as a perchlorate salt [2(ClO4)3·H2O]. Susceptibility measurements and Raman and UV/Vis investigations on the powder and/or an acetonitrile solution confirmed the presence of an intramolecular hydrogen bond between the coordinated water molecule and the hydroxide group leading to a bent [Fe(μ-O)Fe]4+ core structure.

Biomimetic approach to the oxygen evolving center: resonance Raman investigation of a manganese µ-oxo dimer in three oxidation states

Abstract: A biologically relevant dinuclear manganese mono-µ-oxo complex with a bound phenolate ligand in three oxidation states, (III,III), (III,IV) and (IV,IV), was studied using resonance Raman spectroscopy. Depending upon the excitation frequency, phenolate vibrations or µ-oxo vibrations were enhanced, which allowed us to assign the UV-visible absorption spectra. In the case of the mixed valence species (III,IV), the µ-oxo vibration at 854 cm–1 has been assigned by isotopic substitution (H218O) to νas(Mn-O-Mn). This preferential enhancement of the asymmetric vibration stresses the asymmetric character of the bridge.