Catalytic Nitrene Transfer by an FeIV-Imido Complex Generated by a Comproportionation Process

Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from Fe^II and Fe^III precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an Fe^IV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the Fe^II precursor was expected by a two-electron oxidative addition, its formation from an Fe^III precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the Fe^III precursor, an Fe^III tosyliodinane adduct was formed and decomposed into an Fe^V tosylimido species which generated the catalytically active Fe^IV tosylimide through a comproportionation process with the Fe^III precursor.     

Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Effect of the activation conditions on the catalytic properties of Pt/Al2O3 catalysts

The effect of the activation conditions of Pt/Al₂O₃ catalysts has been investigated in the hydrogenation of benzene and in the hydrogenolysis of ethane. Whatever the conditions of calcination or reduction, specific activities of all catalysts for benzene hydrogenation remain constant. On the other hand, for identical dispersities, the cacination in a wet argon flow increases the specific activity of platinum for hydrogenolysis of ethane, pointing out the role of wet pretreatment on defect building or on the faceting of supported metallic catalysts.

---

Pt/Al₂O₃ . , . , , . .

     

Catalytic wet air oxidation of oleic acid on ceria-supported platinum catalyst.effect of pH

Summary Catalytic wet air oxidation (CWAO) of oleic acid was carried out in a batch reactor on platinum supported ceria catalyst (Pt/CeO₂). Oleic acid is a water insoluble linear unsaturated fatty acid of 18 carbon atoms. To increase the homogeneity of the solution by saponification, the influence of NaOH additions in oleic acid CWAO mechanism and catalyst performances have been investigated. The oxidation of such molecule occurs by two types of mechanisms: successive carboxy-decarboxylation which leads essentially to CO₂and/or C-C bonds splitting in the alkyl chain inducing a high formation of acetic acid. With or without NaOH, the 5%Pt/CeO₂catalyst is active in the conversion of oleic acid and selective to carbon dioxide. In alkaline medium, oleic acid is initially saponified which increases the solubility of the reactant before it to be oxidized. Finally the oxidation is slightly delayed by the presence of NaOH. The catalyst characterizations show no significant difference before and after reaction.</o:p>     

Fully automated high-performance liquid chromatographic assay for the analysis of free catecholamines in urine

A totally automated and reliable high-performance liquid chromatographic method is described for the routine determination of free catecholamines (norepinephrine, epinephrine and dopamine) in urine. The catecholamines were isolated from urine samples using small alumina columns. A standard automated method for pH adjustment of urine before the extraction step has been developed. The extraction was performed on an ASPEC (Automatic Sample Preparation with Extraction Columns, Gilson). The eluate was collected in a separate tube and then automatically injected into the chromatographic column. The catecholamines were separated by reversed-phase ion-pair liquid chromatography and quantified by fluorescence detection. No manual intervention was required during the extraction and separation procedure. One sample may be run every 15 min, ca. 96 samples in 24 h. Analytical recoveries for all three catecholamines are 63-87%, and the detection limits are 0.01, 0.01, and 0.03 microM for norepinephrine, epinephrine and dopamine, respectively, which is highly satisfactory for urine. Day-to-day coefficients of variation were less than 10%.     

Calcul de constantes de couplage nucléaires spin-spin par la méthode des orbitales moléculaires à l'aide de fonctions d'onde non-empiriques

Résumé Un calcul complet de constantes de couplage nucléaires J _HH, J _XH et J _XX (X = C, N, P) a été fait pour une série de molécules organiques dont les fonctions LCAO SCF MO exactes sont connues. L'influence de la charge nucléaire efficace des orbitales atomiques de base a été étudiée dans le cas particulier du méthane et de l'éthane. La décomposition des constantes de couplage en éléments de symétrie est employée pour la comparaison des résultats théoriques et expérimentaux.

---

Numerical calculations of spin-spin coupling constants with exact LCAO SCF MO functions

Complete calculations of nuclear spin-spin coupling constants J _HH, J _XH and J _XX (X = C, N, P) have been carried out for some organic molecules the exact LCAO SCF MO functions of which are known. The results obtained using atomic basis sets with different orbital exponents are discussed in the case of methane and ethane. Theoretical values are compared to experimental data in terms of components arising from the symmetry analysis of actual coupling constants.

---

Zusammenfassung VollstÄndige Berechnungen der Spin-Spin-Kopplungskonstanten J _HH, J _XH und J _XX (X = C, N, P) werden für einige organische Moleküle durchgeführt, deren genaue LCAO-SCF-MO-Funktionen bekannt sind. Der Einflu\ der effektiven Kernladungszahlen der Basisfunktionen wurde im Falle von Methan und Äthan untersucht. Die theoretischen und experimentellen Werte werden nach ihrer Zerlegung in Symmetriekomponenten miteinander verglichen.