Elektronenstruktur,Spektren und Magnetismus von Chinon-π-Komplexen des Nickels

Zusammenfassung Die Elektronenstrukturen von Bis-durochinon-nickel(0) und der Komplexe vom Typ Olefin-Ni(0)-Chinon werden im Rahmen der LCAO-MO-Näherung diskutiert und zur Deutung der Absorptionsspektren herangezogen. Den im freien Durochmon auftretenden Übergängen lassen sich in den Komplexspektren jeweils nur wenig verschobene Banden zuordnen. Darüber hinaus wird eine intensive Charge-Transfer-Bande beobachtet, die einem Übergang vom höchsten besetzten Nickelzustand zum tiefsten unbesetzten Chinon-Orbital entspricht. Aus der Intensität der Bande, die im freien Chinon dem b _3g 2b ₂ g-Übergang zugeordnet wird, ergibt sich für das gelöste Bis-durochinon-nickel(0)-Molekül die Symmetrie D _2h . Während die Komplexe mit Durochinon in Übereinstimmung mit der Theorie diamagnetisch sind, weisen die analogen Verbindungen der Dimethylchinone magnetische Momente von 1,52 bzw. 2,75 B. M. auf, woraus auf eine Mitbeteiligung polarer Strukturen am Grundzustand dieser Komplexe geschlossen wird.

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The electronic structures of bis-duroquinone-nickel(0) and complexes of the type olefine-Ni(0)-quinone are discussed in the MO-LCAO approximation and used for an interpretation of the absorption spectra. The transitions of the free duroquinone can be correlated with transitions of the complexes at nearly the same wavelengths. In addition, an intense charge transfer band is observed which corresponds to a transition from the highest occupied nickel orbital to the lowest unoccupied quinone orbital. From the intensity of the band which corresponds to b _3g 2b_2g in the free quinone, the symmetry D _2h for the dissolved bis-duroquinone-nickel(0) molecule is deduced. Whereas the duroquinone complexes are diamagnetic in agreement with theory, analogous compounds of the diméthylquinones exhibit magnetic momenta of 1.52 and 2.75 B. M. suggesting the participation of polar structures in the ground state of these complexes.

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Résumé Les structures électroniques du bis-duroquinone-nickel(0) et des complexes du type oléfine-Ni(0)-quinone sont discutées dans le cadre del'approximationMO-LCAO et utilisées pour l'interprétation des spectres d'absorption. Aux transitions de la duroquinone libre peuvent être attribuées des bandes peu déplacées dans les spectres des complexes. En outre on observe une bande intense correspondant à une transition de la plus haute orbitale occupée du nickel à la plus basse orbitale libre de la quinone. L'intensité de la bande nommée b _3g 2b _2g dans la quinone libre indique la symétrie D _2h pour la molécule dissoute du bis-duroquinone-nickel(0). Tandis que les complexes de la duroquinone sont diamagnétiques en accord avec la théorie, des composés analogues des diméthylquinones présentent des moments magnétiques de 1,52 et de 2,75 B. M. d'où l'on infère la participation de structures polaires à l'état fondamental de ces complexes.

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6. Mitteilung über Komplexe vom Typ des Bis-durochinon-nickel(0). 5. Mitt. vgl. [11].     

Nachweis von Farbstoffen auf alten Textilien

A simple method of identifying the more important natural dyes that have found widespread use for dyeing textiles is described. This involves thin-layer chromatographic comparison on Mikropolyamid F 1700 (Schl. & Sch.). The reliability of dye recognition is increased by combining various methods of identification on the chromatogram by employing the following procedure: (1) The normal coloration, (2) the fluorescent colour in UV light, (3) the change in shade with ammoniacal steam, and (4) the colour reaction with aluminium salts or, where hydroxyflavones have already been identified by reaction (3), with iron(III) chloride. In addition, various specific reactions for identifying individual natural colours are given. Furthermore, methods are indicated whereby identification can be effected by comparing infra-red spectra after a simple preparation of the sample.     

Basische metalle : XXXVII. Zur reaktivität der ethylen(hydrido)rhodium-komplexe [C5H5RhH(C2H4)PR3]X gegenüber nucleophilen: insertion versus substitution

The complex [C₅H₅RhH(C₂H₄)PMe₃]BF₄ (I) reacts with NaF and NaCN by deprotonation to give C₅H₅Rh(PMe₃)C₂H₄ but with NaCl, NaBr and NaI the ethylrhodium compounds C₅H₅RhC₂H₅(PMe₃)X (II–IV) are obtained. The reactions of I with CO and PPrⁱ₃ yield the BF₄ salts of the cations [C₅H₅RhH(CO)PMe₃]⁺ and [C₅H₅RhH(PPrⁱ₃)PMe₃]⁺ (V, VI), respectively, from which the uncharged complexes C₅H₅Rh(CO)PMe₃ (VII) and C₅H₅Rh(PPRⁱ₃)PMe₃ (VIII) are prepared. The carbonyl compound VII is also accessible either from C₅H₅Rh(CO)₂ and PMe₃ or from C₅H₅Rh(PMe₃)₂ and CO. The reaction of I with ethylene leads to the BF₄ salt of the cation [C₅H₅RhC₂H₅(PMe₃)C₂H₄]⁺ (X) which on treatment with PMe₃ forms the complex [C₅H₅RhC₂H₅(PMe₃)C₂H₄PMe₃]BF₄ (XI). The compound [C₅H₅RhH(C₂H₄)PPrⁱ₃]BF₄ (XII) reacts with NaI by insertion to yield C₅H₅RhC₂H₅(PPrⁱ₃)I (XIII) whereas with PPrⁱ₃ the salt [C₅H₅RhH(PPrⁱ₃)₂]BF₄ (XIV) is produced. The bis(triisopropylphosphine) complex C₅H₅Rh(PPrⁱ₃)₂ (XVI) is obtained from XIV and NaH.     

Definitive Proof for the Operation of Isotopically Sensitive Branching (‘Metabolic Switching’) in FeI-Mediated C?H Bond Activation in the Gas Phase Short Communication

Rigorous regio- and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of ‘isotopically sensitive branching’ in Fe^I-mediated C? H bond activation. For the hexane-1,6-diol/Fe⁺-complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D ,L - and meso-[3,4-D₂]-isotompomers 1e and 1f demonstrates that dehydrogenation proceedes via two competing pathways (i.e. ‘anti’- vs. ‘syn’-route). The contribution of these routes to the product formation is – due to a kinetic isotope effect – controlled by the relative configuration at the labeled positions C(3)/C(4). For the D ,L -form 1e , we estimate a ratio of 49:1 in favor of the ‘anti’-route; due to an isotope effect, this ratio drops to 4.3:1 for the meso-form 1f .     

Preparation of lipids from plant and animal tissues: Pure compounds and reference mixtures

Summary The systematic analysis of complex lipid mixtures is based on the consecutive application of complementary principles of chromatography. Pure compounds, synthetic standard mixtures, and biological lipid extracts are required as reference materials. Procedures for the preparation of individual compounds and standard mixtures are outlined, and recommendations are offered regarding the choice of biological reference materials and their certification.

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Gewinnung von Lipiden aus pflanzlichen und tierischen Geweben: reine Verbindungen und Referenzgemische

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In this article, lipids have been named according to the Recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature (see Eur J Biochem (1977) 79:11–21)     

Synthesen von Xyluron- und Riburonsäurederivaten

Zusammenfassung Durch acylierende Dehydratisierung von 1,2-Isopropyliden-d-xylo-und-d-ribo-pentodialdo-furanoseoxim bzw. aus Furanuronsäureestern und-amiden werden über eine Reihe von Zwischenstufen verschiedene 3-O-Acyl-pentofuranuronsäurenitrile synthetisiert und deren Reaktionen untersucht.

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Synthesis of xyluronic and riburonic acid derivatives

Various 3-O-acyl-pentofuranurononitrils were synthesized by acylating dehydration of 1,2-isopropylidene-d-xylo- andd-ribo-pentodialdo-furanose oximes, or pentofuranuronic acids via intermediates. Their reactions were investigated.

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Mit 1 Abbildung

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Aus den DissertationenH. W. Oberwalder (1970) undE. Wildschek (1967), Technische Hochschule in Graz.     

Amperometric determination of hydrogen peroxide with a manganese dioxide film-modified screen printed carbon electrode

A carbon thick film electrode modified with an MnO₂-film is investigated as an amperometric detector for hydrogen peroxide in flow-injection analysis (FIA). At an operating potential of +0.48 V vs. Ag/AgCl catalytic oxidation of the analyte is exploited for amperometric monitoring. Experimental parameters, such as pH of the carrier, working potential, flow rate and injection volume, are optimized. The amperometric signals are linearly proportional to the concentration of H₂O₂ in the range from 0.005 to 10 mg/L, showing a detection limit (3σ) of 2.3 μg/L. The method is applied to the determination of H₂O₂ in rain water and to a simple assay to quantify glucose in human plasma.     

Tetragonal low-temperature structure of LiAl

The cubic face-centered structure of LiAl (, at ) transforms into a tetragonal body-centered structure (I4₁/amd, , at ). This first-order phase transition at about during heating is probably the reason for the so-called “ anomalies” in some physical properties like specific heat, electrical resistivity and nuclear-spin lattice relaxation. This transition seems to be correlated with the composition Li:Al of the alloy and the amount of Li vacancies.     

exo/endo-Selectivity in the Reaction of ‘Bare’ FeO+ with Bicyclo[2.2.1]heptane (Norbornane)

‘Bare’ FeO⁺ reacts in the gas phase with norbornane with collision efficiency, and the most prominent cationic products correspond to [FeC₅H₆]⁺ (32%), [FeC₇H₈]⁺ (19%), [FeC₃H₆O]⁺ (19%) and [FeC₆H₆]⁺ (14%), which are structurally characterized by ligand exchange as well as collision-induced dissociation experiments. Circumstantial evidence is provided which indicates that the complexes [FeC₅H₆]⁺, [FeC₇H₈]⁺, and [FeC₆H₆]⁺ originate from an Fe(norbornene)⁺ intermediate which itself is formed by elimination of H₂O from the [FeO(norbornane)]⁺ encounter complex. Although the reactions are preceded and/or accompanied by partial H/D exchange, the isotope distribution in the productions clearly points to a preferential endo-attack of bare FeO⁺, with an endo/exo-ratio of ca. 10.3 and kinetic isotope effects k_H/k_D for the endo-abstraction of 2.4 and of 7.7 for approaching an exo-C? H bond. The preferred endo-approach of bicyclo[2.2.1]heptane by ‘bare’ FeO⁺ is in distinct contrast to the P-450-mediated or the iron(III)porphyrin-catalyzed hydroxylation of this substrate which favor reactions at the exo-face.