Electrochemical Reduction of Arylxenon Tetrafluoroborates

Reduction potentials of arylxenon(II) tetrafluoroborates have been measured by cyclic voltammetry method on platinum disc and ultramicro electrodes. The electrochemical properties of the arylxenon(II) tetrafluoroborates are quite different to those of corresponding arylperfluoralkyliodine(III) salts.     

BINAS - synthesis and use of a new ligand for propylene hydroformylation

BINAS is a new, very efficient ligand for propylene hydroformylation. BINAS is made by the sulfonation of NAPHOS. Different synthetic routes to NAPHOS are discussed. A new two step synthesis starting from 2,2′-bis(bromomethyl)-1,1′-binaphthyl is described.     

Ab initio and DFT calculations on the initial step in thiamin catalysis

The diphosphate ester (ThDP) of thiamin (vitamin B₁) is an important cofactor of enzymes within the carbohydrate metabolism. The initial reaction step shared by all ThDP-dependent enzymes is the deprotonation of the C2–H of the thiazolium ring. The replacement of the 4′-amino group by a hydroxyl one in the pyrimidine ring leads to the oxy-ThDP analogue which is known as an antagonist in thiamin catalysis.

Ab initio and DFT calculations on the MP2/6-31G* and B3LYP/6-31G* level were performed to study the proton relay function in thiamin and oxythiamin systems. Both MP2 and B3LYP calculations show significant differences of the reaction coordinate of the ylide formation in the systems. Tautomers, protonated and deprotonated species of both systems show different trends regarding their stability. The influence of correlation effects on the results is discussed by comparison with the HF-SCF/6-31G* data. Frequency calculations on the B3LYP/6-31G* level were performed to characterize the minima and transition state structures, respectively.     

The coordinative properties of the ligands Ph2ECH2EPh2 (E = P,As, Sb) in carbonylvanadium complexes,and the molecular structure of η5-C5H5V(CO)3As2Ph4

Photo-reaction between the ligands Ph₂ECH₂EPh₂ (E = P: dppm, E = As: dpam, E = Sb: dpsm), L, and the vanadium complexes η⁵-C₅H₅V(CO)₄ and [Et₄N][V(CO)₆] yields monosubstituted mononuclear (dpsm) and dinuclear, ligand-bridged complexes (dpam, dpsm). With dppm, the final products are disubstituted chelate complexes, but monosubstituted mono- and dinuclear species are formed as intermediates.The shielding of the ⁵¹V nucleus decreases in the series dpsm > dppm > dpam and {M(CO)_n} > {M(CO)_n?1} L > {M(CO)_n?1}₂μ-L > {M(CO)_n?2}dppm ({M(CO)_n}[V(CO)₆]^?, η⁵-C₅H₅V(CO)₄). The half-widths of the NMR signals are greater for dinuclear than for mononuclear complexes.The crystal and molecular structures of η⁵-C₅H₅V(CO)₃As₂Ph₄ have been determined. The compound crystallizes in the space group P2₁/c with a = 1347.8, b = 1020.0, c = 2085.2 pm and β = 82.3°. Due to steric crowding, the ⁵¹V shielding is low composed to that of {η⁵-C₅H₅V(CO)₃}₂μ-dpam.     

Some new fluorine exchange reactions of perfluoroalkyliodine(V)fluorides

The perfluoroalkyliodine (V) fluorides CF₃IF₄ and CF₃IOF₂ react with many alcohols, acids and anhydrids in solution to give fluorine exchange. In all these reactions we observed equilibria, e.g.:

These reactions depend strongly on the kind of the reacting compounds and on the conditions, and they can be followed by n.m.r. spectroscopy. When trying to isolate the new derivatives always decomposition takes place.These reactions, the n.m.r. spectra, the properties of the new compounds and the decomposition reactions will be reported.     

Thermoanalytical investigations on the decomposition of double salts

The melting and decomposition behaviour of carnallite was investigated in the closed system under dynamic heating conditions and in the open system under dynamic and quasi-isothermal and quasi-isobaric conditions in the temperature range between 20 and 300°. DTA heating and cooling cycles in the closed system illustrate the incongruent melting of carnallite and the occurrence of different magnesium chloride hydrate phases. The thermal decomposition under quasi-isothermal and quasi-isobaric conditions begins at a pressure of at least 100 kPa from the melt and under reduced pressure from the solid. In any case KCl · MgCl₂ · 2 H₂O is formed which is decomposed to a basic product KMgCl_2.84–2.90(OH_0.10–0.16.

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Zusammenfassung Die Schmelz- und Zersetzungseigenschaften des Carnallits wurden im geschlossenen System unter dynamischen Heizbedingungen und im offenen System under dynamischen und quasi-isothermen und quasi-isobaren Bedingungen im Temperaturbereich von 20 bis 300°C untersucht. DTA Heiz- und Kühlzyklen im geschlossenen System verdeutlichen das inkongruente Schmelzen des Carnallits und das Auftreten verschiedener Magnesiumchlorid-Hydratphasen. Die thermische Zersetzung beginnt unter quasi-isothermen und quasi-isobaren Bedingungen bei einem Druck von mindestens 100 kPa aus der Schmelze und unter verminderten Druck aus der festen Phase. Die Zersetung verläuft stets über KCl · MgCl₂ · 2 H₂O zu einem basischen Produkt KMgCl_2.84–2.90(OH)_0.10–0.16.

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— -, - V 20–300°. . - - 100 , — . KCl · l₂ · 2 ₂, Kgl_2.84–2.90()_0.10–0.16.

     

Alkynylxenon(II) fluorides

Alkynylxenon(II) fluorides, RCC(triple bond)XeF, have been prepared from the reactions of the corresponding trimethyl(alkynyl)silanes, Me3(-)SiC(triple bond)CR, and XeF2 in the presence of [NMe4F in common organic solvents at low temperature. The existence of the linear unit C(triple bond)C-Xe-F was proved for PhC(triple bond)CXeF by the 19F-13C NMR correlation method using the HMBC pulse sequence.     

The Structure of Tetrakis(pentafluorophenyl)tellurium(IV), Te(C6F5)4

Tetrakis(pentafluorophenyl)tellurium(IV), Te(C₆F₅)₄, was prepared from the reaction of TeCl₄ and Mg(C₆F₅)Br. Crystallization of the crude product from n‐pentane at ?25 °C gave suitable single crystals. The title compound crystallizes in the monoclinic space group P2₁/c (Z = 8) with two independent molecules per unit cell.     

Strukturen von Bis(trifluormethyl)halogeno‐ und ‐thiocyanato‐mercuraten, [Hg(CF3)2X]— (X = Br,I, SCN), und ein Vergleich der Strukturparameter der CF3‐Gruppen

Structures of Bis(trifluoromethyl)halogeno and thiocyanato Mercurates, [Hg(CF₃)₂X]^— (X = Br, I, SCN), and a Comparison of the Structural Parameters of the CF₃ Groups [(18‐C‐6)K]₂[Hg(CF₃)₂SCN]₂ (1) and [P(CH₃)(C₆H₅)₃]₂[Hg(CF₃)₂X]₂ (X = Br (2) , I (3) ) are prepared and their crystal structures are determined. [(18‐C‐6)K]₂[Hg(CF₃)₂SCN]₂ (1) crystallizes in the monoclinic space group P2₁/c with Z = 2, [P(CH₃)(C₆H₅)₃]₂[Hg(CF₃)₂Br]₂ (2) in the monoclinic space group P2₁/n with Z = 2 and [P(CH₃)(C₆H₅)₃]₂[Hg(CF₃)₂I]₂ (3) in the triclinic space group P1¯ with Z = 1. In the solid state the three compounds form dimeric anions with planar Hg₂X₂ rings. The structural parameters of the Hg(CF₃)₂ units in the till now known bis(trifluoromethyl)halogeno mercurates are compared. In all compounds one nearly symmetric and one distorted CF₃ group exist. The largest differences of the C—F bond lengths is found for [(18‐C‐6)K][Hg(CF₃)₂I]. This can be regarded as the experimental evidence for the properties of trifluoromethyl mercury compounds to act as excellent difluorocarbene sources in the presence of alkali iodides.     

Titration von Sulfid mit einer sulfidionensensitiven Elektrode

Zusammenfassung Eine Methode zur potentiometrischen Titration von Sulfid mit Natriumplumbat(II)lösung an einer sulfidsensitiven Membranelektrode wird beschrieben. Sie eignet sich zur Bestimmung von 10^–4% Sulfid in Gegenwart von Cl^–, Br^–, J^–, SCN^–, SO₃ ^2–, S₂O₃ ^2–

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Titration of sulphide with a sulphide-ion sensitive electrode

A method is described for the titration of sulphide with sodium plumbate(II) solution using a sulphide-sensitive electrode. The method is suitable for the determination of 10^–4% of sulphide in the presence of Cl^–, Br^–, J^–, SCN^–, SO₃ ^2–, S₂O₃ ^2–.

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Wir danken Herrn Dr. K. Obst für wertvolle Hinweise und Diskussionen.