Localization of electronic excitation energy in Ru(2,2′-bipyridine)2(2,2′-bipyridine-4,4′-dicarboxylic acid)2+ and related complexes

The absorption spectra of Ru(2,2′-bipyridine)₂ (2,2′-bipyridine-4,4′-dicarboxylic acid)²⁺ (I) and its diethyl ester (II) are closely related and are both significantly different from the spectra of the mono-protonated (Ia) and deprotonated (Ib) complexes. Luminescence polarization measurements show that for I and II the luminescent states have the transferred electron in the bipy-4,4′(COOH)₂ and bipy-4,4′(COOEt)₂ ligands, respectively, rather than in the unsubstituted bipy ligands.     

On the Stereochemistry of Natural Irones,Dihydroirones, and their Precursors

Natural irones from the essential oil of Iris rhizomes develop by oxidative degradation of C₃₁-triterpenoids produced by the plant. Two enantiomeric forms of irones are found in Iris, oils of different origin. The optical properties and CD spectra of irones, dihydroirones and their C₃₁-precursors are reported and their absolute stereochemistry is determined.     

Chlor-dimethylaminosulfonium-Salze Darstellung und IR-Spektren

Chloro-dimethylaminosulfonium Salts. Preparation and I. R. Spectra By reaction of bis-dimethylamino-mono- resp. -disulfane with a mixture of chlorine/antimony(V) chloride the chloro dimethylaminosulfonium hexachloroantimonates(V) [(CH₃)₂N]₂SCI^⊕SbCl₆^? (I) and (CH₃)₂NSCI₂^⊕SbCl₆^? (II) are yielded. The i. r. spectra of these compounds were measured and assigned.     

Beitrag zur Mikrobestimmung des aktiven Wasserstoffs

Zusammenfassung Es wird über eine modifizierte Methode zur mikroanalytischen Bestimmung des aktiven Wasserstoffs in organischen Substanzen berichtet. Die von Lieb und Schöniger, als Ersatz der Grignard-Reaktion in die Mikroanalyse eingeführte Umsetzung mit dem wesentlich stärker und auch rascher reagierenden Lithiumaluminiumhydrid, konnte sich trotz vieler Vorteile nicht allgemein durchsetzen. Dies lag in erster Linie daran, daß das reine Lithiumalanat nur in sehr wenigen Lösungsmitteln, die zudem wegen ihres hohen Dampfdruckes für eine exakte Mikrobestimmung ungeeignet sind, löslich ist. Ersetzt man jedoch ein oder mehrere Wasserstoffatome des Alanats durch eine Alkyl- bzw. Alkoxygruppe, so führt dies zu einer wesentlichen Löslichkeitserhöhung. Unter den mög- lichen substituierten Alanaten, die wir auf ihre Brauchbarkeit zur Bestimmung aktiver Wasserstoffatome getestet haben, entsprach insbesondere das Natriumaluminiumdiäthyldihydrid weitgehend unseren Anforderungen. Es ist in Kohlenwasserstoffen, wie auch in stark polaren Lösungsmitteln sehr gut löslich. Dadurch ist auch die Möglichkeit für vergleichende Analysen mit Methylmagnesiumjodid gegeben, wodurch in manchen Fällen auf eine bestimmte Stellung oder auch sterische Hinderung der funktionellen Gruppe in der Molekel geschlossen werden kann. Die Anwendungsbreite wie auch die Genauigkeit der Alanatmethode wird an Hand der Analysendaten zahlreicher Testsubstanzen demonstriert.     

Metal Nanoparticles on Stainless Steel Surfaces as Novel Heterogeneous Catalysts

The goal of this work was the development of a novel type of heterogeneous catalyst, consisting of bare metal nanoparticles on stainless steel foils, which can be shaped to any kind of architecture and, if necessary, heated electrically. Solutions of pre-prepared, ligand protected and monodispersed gold, palladium, platinum and rhodium nanoparticles were sprayed onto stainless steel foils, followed by the careful removal of the ligand molecules by an oxygen plasma treatment. Due to this, bare particles become irreversibly fixed on the steel support. It could be shown that the original particle sizes do not change during the plasma treatment. Foils, densely coated with the nanoparticles, were used for gas phase catalyses in a self-made reactor at room temperature or at 60 °C. Hydrogenation of 1,3-butadiene at 15 nm Pd and 2 nm Pt, CO oxidation at 16 nm, 8 nm and 1.4 nm gold and NO reduction with NH₃ at 2 nm Rh particles were performed, indicating that the novel catalysts might in principle be applicable in technical processes if the experimental conditions like form and temperature would be optimized. Dedicated to Professor Dieter Fenske on the occassion of his 65th birthday.     

Synthesis and characterization of Cu,Ni and Zn binding capability of some amino- and imidazole hydroxamic acids: Effects of substitution of side chain amino-N for imidazole-N or hydroxamic-N-H for -N-CH3 on metal complexation

Solution equilibrium studies on Cu(II)-, Ni(II)- and Zn(II)-N-Me-β-Alaninehydroxamic acid (N-Me-β-Alaha), -N-Me-α-alaninehydroxamic acid (N-Me-α-Alaha), -Imidazole-4-carbohydroxamic acid (Im-4-Cha), -N-Me-imidazole-4-carbohydroxamic acid (N-Me-Im-4-Cha) and -Imidazole-4-acetohydroxamic acid (Im-4-Aha) systems have been performed by pH-potentiometry, UV–Vis spectrophotometry, EPR, CD, ESI-MS and ¹H NMR methods. According to the results: (i) the amino-N atoms are more basic in N-Me-α-Alaha and N-Me-β-Alaha than the hydroxamate function, but the trend is just the opposite between the imidazole-N(3) and hydroxamate. (ii) The metal ion anchor is always the hydroxamate part in the amino acid derivatives, while it is always the imidazole-N(3) in the studied imidazolehydroxamic acids. (iii) The three studied N-Me derivatives do not form metallacrowns. Only hydroxamate type chelate is formed with N-Me-β-Alaha, but with N-Me-α-Alaha a new type of coordination mode (via amino-N and hydroxamate-O) also exists. N-Me-Im-4-Cha also forms a dinuclear complex, [M₂L₃], with Cu(II) and Ni(II) (but not with Zn(II)). In this complex, one of the three ligands might bridge the two metal ions (five-membered hydroxamate-(O,O) plus five-membered (N_im, O_carb) bridging bis-chelating mode), while each of the additional two ligands binds to one metal. (iv) The two studied N–H derivatives, having dissociable proton on the hydroxamic-N, are able to form metallacrown species. A pentanuclear complex, [M₅L₄H₋₄], is exclusively formed above pH 4 between Cu(II) and Im-4-Aha. Interestingly, this 12-metallacrown-4 type complex, although together with various mononuclear binding isomers, appears also with Ni(II) and Zn(II). Unfortunately, the complexes of Im-4-Cha are not soluble in water at physiological pH at all.     

The Azo(Azoxy) Functionality as a π2 Component in Photo [2+2] cycloadditions ‘syn’- and ‘anti’-3,4-diazatricyclo[4.2.2.22,5]dodeca-3,7-diene,syntheses, photolyses,X-ray-structure analysis,and PE spectra

The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I₁ = 8.0₀, I₂ = 9.0₅ eV; 2 ; I₁ = 8.0₀, I₂ = 9.2₅eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond.     

Catalytic Intramolecular Palladium-Ene Reactions. Preliminay Communication

Pd(dba)₂[dba = dibenzylideneacetone]/PPh₃-or Pd(PPh₃)₄-catalyzed cyclizations of acetoxy-dienes 2 → 3 and 10 → 11 gave 1-vinyl-2-methylidene-subsituted cyclopentances and cyclohexanes in high yield, consistent with a palladium-ene/β-elimination mechanism ( D → E → F , Scheme 2). The efficient and highly stereoselective cyclizations 7 → 7 and 8 → 9 illustrate intramolecular allylpalladium insertions into 1,2-dialkyl-, trialkyl-, trialkyl-, and cyclic alkenes followed by elimination of the exocyclic β–H giving 1,2-divinylcyclopentanes. These new olefin insertions proceed faster in AcOH (compared to THF) and occur preferentially cis relative to the Pd ( 13 → 14 → 15 ).     

A reinvestigation of asymmetric induction in diels-alder reactions to chiral acrylates.

The chiral induction in the Diels-Alder addition $\text{1}$ → $\text{2}$, assessed reliably by ¹⁹F-NMR-spectroscopy of the endo-esters $\text{4}$, varied between 47 - 93% in favor of the 2-(R)-adducts $\text{2}$ depending on the auxiliary chiral group and the Lewis-acid catalyst.     

Quantitative goldbestimmung in filmmaterialien mittels flammenloser atomabsorption

A graphite rod electrothermal atomizer has been used for the AAS determination of traces of gold in hydrochloric and in hydrobromic acid solutions, and also after extraction into HBr-saturated methyl isobutyl ketone. Photographic film samples were decomposed first by enzyme action then by nitric acid/peroxide oxidation, and the gold was extracted into MIBK. For 10-μl aliquots of solution the 3s limits of detection were 3 × 10^?10g for aqueous solutions, 7 × 10^?10g for MIBK, and 7 × 10^?9 g/cm² for film.