A new route to achiral and chiral 1,2-bis(phosphino)ethanes, 1-arsino-2-phosphinoethanes, and 1,3-bis(phosphino)propanes and the molecular structure and catalytic activity of some rhodium(I) complexes derived thereof

A series of unsymmetrical 1,2-bis(phosphino)ethanes R(2)PCH(2)CH(2)PR'(2) and 1-arsino-2-phosphinoethanes R(2)AsCH(2)CH(2)PR'(2) mainly with bulky substituents R and R' were prepared from the cyclic sulfate by stepwise cleavage of the carbon-oxygen bonds by LiPR(2) and LiPR'(2) or LiAsR(2) and LiPR'(2), respectively. Analogously, racemic mixtures of R(2)PCH(2)CH(Me)PPh(2)(R =iPr, Cy ) as well as the enantiomers (R)-, (R)- and (R)-tBu(2)PCH(2)CH(Me)PPh(2)(R)- were obtained from the corresponding unsymmetrical cyclic sulfates and (S)-. On a similar route, the racemates of the 1,3-bis(phosphino)propanes R(2)PCH(2)CH(2)CH(Me)PPh(2)(R =iPr, tBu ), optically pure (R)- and (S,S)-iPr(2)PCH(Me)CH(2)CH(Me)PPh(2)(S,S)- were prepared. The reaction of [[RhCl([small eta](4)-C(8)H(12))](2)] with chelating ligands L-L, where L-L is R(2)PCH(2)P(men)(2)(R =iPr, Ph; men =(1S,2R,5S)-menthyl), Cy(2)AsCH(2)P(men)(2), or (R)-, (R)-, (R)-, (R)- and (S,S)-, in the presence of AgPF(6), gave the complexes [Rh(eta(4)-C(8)H(12))(L-L)]PF(6) which were used as pre-catalysts in the hydrogenation of the methyl ester of alpha-acetamidocinnamic acid (ACM). Depending on L-L, the solvent, the temperature and the pressure of H(2), optical yields of up to 69% ee were achieved. For two of the rhodium complexes, and, the molecular structures were determined by X-ray crystallography.     

Characterization of Carbohydrates in Paper and Paper Pulps Using Anion Exchange Chromatography and Principal Component Analysis

In the course of this investigation, a method for the characterization and differentiation of paper pulps was developed. After hydrolyzation of the papers and the respective raw pulps with trifluoroacetic acid, the hydrolyzates were analyzed with respect to their carbohydrate composition using ion exchange chromatography. The variations in carbohydrate composition mainly arise from the various hemicelluloses of the papers and pulps. The chromatographic results were then further processed using principal component analysis which allows correlating the various papers to different pulp materials.     

Pyrolysis studies of aromatic polyesters

The products of pyrolysis, at 400°C in vacuo (1 Pa), of poly(ethyleneterephthalate) (PET) and poly(butyleneterephthalate) (PBT) were studied. The products were identified by gas chromatography/mass spectrometry technique. The highly volatile products of PET contained acetaldehyde, benzene, toluene, styrene and ethylbenzene and in the case of PBT, butadiene, tetrahydrofuran, vinylcyclohexene and ethylbenzene were the major products. A qualitative analysis of the products of low volatility revealed that the main components were benzoic acid, terephthalic acid, monovinyl esters of terephthalic acid and higher oligomers in the case of PET, whereas benzoic acid, monobutenyl esters of terephthalic acid and higher oligomers were the main products from PBT. The results obtained were in good agreement with those obtained from pyrolysis experiments, carried out directly in the mass spectrometer. Mechanisms to explain the occurrence of the different products are proposed.     

Transition metal hydrides : (Advances in Chemistry Series No. 167), R. Bau,ed., American Chemical Society,Washington, D.C., 1978, ix + 429 pages, $ 42.00

The transition metal cluster hydride complex H₂Os₃(CO)₁₀ reacts with aryl isocyanates and isothiocyanates to yield products containing N-aryl-formamido and -thioformamido ligands. The compound (μ-p-CH₃C₆H₄NC(H)O) (μ-H)Os₃(CO)₁₀ has been analyzed by x-ray crystallographic methods and is shown to contain a formamido ligand bridging the edge of the triosmium cluster.     

Die Verwendung alkoholischer Lösungen bei der flammenphotometrischen Analyse

Zusammenfassung Wenn man die Genauigkeit und Empfindlichkeit der flammenphotometrischen Bestimmung von Calcium und Magnesium bei der Verwendung einfacher Flammenphotometer besonders steigern will, so eignen sich hierzu die alkoholischen Lösungen von einigen bestimmten Salzen dieser Metalle. So tritt mit steigenden Verbrennungswärmen der homologen Alkohole: Methyl-, Äthyl-, Propyl-, Butyl-, Amylalkohol usw. eine Steigerung der Linienemission ein. Für Calcium und Magnesium ergibt sich in amylalkoholischer Lösung gegenüber Wasser eine Erhöhung des Photostromes des Selenmeßinstrumentes um das Dreifache. Da Ca(NO₃)₂ und CaCl₂, sowie Mg(NO₃)₂, MgCl₂ und MgSO₄ bis zu großen Konzentrationen in Amylalkohol löslich sind, eignen sich diese Salze für die flammenphotometrische Bestimmung von Calcium bzw. Magnesium. Zu den Messungen wird ein Flammenphotometer von Dr. Lange, Berlin, verwendet, das für das Versprühen brennbarer Probeflüssigkeiten umgebaut wurde. Bisher wurde diese Methode zur Bestimmung kleinster Mengen von Ca(NO₃)₂ in technischen Produkten mit großem Erfolg verwendet. Die Reproduzierbarkeit liegt bis 1,00% bei ± 0,02% Ca(NO₃)₂. Für Magnesium liegen die Verhältnisse etwas ungünstiger.

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Summary If it is desired to increase considerably the accuracy and sensitivity of the flame photometric determination of calcium and magnesium when a simple flame photometer is used, it is well to use alcohol solutions of several particular salts of these metals. Thus, with increasing heats of combustion of the homologous alcohols: methyl-, ethyl-, propyl-, butyl-, amyl alcohol, etc., there is an increase of the line emission. For calcium and magnesium, there is a threefold increase of the photocurrent of the selenium instrument when amyl alcohol is used as solvent rather than water. Since calcium nitrate and chloride and likewise magnesium nitrate, chloride, and sulfate are soluble to high concentrations in amyl alcohol, these salts are suitable for the flame photometric determination of these metals. A flame photometer by Dr. Lange of Berlin was employed for the measurements; it was remodeled for the spraying of combustible liquid samples. Up to the present, this method has been employed with great success for determining extremely small amounts of calcium nitrate in technical products. The reproducibility is up to 1% at ± 0.02% calcium nitrate. The results are not so favorable in the case of magnesium.

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Résumé Si l'on désire augmenter beaucoup la sensibilité et la précision de la détermination par photométrie de flamme du calcium et du magnésium à l'aide d'un photomètre à flamme simple, il est commode d'employer des solutions alcooliques de certains sels de ces métaux. Ainsi l'augmentation des chaleurs de combustion des alcools homologues: méthylique, éthylique, propylique, butylique, amylique etc. entraine une augmentation dans l'émission spectrale. Pour le calcium et le magnésium le courant photoélectrique d'une cellule au sélénium est triplé quand on emploie comme solvant l'alcool amylique à la place de l'eau. Puisque le nitrate de calcium, ie chlorure de magnésium ainsi que le sulfate et le nitrate de ce métal, sont très solubles dans l'alcool amylique, ces sels conviennent pour déterminer ces métaux par photométrie de flamme. On a employé pour ces mesures un photomètre de flamme du Dr. Lange de Berlin. Il était modifié pour permettre la pulvérisation de liquides combustibles. Jusqu'à présent cette méthode a été employée avec succès pour la détermination de très petites quantités de nitrate de calcium dans des produits techniques. Jusqu'à 1% la reproductibilité est ± 0,02%. Les résultats ne sont pas aussi favorables dans le cas du magnésium.

     

Reactions of dicobalt octacarbonyl and related compounds with gem-dihalides

Dicobalt octacarbonyl and some of its derivatives (NaCo(CO)₄, Co₄(CO)₁₂, Hg[Co(CO)₄]₂, [Co(CO)₃PPh₃]₂, NaCo(CO)₃PPh₃) react with activated gem-dihalides, R₂CX₂, such as dichlorodiphenylmethane, 9,9-dihalofluorenes and dimethyl dibromomalonate, to give the ‘dimer’ olefin, R₂CCR₂. The course of this conversion involves formation of the coupling product, R₂XCCXR₂, followed by dehalogenation of the latter. These separate steps have been confirmed for activated monohalides (bromodiphenylmethane, 9-bromofluorene, dimethyl bromomalonate) which were readily coupled by cobalt carbonyls, and for activated vicinal dihalides (D,L and meso-dibromostilbene, 9,9′-dichlorobisfluorenyl) which cobalt carbonyls readily dehalogenated. A radical mechanism is favored for these processes, and indirect evidence in its favor is presented.     

Biosynthesis of 4-methylproline in cyanobacteria: cloning of nosE and nosF genes and biochemical characterization of the encoded dehydrogenase and reductase activities

The biosynthesis of the unusual amino acid 4-methylproline in the Nostoc genus of cyanobacteria was investigated on the genetic and enzymatic level. Two genes involved in the biosynthesis were cloned and the corresponding enzymes, a zinc-dependent long-chain dehydrogenase and a Delta(1)-pyrroline-5-carboxylic acid (P5C) reductase homologue, were overexpressed in Escherichia coli and biochemically characterized. Putative substrates were synthesized to test enzyme substrate specificities, and deuterium labeling studies were carried out to reveal the stereospecificities of the enzymatic reactions with respect to the substrates as well as to the coenzymes.     

Über siliciumschwefel-verbindungen : III. Neue organylthiosilane

Novel organylthio(alkoxy)silanes (I, II, III and XII) and organylthio(diethylamino)silanes (IV, V) are described. They were prepared by treating lithium or lead thiolates with the corresponding chlorosilanes or by cleavage of dimethylbis(diethylamino)silane with thiols. Phenylthiosilanes (Me₃SiSPh, III and XIII) furthermore can be obtained by reaction of chlorosilanes with benzenethiol in the presence of tertiary amines. The SiS bond of Me₃SiSPh is cleaved by chlorosilanes like Me₂Si(NEt₂)Cl or Me₂Si(OPr)Cl. This reaction is a convenient route to prepare compounds I and IV. The physical and chemical properties of the novel compounds were investigated.     

Polymorphism of Ph2P(CH2Py)(NSiMe3) and the Staudinger Reaction of Ph2P(CH2Py) with Hydrogenazide1)

A new polymorph of the iminophosphorane Ph₂P(CH₂Py)(NSiMe₃), ( 1 ), is compared to a just recently published. The reaction of the starting material, the phosphane Ph₂P(CH₂Py) with N₃SiMe₃ in the presence of water gives [Ph₂P(CH₂Py)(NH₂)][N₃], ( 2 ). A comparison of the structural and NMR parameters of 2 with previously reported derivatives of 1 , suggests that 2 is best described as a phosphonium salt in which the negatively charged imino nitrogen atom is protonated, according to [Ph₂(CH₂Py)P⁺—NH₂][N₃]^—, rather than as an iminiumphosphane salt [Ph₂(CH₂Py)P=⁺NH₂][N₃]^—.     

Structure and properties of the dendron-encapsulated polyoxometalate (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], a first generation dendrizyme

Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins.