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568 results on '"Walter, Olaf"'

237. Syntheses, Structures, and Properties of Copper(II) Complexes of Bis(2-pyridylmethyl) Derivatives of o-, m-, and p-Phenylenediamine and Aniline.

Author

Turba, Sabrina, Walter, Olaf, Schindler, Siegfried, Nielsen, Lars Preuss, Hazell, Alan, McKenzie, Christine J., Lloret, Francesc, Cano, Joan, and Julve, Miguel

Subjects
*COPPER, *PHENYLENEDIAMINES, *ANILINE, *COMPLEX compounds, *OPTICAL polarization
Abstract

Copper(II) complexes of the ligand 1,n-bis[bis(2-pyridylmethyl)amino]benzene with n = 2-4 (1,n-tpbd) and its mononuclear derivative bis(2-pyridylmethyl)aniline (phbpa) were synthesized and structurally characterized. Magnetic measurements and DFT calculations were performed on [CuCl2(phbpa)], [Cu2Cl4(1,3-tpbd)], [(Cu2Cl2(ClO4)(1,3-tpbd))Cl(Cu2Cl2(OH2)(1,3-tpbd))](ClO4)2, and [Cu2(OH2)2(S2O6)(1,3-tpbd)]S2O6, and the exchange-polarization mechanism was successfully demonstrated. [ABSTRACT FROM AUTHOR]

Published
2008
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239. Phosphino-functionalised acetals of polyvinyl alcohol as the matrix for the immobilisation of Rh-based pre-catalysts for interfacial catalysis

Author

Ahlmann, Martin, Walter, Olaf, Frank, Melany, and Habicht, Wilhelm

Subjects
*POLYVINYL alcohol, *PHOSPHORUS compounds, *ORGANIC solvents, *HYDROFORMYLATION
Abstract

Abstract: Use of polyvinyl alcohol (PVA) to support the immobilisation of phosphines shall be presented. Phosphino functionalisation is introduced in the polymer by a one-step transacetalation reaction and high acetalation degrees are reached. By complexation of the phosphino groups to a [(COD)RhCl] complex fragment, [Rh]-modified polymers are obtained with Rh contents of higher than 15% and the transition metal in a defined molecular environment. The phosphino or [Rh]-modified PVAs are characterised unambiguously by comparing their spectroscopic data with those of model compounds, the syntheses of which are reported as well. Use of the [Rh]-modified polymers as pre-catalysts will be presented with the hydroformylation of 1-octene being taken as an example. It leads to a selectivity in the product distribution that is identical to that of the model complexes. Recycling experiments were performed and the catalyst rest state on the polymer was identified after 10 consecutive runs. Adsorption of the [Rh]-modified PVA on an inorganic support leads to the formation of stable polymer layers on its surface, which cannot be mobilised by extraction with organic solvents. The stability of these layers, together with their tuneable polarity, allow for their application in interfacial catalysis comparable to SAPC or SILC. [Copyright &y& Elsevier]

Published
2006
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240. Zinc coordination polymers with 1-(3-aminopropyl)-imidazole as bridging bidentate unit

Author

Arnold, Ulrich, Walter, Olaf, and Döring, Manfred

Subjects
*IMIDAZOLES, *MACROMOLECULES, *INTERMEDIATES (Chemistry), *SOLUTION (Chemistry)
Abstract

Abstract: The reaction of Zn(SCN)2 with one or two equivalents of 1-(3-aminopropyl)-imidazole (api) yields the coordination polymers [Zn(SCN)2(api)] n (1) and [Zn(SCN)2(api)2] n (2), respectively. Single-crystal X-ray diffraction analysis reveals one-dimensional polymeric chain structures for both compounds. The structure of 1 consists of tetrahedral Zn(SCN)2(api)2 units linked by one molecule 1-aminopropyl imidazole in an unsymmetric mode, i.e., each metal center is coordinated by an imidazole nitrogen as well as a nitrogen of the aminopropyl group. The metal ions in 2 display an octahedral coordination geometry with each Zn(SCN)2(api)2 unit linked by two molecules of the imidazole, thus, exhibiting two imidazole and two amino groups in the coordination sphere. The polymers were further characterized by IR-, 1H NMR- and 13C NMR-spectroscopy. [Copyright &y& Elsevier]

Published
2006
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247. Synthesis of α‐Amino Acids through Samarium(II) Iodide Promoted Reductive Coupling of Nitrones with CO2

Author

Prikhod'ko, Alexander, Walter, Olaf, Zevaco, Thomas A., Garcia‐Rodriguez, Jaime, Mouhtady, Omar, and Py, Sandrine

Abstract

Several N‐benzylnitrones reacted with carbon dioxide in the presence of samarium(II) iodide leading to α‐amino acids as the products of reductive C–C coupling. The best selectivities were observed at a carbon dioxide pressure of 50 bar at ambient temperature. The influences of different functional groups in the nitrone backbone and of the coordinating additives to samarium(II) iodide on the product distribution were investigated. The racemic α‐amino acids were obtained in up to 70 % yield based on HPLC data.

Published
2012
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249. The solution structure of cytochrome c from the green alga Monoraphidium braunii.

Author

Banci, Lucia, Bertini, I., Quacquarini, G., Walter, Olaf, Díaz, Antonio, Hervás, Manuel, and de la Rosa, Miguel A.

Abstract

The three-dimensional structure in solution of the reduced form of cytochrome c from the green alga Monoraphidium braunii has been solved through NMR data. Cytochrome c acts as a small mono-heme electron carrier protein between the two membrane-embedded complexes cytochrome f and photosystem I. The structure was determined using 1278 relevant interproton NOEs out of 1776 assigned NOEs with distance geometry (DG) calculations which included 36 stereospecific assignments and 20 experimentally found angle constraints. The family of structures obtained from the DG calculations was subjected to energy minimization and molecular dynamics simulation using previously defined force field parameters for the heme and its ligands. In all stages of the calculations, the solution structure is well defined and similar to the now available X-ray structure. [ABSTRACT FROM AUTHOR]

Published
1996
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250. Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente 44 [1]. Erstmalige parametrische Analyse des Absorptionsspektrums einer Molekülverbindung des trivalenten Urans: Tris[hydrotris(1‐pyrazolyl)borato]uran(III)

Author

Apostolidis, Christos, Morgenstern, Alfred, Rebizant, Jean, Kanellakopulos, Basil, Walter, Olaf, Powietzka, Bernhard, Karbowiak, Miroslav, Reddmann, Hauke, and Amberger, Hanns‐Dieter

Abstract

The absorption spectrum of tris[hydrotris(1‐pyrazolyl)borato]uranium(III) (UTp3) was run at room and low temperatures. From the spectra obtained, a truncated crystal field (CF) splitting pattern could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian achieving an r.m.s. deviation of 37.7 cm–1for 29 assignments. The parameters used allow the insertion of the Tp ligand into empirical spectrochemical, nephelauxetic and relativistic nephelauxetic series of UIIIcompounds, and the set‐up of experimentally based nonrelativistic and relativistic molecular orbital schemes of UTp3in the f range. Using the wavefunctions and eigenvalues of the fit, the experimentally determined temperature dependence (in the range 1.34–294.4 K) of μ2effcould be reproduced adopting an orbital reduction factor k = 0.99.

Published
2010
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