03 Fakultät Chemie
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Item Open Access Asymmetric Rh diene catalysis under confinement : isoxazole ring‐contraction in mesoporous solids(2024) Marshall, Max; Dilruba, Zarfishan; Beurer, Ann‐Katrin; Bieck, Kira; Emmerling, Sebastian; Markus, Felix; Vogler, Charlotte; Ziegler, Felix; Fuhrer, Marina; Liu, Sherri S. Y.; Kousik, Shravan R.; Frey, Wolfgang; Traa, Yvonne; Bruckner, Johanna R.; Plietker, Bernd; Buchmeiser, Michael R.; Ludwigs, Sabine; Naumann, Stefan; Atanasova, Petia; Lotsch, Bettina V.; Zens, Anna; Laschat, SabineCovalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo‐C2‐symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh‐catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2‐additions of phenylboroxine to N‐tosylimine and (b) monomolecular isomerization of isoxazole to 2H‐azirne. Polar support materials performed better than non‐polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i. e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.Item Open Access Highly ordered LB films of DHAP : a donor acceptor substituted polyene(1993) Schmelzer, Michael; Roth, Siegmar; Niesert, Claus-Peter; Effenberger, Franz; Li, Rui ChengThe donor acceptor substituted polyene 5-(4-dihexadecylaminophenyl)-2-methyl-2,4-pentadienal (DHAP) is - due to its amphiphilic nature - a promising candidate for the Langmuir-Blodgett (LB) technique. The molecule was studied as a monolayer on a pure water surface under argon atmosphere. Monolayers and multilayers were transfered onto solid support. The films showed a high degree of order in the monolayer as well as in thick multilayers. LB films were investigated with polarisation dependent UV/VIS absorption spectroscopy. The film spectra showed additional absorption peaks which were not present in the spectra of the molecules in solution. The relative peak intensities were highly dependent on the orientation of the electric field vector with respect to the substrate normal. To get a detailed picture of the arrangement of the films on the molecular level, we studied the polarisation dependence of the FTIR spectra in different experimental set-ups. The spectra showed a perpendicular orientation of the conjugated system with respect to the substrate, whereas the backbone of the saturated hydrocarbon chains showed a medium tilt angle of 20.0° with respect to the substrate normal. X-ray small angle diffraction measurements were applied to investigate the thickness of the LB layers. From the position of the Bragg peaks, a thickness of 5.45 nm per bilayer can be calculated, in agreement with a bilayer model showing different molecular alignment of the molecules transferred during upstroke and downstroke.Item Open Access Crystal structure of 3-O-benzy 1-6,8-di-O-benzylidene-5,7-dideoxy-1,2-di-O-isopropylidene-5-nitro-L-glycero-D-galacto-octitol, (C6H5)(C4H6O2)[C3H3(NO2)(0H)(OCH2C6H5)][(C3H3O2)(CH3)2](2014) Peters, K.; Peters, E.-M.; Raczko, Jerzy; Jäger, VolkerC25H31NO8, orthorhombic, P212121 (No. 19), a = 10.137(2) Å, b = 28.990(4) Å, c = 8.190(2) Å, V= 2406.8 Å3, Ζ = 4, Rgt(F) = 0.071, Rw(F) = 0.046, T= 293 K.Item Open Access Crystal structure of (1'S)-4,6-di-O-benzylidene-2,5-dideoxy-2-nitro-L-ribo-hexose diethyl acetal,(C6H5)(C4H6O2)[C3H3(OH)(NO2)](OC2H5)2(2014) Peters, Κ.; Peters, E.-M.; Raczko, Jerzy; Jäger, VolkerC17H25NO7, monoclinic, P1211 (No. 4), a = 12.296(9) Å, b = 8.866(3) A,c = 8.782(4) Å, β = 103.48(5)°, V= 930.9 Å3, Ζ = 2, Rgt(F) = 0.041, Rw(F) = 0.040, T = 293 K.