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Institute: search.filters.UBSInstitut.Institut für Physikalische ChemieAuthor: search.filters.author.Frey, Wolfgang

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    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, Sabine
    Covalent 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.
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    Efficient and spatially controlled functionalization of SBA‐15 and initial results in asymmetric Rh‐catalyzed 1,2‐additions under confinement
    (2021) Beurer, Ann‐Katrin; Kirchhof, Manuel; Bruckner, Johanna R.; Frey, Wolfgang; Baro, Angelika; Dyballa, Michael; Giesselmann, Frank; Laschat, Sabine; Traa, Yvonne
    Selectively functionalized mesoporous silica may considerably advance heterogeneous catalysis through the controlled immobilization of highly selective complex catalysts inside the mesopores. However, spatially controlled functionalization and the precise analytical verification are still a challenge. In this publication, we report a method, which ensures a selective functionalization of the mesopore surface with a clickable linker and thus makes it possible to study confinement effects during catalyzed reactions. First, we passivate the silanol groups on the particle surface and in the pore entrances of the mesoporous silica material SBA‐15 with 1,1,1‐trimethyl‐N‐(trimethylsilyl)silanamine. Then we remove the template by solvent extraction and functionalize the pore walls with 3‐azidopropyltriethoxysilane before we click the catalyst. In initial experiments of asymmetric Rh‐catalyzed 1,2‐addition, we investigate the performance of a catalyst clicked selectively in the mesopores and compare it to the dissolved catalyst as well as to the catalyst immobilized exclusively on the external surface of SBA‐15.
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    Precursor molecules for 1,2-diamidobenzene containing cobalt(ii), nickel(ii) and zinc(ii) complexes : synthesis and magnetic properties
    (2024) Hunger, David; Suhr, Simon; Bayer, Valentin; Albold, Uta; Frey, Wolfgang; Sarkar, Biprajit; Slageren, Joris van
    Molecular magnetic materials based on 1,2-diamidobenzenes are well known and have been intensively studied both experimentally and computationally. They possess interesting magnetic properties as well as redox activity. In this work, we present the synthesis and investigation of potent synthons for constructing discrete metal-organic architectures featuring 1,2-diamidobenzene-coordinated metal centres. The synthons feature weakly bound dimethoxyethane (dme) ligands in addition to the 1,2-diamidobenzene. We characterize these complexes and investigate their magnetic properties by means of static and dynamic magnetometry and high-field electron paramagnetic resonance (HFEPR). Interestingly, the magnetic and magnetic resonance data strongly suggest a dimeric formulation of these complexes, viz. [MII(bmsab)(dme)]2 (bmsab = 1,2-bis(methanesulfonamido)benzene; dme = dimethoxyethane) with M = Co, Ni, Zn. A large negative D-value of -60 cm-1 was found for the Co(ii) synthon and an equally large negative D of -50 cm-1 for the Ni(ii) synthon. For Co(ii), the sign of the D-value is the same as that found for the known bis-diamidobenzene complexes of this ion. In contrast, the negative D-value for the Ni(ii) complex is unexpected, which we explain in terms of a change in coordination number. The heteroleptic Co(ii) complex presented here does not feature slow relaxation of the magnetization, in contrast to the homoleptic Co(ii) 1,2-diamidobenzene complex.
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    Hierarchical silica inverse opals as a catalyst support for asymmetric molecular heterogeneous catalysis with chiral Rh‐diene complexes
    (2021) Deimling, Max; Kousik, Shravan R.; Abitaev, Karina; Frey, Wolfgang; Sottmann, Thomas; Koynov, Kaloian; Laschat, Sabine; Atanasova, Petia
    The efficacy of heterogeneous catalysis relies heavily on diffusion and distribution of reactants within catalyst supports. However, the presence of confinement, essential for reaction selectivity, drastically slows down molecular transport. Here, macro‐mesoporous silica inverse opal (SiO2-IO) films were used as a model system to study the rather unexplored molecular infiltration behavior using a probe molecule resembling a catalyst via confocal laser scanning microscopy (CLSM). CLSM analysis revealed homogeneous tracer distribution in SiO2-IO and attachment to both transport and mesopores. Bulk macro‐mesoporous SiO2-IO support was used for the attachment of mono‐ and bis‐functionalized chiral Rh‐diene complexes, and the catalytic activity and selectivity with respect to the support was studied. Lower enantioselectivity was observed with the bis‐functionalized ligand due to ligand entanglement and reduced accessibility of the active site, while the mono‐functionalized ligand gave an excellent enantioselectivity of 94 %ee in the asymmetric 1,2‐addition of triphenylboroxine to N‐tosylimines and could be recycled up to three times.