Entwicklung anion-chiraler ionischer Flüssigkeiten und ihre Anwendung in der Katalyse
The aim of this dissertation was the investigation of anion-chiral ionic liquids (ILs) in catalytic reactions in order to investigate a potential chirality transfer. Thus chirality has been incorporated into the anion of the molten salt. There are several examples of catalytic reactions known in literature to be heavily influenced by the choice of the anions covering a large scope of influence from conversion to even enantioselectivity. It was aimed to combine this effect with the structural variability of the ionic liquids as neoteric solvents. In the first part of this project the structural motive, i.e. complexes of aluminum and boron using chiral alcohols as ligands, could successfully be applied in the synthesis of anion-chiral salts. This motive showed a large variability concerning the choice of the ligand. Within this work it was possible to synthesize five borates that could be attributed as ionic liquids because of their low melting point of below 100°C. Room temperature liquids seemed to be accessible using asymmetric cations and ligands with low molecular weight. For sodium dimalatoborat as a representative for borates the structural stability of these salts has been discussed. This was based on the results of an X-ray single crystal structure analysis and NMR-experiments of this compound. A main focus has been laid upon the central chirality, which has been introduced through the application of a dissymmetric ligand. In addition to the aluminum and boron based compounds also the synthesis of a chiral sulfate-based IL using chiral alcohols has been examined. A room temperature IL could be yielded with (S)-lactic acid as ligand. In the second part of the dissertation the hitherto synthesized room temperature ILs have been applied as solvents in the organocatalytic aza-Baylis-Hillman reaction, a rhodium-catalyzed hydrogenation, as well as in the synthesis of alpha-aminophosphonates using lanthanum triflate as catalyst. In the latter reaction diethylphenyl-(alpha-phenylamino)methylphosphonate could be observed as enantiomericaly pure single crystals for the first time. The results of the X-ray single crystal structure analysis have been discussed in relation to the known racemic mixture. Work-up of reactions in these new reaction media has been of special concern, mainly for the aza-Baylis-Hillman reaction. Thus a large number of work-up-methods has been screened and investigated. Finally a reactive work-up using a cation-exchange reaction has built the basis to further investigate these solvents. In the organometallic hydrogenation and in the synthesis of alpha-aminophosphonates either a chromatographic work-up or the use of extraction methods with supercritical carbon dioxide could successfully be applied. In the aza-Baylis-Hillman reaction described in this work the first example could be presented yielding high enantioselectivities of up to 84% ee with an asymmetric reaction medium as the sole source of chirality. The ionic liquid methyltrioctylammonium dimalatoborate used in this reaction bore the chirality in the anion of the salt. As catalyst the simple nucleophile triphenylphosphine has been used. Through this dissertation for the first time a chiral reaction medium could transfer chirality upon product molecules to a valuable extent. Besides the use of chiral catalysts or auxiliaries this displays a third alternative for chirality transfer. For a successful chirality transfer strong intermolecular interactions seem to be necessary like electrostatic interactions and hydrogen bonding between the solvent molecules and the intermediates or transitions states of the enantiodiscriminating step. Functionalized ionic liquids offer a unique possibility to adjust the spatial arrangement to numerous reactions.
info:eu-repo/classification/ddc/540, Homogene Katalyse, Salzschmelze, Chiralität <Chemie>, Borate, Aluminate, Chemie, aza-Baylis-Hillman, Organokatalyse, chirales Lösungsmittel, Anioneneinfluss, chirality, ionic liquid, chiral reaction medium, organocatalysis, chiral solvent
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