Combination of Chemical Reaction and Analysis - Catalyst Screening by On-Column Reaction Chromatography

Abstract

The combination of catalysis and analysis in a single chromatographic reactor is an efficient method for the comprehensive kinetic characterization of catalysts and materials. This concept, called on-column reaction chromatography, incorporates catalytic activity and separation selectivity in the polymeric stationary phase of a chromatographic separation capillary. This thesis aims to study mechanistic details of (enantioselective) catalytic processes by applying this strategy. After an introduction about general aspects of on-column reaction chromatography in chapter 1, the combination of enantioselective hydrogenations of alpha-keto esters over quinine-modified Pt and Pd nanoparticles and the consecutive separation of the obtained enantiomers in microcapillaries is reported in chapter 3. This combination makes it possible to simultaneously determine enantiomeric excesses and reaction kinetics for entire substrate libraries by injecting a broad variety of different substrates at the same time. Chirally modified Pt and Pd nanoparticles, embedded in a stabilizing polysiloxane matrix, serve as catalysts and selective chromatographic stationary phases for these multiphase (gas-liquid-solid) reactions. These polymer embedded catalysts are coated as a thin film onto the inner surface of fused-silica capillaries. A systematic kinetic study for the Pt-catalyzed enantioselective hydrogenation of ethyl pyruvate (1) is presented. Furthermore, the high-throughput screening of a substrate library consisting of different alpha-keto esters over chirally modified Pt- and Pd-catalysts was investigated. A study about the activity of different ruthenium olefin metathesis catalysts in ring-closing metathesis (RCM) reactions is described in chapter 4. The Grubbs-type catalysts 1st (22) and 2nd generation (23) as well as Hoveyda-Grubbs-type catalysts 1st generation (24) were dissolved in polysiloxanes and coated onto the inner surface of microcapillaries. Temperature- and flow-dependent conversion measurements with Grubbs-type catalysts for RCM allowed the determination of reaction rate constants k and activation parameters. The obtained comprehensive experimental kinetic data are a prerequisite for a better understanding of catalytic mechanisms. In chapter 5, the concept of on-column reaction gas chromatography was used to combine separation selectivity of ionic liquids (ILs) and catalysis by Grubbs-type catalyst 1st generation (22) in RCM reactions. This combination allows the investigation of catalyst stability and recyclability, which are important aspects for future catalyst applications. With this combination, it is possible to investigate the catalyst stability and recyclability. Reaction rate constants k that are hardly accessible by other techniques can be efficiently determined for various substrates with this approach. Chapter 6 describes the synthesis and application of polysiloxane-immobilized chiral camphor-based transition metal catalysts. The enantioselective separation efficiency and catalytic activity of these novel stationary phases are investigated. The synthetic applicability of polysiloxane-supported chiral Co-salen-complexes is described in chapter 7. A modular, covalent immobilization method for monofunctionalized enantiopure unsymmetrical salen ligands by an ether linkage has been elaborated.