Hydrierung biogener Substrate mit maßgeschneiderten Ruthenium-Triphos-Katalysatoren : vom mechanistischen Verständnis bis zur Anwendung

• Hydrogenation of biogenic substrates using tailor-made ruthenium-triphos catalysts

Limper, Dominik; Leitner, Walter (Thesis advisor); Klankermayer, Jürgen (Thesis advisor)

Aachen (2016)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2016

Abstract

This thesis deals with the development and investigation of tailor-made Ruthenium Triphos catalysts for the selective hydrogenation of biogenic substrates. To enable a targeted application of tailor made catalysts, a deep understanding of the mechanistic aspects of molecular catalysts is required. Thus the activation behaviour of the [Ru(Triphos)TMM] catalyst has been investigated and identified with respect to various reaction parameters. It has been shown that the neutral hydride complex [Ru(Triphos)(S)(H)2] acts as the active species under neutral reaction conditions, while in presence of HNTf2 as acidic additive the ionic [Ru(Triphos)(S)(H2)H][NTf2] is the active species. Furthermore, it was shown that these two activation mechanisms are not independent from each other, in which the neutral complex can be transformed into the ionic complex by addition of an acid to the reaction mixture. Hence a control of the activation process and the desired reaction mechanism is possible, depending on the proton concentration.Having a detailed knowledge about the proceeding activation processes in hand, a molecular design via variation of the TMM ligand was conducted and the impact on the catalyst activation was investigated. Variations on the aromatic substitutens of the Triphos ligand lead to an inhibition of catalyst deactivation via dimerization and therefore a significant increase of the catalytic activity in the hydrogenation of methyl benzoate. The initial activities observed here, exceeded the original ones by far, reaching the range of the most active systems known from literature.For the additive free catalytic system [Ru(Triphos)(methylallyl)][NTf2], kinetic investigations have been made to extend the mechanistic understanding beyond the activation processes. For the [Ru(Triphos)TMM] catalyst itself, experimental data and DFT-based kinetic information combined, have been implemented in a DAE simulation model. Thereby a precise comparison of the proposed mechanism with experimental data was achieved.This versatile and flexible, molecular catalytic system has been transferred to a semicontinuous hydrogenation setup for the transformation of itaconic acid to 3 MTHF. Besides the development and optimization of a reactor concept, purification using distillation procedure allowed for the isolation of pure and water free 3 MTHF. Further, two potential process schemes have been proposed towards a continuous one- or two-step process.Initiated by the new accessibility of 3 MTHF as a potential biogenic solvent, it was compared against THF and 2 MTHF as solvent for various catalytic reactions. 3 MTHF possessed promising solvent properties in hydrogenation/dehydrogenation and C C coupling reactions.