Development of tailored homogeneous ruthenium catalysts for the application in the hydrogenation of biogenic substrates

• Entwicklung maßgeschneiderter homogener Ruthenium Katalysatoren für die Anwendung in der Hydrierung biogener Substrate

Jung, Celine Laura; Klankermayer, Jürgen (Thesis advisor); Jupke, Andreas (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

The present thesis describes the development of tailored molecular ruthenium catalyst systems for the selective hydrogenation of biogenic platform chemicals. Chapter 1 provides an introduction on the state of the art in the synthesis of the two bio-based compounds levulinic and itaconic acid and their potential as renewable building blocks for future chemical value chains. Complementary, a short overview of homogeneous catalytic systems describes the challenges linked to the hydrogenation of acids and esters with special focus on ruthenium triphos systems. In Chapter 2, the development of a catalyst lead structure is explained, enabling the tailoring of molecular complexes for the catalytic application. In detail, the preparation of a series of ruthenium triphos-xyl complexes bearing acetato, naphtholato or phenolato ligands from [Ru(triphos-xyl)(tmm)] is described and completed with the characterization of the complex molecules.The subsequent results of the catalytic hydrogenation of levulinic acid and γ-valerolactone to 1,4-pentanediol by selected ruthenium triphos-xyl complexes are reported in Chapter 3. High activities at low catalyst concentrations could be observed in batch experiments and multiple substrate reloading cycles revealed a correlation of catalyst deactivation with thermal stress in the absence of substrate. Moreover, the successful dehydrogenation of 1,4-pentanediol to γ-valerolactone showed the presence of a dynamic lactone-diol equilibrium. NMR-spectroscopic investigations revealed the formation of a bis(levulinato) complex on dissolving the catalysts in levulinic acid prior to the hydrogenation.The challenging hydrogenation of itaconic acid, itaconates and 2-methyl-γ-butyrolactone to 2-methyl-1,4-butanediol with adapted ruthenium triphos-xyl complexes is reported in Chapter 4. Selected fluorinated phenolato and naphtholato ruthenium triphos-xyl catalyst systems showed significantly improved activities compared to established systems. Besides the fluorinated phenols, also hexafluorobenzene could be identified as beneficial additive leading to a closer investigation on its reactivity with [Ru(triphos-xyl)(tmm)] in Chapter 5. As a result, the dimeric fluorine-bridged complex [{Ru(triphos-xyl)}2(μ-F)3]+ could be isolated and successfully applied in the hydrogenation of selected acids, esters and amides. In particular, it was found to be active at very low catalyst concentrations in the hydrogenation of levulinic acid and γ-valerolactone. Moreover, an unprecedented complex with coordinated PF6− anion to the ruthenium center could be developed and characterized.