POP Pincer Complexes of Ruthenium and Manganese for Small Molecule Transformations

This thesis summarizes and discusses the results of six separate projects within the PhD studies and totals eight chapters, followed by ten appendices containing general instrumentation, synthesis protocols, spectroscopic data, and a list of planned publications and scientific disseminations based on this work.
After first opening up with a general introduction towards the topic of POP pincer complexes, the thesis discusses the synthesis of a family of related ruthenium(II) hydrido complexes containing POP pincer ligands. All of them were spectroscopically characterized and their structures confirmed by means of crystallography.
In the third chapter, the application of the previously synthesized family of Ru(II) complexes for the upgrading of ethanol to 1-butanol and related higher alcohols as a means of biofuel synthesis was investigated. At a temperature of 120 °C, they reached moderate yields of around 28% over two days after various condition screenings.
The complexes were then further tested for their activity in the dehydrogenation of formic acid using an ionic liquid as a solvent. This was an attempt to simplify the reaction conditions for formic acid dehydrogenation in order to make the reaction more industrially attractive. The set of complexes showed high activities at 90 °C and were active at temperatures as low as 60 °C.
In the fifth chapter, a new set of Ru(II)-POP complexes bearing nitrosyl groups was synthesized. This gives a fundamental insight into binding properties of POP pincer complexes, especially their hemilability between different binding modes. All complexes were investigated by spectroscopic techniques and their structures verified by crystallography.
The sixth chapter aimed to develop a novel set of previously unknown POP pincer complexes of manganese. Three catalysts could be synthesized and spectroscopically analyzed to various degrees. To my knowledge, this work represents the first reported example of Mn(I) POP pincer complexes. They were then used in formic acid dehydrogenation reactions in conditions identical to those used for the ruthenium complexes and showed moderate activity.
Finally, the seventh chapter, done in collaboration with the Leibniz Institute for Catalysis (LIKAT) in Rostock/Germany, investigates the reactivity of CO2 adducts of very electron-rich phosphines. Breaking the molecule symmetry of CO₂, these adducts are interesting as co-catalysts for the hydrogenation of CO₂ to formic acid and other bulk chemicals in a future hydrogen economy. Catalytic reactions were attempted using the commercially available Ru-MACHO-BH catalyst under harsh conditions, and small amounts of formate signals were detected, opening up the possibility of further investigation.
In conclusion, this thesis contributes to the further understanding of catalytic processes using POP pincer complexes of ruthenium and manganese for applications in
the field of green chemistry, specifically biofuel development and energy storage solutions.