Doctor of Philosophy
Blacquiere, Johanna M.
This thesis attempts to elucidate the mechanistic understanding for metal complexes ligated with 1,5-R-3,7-Rʹ-1,5-diaza-3,7-diphosphacyclooctane (PR2NRʹ2) ligands, which were utilized for organic transformations. Alkyne hydrofunctionalization reactions, including hydroamination and hydroalkoxylation, were previously catalyzed with [Ru(Cp/Cp*)(PR2NRʹ2)(MeCN)]PF6 catalysts. However, validation of the proposed mechanistic pathway for these complexes has not yet been realized. Investigation of these catalysts through substrate studies, intermediate isolation, kinetic analysis, and isotopic labelling was performed in an attempt to better understand the mechanism. Ligand and substrate interactions were identified that stabilized the coordinatively unsaturated complexes. Ligand modification enabled mitigation of a previously observed deactivation species, which enabled investigations for previously problematic hydroalkoxylation reactions. Formation of a new deactivation species was observed, which completely arrested productive catalysis, but gave insight into organic product release steps of the mechanism. Isolation of two vinylidene complexes enabled stoichiometric investigations to assess intermolecular hydroamination. Stoichiometric reactions with the vinylidene complex and amine nucleophiles resulted in the formation of a ruthenium acetylide complex, confirmed via independent synthesis, via deprotonation of Cβ instead of the desired nucleophilic attack of Cα. Formation of the ruthenium acetylide complex was not observed with stoichiometric reactions with aniline which was then targeted for attempted intermolecular hydroamination. Finally, investigation of palladium PR2NRʹ2 complexes were assessed for the Heck coupling of phenyltriflate and styrene, which showed regioselective formation of linear or branched product formation based on the phosphorus R substituent. Investigations into the factors controlling the regioselective product formation were performed through attempted synthesis of reaction intermediates and kinetic studies.
Summary for Lay Audience
Catalysts are chemicals which make chemical reactions occur more readily. The work in this thesis looks to form a better understanding as to how a particular family of ruthenium and palladium catalysts work. Two of the three reactions that were investigated involved the synthesis of compounds containing nitrogen and oxygen atoms, which are commonly found in high-value chemicals in nature or medicine. The studies established the performance of the catalysts, with slight alterations to its chemical structure. These changes were identified to influence the catalyst performance through helpful interactions that increased stability and reduced catalyst death. The catalysts were further utilized on chemicals that have not previously been looked at, which helped establish previously unsuccessful reactions, and inform on the limitations of the catalysts. Unproductive interactions were also observed which were detrimental to the catalysts and resulted in deactivation of the catalyst. The other reaction that was investigated looked at selective formation of two compounds, which were biased based on the structure of the catalyst used for the reaction. Exploration to determine why a particular catalyst favoured formation of one of the compounds over the other was performed. The aspects of the catalyst that were thought to control the formation were the number of metals per catalyst or how large parts of the catalyst were. Overall, a deeper understanding of the ruthenium and palladium catalysts discussed within was achieved which will be applied to future studies to further improve their performance for established and unestablished chemistry.
Chapple, Devon E., "Mechanistic Elucidation of M-PR2NRʹ2 Catalysts for Hydrofunctionalization and Cross Coupling Reactions" (2022). Electronic Thesis and Dissertation Repository. 8991.
Available for download on Saturday, December 30, 2023