Mechanistic Elucidation of M-PR2NRʹ2 Catalysts for Hydrofunctionalization and Cross Coupling Reactions

Devon E. Chapple, The University of Western Ontario

Abstract

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 (P^R₂N^Rʹ₂) ligands, which were utilized for organic transformations. Alkyne hydrofunctionalization reactions, including hydroamination and hydroalkoxylation, were previously catalyzed with [Ru(Cp/Cp*)(P^R₂N^Rʹ₂)(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 C_β instead of the desired nucleophilic attack of C_α. 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 P^R₂N^Rʹ₂ 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.