Doctor of Philosophy
Blacquiere, Johanna M.
Exploring efficient and environmentally-friendly routes to synthesize molecules is critical for the pharmaceutical and fine chemical industries. One method is to study current catalytic methods to increase selectivity and performance for challenging reactions. Inclusion of an intramolecular acid/base site on the ligand manifold of an organometallic complex has allowed for new mechanistic pathways and enhanced reactivity. This thesis delves into understanding organometallic complexes in catalysis by systematic tuning the ligand properties. Synthesis of PR2NR′2 ligands was performed to enable the systematic tuning as R and R′ alter the electronic and steric properties of the primary and secondary coordination sphere, respectively. Metalation of PR2NR′2 ligands with Ru gave a series of MLC proton shuttling complexes for catalytic testing. From catalytic performance, structure-activity relationships were extracted for two types of reactions that exploit a proton shuttling relay: 1) the intramolecular cyclization of ethynyl amine and alcohol substrates; and 2) the acceptorless dehydrogenation of amines. Optimization for cyclization of ethynyl amines revealed sterically bulky, electron rich Ru complexes operate at turnover frequencies of above 1500 h-1 and reach turnovers of 800, both significantly better than previous systems. Optimization for acceptorless dehydrogenation of indolines has shown sterically bulky phosphines to be beneficial. Furthermore, in both acceptorless dehydrogenation of amines and cyclization of ethynyl amines the acid/base site of the secondary coordination sphere displays a significant effect on catalytic performance. Pendent amines within the secondary coordination sphere operate best when tuned to have the same approximate basicity as the target substrate. Mechanistic analysis of both reactions revealed key catalyst deactivation routes occur as a function of the pendent amine. These findings allow for structure-activity relationships to be developed for the next generation of proton shuttling catalysts.
Stubbs, James M., "Developing Structure-Activity-Relationships for Metal-Ligand-Cooperative (MLC) Complexes using PR2NR′2 Ligands" (2018). Electronic Thesis and Dissertation Repository. 6011.
Available for download on Thursday, February 04, 2021