Conventional ligand design in transition metal catalysis capitalizes on the ability of phosphorous, nitrogen, carbon, oxygen, and sulfur-based donors to modify the steric and electronic properties of a reactive metal center. Heterobimetallic transition metal complexes that contain a dative metal-metal bond provide a unique approach to ligand design where the reactivity of the metal center can be modified by metal-metal electronic communication. Our laboratory is interested in using the unique properties of heterobimetallic complexes to address significant limitations in current transition metal catalysis. My PhD work has focused on the ability of early/late transition metal heterobimetallic complexes to facilitate catalysis by speeding up reductive processes that occur at the late transition metal center. My initial studies were aimed at understanding the importance of the metal-metal interaction to catalysis in allylic amination reactions catalyzed by Pd–Ti heterobimetallic complexes and the potential of these catalysts to enable reactivity with challenging nitrogen nucleophiles. We also explored the substrate scope of the allylic amination with a variety of hindered amines and allylic chloride substrates under mild conditions. Aminations of this type have previously been shown to require harsh reaction conditions and tend to give low yields. A variety of sterically hindered secondary amine nucleophiles were able to readily undergo allylic substitution. Many of these aminations were complete within ten minutes. A series of allylic electrophiles were also shown to undergo the reaction. We have also looked at the ability of hindered amines to undergo intramolecular cyclizations to produce pyrrolidine and piperidine products. My continuing efforts in the laboratory are focused on developing chiral titanium-phosphinoamide ligands for enantioselective heterobimetallic catalysis. We have synthesized a series of chiral diamine-based phosphinoamide-titanium ligands in order to investigate enantioselective intramolecular aminations. Importantly, each of these new Ti-ligands enables room temperature catalysis in intramolecular aminations with hindered amines, suggesting contributions by the Ti center. Similar reactivity has not been achieved with monometallic chiral Pd catalysts in our lab. Importantly, many of these ligands enable modest enantioselectivity in the allylic aminations.
College and Department
Physical and Mathematical Sciences; Chemistry and Biochemistry
BYU ScholarsArchive Citation
Walker, Whitney Kaye, "Electrophilic Catalysis Using Heterobimetallic Complexes" (2017). All Theses and Dissertations. 6962.
heterobimetallic, catalysis, allylic aminations, enantioselective