UBC Theses and Dissertations
UBC Theses and Dissertations
Hydroamination and C-H activation reactivity of tetrakis(amido), bis(amidate) and bis(2-pyridonate) complexes of titanium and zirconium Bexrud, Jason
The work reported herein focuses on expanding the reaction scope of known group four bis(amidate) and tetrakis(amido) complexes in hydroamination catalysis. The development of new titanium and zirconium complexes exhibiting improved reactivity in hydroamination catalysis and unexpected C-C bond formation are disclosed. The exceptional hydroamination activity of a bis(amidate) titanium bis(amido) precatalyst towards alkynes in the presence of aryl amine co-substrates is elucidated, and the scope of this reactivity was found to include examples of room temperature intermolecular hydroamination. The application of commercially available tetrakis(dialkylamido) titanium(IV) as a precatalyst for the cyclohydroamination of aminoalkenes to form N heterocyclic products is a particularly attractive contribution due to the ready availability and ease of use associated with this catalyst system. The second section involves efforts to develop more reactive and selective bis(amidate) bis(amido) hydroamination precatalysts by the rational design and implementation of new amidate ligands modified for enhanced reactivity and selectivity including attempts at enantioselective catalysis. The synthesis and characterization of a bis(amidate) titanium bis(amido) complex incorporating electron withdrawing perfluorophenyl groups for enhanced reactivity, along with the assessment of this system in terms of hydroamination is presented. The synthesis, characterization and evaluation of chiral amidate ligands for the asymmetric cyclohydroamination of aminoalkenes is also described. In order to generate more reactive group four hydroamination precatalysts, 2- pyridone and its derivatives were investigated as a new class of amidate N,O chelating proligand. The synthesis and characterization of the first group four bis(2-pyridonate) bis(amido) complexes is presented along with their reactivity towards aminoalkenes. These novel complexes were found to be reactive for both cyclohydroamination and catalytic intramolecular a-functionalization. The initial findings along with a substrate scope analysis, and preliminary mechanistic investigations for this unique and exciting 100% atom economic, catalytic C-C bond forming reaction is included. The work described in this dissertation contributes to understanding of group four metal catalyzed reactions by illuminating some previously unknown reactivity associated with titanium and zirconium as well as by providing further insight into how ligand structure influences complex reactivity.
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