UBC Theses and Dissertations
Synthetic applications of zirconium and titanium amidate complexes Yim, Jacky Chun-Ho
The use of titanium or zirconium amidate complexes as either reagents or catalysts for targeted applications is described herein. The investigation is focused on a novel class of zirconocene amidate hydride complexes primarily used for the hydrozirconation reaction and a previously disclosed bis(amidate) bis(amido) titanium complex for the regioselective alkyne hydroamination reaction. A novel class of zirconocene amidate hydride complexes is synthesized and characterized. The amidate binding mode is significantly influenced by sterics. A rare example of an equilibrium between the structural isomers where the amidate ligand adopts either the κ¹ O-bound or κ² is shown. Reaction of styrene with these complexes resulted in the formation of the branched insertion products, which is in contrast to the observed regioselectivity when the well-known Schwartz’s reagent is used. Asymmetric insertion was attempted with a complex bearing an amidate ligand with a stereocenter. Reactivity with other alkenes and phenylacetylene were explored. Under harsh reaction conditions, the zirconocene amidate hydride complexes undergo a halide exchange reaction with phenyl halides. A competition experiment suggests two separate mechanistic pathways for styrene insertion and halide exchange. A primary kinetic isotope effect suggests Zr─H cleavage is involved in the rate-determining step. Experimental evidence is consistent with a coordination-insertion mechanistic proposal. The synthetic utility of a previously reported bis(amidate) bis(amido) titanium complex for the regioselective alkyne hydroamination reaction is further explored. The reactivity and regioselectivity of hydroamination with benchmark substrates using this bis(amidate) titanium complex is directly compared to other titanium based hydroamination catalysts. The substrate scope of this bis(amidate) titanium hydroamination catalyst is extended to include more difficult substrates, such as protected propargyl alcohols. Modifications to the reaction protocol allow for facile bench-top use. The bis(amidate) titanium complex was applied to tandem sequential reactions featuring hydroamination to afford secondary amines, a primary amine and a substituted primary allylamine. This hydroamination catalyst is also used for the oligomerization of alkynylanilines. By tuning the alkynylaniline monomer, a soluble N-containing oligomer was synthesized, which shows a degree of conjugation. This bis(amidate) titanium hydroamination catalyst was employed to assemble a small library of aminoether compounds targeted as T-type calcium channel blockers.
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Attribution-NonCommercial-NoDerivs 2.5 Canada