UBC Theses and Dissertations
Trifluoromethylated zirconium amidate complexes : new directions for the catalytic hydroamination of alkenes Courtney, Sarah Turner
Hydroamination is the addition of an N–H bond across a C–C multiple bond. Nitrogen containing small molecules, typically accessed through multi-step synthetic pathways, are greatly important to both the pharmaceutical and fine chemical industries. Hydroamination is a rapidly expanding field due to the recent emphasis on sustainable chemistry for industrial applications as it provides an atom economical route to N-heterocycles, imines and amines. Group 4 catalysts have been greatly successful in this area however, intramolecular hydroamination of aminoalkenes typically proceeds only under high temperature reaction conditions. Low temperature reactivity is preferred from a practical perspective and is targeted here as a valuable probe to identify precatalysts most likely to display intermolecular alkene reactivity. The facile synthesis of organic amides provides a desirable means to adjust and optimize the steric and electronic properties of the proligand framework. Trifluoromethyl groups have been identified as desirable electron-withdrawing ligand substituents for the generation of reactive electrophilic zirconium hydroamination precatalysts. Proligand synthetic investigations revealed unforeseen challenges due to the electronic and steric effects imparted by trifluoromethyl substituents and unfortunately, the attractive 2,4,6-tris(trifluoromethyl) aryl-amides are of limited practical usefulness. In complex synthesis, the structure, bonding and reactivity screening of these novel electrophilic zirconium complexes will be presented as well as challenges associated with increased solubility. Importantly, these fluorinated systems have been shown to enhance reactivity of zirconium bis(amidate)bis(amido) complexes in the intramolecular hydroamination of alkenes. Progress toward low temperature (65 °C) reactivity will be discussed.
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