STRATEGIES FOR ACHIEVING SELECTIVITY IN HOMOGENEOUS CATALYSIS Public Deposited

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  • March 20, 2019
Creator
  • Roselli, Christina
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • A hallmark of gold(I)-catalyzed enyne cycloisomerization reactions is their unique ability to generate complex scaffolds from simple unsaturated starting materials. Initial work focused on the development of a gold-catalyzed cascading cycloisomerization of alkylidene cyclopropane bearing 1,5-enynes that terminated in a cyclo-addition of aldehydes. In one pot, we transformed a simple enyne starting material into a complex terpene-like polycyclic scaffold. This diastereoselective reaction provides convergent access to novel molecular scaffolds and tolerates a diverse scope of aldehydes. Mechanistic studies revealed the catalyst rests as an off-cycle digold vinyl intermediate. Further investigations focused on expanding the scope and diversity of the products. We found that an enantioselective variant was not feasible and that electrophilic halogenation could not outcompete protodemetallation. Through the development of an alternate reactivity pathway, we incorporated ketone and nitrile nucleophiles into our scaffold to develop more diverse heterocycles. A second area of research focused on a computational study on the transfer of silylium from triphenylphosphine to other heteroatom containing Lewis bases. In various examples of tris(pentafluorophenyl)borane (BCF) catalyzed hydrosilylative reductions, phosphine additives attenuate the reactivity of the system, acting as silylium ion carriers. With these studies in mind, we computed the relative “silaphilicity” of various Lewis bases to understand how Lewis base preferences might correlate with the observed chemoselectivity in complex molecules. The relative free energies of various Lewis base relevant to catalysis were compared to develop a thermodynamic scale of stabilities. As expected from experimental studies, both the choice of phosphine and silane impact the thermodynamics of this transfer. The final chapter focuses on the development of a living, chain-growth polymerization of a donor-acceptor (D-A)monomer. While donor-acceptor conjugated polymers have many applications in organic electric materials, they are typically synthesized through step-growth methods, leading to little control over polymer composition and molecular weight. We described the synthesis of a novel monomer and explored a variety of metal complexes for the living polymerization. While catalyst loading studies and chain extension experiments are not fully consistent with a living chain-growth mechanism, we identified a new D-A polymer and worked towards expanding the current methodologies to develop alternating D-A polymers.
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Rights statement
  • In Copyright
Advisor
  • You, Wei
  • Leibfarth, Frank
  • Meyer, Gerald
  • Miller, Alexander
  • Gagné, Michel
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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