Design of polymer architectures for catalysis

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Hoyt, Caroline B.
Jones, Christopher W.
France, Stefan
Sadighi, Joseph P.
Collard, David M.
Bucknall, David G.
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Polymer structures provide tunable platforms for catalyst design due to the high degree of structural control possible in their synthesis. In this study, several different molecular catalysts have been prepared on polymer supports targeting applications in organic synthesis and fundamental catalysis. An overall goal of this thesis was to demonstrate the benefits of various polymer catalyst architectures in a variety of catalytic reactions including cooperative and cascade catalysis using acid and base sites, acid catalyzed hydroboration reactions, and Pd catalyzed C–H arylation. This thesis is organized into six chapters. The first chapter gives an overview of the use of polymer supported catalysts in organic synthesis, with a special emphasis on the use of polymer supports in organocatalysis. The second chapter explores the application of a linear polymer support in cooperative catalysis of the aldol reaction, which is a system that has been extensively studied on mesoporous silica supports. The new linear polymer catalyst demonstrated comparable reactivity to the mesoporous silica supports, and the importance of monomer unit placement, strength of the acid and base, and the acid-base ratio are demonstrated. The third chapter extends the concepts learned from the second chapter with regard to acid-base cooperative catalysis to polymer-silica hybrid catalysts in which the acid and base sites are confined into separate domains within the catalyst. In this chapter, the acid and base functionalities are incorporated into mesoporous silica and polymer brush domains to yield a polymer brush catalyst that targets a 3-step cascade reaction. The next chapter is a fundamental kinetic and mechanistic study of the hydroboration of various alkynes with pinacolborane utilizing a carboxylic acid polymer catalyst. The study elucidated the kinetic order of the reaction in catalyst and substrates, and a proposed mechanism was supported by a kinetic isotope effect and 11B NMR studies. The linear polymer catalyst was the first example of an organocatalytic polymer catalyst for the hydroboration of functionalized alkynes. Chapter five discusses the utility of a polymer micelle support for the Pd-catalyzed C(sp3) – H monoarylation. Using this micelle support, steric and electronic effects were invoked to direct the C – H monoarylation of an unnatural amino acid with substituted aryl iodides. The support demonstrated high tolerance for substituted aryl iodide coupling partners, while also recycling the support. The use of the polymer micelle was one of the first demonstrations of this support applied to C – H activation, and the support has many tunable properties that can be adjusted in future applications. Lastly, the final chapter outlines possible future directions for these different projects as well as summarizes the fundamental findings from each of these studies. Understanding the fundamental aspects that were tuned for each support and applied to these organocatalytic reactions provides a basis for future improvements on these supports as well as applications in synthetic organic chemistry.
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