Developing New Catalysts and Methods for Catalyst-transfer Polycondensations (CTP).

Abstract

Chapter 1 provides a general introduction and brief history of the controlled synthesis of pi-conjugated polymers via catalyst-transfer polycondensation (CTP). We focus on the mechanistic underpinnings, as well as controversial hypotheses supporting information. The monomer scope is investigated, illustrating the current limitation of primarily electron-rich monomers. We also examine new materials that have been accessed via CTP. Chapter 2 discusses the impact of an associative intermediate in Ni-catalyzed Kumada cross-couplings and CTP. We observed preferential intramolecular oxidative addition even when a stoichiometric amount of competitive agent was present. At higher concentrations of competitive agent, we observed electron-rich bidentate phosphines showed higher amounts of intramolecular oxidative addition compared to electron-poor ligand analogues. Further study illustrated that these trends were also present in CTP polymerizations stylizing Ni catalysts. Chapter 3 describes an N-heterocyclic carbene-ligated catalyst as a new route for CTP. Using a Pd-NHC catalyst, we observed the controlled polymerization of both phenylene and thiophene monomers. Additionally, this catalyst was able to synthesize block copolymers of thiophene and phenylene, regardless of addition order, indicating more complicated block structures could be achieved. Chapter 4 examines a new approach to try and address the limited monomer scope. We developed a small molecule model system for screening new CTP conditions for the synthesis of poly(2,5-bis(hexyloxy)phenylene ethynylene) (PPE). We specifically targeted conditions that showed preferential multi-functionalization under sub-stoichiometric quantities. Hundreds of screens lead to several conditions that favored multi-functionalization, but unfortunately these conditions exhibited step-growth behavior when PPE monomer was used. Further investigation revealed the intermediates in the small molecule model system were significantly more reactive than the starting materials, leading to preferential multi-functionalization without the presence of intramolecular oxidative addition. Comparison to Kumada CTP catalysts illustrated the need for small molecule screens to be tested over a range of starting material ratios. Chapter 5 describes our efforts at understanding the CTP mechanism and applying them towards new polymerization conditions. Future directions are outlined for each chapter, highlighting areas of needed research to address limited monomer scope of CTP. Additionally, relevant external papers that have been influenced by our work are also briefly discussed.