Mechanistic Studies of Nickel-Catalyzed Chain-Growth Polymerizations:Additive and Ligand Effects.

[摘要] Chapter 1 provides an introduction to the field of organic π-conjugated polymer synthesis and places this work in context. Organic π-conjugated polymers are promising materials for flexible electronic devices. Chain-growth methods can provide access to well-defined polymers suitable for these applications. Yokozawa and McCullough reported the first chain-growth synthesis of poly(3-hexylthiophene) in 2004. Although this initial result garnered much interest, efforts to expand it beyond a small set of monomers have been hindered by the need to empirically develop unique reaction conditions for each monomer. This work tackles these challenges by providing an understanding of the role of monomer, ligand and additives on the reaction pathways. Chapter 2 describes the mechanistic influence of monomer structure and additives on Ni(dppe)Cl2-catalyzed syntheses of poly(p-(2,5-bishexyloxy)phenylene) and poly(3-hexylthiophene). For both monomers, we found that rate and spectroscopic studies were consistent with rate-limiting reductive elimination. Further studies showed that although LiCl formed a mixed aggregate with the arene monomer, the salt did not affect either the polymerization rate or mechanism. Chapter 3 describes evidence for a ligand-dependent change in rate-determining step. We demonstrated while that Ni(dppe)Cl2 catalyzed polymerizations proceeded through rate-determining reductive elimination, Ni(dppp)Cl2 catalyzed polymerizations proceeded through rate determining transmetallation. Moreover, we showed that in Ni(dppp)Cl2 catalyzed polymerizations LiCl influences the reaction order in monomer. Chapter 4 describes how we developed new catalysts with alkyl-based phosphines. Polymerization studies indicated that ligand steric properties were critical, with the least and most hindered ligands performing poorly. In contrast, Ni(depe)Cl2 demonstrated a chain-growth mechanism and the rate-limiting step was reductive elimination. Though the mechanism is similar to dppe, the relative rates of polymerization were different. These results suggest that ligand-based electronic properties are also important.Chapter 5 provides concluding thoughts on the state of the field and its future. Notably, our results provide a foundation for development of new ligand scaffolds by elucidating the dependence of the chain-growth mechanism on the steric and electronic properties of the ligand. Additionally, ours results suggest that this method is poised to produce new, well-defined materials that will have a significant impact on future applications of π-conjugated polymers.

[发布机构] University of Michigan

[效力级别] Conjugated Polymers

[关键词] Catalysis;Conjugated Polymers;Cross-Coupling;Nickel-Catalyzed Synthesis of Conjugated Polymers;Mechanism;Chemistry;Chemistry;Science;Chemistry