Synthesis and reactivity of actinide phosphorano-stabilized carbene and phosphido complexes
Nuclear power plants have been operated in the United States for over 60 years, generating over 800 terawatt-hours of energy per year. However, there is still no reliable process to recycle the spent nuclear fuel. This dissertation looks at the formation of actinide-ligand multiple bonds, which may give us insights into how to improve the process of separation of actinides from the spent nuclear fuels contaminated with lanthanides. This is because lanthanides cannot participate in multiple bonding and a difference in coordination chemistry between actinides and lanthanides is important in separation methods. This dissertation contains two parts, both of which involve using phosphorus to create new actinide complexes. Chapters 1 and 2 outline the use of phosphorano-stabilized carbene complexes to make short actinide-carbon bonds. In fact, these complexes exhibit the shortest uranium and thorium-carbon bonds reported in the literature. Chapter 3 revolves around investigating the synthesis, characterization, and reactivity of actinide phosphido (monoanionic phosphine) complexes. In this regard, I have synthesized the first trivalent uranium phosphido complex, (C5Me5)2U[P(SiMe3)(2,4,6- Me3C6H2)](THF). The investigation of its reactivity revealed that the complex is capable of 4-electron reduction chemistry. For example, the reaction of (C5Me5)2U[P(SiMe3)(2,4,6-Me3C6H2)](THF) with azidotrimethylsilane, N3SiMe3, produces a U(VI) complex. Three electrons are from the metal center, U(III) to U(VI), and one electron is from reductive coupling of the phosphido ligand. The phosphido chemistry can also be extended to tetravalent uranium and thorium. Chapter 4 outlines the synthesis of thorium phosphido complexes which exhibit an unusual absorption in the visible region which we contributed to a ligand to metal charge transfer. Just by varying the ligand design, we were able to manipulate the HOMO/LUMO gap, which results in an absorption in a different part of the visible region. Appendix A summaries the synthesis of copper(I) complexes with bulky terphenyl ligands. The steric properties of the complex center can be tuned by changing the substituent on the terphenyl. By carefully controlling the steric properties, different coordinating environments around the metal center can be achieved. Finally, Appendix B describes the reactivity of U(IV) phosphido complexes with organic azide and tert-butyl isocyanide.
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