Date of Award

2026-08-01

Degree Name

Doctor of Philosophy

Department

Chemistry

Advisor(s)

Skye Fortier

Abstract

Organometallic chemistry has been pivotal for defining the redox properties, reactivity, and molecular bonding of the actinides. This information is critical as actinides are a persistent component of nuclear waste streams and contain isoradial lanthanide contaminants, complicating their isolation. Therefore, it is necessary to define the uniqueness of each f-element in efforts to engineer more efficient nuclear waste separation techniques. Despite the great effort undertaken during the Manhattan Project, the actinides remain some of the least understood elements on the periodic table. This is further complicated by their complex electronic structure and pronounced relativistic effects, making them difficult to model computationally. This leaves a critical knowledge gap in our understanding of the actinides, particularly how to precisely manipulate their electronic structure and what metal/ligand combinations invoke participation of the 5f and 6d orbitals in bonding. In efforts to expand our fundamental knowledge of the actinides our laboratory has focused on the utilization of the organo-phosphaylide ligand H2CP(Ar)3 and its coordination chemistry with actinide elements. We have synthesized the uranium complexes trans-UX4[CH2P(Ar)3]2 (X = Cl, Br, I; Ar = Ph, 3,5-tBu2C6H3 (tBuAr)) and mer-UI3[CH2P(tBuAr)3]3 demonstrating the competency of H2CP(Ar)3 to support uranium in multiple oxidation states. Additionally, we have expanded this chemistry to the transuranium elements Np and Pu, furnishing trans-NpCl4[CH2P(tBuAr)3]2 and mer-AnI3[CH2P(tBuAr)3]3 (An = Np, Pu), rare examples of transuranium compounds containing σ type hydrocarbyl interactions. A systematic comparison study of early versus later actinides, lanthanides, and transition metals will be presented to parse the differences in their bonding. Furthermore H2CP(Ar)3 contains two acidic protons and can be used to generate carbene and carbyne complexes. Treatment of the metallocene complex Cp*2UMe2 with two equiv. H2CPPh3 resulted in the isolation of the first example of an unsupported bis(carbene) complex of uranium Cp*2U[=C(H)PPh3]2. This complex contains two short U=C bonds and serves as a starting material for the mixed alkoxide-carbene complexes Cp*2U(OR)[=C(H)PPh3] (R = dipp C(CF3)3). Interestingly, we have seen a drastic change in nature in these uranium carbene complexes upon altering the ligand to the sterically bulky tBuAr group. This led to the kinetic trapping of the alky-carbene complex Cp*2U(Me)[=C(H)P(tBuAr)3], leading to the identification of an unprecedented uranium phosphacarbyne Cp*2U[≡CP(tBuAr)3], possessing a formal uranium-carbon triple bond. This species facilitates challenging reactivity such as C-H activation of inert substrates and an example of a single carbon atom insertion reaction. Kinetic studies and isotopic labeling support the formation of the phosphacarbyne and will be discussed herein.

Language

en

Provenance

Received from ProQuest

File Size

215 p.

File Format

application/pdf

Rights Holder

Frank Alexander MacGregor

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