UC Irvine

This Dissertation details a series of investigations into the factors that influence the isolation, properties, and reactivity of low oxidation state rare-earth and actinide metal coordination complexes through exploratory synthesis. Specifically, the role that both steric and electronic effects play on rare-earth and actinide metal chemistry is explored through subtle variations in the ligands employed. Chapter 1 provides an introduction into the landscape of low oxidation state f-element chemistry in the context of this work and describes the importance of a better understanding of how steric and electronic effects influence the isolation and properties of low oxidation state rare-earth and actinide metal coordination complexes. Chapter 2 describes the unusual and unexpected products isolated when the pentamethylcyclopentadienide reagent used in the synthesis of (C5Me5)2Sm(THF)2 starting from SmI2(THF)2 is replaced with the chemically similar tetramethylcyclopentadienide reagent. Chapter 3 describes the synthesis of tris(mono-silylcyclopentadienyl) Th(III) and Th(II) complexes not available with the tri-methylsilyl substituted ligand, (C5H4SiMe3)1−, that can be synthesized with the tri-isopropylsilyl substituted (C5H4SiiPr3)1− ligand. The dramatic increase in thermal stability as a result of this substitution ultimately led to the crystallographic characterization of these rare classes of thorium complexes. Chapter 4 explores a different Th(III) system, specifically the tetrakis(aryloxide) Th(III) complexes, which are unexpectedly square planar. The role that steric and electronic effects play in the isolation of this rare class of 6d1 square planar Th(III) complexes is probed by varying the ortho and para substituents of the aryloxide ligands. Chapter 5 details attempts to synthesize Th(II) complexes in the bis(cyclopentadienyl) amidinate ligand environment and an investigation into the synthesis of other low oxidation state bis(cyclopentadienyl) thorium amidinate complexes as candidates for reduction to Th(II). Chapter 6 extends the coordination chemistry of the (C5H4SiiPr3)1− ligand from thorium as described in Chapter 3 to uranium and the rare-earth metals to evaluate the importance of steric and electronic effects in isolating reduced uranium and rare-earth metal complexes. Chapter 7 examines the effect of switching the tri-methylsilyl substituent in the [C5Me4(SiMe3)]1− ligand to the phenylsilyl substituents SiMe2Ph and SiMePh2 with regards to Mg(II) and U(IV) chemistry. The unusual preference for forming magnesocenes is described. Chapter 8 explores the U(III) and U(IV) coordination chemistry of the [C5Me4(SiMe2tBu)]1− ligand in efforts to synthesize more soluble organouranium complexes. The complexes generated were found to be more challenging to crystallize and purify and the ligand promoted polymorphism. Chapter 9 surveys the synthesis and characterization of bis(cyclopentadienyl) Sc(III) halide complexes to increase the number of bis(cyclopentadienyl) Sc(III) halide complexes available for reduction to Sc(II) compounds. Chapter 10 applies some of the work described in Chapter 9 and details the reduction studies of the bis(cyclopentadienyl) Sc(III) halide complex [C5Me4(SiMe2tBu)]2ScI to synthesize the first example of a linear Sc(II) metallocene. The spectroscopy, reactivity, and an investigation into the factors that enforce the linearity are discussed. Appendix A details an investigation into the unusual reaction of (C5Me5)2Y(μ-Ph)2BPh2 and NaC≡CH which has yielded an unusual bridging butatrienylidene ligand presumably formed from a C–C coupling reaction of two (C≡CH)1− ligands. Appendix B describes a study on the coordination chemistry of the (C5Me4SiMe3)1− ligand with thorium which has led to a rare example of a double tuck-in thorium metallocene. Appendix C extends the coordination chemistry of the (C5Me4SiMe3)1− ligand to Sm, Yb, and Eu and investigates the reactivity of the generated divalent metallocenes with 2,2′-bipyridine and 2,2′;6′,2″-terpyridine. Finally, Appendix D contains a table of the crystallographic data collected throughout the course of the work described in this Dissertation including information about unit-cell parameters.