UC Irvine

This dissertation details synthetic investigations into the role that steric factors play in the successful isolation of new molecular complexes containing low oxidation state rare-earth metal or actinide metal ions. Although a plethora of molecular complexes containing +2 ions for all the rare-earth metals (Ln; Ln = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), except radioactive Pm, have been isolated, the factors which determine the successful synthesis and subsequent stability of these Ln(II) complexes are unclear. Molecular complexes containing a +3 or +2 thorium metal ion are far more scarce. Consequently, the factors affecting their successful synthesis are even less understood. This dissertation aims to expand our understanding of low oxidation state rare-earth metal and actinide metal containing complexes. Chapter 1 provides a summary of the core properties of the rare-earth and actinide metals followed by a summary of the molecular chemistry that lays the foundation for the research to follow. Chapters 2 and 3 describe the capacity of the sterically demanding aryloxide ligand (OC6H2Ad2-2,6-tBu-4)1– (OAr*; Ad = 1-adamantyl) to support molecular complexes of both traditional 4fn+1 and non-traditional 4fn5d1 Ln(II) metal ions. Synthetic, spectroscopic, and crystallographic studies on the Ln(II) complexes [Ln(OAr*)3]1– for Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, and Yb and Ln(OAr*)2(THF)2 for Ln = Sm, Eu, and Yb are also described in these Chapters. Chapter 4 describes the ability of the di(silyl)-substituted cyclopentadienyl ligand C5H3(SiMe3)2 (Cp") to support the Sc(II) metallocene iodide complex [K(crypt)][Cp"2ScI]. Additionally, the steric profile and thermal stability of [K(crypt)][Cp"2ScIII] is compared to those of the crystallographically characterized Sc(II) bent metallocene Cpttt2Sc and putative Sc(II) species “Cp*2Sc” in this Chapter. Chapter 5 reports on the synthesis and characterization of two reduced-arene inverse sandwich complexes of thorium supported by the same di(silyl)-substituted Cp" ligand: [Cp"2Th][µ-η6:η6-C6H6), 1-Th, and [Cp"2Th][µ-η6:η6-C7H8), 2-Th. Chapter 6 discusses the syntheses of low oxidation state complexes of Y, Dy, and Lu supported by the chelating ansa-cyclopentadienyl ligand CpAn [CpAn = Me2Si[C5H3(SiMe3-3)2 (CpAn]. Appendices A and B expand the molecular chemistry of the OAr* ligand to thorium and bismuth, reporting the syntheses and crystallographic characterizations of BrThIV(OAr*)3 and Bi(OAr*)3, respectively. Appendix C details the crystal structures of the two aryloxide clusters Dy4(OAr*)4(THF)4(µ4-O)(µ2-O)6 and EuIIIxEuIIy(OAr*)6(µ6-O)(µ3-OH)a(µ3-O)x (x + y = 6; a + x = 4; y = 0–6; a = 0–4).