UC Irvine

This dissertation focuses on the utilization of uncommon ligands for the stabilization of rare-earth metal complexes in unusual oxidation states (rare-earth metal = Y, Sc, and the lanthanides). Discussed here are the syntheses and spectroscopic and crystallographic characterization of complexes of these ligands and an evaluation of their value in stabilizing unusual oxidation states. An introduction to the nuances of rare-earth metal coordination chemistry, details of the redox chemistry of these metals and the definitions of “traditional” 4fn+1 and “nontraditional” 4fn5d1 rare-earth metal ions in the +2 oxidation state can be found in Chapter 1.Chapter 2 discusses the coordination chemistry of the hexa-iso-propyl-terphenylthiolate ligand with various lanthanide metals. In this Chapter, the synthesis of new La(II), Nd(II) and Tm(II) complexes this thiolate ligand are described as well as their characterization by analytical techniques including EPR spectroscopy and density functional theory. Use of this ligand with lanthanum led to the formation of a long-lasting 4f05d1 Ln(II) species with a very small eight-line hyperfine coupling constant of 67.3 MHz. Chapters 3 and 4 are concerned with the electron-deficient alkoxide analog, di(mesityl)boroxide, (OBMes2)– (Mes = C6H2-2,4,6-Me3), and the various lanthanide oxidation states that it can support. In Chapter 3, the (OBMes2)– ligand was explored as a possible less- electron-rich ligand that may better coordinate the less-electropositive +2 oxidation state lanthanides. This ligand was shown to coordinate to +3 lanthanide ions in a plethora of modalities. Structural and spectroscopic information is described for many complexes including dimeric compounds like [(Mes2BO)2Ln(μ-OBMes2)]2 (Ln = La, Ce, Nd, Gd) and monomers like 1Ln(OBMes2)3(THF)3 (Ln = La, Nd), as well as mixed ligand complexes like Nd(OBMes2)(NR2)2(THF). Although reduction of these di(mesityl)boroxide complexes did not result in identifiable Ln(II) complexes, crystallographic analysis of the complexes such as K(μ- Mes2BO)3Sm(OBMes2)(THF) led to the discovery that many of the complexes are able to form “ate-salts” in which four (OBMes2)– ligands bind to a single Ln(III) ion in a compound that is charge-balanced by a potassium countercation that is encapsulated by ligands. However, a complex of a +2 lanthanide ion was isolated for samarium from reactions with SmI2: the tetrameric Sm(II) oxo cluster, Sm4(OBMes2)6(μ4-O). This complex reacts with the xylyl isocyanide CNXyl (Xyl = C6H3-2,6-Me2) to form an unusual pair of closely related cocrystallized Sm(III) complexes, Sm(OBMes2)3(CNXyl)(Et2O) and Sm(OBMes2)3(CNXyl)3. This potassium-encapsulation theme is the basis of Chapter 4 which explores the di(mesityl)boroxide ligand in heteroleptic K(μ-Mes2BO)2Ln(NR)2)2 (Ln = Ce, Pr, Nd, Sm, Tb; R = SiMe3) complexes as starting materials to form Ln(IV) complexes. For K(μ- Mes2BO)2Ce(NR)2)2, treatment with AgI led to the elimination of KI and Ag metal, along with the formation of a new tetravalent cerium complex, CeIV(OBMes2)2(NR2)2. Treatment of these heteroleptic complexes with the strong oxidizing agent, “magic blue,” [N(C6H4-4-Br)3][SbCl6], led to characterization of the unexpected complex complex Sb(OBMes2)3. Additionally, another Ce(IV) complex could be formed from the treatment of CeIV(OTf)4 with four equivalents of KOBMes2. Chapter 5 of this dissertation describes the use of the di-tert-butylmethylsilanide ligand, [ (SiMetBu2)–, to make the “ate-salt” (Na(THF)3Cl-μ)Y(SiMetBu2)3(THF). This is the first example of a rare-earth metal complex containing three Y-Si bonds. 2 Chapter 6 describes the use of a ligand isoelectronic to the widely used cyclopentadienide and its derivatives, the tripodal oxygen donor ligand, tris(2-oxo-1-tert- butylimidazolyl)hydroborato (TpOtBu). The formation of YbII(TpOtBu)2 shows that the ligand can coordinate to a traditional Ln(II) ion. In Appendix A, the synthesis and spectroscopic information on the complex Bi(OBMes2)3 are described in detail. Finally, in Appendix B, the synthesis and characterization of heteroleptic terphenyl complexes Y(SAriPr6)I2(THF)3 and Sm(SAriPr6)(NPh2)I(THF), as well as the samarium bisamide iodide, Sm(NPh2)2I(THF)2) are described.