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Synthesis and Reductive Chemistry of Bimetallic Complexes of the Rare-Earth Metals

  • Author(s): Dumas, Megan T
  • Advisor(s): Evans, William J.
  • et al.

This dissertation describes an expansion of reductive rare-earth metal chemistry focused on the synthesis and reduction of bimetallic complexes with the goal of examining metal-metal bond formation between two rare-earth ions. While rare-earth species with definitively identifiable metal-metal bonds were not obtained, this thesis analyzes the properties and reductive chemistry of a variety of bimetallic complexes of the rare-earth metals. Chapter 1 describes the synthesis of the bimetallic bridged-hydride precursors, [Cp′2Ln(μ–H)(THF)]2. (Ln = Y, Tb, Dy; Cp′ = C5H4SiMe3). Chapter 2 describes their reduction with potassium graphite to form dark-colored products characteristic of Ln(II) ions. The room temperature EPR spectrum of the yttrium product contains a broad signal at g = 1.983. Chapter 3 describes the synthesis and reduction of the methyl analogs of the hydrides, [Cp′2Ln(μ–CH3)]2 (Ln = Y, Tb, Dy). Reduction of these complexes generates dark-colored solutions and the yttrium complex has an axial EPR spectrum at 77 K consistent with an Y(II) ion. In Chapter 4, reduction with KC8 of the ansa-metallocene hydride, [CpAnY(μ–H)(THF)]2, [CpAn = Me2Si(C5H3SiMe3)2], is described. This generates [K(crypt)][CpAnY(μ–H)]2, the first structurally characterizable reduced bimetallic yttrium metallocene. This dark red-brown complex has a two-line EPR spectrum at room temperature characteristic of an Y(II) ion. The structural and spectroscopic characterization of the analogous reduced bimetallic dysprosium complex, [K(18-crown-6)(THF)2][CpAnDy(μ–H)]2, is presented in Chapter 5. Chapter 6 describes a new class of bimetallic complexes, {(C5Me5)2Ln[μ–O(C6H4)μ–NC]}2 (Ln = Y, Tb, Dy), discovered through the ring opening of benzoxazole to form a rare example of a bridging 2-isocyanophenolate ligand. Reduction of {(C5Me5)2Y[μ–O(C6H4)μ–NC]}2 forms a red-purple solution with an EPR spectrum consistent with reduction of the bridging ligand. Chapter 7 describes the spectroscopic characterization of the reduction of three additional classes of yttrium metallocene hydrides, (C5Me5)2Y(μ–H)(μ–η1:η5–CH2C5Me4)Y(C5Me5), [(C5Me4H)2Y(μ–H)]2, and {[SiMe2(C5Me4)2]Y(μ–H)}2. The reduction of [(C5Me4H)2Y(μ–H)]2, and the tuckover complex (C5Me5)2Y(μ–H)(μ–η1:η5–CH2C5Me4)Y(C5Me5) with KC8 provided EPR spectra at 77 K consistent with reduction. The attempted reduction of {[SiMe2(C5Me4)2]Y(μ–H)}2 with KC8 in toluene was not successful. Chapter 8 describes the synthesis of complexes with an unusual triphenylboranecarbonitrile ligand, (NCBPh3)1−, LnCl2(THF)4(NCBPh3) (Ln = Y, Dy). Exploration of this reaction led to the crystallization of LnCl2(THF)5[BPh4], [Ln(H2O)6Cl2]Cl (Ln = Y, Dy), [NEt4][PhBOBPhOBPh2], [K(crypt)]2[PhBOBPhOBPh2][BPh2(Me)(CN)], and [NEt4][Ph2BOBPh2CN].

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