Empowering the Base Metals: Rational Design of Homogeneous Catalysts for Hydrotreatment, and Reduction of Organic Unsaturates

• Author / Creator

  Bunquin, Jeffrey

• Hydrocarbon-soluble, low-coordinate, phosphoranimide-supported complexes of the base metals (iron, cobalt and nickel) were developed and evaluated for a range of stoichiometric and catalytic bond-forming and bond-breaking transformations. An unprecedented family of tetrametallic clusters of Co(I) and Ni(I), with formula [M(NPtBu3)]4, was synthesized in high yields and characterized by single crystal X-ray analysis and by solution-phase magnetic susceptibility measurements. These ancillary-ligand-free clusters exhibit high room-temperature magnetic susceptibility and are structurally unique; each metal center in the coplanar, tetranuclear core is linear, two-coordinate. A rare homoleptic, mononuclear, three-coordinate Co(III) d6 complex [Co(NPtBu3)3] was also synthesized in high yield and characterized using NMR spectroscopy and single crystal X-ray analysis.

  The ancillary ligand-free “surface-mimetic” clusters constitute a new class of high-activity homogeneous catalysts for room-temperature hydrogenation and hydrosilylation of polar and nonpolar unsaturates. Both clusters hydrogenate unactivated and sterically hindered alkenes and alkynes to the corresponding alkanes (1 atm H2). These clusters also hydrosilylate a range of functionalized aldehydes and ketones, utilizing a diverse scope of organosilyl hydride reagents. Radical clock hydrosilylation studies revealed differences in the mechanistic behavior of the isostructural Co(I) and Ni(I) clusters: the cobalt catalyst functions through a non-radical mechanism while nickel catalyst shows contributions from radical-type pathway(s).

  More importantly, both Co(I) and Ni(I) clusters are high-activity catalysts for the hydrogenolysis of carbon-heteroatom bonds under remarkably mild conditions (90-150 °C, 1 atm H2). Both clusters constitute the very first set of homogeneous, first-row transition metal catalysts for the mild-condition hydrodesulfurization of dibenzothiophene derivatives. The tetranuclear clusters also activate C-O bonds in symmetrical and unsymmetrical aryl ethers and dibenzofuran-type substrates, producing aromatic hydrocarbons and phenols. In some preliminary experiments, the Ni(I) cluster and the mononuclear Co(III) complex were shown active for the hydrogenolysis of C-N bond in neutral and basic aromatic nitrogenous substrates. Results of hydrogenolysis studies show catalyst selectivity for the direct hydrogenolysis of Caryl–X bonds (X = S, O, N) with complete suppression of aromatic ring hydrogenation pathways. Lastly, the both Co(I) and Ni(I) clusters effect the deoxygenation of a range of functionalized carbonyl substrates, producing unique mixtures of hydrocarbons under mild hydrosilylation conditions.

• Subjects / Keywords

  • Nickel
  • Hydrosilylation
  • Catalysis
  • Hydrogenation
  • Hydrotreatment
  • Organometalics
  • Hydrodesulfurization
  • Phosphorane imide
  • Cobalt

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3377636K

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.