Exploring the Use of Transition Metals in the Synthesis of Novel Metal-Ligand Multiple Bonds, Azide Complexes, and Unprecedented Reactivity with the Phosphaethynolato Reagent / Lauren N Grant.

Grant, Lauren N., author.
[Philadelphia, Pennsylvania] : University of Pennsylvania ; Ann Arbor : ProQuest Dissertations & Theses, 2019.
1 online resource (330 pages)
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Dissertations Abstracts International 81-04B.

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Chapter 1: Titanium Nitrides: Synthesis and Reactivity as Powerful Nucleophiles. In this chapter we explore the synthesis and reactivity of a titanium nitride anion complex [μ2-K(OEt2)]2[(PN)2Ti≡N]2, supported by two phosphino anilido ligands (PN− = (N-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide). Reactivity studies discussed include the synthesis of a series of imide moieties including rare examples such as methylimido, borylimido, phosphonylimido, and a parent imido. For the parent imide, using various weak acids allowed us to narrow the pKa range of the NH group to be between 26-36. The synthesis of the nitride was accomplished by reductively promoted elimination of N2 from the azide precursor (PN)2TiN3, whereas reductive splitting of N2 could not be achieved using the dinitrogen complex (PN)2Ti=N=N=Ti(PN)2 and a strong reductant. Complete N-atom transfer reactions could also be observed when the nitride complex was treated with ClC(O)tBu and OCCPh2 to form NCtBu and KNCCPh2, respectively, along with the terminal oxo complex, (PN)2Ti≡O, which was also characterized. A combination of solid state 15N NMR (MAS) in collaboration with Prof. Gang Wu and theoretical studies in collaboration with Prof. Balazs Pinter describe the shielding effect of the counter cation in the nitride anion as well as the discrete salt [K(18-crown-6)][(PN)2Ti≡N] and the putative anion [(PN)2Ti≡N]−, and also to probe the origin of the highly downfield 15N NMR resonance when shifting from dimer to monomer or to a terminal nitride (discrete salt). The upfield shift of the 15N nitride resonance in the 15N NMR spectrum was found to be linked to the K+ induced electronic structural change of the titanium-nitride functionality by using a combination of MO analysis and quantum chemical analysis of the corresponding shielding tensors.Chapter 2: Titanium Nitrides: Reactivity Spanning from the Generation of Nitridyl Radicals to Electrophilic Behavior. The titanium nitride complex discussed in Chapter 1 is instead showcased as a potent source of a nitridyl radical upon oxidation of the nitride with trityl chloride or iodine. This chapter presents a thorough mechanistic study that shows this nitridyl radical is capable of abstracting H-atoms from the PN ligand scaffold to make the rare parent imido discussed in Chapter 1. Alternatively, the nitridyl moiety is competent at oxidation of the phosphorous arm of the PN− ligand to form an asymmetric NPN' scaffold. A thorough reactivity study to detail all aspects of this mechanism is presented. Eventually, all intermediates result in the formation of halide complexes, (NPN')(PN)TiX (X = I, Cl), based on two mechanistic pathways. In addition to the oxidation of the nitride, we show that this nitridyl radical can also be formed from photolysis of the azido complex (PN)2TiN3, originally presented in Chapter 1. In addition to reactivity, we also explore matrix EPR studies of (PN)2TiN3 in collaboration with the de Bruin group. From a different reactivity viewpoint, we showcase that the titanium nitride can behave electrophilically in reactivity with isocyanides to form Ti(II) complexes [(PN)2Ti(NCNR)][K(solv)], where the R = Ad or tBu and the interaction of the countercation varies depending on the use of DME (not charge separated) or kryptofix (completely charge separated species). A discussion of the characterization of these complexes, complete with a discussion of other known Ti(II) chemistry is presented.Chapter 3: Extending Reactivity: Synthesis of A Molecular Zirconium Nitrido Superbase and A Transient Uranium Nitrido. In this chapter, the preparation and characterization of a zirconium complex having a terminally bound parent imide motif, (PN)2Zr≡NH is discussed, along with the zirconium nitride complex {(PN)2Zr≡N[μ2-Li(THF)]}2. This latter complex represents the first structurally characterized terminally bound Zr nitride complex. (PN)2Zr≡NH was prepared by reduction of trans-(PN)2Zr(N3)2 with KC8. Isotopic labeling and spectroscopic studies are described, which were prepared using the respective 15N enriched isotopologues, whereas solid-state structural studies confirmed some of the shortest Zr≡N distances known to date (Zr≡NH, 1.830(3) A; Zr≡N‒, 1.822(2) A). It was found that the nitride in {(PN)2Zr≡N[μ2-Li(THF)]}2 is super basic and in the range of −36 to −43 pKb units. Computational studies in collaboration with Prof. Balazs Pinter have been applied to probe the bonding and structure for this new class of zirconium-nitrogen multiple bonds. In addition to this study, the synthesis of U(III) and U(IV) complexes supported by the PN ligand is also discussed, which was conducted in collaboration with the Schelter and Baik labs. New complexes include the halide starting materials, (PN)2UI and (PN)2UCl2, which both yield (PN)2U(N3)2 when treated with NaN3. When reduced. (Abstract shortened by ProQuest).
Source: Dissertations Abstracts International, Volume: 81-04, Section: B.
Advisors: Mindiola, Daniel J.; Committee members: Neil Tomson; Patrick Walsh; Ivan Dmochowski.
Department: Chemistry.
Ph.D. University of Pennsylvania 2019.
Local notes:
School code: 0175
Mindiola, Daniel J., degree supervisor.
University of Pennsylvania. Department of Chemistry, degree granting institution.
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