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Scholarly Works (21 results)

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UC Berkeley Electronic Theses and Dissertations (2019)

Chapter 1. Previous work with group 5 imido β-diketiminates and rhenium terminal oxo complexes is summarized, which in combination provide the theoretical basis for the subsequent chapters. The overarching hypothesis and goals of this work are stated.

Chapter 2. Synthetic access to the first rhenium oxo β-diketiminate is achieved. Subsequently, the oxygen atom transfer (OAT) reactivity of this complex is gauged. It is determined that OAT from this complex is limited to trialkylphosphines of a moderate steric profile (e.g. PEt3), as small trialkylphosphines (e.g. PMe3) bind strongly to the metal center, and larger phosphines (e.g. PPh3) are kinetically limited due to the encumbering β-diketiminate ligand. Nitrene transfer from the β-diketiminate ligand to the metal is also observed, implying an ancillary limitation of this ligand in low valent rhenium complexes at high temperatures.

Chapter 3. Attempts to incorporate a cyclopentadienyl ligand into the rhenium oxo β-diketiminate system using NaCp led to the isolation of an olefin-supported rhenium(III) terminal oxo complex. It was found that using SnCp2 rather than NaCp leads to the intended rhenium(V) oxo Cp complex. The reactivity of this rhenium(V) complex suggested that both the Cp ligand and oxo ligand are susceptible to nucleophilic attack, yielding a variety of rhenium(III) complexes. Computational studies suggest some degree of metal-ligand conjugation (“π-loading”) exists between the Cp and oxo ligands in the starting rhenium(V) complex, which supports the observations made during reactivity studies.

Chapter 4. The oxygen atom transfer reactivity of a rhenium(III) terminal oxo β-diketiminate complex is evaluated. It is shown that this compound will only transfer its oxo ligand to electrophilic reagents (e.g. isocyanides and CO) rather than nucleophilic ones (e.g. PMe3). A number of rhenium(I) isocyanide and carbonyl complexes are isolated as products of the oxygen atom transfer process. In all, the results suggest that the oxo moiety of the starting rhenium(III) complex behaves as a nucleophile, and has no demonstrable electrophilic character.

Chapter 5. Reduction of a cationic rhenium(V) oxo Cp β-diketiminate with metallic sodium yields an anionic rhenium(I) complex that is both strongly reducing and basic. Accordingly, the corresponding neutral rhenium(II) and rhenium(III) hydride complexes are isolated following oxidation and protonation, respectively, of the anionic compound. Combination of the anionic rhenium(I) compound with ZnCl2 formed a tetrametallic Re(I)-Zn(I)-Zn(I)-Re(I) complex where the four metal centers are arranged in a nearly linear fashion. This compound is the first example of a Zn(I) compound to be supported exclusively by bonding to other metal centers. Computational and reactivity studies of this tetrametallic compound are also presented.

    Cover page: Diverse Reactivity of Rhenium β-Diketiminates
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    UC Berkeley Previously Published Works (2020)
    A lithiated m-terphenyl ligand bearing fluorine atoms at the ortho positions of the flanking aryl rings was synthesized and characterized using single crystal X-ray diffraction, variable-temperature multinuclear NMR spectroscopy, and computational methods. Changes in 1JC,F on coordination to lithium as a spectroscopic observable parametrizing the strength of the C-F···Li interaction are described, and a general, qualitative relationship between C-F bond lengths, Δ1JC,F values, and the extent of C-F bond activation as a result of Lewis acid coordination is proposed.
      Cover page: Perturbation of 1 J C,F Coupling in Carbon–Fluorine Bonds on Coordination to Lewis Acids: A Structural, Spectroscopic, and Computational Study
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      UC Berkeley Previously Published Works (2017)
      We report the synthesis and reactivity of paramagnetic heterometallic complexes containing a Ti(iii)-μ-H-Al(iii) moiety. Combining different stoichiometries amounts of Cp2TiCl and KH3AlC(TMS)3 (Cp = cyclopentadienyl, TMS = trimethylsilyl) resulted in the formation of either bimetallic Cp2Ti(μ-H)2(H)AlC(TMS)3 (2) or trimetallic (Cp2Ti)2(μ-H)3(H)AlC(TMS)3 (3) via salt metathesis pathways. While these complexes were indefinitely stable at room temperature, the bridging hydrides were readily activated upon exposure to heteroallenes, heating, or electrochemical oxidation. In each case, formal hydride oxidation occurred, but the isolated product maintained the +3 oxidation state at both metal centers. The nature of this reactivity was explored using deuterium labelling experiments and Density Functional Theory (DFT) calculations. It was found that while C-H activation from the Ti(iii) bimetallic may occur through a σ-bond metathesis pathway, chemical oxidation to Ti(iv) promotes bimolecular reductive elimination of dihydrogen to form a Ti(iii) product.
        Cover page: Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity
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        UC Berkeley Previously Published Works (2020)
        A multicomponent reaction among dipyrranes, aryl-propargyl aldehydes, and p-chloranil leading to 10-(benzofuran-2-yl)corroles is described. p-Chloranil was identified as a crucial reagent playing a twofold role: an oxidant taking part in the formation of the corrole macrocycle and a component undergoing heteroannulation to the incipient 10-arylethynylcorrole. A series of corroles bearing persubstituted benzofuran-2-yl moieties have been synthesized, and their fundamental electronic properties have been studied via UV-vis absorption and fluorescence spectroscopies.
          Cover page: Access to Corrole-Appended Persubstituted Benzofurans by a Multicomponent Reaction: The Dual Role of p‑Chloranil
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          UC Berkeley Previously Published Works (2016)
          The first synthesis of anion capped cerium corrole complexes is reported. Unusual clustering of the lanthanide corrole units has been found and the degree of aggregation can be controlled by the choice of the capping ligand. A polymeric structure 1a, with the general formula [Cor-Ce(THF)-Cp-Na]n (Cor = 5,15-bis(2,4,6-trimethylphenyl)-10-(4 methoxyphenyl)-corrole, THF = tetrahydrofuran), is formed using sodium cyclopentadienide (NaCp) and a dimeric structure 2a, with the general formula [Cor-Ce-Tp]2, is formed when potassium tris(pyrazolyl)borate (KTp) is used. Encapsulation of the counter-cation leads to the isolation of the monomeric structures 1b and 2b, with the general formulas [AM(2.2.2-cryptand)][Cor-Cp-X] (AM = Na or K, X = Cp or Tp). The structural and spectroscopic properties of the complexes have been investigated.
            Cover page: Control of clustering behavior in anionic cerium( iii ) corrole complexes: from oligomers to monomers
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            UC Berkeley Previously Published Works (2018)
            The toxicity of heavy metals such as lead (Pb), cadmium (Cd) and tin (Sn) has long been known but accidental exposures of large populations to these elements remain unfortunately a topical issue. Chelating agents against Pb, Cd, or Sn poisoning are still limited to classical ligands such as ethylenediamine tetraacetic acid (EDTA). Here, we evaluate the ability of 3,4,3-LI(1,2-HOPO) (L4-), an octadentate ligand currently under evaluation for actinide decorporation, to bind Pb, Cd and Sn metal ions in aqueous solutions. This ligand forms 1:1 complexes with Pb(ii), Cd(ii) and Sn(iv) as well as bimetallic 2:1 species with Pb(ii) and Cd(ii), all of which were characterized by high resolution mass spectrometry and spectrophotometric titrations. The 3,4,3-LI(1,2-HOPO) ligand exhibits an extreme affinity for Sn(iv) ions (logβ110 > 40), with the complex remaining stable from highly acidic conditions to alkaline media (from 3 M HCl to pH 8). Single crystals of the neutral complex [SnIV3,4,3-LI(1,2-HOPO)·3H2O] were obtained and its structure determined, revealing a chiral conformation. Although not initially designed for hexacoordinated metals such as Pb(ii) and Cd(ii), the octadentate ligand shows promise for the in vitro or in vivo sequestration of toxic heavy metals, as evidenced by decorporation experiments performed in mice contaminated with 210Pb(ii) and treated with either EDTA or 3,4,3-LI(1,2-HOPO).
              Cover page: Toxic heavy metal – Pb, Cd, Sn – complexation by the octadentate hydroxypyridinonate ligand archetype 3,4,3-LI(1,2-HOPO)
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              UC Berkeley Previously Published Works (2021)
              Salt metathesis reactions between a low-valent rhenium(i) complex, Na[Re(η5-Cp)(BDI)] (BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate), and a series of amidinate-supported tetrylenes of the form ECl[PhC(NtBu)2] (E = Si, Ge, Sn) led to rhenium metallotetrylenes Re(E[PhC(NtBu)2])(η5-Cp)(BDI) (E = Si (1a), Ge (2), Sn (4)) with varying extents of Re-E multiple bonding. Whereas the rhenium-stannylene 4 adopts a σ-metallotetrylene arrangement featuring a Re-E single bond, the rhenium-silylene (1a) and -germylene (2) both engage in π-interactions to form short Re-E multiple bonds. Temperature was found to play a crucial role in reactions between Na[Re(η5-Cp)(BDI)] and SiCl[PhC(NtBu)2], as manipulation of reaction conditions led to isolation of an unusual rhenium-silane, (BDI)Re(μ-η5:η1-C5H4)(SiH[PhC(NtBu)2]) (1b) and a dinitrogen bridged rhenium-silylene, (η5-Cp)(BDI)Re(μ-N2)Si[PhC(NtBu)2] (1c), in addition to 1a. Finally, the reaction of Na[Re(η5-Cp)(BDI)] with GeCl2·dioxane led to a rare μ2-tetrelido complex, μ2-Ge[Re(η5-Cp)(BDI)]2 (3). Bonding interactions within these complexes are discussed through the lens of various spectroscopic, structural, and computational investigations.
                Cover page: σ or π? Bonding interactions in a series of rhenium metallotetrylenes
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                UC Berkeley Previously Published Works (2019)
                Homoleptic uranium(IV) amidate complexes have been synthesized and applied as single-source molecular precursors for the chemical vapor deposition of UO2 thin films. These precursors decompose by alkene elimination to give highly crystalline phase-pure UO2 films with an unusual branched heterostructure.
                  Cover page: Chemical Vapor Deposition of Phase‐Pure Uranium Dioxide Thin Films from Uranium(IV) Amidate Precursors
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                  UC Berkeley Previously Published Works (2019)
                    Cover page: Chemical Vapor Deposition of Phase‐Pure Uranium Dioxide Thin Films from Uranium(IV) Amidate Precursors
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                    UC Berkeley Previously Published Works (2020)
                    The bis(imido) complexes (BDI)Nb(N t Bu)2 and (BDI)Nb(N t Bu)(NAr) (BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate; Ar = 2,6-diisopropylphenyl) were shown to engage in 1,2-addition and [2 + 2] cycloaddition reactions with a wide variety of substrates. Reaction of the bis(imido) complexes with dihydrogen, silanes, and boranes yielded hydrido-amido-imido complexes via 1,2-addition across Nb-imido π-bonds; some of these complexes were shown to further react via insertion of carbon dioxide to give formate-amido-imido products. Similarly, reaction of (BDI)Nb(N t Bu)2 with tert-butylacetylene yielded an acetylide-amido-imido complex. In contrast to these results, many related mono(imido) Nb BDI complexes do not exhibit 1,2-addition reactivity, suggesting that π-loading plays an important role in activating the Nb-N π-bonds toward addition. The same bis(imido) complexes were also shown to engage in [2 + 2] cycloaddition reactions with oxygen- and sulfur-containing heteroallenes to give carbamate- and thiocarbamate-imido complexes: some of these complexes readily dimerized to give bis-μ-sulfido, bis-μ-iminodicarboxylate, and bis-μ-carbonate complexes. The mononuclear carbamate imido complex (BDI)Nb(NAr)(N( t Bu)CO2) (12) could be induced to eject tert-butylisocyanate to generate a four-coordinate terminal oxo imido intermediate, which could be trapped as the five-coordinate pyridine or DMAP adduct. The DMAP adducted oxo imido complex (BDI)NbO(NAr)(DMAP) (16) was shown to engage in 1,2-addition of silanes across the Nb-oxo π-bond; this represents a new reaction pathway in group 5 chemistry.
                      Cover page: 1,2-Addition and cycloaddition reactions of niobium bis(imido) and oxo imido complexes
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