<p> The abstract is not available from PDF copy and paste.</p>

<p>Uranium oxides are the most common form of uranium in both nuclear waste and in the environment. As such, the uranyl <i>di</i>oxo framework (UO₂)²⁺, and its strong U&equiv;O triple bond interactions, dominate the research. It is well-established the oxo ligands are thermodynamically robust and kinetically inert, thus making the uranyl fragment very unreactive. Interestingly, microbial activation of uranyl is a vital component in the sequestration of uranium in uranium-contaminated environments, likely requiring functionalization of the normally unreactive oxo ligands. However, there is little evidence available for the mechanism of this process and model systems describing this chemistry are scarce. </p><p> In contrast to uranium oxide chemistry, the chemistry of uranium and the softer Group 16 elements (e.g., S, Se, Te) is substantially less developed even though it has been proposed that separation of radiotoxic fission products in spent nuclear fuel would be greatly enhanced by employment of soft-donor extractants. This postulation has been rationalized on the basis of increased covalency within actinide-chalcogenide bonds. As such, developing soft-donor, heteroatom-substituted analogues of the uranyl moiety will allow for greater insight into the extent of <i>f</i>-orbital participation, and thus, covalency, within uranium-ligand multiple-bonding frameworks and facilitate the design of novel waste extractants. </p><p> This first part of this dissertation describes the activation of uranyl via reductive silylation. By employing strongly donating equatorial co-ligands, the nucleophilic nature of the oxo-ligands is exploited by addition of Me₃SiI. This substrate promotes reduction to U(V) and silylation of <i> both</i> oxo ligands. Subsequent addition of Lewis bases results in facile reduction to U(IV) and clearly displays the complete transformation of the uranyl fragment to better described 'alkoxide-like' complexes. </p><p> The second part of the dissertation attempts to expand the library of uranium-chalcogenide complexes, targeting molecules which exhibit multiple-bonding ligation modes reminiscent of uranyl. In this regard, a highly reducing U(III) starting material was employed and found to readily activate chalcogen sources to yield several complexes which exhibit <i>terminally</i>-bound chalcogenide ligands. These complexes were fully characterized to better understand the electronic nature of the uranium chalcogenide bonds.</p>

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<p> Transition-metal catalysis has enabled the development of an unprecedented number of mild and selective C-C bond-forming reactions. We sought to access the reactivity of palladium and nickel catalysts for two types of transformations: conjugate allylations and sp³-sp³ cross-coupling reactions. </p><p> Conjugate allylation of malononitriles was evaluated with N-heterocyclic carbene-ligated palladium complexes. The allylation was found to yield a variety of mono-allylated products. These results are in contrast to the bis-allylation of malononitriles using other palladium-based catalysts. Additionally, conjugate addition of &alpha;,&beta;-unsaturated <i>N</i>-acylpyrroles was found to be accelerated in the presence of sulfoxide substitution on the pyrrole ring. These substrates are lead compounds for the development of an enantioselective allylation reaction. </p><p> Transition metal-catalyzed cross-coupling reactions have become standard practice in organic synthesis. Recent advances in alkyl-alkyl couplings have been transformative in the way organic chemists approach the construction of target molecules. This dissertation focuses on the development of stereospecific sp³-sp³ cross-coupling reactions. We discovered that in the presence of nickel catalysts, secondary benzylic ethers were found to undergo stereospecific substitution reactions with Grignard reagents. Reactions proceeded with inversion of configuration and high stereochemical fidelity. This reaction allows for facile enantioselective synthesis of biologically active diarylethanes from readily available optically enriched carbinols. </p><p> Subsequently, this reaction was expanded to dialkylzinc reagents and the first stereospecific Negishi cross-coupling reaction of secondary benzylic esters was developed. A series of traceless directing groups were evaluated for their ability to promote cross-coupling with dimethylzinc. Esters with a chelating thioether derived from commercially-available 2-(methylthio)acetic acid were found to be the most effective. The products were formed in high yield and with excellent stereospecificity. A variety of functional groups were tolerated in the reaction including alkenes, alkynes, esters, amines, imides, and <i>O</i>-, <i>S</i>-, and <i>N</i>-heterocycles. The utility of this transformation was highlighted in the enantioselective synthesis of a retinoic acid receptor (RAR) agonist.</p>

<p> Several metal-tetracyanoethylene (TCNE) compounds, including the [bis(pentamethylcyclopentadienyl)iron(III)][tetracyanoethylene], [FeCp*²][TCNE], family of molecule-based magnets and two cyanide based MBMs were investigated by pressure dependent DC magnetic measurements. The 0-D electron transfer salts: [FeCp*²][TCNE], ferromagnetic [FeCp*²][TCNQ] (TCNQ = 7,7,8,8-tetracyanoquinodimethane), metamagnetic [FeCp*²][TCNQ], [FeCp*²][HCBD] (HCBD = hexacyanobutadiene), and [FeCp*²][DDQ] (DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone) exhibited an array of magnetic behavior both at ambient and applied pressure. [FeCp*²][TCNE] and [FeCp*²][HCBD] exhibited weak ferromagnetism above 4.2 and 3.1 kbar, respectively. The ferromagnetic polymorph of [FeCp*²][TCNQ] displayed linear increase to the critical temperature, <i>T</i>_c, and the bifurcation temperature, <i>T</i>_b, reaching 5.01 and 5.46 K, respectively at 10.3 kbar. The coercive field, <i>H</i>_cr, displayed exponential-like increase, reaching 550 Oe at 10.3 kbar. The metamagnetic polymorph of [FeCp*²][TCNQ] displayed linear increase of the Tc at low applied pressure, reaching 2.90 at 2.9 kbar, then transitioned to a paramagnetic state at further applied pressure. [FeCp*²][HCBD] transitioned from a paramagnetic state at ambient pressure to a weak ferromagnetic state at 3.1 kbar with a <i>T</i>_c, <i>H</i>_cr, and <i>H</i>_c of 2.46 K, 25 Oe, and 2,200 Oe, respectively. The <i>T</i>_c and <i>H</i>_c then increased linearly with further applied pressure to 4.80 K and 10,000 Oe, while the <i>H</i>_cr increased exponentially to 795 Oe, at 11.4 kbar. [FeCp*²][DDQ] exhibited paramagnetic behavior at ambient and applied pressures up to 9.2 kbar. The structurally related 2-D Mn^II(TCNE)I(H₂O) and 3-D MnII(TCNE)_3/2(I₃)_1/2, showed significant increases to the <i> T</i>_c, T_b, and <i>H</i>_cr with applied pressure. A high- and low-pressure regions were observed for Mn^II(TCNE)I(H₂O). 2-D [Ru₂(O₂CBu^t)₄][M(CN)₆] &middot; H2O (M = Fe, Cr) displayed suppression of hysteretic properties at high applied pressure and irreversibility of the suppression. A Mean Field (MF) analysis of three structurally related non-cubic Prussian blue analogues (PBA) was performed to assess the intensity of their coupling modes. These values were framed by the reinvestigation of several known cubic PBAs and comparing the coupling intensities, as well as evaluating the MF theory in the context of these structures as several had been evaluated by other means.</p>