Steric control of redox events in organo-uranium chemistry: synthesis and characterisation of U(V) oxo and nitrido complexes

The synthesis and molecular structures of a U(V) neutral terminal oxo complex and a U(V) sodium uranium nitride contact ion pair are described. The synthesis of the former is achieved by the use of tBuNCO as a mild oxygen transfer reagent, whilst that of the latter is via the reduction of NaN3. Both mono-uranium complexes are stabilised by the presence of bulky silyl substituents on the ligand framework that facilitate a 2e- oxidation of a single U(III) centre. In contrast, when steric hindrance around the metal centre is reduced by the use of less bulky silyl groups, the products are di-uranium, U(IV) bridging oxo and (anionic) nitride complexes, resulting from 1e- oxidations of two U(III) centres. SQUID magnetometry supports the formal oxidation states of the reported complexes. Electrochemical studies show that the U(V) terminal oxo complex can be reduced and the [U(IV)O]- anion was accessed via reduction with K/Hg, and structurally characterised. Both the nitride complexes display complex electrochemical behaviour but each exhibits a quasi-reversible oxidation at ca. -1.6 V vs Fc+/0

Reduction Chemistry of Neptunium cyclopentadienide complexes: from structure to understanding

Neptunium complexes in the formal oxidation states II, III, and IV supported by cyclopentadienyl ligands are explored, and significant differences between Np and U highlighted as a result. A series of neptunium(III) cyclopentadienyl (Cp) complexes [Np(Cp)3], its bis-acetonitrile adduct [Np(Cp)3(NCMe)2], plus its KCp adduct K[Np(Cp)4] and [Np(Cp')3] (Cp' = C5H4SiMe3) have been made and characterised providing the first single crystal x-ray analyses of NpIII Cp complexes. In all NpCp3 derivatives there are three Cp rings in eta5-coordination around the NpIII centre; additionally in [Np(Cp)3] and K[Np(Cp)4] one Cp ring establishes a mu-eta1-interaction to one C atom of a neighbouring NpCp3 unit. The solid state structure of K[NpCp4] is unique in containing two different types of metal-Cp coordination geometries in the same crystal. NpIIICp4 units are found exhibiting four units of eta5-coordinated Cp rings like in the known complex [NpIV(Cp)4], the structure of which is now reported. A detailed comparison of the structures gives evidence for the change of ionic radii of ca. -8 pm associated with change in oxidation state between NpIII and NpIV. The rich redox chemistry associated with the syntheses is augmented by the reduction of [Np(Cp')3] by KC8 in the presence of 2.2.2 cryptand to afford the putative neptunium(II) K(2.2.2 cryptand)[Np(Cp')3] that is thermally unstable above -10 °C like its U and Th congeners. Together, these spontaneous and controlled redox reactions of organo-neptunium complexes, along with information from structural characterisation, show the relevance of organometallic Np chemistry to understanding fundamental structure and bonding in the minor actinides.JRC.G.I.5-Advanced Nuclear Knowledg

Mixed sandwich imido complexes of Uranium(V) and Uranium(IV): Synthesis, structure and redox behaviour

The mixed sandwich U(III) complex {U[η ^8 -C8H6(1,4-Si( iPr)3)2](Cp*)(THF)} reacts with the organic azides RN3 (R = SiMe3, 1-Ad, BMes2) to afford the corresponding, structurally characterised U(V) imido complexes {U[η ^8 -C8H6(1,4-Si( iPr)3)2](Cp*)(NR)}. In the case of R=SiMe3, the reducing power of the U(III) complex leads to reductive coupling as a parallel minor reaction pathway, forming R-R and the U(IV) azide-bridged complex{[U]}2(µ-N3)2, along with the expected [U]=NR complex. All three [U] =NR complexes show a quasi-reversible one electron reduction between -1.6 to -1.75 V, and for R= SiMe3, chemical reduction using K/Hg affords the anionic U(IV) complex K+ {U[η ^8 -C8H6(1,4-Si( iPr)3)2](Cp*)=NSiMe3} - . The molecular structure of the latter shows an extended structure in the solid state in which the K counter cations are successively sandwiched between the Cp* ligand of one [U] anion and the COTtips2 ligand of the next

Synthesis, Characterization and Reactivity of Organometallic Complexes of Uranium and Plutonium in the +2 and +3 Oxidation States

Synthesis, Characterization and Reactivity of Organometallic Complexes of Uranium and Plutonium in the +2 and +3 Oxidation StatesByCory J. WindorffDoctor of Philosophy in ChemistryUniversity of California, Irvine, 2017Professor William J. Evans, ChairThis dissertation focuses on the synthesis, characterization, and reactivity of unique organometallic complexes of uranium, plutonium, and the lanthanides in efforts to expand the limits of known redox chemistry of these elements. The results in this dissertation extend investigations of previously established reduction reactions involving these metal ions to extend them to more challenging systems. These reactions utilized the tri(cyclopentadienide) coordination environment examining the differences in the substitution pattern on the cyclopentadienide rings, particularly the Cp′′ ligand [Cp′′ = C5H3(SiMe3)–1,3]. In the course of these studies, the +2 oxidation state for plutonium was confirmed, and the most stable form of UII to date was isolated. To accomplish the plutonium chemistry, several surrogate syntheses were performed using lanthanides of similar size and reactivity to that of plutonium, namely cerium and neodymium. These experiments examined the electronic structure to compare and contrast the +2 oxidation state across the actinide series. In Chapter 1 29Si NMR spectra were recorded for a series of uranium complexes containing silicon and the data have been combined with results in the literature to determine if any trends exist between chemical shift and structure, ligand type, or oxidation state. Data on 48 paramagnetic inorganic and organometallic uranium complexes are presented. The survey reveals that although there is some overlap in the range of shifts of UIV complexes versus UIII complexes. In general UIII species have more negative shifts than their UIV analogs. The single UII example has the most negative shift of all at −322 ppm at 170 K. With only a few exceptions, UIV complexes have shifts between 0 and −150 ppm (vs. SiMe4) whereas UIII complexes resonate between −120 and −250 ppm. The small data set on UV species exhibits a broad 250 ppm range centered near 40 ppm. The data also show that aromatic ligands such as cyclopentadienide, cyclooctatetraenide, and the pentalene dianion, exhibit less negative chemical shifts than other types of ligands. Chapter 2 describes the synthesis of new molecular complexes of UII that were pursued to make comparisons in structure, physical properties, and reactivity with the first UII complex, [K(crypt)][Cp′3U], 21-U (Cp′ = C5H4SiMe3, crypt = 2.2.2-Cryptand). Reduction of Cp′′3U, 20-U, [Cp′′ = C5H3(SiMe3)2–1,3] with KC8 in the presence of crypt or 18-crown-6 generates [K(crypt)][Cp′′3U], 22-U, or [K(18-crown-6)(THF)2][Cp′′3U], 23-U, respectively. The UV/vis spectra of 22-U and 21-U are similar, and they are much more intense than those of UIII analogs. Variable temperature magnetic susceptibility data for 21-U and 22-U reveal a lower room temperature χMT value relative to the experimental value for the 5f 3 UIII precursors. Stability studies monitored by UV/vis spectroscopy show that 22-U and 23-U have t1/2 values of 20 and 15 h at room temperature, respectively, vs 1.5 h for 21-U. Complex 23-U reacts with H2 or PhSiH3 to form the uranium hydride, [K(18-crown-6)(THF)2][Cp′′3UH], 26. 21-U and 23-U both reduce cyclooctatetraene to form uranocene, (C8H8)2U, as well as the UIII byproducts [K(crypt)][Cp′4U], 28-U, and Cp′′3U, 20-U, respectively. In Chapter 3 Cp′4U, 37-U, was synthesized from (a) KCp′ and [Cp′3U(THF)][BPh4], 36, (b) Cp′3U, 8-U, and Cp′2Pb,30, and (c) [K(crypt)][Cp′4U], 28-U, and AgBPh4 and identified by X-ray crystallography as a rare example of a structurally-characterized tetrakis(cyclopentadienyl)UIV complex. The corresponding Th complex, Cp′4Th, 37-Th, was obtained from the direct combination of ThBr4(THF)4 with excess KCp′ in low yield. During the preparation of Cp′3UMe, 35, the precursor of the [Cp′3U(THF)][BPh4], 36, reagent used above, it was discovered that the reaction of Cp′3UCl, 33-U, and MeLi gives a mixture of Cp′3UMe, 35 and 33-U that can co-crystallize better than 35 in pure form. Although 35 typically is an oil, a mixture of 35 and 33-U forms single crystals that are suitable for X-ray crystallography and contain a 4:1 ratio of the compounds. Hence, forming a mixture provided a new way to get structural data on the oil, 35. 33-U and Cp′3UI, 34, were also crystallographically characterized for comparison with the Cp′3UMe/Cp′3UCl, 35/33 crystals. Chapter 4 examines the optimization of reaction conditions for milligram scale plutonium reactions. Starting from the metal, small-scale reactions of the Pu surrogates, La, Ce, and Nd, were explored. Oxidation of these lanthanide metals with iodine in ether or pyridine was studied and it was found that LnI3(Et2O)x, 39-Ln (x = 1.5–1.8), and LnI3(py)4, 40-Ln (py = pyridine, NC5H5), can be synthesized on scales ranging from 15 mg to 2 g. The THF adducts LnI3(THF)4, 41-Ln, were synthesized by dissolving 39-Ln in THF which was found to be preferable to synthesis from the metal in THF on this small scale. The viability of these small scale samples as starting materials for amide and cyclopentadienyl f–element complexes was tested by reacting in situ generated 39-Ln with KN(SiMe3)2, KCp′, Cp′′, and KC5Me4H. This produced Ln[N(SiMe3)2]3, 15-Ln, Cp′3Ln, 8-Ln, Cp′′3Ln, 20-Ln, and (C5Me4H)3Ln, 32-Ln. Small scale samples of Cp′3Ce, 8-Ce, and Cp′3Nd, 8-Nd, were reduced with potassium graphite (KC8) in the presence of crypt to check the viability for generation of crystallographically-characterizable LnII complexes, [K(crypt)][Cp′3Ln], 21-Ln (Ln = Ce, Nd). Similar reactions of Cp′′3Nd, 20-Nd, with KC8 in the presence of crypt gave [K(crypt)][Cp′′3Nd], 22-Nd, as a crystallographically characterizable complex.Chapter 5 combines and extends the chemistry described in Chapters 2 and 4 to plutonium. Over seventy years of chemical investigations have shown plutonium exhibits some of the most complicated chemistry in the periodic table. Six Pu oxidation states have been unambiguously confirmed (0, +3 to +7) and five different oxidation states can exist simultaneously in solution. The synthesis and characterization of a new formal oxidation state for plutonium, namely PuII in [K(crypt)][Cp′′3Pu], 22-Pu, is examined. The synthetic precursor, Cp′′3Pu, 20-Pu, is also synthesized and discussed, comprising the first structural characterization of a Pu–C bond. Absorption spectroscopy and DFT calculations indicate that the PuII ion has predominantly a 5f 6 electron configuration with some 6d-mixing. Reactivity studies show that 22-Pu reacts with AgBPh4 to reform 20-Pu in high yield

Social Media War on Journalism

This presentation will focus on Journalism in the 21st century. With the ever changing times in our digital age, social media has become the main medium in which we transmit and receive our news. With this newer medium also comes a set of uncharted ethical and legal issues that are constantly changing as we are able to have easier, quicker access to information worldwide. Through our research we have discovered several ethical dilemmas when it comes to the utilization of social media and journalists. Many times Journalists utilize their own social media accounts to spread their work. Able to constantly keep up with the changing news, social media platforms have become key. There is not always a concise agreement between a journalist and the media publication over whether the social media account is company owned or not. This leads to unclear decisions on what should be posted and what happens to the account once the journalist leaves the publication. We will explore cases where Journalists were sued for their alleged misuse of social media accounts. Eight out of ten journalists use social media in the course of their work. The presence of reporters on social media is an essential one, yet many journalists have been fired from their respective companies due to posts regarding their opinions on social media. A journalist being removed for expressing their opinion on a social media platform may be legally justified, but is it ethically right? After all, other citizens have the right to express their personal opinions without impediment. We will look at cases where journalists have been fired for their uses of social media and discuss the ethical (and legal) issues, and what these events may lead to in the future. Another issue at large is the right of journalists to utilize posts on social media for their own stories. Several issues of privacy invasion have been brought against major media publications because either permission was not asked or permission was denied to be able to use social media posts such as pictures and video. The question comes to mind whether these type of posts are for the private use of the social media user or are they public domain once published online

²⁹Si NMR Spectra of Silicon-Containing Uranium Complexes

²⁹Si NMR spectra have been recorded for a series of uranium complexes containing silicon, and the data have been combined with results in the literature to determine if any trends exist between chemical shift and structure, ligand type, or oxidation state. Data on 52 paramagnetic inorganic and organometallic uranium complexes are presented. The survey reveals that, although there is some overlap in the range of shifts of U⁴⁺ complexes versus U³⁺ complexes, in general U³⁺ species have shifts more negative than those of their U⁴⁺ analogues. The single U²⁺ example has the most negative shift of all at −322 ppm at 170 K. With only a few exceptions, U⁴⁺ complexes have shifts between 0 and −150 ppm (vs SiMe₄), whereas U³⁺ complexes resonate between −120 and −250 ppm. The small data set on U⁵⁺ species exhibits a broad 250 ppm range centered near 40 ppm. The data also show that aromatic ligands such as cyclopentadienide, cyclooctatetraenide, and the pentalene dianion exhibit chemical shifts less negative than those of other types of ligands