<p>  </p> <p>Actinide complexes have been targeted for their potential in group transfer applications. The study of these metals, such as thorium and uranium, is essential to better understand the reactions these metals are capable of facilitating.  Hydrotris(pyrazolyl)borates such as hydrotris(3,5-dimethylpyrazolyl)-borate (Tp*) and hydrotris(pyrazolyl)-borate (Tp) are superbulky, scorpionate ligands that have previously been used to synthesize novel uranium complexes and probe the reactivity of these materials. Similar thorium analogs have also been synthesized, but their reactivity has yet to be explored in great depth. Tp*ThCl3(THF) and Tp2ThCl2 have been reproduced and investigated as possible starting materials for such reactivity studies. While the former was found to be largely unreactive, the latter presents promising reactivity for the synthesis of thorium-element multiple bonds, and a novel thorium imido, Tp2Th(NDipp)(THF), has been synthesized and characterized using this scaffold. </p> <p><br></p> <p>The reactivity of a uranium tetrakis(imido), [U(NDipp)4][K2], has also been investigated to probe the prospect of group transfer reactions for potential catalysis applications in the future. An isocyanate, PhNCO, was reacted with this compound; the observed product showed that group transfer was incomplete, and a four-membered metallocycle product is likely formed instead. The synthesis of a novel thorium tris(imido) has also been targeted, and preliminary results are outlined. </p>

No description available.

The chemistry of late first row transition metals supported by dipyrromethane and dipyrromethene ligands bearing sterically bulky substituents was explored. Transition metal complexes (Mn, Fe, Co, Ni, Zn) of the dipyrromethane ligand 1,9-dimesityl-5,5-dimethyldipyrromethane (dpma) were prepared. Structural and magnetic characterization (SQUID, EPR) of the bis-pyridine adducts \((dpma)Mn(py)_2\), \((dpma)Fe(py)_2\), and \((dpma)Co(py)_2\) showed each tetrahedral divalent ion to be high-spin, while square planar \((dpma)Ni^{II}(py)_2\) and tetrahedral \((dpma)Zn(py)_2\) were shown to be diamagnetic. Electrochemical experiments revealed oxidative events at common potentials independent of metal identity or spin state, consistent with ligand-based oxidation. Dipyrromethene ligand scaffolds were synthesized bearing large aryl \((Ar = 2,4,6-Ph_{3}C_{6}H_{2}, Mes = 2,4,6-Me_{3}C_{6}H_{2})\) or alkyl \((^{t}Bu = CMe_3, Ad = 1-adamantyl)\) flanking groups to afford three new disubstituted ligands \((^{R}dpme, 1, 9-R_2-5-mesityldipyrromethene, R = Ar, Mes, ^{t}Bu, Ad)\). While high-spin \((S=2)\), four-coordinate iron complexes of the type \((^{R}dpme)FeCl(solv)\) were obtained when R was Mes, tBu, or Ad, use of the sterically encumbered aryl-substituted ligand gave a three-coordinate high-spin \((S=2)\) complex \((^{Ar}dpme)FeCl\). Intramolecular C−H amination was discovered in the reaction of organic azides with \((^{Mes}dpme)FeCl(thf)\), though no intermediate was observed by UV/Vis, IR, or \(^{1}H\) VT-NMR experiments. Reaction of \((^{Ad}dpme)FeCl(OEt_2)\) with alkyl azides resulted in the catalytic amination of C–H bonds or aziridination of olefins at room temperature. Reaction of \(p-^{t}BuC_{6}H_{4}N_{3}\) with \((^{Ar}dpme)FeCl\) permitted isolation of a high-spin \((S=2)\) iron complex \((^{Ar}dpme)FeCl(N(p-^{t}BuC_6H_4))\), featuring a terminal imidyl radical antiferromagnetically coupled to high-spin \(Fe^{III}\), as determined by \(^{1}H\) NMR, X-ray crystallography, and \(^{57}Fe\) Mössbauer. A three-coordinate CoI complex \((^{Ar}dpme)Co(py)\) was synthesized and characterized by \(^{1}H\) NMR, SQUID magnetometry, and X-ray crystallography. Reaction of \((^{Ar}dpme)Co(py)\) with \(^{t}BuN_3\) afforded an isolable three-coordinate Co imide complex \((^{Ar}dpme)Co(N^{t}Bu)\) that exhibits spin crossover from a singlet to a quintet. Reaction of \((^{Ar}dpme)Co(py)\) with mesityl azide produces a spectroscopically observed intermediate, consistent with an \(S=1\) terminal imide complex, that converted via benzylic C–H activation into the metallacycloindoline \((^{Ar}dome)Co(\kappa^{2}-NHC_{6}H_{2}-2,4-Me_{2}-6-CH_2)\). / Chemistry and Chemical Biology

Doctor of Philosophy / Department of Chemistry / Eric A. Maatta / Polyoxometalates have attracted much attention over the last few decades and have been studied in a wide variety of fields such as catalysis, medicine, imaging, photochromism, and magnetic materials. While many of these systems are easy to prepare, the ability to functionalize polyoxometalates is an ongoing challenge. Two approaches used to functionalize polyoxometalates involve insertion of metal fragments into a lacunary polyoxometalate or the direct replacement of terminal oxo ligands with the isoelectronic organoimido ligand. This process has been proven successful in many cases and with a wide variety of organoimido compounds. One of our group’s goals has been to synthesize a functionalized hexamolybdate species that is capable of metal coordination. However, previous results have been hindered because the electron withdrawing effect of the cluster is transmitted to the metal binding sites. In order to combat the electron withdrawing effect of the cluster, 4-amino piperidine dithiocarbamate ligands, which have no conjugation in the ring and are capable of metal binding, have been synthesized and characterized. A series of transition metal complexes have been made and a single crystal has been grown of a nickel(II) complex. Attempts to attach these species to clusters are described. Imido hexamolybdate clusters have been functionalized with styryl and iodophenyl groups. The styrene functionalized hexamolybdate was copolymerized with 4- chloromethylstyrene in moderate yields. This copolymer has the capabilities for further substitution at the chloromethyl group. The iodophenyl functionalized hexamolybdate was fully characterized including a single-crystal X-ray structural determination. This functionalized hexamolybdate can be used in carbon-carbon bond formation through coupling reactions. A chromium(V) nitrido polyoxometalate has been synthesized from a lacunary Keggin precursor and characterized. This nitrido species shows promise as a nitrogen transfer agent. Likewise, this nitrido species could be an entry point to other derivatives through reactions with various nucleophiles and electrophiles.

No description available.

<p>Uranium imido compounds have been traditionally studied due to their analogous nature to uranyl compounds. The investigation of uranium imido bonds can open the door to the activation of uranium oxygen bonds, which is important for the recyclization of spent nuclear fuel. This research encompasses further characterization of imido compounds utilizing electrochemical techniques which will better the understanding of these compounds. Utilizing what we already know about uranium imido compounds, further reactivity studies were conducted. Additionally, uranium is a suitable candidate for modeling synthesis of transuranic elements, specifically neptunium. Therefore, additional pathways to synthesize uranium tris(imido) and uranium tertrakis(imido) complexes were explored as a modeling system.  </p>

L'activation de petites molécules azotées telles que l'azote et l'ammoniac a été développé dans notre laboratoire via la chimie organométallique de surface (COMS). Les recherches effectuées durant cette thèse ont permis d'établir la réactivité de complexe de tantale imido amido supporté sur silice, [(SiO)2Ta(=NH)(NH2)] vis-à-vis de l'hydrogène et de l'ammoniac. Des étapes élémentaires de clivage hétérolytique de liaison H-H ou N-H ont été établies. En particulier, l'importance d'une molécule d'ammoniac dans la deuxième sphère de coordination (outer sphere assistance) du système s'est avérée cruciale pour la diminution des barrières d'énergie des états de transition pendant le transfert de protons. Les études ont été faites pour déterminer et expliquer le mécanisme de réduction de N2 par les complexes d'hydrures de tantale. La compréhension du mécanisme a été établie grâce aux études avec N2, N2H4 et N2H2 pour trouver les intermédiaires de cette réduction suivis par in-situ infrarouge, RMN et l'analyse élémentaire, et à l'aide de calcul DFT. Un mécanisme de clivage de N2 par des complexes dihydrogènes de Ta(V) est proposé. Enfin, la réactivité du complexe [(SiO)2Ta(=NH)(NH2)] vers l'activation de liaison C-H de C6H6, C6H5-CH3, t-Bu-Ethylène et CH4 a été étudié par la spectroscopie infrarouge / The activation of small molecules such as nitrogen and ammonia was already developed in our laboratory using the surface organometallic chemistry (SOMC) approach. This thesis focused on understanding the reactivity of tantalum imido amido complex [(SiO)2Ta(=NH)(NH2)], under hydrogen and/ or ammonia atmosphere. Heterolytic H-H and N-H cleavage across Ta-NH2 and Ta=NH bonds appeared crucial. The assistance of an additional ammonia molecule in the outer sphere of the d0 tantalum(v) imido amido ammonia model complex in order to reduce the energy barriers of the transition states during proton transfer was also shown. Studies were done to identify the mechanism of N2 reduction by tantalum hydride complexes. Studies with N2, N2H4 and N2H2 allowed identifying the intermediaries via in situ IR, NMR and elemental analysis. Combined with DFT calculations, these experiments led to the proposal of a novel mechanism for N2 cleavage based on the central role of Ta(H2) adducts. Finally, the reactivity of imido amido complex toward C-H bond activation was studied with C6H6, C6H5-CH3, t-Bu-Ethylene and CH4

No description available.

This Thesis describes the synthesis and reactivity of Group 5 imido and hydrazido complexes with tridentate, trianionic ligands. Various synthetic routes towards these hydrazido compounds were explored and in which several intermediates were synthesised and their chemistry was explored. The reactivity of the imido and hydrazido complexes with unsaturated and other small molecules was also studied. <b>Chapter One</b> provides a general introduction to tridentate pincer and tripodal ligands. The structure, synthesis and reactivity of Group 4 and 5 imido and hydrazido complexes is also reviewed. <b>Chapter Two</b> describes three different synthetic routes towards tantalum hydrazido complexes with tridentate, trianionic ligands. Synthesis, characterization and bonding analysis of the precursor dichloride species Ta(NN₂^SiMe3)Cl₂, which is used as starting material for two of the synthetic routes, is also described. The synthesis, characterization and bonding analysis of the tantalum dialkyl and alkyl-amido precursors prepared in the multistep route is also explored. <b>Chapter Three</b> describes the synthesis and characterisation of Group 5 imido complexes with tridentate, trianionic ligands of the type Li₃(NN₂^R) and Li₃(NNN^SiMe3). Reactivity studies of the imido complex Nb(NN₂iPr)(N^tBu)(py)₂ with unsaturated and other small molecules are also explored. <b>Chapter Four</b> describes the synthesis and characterisation of Group 5 hydrazido complexes with tridentate, trianionic ligands by two different synthetic routes, alongside a bonding analysis of the imido compounds M(NN₂^R)(N^tBu)(py)₂ and their hydrazido analogues M(NN₂^R)(NNPh₂)(L)_x. Reactivity studies of the hydrazido complex Nb(NN₂^iPr)(NNPh₂)(py)₂ with unsaturated and other small substrates are also described. <b>Chapter Five</b> presents full experimental procedures and characterising data for the new methodologies and complexes reported in this Thesis.

In the organometallic chemistry, the imido complexes are an interesting species because it of their rich reactivity. Imido has two forms, where M=N-R form is nucleophilic and M¡ÝN-R form is elctrophilic. The thermo- or photochemical- decomposition of metal azido complexes is known to result in the formation of the corresponding metal nitride(M¡ÝN) or imido complexes. These reactions are oxidative cleavage type. As far as we know, imido species have not been generated on metal surfaces; therefore, we attempt to use the azidotrimethylsilane((CH3)3Si-N3 ; TMSN3) as precursors to produce imido species(TMSN=Cu) by N2 extrusion mechanism on Cu(111). The process was explored by a combination of temperature-programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), and X-ray photoemission spectroscopy (XPS) techniques. In addition, density functional theory (DFT) calculations were conducted to obtain the optimized geometries for the various surface intermediates. The computed IR spectra facilitated the vibrational mode assignments. TPD spectra show that TMSN=Cu was hydrogenated to the TMSNH2 amine product around 520 K. We propose that the hydrogen source is adsorbed methyl groups, invoking the cleavage of the Si-C bond. TMSCH2N3 molecule was also investigated. In this case, N2 and H2 molecules were found to desorb around 260 K and 320K. A novel TMSC¡ÝN product was observed around 280K. We suggest it is a result of the metathesis reaction from ethylidyne (TMSC¡ÝCu) and nitride(N¡ÝCu) species. The TMSC¡ÝCu species are produced by double £\-hydride elimination of TMSCH2-Cu groups. The N¡ÝCu may be generated by the thermaldecomposition of copper azide(N=N=N-Cu). RAIRS reveal that there are three kinds of azido vibrations,where the higher frequency is assigned to the N=N=N-Cu species. This product is verified by the TPD of adsorbed TMSC¡ÝN molecule. Intriguingly, the thermal chemistry of TMSC¡ÝN molecule indicates that the isomeric molecule TMSN¡ÝC could be formed around 210 K, evidenced by a notable change in the RAIRS. The higher frequency £hC¡ÝN of TMSC¡ÝN transforms into a lower frequency £hC¡ÝN for TMSN¡ÝC. The coverage-dependent studies of RAIRS and XPS performed at 160 K surface temperature show that the isomerization may be intermolecular. The back-£k bonded TMSN¡ÝC molecule is desorbed around 410 K. XPS and RAIRS at 800 K show that isocyanide could polymerize to polyisocyanide, with an imine structure, and the characteristic C¡ÝN stretching mode disappeared.