The initial part of this investigation was to determine the ternary isothermal sections for the Cr-Co-Cu system and the Crâ Mm-Cu system at lOOO°C. and 975°C., respectively. This was done by vacuum melting the Cr-Co~Cu alloys and annealing these alloys in an inert atmosphere of a helium-hydrogen gas mixture. The Cr-Mn-Cu alloys were melted under a helium atmosphere and annealed in evacuated Vycor tubes. By the use of metallographic techniques and x-ray analysis the phases present in each alloy were determined and the two ternary isotherml sections constructed. It was found that copper had a very limited solid solubility in the sign phase of both systems. The sigma field in the Cr-Co-Cu 1000°C. ternary isothermal comes into equilibrium with the terminal solid solutions of chromium, cobalt, and copper. In the Cr-Mn-Cu ternary isothermal section sigma comes into equilibrium with the terminal solid solution of chromium and cobalt and the face-centered cubic solid solution of copper in manganese. From these data the electron vacancy scheme(16) may not be extended to include copper due to the limited solid solubility of copper in sigma. Also, the extent of copper solubility in the sigmas cannot be related to the solubility of the copper in cobalt or manganese. / Master of Science

Thesis (M.Sc.)--Memorial University of Newfoundland, 2002. / Bibliography: leaves 92-95.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [158]-172).

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [114]-123).

Thesis (Ph.D.)--Baylor University, 2009. / Includes bibliographical references (p. 233-237).

Reaction of the tetracobalt cluster Co4(CO)10(t 4-PPh)2 with 1,2-bis(dimethylphosphino)ethane (dmpe) affords the bis-substituted cluster Co4(CO)8(dmpe)(t 4-PPh)2. The bidentate dmpe ligand is shown to bind to the cluster in a chelating fashion by IR, NMR, and X-ray diffractions analyses. The fluxional nature of the ancillary carbonyl groups has been studied by variable temperature 13C NMR measurements which reveal two distinct carbonyl scrambling pathways. The stability of the phosphine-ligated cluster has been examined using in situ Cylindrical Internal Reflection (CIR) Spectroscopy. The effect of the dmpe ligand on the cluster polyhedron will be discussed with respect to the observed crystallographic and spectroscopic results

Ph.D. / Compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L2) were prepared by phase transfer alkylation of 2,6-bis(bromomethyl)pyridine with two mole equivalents of the appropriate pyrazole. Ligands L1 and L2 reacted with either [PdCl2(NCMe)2] or [PdClMe(COD)] to form mononuclear palladium complexes [(PdCl2(L1)] (1), [(PdClMe(L1)] (2), [(PdCl2(L2)] (3), [(PdClMe(L2)] (4). All new compounds prepared were characterised by a combination of 1H NMR, 13C NMR spectroscopy and microanalyses. The coordination of L2 in a bidentate fashion through the pyridine nitrogen atom and one pyrazolyl nitrogen atom has been confirmed by single crystal X-ray crystallography of complex 3. Reactions of 1, 2 and 3 with the halide abstractor NaBAr4 (Ar = 3,5-(CF3)2C6H3) led to the formation of the stable tridentate cationic species [(PdCl(L1)]BAr4 (5), [(PdMe(L1)]BAr4 (6) and [(PdCl(L2)]BAr4 (7) respectively. Tridentate coordination of L1 and L2 in the cationic complexes has also been confirmed by single X-ray crystallography of complexes 5 and 6. The analogous carbonyl linker cationic species, [Pd{(3,5-Me2pz-CO)2-py}Cl]+ (9) and [Pd{(3,5-tBu2pz-CO)2-py}Cl]+ (10), prepared by halide abstraction from [Pd{(3,5-Me2pz-CO)2-py}Cl2] and [Pd{(3,5-tBu2pz-CO)2-py}Cl2] with NaBAr4, were however less stable. While cationic complexes 5-7 showed indefinite stability in solution, 9 and 10 had t1/2 of 14 and 2 days respectively. Attempts to crystallise 1 and 3 from the mother liquor resulted in the isolation of the salts [PdCl(L1)]2[Pd2Cl6] (11) and [PdCl(L2)]2[Pd2Cl6] (12). Although when complexes 1-4 xviii were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerisation or polymerisation were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerised and polymerised phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) were prepared by phase transfer alkylation of 2-picolylchloride hydrochloride with one mole equivalent of the appropriate pyrazole. Compounds 2-(3,5-bis-trifluoromethyl-pyrazol-1-ylmethyl)-6-(3,5-dimethyl-pyrazol-1-ylmethyl)-pyridine (L5) and 2-(3,5-dimethyl-pyrazol-1-ylmethyl)-6-phenoxymethyl-pyridine (L6) were isolated in good yields by reacting (2-chloromethyl-6-3,5-dimethylpyrazol-1-ylmethyl)pyridine with an equivalent amount of potassium salt of 3,5-bis(trifluoromethyl)pyrazolate and potassium phenolate respectively. L3-L6 react with either [Pd(NCMe)2Cl2] or [PdClMe(COD)] to give mononuclear palladium complexes 13-18 of the general formulae [PdCl2(L)] or [PdClMe(L)] where L = is the bidentate ligands L3, L4, L5 and L6 respectively. Single crystal X-ray crystallography of complexes 13, 15 and 16 has been used to confirm the solid state geometry of the complexes. In attempts to generate active olefin oligomerisation catalysts, the chloromethyl Pd(II) complexes 14 and 16 were reacted with the halide abstractor NaBAr4 in the presence of stabilising solvents (i.e Et2O or NCMe) but no catalytic activities were observed. Decomposition was evident as observed from the deposition of palladium black in experiments using Et2O. In experiments where NCMe was used as the stabilising solvent, the formation of cationic species stabilised by NCMe was evident from 1H NMR analyses. Reaction of complex 14 with NaBAr4 on a preparative scale in a mixture of CH2Cl2 and NCMe solvent gave the cationic complex [[PdMeNCMe(L3)]BAr4 (19) in good yields. Complex 17 reacted with NABAr4 to give tridentate cationic species [[PdMe(L5)]BAr4 (20) which is inactive towards ethylene oligomerisation or polymerisation reactions. The tridentate coordination of L5 in 20 has also been established by single crystal X-ray structure of 20. Catalysts generated from 18 and 19 catalysed ethylene polymerisation at high pressures to branched polyethylene; albeit with very low activity. The Choromethyl palladium complex 14 reacted with sulfur dioxide to form complex 21. The nature of the product has been established by 1H NMR, 13C NMR and mass spectrometry to be an insertion product of SO2 into the Pd-Me bond of 14. Compounds L1-L4 reacted with the nickel salts NiCl2 or NiBr2 in a 1:1 mole ratio to give the nickel complexes [NiCl2(L1)] (22), [NiBr2(L1)] (23), [NiCl2(L2)] (24), and [NiBr2(L2)] (25), [Ni2(μ2-Cl)2Cl2(L3)2] (26), [Ni2(μ2-Br)2Br2(L3)2] (27), [NiCl2(L4)] (29) and [NiBr2(L4)] (30) in good yields. Reaction of L3 with NiBr2 in a 2:1 mole gave the octahedral complex [NiBr2(L4)2] (28) in good yields. Complexes 22-30 were characterised by a combination micro-analyses, mass spectrometry and single crystal X-ray analyses for 27 and 30. No NMR data were acquired because of the paramagnetic nature of the complexes. When complexes 22-30 were activated with EtAlCl2, highly active olefin oligomerisation catalysts were formed. In the ethylene oligomeristion reactions, three oligomers: C11, C14 xx and C16 were identified as the major products. Selectivityof 40% towards α-olefins were generally obtained. In general catalysts that contain the bidentate ligands L3 and L4 were more active than those that contain the tridentate ligands L1 and L2. Dichloride complexes exhibited relatively higher catalytic activities than their dibromide analogues. Turn over numbers (TON) for oligomer formation showed high dependence on ethylene concentration. A Lineweaver-Burk analysis of reactions catalysed by 22 and 26 showed TON saturation of 28 393 kg oligomer/mol Ni.h and 19 000 kg oligomer/mol Ni.h respectively. Catalysts generated from complexes 22-30 also catalysed oligomerisation of the higher olefins, 1-pentene, 1-hexene and 1-heptene and displayed good catalytic activities. Only two products C12 and C15 were obtained in the 1-pentene oligomerisation reactions. The 1-hexene reactions also gave two products, C12 and C18, while 1-heptene oligomerisation reactions gave predominantly C14 oligomers. Five benzoazoles were used to prepare a series of palladium complexes that were invesitigated as Heck coupling catalysts. The compounds 2-pyridin-2-yl-1H-benzoimidazole (L7) and 2-pyridin-2-yl-benzothiazole (L8) were prepared following literature procedures. The new ligands 2-(4-tert-butylpyridin-2-yl)-benzooxazole (L9) and 2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L10) were prepared by ring closure of aminophenol and aminothiophenol with tert-butyl picolinic acid respectively. The ligand 6-tert-Butyl-2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L11) was prepared by intramolecular cyclisation under basic conditions is described. Reactions of L7-L11 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] afforded the corresponding mononuclear palladium complexes [PdClMe(L7)] (31), [PdClMe(L8)] (32), [PdCl2(L9)] (33), [PdMeCl(L9)] (34), [PdCl2(L10)] (5), [PdMeCl(L10)] (36) and [PdMeCl(L11)] (37) as xxi confirmed by mass spectrometry and micro-analyses. The palladium complexes 31-37 were efficient Heck coupling catalysts for the reaction of iodobenzene with butylacrylate under mild conditions and showed good stability.

In this research the validity of various computational techniques has been determined and applied the appropriate techniques to investigate and propose a good catalytic system for C-H bond activation and functionalization. Methane being least reactive and major component of natural gas, its activation and conversion to functionalized products is of great scientific and economic interest in pure and applied chemistry. Thus C-H activation followed by C-C/C-X functionalization became crux of the synthesis. DFT (density functional theory) methods are well suited to determine the thermodynamic as well as kinetic factors of a reaction. The obtained results are helpful to industrial catalysis and experimental chemistry with additional information: since C-X (X = halogens) bond cleavage is important in many metal catalyzed organic syntheses, the results obtained in this research helps in determining the selectivity (kinetic or thermodynamic) advantage. When C-P bond activation is considered, results from chapter 3 indicated that C-X activation barrier is lower than C-H activation barrier. The results obtained from DFT calculations not only gave a good support to the experimental results and verified the experimentally demonstrated Ni-atom transfer mechanism from Ni=E (E = CH2, NH, PH) activating complex to ethylene to form three-membered ring products but also validated the application of late transition metal complexes in respective process. Results obtained supported the argument that increase in metal coordination and electronic spin state increases catalytic activity of FeIII-imido complexes. These results not only encouraged the fact that DFT and multi-layer ONIOM methods are good to determine geometry and thermodynamics of meta-stable chemical complexes, but also gave a great support to spectroscopic calculations like NMR and Mossbauer calculations.

Computational methods were employed to investigate catalytic processes. First, DFT calculations predicted the important geometry metrics of a copper–nitrene complex. MCSCF calculations supported the open-shell singlet state as the ground state of a monomeric copper nitrene, which was consistent with the diamagnetic character deduced from experimental observations. The calculations predicted an elusive terminal copper nitrene intermediate. Second, DFT methods were carried out to investigate the mechanism of C–F bond activation by a low-coordinate cobalt(I) complex. The computational models suggested that oxidative addition, which is very rare for 3d metals, was preferred. A π–adduct of PhF was predicted to be a plausible intermediate via calculations. Third, DFT calculations were performed to study ancillary ligand effects on C(sp3)–N bond forming reductive elimination from alkylpalladium(II) amido complexes with different phosphine supporting ligands. The dimerization study of alkylpalladium(II) amido complexes indicated an unique arrangement of dative and covalent Pd-N bonds within the core four-membered ring of bimetallic complexes. In conclusion, computational methods enrich the arsenal of methods available to study catalytic processes in conjunction with experiments.

The present work was initiated to investigate the stability, structural and thermodynamic properties of transition metal carbides, nitrides and carbo-nitrides by atomistic simulations and experimentations. The interatomic pair potentials of Cr-Cr, Mn-Mn, Fe-Fe, C-C, Cr-C, Mn-C, Fe-C, Cr-Fe, Cr-N and Mn-N were inverted by the lattice inversion method and ab initio cohesive energies, and then employed to investigate the properties of Cr-, Mn- and Fe-carbides by atomistic simulations in this work. For the binary M7C3 carbide, the structural properties of M7C3 (M = Cr, Mn, Fe) were investigated by atomistic simulations. The results show that the stable structure for these compounds is hexagonal structure with P63mc space group. The cohesive energy of M7C3 calculated in this work indicates that the stability of carbides decreases with the increasing in metal atomic number. Further, the vibrational entropy of Cr7C3 was calculated at different temperatures and compared with the entropy obtained by experimentations. The comparison demonstrates that the main contribution to the entropy is made by the vibrational entropy. For the binary τ-carbides, the structural properties of Cr23C6 and Mn23C6, as well as the vibrational entropy of Cr23C6 were computed. Further, the site preference of ternary element Fe among 4a, 8c, 32f and 48h symmetry sites in Cr23-xFexC6 was studied. It has been seen that Fe atoms would firstly occupy 4a sites and then 8c sites. The lattice constant and stability of Cr23-xFexC6 were also computed with different Fe content. In order to understand the relative stability of the transition metal carbides and nitrides, the standard formation Gibbs energies of carbides and nitrides for Cr, Mn and Fe were compared. The order of carbon and nitrogen affinities for Cr, Mn and Fe was further clarified by the comparison of the interatomic pair potentials among Cr-C, Mn-C, Fe-C, Cr-N and Mn-N. It was found that Cr-N interaction was very strong in comparison with other binary interactions above and consequently, nitrogen addition would lead to a strong decrease in the thermodynamic activity of chromium in Cr-containing alloys. This was confirmed by the investigations of thermodynamic activities of Cr in the Fe-Cr-N and Fe-Cr-C-N alloys. The activities were measured in the temperature range 973-1173 K by solid-state galvanic cell method involving CaF2 solid electrolyte under the purified N2 gas. In addition, the analysis of nitrogen content and phase relationships in the Fe-Cr-N and Fe-Cr-C-N alloys equilibrated at 1173 K were carried out by inert-gas fusion thermal conductivity method, X-ray diffraction and scanning electron microscopy technique. The experimental results show that the solubility of nitrogen in the alloys decreases with the decreasing chromium content, as well as the increasing temperature. The addition of nitrogen to the alloys was found to have a strong negative impact on the Cr activity in Fe-Cr-N and Fe-Cr-C-N systems. / QC 20100929