An investigation into the chemistry of solutions of titanium dioxide in fused alkali metal borates has been made, with the emphasis on the ability of the alkali borate melts to dissolve TiO2 and subsequently crystallize TiO2 and/or complex alkali metal titanates. The preparation and properties of potassium titanates with K2O/TiO2 mol ratio ≤1 has been studied. In addition the thermal decomposition of potassium hexafluorotitanate monohydrate (reported to yield potassium tetratitanate) has been investigated. The decomposition product has been identified as an oxyfluorotitanate. The compounds crystallized on slow cooling of alkali borate + TiO2 melts have been identified. The titanium containing product(s) have been correlated with the concentration of borate groups containing non-bridging oxygens, which depends on the alkali metal cation. Phase diagrams for the M2O.B2O3 + TiO2 (M = Na, K) systems have been obtained. Mass transport in M2O.2B2O3 + TiO2 (M = Li, Na, K) systems has been studied, via measurements of electrical conductivity, as a function of temperature and TiO2 concentration. Additional information on the alkali borate melts has been obtained from measurements of the optical basicity of M2O + B2O3 (M = Li, Na, K, Rb, Cs) glasses, using Pb(II) as probe ion. The results of these measurements have confirmed that the nature of the alkali metal cation significantly affects the basicity of fused alkali borate solvents. Extraction of TiO2 from ilmenite and titaniferous slag, using selected low-basicity alkali borate solvents has been attempted. The results indicate that TiO2 may be separated from ilmenite in essentially a one-step process.

An investigation into the chemistry of solutions of titanium dioxide in fused alkali metal borates has been made, with the emphasis on the ability of the alkali borate melts to dissolve TiO2 and subsequently crystallize TiO2 and/or complex alkali metal titanates. The preparation and properties of potassium titanates with K2O/TiO2 mol ratio ≤1 has been studied. In addition the thermal decomposition of potassium hexafluorotitanate monohydrate (reported to yield potassium tetratitanate) has been investigated. The decomposition product has been identified as an oxyfluorotitanate. The compounds crystallized on slow cooling of alkali borate + TiO2 melts have been identified. The titanium containing product(s) have been correlated with the concentration of borate groups containing non-bridging oxygens, which depends on the alkali metal cation. Phase diagrams for the M2O.B2O3 + TiO2 (M = Na, K) systems have been obtained. Mass transport in M2O.2B2O3 + TiO2 (M = Li, Na, K) systems has been studied, via measurements of electrical conductivity, as a function of temperature and TiO2 concentration. Additional information on the alkali borate melts has been obtained from measurements of the optical basicity of M2O + B2O3 (M = Li, Na, K, Rb, Cs) glasses, using Pb(II) as probe ion. The results of these measurements have confirmed that the nature of the alkali metal cation significantly affects the basicity of fused alkali borate solvents. Extraction of TiO2 from ilmenite and titaniferous slag, using selected low-basicity alkali borate solvents has been attempted. The results indicate that TiO2 may be separated from ilmenite in essentially a one-step process.

<p dir="ltr">This work describes the electronic and geometric structure of molecular metal complexes involving different ligand environments. These include the Cu-redox active ligand reduction series, Tp*₂U imido and anilido transformations, Lewis base activation by Tp*₂U, silyluranium synthesis and reactivity, and electrochemistry of plutonyl.</p>

Grâce à l’utilisation de catalyseurs sacrifiables issus, la plupart du temps, du groupe principal ou de la première période des éléments de transition, des nouvelles méthodologies de synthèse pour accéder à des molécules complexes ont été développées au cours de cette thèse. i) Des bicyclolactones ont été synthétisées par addition intramoléculaire de β-cétoesters sur des diènes-1,3 catalysée par un système coopératif de Bi(OTf)₃ et d’HOTf. ii) le motif 7-alcynylcycloheptatriène a été étudié et a permis d’accéder sélectivement à différents produits issus soit d’une cycloisomérisation d’énynes-1,6 ou d’une hydroarylation d’allènes, en fonction du caractère dur ou mou de l’acide de Lewis utilisé. iii) Ce motif a ensuite été utilisé comme plateforme pour accéder à des molécules polycycliques en présence d’acides de Lewis ou à des bromophénylallènes en présence d’un agent de bromation. Les bromoallènes ainsi formés ont pu être engagé dans des réactions de couplages C-C et C-N ou dans une réaction de CH-propargylation. iv) La N-éthylation réductrice d’imines en présence d’éthanol et d’un complexe de fer facilement accessible a été étudiée et a conduit à la formation d’amines tertiaires portant trois substituants différents. / Due to the use of sacrificial catalysts, most of the time derived from main group elements or 1st row transition metal, new methodologies were developed in this thesis to access complex molecules. i) Bicyclolactones were synthesized by an intramolecular addition of β-ketoesters into 1,3-dienes catalyzed by a cooperative Bi(OTf)₃ / HOTf catalytic system. ii) The 7-alkynylcyclohepatriene moiety was studied and afforded different products provided by a cycloisomerization of 1,6-enynes or an hydroarylation of allenes. The selectivity of this reaction is dependent of the soft or hard character of the Lewis acids engaged. iii) Afterward, the 7-alkynylcycloheptatriene moeity was used as a plateform to access various polycyclic molecules in presence of Lewis acids or bromophenylallenes in presence of a bromation agent. Thus the bromoallene formed can be engaged in C-C and C-N cross coupling reactions or in a CH propargylation reaction. iv) The reductive ethylation of imines using ethanol and a simple iron complex was developed and led to the formation of tertiary amines with three different substituents.