Advancing Uranium(III) reductive chemistry through hetroleptic metallocene aryloxide ligand frameworks
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This dissertation looks at the reductive chemistry of Uranium (III)bis- pentamethylcyclopentadienyl arylox-ide complexes. For chapter two, the reactivity of two metallocene aryloxide U(III) complexes, [(C5Me5)2U(O-Ar)], R = 4-tBuC6H4, R = 2,6-tBu2-4-CH3C6H2 (BHT), with CO2 and CS2 are investigated. For chapter three, the U(III) complex, [(C5Me5)2U(OMes)(THF)], Mes = 2,4,6-Me3C6H2, with Fe(CO)5 forms [{(C5Me5)2(MesO)U}2([mu]2-(OC)2Fe(CO)2)] with the bridging, tetrahedral Fe(CO)4 moiety. This complex has been studied using 1H NMR, IR vibrational, UV-vis electronic absorption, and zero-field 57Fe Mossbauer spectroscopy as well as single-crystal X-ray diffraction analysis, magnetic measurements and DFT calculations. Chapter four addresses the synthesis and reactivity of [{(C5Me5)2(MesO)U}2([mu]2-OCCO)] and [(C5Me5)2U(O-2,6-tBu2-4-MeC6H2)(CO)]. When the U(III) complex, [(C5Me5)2U(O-2,6-tBu2-4-MeC6H2)] is exposed to 1 atm of CO, only coordination is observed by IR spectroscopy as well as X-ray crystallography, unveiling a rare structurally characterized f element carbonyl. However, using [(C5Me5)2(MesO)U (THF)], Mes = 2,4,6-Me3C6H2, reaction with CO forms the bridging ethynediolate species, [{(C5Me5)2(MesO)U}2([mu]2-OCCO)]. The addition of more CO to the ethynediolate complex with heating forms a ketene carboxylate, [{(C5Me5)2(MesO)U}2([mu]2:[kappa]2:[eta]1-C3O3)], which can be further reacted with CO2 to yield a ketene dicarbox-ylate complex, [{(C5Me5)2(MesO)U}2([mu]2:[kappa]2:[kappa]2-C4O5)]. A [2+2] cycloaddition is observed with diphenylke-tene to yield [{(C5Me5)2U}2(OC(CPh2)C(=O)CO)] with concomitant formation of [(C5Me5)2U(OMes)2]. Sur-prisingly, reaction with SO2 shows rare S-O bond cleavage to yield the unusual [(O2CC(O)(SO)]2- bridging ligand between two U(IV) centres. All complexes have been characterized using spectroscopic and structural methods, and the reaction of the ethynediolate with CO to form the ketene carboxylate has been investigated computationally as well as the reaction with SO2 In chapter five, the molecular and electronic structure of rare examples of complexes containing uranium-aluminum and -gallium bonds, [(C5Me5)2(MesO)U-E(C5Me5)], E = Al, Ga, is described. The reaction of H2 with the U(III)-Al(I) complex forms a trihydride bridged complex, [(C5Me5)2(MesO)U([mu]2-(H)3-Al(C5Me5)] through three-electron metal-based reduction, while the reaction with the U-Ga complex only forms a termi-nal U(IV) hydride, [(C5Me5)2(MesO)U(H)], with loss of [(C5Me5)Ga].
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Ph. D.