Bou-Moreno, R.; (2010) The design and synthesis of complexes for the activation of carbon dioxide. Doctoral thesis , UCL (University College London).

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Abstract

This thesis describes developments in the studies of the activation and use of carbon dioxide as a building block in synthesis by early transition metal complexes. The proposed route required the reaction of carbon dioxide with a metal-imido complex via a heterocumulene metathesis to produce an isocyanate. An attempt at the use of molybdenum-imido complexes for the process generated a novel low valent molybdenum bisimido complex with no success in the activation of carbon dioxide. Generation of simple 12-electron titanium-imido complexes showed successful heterocumulene metathesis with isocyanates to develop a novel methodology for the synthesis of carbodiimides and ureas. The studies of this methodology proved a fourmembered ring metallocycle was an intermediate and suggested the mechanism of the process as plausible, as well as showing the activation of carbon dioxide. Our studies were concluded by the generation and modification of titanium-imido complexes to synthesise families of complexes containing aromatic imido ligands, which showed no reactivity with carbon dioxide with the exception of the 2,6- diisopropylphenylimido ligand. Unsuccessful isolation of alkylimido titanium complexes impeded the generation of families of complexes. In situ generation of alkylimido titanium complexes showed activation of carbon dioxide to generate ureas, proposing two consecutive heterocumulene metatheses first with carbon dioxide and a second with the generated isocyanate. Studies with intermediates and comparisons with the generation of carbodiimides support this mechanism.

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