Mixed-sandwich complexes of low-valent uranium for the reductive activation of small molecules

Recent work in our laboratory has shown that cyclopentadienyl mixed-sandwich complexes of uranium(III) display novel reactivity towards small molecules; a particular result is the reductive coupling of CO, which depending on steric constraints can react selectively to form several members of the oxocarbon series. This reaction takes a poisonous and readily available C1 source and transforms it into a biologically useful compound. This thesis is in three parts. The first seeks to expand on the reactivity already observed by extending it to other small molecules and although well-defined coupling reactions were not achieved, several novel complexes were isolated. The chemical removal of the coupled CO product was also investigated. The second and third parts are linked as they examine the effects on stability and reactivity of the uranium(III) complex, of substituting two very different monoanionic ligand classes in the place of the cyclopentadienyl ligand. Two novel complexes were synthesised using the trispyrazolylborate and the cyclooctatetraenyl or pentalenyl ligands. The complexes display very different reactivity to each other and to the cyclopentadienyl ligands. Density functional calculations support the experimental findings. The final class of ligand, the indenyl ligand is much closer in type to the original system. The two novel indenyl complexes synthesised display reactivity towards CO and CO2, including the isolation of a reductively coupled CO complex. This demonstrates that the novel reactivity exhibited by the cyclopentadienyl mixed-sandwich complexes of uranium(III) can be replicated using a different ligand system. However, the reactivity observed is not only comparable, but also complementary. The structural and reactivity data presented in this thesis are instructive to our understanding of low-valent uranium chemistry and provide an insight into how the use of different ligand classes can effect the overall reactivity of the low-valent system.