Reactivity And Electronic Structures Of Uranium Complexes With Nitrogen And Oxygen Donors In Axial Symmetries

The effects of the ligand field are generally on the same order of magnitude as spin-orbit coupling for uranium complexes. However, significant impacts on the electronic structure, reactivity, and stability of uranium complexes have been observed as a result of changing the ligand framework. In the work presented here, uranium complexes in a variety of ligand frameworks are synthesized, and their unique electronic structures and reactivities are studied. Uranium imido complexes with varying substitution at the imido nitrogen are contrasted with uranium oxo complexes, showing that their ability to impart an inverse trans influence, a thermodynamic phenomenon in which strong donor ligands gain stability from trans axial geometries, was comparable. We also synthesized uranium complexes with a weakly donating phosphino-anilide ancillary ligand. This ligand stabilized the uranium(III/IV) couple and allowed the synthesis of a rare uranium(IV) parent imido moiety. In contrast, the bis(trimethysilyl)amide ligand framework resulted in more reducing complexes and afforded reactivity in which reactive amide radical anions could be stabilized, and other carbonyl functional groups were reduced. In this same ancillary ligand framework, we synthesized uranium(VI) oxo phenyl(acetylide) complexes and observed that distal para aryl substituents could affect covalency in U–C bonding.