U^4+/5+/6+ in a Conserved Pseudotetrahedral Imidophosphorane Coordination Sphere

While several ligand systems support uranium across a range of oxidation states, spanning more than two oxidation states in a conserved coordination geometry is uncommon among structurally authenticated complexes. Imidophosphorane ligands significantly stabilize high-valent lanthanide and actinide complexes. Here, we report a series of homoleptic uranium imidophosphorane complexes, spanning the +4, +5 and +6 oxidation states in a four-coordinate pseudotetrahedral ligand field. The +6 oxidation state is accessible using a mild ferrocenium oxidant, yielding a rare example of U⁶⁺ in a pseudotetrahedral coordination environment. As the formal oxidation state increases, the U-N distances gradually contract, consistent with the Shannon ionic radii of U^4+/5+/6+. Compared to reported complexes, the short U-N distances observed in the U⁶⁺ complex are more comparable to dianionic imido ligands than monoanionic amido ligands.