Uranium Tetrakis-Aryloxide Derivatives Supported by Tetraazacyclododecane: Synthesis of Air-Stable, Coordinatively-Unsaturated U(IV) and U(V) Complexes

We present the synthesis,
characterization, and one-electron oxidation of two uranium­(IV) complexes,
coordinated to the cyclen-anchored tetrakis­(aryloxide) ligands tetrakis-hydroxybenzyl-1,4,7,10
tetraazacyclododecane, (R,RArOH)4cyclen; R = tBu, Me. The new uranium­(IV) and (V) complexes
exhibit an eight-coordinate, tetragonal ligand environment, effecting
exceptional stability of the coordinatively unsaturated uranium compounds.
Cyclic voltammetry studies reveal redox events ranging from tri- to
hexavalent species, covering an electrochemical window of ∼4
V.