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 = ^<i>t</i>Bu, 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