Uranium(III) Redox Chemistry Assisted by a Hemilabile Bis(phenolate) Cyclam Ligand: Uranium–Nitrogen Multiple Bond Formation Comprising a trans-{RNU(VI)NR}2+ Complex

A new monoiodide U­(III) complex anchored on a hexadentate dianionic 1,4,8,11-tetraazacyclotetradecane-based bis­(phenolate) ligand, [U­(κ6-{(tBu2ArO)2Me2-cyclam})­I] (1), was synthesized from the reaction of [UI3(THF)4] (THF = tetrahydrofuran) and the respective potassium salt K2(tBu2ArO)2Me2-cyclam and structurally characterized. Reactivity of 1 toward one-, two-, and four-electron oxidants was studied to explore the reductive chemistry of this new U­(III) complex. Complex 1 reacts with one-electron oxidizers, such as iodine and TlBPh4, to form the seven-coordinate cationic uranium­(IV) complexes [U­(κ6-{(tBu2ArO)2Me2-cyclam})­I]­[X] (X = I (2-I), BPh4 (2-BPh4)). The new uranium­(III) complex reacts with inorganic azides to yield the pseudohalide uranium­(IV) complex [U­(κ6-{(tBu2ArO)2Me2-cyclam})­(N3)2] (4) and the nitride-bridged diuranium­(IV/IV) complex [(κ4-{(tBu2ArO)2Me2-cyclam})­(N3)­U­(μ-N)­U­(κ5-{(tBu2ArO)2Me2-cyclam})] (5). Two equivalents of [U­(κ6-{(tBu2ArO)2Me2-cyclam})­I] (1) effect the four-electron reduction of 1 equiv of PhNNPh to form the bis­(imido) complex [U­(κ4-{(tBu2ArO)2Me2-cyclam})­(NPh)2] (6) and the U­(IV) species 2-I. Moreover, the hemilability of the hexadentate ancillary ligand (tBu2ArO)2Me2-cyclam2– allows to perform the reductive cleavage of azobenzene with an unprecedented formation of a trans-bis­(imido) complex. The complexes were characterized by NMR spectroscopy, and all the new uranium complexes were structurally authenticated by single-crystal X-ray diffraction.