Uranium(III) Redox Chemistry Assisted by a Hemilabile
Bis(phenolate) Cyclam Ligand: Uranium–Nitrogen Multiple Bond
Formation Comprising a <i>trans</i>-{RNU(VI)NR}<sup>2+</sup> Complex
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Abstract
A new
monoiodide U(III) complex anchored on a hexadentate dianionic
1,4,8,11-tetraazacyclotetradecane-based bis(phenolate) ligand, [U(κ<sup>6</sup>-{(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam})I]
(<b>1</b>), was synthesized from the reaction of [UI<sub>3</sub>(THF)<sub>4</sub>] (THF = tetrahydrofuran) and the respective potassium
salt K<sub>2</sub>(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam
and structurally characterized. Reactivity of <b>1</b> toward
one-, two-, and four-electron oxidants was studied to explore the
reductive chemistry of this new U(III) complex. Complex <b>1</b> reacts with one-electron oxidizers, such as iodine and TlBPh<sub>4</sub>, to form the seven-coordinate cationic uranium(IV) complexes
[U(κ<sup>6</sup>-{(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam})I][X] (X = I (<b>2-I</b>), BPh<sub>4</sub> (<b>2-BPh</b><sub><b>4</b></sub>)). The new uranium(III) complex
reacts with inorganic azides to yield the pseudohalide uranium(IV)
complex [U(κ<sup>6</sup>-{(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam})(N<sub>3</sub>)<sub>2</sub>] (<b>4</b>) and
the nitride-bridged diuranium(IV/IV) complex [(κ<sup>4</sup>-{(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam})(N<sub>3</sub>)U(μ-N)U(κ<sup>5</sup>-{(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam})] (<b>5</b>). Two equivalents of [U(κ<sup>6</sup>-{(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam})I]
(<b>1</b>) effect the four-electron reduction of 1 equiv of
PhNNPh to form the bis(imido) complex [U(κ<sup>4</sup>-{(<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam})(NPh)<sub>2</sub>] (<b>6</b>) and the U(IV) species <b>2-I</b>.
Moreover, the hemilability of the hexadentate ancillary ligand (<sup>tBu2</sup>ArO)<sub>2</sub>Me<sub>2</sub>-cyclam<sup>2–</sup> allows to perform the reductive cleavage of azobenzene with an unprecedented
formation of a <i>trans</i>-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
