Synthesis, Characterization, and Reactivity of a Uranyl β-Diketiminate Complex

2008-02-13T00:00:00Z (GMT) by Trevor W. Hayton Guang Wu
Addition of 1 equiv of Li(Ar<sub>2</sub>nacnac) (Ar<sub>2</sub>nacnac = (2,6-<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)<i>N</i>C(Me)CHC(Me)<i>N</i>(2,6-<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)) to an Et<sub>2</sub>O suspension of UO<sub>2</sub>Cl<sub>2</sub>(THF)<sub>3</sub> generates the uranyl dimer [UO<sub>2</sub>(Ar<sub>2</sub>nacnac)Cl]<sub>2</sub> (<b>1</b>) in good yield. A second species can be isolated in low yield from the reaction mixtures of <b>1</b>, namely [Li(OEt<sub>2</sub>)<sub>2</sub>][UO<sub>2</sub>(Ar<sub>2</sub>nacnac)Cl<sub>2</sub>] (<b>2</b>). The structures of both <b>1</b> and <b>2</b> have been confirmed by X-ray crystallography. Complex <b>1</b> reacts with Ph<sub>3</sub>PO to generate UO<sub>2</sub>(Ar<sub>2</sub>nacnac)Cl(Ph<sub>3</sub>PO) (<b>3</b>). In addition, <b>1</b> reacts with AgOTf and either 1 equiv of DPPMO<sub>2</sub> or 2 equiv of Ph<sub>2</sub>MePO to provide [UO<sub>2</sub>(Ar<sub>2</sub>nacnac)(DPPMO<sub>2</sub>)][OTf] (<b>4</b>) and [UO<sub>2</sub>(Ar<sub>2</sub>nacnac)(Ph<sub>2</sub>MePO)<sub>2</sub>][OTf] (<b>5</b>), respectively. Both <b>4</b> and <b>5</b> have been fully characterized, including analysis by X-ray crystallography and cyclic voltammetry. Reduction of <b>4</b> with Cp<sub>2</sub>Co provides UO<sub>2</sub>(Ar<sub>2</sub>nacnac)(CH{Ph<sub>2</sub>P<i>O</i>}<sub>2</sub>) (<b>6</b>), a uranyl(VI) complex that is generated by the formal loss of H• from the DPPMO<sub>2</sub> ligand. Labeling studies have been performed in an attempt to elucidate the mechanism of hydrogen loss. In contrast, reduction of <b>5</b> with Cp<sub>2</sub>Co provides UO<sub>2</sub>(Ar<sub>2</sub>nacnac)(Ph<sub>2</sub>MePO)<sub>2</sub> (<b>7</b>), a rare example of a uranyl(V) complex. As expected, the solid-state molecular structure of <b>7</b> reveals slightly longer U−O(oxo) bond lengths relative to <b>5</b>. Furthermore, complex <b>7</b> can be converted back into <b>5</b> by oxidation with AgOTf in toluene.