Synthesis, characterization, and reactivity of a uranyl β-diketiminate complex

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