A Uranium(VI)-Oxo-Imido Dimer Complex Derived from a Sterically Demanding Triamidoamine

The reaction of [UO2(mu-Cl)(4){K(18-crown-6)}(2)] with [{N(CH2CH2NSiPr3i)(3)}Li-3] gives [{UO(mu-NCH2CH2N-[CH2CH2NSiPr3i](2))}(2)] (1), [{(LiCl)(KCl)(18-crown-6)}(2)] (2), and [LiOSiPr3i] (3) in a 1:2:2 ratio. The formation of the oxoimido 1 involves the cleavage of a N-Si bond and the activation of one of the usually robust U=O bonds of uranyl(VI), resulting in the formation of uranium(VI)-imido and siloxide linkages. Notably, the uranium oxidation state remains unchanged at +6 in the starting material and product. Structural characterization suggests the dominance of a core RN=U=O group, and the dimeric formulation of 1 is supported by bridging imido linkages in a highly asymmetric U2N2 ring. Density functional theory analyses find a sigma > pi orbital energy ordering for the U=N and U=O bonds in 1, which is uranyl-like in nature. Complexes 1 -3 were characterized variously by single crystal X-ray diffraction, multinuclear NMR, IR, Raman, and optical spectroscopies; cyclic voltammetry; and density functional theory.