Tris(pyrazolyl)borate half-sandwich complexes of trivalent uranium incorporating the [C8H6{SiiPr3-1,4}2]2− and [C8H4{SiiPr3-1,4}2]2− ligands

The reaction of UI3 in THF with KTpMe2 and the subsequent addition of [K2(C8H6{SiiPr3-1,4}2)] or [K2(C8H4{SiiPr3-1,4}2)] yields dark red [U(κ3-TpMe2)(C8H6{SiiPr3-1,4}2)] 1 and purple [U(κ3-TpMe2)(C8H4{SiiPr3-1,4}2)] 2, respectively. The 1H NMR of 1 at room temperature suggests a rigid structure, whereas 2 is fluxional in solution on the NMR timescale. 1 is unreactive towards CO, CO2 and MeNC under mild conditions; density functional calculations were used to compare the electronic and steric effects of the TpMe2vs. Cp* ligands in mixed sandwich complexes of the type [U(L)(C8H6{SiH3-1,4}2)] (L = Cp* or (κ3-TpMe2)). On heating at 80 °C, 1 reacts with excess MeNC to yield [U(C8H6{SiiPr3-1,4}2)(κ2-dmpz)2(η1-CNMe)] 3. The structures of 1–3 have been determined by single crystal X-ray diffraction.