Tuning Reactivity of Nitride Bridged Uranium Complexes with
Amide and Siloxide Ligands
Uranium nitride compounds have been implicated in dinitrogen fixation, N-atom transfer catalysis, and are proposed as advanced fuels in generation IV nuclear reactors. The chemistry of uranium nitride complexes is less developed than that of transition metals, but the highly polarizing nature of uranium, its large ionic radius, and f electrons that can interact with the ligands could allow new types of transformations. Recently, a bimetallic U4+ nitride complex supported by the tris(tertbutoxy)siloxide ligand, [Cs{((ButO)3SiO)3U}2(µ-N)],1 was reported and reacts with CO2, CO, and H2 to yield complexes of dicarbamate (N(CO2)2)3−, cyanide CN−, and an imide hydride complex, respectively; the H2 reactivity is reversible.2–4 Further, reduction of [Cs{((ButO)3SiO)3U}2(µ-N)] with excess KC8 generated for the first time an isolable U3+ nitride complex, K3[{((tBuO)3SiO)3 U}2(μ-N)],5 which reduces N2 to its tetraanion (N2)4− to give a complex that facilitates subsequent functionalization.6 The results to be presented describe attempts to prepare reactive uranium nitride complexes including those of U3+ since K3[{((tBuO)3SiO)3U}2(μ-N)] is the only known to date. Specifically, syntheses of complexes with amide ligands will be presented and comparisons between amide and siloxide ligands on small molecule and reduction reactivity will be made.
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