New chemistry from an old reagent: mono- and dinuclear macrocyclic uranium(III) complexes from [U(BH4)3(THF)2]

A new robust and high-yielding synthesis of the valuable U^III synthon [U(BH₄)₃(THF)₂] is reported. Reactivity in ligand exchange reactions is found to contrast significantly to that of uranium triiodide. This is exemplified by the synthesis and characterization of azamacrocyclic U^III complexes, including mononuclear [U(BH₄)(L)] and dinuclear [Li(THF)₄][{U(BH₄)}₂(μ-BH₄)(L^Me)] and [Na(THF)₄][{U(BH₄)}₂(μ-BH₄)(L^A)(THF)₂]. The structures of all complexes have been determined by single-crystal X-ray diffraction and display two new U^III₂(BH₄)₃ motifs.