A new robust and high-yielding synthesis of the valuable UIII 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 UIII complexes, including mononuclear [U(BH4)(L)] and dinuclear [Li(THF)4][{U(BH4)}2(μ-BH4)(LMe)] and [Na(THF)4][{U(BH4)}2(μ-BH4)(LA)(THF)2]. The structures of all complexes have been determined by single-crystal X-ray diffraction and display two new UIII2(BH4)3 motifs.