ions in nuclear waste is very difficult. The selectivity of the best available An III extractants is attributed to subtly higher bonding covalency, but is not well understood and theory cannot yet make predictions.Unlike the organometallic chemistry of uranium, which has focused strongly on U III and seen spectacular advances [2][3][4] , that of the transuranics has remained dormant and, in the case of neptunium, is limited mainly to Np IV . The only known organometallic compounds of neptunium, the first transuranic element, are a

Actinide complexes of a small-cavity, dipyrrolide macrocycle exhibit unusual bent metallocene-type binding, or bis(arene)-type binding, or both at once in a di-uranium adduct.

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(III)2(BH4)3 motifs.

A new dinitrogen adduct of a homoleptic uranium tris(siloxide) complex, [U{OSi(Mes)3}3]2(μ-η2:η2-N2), is reported. Synthesis of the 15N-labeled isotopomer and Raman spectroscopy confirm the reductive activation of N2 to a (N2)2– dianion. The 15N NMR shift of the 15N2-labeled isotopomer is also reported. Crystallographic characterization shows a side-on (N2)2– coordinated in either an eclipsed or staggered conformation in different crystals. The U–N2–U complex is stable to vacuum and shows high thermal stability, retaining the formally reduced dinitrogen at 100 °C. The parent three-coordinate uranium(III) [U{OSi(Mes)3}3] could not be isolated in our hands, with N2-free syntheses affording only uranium(IV) compounds. The rational synthesis and full characterization of two such U(IV) byproducts, [U{OSi(Mes)3}{N(SiMe3)2}3] and [U{OSi(Mes)3}4], is also reported.