No abstract

The reactivity of the nitride ligand is increased in complexes of uranium(iv) when bound by the OSi(OtBu)3 ligand as opposed to N(SiMe3)2, but magnetic exchange coupling is decreased.

The concept of oxidation state plays a fundamentally important role in defining the chemistry of the elements. In the f block of the periodic table, well-known oxidation states in compounds of the lanthanides include 0, +2, +3 and +4, and oxidation states for the actinides range from +7 to +2. Oxidation state +1 is conspicuous by its absence from the f-block elements. Here we show that the uranium­(II) metallocene [U­(η5-C5 i Pr5)2] and the uranium­(III) metallocene [IU­(η5-C5 i Pr5)2] can be reduced by potassium graphite in the presence of 2.2.2-cryptand to the uranium­(I) metallocene [U­(η5-C5 i Pr5)2]− (1) (C5 i Pr5 = pentaisopropylcyclopentadienyl) as the salt of [K­(2.2.2-cryptand)]+. An X-ray crystallographic study revealed that 1 has a bent metallocene structure, and theoretical studies and magnetic measurements confirmed that the electronic ground state of uranium­(I) adopts a 5f3(7s/6d z 2 )1(6d x 2–y 2 /6d xy )1 configuration. The metal–ligand bonding in 1 consists of contributions from uranium 5f, 6d, and 7s orbitals, with the 6d orbitals engaging in weak but non-negligible covalent interactions. Identification of the oxidation state +1 for uranium expands the range of isolable oxidation states for the f-block elements and potentially signposts a synthetic route to this elusive species for other actinides and the lanthanides.

A diuranium(v) bis-nitride complex supported by siloxide ligands displays remarkable reactivity in ambient conditions with small molecules such as CS2, CO2, CO and H2 resulting in N–C and N–H bond formation. The nitride linker also leads to an unusually strong antiferromagnetic coupling between uranium(v) ions.