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.

Terminal uranium nitrides have so far proven impossible to isolate by photolysis of azides. Here we report the second ever example of an isolated terminal uranium­(VI) nitride. We show that the terminal nitride [NBu4]­[U­(OSi­(OtBu)3)4(N)], 3, can be prepared upon photolysis with UV light of the U­(IV) azide analogue. This is achieved by careful tailoring of the azide precursor and of the reaction conditions. Complex 3 is stable under ambient conditions but reacts readily with electrophiles (H+ and CO).

Multimetallic cooperativity is believed to play a key role in the cleavage of dinitrogen to nitrides (N3–), but the mechanism remains ambiguous due to the lack of isolated intermediates. Herein, we report the reduction of the complex [K2{[UV(OSi­(OtBu)3)3]2(μ-O)­(μ-η2:η2-N2)}], B, with KC8, yielding the tetranuclear tetranitride cluster [K6{(OSi­(OtBu)3)2UIV}3­{(OSi­(OtBu)3)2UVI}­(μ4-N)3­(μ3-N)­(μ3-O)2], 1, a novel example of N2 cleavage to nitride by a diuranium complex. The structure of complex 1 is remarkable, as it contains a unique uranium center bound by four nitrides and provides the second example of a trans-NUVIN core analogue of UO2 2+. Experimental and computational studies indicate that the formation of the U­(IV)/U­(VI) tetrauranium cluster occurs via successive one-electron transfers from potassium to the bound N2 4– ligand in complex B, resulting in N2 cleavage and the formation of the putative diuranium­(V) bis-nitride [K4{[UV(OSi­(OtBu)3)3]2­(μ-O)­(μ-N)2}], X. Additionally, cooperative potassium binding to the U-bound N2 4– ligand facilitates dinitrogen cleavage during electron transfer. The nucleophilic nitrides in both complexes are easily functionalized by protons to yield ammonia in 93–97% yield and with excess 13CO to yield K13CN and KN13CO. The structures of two tetranuclear U­(IV)/U­(V) bis- and mononitride clusters isolated from the reaction with CO demonstrate that the nitride moieties are replaced by oxides without disrupting the tetranuclear structure, but ultimately leading to valence redistribution.

Uranium nitride compounds are important molecular analogues of uranium nitrides materials such as UN and UN2 which are effective catalysts in the Haber-Bosch synthesis of ammonia, but the synthesis of...

Thorium nitrides are likely intermediates in the reported cleavage and functionalization of dinitrogen by molecular thorium complexes and are attractive compounds for the study of multiple bond formation in felement chemistry, but only one example of thorium nitride isolable from solution was reported. Here, we show that stable multimetallic azide/nitride thorium complexes can be generated by reduction of thorium azide precursorsa route that has failed so far to produce Th nitrides. Once isolated, the thorium azide/nitride clusters, M 3 ThNTh (M = K or Cs), are stable in solutions probably due to the presence of alkali ions capping the nitride, but their synthesis requires a careful control of the reaction conditions (solvent, temperature, nature of precursor, and alkali ion). The nature of the cation plays an important role in generating a nitride product and results in large structural differences with a bent ThNTh moiety found in the Kbound nitride as a result of a strong K−nitride interaction and a linear arrangement in the Cs-bound nitride. Reactivity studies demonstrated the ability of Th nitrides to cleave CO in ambient conditions yielding CN − .