Uranium Metallocene Azides, Isocyanates, and Their Borane-Capped Lewis Adducts.

Uranium(IV) metallocene complexes (Cp)U(N) (), (Cp)U(NCO) (), and (Cp)U(OTf) () containing the bulky Cp ligand (Cp = tetra(isopropyl)cyclopentadienyl) were prepared directly from reactions between (Cp)UI or (Cp)UI and corresponding pseudohalide salts. The mixed-ligand complex (Cp)U(N)(OTf) () was isolated after heating a 1:1 mixture of and . The coordination of 1 equiv B(CF) to produced the borane-capped azide (Cp)U(N)[(μ-η:η-N)B(CF)] (), while the reaction of 1 equiv B(CF) with yielded (Cp)U(NCO)[(μ-η:η-OCN)B(CF)] () in which the borane-capped cyanate ligand had rearranged to become O-bound to uranium. The reaction of (Cp)UI and NaOCN led to the isolation of the uranium(III) cyanate-bridged "molecular square" [(Cp)U(μ-η:η-OCN)] (). Cyclic voltammetry and UV-vis spectroscopy revealed small differences in the electronic properties between azide and isocyanate complexes, while X-ray crystallography showed nearly identical solid-state structures, with the most notable difference being the geometry of borane coordination to the azide in versus the cyanate in . Reactivity studies comparing to the azide analogue [(Cp)U(μ-η:η-N)] () demonstrated significant differences in the chemistry of cyanates and azides with trivalent uranium. A computational analysis of , , , and has provided a basis for understanding the energetic preference for specific linkage isomers and the effect of the B(CF) coordination on the bonding between uranium, azide, and isocyanate ligands.