Mono(pentamethylcyclopentadienyl)uranium(III) Complexes:  Synthesis, Properties, and X-ray Structures of (η-C₅Me₅)UI₂(THF)₃, (η-C₅Me₅)UI₂(py)₃, and (η-C₅Me₅)U[N(SiMe₃)₂]₂

The uranium(III) iodide complex UI 3 (THF) 4 reacts cleanly at ambient temperature with 1 equiv of sodium and potassium pentamethylcyclopentadienide salts in tetrahydrofuran to form the mono-ring uranium(III) complex (η-C 5 Me 5 )UI 2 (THF) 3 ( 1 ). Additionally, reaction of UI 3 (THF) 4 with 2 equiv or more of K(C 5 Me 5 ) in THF solution leads to the formation of the bis-ring adduct (η-C 5 Me 5 ) 2 UI(THF) ( 2 ) in high yield. In the solid state 1 exhibits a pseudo-octahedral mer,trans ligand geometry with the C 5 Me 5 ligand occupying one axial position. U−I bond lengths range from 3.161(1) to 3.179(1) Å, while U−O distances to the THF ligands lie in the range 2.496(8)−2.594(10) Å. 1 also provides a convenient entry into a variety of other mono-ring complexes of uranium(III). In the presence of excess pyridine, the coordinated THF ligands of 1 are readily displaced to form the tris(pyridine) adduct (η-C 5 Me 5 )UI 2 (py) 3 ( 3 ), which exhibits a mer,trans ligand geometry in the solid state similar to that of 1 . Metathesis of the iodide ligands in 1 with 2 equiv of KN(SiMe 3 ) 2 affords the bis(amido) complex (η-C 5 Me 5 )U[N(SiMe 3 ) 2 ] 2 ( 4 ). An X-ray diffraction study of this molecule reveals that methyl groups from both amido ligands are involved in agostic interactions with the uranium(III) center.