Six-coordinate uranium complexes featuring a bidentate anilide ligand

The synthesis of a new bidentate anilide ligand and four uranium amide complexes utilizing the ligand are reported. The secondary aniline HNR]Ar_MeL (R = C(CD₃)₂CH₃, Ar_MeL = 2-NMe₂-5-MeC₆H₃) is prepared by condensation of H₂NAr_MeL and acetone-d₆ followed by alkylation of the resulting imine with MeLi. The ligand precursors (Et₂O)Li(NR]Ar_MeL) and K(NR]Ar_MeL) are prepared through deprotonation of HNR]Ar_MeL with n-BuLi and KH, respectively. Treatment of UI₃(THF)₄ with (Et₂O)Li(NR]Ar_MeL) (2 equiv) provides the uranium(III) -ate complex LiI₂U(NR]Ar_MeL)₂] (Li1]), while treatment of UI₃ with three equiv. of K(NR]Ar_MeL) provides the neutral uranium(III) complex U(NR]Ar_MeL)₃ (2). Both uranium(III) complexes are susceptible to 1e oxidation, as is demonstrated by the syntheses of the uranium(IV) derivatives I₂U(NR]Ar_MeL)₂ (1) and U(NR]Ar_MeL)₃]OTf] (2]OTf]; OTf = CF₃SO₃). The spectroscopic and X-ray structural characterization of all four uranium complexes is described. The structures of 2 and 2]OTf] exhibit a large degree of steric pressure about the uranium center, effectively preventing the 2]⁺ ion from achieving a seven-coordinate structure.