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 HN[R]ArMeL (R = C(CD3)2CH3, ArMeL = 2-NMe2-5-MeC6H3) is prepared by condensation of H2NArMeL and acetone-d6 followed by alkylation of the resulting imine with MeLi. The ligand precursors (Et2O)Li(N[R]ArMeL) and K(N[R]ArMeL) are prepared through deprotonation of HN[R]ArMeL with n-BuLi and KH, respectively. Treatment of UI3(THF)4 with (Et2O)Li(N[R]ArMeL) (2 equiv) provides the uranium(III) -ate complex Li[I2U(N[R]ArMeL)2] (Li[1]), while treatment of UI3 with three equiv. of K(N[R]ArMeL) provides the neutral uranium(III) complex U(N[R]ArMeL)3 (2). Both uranium(III) complexes are susceptible to 1e oxidation, as is demonstrated by the syntheses of the uranium(IV) derivatives I2U(N[R]ArMeL)2 (1) and [U(N[R]ArMeL)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.