Synthesis and Characterization of Uranium Complexes Supported by Substituted Aryldimethylsilylanilide Ligands

Abstract

We report the synthesis and characterization of substituted aryldimethylsilyldiisopropylanilide ligands and their respective bisamido complexes of U(III), (3,5-R2-PhMe2SiNDipp)2UI(dioxane)x (1, R = H, x= 0; 2, R = Me, x = 0; 3, R = tBu, x = 1). We found that the steric bulk of the 3,5-R2-Ph ring affects the hapticity of the U-arene interaction. In the solid-state, 1 is a U-(η6-arene) complex, while 2 is a bis(U-(η1-arene)) complex. Theoretically calculated bond orders at PBE0 and PBE0-D3 levels of theory support these hapticity assignments. The 3,5-tBu2-Ph rings of 3 are too bulky to interact with U and solid-state metrical parameters initially suggested a U-(η1-arene) interaction with one of the Dipp rings. However, bond order calculations show that this interaction is even weaker than in the previously reported ((PhMe2Si)2N)3U complex, leading to the conclusion that 3 is best described as a U-(η0-arene) complex. Molecular orbital analyses in conjunction with electron localization methods reveal that the U-(η6-arene) bonding in 1 is primarily electrostatic in nature. Some charge transfer takes place from the arene π orbitals to the U 6d/5f hybrid orbitals in addition to subtle δ-back-bonding. In 2 and 3, both π and δ interactions are substantially weaker, in agreement with the differences in the U-arene coordination modes. Surprisingly, attempts to generate less sterically bulky (3,5-R2-PhMe2SiNPh)2UI complexes results in disproportionation to homoleptic tetraamido (3,5-R2-PhMe2SiNPh)4U(IV) (4, R = H; 5, R = Me) complexes.