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