Evaluating f-Orbital Participation in the U V ═E Multiple Bonds of [U(E)(NR 2 ) 3 ] (E = O, NSiMe 3 , NAd; R = SiMe 3 ).

The reaction of 1 equiv of 1-azidoadamantane with [U III (NR 2 ) 3 ] (R = SiMe 3 ) in Et 2 O results in the formation of [U V (NR 2 ) 3 (NAd)] ( 1 , Ad = 1-adamantyl) in good yields. The electronic structure of 1 , as well as those of the related U(V) complexes, [U V (NR 2 ) 3 (NSiMe 3 )] ( 2 ) and [U V (NR 2 ) 3 (O)] ( 3 ), were analyzed with EPR spectroscopy, SQUID magnetometry, NIR-visible spectroscopy, and crystal field modeling. This analysis revealed that, within this series of complexes, the steric bulk of the E 2- (E═O, NR) ligand is the most important factor in determining the electronic structure. In particular, the increasing steric bulk of this ligand, on moving from O 2- to [NAd] 2- , results in increasing U═E distances and E-U-N amide angles. These changes have two principal effects on the resulting electronic structure: (1) the increasing U═E distances decreases the energy of the f σ orbital, which is primarily σ* with respect to the U═E bond, and (2) the increasing E-U-N amide angles increases the energy of f δ , due to increasing antibonding interactions with the amide ligands. As a result of the latter change, the electronic ground state for complexes 1 and 2 is primarily f φ in character, whereas the ground state for complex 3 is primarily f δ .