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

The reaction of 1 equiv of 1-azidoadamantane with [U(NR)] (R = SiMe) in EtO results in the formation of [U(NR)(NAd)] (, Ad = 1-adamantyl) in good yields. The electronic structure of , as well as those of the related U(V) complexes, [U(NR)(NSiMe)] () and [U(NR)(O)] (), 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 (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 to [NAd], results in increasing U═E distances and E-U-N angles. These changes have two principal effects on the resulting electronic structure: (1) the increasing U═E distances decreases the energy of the f orbital, which is primarily σ* with respect to the U═E bond, and (2) the increasing E-U-N angles increases the energy of f, due to increasing antibonding interactions with the amide ligands. As a result of the latter change, the electronic ground state for complexes and is primarily f in character, whereas the ground state for complex is primarily f.