Probing the 5f Orbital Contribution to the Bonding in a U(V) Ketimide Complex

Reaction of UCl4 with 5 equiv of Li­(NCtBuPh) generates the homoleptic U­(IV) ketimide complex [Li­(THF)2]­[U­(NCtBuPh)5] (1) in 71% yield. Similarly, reaction of UCl4 with 5 equiv
of Li­(NCtBu2) affords [Li­(THF)]­[U­(NCtBu2)5] (2) in 67% yield.
Oxidation of 2 with 0.5 equiv of I2 results
in the formation of the neutral U­(V) complex U­(NCtBu2)5 (3). In contrast, oxidation
of 1 with 0.5 equiv of I2, followed by addition
of 1 equiv of Li­(NCtBuPh), generates the octahedral
U­(V) ketimide complex [Li]­[U­(NCtBuPh)6] (4) in 68% yield. Complex 4 can be further
oxidized to the U­(VI) ketimide complex U­(NCtBuPh)6 (5). Complexes 1–5 were characterized by X-ray crystallography, while SQUID magnetometry,
EPR spectroscopy, and UV–vis–NIR spectroscopy measurements
were also preformed on complex 4. Using this data, the
crystal field splitting parameters of the f orbitals were determined,
allowing us to estimate the amount of f orbital participation in the
bonding of 4.