Stable Uranium(VI) Methyl and Acetylide Complexes and the Elucidation of an Inverse Trans Influence Ligand Series

Thermally
stable uranium­(VI)–methyl and −acetylide
complexes: UVIOR­[N­(SiMe3)2]3 R = −CH3, −CCPh were prepared in
which coordination of the hydrocarbyl group is directed trans to the
uranium–oxo multiple bond. The stability of the uranium–carbon
bond is attributed to an inverse trans influence. The hydrocarbyl
complexes show greater ITI stabilization than that of structurally
related UVIOX­[N­(SiMe3)2]3 (X = F–, Cl–, Br–) complexes, demonstrated both experimentally and computationally.
An inverse trans influence ligand series is presented, developed from
a union of theoretical and experimental results and based on correlations
between the extent of cis-destabilization, the complexes
stabilities toward electrochemical reduction, the thermodynamic driving
forces for UO bond formation, and the calculated destabilization
of axial σ* and π* antibonding interactions.