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: U^VIOR­[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 U^VIOX­[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 <i>cis</i>-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