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: (UOR)-O-VI[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 (UOX)-O-VI[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 sigma and pi* antibonding interactions.