Synthesis of organo-uranium(II) species in the gas-phase using reactions between [UH]⁺ and nitriles

One challenge in the quest to map the intrinsic reactivity of model actinide species has been the controlled synthesis of organo-actinide ions in the gas phase. We report here evidence that a series of gas-phase, σ-bonded [U-R]⁺ species (where R = CH₃, C₂H₃, C₂H₅, C₃H₇, or C₅H₆) can be generated for subsequent study of ion-molecule chemistry by using preparative tandem mass spectrometry (PTMS) via ion-molecule reactions between [UH]⁺ and a series of nitriles. Density functional theory calculations support the hypothesis that the [U-R]⁺ ions are created in a pathway that involves intramolecular hydride attack and the elimination of neutral HCN. Subsequent reactivity experiments revealed that the [UCH₃]⁺ readily undergoes hydrolysis, yielding cationic uranium hydroxide ([UOH]⁺) and methane (CH₄). Other possible reaction pathways, such as the spontaneous rearrangement to [HUCH₂]⁺, are shown by theoretical calculations to have energy barriers, strengthening the evidence for the formation of a σ-bonded [U-CH₃]⁺ complex in the gas-phase.