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 (PTMSn) 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.