Creation of Gas-Phase Organo-Uranium Species by Removal of “yl” Oxo Ligands From UO22+ Carboxylate Precursor Ions

Rationale

These experiments were conducted to measure the diversity of organo-U (IV) and U (III) ions created using multiple-stage tandem MS and collision-induced dissociation of halogen-substituted U^VIO₂-phenide complexes [UO₂(C₆H₃FX)]⁺, X = Cl, Br, or I.

Methods

Samples of UO₂(O₂C-C₆H₃FX)₂ were prepared by digesting UO₃ with appropriate halogen-substituted carboxylic acids in deionized water. Solutions for ESI were created by diluting the digested sample in 50:50 H₂O/CH₃OH. Precursor ions for multiple-stage tandem MS were generated by electrospray ionization (ESI). Multiple-stage collision-induced dissociation (He collision gas) in a linear quadrupole ion trap mass spectrometer was used to prepare species such as [U^IVFX(C≡CH)]⁺ and U^IIIF(C≡CH)]⁺ for subsequent study of ion-molecule reactions with adventitious neutrals in the ion trap.

Results

Multiple-stage CID of the [UO₂(C₆H₃FX)]⁺, X = Cl, Br, or I, complexes caused removal of both “yl” oxo ligands from of the UO₂²⁺ moiety to create ions such as [U^IVFX(C≡CH)]⁺ and [U^IIIFX]⁺. For [U^IVFXC≡CH]⁺ and [U^IIIFC≡CH]⁺ products, hydrolysis to generate [U^IVFX (OH)]⁺ and [U^IIIF (OH)]⁺, with concomitant loss of HC≡CH, was observed. CID of [UO₂(C₆H₃FBr)]⁺ and [UO₂(C₆H₃FI)]⁺ caused reductive elimination of the respective halogen radicals to generate interesting organo-U (III) species such as [U^IIIF(C≡CH)]⁺ and [U^IIIC₂]⁺.

Conclusions

The use of “preparative” tandem mass spectrometry and a suite of halogen substituted benzoic acid ligands can be used to remove both oxo ligands of UO₂²⁺ and generate a group of homologous organo-U (IV) and organo-U (III) ions for studies of intrinsic reactivity.