Distonic ions of the “ate” class

Distonic ions of the “Ate” class

The gas phase synthesis, structure, and reactivity of distonic negative ions of the “ate” class are described. “Ate”-class negative ions are readily prepared in the gas phase by addition of neutral Lewis acids, such as BF₃, BH₃, and AlMe₃, to molecular anions, carbene negative ions, and radical anions of biradicals. The ions contain either localized σ- or delocalized π-type radical moieties remote from relatively inert borate and aluminate charge sites. The free radical reactivity displayed by these ions appears to be independent of the charge site. As an example, the distonic alkynyl radical (·C≡CBF₃⁻) is highly reactive and undergoes radical coupling reactions with NO₂, NO, H₂C=CH-CN, and H₂C=CH-CH₃. Radical-mediated group and atom transfers are observed with O₂, CS₂, and CH₃SSCH₃. Furthermore, H-atom abstraction reactions are observed, in accordance with the predicted high C-H bond strength of this species DH₂₉₈(H-C₂BF₃⁻)=130.8 kcal mol⁻¹]. High level ab initio molecular orbital calculations on the prototype “ate”-class distonic ion · CH₂BH₃⁻ and its conventional isomer CH₃BH₂^·− reveal that CH₃BH₂^·− is 3.2 kcal/mol more stable than the α-distonic form. However, the calculations also show that CH₃BH₂^·− is unstable with respect to electron detachment, and only the α-distonic form ·CH₂BH₃⁻ should be experimentally observed in the gas phase.