Distonic ions of the “Ate” class

Abstract

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 BF 3, BH 3, and AlMe 3, 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CBF 3 −) is highly reactive and undergoes radical coupling reactions with NO 2, NO, H 2CCH–CN, and H 2CCH–CH 3. Radical-mediated group and atom transfers are observed with O 2, CS 2, and CH 3SSCH 3. Furthermore, H-atom abstraction reactions are observed, in accordance with the predicted high C–H bond strength of this species [DH 298(H–C 2BF 3 −) = 130.8 kcal mol −1]. High level ab initio molecular orbital calculations on the prototype “ate”-class distonic ion · CH 2BH 3 − and its conventional isomer CH 3BH 2 ·− reveal that CH 3BH 2 ·− is 3.2 kcal/mol more stable than the α-distonic form. However, the calculations also show that CH 3BH 2 ·− is unstable with respect to electron detachment, and only the α-distonic form · CH 2BH 3 − should be experimentally observed in the gas phase.