Reactivity and structure of the 5-dehydro-m-xylylene anion

The electronic structure of dehydro-m-xylylene anion (DMX-) has been investigated by using chemical reactivity studies and electronic structure calculations. DMX- has been generated in the gas phase via the sequential reaction of trimethyl-3,5-bis(trimethylsilylmethyl)phenylsilane with F- and two molecules of F-2. Reactivity and thermochemical properties of the ion indicate a phenyl-like anion (1a), consistent with theoretical predictions. Density functional calculations predict a nonplanar triplet anion, with an allenic singlet anion slightly higher in energy. The driving force for the out-of-plane distortion is more efficient charge delocalization that is achieved at lower symmetry.