Full Electron Delocalization across the Cluster in 1,12-bisBMes 2 - p -carborane Radical Anion.

Conjugation between three-dimensional (3D) carboranes and the attached substituents is commonly believed to be very weak. In this paper, we report that reducing 1,12-bis(BMes ₂ )- p -carborane ( B ₂ p Cab ) with one electron gives a radical anion with a centrosymmetric semiquinoidal structure. This radical anion shows extensive electron delocalization between the two boron centers over the p -carborane bridge due to the overlap of carborane lowest unoccupied molecular orbital (LUMO) and the BMes ₂ LUMO. Unlike dianions of other C ₂ B ₁₀ H ₁₂ carboranes, which rearrange to a nido -form, two-electron reduction of B ₂ p Cab leads to a rearrangement into a basket-shaped intermediate.