Full Electron Delocalization across the Cluster in 1,12-bisBMes₂-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(BMes₂)-p-carborane (BCab) 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 BMes₂ LUMO. Unlike dianions of other C₂B₁₀H₁₂ carboranes, which rearrange to a nido-form, two-electron reduction of BCab leads to a rearrangement into a basket-shaped intermediate.