Hidden silylium-type reactivity of a siloxane-based phosphonium-hydroborate ion pair.

A new class of siloxane-based cations with hidden silylium-type reactivity is provided, which, in combination with an arylborate counteranion, initiates a highly selective -C(sp)-F defunctionalization of a perfluorinated aryl group. The hydrodefluorinated aryl borane is obtained as a crystalline solid continuous sublimation during the reaction. The heterocyclic six-membered cation could be obtained single-crystalline after dehydrogenative anion exchange. DFT calculations give insight into the bonding within the siloxane-based cation and the mechanism of the ion pair reaction.