Reaction of an Invisible Frustrated N/B Lewis Pair with Dihydrogen

D-(+)-Camphor forms the enamine 2 with piperidine. Compound 2 adds HB(C6F5)(2) at the enamine carbon atom C3 to form a Lewis acid/Lewis base adduct (exo-/endo-isomers of 3). Exposure of 3 to dihydrogen (2.5 bar, room temperature) leads to heterolytic splitting of H-2 to form the H+/H- addition products (4, two diastereoisomers) of the invisible frustrated Lewis pairs (5, two diastereoisomers) that were apparently generated in situ by enamine hydroboration under equilibrium conditions.