Ambiphilic BP Fragments in Dicoordinate Boron Cations as a Platform for C─H and C─C Multiple Bond Activation.

Herein, we report the application of a boron cation containing a BP ambiphilic fragment in the activation of unsaturated hydrocarbons. The in situ generated phosphinoborinium ion reacts with phenylacetylene, resulting in C─H bond activation and formation of the first borenium ion bearing an acetylide ligand as the main product. A second, minor product is formed via hydroboration of phenylacetylene and features a four-membered BPCN ring with a vinyl group attached to the boron atom. The reactions of the BP cation with styrene or diphenylacetylene afford unprecedented adducts between the borinium ion and the alkene or alkyne, resulting from a cycloaddition between the CC and BP fragments. The structures of the obtained products were elucidated by multinuclear NMR spectroscopy and single-crystal X-ray diffraction. Density functional theory (DFT) calculations of the reaction mechanisms confirm the crucial role of the BP ambiphilic fragment in the activation of C─H and C─C multiple bonds.