A Stable but Highly Reactive Phosphine‐Coordinated Borenium: Metal‐free Dihydrogen Activation and Alkyne 1,2‐Carboboration

Abstract

Abstract Borenium cations have been found to be valuable analogues of boranes as a result of their cationic character which imparts high electrophilicity. Herein, we report the synthesis, characterization, and reactivity of a new type of borenium cation employing a naphthyl bridge and a strong intramolecular P→B interaction. The cation reacts with H 2 in the presence of P t Bu 3 (frustrated Lewis pair (FLP) approach) but also on its own. The mechanism of the reaction between the borenium cation and H 2 in the absence of P t Bu 3 has been investigated using deuterium‐labeling experiments and DFT calculations. Both experiments and calculations imply the side‐on coordination of H 2 to the B center, followed by heterolytic splitting and BC bond cleavage. An uncommon syn 1,2‐carboboration has also been observed upon reaction of the borenium ion with 3‐hexyne.