Flash Communication: Formation of a Nickel(η²‑stilbene) Complex as an Intermediary Product in the C(sp²)–H Alkenylation of Benzene on a Nickel Center

The C–H alkenylation of arenes using alkynes is an attractive atom-economical method for the construction of vinyl arenes. However, the alkenylation of nonactivated arenes such as unsubstituted benzene remains challenging, particularly when using base metal catalysts such as nickel complexes. Here, we present the stoichiometric C(sp2)–H alkenylation of benzene using an in situ-generated nickel(η2-alkyne) complex to afford a nickel(η2-alkene) complex that represents a key step in the catalytic C(sp2)–H alkenylation of benzene. The reactivity of the obtained nickel(η2-alkene) complex was examined, and an alkenylation mechanism via a ligand-to-ligand hydrogen transfer (LLHT) reaction is proposed based on DFT calculations.