Nickel-Catalyzed Hydroimination of Alkynes

A modular and atom-efficient synthesis of 2-aza-1,3-butadiene derivatives has been developed via nickel-catalyzed intermolecular coupling between internal alkynes and aromatic N–H ketimines. This novel alkyne hydroimination process is promoted by a catalyst system of a Ni(0) precursor ([Ni­(cod)2]), N-heterocyclic carbene (NHC) ligand (IPr), and Cs2CO3 additive. The exclusive formation of (Z)-enamine stereoisomers is consistent with a proposed anti-iminometalation of alkyne by π-complexation with Ni(0) and subsequent attack by the N–H ketimine nucleophile. An NHC-ligated Ni(0) π-imine complex, [(IPr)­Ni­(η1-HNCPh2)­(η2-HNCPh2)], was independently synthesized and displayed improved reactivity as the catalyst precursor.