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(η(1)-HN═CPh2)(η(2)-HN═CPh2)], was independently synthesized and displayed improved reactivity as the catalyst precursor.