Nickel-catalyzed hydroimination of alkynes

Article abstract of DOI:10.1021/jacs.5b02272

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.