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.