Nickel-Catalyzed Intermolecular Alkyne Hydrohydrazonation

We report a method for mild and atom-efficient synthesis of ketazines via nickel-catalyzed intermolecular hydroamination of internal alkynes with NH2-hydrazones. This alkyne hydrohydrazonation process is promoted by [Ni(cod)2] as a Ni(0) precatalyst and IPr as a N-heterocyclic carbene (NHC) ligand. A stoichiometric reaction between in situ generated [Ni(IPr)2] and benzophenone hydrazone (Ph2C=NNH2) led to the isolation of IPr-coordinated and hydroxo-bridged dinuclear Ni(II) hydrazonato complex [(IPr)Ni(HNN=CPh2)(miu2-OH)]2 that displayed high activity as a hydrohydrazonation pre-catalyst. We propose a catalytic cycle involving C-N bond formation via alkyne insertion into the Ni-N linkage of Ni(II) hydrazonato intermediates.