Intramolecular Oxidative Cyclization of Alkenes and Nitriles with Nickel(0)

The use of Me2AlCl as an additive was found to allow the oxidative addition of the Ar–CN bond in 2-(2-methylallyl)benzonitrile on nickel(0) in the presence of PnBu3, giving a trans-arylnickelcyanide complex. In contrast, in the presence of PCy3, the intramolecular oxidative cyclization on nickel(0) took place to afford a nickeladihydropyrrole. Without the addition of Me2AlCl, the quantitative generation of an η2:η2-5-ene-nitrile Ni(0) species, which was definitely converted to the nickeladihydropyrrole after treatment with Me2AlCl, was observed. In addition, TfOH also promoted the oxidative cyclization of the η2:η2-5-ene-nitrile complex to yield the corresponding five-membered aza-nickelacycle. A similar intramolecular oxidative cyclization occurred when 2-allylbenzonitrile was used in the presence of a Lewis acid, such as Me2AlCl, Me2AlOTf, and Me3SiOTf, or of TfOH to give the corresponding nickeladihydropyrroles in quantitative yield. The molecular structures of a series of nickeladihydropyrroles were unambiguously determined by means of X-ray crystallography. The nickeladihydropyrrole derived from (2-methylallyl)benzonitrile and TfOH was found to react with HSiMe2Ph at 80 °C to furnish a silanamine derivative. The reaction was expanded to a Ni(0)/PCy3/TfOH-catalyzed coupling reaction of 5-ene-nitrile and HSiMe2Ph, yielding the corresponding silanamine in 84% yield.