Iron-Catalyzed Alkyne Carboamination via an Isolable Iron Imide Complex

Abstract

Transition metal imide-mediated C–N bond formation is a powerful strategy for the introduction of nitrogen into organic compounds. We have discovered that the reaction of N-mesityl(β-diketiminato)iron imide complex tBuLFeNMes (tBuL = 3,5-bis(2,6-diisopropylphenylimino)-2,2,6,6-tetramethylheptyl and Mes = 2,4,6-trimethylphenyl) with a terminal alkyne substrate gives a β-alkynyl enamine product by a novel alkyne carboamination process. Stoichiometric experiments revealed a catalyst deactivation pathway involving generation of the acetylide complex, tBuLFeCCPh, and mesityl amine (MesNH2) from the acetylene complex, tBuLFe(HCCPh), and mesityl azide (MesN3). This reactivity is suppressed in the presence of coordinating additive 4-tert-butylpyridine (tBuPy), likely through formation of the four-coordinate complex tBuLFe(HCCPh)(tBuPy). These insights were instrumental in identifying reaction conditions that allow for turnover of the iron catalyst.