Iron-Catalyzed Alkyne Carboamination via an Isolable Iron Imide Complex

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.