Iron-catalyzed alkyne carboamination via an isolable iron imide complex

Research in our group aims to develop new methods for the synthesis of valuable nitrogen-containing products using Earth-abundant transition metal catalysts. Our approach focuses on the underlying reactivity of transition metal complexes proposed as intermediates in the targeted catalytic cycle, taking advantage of stoichiometric studies to gain fundamental insights about the overall transformation. We recently discovered a novel alkyne carboamination process that constructs new C-N and C-C bonds in the reaction of an isolable iron imide complex with a terminal alkyne substrate. The β-alkynyl enamine product formed may serve as a precursor to the 2,4-disubstituted pyrrole via copper(I)-catalyzed cyclization. Reaction of the resultant iron acetylene complex and aryl azide leads to formation of the iron acetylide complex and aniline in a catalyst deactivation pathway. This reactivity is suppressed in the presence of a coordinating additive like tert-butyl pyridine. These observations were vital in rendering the carbomination process catalytic in iron. Other stoichiometric experiments lend support to a reaction mechanism involving [2+2] cycloaddition of the iron imide and alkyne.