Iron- and Ruthenium-Catalyzed C-N Bond Formation Reactions. Reactive Metal Imido/Nitrene Intermediates

Transition-metal-catalyzed direct C-N bond formation via metal nitrenoid (metal imido/nitrene complexes) transfer reactions such as C-H bond amination/amidation and alkene aziridination is a versatile synthetic strategy for the preparation of nitrogen-containing compounds. In this area of development, iron catalysts are appealing in the context of cost, biocompatibility, and environmental sustainability, and iron-catalyzed direct amination reactions have become a complementary approach in the preparation of nitrogen-containing organic compounds with complexity. Reactive iron imido/nitrene species have been widely proposed as the reaction intermediates for direct reactions with C-H and C═C bonds. However, their short lifetimes in solution make the study of these species difficult. In comparison with iron, ruthenium nitrenoids are considerably more stable but yet are reactive enough for amination reactions, leading to reliable surrogates in understanding the reaction mechanism. In this Perspective, the developments in iron and ruthenium complexes supported by macrocyclic or polydentate ligands for the catalytic amination reactions that occur via metal imido/nitrene intermediates are summarized, as well as the mechanisms involved with highlights on the reactive intermediates. Current limitations, challenges, and potential opportunities for future developments are also discussed.