Complexes with Nitrogen-Centered Radical Ligands: Classification, Spectroscopic Features, Reactivity, and Catalytic Applications

The electronic structure, spectroscopic features, and (catalytic) reactivity of complexes with nitrogen‐centered radical ligands are described. Complexes with aminyl ([M(.NR2)]), nitrene/imidyl ([M(.NR)]), and nitridyl radical ligands ([M(.N)]) are detectable and sometimes even isolable species, and despite their radical nature frequently reveal selective reactivity patterns towards a variety of organic substrates. A classification system for complexes with nitrogen‐centered radical ligands based on their electronic structure leads to their description as one‐electron‐reduced Fischer‐type systems, one‐electron‐oxidized Schrock‐type systems, or systems with a (nearly) covalent MN π bond. Experimental data relevant for the assignment of the radical locus (i.e. metal or ligand) are discussed, and the application of complexes with nitrogen‐centered radical ligands in the (catalytic) syntheses of nitrogen‐containing organic molecules such as aziridines and amines is demonstrated with recent examples. This Review should contribute to a better understanding of the (catalytic) reactivity of nitrogen‐centered radical ligands and the role they play in tuning the reactivity of coordination compounds. Radical character is found in many complexes with nitrogen ligands, as shown by studies of their electronic structure, spectroscopic features, and (catalytic) reactivity. The Review focuses on the reactivity of detectable aminyl ([M(.NR2)]), nitrene/imidyl ([M(.NR)]), and nitridyl radical complexes ([M(.N)]), and their application in the (catalytic) synthesis of nitrogen‐containing organic molecules such as aziridines and amines.