Low-valent transition-metal species that concomitantly have low coordination numbers are important reactive species proposed in inert bond-activation reactions.The knowledge on their formation,structure,and reactivity thus lays the basis for many challenging chemical transformations.Aiming to deep our understanding on dinitrogen activation by low-valent iron and cobalt species,we have initiated the study on low-valent iron and cobalt complexes with N-heterocyclic carbenes as supporting ligands.This presentation will introduce our recent studies on the synthesis,structure,and reactivity of two-and three-coordinate iron(0,I)and cobalt(-I,0,I)complexes(see figure below).The coordination chemistry of these low-coordinate low-valent species with dinitrogen will be discussed.