Alkali-Controlled C-H Cleavage or N-C Bond Formation by N2-Derived Iron Nitrides and Imides

Formation of N-H and N-C bonds from functionalization of N-2 is a potential route to utilization of this abundant resource. One of the key challenges is to make the products of N-2 activation reactive enough to undergo further reactions under mild conditions. This paper explores the strategy of alkali control, where the presence of an alkali metal cation enables the reduction of N-2 under mild conditions, and then chelation of the alkali metal cation uncovers a highly reactive species that can break benzylic C-H bonds to give new N-H and Fe-C bonds. The ability to turn on this C-H activation pathway with 18-crown-6 is demonstrated with three different N-2 reduction products of N-2 cleavage in an iron potassium system. The alkali control strategy can also turn on an intermolecular reaction of an N-2-derived nitride with methyl tosylate that gives a new N-C bond. Since the transient K+-free intermediate reacts with this electrophile but not with the weak C-H bonds in 1,4-cyclohexadiene, it is proposed that the C-H cleavage occurs by a deprotonation mechanism. The combined results demonstrate that a K+ ion can mask the latent nudeophilicity of N-2-derived nitride and imide ligands within a trimetallic iron system and points a way toward control over N-2 functionalization.