Alkali Metal Control over N–N Cleavage in Iron Complexes

[Image: see text] Though N(2) cleavage on K-promoted Fe surfaces is important in the large-scale Haber–Bosch process, there is still ambiguity about the number of Fe atoms involved during the N–N cleaving step and the interactions responsible for the promoting ability of K. This work explores a molecular Fe system for N(2) reduction, particularly focusing on the differences in the results obtained using different alkali metals as reductants (Na, K, Rb, Cs). The products of these reactions feature new types of Fe–N(2) and Fe-nitride cores. Surprisingly, adding more equivalents of reductant to the system gives a product in which the N–N bond is not cleaved, indicating that the reducing power is not the most important factor that determines the extent of N(2) activation. On the other hand, the results suggest that the size of the alkali metal cation can control the number of Fe atoms that can approach N(2), which in turn controls the ability to achieve N(2) cleavage. The accumulated results indicate that cleaving the triple N–N bond to nitrides is facilitated by simultaneous approach of least three low-valent Fe atoms to a single molecule of N(2).