Cooperativity between low-valent iron and potassium promoters in dinitrogen fixation.

A density functional theory (DFT) study was performed to understand the role of cooperativity between iron-β-diketiminate fragments and potassium promoters in N(2) activation. Sequential addition of iron fragments to N(2) reveals that a minimum of three Fe centers interact with N(2) in order to break the triple bond. The potassium promoter stabilizes the N(3-) ligand formed upon N(2) scission, thus making the activated iron nitride complex more energetically accessible. Reduction of the complex and stabilization of N(3-) by K(+) have similar impact on the energetics in the gas phase. However, upon inclusion of continuum THF solvent effects, coordination of K(+) has a reduced influence upon the overall energetics of dinitrogen fixation; thus, reduction of the trimetallic Fe complex becomes more impactful than coordination of K(+) vis-à-vis N(2) activation upon the inclusion of solvent effects.