Effects of N Binding Mode on Iron-Based Functionalization of Dinitrogen to Form an Iron(III) Hydrazido Complex.

Distinguishing the reactivity differences between N complexes having different binding modes is crucial for the design of effective N-functionalizing reactions. Here, we compare the reactions of a K-bridged, dinuclear FeNNFe complex with a monomeric Fe(N) complex where the bimetallic core is broken up by the addition of chelating agents. The new anionic iron(0) dinitrogen complex has enhanced electron density at the distal N atoms of coordinated N, and though the N is not as weakened in this monomeric compound, it is much more reactive toward silylation by (CH)SiI (TMSI). Double silylation of N gives a three-coordinate iron(III) hydrazido(2-) complex, which is finely balanced between coexisting S = 1/2 and S = 3/2 states that are characterized by crystallography, spectroscopy, and computations. These results give insight into the interdependence between binding modes, alkali dependence, reactivity, and magnetic properties within an iron system that functionalizes N.