Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate.

We report the use of electron rich iron complexes supported by a dianionic diborate pentadentate ligand system, , for the coordination and activation of ammonia (NH) and hydrazine (NHNH). For ammonia, coordination to neutral (BPzPy)Fe(ii) or cationic [(BPzPy)Fe(iii)] platforms leads to well characterized ammine complexes from which hydrogen atoms or protons can be removed to generate, fleetingly, a proposed (BPzPy)Fe(iii)-NH complex (). DFT computations suggest a high degree of spin density on the amido ligand, giving it significant aminyl radical character. It rapidly traps the H atom abstracting agent 2,4,6-tri--butylphenoxy radical (ArO˙) to form a C-N bond in a fully characterized product (), or scavenges hydrogen atoms to return to the ammonia complex (BPzPy)Fe(ii)-NH (). Interestingly, when (BPzPy)Fe(ii) is reacted with NHNH, a hydrazine bridged dimer, (BPzPy)Fe(ii)-NHNH-Fe(ii)(BPzPy) (), is observed at -78 °C and converts to a fully characterized bridging diazene complex, , along with ammonia adduct as it is allowed to warm to room temperature. Experimental and computational evidence is presented to suggest that (BPzPy)Fe(ii) induces reductive cleavage of the N-N bond in hydrazine to produce the Fe(iii)-NH complex , which abstracts H˙ atoms from to generate the observed products. All of these transformations are relevant to proposed steps in the ammonia oxidation reaction, an important process for the use of nitrogen-based fuels enabled by abundant first row transition metals.