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

International audienceWe report the use of electron rich iron complexes supported by a dianionic diborate pentadentate ligand system, B(2)Pz(4)Py, for the coordination and activation of ammonia (NH3) and hydrazine (NH2NH2). For ammonia, coordination to neutral (B(2)Pz(4)Py)Fe(ii) or cationic [(B(2)Pz(4)Py)Fe(iii)](+) platforms leads to well characterized ammine complexes from which hydrogen atoms or protons can be removed to generate, fleetingly, a proposed (B(2)Pz(4)Py)Fe(iii)-NH2 complex (3(Ar)-NH2). 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-tert-butylphenoxy radical (ArO) to form a C-N bond in a fully characterized product (2(Ar)), or scavenges hydrogen atoms to return to the ammonia complex (B(2)Pz(4)Py)Fe(ii)-NH3 (1(Ar)-NH3). Interestingly, when (B(2)Pz(4)Py)Fe(ii) is reacted with NH2NH2, a hydrazine bridged dimer, (B(2)Pz(4)Py)Fe(ii)-NH2NH2-Fe(ii)(B(2)Pz(4)Py) ((1(Ar))(2)-NH2NH2), is observed at -78 degrees C and converts to a fully characterized bridging diazene complex, 4(Ar), along with ammonia adduct 1(Ar)-NH3 as it is allowed to warm to room temperature. Experimental and computational evidence is presented to suggest that (B(2)Pz(4)Py)Fe(ii) induces reductive cleavage of the N-N bond in hydrazine to produce the Fe(iii)-NH2 complex 3(Ar)-NH2, which abstracts H atoms from (1(Ar))(2)-NH2NH2 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