Decay of iron(V) nitride complexes by a N-N bond-coupling reaction in solution: a combined spectroscopic and theoretical analysis.

Cryogenically trapped Fe(V) nitride complexes with cyclam-based ligands were found to decay by bimolecular reactions, forming exclusively Fe(II) compounds. Characterization of educts and products by Mössbauer spectroscopy, mass spectrometry, and spectroscopy-oriented DFT calculations showed that the reaction mechanism is reductive nitride coupling and release of dinitrogen (2 Fe(V)≡N→Fe(II)-N=N-Fe(II)→2 Fe(II)+N2). The reaction pathways, representing an "inverse" of the Haber-Bosch reaction, were computationally explored in detail, also to judge the feasibility of yielding catalytically competent Fe(V)(N). Implications for the photolytic cleavage of Fe(III) azides used to generate high-valent Fe nitrides are discussed.