Redox non-innocence of a nitrido bridge in a methane-activating dimer of iron phthalocyanine

A nitrido-bridged iron phthalocyanine has recently been shown to catalyze hydrocarbon activation, displaying in this respect distinctly different reactivity than the monomeric phthalocyanine or the oxo-bridged dimer. Here, DFT calculations are shown on models of this catalyst, indicating a distinct difference in electronic structures between the mu-oxo and mu-nitrido-bridged dimers, with the nitride acting as a remarkable charge reservoir and acquiring S = 1 N-character while the oxo bridge remains redox-inert; this difference in charge localization appears to be mirrored by a tendency towards higher symmetry in the Fe-N/O bonds with the nitrido bridge compared to the oxo one, and by a tendency of the nitride to favour lower-spin states more efficiently than the oxide.