Electrochemical behaviors of a pincer-type NNN-Fe complex and catalytic H2 evolution activity.

We describe electrochemical reactivity of a pincer-type [NNN-Fe(tBuNC)3](ClO4)2 complex. Upon electron reduction, the Fe(i) species experienced disproportionation to Fe(0) and Fe(ii). An electron-reduced Fe center dissociated a tBuNC ligand to make an open coordination site, where a proton could be transferred. The low-spin Fe center, assisted by isocyanide and a pyridine-based NNN-pincer ligand, catalyzed efficiently the proton reduction reaction. Also, a Lewis basic amine site in the side 'arm' of the NNN-pincer ligand lowered the free energy for the protonation of an Fe center during the proton reduction process. DFT calculations provided insight into a plausible catalytic pathway.