Proton-Coupled Reduction of an Iron Cyanide Complex to Methane and Ammonia.

Nitrogenase enzymes mediate the six-electron reductive cleavage of cyanide to CH4 and NH3 . Herein we demonstrate for the first time the liberation of CH4 and NH3 from a well-defined iron cyanide coordination complex, [SiP(iPr) 3 ]Fe(CN) (where [SiP(iPr) 3 ] represents a tris(phosphine)silyl ligand), on exposure to proton and electron equivalents. [SiP(iPr) 3 ]Fe(CN) additionally serves as a useful entry point to rare examples of terminally-bound Fe(CNH) and Fe(CNH2 ) species that, in accord with preliminary mechanistic studies, are plausible intermediates of the cyanide reductive protonation to generate CH4 and NH3 . Comparative studies with a related [SiP(iPr) 3 ]Fe(CNMe2 ) complex suggests the possibility of multiple, competing mechanisms for cyanide activation and reduction.