Conversion of Fe–NH₂ to Fe–N₂ with release of NH₃

Tris­(phosphine)­borane ligated Fe­(I) centers featuring N2H4, NH3, NH2, and OH ligands are described. Conversion of Fe–NH2 to Fe–NH3+ by the addition of acid, and subsequent reductive release of NH3 to generate Fe–N2, is demonstrated. This sequence models the final steps of proposed Fe–mediated nitrogen fixation pathways. The five-coordinate trigonal bipyramidal complexes described are unusual in that they adopt S = 3/2 ground states and are prepared from a four-coordinate, S = 3/2 trigonal pyramidal precursor.