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-N-2, 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.