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

Tris(phosphine)borane ligated Fe(I) centers featuring N(2)H(4), NH(3), NH(2), and OH ligands are described. Conversion of Fe-NH(2) to Fe-NH(3)(+) by the addition of acid, and subsequent reductive release of NH(3) 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.