The reactions of a dinitrogen-bridged Fe(II)/Fe(II) complex [(FeH(PP3))(2)(mu-N-2)](2+) (3) (PP3 = P(CH2CH2PMe2)(3)) with base were investigated usin N-15 labeling techniques to enhance characterization. In the presence of base, 3 is initially deprotonated to the Fe(II)/Fe(0) dinitrogen-bridged complex [(FeH(PP3))(kt-N-2)(Fe(PP3))]' (4) and then to the symmetrical Fe(0)/Fe(0) dinilrogen-bridged complex (Fe(PP3))(2)(u-N-2) (5). [(FeH(PP3))(j4-N2)(Fe(PP3))](+) (4) exhibits unusual long-range 31P-31P NMR coupling through the bridging dinitrogen ligand from the phosphines at the Fe(0) center and those at the Fe(II) center. Reaction of 4 with base under an atmosphere of argon resulted in the known dinitrogen Fe(0) complex Fe(N-2)(PP3) (6) and a solvent C H activation product. Complexes 3, 4, and 5 were fully characterized by multinuclear NMR spectroscopy, and complexes 3 and 4 by X-ray crystallography.