Mixed-Valence Dinitrogen-Bridged Fe(0)/Fe(II) Complex

The reactions of a dinitrogen-bridged Fe(II)/Fe(II) complex [(FeH(PP3))2(μ-N2)]2+ (3) (PP3 = P(CH2CH2PMe2)3) with base were investigated using 15N 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))(μ-N2)(Fe(PP3))]+ (4) and then to the symmetrical Fe(0)/Fe(0) dinitrogen-bridged complex (Fe(PP3))2(μ-N2) (5). [(FeH(PP3))(μ-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(N2)(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.