Nitrogen Complexes as Models for Nitrogenase with Nitrogen on the Active Site
NITROGEN gas reacts in mild conditions in protic media to give the nitrogen complexes [CoH(N2)(PPh3)3]1, and [Ru(NH3)5(N2)]X2 (X = mono anion)2, and related complexes, but the complexed nitrogen molecule has not yet been reduced to ammonia3. Nevertheless, the mechanism of nitrogen uptake in the formation of these complexes may represent the process by which nitrogen is bound in nitrogenase, and the reduction to ammonia could occur in nature by protonation of the complexed nitrogen with simultaneous influx of electrons from the metal. We have therefore studied quantitatively the reactions with strong acids of [CoH(N2)(PPh3)3]1, the substance formulated as [Co(N2)(PPh3)3]4, trans-[IrCl(N2)(PPh3)2]5, and [Ru(NH3)5-(N2)]X2 (X = Cl or BF4)6,7. If protonation occurred, some reduction of the nitrogen with simultaneous oxidation of the metal would be expected. We have found that in general there is oxidation of the metal by the acid, but it leads to nitrogen evolution, often together with hydrogen, and no ammonia.