An Overview of the Possible Mechanism of Nitrogenase
This page is based largely on the excellent computational work listed in reference [5]. Aside from being very recently done, the reference also contains a fairly long list of other references of past work. Besides fixing dinitrogen, nitrogenase also catalyzes the formation of HD from H2 and D2 mixtures and is inhibited by CO binding.
The most pressing question to consider in the reduction of N2 is how does it coordinate to the active site? Proponents of Fe-binding of N2 reasoned that Fe is the only common metal to all nitrogenases1 (there are all Fe-clusters as well as V and Mo) therefore it is reasonable that N2 reduction occurs there. The very recent study in reference [5] actually concludes that Fe is the binding atom but the mechanism is far more subtle than anyone first suspected.
The FeMo core is large and somewhat flexible. Rod and Norskov postulate that the FeMo core is much more metallic than anyone has guessed before, in effect "passivated" by the S ligation. The calculations suggest that upon coordination of N2 the cluster is flexible enough to expose a single, unsaturated Fe atom for N2 coordination and subsequent reduction to NH3. I was unable to properly adapt the wonderfully illustrative pictures in the original reference to the web so I highly recommend reading this very insightful computational work on the FeMo core. Rod, T. H., and Norskov, J. K., J. Am. Chem. Soc., 2000, 122, 12751
Next: The references used to prepare this page.