ELEMENTARY REACTIONS, STRUCTURE-FUNCTION-RELATIONSHIPS, AND THE POTENTIAL RELEVANCE OF LOW-MOLECULAR-WEIGHT METAL-SULFUR LIGAND COMPLEXES TO BIOLOGICAL N-2 FIXATION

This article tries to rationalize the shortcomings of various model co mpounds and discusses requirements that a low-molecular compound must fulfill in order to become a potentially competitive catalyst for nitr ogenases. For fundamental reasons, such a synthetic catalyst cannot be a precise structural duplicate of the active centers of nitrogenase. Results obtained with iron-sulfur carbonyl and diazene complexes furth er indicate that (1) the coupling and chronology of proton and electro n transfer steps, (2) invariance of iron-sulfur distances within a wid e range of electron density changes at the iron centers, and (3) Brons ted basic thiolate donors favoring the protonation of metal-sulfur cor es and the formation of N-H ... S bridges may be essential in order to reduce N-2 via N2H2 and N2H4 to NH3 under mild conditions.