Elementary reactions, structure-function relationships, and the potential relevance of low molecular weight metal-sulfur ligand complexes to biological N₂ fixation

Abstract

 This article tries to rationalize the shortcomings of various model compounds and discusses requirements that a low-molecular compound must fulfill in order to become a potentially competitive catalyst for nitrogenases. 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 further indicate that (1) the coupling and chronology of proton and electron transfer steps, (2) invariance of iron-sulfur distances within a wide range of electron density changes at the iron centers, and (3) Brönsted basic thiolate donors favoring the protonation of metal-sulfur cores and the formation of N–H···S bridges may be essential in order to reduce N₂ via N₂H₂ and N₂H₄ to NH₃ under mild conditions.