New Synthetic Routes to Metal‐Sulfur Clusters Relevant to the Nitrogenase Metallo‐Clusters

The nitrogenase metallo‐clusters, namely P‐cluster and FeMo‐cofactor, have been attracting considerable interests because they are indispensable for biological reduction of N 2 to ammonia. These clusters contain eight transition metals and several sulfur atoms in the core, and represent the most complex class of the active sites of metallo‐enzymes. The complexity of these metallo‐clusters should be associated with their roles in the nitrogenase reaction, whereas the relationship between their structures and functions still remains unclear. Mutagenesis studies and spectroscopic techniques are useful to provide insights into properties of the P‐cluster and the FeMo‐cofactor. A complementary approach to gain better understanding of these clusters would be the chemistry of their molecular models based on inorganic synthesis. This review summarizes the recent progresses in the synthesis and properties of metal‐sulfur clusters relevant to the P‐cluster or the FeMo‐cofactor of nitrogenase. Although synthesis of reliable models of FeMo‐cofactor is still a matter of substantial challenges, the synthetic analogues of P‐cluster are approaching the stage that enables the comparison of the structures and properties with the native cluster.