Synthesis of a Nitrogenase P -Cluster Model with [Fe S (μ-S ) ] Core from the All-Ferric [Fe S (S ) ] Cubane Synthon.

Constructing synthetic models of the nitrogenase P -cluster has been a long-standing synthetic challenge. Here, we report an optimal nitrogenase P -cluster model [{(TbtS)(OEt )Fe S } (μ-STbt) (μ -S)] (2) [Tbt=2,4,6-tris{bis(trimethylsilyl)methyl}phenyl] that is the closest synthetic mimic constructed to date. Of note is that two thiolate ligands and one hexacoordinated sulfide are connecting the two Fe S incomplete cubanes similar to the native P -cluster, which has never been achieved. Cluster 2 has been characterized by X-ray crystallography and relevant physico-chemical methods. The variable temperature magnetic moments of 2 indicate a singlet ground state (S=0). The Mössbauer spectrum of 2 exhibits two doublets with an intensity ratio of 3:1, which suggests the presence of two types of iron sites. The synthetic pathway of the cluster 2 could indicate the native P -cluster maturation process as it has been achieved from the Fe S cubane Fe S (STbt) (1).