Controlled Incorporation of Nitrides into W-Fe-S Clusters.

Incorporation of monatomic 2p ligands into the core of iron-sulfur clusters has been researched since the discovery of interstitial carbide in the FeMo cofactor of Mo-dependent nitrogenase, but has proven to be a synthetic challenge. Herein, two distinct synthetic pathways are rationalized to install nitride ligands into targeted positions of W-Fe-S clusters, generating unprecedented nitride-ligated iron-sulfur clusters, namely [(Tp*)2 W2 Fe6 (µ4 -N)2 S6 L4 ]2- (Tp*=tris(3,5-dimethyl-1-pyrazolyl)hydroborate(1-), L=Cl- or Br- ). 57 Fe Mössbauer study discloses metal oxidation states of WIV2 FeII4 FeIII2 with localized electron distribution, which is analogous to the mid-valent iron centres of FeMo cofactor at resting state. Good agreement of Mössbauer data with the empirical linear relationship for Fe-S clusters indicates similar ligand behaviour of nitride and sulfide in such clusters, providing useful reference for reduced nitrogen in a nitrogenase-like environment.