Biological nitrogen fixation occurs in nitrogenase enzymes at an Fe-M (M = Mo, V, Fe) cluster cofactor (FeMco). This cluster displays a complex MFe7S8C structure, with sulfides bridges and an unusual central carbide. The function of this biologically unique interstitial carbide motif is not well understood. In order to gain insight into the effect of the bridging carbide on the physical and chemical properties of the cluster, we synthesized a partial model of the form MFe3S3C containing bridging sulfide and a chelating carbyne ligand. We performed a structure-property study using a series of structurally related clusters of the form [Tp*M’Fe3S3X]n-, where M’ = Mo or W, the bridging ligand X = CR, N, NR, S, and Tp* = tris(3,5-dimethyl-1-pyrazolyl)hydroborate. While changing M’ only leads to minor differences, the chelating, μ3-bridging carbyne leads to large shifts in reductions potential, up to 1 V more reducing than the nonchelating N and S analogs.

Partial synthetic models of FeMoco with sulfide and carbyne ligands: Effect of interstitial atom in nitrogenase active site

ACS Spring 2022

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