Heterometal cubane-type WFe3S4 and related clusters trigonally symmetrized with hydrotris(3,5-dimethylpyrazolyl)borate

The scope of formation and structures of tungsten–iron–sulfur clusters has been explored using reactions based on [(Tp*)WS3]1− (1) as the ultimate precursor. The reaction system 1/FeCl2/NaSEt/S affords the cubane cluster [(Tp*)WFe3S4Cl3]1− (2), which with NaSEt is converted to [(Tp*)WFe3S4(SEt)3]1− (3).Clusters 2 and 3 contain the cubane [WFe3(μ3-S)4]3+ core.Complex 1 with FeCl2/NaSEt forms [(Tp*)WFe2S3Cl2(SEt)]1− (4) with the cuboidal [WFe2(μ2-S)2(μ3-S)(μ2-SR)]2+ core.Treatment of 2 with excess Et3P yields the edge-bridged double [(Tp*)2W2Fe6S8(PEt3)4] (5) with the [W2Fe6(μ3-S)6(μ4-S)2] core. Reaction of 2 with excess View the MathML sourceEt3P/BH4-/HS- leads a mixture of products, from which [(Tp*)2W2Fe5S9Na(SH)(MeCN)]3−(6) was identified.This cluster, as closely related [(Tp)2Mo2Fe6S9(SH)2]3−, exhibits a core topology [W2Fe5Na(μ2-S)2(μ3-S)6(μ6-S)] very similar to the PN cluster of nitrogenase. All reactions were carried out in acetonitrile. The structures of 2–6 were established crystallographically as Et4N+ salts. In the cubane series, substitution of tungsten for molybdenum decreases the [MFe3S4]3+/2+ redox potential by ca. 0.20 V but has a negligible effect on electron distribution. This work expands the small set of previously known weak-field W–Fe–S clusters, demonstrates the existence of tungsten-containing edge-bridged double cubanes and clusters with the PN core topology, and introduces a new cuboidal core structure as found in 4 (Tp = hydrotris(pyrazolyl)borate, Tp* = hydrotris(3,5-dimethylpyrazolyl)borate)