Heterometal cubane-type WFe 3S 4 and related clusters trigonally symmetrized with hydrotris(3,5-dimethylpyrazolyl)borate

Abstract

The scope of formation and structures of tungsten–iron–sulfur clusters has been explored using reactions based on [(Tp*)WS 3] 1− ( 1) as the ultimate precursor. The reaction system 1/FeCl 2/NaSEt/S affords the cubane cluster [(Tp*)WFe 3S 4Cl 3] 1− ( 2), which with NaSEt is converted to [(Tp*)WFe 3S 4(SEt) 3] 1− ( 3).Clusters 2 and 3 contain the cubane [WFe 3(μ 3-S) 4] 3+ core.Complex 1 with FeCl 2/NaSEt forms [(Tp*)WFe 2S 3Cl 2(SEt)] 1− ( 4) with the cuboidal [WFe 2(μ 2-S) 2(μ 3-S)(μ 2-SR)] 2+ core.Treatment of 2 with excess Et 3P yields the edge-bridged double [(Tp*) 2W 2Fe 6S 8(PEt 3) 4] ( 5) with the [W 2Fe 6(μ 3-S) 6(μ 4-S) 2] core. Reaction of 2 with excess Et 3 P / BH 4 - / HS - leads a mixture of products, from which [(Tp*) 2W 2Fe 5S 9Na(SH)(MeCN)] 3−( 6) was identified.This cluster, as closely related [(Tp) 2Mo 2Fe 6S 9(SH) 2] 3−, exhibits a core topology [W 2Fe 5Na(μ 2-S) 2(μ 3-S) 6(μ 6-S)] very similar to the P N cluster of nitrogenase. All reactions were carried out in acetonitrile. The structures of 2– 6 were established crystallographically as Et 4N + salts. In the cubane series, substitution of tungsten for molybdenum decreases the [MFe 3S 4] 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 P N core topology, and introduces a new cuboidal core structure as found in 4 (Tp = hydrotris(pyrazolyl)borate, Tp* = hydrotris(3,5-dimethylpyrazolyl)borate).