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(mu(3)-S)(4)](3+) core. Complex 1 with FeCl2/ NaSEt forms [(Tp*)WFe(2)S(3)Ck(SEt)](1-) (4) with the cuboidal [WFe2(mu(2)-S)(2)(mu(3)-S)(mu(2)-SR)](2+) core. Treatment of 2 with excess Et3P yields the edge-bridged double [(Tp*)(2)W(2)Fe(6)Ss(PEt3)(4)] (5) with the [W2Fe6(mu(3)-S)(6)(mu(4)-S)(2)] core. Reaction of 2 with excess Et3P/BH4- /HS- leads a mixture of products, from which [(Tp*)(2)W2Fe6S8Na(SH)(MeCN)](3-) (6) was identified. This cluster. as closely related [(Tp)(2)Mo2Fe6S9(SH)(2)](3-), exhibits a core topology [W2Fe5Na(mu(2)-S)(2)(mu(3)-S)(6)(mu(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 Et4N perpendicular to 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 P-N core topology, and introduces a new cuboidal core structure as found in 4 (Tp = hydrotris(pyrazolyl)borate, Tp* = hydrotris(3,5-dilnethylpyrazolyl)borate). (c) 2005 Elsevier B.V. All rights reserved.