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 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 P^N 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 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).