Site-differentiated ligand substitutions of the incomplete-cubane type W-Fe-S clusters

A comprehensive study of the reactivity at the core bridging sites and the terminal site of Fe-S cluster will provide a useful reference for understanding the potential N₂ binding sites in FeMo-cofactor. While traditional Fe-S clusters exhibit no chemical reactivity within the core due to the saturated Fe coordination by S-containing ligands, the previously synthesized incomplete-cubane cluster [(Tp*)WFe₂S₃(η-Cl)₂(μ₂-Cl)]⁻ (1) [Tp*=tris(3,5-dimethyl-1-pyrazolyl)hydroborate(1−)] provides a good platform for such investigations. In this work, the reactivity of the cluster at different ligand sites within and outside the core has been studied. The µ₂-bridging chloride within the core demonstrates higher reactivity toward ligand metathesis by methanethiolate or thiophenolate ligand, as compared with the terminally bound chlorides outside the core. Interestingly, the reactivity of the bridging and terminal chlorides could not be differentiated when p-thiocresolate is employed as the substituent for room temperature reaction. Single-crystal structures and redox behaviors of the thus synthesized W-Fe-S clusters have been studied systematically.