Cubane-type tungsten–iron–sulfur clusters with a nitrogen atom in the core: terminal ligand substitutions and redox behaviors

Abstract

The lack of M–Fe–S (M = Mo or W) clusters incorporating a second period (2p) atom in the core has resulted in limited investigations and poor understanding of the physical and chemical properties of the M–Fe–S clusters closely related to the FeMo cofactor. In this work, systematic studies have been carried out to explore the chemical reactivities at the terminal ligand sites and the redox properties of a series of clusters comprising a [WFe₃S₃N] cubane core, based on the previously developed cluster [(Tp*)WFe₃S₃(μ₃-NSiMe₃)Cl₃]¹⁻. Substitutions of the terminal chlorides with ethanethiolate, methanethiolate, thiophenolate, p-thiocresolate and azide occurred smoothly, while the replacement of the chlorides with carbene ligands required the reduction of the precursor into [(Tp*)WFe₃S₃(μ₃-NSiMe₃)Cl₃]²⁻ first. The reduced cluster core could also be supported by thiophenolates as terminal ligands, but not thiolates or azides. It is remarkable that the thiophenolate ligated reduced cluster can be synthesized from the precursor [(Tp*)WFe₃S₃(μ₃-NSiMe₃)Cl₃]¹⁻via different synthetic routes, either reduction followed by substitution or substitution followed by reduction, either in situ or stepwise. This work indicates that terminal ligands contribute significantly to determine the chemical and physical properties of the clusters, even though they might affect the cluster core to a limited extent from a structural point of view, which raises the possibility of delicate control in regulating the physical/chemical properties of M–Fe–S clusters with a heteroleptic core incorporating 2p atom(s).