Metal Clusters as Ligands. Substitution of Fe Ions in Fe/Mo/S Clusters by Thiophilic Cu^I Ions

The reactivity of Fe/S and Fe/Mo/S clusters, similar or analogous to those occurring in biological systems, with thiophilic metal ions has not been explored. In this Communication, we demonstrate that synthesis of heteropolynuclear clusters with different coordination geometries for different metals at different sites is possible by metal substitution or by metal addition reactions. The two clusters we report herein ([(Cl₄-cat)₂Mo₂Cu₅Fe₄S₉(PⁿPr₃)₇(SPⁿPr₃)₂]PF₆ and [(Cl₄-cat)₂Mo₂Cu₆Fe₄S₁₀(PⁿPr₃)₈]) contain Fe, Mo, and Cu, which display pseudotetrahedral, pseudooctahedral, and pseudotrigonal geometries, respectively. The synthesis of these clusters is achieved by the addition of appropriate amounts of [Cu(CH₃CN)₄]⁺ to [(Cl₄-cat)₂Mo₂Fe₈(PⁿPr₃)₆]. The formation of the different products is temperature- and solvent-dependent. The Cu^I units incorporated into the metal cluster framework, either bind to available lone pairs of the already bridging S ligands or displace the less thiophilic Fe atoms. Among the essential features of these new molecules are recognizable Fe/S fragments including an Fe₆S₉ core in the first cluster and the pentlandite Fe₄Cu₄S₆ core in the second cluster.