Solvent- and Halide-Induced (Inter)conversion between Iron(II)-Disulfide and Iron(III)-Thiolate Complexes

Abstract

Disulfide/thiolate interconversion controlled by Cu is proposed to be involved in relevant biological processes. In analogy to Cu, it can be envisaged that Fe also participates in the control of similar biological processes. We describe here Fe complexes that undergo Fe^III -thiolate/Fe^II -disulfide (inter)conversion mediated by halide (de)coordination, and by the nature of the solvent. The dinuclear Fe^II -disulfide complex [Fe^II₂ (LSSL)]²⁺ ((LS)^2- =2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1-diphenylethanethiolate), (LSSL)^2- =the corresponding disulfide ligand) shows solvent-dependent properties. Whereas in a non-coordinating solvent (CH₂ Cl₂ ) the dinuclear Fe^II -disulfide complex is the only stable form, in the presence of coordinating solvents like MeCN or DMF it is partly or fully converted into mononuclear Fe^III -thiolate species having a bound solvent molecule ([Fe^III (LS)(Solv)]⁺ , Solv=DMF, MeCN). Addition of Cl^- to a CH₂ Cl₂ solution containing the Fe^II -disulfide dinuclear complex leads to the fast and quantitative formation of a mononuclear Fe^III -thiolate species with a bound Cl^- , that is, ([Fe^III (LS)Cl]). The reverse reaction can be achieved by addition of Li[[B(C₆ F₅ )₄ ]. In relation to the metal-sulfur electronic distribution, the comparison between the redox properties of the Fe, Mn and Co complexes involved in these M^III -thiolate/M^II -disulfide interconversion processes allow one to rationalize their respective efficiency.

Keywords: iron complexes; metal-thiolate; molecular switches; redox chemistry; thiolate-disulfide interconversion.