Desulfurization and N2 Binding at an Iron Complex Derived from the C–S Activation of Benzothiophene

Metal insertion into the C–S bonds of thiophenes is a facile route to interesting polydentate ligand scaffolds with C and S donors. Here, we describe iron-mediated C–S activation of a diphenylphosphine-functionalized benzothiophene proligand. Metalation of the proligand with Fe(PMe3)4 gives an initial five-coordinate, diamagnetic iron(II) species with two PMe3 ligands and a dianionic PCS pincer ligand. Upon one-electron reduction, a reactive anionic iron(I) complex is formed. This species then undergoes deep-seated changes, notably cleavage of C–S and C–P bonds in the supporting ligand. Substantial coordination sphere alterations accompany the ligand C–S bond activation, including loss of a sulfur anion from the S–Fe–C metallacycle and reorganization of the two PMe3 ligands. The resulting desulfurized six-coordinate PCC iron complex also has a N2 ligand trans to the vinyl carbon. Reducing this complex then cleaves a C–P bond in the appended diphenylphosphine, giving a phosphido arm. These ligand transformations demonstrate novel approaches to pincers with thiolates and phosphides, which would be difficult to synthesize using typical methods through free ligand salts.