Synthesis and Characterization of a Redox-Active Bis(thiophenolato)amide Ligand, [SNS]^3–, and the Homoleptic Tungsten Complexes, W[SNS]₂ and W[ONO]₂

A new tridentate redox-active ligand platform, derived from bis­(2-mercapto-p-tolyl)­amine, [SNS^cat]­H₃, has been prepared in high yields by a four-step procedure starting from commericially available bis­(p-tolyl)­amine. The redox-active pincer-type ligand has been coordinated to tungsten to afford the six-coordinate, homoleptic complex W­[SNS]₂. To benchmark the redox behavior of the [SNS] ligand, the analogous tungsten complex of the well-known redox-active bis­(3,5-di-tert-butylphenolato)­amide ligand, W­[ONO]₂, also has been prepared. Both complexes show two reversible reductions and two partially reversible oxidations. Structural, spectroscopic, and electrochemical data all indicate that W­[ONO]₂ is best described as a tungsten­(VI) metal center coordinated to two [ONO^cat]^3– ligands. In contrast, experimental data suggests a higher degree of S→W π donation, giving the W­[SNS]₂ complex non-innocent electronic character that can be described as a tungsten­(IV) metal center coordinated to two [SNS^sq]^2– ligands.