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-toly)amine, [SNScat]H-3, 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 [ONOcat](3-) ligands. In contrast, experimental data suggests a higher degree of S -> W pi donation, giving the W[SNS](2) complex non-innocent electronic character that can be described as a tungsten(IV) metal center coordinated to two [SNSsq](2-) ligands.