Synthesis and Characterization
of a Redox-Active Bis(thiophenolato)amide Ligand, [SNS]<sup>3–</sup>, and the Homoleptic Tungsten Complexes, W[SNS]<sub>2</sub> and W[ONO]<sub>2</sub>
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Abstract
A new tridentate redox-active ligand platform, derived
from bis(2-mercapto-<i>p</i>-tolyl)amine, [SNS<sup>cat</sup>]H<sub>3</sub>, has been prepared in high yields by a four-step procedure
starting from commericially available bis(<i>p</i>-tolyl)amine.
The redox-active pincer-type ligand has been coordinated to tungsten
to afford the six-coordinate, homoleptic complex W[SNS]<sub>2</sub>. To benchmark the redox behavior of the [SNS] ligand, the analogous
tungsten complex of the well-known redox-active bis(3,5-di-<i>tert</i>-butylphenolato)amide ligand, W[ONO]<sub>2</sub>, 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]<sub>2</sub> is best
described as a tungsten(VI) metal center coordinated to two [ONO<sup>cat</sup>]<sup>3–</sup> ligands. In contrast, experimental
data suggests a higher degree of S→W π donation, giving
the W[SNS]<sub>2</sub> complex non-innocent electronic character that
can be described as a tungsten(IV) metal center coordinated to two
[SNS<sup>sq</sup>]<sup>2–</sup> ligands