A Substrate-Dependent Redox Catalysis of Tellurenyl Species Involving Oxidation States +I, +II, and +IV

Neutral Te(II) species 2-(<i>t</i>BuNCH)C₆H₄TeCl (<b>[I]Cl</b>) as well as tellurenyl Te(II)⁺ cations [2-(<i>t</i>BuNCH)C₆H₄Te][X] (X = OTf or SbF₆), i.e., <b>[I][OTf]</b> and <b>[I][SbF</b>_<b>6</b><b>]</b>, exhibit a wide range of reactivity toward various <i>ortho</i>-quinones. While the reaction of <i>ortho</i>-chloranil leads to the oxidation of Te(II) into Te(IV), 3,5-di-<i>tert</i>-butyl-<i>ortho</i>-benzoquinone leads only to partial oxidation due to an ongoing dynamic reversible reaction, being the first example of a chemically reversible two electron Te(II)/Te(IV) redox couple. By contrast, 9,10-phenanthrenequinone as a very weak oxidant shows no reaction; however, the most Lewis acidic <b>[I][SbF</b>_<b>6</b><b>]</b> produces a corresponding Lewis adduct interacting by both electrostatic and weak chalcogen bond interactions. The diverse reactivity scope is further complemented by DFT computed thermochemistry data. Furthermore, <b>[I][OTf]</b> is successfully utilized for the catalytic transfer of silanes (Et₃SiH, Ph₃SiH, Ph₂SiH₂, and (EtO)₃SiH) to <i>ortho</i>-quinones via redox single or double Si-H bond activation, yielding silylated catechols, monomeric cyclic catecholatosilanes, or bis(catecholato)silanes. Surprisingly, in the absence of the catalyst <b>[I][OTf]</b>, the reactivity spans from no reaction to the formation of hexachloro-dibenzo[1,4]dioxine-2,3-dione. The latter product is an entirely different substance class compared to the one formed during the catalyzed reaction.