Redox Reactions between Phosphines (R3P; R = nBu, Ph) or Carbene (iPr2IM) and Chalcogen Tetrahalides ChX4 (iPr2IM = 2,5-diisopropylimidazole-2-ylidene; Ch = Se, Te; X = Cl, Br)

The reactions between chalcogen tetrahalides (ChX4; Ch = Se, Te; X = Cl, Br) and the neutral donors nBu3P, Ph3P, or the N-heterocyclic carbene, 2,5-diisopropylimidazole-2-ylidene (iPr2IM), have been investigated. In cases involving a phosphine, the chemistry can be understood in terms of a succession of two-electron redox reactions, resulting in reduction of the chalcogen center (e.g., Se(IV) → Se(II)) and the oxidation of phosphorus to the [R3P−X] cation (P(III) → P(V)). The stepwise reduction of Se(IV) → Se(II) → Se(0) → Se(−II) occurs upon the successive addition of stoichiometric equivalents of Ph3P to SeCl4, which can readily be monitored by 31P{1H} NMR spectroscopy. In the case of reacting SeX4 with iPr2IM, a similar two-electron reduction of the chalcogen is observed and there is the concomitant production of a haloimidazolium hexahaloselenate salt. The products have been comprehensively characterized, and the solid-state structures of [R3PX][SeX3] (9), [Ph3PCl]2[TeCl6] (10), iPr2IM−SeX2 (11), and ...