Positively Charged Selenium‐ and Tellurium‐Stabilized Species

Cationic chalcogenium species have attracted some attention due to the ability of these highly electropositive centers to interact with organic molecules or to provide strong π‐accepter ligands for transition metals. Though the cationic selenium and tellurium species are very useful for organic synthesis, most of the naked cationic chalcogen species, with the exception of tricoordinated chalcogenium salt (R 3 Ch + , Ch = chalcogen atoms), are unstable and difficult to isolate as a result of their intrinsic high reactivity. However, if the cationic chalcogen species are supported by the coordination of neighboring p ‐block elements bearing a lone electron pair, they are often stabilized dramatically. Several cationic selenium and tellurium species which are naturally unstable have been synthesized and isolated by the intra‐ and intermolecular coordination of various ligands. The main purpose of this chapter is to introduce the recent progress of positively charged selenium and tellurium species, mainly focused on the dicationic selenium(II, IV, VI) and tellurium(II, IV, VI) species, which are stabilized by the coordination with p ‐block elements.