Synthesis and characterization of cationic selenium-nitrogen heterocycles from tert-butyl-DAB (DAB=1,4-di-tert-butyl-1,3-diazabutadiene) and SeX(4) via the reductive elimination of X(2) (X = Cl, Br): a distinct contrast with tellurium

The synthesis and comprehensive characterisation of a series of 1,2,5-selenadiazolium salts, which were generated from the direct reaction between the neutral bidentate ligand tert-butyl-DAB and a variety of heavy chalcogen halides, are reported. The formation of the cationic heterocycle from the reaction of SeX(4) (X = Cl, Br) and the ligand results in a two electron redox process where the chalcogen undergoes a two electron reduction concomitant with the elimination of X(2), the oxidation by-product. A reaction pathway for this chemistry has been proposed necessitating several key intermediates. These species have been synthesized and used in a stepwise series of transformations that strongly supports this very unusual reactivity for the chalcogens. In contrast, the reaction between tert-butyl DAB and TeX(4) (X = Cl, Br, I), does not result in redox, rather an octahedral Te(IV) center dot DAB complex is formed or no reaction was observed.