New 3,1,2,4-benzothiaselenadiazines, related π-heterocycles including Herz cations, radicals and molecular complexes, and Bunte salts

New chalcogen–nitrogen π-heterocycles covering 3,1,2,4-benzothiaselenadiazines, 1,3,2,4-benzodithiadiazines and 1,2,4,3,5-benzotrithiadiazepines were synthesized via the electrophilic cyclization of compounds Ar–NSN–SiMe3 under the action of SeCl2, SeCl4/FeCp2, SCl2 and S2Cl2. Heterocycles obtained were thermolyzed into persistent 2,1,3-benzothiaselenazolyls and 1,2,3-benzodithiazolyls (Herz radicals), which were characterized using EPR spectroscopy and DFT calculations. Reaction of the archetypal 3,1,2,4-benzothiaselenadiazine with SCl2 afforded 2,1,3-benzothiaselenazolium chloride (Herz salt), whereas that of sterically hindered 1,3,2,4-benzodithiadiazine resulted in a complex of the corresponding Herz salt with unexpected carbocycle-chlorinated and non-chlorinated 3,3-dioxides of the starting material, which is a rare example of a molecular complex involving a Herz cation. Formation of the dioxides can be explained through intermediate participation of the benzodithiadiazine radical cation. Hydrolysis of 3,1,2,4-benzothiaselenadiazine or 1,3,2,4-benzodithiadiazine led to Se-(2-aminophenyl)selenosulfate (Se-Bunte salt) or S-(2-aminophenyl)thiosulfate (Bunte salt), respectively.