Formation of Unusual Valent Organic Sulfur and Selenium Compounds via Transannular Interaction

Abstract

1,5-Dithia- and diselenacyclooctane [1,5-DTCO and 1,5-DSeCO] were prepared and converted to the dication salts using NOPF₆ or conc. H₂SO₄. The structures of the salts were determined by the x-ray crystallographic analysis revealing that σ-bond is formed between the two sulfur or selenium atoms. Several other sterically congested dications derived from dibenzothiocin, 1,9-disubstituted dibenzothiophenes and the corresponding selenium compounds were synthesized and their structures were estimated on the basis of their ¹H-, ¹³C- and ⁷⁷Se nmr spectroscopy. The dications of trissullde, 1,11-(methanothiomethano)-5H,7H-dibenzo[b,g][1,5]-dithiocin and the selenium analog were generated. Inspection of their nmr spectra revealed that the central sulfur or selenium atom in these salts should have a hypervalent bonding structure, 10-S-4(C₂S₂), or 10-Se-4(C₂Se₂) which was further confirmed by the ⁷⁷Se-nmr coupling constants.