Studies on Dichalcogena Dications of 2-Center-2-electron and 3-Center-4-electron Bonds: Isolation and Intermediary Formation

Abstract

Abstract 1,5-(Dithia and diselena)cyclooctanes gave the dithia and diselena dications. Their structures were determined by X-ray crystallographic analyses. Similarly, dithia and diselena dications were produced on oxidation with 2 equiv of NOBF4 or NOPF6 or on treatment of the corresponding monooxides with Tf2O or concd H2SO4 from the sterically congested bis-sulfides or bis-selenides, such as 1,9-bis(thio- or seleno-substituted)dibenzochalcogenophene, 1,8-bis(thio- or seleno-substituted)naphthalenes and 2,2′-(thio- or seleno-substituted) 1,1′-biphenyls. These dications, however, were found to be unstable and to release the substituents attached at the chalcogen atoms. These either generated reactive species, i.e., quinodimethane and alkyl cations or demonstrated new reactions such as thio-Claisen rearrangement or photochemical conversion of naphtho[1,8-de]-1,3-dithiin derivatives. Diphenyl chalcogenides bearing 2,6-bis(methylthiomethyl), 2,6-bis(methylselenomethyl) and 2,6-bis[(dimethylamino)methyl] substituents produced the hypervalent chalcogenuranes(λ4). Their structures were determined by X-ray crystallographic analyses and their charge distributions were estimated by the ab initio MO-calculation and 77Se- or 125Te-NMR spectroscopy. Methyl 2,6-bis[(dimethylamino)methyl]phenyl selenide and telluride gave stable monoselenenium and monotellurenium cations on oxidative demethylation by the reaction with t-BuOCl. These are the first monovalent selenenium and tellurenium cation species.