Interconversion Pathways of Chalcogen Rings. An Ab Initio MO Study of Model Reactions Involving Hypervalent Sulfur and Selenium Hydrides

Article type: Research Article

Authors: Suontamo, Reijo J. | Laitinen, Risto S.

Affiliations: Department of Chemistry, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä | Department of Chemistry, University of Oulu, Linnanmaa, FIN-90570 Oulu, Finland

Note: [] Corresponding author.

Abstract: Chalcogen ring molecules are known to undergo facile interconversion reactions in organic solvents and in the melts, e.g. polymerization of liquid sulfur or the formation of Se6 and Se7 upon dissolving Se8 in CS2. These interconversion reactions have been suggested to proceed via the homolytic cleavage of the chalcogen-chalcogen bonds or through the formation of hypervalent intermediates. The experimental evidence on the actual mechanism, however, is rather sparse. The energetics of the various suggested interconversion pathways have been studied by ab initio MO techniques using suitable model reactions involving sulfur and selenium hydrides. Full geometry optimization has been performed for hypervalent chalcogen hydrides H2EE and H2E(EH)2 as well as for the radicals HE and HEE (E = S or Se in the case of each chalcogen atom) utilizing the MIDI-4* basis sets. The energy changes in their formation from appropriate unbranched chalcogen hydrides HEnH(n = 1,2 or 4) and HEnE′mH (m, n = 0–4; n + m = 2,4; E, E′ = S or Se) have been calculated including the corrections for the electron correlation by the second-order Møller-Plesset perturbation theory and for the zero-point vibrational energy. The formation of hypervalent interconversion intermediates is seen as an energetically plausible alternative for the homolytic cleavage of the chalcogen-chalcogen bonds. The present calculations help to understand why the interconversion of heterocyclic selenium sulfides proceeds principally with selenium-atom transfer.

DOI: 10.1080/13583149612331338475

Journal: Main Group Chemistry, vol. 1, no. 2, pp. 241-251, 1996