Synthesis and trapping of transient 1,2-diselones to yield 1,4-diselenin derivatives: Calculated structures of 1,2-diselones, 1,2-diselenetes and their sulfur analogues

Two conceptually different routes to transient 1,2-diselones are reported: 1) via ring fragmentation of the 1,4,2-diselenazine system 6, and 2) by the tributylphosphane-induced depolymerisation of the shelf-stable organoselen ium polymer 15. Evidence for the intermediacy of 1,2-diselone species 7 and 16 is provided in both cases by in situ trapping with dimethyl acetylenedi carboxylate (DMAD) to yield 1,4-diselenin derivatives. The route via 15 is especially expedient and trapping of 16 is efficient. Subsequent reactions of adduct 17 afford [1,2-ethanediylbis(diphenylphosphane)] [5,6-bis(methoxy carbonyl)-1,4-diselenin-2,3-dithiolato]nick el(IV) (20). Theoretical calcul ations at Hartree-Fock (HF) and Moller-Plesset electron-correlated levels ( MP2) suggest that the cyclic 1,2-diselenete structure 7c is significantly m ore stable than the acyclic 1,2-diselone structure 7a. For the bicyclic sys tem 16, the difference in energy between the cyclic and acyclic structures is considerably reduced due to the conformational rigidity imposed by the f used 1,3-dithiole ring. In contrast, the acyclic structures of the 1,2-dith ione analogues 13a and 25a are computed to be more stable than their corres ponding cyclic 1,2-dithiete structures 13c and 25c.