Combined Experimental and Theoretical Studies on the Radical Nucleophile Addition Reaction for Sulfide and Selenide Centered Anions.

Abstract

The reactivity of sulfur and selenium centered nucleophiles towards 1-naphthyl radicals was studied in DMSO. The photostimulated reaction of sulfide anions, -SC(NH)C6H5 (1), -SC(NH)NH2 (2), and -SC(NH)CH3 (3) renders, after the addition of MeI, methyl 1-naphthyl sulfide as a main product together with bis (1-naphthyl) sulfide and naphthalene under irradiation. Concordantly, the reaction of selenide anions, -SeC(NH)C6H5 (4), -SeC(NH)NH2 (5), -SeCN (6), produces methyl 1-naphthyl selenide, bis (1-naphthyl) selenide and naphthalene in the presence of potassium tert-butoxide anion (entrainment conditions). Absolute rate constants for the coupling of ions 1-6 to 1-naphthyl radicals were determined; as a general trend the selenide centered nucleophiles enhance in two times the reactivity of their sulfide analogues. From the mechanistic study it is proposed that the unstable radical anion produced by the addition of the nucleophile to 1-naphthyl radical affords, after fragmentation, 1-naphthylsulfide/selenide anion. In addition, experimental results are discussed in terms of DFT calculations. There is a general good agreement between the experimental and the calculated reactivity, being the spin density the main parameter to describe the difference found among the anions under study. Moreover, the calculations predict that anion -SeC(NH)CH3 (7) would be a good candidate for the synthesis of selenide derivatives.