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 toward 1-naphthyl radicals was studied in dimethylsulfoxide. 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-naphthylsulfide 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), and –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 2 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 density functional theory calculations. There is a generally good agreement between the experimental and the calculated reactivities, the spin density being 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.