par Boué, Stéphane ;Jung, Céline Gisèle ;Castillo, José ;Vander Donckt, Emile
Référence Journal of the Chemical Society. Perkin Transactions 2, 8, page (1691-1697)
Publication Publié, 1996-08
Article révisé par les pairs
Résumé : The non-alternant aromatic hydrocarbon fluoranthene (Ar 0) has been reduced, either chemically with Na or Li or by electrolysis, to the radical anion Ar .-; in the three solvents THF (tetrahydrofuran), DME (dimethoxyethane) and HMPA (hexamethylphosphoric triamide). The UV-VIS absorption spectrum of the orange-brown Ar .- is quite similar in the three solvents and in all instances addition of H +-H 2O has resulted in quantitative electron-back-donation along with H 2 evolution and recovery of unchanged fluoranthene Ar 0. Thus the usual Birch-type reduction to a dihydro derivative is totally inefficient in the cases under investigation. The two-electron reduction has also been achieved in these three solvents. The greenish-yellow dianion Ar 2- produced in THF exhibits characteristic UV-VIS absorption patterns, disproportionates with Ar 0 and reacts with H +-H 2O only to evolve H 2. With DME or HMPA a blood-red species is produced whose absorption spectrum is virtually the same and quite different from that observed in THF. In both solvents addition of H +-H 2O leads to tetrahydrofluoranthene as a main reaction product but disproportionation is not observed at all in HMPA and this is not compatible with a regular dianion Ar 2-. Reaction with D +-D 2O instead of H +-H 2O has shown that hydrogenation involves radical abstraction of H atoms from the solvent in both cases; this sheds new light onto the reaction mechanism. Furthermore, several other experiments indicate that the dianionic blood-red species is most likely a complex written as [Ar .- ⋯ .-Solvent], in which the Ar .- moiety is bound to a solvated electron localized on a solvent molecule.

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