Gas-phase negative ion chemistry of molecular fluorine. Synthesis of distonic radical anions and related species

摘要

The gas-phase negative ion chemistry of molecular fluorine is described, with an emphasis on its use in the regiospecific synthesis of distonic radical anions and related species. Sequential reaction of organic compounds containing two trimethylsilyl (TMS) substituents with F~- followed by F_2 produces distonic radical anions with the negatively charged and odd-spin sites determined by the locations of the TMS groups. The mechanism of the F_2 reaction involves dissociative electron transfer from the TMS-substituted carbanion to F_2, yielding an F~-/radical complex; subsequent attack by F~- on the TMS group of the radical produces the distonic radical anion product. Experimental evidence in support of the proposed mechanism is presented, including the dependence of the efficiency of radical anion formation on both the electron binding energy of the reactant carbanion and the leaving-group ability of the radical anion product. Selected applications of the F_2 method for distonic anion synthesis are described, including formation of the negative ions of trimethylene methane, the benzynes, oxyallyl and acetoxyl biradicals and α,3-dehydrotoluene. Mechanistic variations in the F_2 reactions with carbanions are described in which the transient F~- ion produced by dissociative electron transfer to F_2 reacts with the organic radical in the long-lived complex by proton transfer, nucleophilic substitution at carbon, and elimination. Formation of distonic biradical anions (ionized triradicals) from neutral precursors containing three TMS groups is described, along with the rational gas-phase synthesis using F_2 of distonic carbene and nitrene anions.