The special role of B(CF) in the single electron reduction of quinones by radicals.

In the presence of two molar equiv. of B(CF) -benzoquinone reacts with persistent radicals TEMPO, trityl or decamethylferrocene by single electron transfer to give doubly -borylated benzosemiquinone radical anions with TEMPO, trityl or ferrocenium counter cations. All three [(CF)B]-semiquinone radical anion salts were characterized by X-ray diffraction. The addition of donor reagent THF or DMSO induced rapid back electron transfer, in the case of the [(CF)B]-semiquinone radical anion oxoammonium salt giving rise to the formation of the (CF)B-DMSO (or THF) Lewis adduct, -benzoquinone and the TEMPO radical. The reaction of 9,10-anthraquinone or acenaphthenequinone with either the Gomberg dimer or in 1 : 1 stoichiometry in the presence of two molar equiv. of B(CF) gave the respective two-fold O-B(CF) containing 9,10-anthrasemiquinone or acenaphthene-semiquinone radical anion salts with either PhC or counter cations. These products were also characterized by X-ray diffraction. The salts showed analogous back electron shuttling behavior upon treatment with DMSO. 9,10-Phenanthrenequinone reacted analogously with B(CF) and the electron rich ferrocene. The [(CF)B]-9,10-phenanthrene-semiquinone salt was characterized by X-ray diffraction. The radical anions were characterized by ESR spectroscopy.