The special role of B(C(6)F(5))(3) in the single electron reduction of quinones by radicals

In the presence of two molar equiv. of B(C(6)F(5))(3)p-benzoquinone reacts with persistent radicals TEMPO, trityl or decamethylferrocene by single electron transfer to give doubly O-borylated benzosemiquinone radical anions with TEMPO(+), trityl or [Image: see text] ferrocenium counter cations. All three [(C(6)F(5))(3)B](2)–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 [(C(6)F(5))(3)B](2)–semiquinone radical anion oxoammonium salt giving rise to the formation of the (C(6)F(5))(3)B–DMSO (or THF) Lewis adduct, p-benzoquinone and the TEMPO radical. The reaction of 9,10-anthraquinone or acenaphthenequinone with either the Gomberg dimer or [Image: see text] in 1 : 1 stoichiometry in the presence of two molar equiv. of B(C(6)F(5))(3) gave the respective two-fold O–B(C(6)F(5))(3) containing 9,10-anthrasemiquinone or acenaphthene-semiquinone radical anion salts with either Ph(3)C(+) or [Image: see text] counter cations. These products were also characterized by X-ray diffraction. The [Image: see text] salts showed analogous back electron shuttling behavior upon treatment with DMSO. 9,10-Phenanthrenequinone reacted analogously with B(C(6)F(5))(3) and the electron rich ferrocene. The [Image: see text] [(C(6)F(5))(3)B](2)–9,10-phenanthrene–semiquinone salt was characterized by X-ray diffraction. The radical anions were characterized by ESR spectroscopy.