On the Causes of Potential Inversion in 1,2,4,5-Tetrakis(amino)benzenes

Three 3,6-difluoro-1,2,4,5-tetrakis(amino)benzene compounds, bearing dimethylamino (1), piperidin-1-yl (3), or morpholin-1-yl (5) substituents, have been synthesized and subsequently defluorinated to give the corresponding 1,2,4,5-tetrakis(amino)benzene compounds 2, 4, and 6; the crystal structures of compounds 1, 4, and 6 have been obtained. Cyclic voltammetry shows that all six compounds will lose two electrons to form dications, and the use of suitable oxidizing agents has allowed isolation and crystallographic characterization of the dications 2²⁺ and 6²⁺ (as [PF₆]₂ salts) and 4²⁺ (as a [I₅][I₃] salt). The separation ΔE between the loss of the first electron and the second varies between compounds, from 0.23 V in 1 to 0.01 V in 6. Eletrochemical studies involving the use of the noncoordinating electrolyte [Bu₄N][B{C₆H₃(CF₃)₂}₄] show that it is possible to increase this separation, stabilizing the intermediate monocationic phase, and this has allowed the isolation and crystallographic characterization of the radical salts 2[B{C₆H₃(CF₃)₂}₄] and 4[B{C₆H₃(CF₃)₂}₄], the first radical cations of this family to be isolated. DFT studies of the ion pairing between oxidized forms of 1 and 2 and anions imply that the location of the ion pairing is different in the two species.