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

Abstract

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 2(2+) and 6(2+) (as [PF(6)](2) salts) and 4(2+) (as a [I(5)][I(3)] salt). The separation DeltaE 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. Electrochemical studies involving the use of the noncoordinating electrolyte [Bu(4)N][B{C(6)H(3)(CF(3))(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{C(6)H(3)(CF(3))(2)}(4)] and 4[B{C(6)H(3)(CF(3))(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.

Guanidines as Reagents in Proton-Coupled Electron-Transfer Reactions and Redox Catalysts

“…However, it has been shown that two separate one-electron redox events could be observed for 4-DMAP if suitable weakly coordinating ions are used in the supporting electrolyte. 71 The importance of steric strain is also evident from comparison between the redox potentials of 6-DMAP and of hexaazaoctahydrocoronene (HOC). 72 Hence for HOC four one-electron redox events occur at E 1/2 = -0.84 V, -0.34 V, +0.12 V, and +0.52 V…”

Guanidinyl‐Functionalized Aromatic Compounds (GFAs) – Charge and Spin Density Studies as Starting Points for the Development of a New Class of Redox‐active Ligands

“…In this case clearly separated one‐electron waves were observed. It is not yet absolutely clear why generally the GFA compounds loose two electrons at the same time 37. Quantum chemical calculations on the gas‐phase disproportionation of ttmgb + radical cations into the dication and the neutral guanidine returned a significantly positive Δ G value (ca.…”

Guanidine Electron Donors and Silver Halides: Interplay and Competition between Redox, Coordination and Polymerization Reactions

“…In comparison to the corresponding amines, 1 and 2 are much stronger Brønsted bases and exhibit a higher reduction capacity. For example, the oxidation potential E 1/2 (CH 2 Cl 2 ) = 0.063 V for 1,2,4,5‐tetrakis(dimethylamino)benzene10 but –0.32 V for 1 3 with respect to SCE. In addition, as shown in a massive body of work, guanidines are versatile ligands that have been used extensively for the synthesis of molecular compounds for manifold applications (e.g., catalysis or deposition of materials from precursors) 11–15…”