Stable N,N’‐Diarylated Dihydrodiazaacene Radical Cations

Abstract

Three stable N,N’‐diarylated dihydroazaacene radical cations were prepared by oxidation of neutral N,N’‐diarylated dihydroazaacenes synthesized via palladium‐catalyzed Buchwald‐Hartwig aminations of aryl iodides with N,N’‐dihydroazaacenes. Both neutral as well as oxidized species were investigated via UV‐vis spectroscopy, single crystal analysis, and DFT calculations. All the radical cations are surprisingly stable—their absorption spectra in dichloromethane remain unchanged in ambient conditions for at least 24 hours.

An Electrochemical Investigation into the Redox Properties of Push‐Pull Dibenzodioxins and Comparative Analysis with Analogous Heteroacenes

“…Compound 11 has cyclic aromatic diamine group and so the oxidation potential is very low + 0.06 V (vs Fc/Fc + ; Figure 9, structure 11), attributable to a stable cation radical formation. [12] Compound 12 [9] shows similar geometry to our compound 3 a (E red = À 1.219 V vs Fc/Fc + ; table 1, entry no. 7).…”

“…This, and our earlier observed ease of oxidation of 2 a and 2 b under anion medium implies that improved electronic charge flow is key to lowering of oxidation potential in a molecule. Compound 11 has cyclic aromatic diamine group and so the oxidation potential is very low +0.06 V (vs Fc/Fc + ; Figure 9, structure 11), attributable to a stable cation radical formation [12] …”

N,N‐Diphenyl Dihydrophenazines: Using π‐Extension to Access Dicationic Multifunctional Materials

“…Recently, in a work by G. Xie et al., chemical 2e − oxidation of a DPA derivative was attempted without success, whereas the corresponding radical cation proved to be persistent (Figure 3e, f). [13] This result again suggests that the dicationic state is plausibly highly reactive in linearly extended derivatives as in the parent compound. This could be connected to an inefficient delocalization of the double charge resulting in high coulombic repulsion, which seems to be consistent with the relatively high Δ e (>0.5 V) between first and second oxidation potentials with the latter presenting similar values for both DPAs and non‐extended derivatives.…”

“…DPAs are the most explored class of π‐extended dihydrophenazines to date and have been synthesized and studied by many research groups. These molecules are easily oxidizable to persistent radical cations due to the decrease in local antiaromaticity arising from removal of one electron, which results in great bathochromic shifts often reaching the NIR region of the spectrum [13] . DPAs are generally synthesized by Buchwald‐Hartwig (B−H) coupling on dihydrophenazines (obtained by reduction of phenazines) or on ortho ‐aryldiamines and thus easily accessible [14] .…”

“…These molecules are easily oxidizable to persistent radical cations due to the decrease in local antiaromaticity arising from removal of one electron, which results in great bathochromic shifts often reaching the NIR region of the spectrum. [13] DPAs are generally synthesized by Buchwald-Hartwig (BÀ H) coupling on dihydrophenazines (obtained by reduction of phenazines) or on orthoaryldiamines and thus easily accessible. [14] In DPAs, the Nbonded aryl rings are perpendicular to the dihydrophenazine plane [14,15] (Figure 3c), however, when steric hindrance is placed in the nearby positions a peculiar saddle shaped conformation is observed (Figure 3b, d).…”