Oxidation Products of Doubly Trimethylene-Bridged Tetrabenzylp-Phenylenediamine Paracyclophane

Abstract

We report synthesis and investigation of doubly trimethylene-bridged tetrabenzyl-p-phenylenediamine 1(Bz) in its singly and doubly charged redox states. The singly oxidized monoradical cation, which is a mixed-valence (MV) system with directly interacting charge-bearing units, shows broad and solvent-sensitive intervalence bands consistent with class II compounds according to the Robin-Day classification. The doubly oxidized diradical dication of 1(Bz) exists in the spin-paired singlet state with thermally accessible triplet state. It has similar conformations as the other dimeric p-phenylenediamines, such as derivatives 1(Me) and 1(Et), in both the solid-state and solution phases. The successful isolation of the single-crystalline 1(Bz)(2+) diradical dications with two different in nature counteranions, relatively highly coordinating SbF6(-) and weakly coordinating carborane [undecamethylcarborane HCB11Me11(-) (CB(-))], reveals the distinct effect of the nature of counterions on the structural features of diradical dication. Cyclic voltammetry measurements of 1(Bz) in dichloromethane reveal separation of the first and second oxidation potential by 0.12 V (2.8 kcal/mol), indicating relatively stable mixed-valence state in the dichloromethane, whereas in the acetonitrile both the first and second oxidation potentials overlap into one unresolved redox peak with minimal separation.

Carboranes in the chemist's toolbox

“…Chemistry graduate of Lafayette College and received his Ph.D. training with William N. Lipscomb at the carbons at room temperature without oxidation. 7 The capability of protonating hydrocarbons under ambient conditions affords a powerful tool for investigation in several areas such as hydrocarbon reformation on zeolites, a process which normally occurs at high temperature and has been difficult to study. In a separate study, Jalilov et al employed HCB 11 Me 11 − as a counter ion to stabilize paracyclophane radical cations.…”

“…As such, they have enabled the successful isolation and full structural characterization of some long-sought salts of a number of carbocations and other elusive species, including R 3 Si + , C − as a counter ion to stabilize paracyclophane radical cations. 7 The capability of protonating hydrocarbons under ambient conditions affords a powerful tool for investigation in several areas such as hydrocarbon reformation on zeolites, a process which normally occurs at high temperature and has been difficult to study. The protonating power of the H + CB 11 X 11 − acids is not limited to hydrocarbons, and has enabled the stabilization, and in some cases structural characterization, of a range of elusive cationic species that were previously inaccessible or whose structures previously had been poorly defined.…”

On the early reaction stages of ozone with N,N′-substituted p-phenylenediamines (6PPD, 77PD) and N,N′,N″-substituted-1,3,5-triazine “Durazone®”: An electron spin resonance (ESR) and electronic absorption spectroscopy study

“…Ethanol has a dielectric constant of 25.6 [22] which is relatively close to that of methanol 32.7 and the presence of a small amount of water ε r = 78.3 increases further the polarity of the medium where the present study was conducted. In addition to the protonation stabilization, the Ss-PPDs semiquinone radical or radical cation has a certain tendency to form a charge transfer complex with the unoxidized parent Ss-PPDs [21] in a situation which recalls the interaction of hydroquinone with p-benzoquinone which form a complex called quinidrone [37]. To complete the description of the complexity of the oxidized Ss-PPDs solutions, it is also necessary to recall that a further one-electron oxidation of the Ss-PPDs radical cation leads to the formation of the quinonediimine derivative which can be represented as dication in acidic medium or a simple quinonediimine derivative in neutral medium (see Scheme 1).…”

“…Based on these studies, making 100 the antioxidant effectiveness of DPPD, that of 6PPD can be found at 38 and that of IPPD at 24 [12][13][14]. Furthermore the oxidation of aromatic amines has been used for the study of the dynamic interaction of radical cations and electron transfer reactions in solution [20][21][22][23][24][25], as model systems of polyaniline formation mechanism [26][27][28].…”

Formation of persistent organic diradicals from N,N′-diphenyl-3,7-diazacyclooctanes

“…Common structural motifs are based on the dimers of benzidine [7] (4,4′–diaminobiphenyl) or N , N , N ′, N ′-tetraaryl-(1,1′-biphenyl)-4,4′-diamines [8–10]. While these usually retain some structural flexibility regarding the π−π-interacting segments, attempts have been made to obtain “confronted arenes” [11] with closer interactions, such as found in cyclophane-like structures [12]. We here report the serendipitous finding of a simple synthetic method to produce highly persistent organic diradicals with strong intramolecular π−π interactions.…”