The Li+-Initiated Twofold Dehydrogenation and C−C Bond Formation of Hexaphenylbenzene to the Dilithium Salt of the 9,10-Diphenyltetrabenz[a,c,h,j]anthracene Dianion

Abstract

Partly solvent-separated and partly solvent-shared, the contact ion triple of the 9,10-diphenyltetrabenz[a,c,h,j]anthracene dianion is formed by the ultrasonically activated reaction of hexaphenylbenzene with lithium metal powder in 1,2-dimethoxyethane (dme) [Eq. (1)]. The proposed microscopic pathway for this reaction-twofold dehydrogenation and C-C bond formation-is supported by quantum-chemical calculations.

Stereodynamics and Characterization of the Hexa(4‐n‐dodecylbiphenylyl)benzene Hexaanion that Includes a Twisted Benzene Core

“…However, the mode of the extended π conjugation and the ion‐pairing situation of the charged species of HDBB leads to a higher thermal stability, thus rendering extensive NMR studies feasible. Two features may finally be mentioned which place the above studies into even wider perspectives: 1) hexaphenylbenzene and hexa(biphenylyl)benzene can undergo electron‐transfer‐induced cyclodehydrogenation processes under appropriate conditions affording extended polycyclic aromatic hydrocarbons,4, 10, 26, 27 and 2) such compounds have been shown to serve as core units for dendritic and hyper‐branched polyphenylenes with penta‐ or hexaphenylbenzenes repeat units 28. Similar reduction experiments thus appear highly promising.…”

Ferromagnetic Coupling in a New Copper(II) Schiff Base Complex with Cubane Core: Structure, Magnetic Properties, DFT Study and Catalytic Activity

“…In the mean‐time, various new results have been added:3, 4 The crystallization of π‐hydrocarbon tetraanion salts1 and of supramolecular contact ion multiples has been accomplished1, 5 and the interaction in the molecular‐ion crystal packings has been calculated and correlated 1. 6…”

“…The clearest indication of these effects is the spreading of the phenyl substituents of the polyanions. This formation of contact‐ion multiples is a consequence of strong Coulombic interactions M + ⋅⋅⋅C 6 2− is a general phenomenon,3, 13 covers a multitude of different contact‐ion structures,3–6 demonstrates essential effects of cation size as well as solvation,14, 15 and provides information on reduction pathways6 or on promising novel materials 16. Three examples of C 6 2− dianions illustrate some of these aspects: Lithium‐metal reduction of hexakis(trimethylsilyl)benzene (Scheme , left)15 generates at strongly distorted C 6 2− dianion in boat‐conformation, which can host two [Li(thf)] + ions.…”

“…The ultrasonically activated reduction of hexaphenylbenzene generates, by twofold dehydrogenation and CC bond formation, a solvent‐separated contact ion triple of the 9,10‐diphenyltetrabenz[ a.c.h.j. ]anthracene dianion with an extreme boat deformation caused by interaction with the small Li + ion (Scheme , middle6). This compound and the corresponding DFT calculations provide evidence for an unexpected microscopic reduction pathway of synthetic usefulness.…”

Polyarene anions: interplay between theory and experiment

“…Another case of anionic formation of polyarenes is the double dehydrogenative cyclization that hexaphenylbenzene (HPB) undergoes when reduced with lithium metal, to give 9,10‐diphenyl‐tetrabenz[ a , c , h , j ]anthracene dianion (Figure 12). After performing the reduction in 1,2‐dimethoxyethane, Bock et al114 performed extensive DFT and MNDO calculations starting from the crystal structure, which helped elucidating the reaction mechanism. The reaction was found to be based on the disrotatory motion of ortho phenyls in HPB, caused by double reduction and ion pair formation, thus enabling CC bond formation and H 2 removal.…”