Synthesis and Structural Characterization of Hexa-tert-butyl- hexa-peri-hexabenzocoronene, Its Radical Cation Salt and Its Tricarbonylchromium Complex

Abstract

The hexa-tert-butyl substituted hexa-peri-hexabenzocoronene was synthesized in an overall yield of 83 % from 4-tert-butylphenylacetylene. The key step was the oxidative cyclodehydrogenation of hexa(4-tert-butylphenyl)benzene with anhydrous FeCl 3 in CH 2 Cl 2. The high solubility of hexa-tertbutyl-hexa-peri-hexabenzocoronene in common organic solvents allowed a comprehensive spectroscopic characterization of this compound in solution.Electrochemical oxidation at À 30 8C in the presence of tetrabutylammonium hexafluoroarsenate led to the formation of a stable radical cation salt. Reaction of hexa-tert-butyl-hexa-peri-hexabenzocoronene with an excess of tricarbonyl-(naphthalene)chromium in THF/diox-ane afforded a mixture of mono-and bis-tricarbonylchromium complexes which could be separated by chromatography. The molecular structures of the parent compound, its radical cation salt and its mono-tricarbonylchromium complex were determined by X-ray analysis and discussed in detail. Remarkably, the crystal structures of these compounds are mainly dominated by the formation of dimers of the aromatic cores. Results and DiscussionThe synthesis of 1 b, outlined in Scheme 1, starts with 4-tertbutylphenylacetylene (2) which is coupled with 4-tert-butyliodobenzene (3) to yield di(4-tert-butylphenyl)acethylene (4) (92 %). [11,12] The [Co 2 (CO) 8 ] mediated cyclotrimerization of 4[a] Prof.

Kekulé versus Lewis: When Aromaticity Prevents Electron Pairing and Imposes Polyradical Character

“…Hexa-peri-hexabenzocoronene is a closed-shell molecule that accepts seven aromatic sextets: six on the outer benzene rings and one in the central ring (Scheme 5, left). [41] The addition of six methylene groups on the external ring apices maintains a singlet multiplicity. At the expense of full quinonization, the molecule may receive full Lewis-type pairing (Scheme 5, middle), but the seven aromatic sextets can be conserved as well, providing each external CH 2 groups bears an unpaired electron, thus giving a hexaradical (Scheme 5, right).…”

Synthesis of Cyclopenta‐HBCs and their Regioselective Chlorination During Oxidative Cyclodehydrogenation

“…The incorporation of a cyclopenta‐ring at the periphery of HBC is expected to distort the geometry of the aromatic core. The X‐ray crystal structures of 10 b and 2 c (Figure and SI) reveal that, although the core shows a deviation from planarity, the curvature is no greater than that seen for other all‐benzenoid HBCs, such as HBC( t Bu) 6 . However, the in‐plane geometrical parameters in the region adjacent to the cyclopenta‐ring are distorted: analysis of 2 c shows that the peripheral bonds are mostly elongated and the internal bonds shortened.…”

“…HBC′s strong optical absorption and emission, as well as its multiple redox states were probed for a range of CpHBCs synthesised and compared to the HBC analogue 1 . Analysis of the cyclic voltammetric data (Table ) shows two pseudo‐reversible oxidations in the range of 0.9–1.3 V (vs. SCE), with 1 and 2 a exhibiting broadened voltammograms due to low solubility and electrode precipitation processes.…”

Hexa-peri-hexabenzocoronene in organic electronics

“…Ketone and ester functional groups such as alkan-1-ones, alkoxycarbonyl and methylene carboxy alkanoate have been reported incompatible with FeCl 3 cyclohehydrogenation conditions [37]. Interestingly, a tert-butyl-substituted 1,4-bis-(2'-biphenyl)yl-2,5-diphenylbenzene precursor required repeated FeCl 3 treatment to arrive at the fully cyclodehydrogenated product [19], whereas the presence of four, five, or six tert-butyl solubilizing chains in HPBs gives HBCs in good to excellent yields with FeCl 3 or DDQ [23,38,39].…”