Synthesis and structural characterization of hexa-tert-butyl-hexa-peri-hexabenzocoronene, its radical cation salt and its tricarbonylchromium complex.

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 FeCl3 in CH2Cl2 The high solubility of hexa-tert-butyl-hexa-peri-hexabenzocoronene in common organic solvents allowed a comprehensive spectroscopic characterization of this compound in solution. Electrochemical oxidation at -30 degrees C 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/dioxane 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.