A pentacene with a 144 degrees twist |
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Authors: | Lu Jun Ho Douglas M Vogelaar Nancy J Kraml Christina M Pascal Robert A |
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Institution: | Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA. |
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Abstract: | 9,10,11,20,21,22-Hexaphenyltetrabenzoa,c,l,n]pentacene (1) was prepared by the reaction of 1,3-diphenylphenanthro9,10-c]furan with the bisaryne equivalent generated from 1,2,4,5-tetrabromo-3,6-diphenylbenzene in the presence of n-butyllithium, followed by deoxygenation of the double adduct with low-valent titanium. The X-ray structure of 1 shows it to be the most highly twisted polycyclic aromatic hydrocarbon known, with an end-to-end twist of 143.6 degrees . Compound 1 was resolved by chromatography on a chiral support, and the pure enantiomers have specific rotations in excess of 7000 degrees , but the molecule racemizes slowly at 25 degrees C (t1/2 = 9.3 h, DeltaGrac = 23.8 kcal/mol). |
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