Synthesis, Structure, and Resolution of Exceptionally Twisted Pentacenes
9,10,11,20,21,22-hexaphenyltetrabenzo[a,c,l,n]pentacene (2) and a dimethyl derivative (2m) were prepared by the reaction of 1,3-diphenylphenanthro[9,10-c]furan with bisaryne equivalents generated from 1,2,4,5-tetrabromo-3,6-diarylbenzenes in the presence of n-butyllithium, followed by deoxygenation of the double adducts with low-valent titanium. Both are bright red solids with a strong orange fluorescence in solution. The X-ray structures of these compounds show them to be the most highly twisted polycyclic aromatic hydrocarbons known. Compound 2 has an end-to-end twist of 144{sup o}, and the two crystallographically independent molecules of 2m have twists of 138{sup o} and 143{sup o}. Both molecules were resolved by chromatography on chiral supports, and the pure enantiomers have extremely high specific rotations (for 2, [{alpha}]{sub D} = 7400{sup o}; for 2m, 5600{sup o}), but the molecules racemize slowly at room temperature ({Delta}G{sup {double_dagger}}{sub rac} = 24 kcal/mol). Both the experimental geometry and the observed racemization barrier for 2 are in good agreement with computational studies of the molecule at a variety of levels. Attempts to prepare compound 2 by reaction of tetraphenylbenzyne with 9,10,12,13-tetraphenyl-11-oxacyclopenta[b]triphenylene (3, a twisted isobenzofuran) gave no adducts, and attempts to prepare tetradecaphenylpentacene by reaction of hexaphenylisobenzofuran (11) with bisaryne equivalents gave only monoadducts.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 930155
- Report Number(s):
- BNL-80813-2008-JA; JACSAT; TRN: US200822%%1206
- Journal Information:
- Journal of the American Chemical Society, Vol. 128; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
Similar Records
Enantioselectivities in electron-transfer and excited state quenching reactions of a chiral ruthenium complex possessing a helical structure
RESEARCH ON SYNTHESIS OF 1000 F STABLE BASE FLUIDS. Quarterly Progress Report, August 1, 1960 to October 31, 1960