Unusual addition patterns in trifluoromethylation of [60]fullerene

Darwish, Adam D, Abdul-Sada, Ala'a K, Avent, Anthony G, Lyakhovetsky, Yury, Shilova, Elena A and Taylor, Roger (2003) Unusual addition patterns in trifluoromethylation of [60]fullerene. Organic and Biomolecular Chemistry, 1 (17). pp. 3102-3110. ISSN 1477-0520

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Abstract

From pyrolytic trifluoromethylation of [60]fullerene with CF3CO2Ag at 300degreesC we have isolated ca. sixty C-60(CF3)n isomers (numbers in parentheses) as follows: n = 2 (1), 4 (8), 6 (13), 8 (21) 10 (11), 12 (5), 14 (4), twenty-one of which have been characterised by F-19 NMR. Compounds with addition levels up to n = 20 have also been identified. With increasing value of n, yields decrease and the separation of compounds of similar HPLC retention time but different addend levels becomes more difficult. Many of the 19F NMR spectra show combinations of quartets and septets (the latter tending to be more down field) due to 'linear' addend arrays. The spectra are consistent with addition across both 6:6- and 5: 6- ring junctions [ double (1,2) and single (1,6) bonds, respectively], giving corresponding coupling constants for adjacent addends of ca. 14.5 and 12.0 Hz respectively, the differences being attributable to the different 1,2- and 1,6- bond lengths. The C-13 NMR spectrum of C-60(CF3)(2) shows the CF3 groups are in either a 1,4- or 1,6-relationship; the UV-vis band appears at 442 nm. Other unsymmetrical tetra-adducts are comprised of isolated pairs of CF3 groups. The exceptionally large number of derivatives and isomers, (much greater than in any other fullerene reaction), no dominant product, and unusual addition pattern indicates that thermodynamic stability is not of primary importance in governing product formation. EI mass spectrometry of trifluoromethylfullerenes is characterised by loss of CF3 groups, the more highly addended compounds also showing fragmentation by CF2 loss, attributable to steric compression. The CF3 group shows strong IR bands at ca. 1260 and 1190 cm(-1). The compounds are stable to aq. acetone, which contrasts to the behaviour of fluorofullerenes. Trifluoromethylation by the Scherer radical (C9F19.) gave addition of up to eight CF3 groups, together with hydrogen in some products. During EI mass spectrometry of some of these, loss of HF attributable to CF3 and H adjacency can occur, giving CF2-containing derivatives.

Item Type: Article
Schools and Departments: School of Life Sciences > Chemistry
Depositing User: Adam Darwish
Date Deposited: 06 Feb 2012 19:48
Last Modified: 14 May 2012 14:04
URI: http://sro.sussex.ac.uk/id/eprint/22262
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