Unusual addition patterns in trifluoromethylation of [60]fullerene

Abstract

From pyrolytic trifluoromethylation of [60]fullerene with CF3CO2Ag at 300 degrees C we have isolated ca. sixty C60(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 19F 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 downfield) 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 13C NMR spectrum of C60(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.

High‐Temperature Synthesis of the Surprisingly Stable C1‐C70(CF3)10 Isomer with a para7–meta–para Ribbon of Nine C6(CF3)2 Edge‐Sharing Hexagons

“…The estimated standard deviations (esds) for individual CÀC and CÀF distances in this structure are all 0.003 (except for the CÀF distances in the two disordered CF 3 groups), making this one of the most precisely determined C 70 -containing structures reported to date (the ranges of esds for CÀC bonds within the cage of known structures include 0.002-0.004 for two Diels-Alder monoadducts, [14] 0.004-0.006 and 0.006-0.007 for C 70 (CH 3 ) 8 [13] and C 70 F 38 , [15] respectively, and 0.02-0.03 for C 70 Br 10 , [6] C 70 (IrCl(PPh 3 ) 2 ), [16] and C 70 (Ru 3 (CO) 9 ) [17] ). In addition to further supporting [12] our earlier conclusion [18] that fullerene(CF 3 ) n compounds in general have their CF 3 groups arranged on m-and p-C 6 (CF 3 ) 2 hexagons (most of which form a continuous ribbon through edge sharing) and are not arranged on adjacent (i.e., ortho) cage C atoms as suggested by others, [19][20][21] the structure of C 1 -C 70 (CF 3 ) 10 has revealed several interesting and unanticipated aspects of C 70 X n stereochemistry. In 1999, Clare and Kepert predicted the relative DH 0 f values for a (necessarily) limited number of isomers of C 70 X 10 at the AM1 level of theory, including the C sp 9 o(loop) and C 2 -p 9 isomers for X = H, F, Br, Ph, and tBu.…”

Synthesis, Characterization, and Theoretical Study of Stable Isomers of C70(CF3)n (n = 2, 4, 6, 8, 10)

“…The 10.3-16.2 Hz uene-extractable mixture of products included many more C 60 A C H T U N G T R E N N U N G (CF 3 ) n derivatives (n 14) as well as a large number of C 60 A C H T U N G T R E N N U N G (CF 3 ) n H m derivatives, many of which could only be isolated as mixtures of products even after HPLC processing. [5,6] Application of our original AgTFA synthetic methodology [1,2] without high-temperature fractional sublimation to the polytrifluoromethylation of C 70 also resulted in complex mixtures of C 70 A C H T U N G T R E N N U N G (CF 3 ) n and C 70 A C H T U N G T R E N N U N G (CF 3 ) n H m derivatives. [5,7] We now report that high-temperature fractional sublimation followed by HPLC processing of C 70 /AgTFA reaction mixtures (with reaction temperatures of 320-340 8C) leads to the isolation of milligram amounts of a single abundant isomer of C 70 A C H T U N G T R E N N U N G (CF 3 …”

“…The products consisted of a wide range of C 60,70 A C H T U N G T R E N N U N G (CF 3 ) n derivatives with n 22. [1] We recently published a 380/500 8C fractional sublimation procedure for a particular C 60 A C H T U N G T R E N N U N G (CF 3 ) n mixture of products (C 60 , AgTFA, 280 8C) that resulted in fewer, [3] more stable [4] isomers of C 60 A C H T U N G T R E N N U N G (CF 3 ) 2,4,6,8,10 as the predominant isolated products. This greatly simplified the HPLC purification and spectroscopic characterization of individual isomers of C 60 A C H T U N G T R E N N U N G (CF 3 ) 2,4,6 .…”

“…[1] We recently published a 380/500 8C fractional sublimation procedure for a particular C 60 A C H T U N G T R E N N U N G (CF 3 ) n mixture of products (C 60 , AgTFA, 280 8C) that resulted in fewer, [3] more stable [4] isomers of C 60 A C H T U N G T R E N N U N G (CF 3 ) 2,4,6,8,10 as the predominant isolated products. This greatly simplified the HPLC purification and spectroscopic characterization of individual isomers of C 60 A C H T U N G T R E N N U N G (CF 3 ) 2,4,6 . [3] Without fractional sublimation, the tolAbstract: Reaction of C 70 with ten equivalents of silver(i) trifluoroacetate at 320-340 8C followed by fractional sublimation at 420-540 8C and HPLC processing led to the isolation of a single abundant isomer of C 70 A C H T U N G T R E N N U N G (CF 3 ) n for n = 2, 4, 6, and 10, and two abundant isomers of C 70 A C H T U N G T R E N N U N G (CF 3 ) 8 .…”

“…The results demonstrate that thermally stable C 70 A C H T U N G T R E N N U N G (CF 3 ) n isomers tend to have their CF 3 groups arranged on isolated para-C 6 A C H T U N G T R E N N U N G (CF 3 ) 2 hexagons and/or on a ribbon of edgesharing meta-and/or para-C 6 A C H T U N G T R E N N U N G (CF 3 ) 2 hexagons. For C s -and C 2 -C 70 A C H T U N G T R E N N U N G (CF 3 ) 8 and for C 2 -C 70 A C H T U N G T R E N N U N G (CF 3 ) 6 , the ribbons straddle the C 70 equatorial belt; for C 1 -C 70 -A C H T U N G T R E N N U N G (CF 3 ) 4 , the para-meta-para ribbon includes three polar hexagons; for C 1 -7,24-C 70 A C H T U N G T R E N N U N G (CF 3 ) 2 , the para-C 6 A C H T U N G T R E N N U N G (CF 3 ) 2 hexagon includes one of the carbon atoms on a C 70 polar pentagon. The 10.3-16.2 Hz uene-extractable mixture of products included many more C 60 A C H T U N G T R E N N U N G (CF 3 ) n derivatives (n 14) as well as a large number of C 60 A C H T U N G T R E N N U N G (CF 3 ) n H m derivatives, many of which could only be isolated as mixtures of products even after HPLC processing.…”