Wednesday, 09 December 2009 3369.fm Mendeleev Communications Mendeleev Commun., 2010, 20, 1–3 – 1 – © 2010 Mendeleev Communications. All rights reserved. Stable trifluoromethylated fullerene radicals C 60 (CF 3 ) 15 and C 60 (CF 3 ) 17 Andrey Kh. Vorobiev,* Vitaly Yu. Markov, Nadezhda A. Samokhvalova, Pavel S. Samokhvalov, Sergey I. Troyanov and Lev N. Sidorov Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation. Fax: +7 495 939 1240; e-mail: a.kh.vorobiev@gmail.com DOI: 10.1016/j.mencom.2010.__.___ Stable C 60 (CF 3 ) 15 and C 60 (CF 3 ) 17 radicals were generated by UV irradiation of C 60 (CF 3 ) n mixture and characterized by ESR and MALDI mass spectroscopy revealing the presence of pentakis- and tris(trifluoromethyl) moieties, respectively. Several free radical C 60 derivatives with methyl, 1 trichloro- methyl and C(O)OMe 2 addends were observed by ESR spectro- scopy. The existence of · CF=CFC(CF 3 ) 3 and · C(O)CF(CF 3 ) 2 radical adducts with C 60 was also reported. 3 Allylic C 60 R 3 · and cyclopentadienyl C 60 R 5 · (R = PhCH 2 ) radical adducts were observed by ESR spectroscopy as relatively stable products. 4 However, the observed species were found to be less stable in solution and to be degraded in the presence of oxygen. Per- fluorinated carbon-centered radicals often demonstrate higher stability in comparison with ordinary alkyl analogues. 5,6 Many trifluoromethylated [60]- and [70]fullerenes, C 60/70 (CF 3 ) n , with even number of addends (n = 2–18) have been synthesized, isolated and structurally investigated, 7,8 whereas the compounds with odd n have not been isolated up to now. However, it was mentioned 9 that the crude product of the reaction between C 60 and CF 3 COOAg contained species with odd number of CF 3 groups, which possessed high reactivity and could be removed from the mixture by sublimation in vacuo. In the present work, we report the formation of stable trifluoromethyl radical derivatives of C 60 and their investigation by ESR and mass- spectroscopic methods. A mixture of C 60 (CF 3 ) n (n = 12–18) was synthesized by the reaction of C 60 (99.98%, Term-USA) with CF 3 I (98%, Apollo) in a glass ampoule at 410–420 °C for 2–3 days as described elsewhere. 10 The MALDI mass spectrum for this sample was constituted by the peaks of C 60 (CF 3 ) n – ions with n = 12–18, those with even n considerably dominating (not shown). † The ESR spectra of the initial C 60 (CF 3 ) n mixture in solid state and in hexane solution (not shown) revealed the presence of stable radical species with g = 2.0031; however, with the content as low as ~0.2 mol%. ‡ To enlarge the content of paramagnetic derivatives, the mixture of C 60 (CF 3 ) n (5 mg) was dissolved in liquid CF 3 I in sealed quartz ampoule and irradiated by low-pressure mercury lamp (254 nm) during 24 h. In fact, free radicals content in the irradiated sample was found to increase up to 4 mol%. Cor- respondingly, its MALDI mass spectrum (Figure 1) showed the considerable increase of relative intensities for stable odd numbered peaks as compared with the untreated sample. The even numbered peaks are known to originate from the corresponding molecules while the odd ones can be either fragments formed by the loss of a CF 3 group or due to stable odd numbered molecules. The formation of fragments is always accompanied by the appearance of metastable peaks (of comparable intensities) shifted from the stable odd numbered peaks by = ~ 13 Da. 11 † MALDI mass spectra in the negative ion mode were obtained with a Bruker AutoFlex II time-of-flight reflectron device, N 2 laser, 337 nm, 1 ns pulse; 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malono- nitrile (DCTB, ³ 99%, Fluka) was used as a matrix. ‡ ESR spectra were recorded using a Varian E-3 (USA) spectrometer. ESR signal of Mn 2+ in MgO was used for magnetic field calibration. The ESR spectra of fraction 2 and fraction 5 were unchanged up to 333 K where slow degradation of ESR signals was observed. To avoid the influence of oxygen ESR spectra were recorded under argon or in solu- tions deaerated by vacuum. A numerical simulation of ESR spectra was carried out with the use of the spin Hamiltonian that includes second- order terms with regard to the energy of nuclear Zeeman interaction. The non-linear least-squares method was used for determination of individual line width and hyper fine constants (hfc). 2 3 4 5 6 7 8 9 10 1500 1600 1700 1800 1900 2000 m/z 1478.9 1616.9 3.94 Retention time/min 3.37 (b) C 60 (CF 3 ) n – 1961.9 1892.9 n = 11 n = 12 n = 13 n = 13* n = 14 n = 15 n = 16 n = 17 n = 18 n = 17* n = 15* 1547.9 1823.9 1754.9 1685.9 (a) fraction 2 fraction 5 Figure 1 HPLC trace (a) and MALDI mass spectrum (b) of the mixture of trifluoromethylated fullerenes after UV irradiation. The metastable peaks are marked with asterisk.