Electrochemical, ESR and theoretical studies of [6,6]-opened C60(CF2), cis-2-C60(CF2)2 and their anions

Abstract

Electrochemical behavior of C(60)(CF(2))(n), n = 1, 2 and C(60)(CCl(2)) has been investigated. [6,6]-Opened C(60)(CF(2)) and cis-2-C(60)(CF(2))(2) exhibit reversible reductions at potentials 150 and 145 mV more positive than C(60), unlike the related [6,6]-closed C(60)(CCl(2)), which shows reduction at the potential close to that for C(60). The structures, electron localization and lifetimes of the observed radical anions C(60)(CF(2))(-*) and cis-2-C(60)(CF(2))(2)(-*) have been elucidated by the ESR study and DFT calculations. The protonation pathway of decay of C(60)(CF(2))(-*) yields [6,6]-opened 1,9-dihydro-(1a,1a-difluoro-1aH-1(9)a-homo(C(60)-I(h))fullerene, C(60)(CF(2))H(2), which becomes the first characterized derivative of [6,6]-opened C(60)(CF(2)). DFT calculations of the structure and electron affinity of a number of homofullerene structures have been carried out to rationalize the experimental findings.

The first representative of a new family of the bridgehead-modified difluoromethylenated homofullerenes: electrochemical properties and synthetic availability

“…With the decrease of the applied voltage, several less intensive peaks with a higher g-factor and smaller hfc values appear in the spectrum, more likely, owing to some side products involving the solvent (oDCB), as it has been reported earlier. [29] The g-value observed for C 60 (CF 2 )H 2 •-(2.0001 (2)), is smaller than that for C 60 (CF 2 ) •-(2.0017 (2)) [12] and is very close to the values measured for C 60 H 2 •-(2.000), [27] C 60 R 2…”

“…The peak-to-peak line width for the C 60 (CF 2 )H 2 •-(typically for doubly functionalized fullerenes [12,16,27,30,31] ) is significantly narrowed (0.7 G) as compared to the C 60 •-radical anion, in which small Jahn-Teller distortions and associated dynamic effects play a significant role. [27,32] Indeed, the DFT calculations of the C 60 (CF 2 ) •-and C 60 (CF 2 )H 2 •-radical anions show that the spin density at the 19 F nuclei is significantly higher than that at the protons (see Table 2).…”

“…[12][13][14] The insertion of the difluorocarbene is accompanied by [6,6]-bond cleavage and relocation of double bonds in the cage yielding so called " [6,6]-open" adducts in which the sp 2 hybridization of the bridging carbon atoms is retained, as well as 60π-or 70π-conjugated systems. According to electrochemical estimations, [6,6]-open C 60 (CF 2 ) and C 70 (CF 2 ) homofullerenes exhibit the highest electron affinity (EA) among doubly functionalized fullerenes studied to date: the first reduction potential is anodically shifted by ca.…”

“…0.15 V with respect to the parent fullerenes. [12,15 Contrary to anionic forms of C 60 in which a negative charge is uniformly distributed over the fullerene cage, [5], 16] the negative charge in the anionic species of difluoromethylenated homofullerenes is mainly localized at the bridgehead carbon atoms [12,15] thus providing a possibility for regioselective electrophilic attack. Recently, we have demonstrated that protonation of the electrochemically generated C 60 (CF 2 ) 2-dianion with triflic acid affords a single isomer of C 60 (CF 2 )H 2 which is regioselectively hydrogenated at the bridgehead carbon atoms (see Fig.…”

“…Recently, we have demonstrated that protonation of the electrochemically generated C 60 (CF 2 ) 2-dianion with triflic acid affords a single isomer of C 60 (CF 2 )H 2 which is regioselectively hydrogenated at the bridgehead carbon atoms (see Fig. 1) [12] and is a close structural analog of C 60 (NH)H 2 . [17] This opens a route to preparative-scale synthesis of C 60 (CF 2 )H 2 which can be considered as the first and the simplest representative of a new family of the bridgehead-modified difluoromethylenated homofullerenes.…”