FULL PAPER DOI: 10.1002/chem.201302946

ACHTUNGRE[6,6]-Open and [6,6]-Closed Isomers of C70ACHTUNGRE(CF2): Synthesis, Electrochemical and Quantum Chemical Investigation Nataliya A. Samoylova,[a] Nikita M. Belov,[a] Victor A. Brotsman,[a] Ilya N. Ioffe,[a] Natalia S. Lukonina,[a] Vitaliy Yu. Markov,[a] Adrian Ruff,[b, c] Alexey V. Rybalchenko,[a] Paul Schuler,[b] Olesya O. Semivrazhskaya,[a] Bernd Speiser,[b] Sergey I. Troyanov,[a] Tatiana V. Magdesieva,*[a] and Alexey A. Goryunkov*[a] Abstract: Novel difluoromethylenated [70]fullerene derivatives, C70ACHTUNGRE(CF2)n (n = 1–3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two major products, isomeric C70ACHTUNGRE(CF2) mono-adducts with [6,6]-open and [6,6]-closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X-ray analysis and high-level spectroscopic techniques. The [6,6]open isomer of C70ACHTUNGRE(CF2) constitutes the first homofullerene example of a non-

hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C70ACHTUNGRE(CF2) isomers showed that it is substantially higher for the [6,6]-open isomer (the 70-electron p-conjugated system is reKeywords: density functional calculations · fullerenes · molecular switches · spectroelectrochemistry · structure elucidation

Introduction Fullerenes and their derivatives are of particular interest for the design and synthesis of molecules with specific properties required for applications in areas such as material science (photovoltaic cells, optical limiters)[1] and medicine (antioxidants, neuroprotective agents, antimicrobial agents, agents for photodynamic therapy and magnetic resonance

[a] N. A. Samoylova, N. M. Belov, V. A. Brotsman, Dr. I. N. Ioffe, Dr. N. S. Lukonina, Dr. V. Y. Markov, A. V. Rybalchenko, O. O. Semivrazhskaya, Prof. Dr. S. I. Troyanov, Prof. Dr. T. V. Magdesieva, Dr. A. A. Goryunkov Chemistry Department Lomonosov Moscow State University Leninskie Gory, 1, 119991, Moscow (Russia) Fax: (+ 7) 495-939-1240 E-mail: [email protected] [email protected] [b] Dr. A. Ruff, P. Schuler, Prof. Dr. B. Speiser Institut fr Organische Chemie Universitt Tbingen, Auf der Morgenstelle 18 72076 Tbingen (Germany) [c] Dr. A. Ruff Institut fr Polymerchemie Universitt Stuttgart, Pfaffenwaldring 55 70569 Stuttgart (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201302946.

Chem. Eur. J. 2013, 19, 17969 – 17979

tained) than the [6,6]-closed form, the latter being similar to the electron affinity of pristine C70. In situ ESR spectroelectrochemical investigation of the C70ACHTUNGRE(CF2) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter-conversion between the [6,6]-closed and [6,6]-open forms of a cage-modified fullerene driven by an electrochemical one-electron transfer. Thus, [6,6]-closed C70ACHTUNGRE(CF2) constitutes an interesting example of a redoxswitchable fullerene derivative.

imaging).[2] Typically, fullerenes are functionalised by various addition reactions to the double bonds, whereas transformations of the fullerene cage itself are much harder to carry out due to high stability of the network of carbon– carbon fullerene bonds. Recently it has been demonstrated[3] that sites of enhanced reactivity can emerge in the fullerene cage upon opening of the [6,6]-bonds. Synthesis of the so-called homofullerene compounds by insertion of a bivalent addend (e.g. the difluoromethylene fragment) into a [6,6]-bond leads to cleavage and associated redistribution of the p-electron bonding in the cage. The resulting [6,6]-open adducts contain the 1,6-difluoromethano[10]annulene moiety in which the sp2 hybridisation of the bridgehead carbon atoms is retained and, accordingly, all carbon atoms of the parent fulACHTUNGRElerene remain within the spherical p system, although its connectivity decreases slightly. These compounds with an open [6,6] C C bond (homofullerenes) are quite unusual amongst fullerene exohedral derivatives. Until recently, only a few examples of [6,6]-open structures were known, all of them with nitrogen-containing bridges.[4–6] Preparation of the first [6,6]-open carbon-containing derivatives C60ACHTUNGRE(CF2) [predicted theoretically in 1998][7] and cis-2-C60ACHTUNGRE(CF2)2 was reported in our pioneering works in 2006.[3, 8, 9] Although still very little is known about the reactivity of homofullerenes, it is clear that preservation of the spherical p system of fullerenes with all carbon atoms remaining sp2 hybridised

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

17969

makes homofullerenes more sensitive than methanofullerenes to further functionalisation. Our recent electrochemical investigation of [6,6]-open C60ACHTUNGRE(CF2)[3] demonstrated that the electron affinity of this compound is well above the values obtained for other known C60 adducts with one bivalent or two mono-valent addends. As an illustration, a plot of the first reduction potentials for various methano[60]fullerenes versus the sum of Hammett constants, sm, of the substituents[10] based on the literature data[11] and our previous findings[3] is provided in Figure 1. Only the C60ACHTUNGRE(CF2) homofuller-

niques and quantum chemical calculations. Notably, one of the reported compounds constitutes the first example of a non-hetero [70]fullerene derivative that has the most reactive bond at the pole of the cage cleaved to give a [6,6]open adduct.

Results and Discussion Synthesis and structures of the C70ACHTUNGRE(CF2) isomers: The synthesis of the difluoromethylenated derivatives of C70 was performed by using a protocol similar to that used for C60 :[9] C70 was heated at reflux with CF2ClCOONa in ortho-dichlorobenzene (oDCB, 180 8C) in the presence of a catalytic amount of [18]crown-6. MALDI mass spectrometric and HPLC analysis showed products of mono-, bis- and tris-addition of CF2 groups to be dominant, whereas tetra-adducts were only minor components (Figure 2). Additional treat-

Figure 1. First reduction potential values of some C60ACHTUNGRE(CR1R2) compounds versus the sum of sm for substituents R1 and R2.

ene shows a marked departure from the conventional linear trend, which reveals a key influence of the bond opening on the redox behaviour. The replacement of C60 with C70 offers broader possibilities for investigation of the influence of the local geometry of the fullerene p system on the electronic properties of the adducts. Compared to C60, in which all [6,6]-bonds are equivalent, the skeleton of C70 contains four distinct types of [6,6]-bonds with somewhat different local curvature of the carbon cage. This introduces more diversity in the functionalisation reactions and makes it possible to obtain both [6,6]-open and [6,6]-closed isomers. A comparative investigation of the electronic structure of such compounds by using high-level experimental methods and quantum chemical calculations will provide deeper insight into the geometric and electronic aspects of the reactivity of homofullerenes. However, targeted synthesis of the [6,6]-open and [6,6]closed isomers is not a trivial task. Previously, we have demonstrated that the bivalent CF2 addend facilitates selective formation of the [6,6]-open form of C60ACHTUNGRE(CF2).[8, 9] For C70, the situation is more complex because theoretically eight different C70ACHTUNGRE(CF2) regioisomers can be expected upon difluorocarbene addition to the C70 cage. The present paper describes the development of a new chemical approach to derivatisation of the [70]fullerene cage with the CF2 addend to yield either [6,6]-open homofullerene or [6,6]-closed methanofullerene isomers. We also elucidate the connections between the structural and electronic properties of these compounds by using a variety of electrochemical and spectroscopic tech-

17970

www.chemeurj.org

Figure 2. a) Negative ion MALDI mass spectrum of the products of [70]fullerene difluoromethylenation; b) HPLC trace (Cosmosil Buckyprep 10 mm I.D.  25 cm, toluene/hexane = 8:2, 4.6 mL min 1) of the reaction mixture.

ment with sodium difluorochloroacetate resulted in a decrease in the relative abundance of C70ACHTUNGRE(CF2), whereas the content of the C70ACHTUNGRE(CF2)n poly-adducts (n = 2–4) was enhanced. Though the reaction was performed under air, only small amounts of the oxygen-containing derivatives C70ACHTUNGRE(CF2)2O and C70ACHTUNGRE(CF2)3O were detected. The reaction mixture was separated by HPLC with toluene/hexane (8:2 v/v) as the eluent (Figure 2 b). Eleven fractions were isolated and identified by MALDI mass spectrometry (Table 1). Three major fractions (p2, p3 and p5) correspond to unreacted C70 and to the two isomers of C70ACHTUNGRE(CF2), respectively. The first eluted fraction (p1) contained the C70ACHTUNGRE(CF2)2 bis-adduct, comparable to the C60ACHTUNGRE(CF2)n mixture from which the early eluted fraction was cis-2-C60ACHTUNGRE(CF2)2.[8] According to MALDI mass spectrometry, fraction p6 contained a third (minor), non-characterised,

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2013, 19, 17969 – 17979

Isomers of C70(CF)2

FULL PAPER

Table 1. HPLC separation and mass spectrometric characterisation of the reaction products. Fraction

tR [min][a]

Composition[b]

p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 p11

18.9–20.1 22.0–22.8 22.8–23.8 25.1–26.5 27.1–28.5 29.0–31.2 31.3–32.6 32.9–34.5 34.5–36.2 36.3–38.0 38.2–38.9

C70ACHTUNGRE(CF2)2 C70 C70ACHTUNGRE(CF2) [isomer I] C70ACHTUNGRE(CF2)n, n = 2, 3 C70ACHTUNGRE(CF2) [isomer II] C70ACHTUNGRE(CF2)n, n = 1–3 C70ACHTUNGRE(CF2)nOm, n = 2–4, C70ACHTUNGRE(CF2)n, n = 2–3 C70ACHTUNGRE(CF2)nOm, n = 2–3, C70ACHTUNGRE(CF2)nOm, n = 2–4, C70ACHTUNGRE(CF2)nOm, n = 2–3,

m = 0–2 m = 0–1 m = 0–2 m = 0–2

[a] Retention time. Conditions: Cosmosil Buckyprep (10 mm I.D.  25 cm), toluene/hexane = 8:2, 4.6 mL min 1. [b] Determined by MALDI MS.

C70ACHTUNGRE(CF2) isomer, along with the bis- and tris-adducts. The other fractions comprised complex mixtures of bis- to tetraCF2 adducts and their oxygenated derivatives. It was found that the optimal method for isolation of the C70ACHTUNGRE(CF2) isomers is a two-step procedure: initial coarse sep-

aration of the desired fractions by elution with toluene, followed by fine chromatographic purification with a less polar eluent (6:4 toluene/hexane; a further increase in hexane content does not improve the separation and considerably increases the retention time, see the Supporting Information, Figure S1, for details). Thus, isomerically pure samples of two C70ACHTUNGRE(CF2) isomers (early eluted C70ACHTUNGRE(CF2)-I and subsequently eluted C70ACHTUNGRE(CF2)-II) were obtained after HPLC separation in amounts sufficient for spectral, X-ray and electrochemical analysis. The C70ACHTUNGRE(CF2) isomers were characterised by 19F and 13 C NMR spectroscopic analysis (Figure 3). The 19F NMR spectra show signals typical for CF2 groups: an AB spin system at d = 126.37 ppm (AB q, DdAB = 2.55 ppm, J = 169.3 Hz, 2 F) for C70ACHTUNGRE(CF2)-I and a more downfield singlet signal (d = 111.9 ppm) for C70ACHTUNGRE(CF2)-II. The presence of an AB spin system in the spectrum of the C70ACHTUNGRE(CF2)-I isomer is an indication that the chemical environment of the fluorine atoms is non-equivalent, contrary to C70ACHTUNGRE(CF2)-II for which the singlet peak suggests equivalence of the fluorine atoms. We found that the fluorine chemical shift is characteristic for distinction of methano- and homofullerene structures,

Figure 3. a), d) 19F NMR and b), c), e), f) 13C NMR spectra of C70ACHTUNGRE(CF2)-I (top) and C70ACHTUNGRE(CF2)-II (bottom); [D4]oDCB 13C NMR signals are marked with asterisks. DFT-optimised structures of C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II, as well as Schlegel diagrams with the numeration of bonds (position of CF2 groups are marked with dumbells), are shown.

Chem. Eur. J. 2013, 19, 17969 – 17979

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

17971

T. V. Magdesieva, A. A. Goryunkov et al.

which differ in hybridisation of the bridgehead carbon atoms. The signal due to C70ACHTUNGRE(CF2)-II is shifted downfield (by about 7 ppm) with respect to that observed for [6,6]-open C60ACHTUNGRE(CF2) (d = 119 ppm), which supports the homofullerene structure of C70ACHTUNGRE(CF2)-II. On the contrary, the AB spin system of C70ACHTUNGRE(CF2)-I is shifted upfield, rather typical for 1,1difluorocyclopropane derivatives with sp3-hybridised bridgehead carbon atoms. For example, CF2 chemical shift values for saturated 7,7-difluoronorcarane[12] are dF = 129 and 159 ppm; for 11,11-difluoro-1,6-methano-[10]annulene[13] and difluorocyclopropabenzene,[14] which contain sp2-bridgehead carbon atoms, d = 126.2 and 80.4 ppm, respectively. The 13C NMR spectrum of C70ACHTUNGRE(CF2)-I features 34 sp2 carbon atom signals in the range d = 124–153 ppm plus two triplet signals at d = 69.4 (3JACHTUNGRE(C,F) = 23 Hz) and 102.8 ppm (1JACHTUNGRE(C,F) = 285 Hz) attributed to the bridgehead sp3 carbon atoms and the sp3 carbon of the CF2 group, respectively. The signals observed within the range d = 68–80 ppm are typical for bridgehead carbon atoms of methanofullerenes, as follows from the literature data obtained for [5,6]-closed C60ACHTUNGRE(GeR2),[15] [6,6]-closed C60ACHTUNGRE(CR2), R = H, Cl, Br, I,[16–19] and C70ACHTUNGRE(CCl2).[20] The 13C NMR spectrum of C70ACHTUNGRE(CF2)-II contains 35 sp2 carbon atom signals in the range d = 125–155 ppm, a triplet signal at d = 111.6 ppm (1JACHTUNGRE(C,F) = 257 Hz; CF2) and two triplet signals at d = 99.2 and 98.2 ppm (3JACHTUNGRE(C,F) = 37.4 and 38.5 Hz, respectively). The last two triplet signals can be ascribed to the two inequivalent bridgehead carbon atoms. The signals of the bridgehead carbon atoms of C70ACHTUNGRE(CF2)-II are dramatically shifted downfield (by about 30 ppm) relative to those in C70ACHTUNGRE(CF2)-I. The apparent reason is pronounced sp2 hybridisation of the bridgehead atoms in C70ACHTUNGRE(CF2)-II. The same effect has been observed for bridgehead cage carbon atoms of the homofullerenes [6,6]-C60ACHTUNGRE(CF2),[9] [5,6]-C70ACHTUNGRE(CCl2)[20] and [6,6]-equatorial C2vC70(CH2)[21] within the range d = 107–119 ppm. Thus the structural predictions from the 19F and the 13C NMR spectra are in good qualitative agreement. The detection of only 34 and 35 sp2 carbon atom signals in the 13C NMR spectra of C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II, respectively, points to Cs symmetry of both molecules. The existence of C2 symmetry can be ruled out because with a single CF2 addend only a more symmetric C2v structure with far fewer NMR spectral lines can possibly form and involve bond 1 (see Figure 3 for bond enumeration). According to 19F NMR spectroscopic data, both fluorine atoms in the C70ACHTUNGRE(CF2)-I isomer should lie in the mirror plane whereas in the C70ACHTUNGRE(CF2)-II case they are symmetric to it. This is only consistent with addition to bond 7 for C70ACHTUNGRE(CF2)-II and to bonds 4, 5, or 8 for C70ACHTUNGRE(CF2)-I. However, addition to the single [5,6]-bonds 4 and 8 is most unlikely because it would result in their inevitable cleavage (the DFT-estimated C···C distances are 2.19 and 2.30 , respectively, see Table 3 below) whereas C70ACHTUNGRE(CF2)-I belongs to the methanofullerene type with the respective C C bond retained according to the 19F and 13C NMR spectroscopic data. Thus, 19F and 13 C NMR spectroscopy unambiguously characterise the

17972

www.chemeurj.org

C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II isomers to be the products of CF2 addition to bonds 5 and 7, respectively (Figure 3). Ultimately, the structure of the C70ACHTUNGRE(CF2)-I isomer was proven by means of single-crystal X-ray diffraction (Figure 4). Crystals of sufficient quality were prepared by

Figure 4. X-ray structure of the C70ACHTUNGRE(CF2)-I adduct with Ni(II) octaethylporphyrin (C70ACHTUNGRE(CF2)·2NiIIACHTUNGRE(OEP)·C6H5ACHTUNGRE(CH3), 50 % probability thermal ellipsoids are shown; toluene molecule and hydrogen atoms are omitted for clarity.

co-crystallisation of C70ACHTUNGRE(CF2)-I and Ni(II) octaethylporphyACHTUNGRErin. The experimental C C bond length between the bridgehead carbon atoms (1.707(8) ) is in good agreement with the DFT estimated value (1.72 ). Typical bond lengths of such C C bonds in methanofullerenes are about 1.65 .[22] The longest C C bond of approximately 1.70  was detected in D3d-C60Cl30.[23] Thus, in spite of significant elongation of C C bond 5 after CF2 addition, one can assume that the bonding between the bridgehead carbon atoms in C70ACHTUNGRE(CF2)-I is preserved. It should be also mentioned that, in addition to the elongation of the aforementioned C C bond 5, noticeACHTUNGREable elongation of all neighbouring C C cage bonds in C70ACHTUNGRE(CF2)-I (  0.015–0.025  relative to the same bonds in pristine fullerene) is observed. This is due to the change in hybridisation of the bridgehead carbon atoms from sp2 to sp3. The CF2-Cbridgehead-Cbridgehead angle in the cyclopropane ring is 54.2(3)8, closer to the perfect 608 than in C60ACHTUNGRE(CF2). The shortest Ni···Ccage and N···Ccage distances are 2.816(4) and 3.026(6) , respectively, which is typical for co-crystals of fullerene derivatives with Ni(II) octaethylporphyrin and is commonly attributed to p–p interactions.[24] The [6,6]-closed and [6,6]-open structures of C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II are also supported by characteristic features of their UV/Vis spectra (Figure 5). The spectra of [6,6]-open C70ACHTUNGRE(CF2)-II and C70 (Figure 5 b, c) are similar, a fact that is

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2013, 19, 17969 – 17979

Isomers of C70(CF)2

FULL PAPER

Figure 6. CV curves obtained for the [6,6]-closed and [6,6]-open C70ACHTUNGRE(CF2) isomers (Pt, 0.15 m Bu4NBF4 , oDCB, scan rate = 100 mV s 1, E vs. Fc0/+).

Figure 5. UV/Vis spectra for C70ACHTUNGRE(CF2) isomers a) I , c = 4.49  10 2 mm; b) II, c = 7.91  10 2 mm and c) C70, c = 7.54  10 2 mm, measured in solution in CH2Cl2.

tions can be observed, their peak potential values and peak current ratios (Ia/Ic) are summarised in Table 2. In all cases, the Ia/Ic values were close to unity, evidence of the stability of the mono-, di- and tri-anions towards any follow-up chemical reactions, at least within the cyclic voltammetry (CV) timescale. The peak currents for both isomers were diffusion controlled, as follows from the linear dependence of the current on the square root of the potential scan rate. The potential separation between the forward and reverse peaks is about 60 mV for all the redox couples observed, which conforms to the reversibility criterion. In the case of the [6,6]-open isomer, after the second reduction a small reversible redox couple (marked with asterisks in Figure 6) at a potential close to the second C70 reduction (C70 /2 ) can be observed in the CV curve. This was possibly the result of a small impurity or an indication that the C70ACHTUNGRE(CF2)2 dianion may slowly decompose. In the latter case, the presence of the corresponding set of peaks for C70 in the reverse

typical for homofullerenes with weakly perturbed p-electron systems.[25] It has been shown that the UV/Vis spectrum of the C60ACHTUNGRE(CF2) homofullerene is almost identical to that of C60.[9] On the contrary, the UV/Vis spectrum of C70ACHTUNGRE(CF2)-I is significantly different from that of C70 (Figure 5 a versus c). In the region of p–p* transitions (l = 300–500 nm), instead of four bands observed for C70, only three bands are detected, and they are blueshifted by Dl  10– Table 2. Electrochemical data (Pt, oDCB, 0.1 m Bu4NBF4, E vs. Fc0/+, scan rate = 20 nm. This shift indicates a slight increase in the 100 mV s 1) for C , C ACHTUNGRE(CF )-I, C ACHTUNGRE(CF )-II and C ACHTUNGRE(CF ). 70 70 2 70 2 60 2 p–p* transfer energy, typical for all methanofuller[a] [b] Compound Process E E DE I ACHTUNGRE(Epc+Epa)/2 [V] pc pa a/Ic enes.[9] This blueshift reflects partial destruction of vs. C70 n/ (n+1) [V] [V] [V] vs. Fc0/+ the fullerene p-electron system due to rehybridisaC70 0/1 1.09 1.02 0.07 0.92 1.06 – tion of two cage carbon atoms to the sp3 state after 1 /2 1.47 1.41 0.06 0.97 1.44 – functionalisation. 2 /3 1.89 1.83 0.06 1.00 1.86 – Voltammetric measurements: With sufficient quantities of the compounds in hand, we next investigated the influence of local perturbation of the fullerene p system on the electronic properties of the molecules. The C70 framework enables the first direct comparison of [6,6]-open and [6,6]-closed derivatives of the same carbon cage. The cyclic voltammograms for the [6,6]-open and [6,6]-closed C70ACHTUNGRE(CF2) isomers are shown in Figure 6. In both cases, at least three reversible one-electron reduc-

Chem. Eur. J. 2013, 19, 17969 – 17979

C70ACHTUNGRE(CF2)-I ACHTUNGRE[6,6]-closed

0/1 1 /2 2 /3

1.08 1.37 1.83

1.02 1.31 1.78

0.06 0.06 0.05

0.98 1.00 0.97

1.05 1.34 1.81

0.01 0.10 0.06

C70ACHTUNGRE(CF2)-II ACHTUNGRE[6,6]-open

0/1 1 /2 2 /3

0.94 1.27 1.85

0.88 1.21 1.79

0.06 0.06 0.06

1.00 0.95 1.00

0.91 1.24 1.82

0.15 0.20 0.04

C60ACHTUNGRE(CF2) ACHTUNGRE[6,6]-open

0/1 1 /2 2 /3

0.91 1.25 1.85

0.86 1.19 1.80

0.05 0.06 0.05

1.00 1.00 0.95

0.89 1.22 1.83

0.17 0.22 0.04

[a] Reduction peak potential. [b] Oxidation peak potential.

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

17973

T. V. Magdesieva, A. A. Goryunkov et al.

anodic scan would also be expected. However, the concentration of hypothetically formed C70 is too small to ensure all peaks are detected. The calculated formal potential values that correspond to the formation of mono-, di- and trianions of both isomers are summarised in Table 2. The potential of the C70ACHTUNGRE(CF2)0/ redox couple is approximately 140 mV more anodic in the case of the [6,6]-open isomer, which means that the electron affinity (EA) of the [6,6]-open isomer is higher than that of the [6,6]-closed form or pristine C70. These results are in line with our previous data; the electrochemical study of [6,6]open C60ACHTUNGRE(CF2) revealed a similar anodic shift (150 mV) of the first reduction potential relative to C60.[3] Furthermore, the experimental results obtained are in agreement with the theoretical estimations; the observed anodic shift correlates with DFT-predicted EA values (2.77, 2.80 and 2.93 eV for C70, C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II, respectively). The EA of [6,6]-closed C70ACHTUNGRE(CF2) almost coincides with that of C70 (the peak potential values for one-electron reduction are almost identical too). Probably, a decrease in EA due to impaired p conjugation (68 electrons versus 70) is compensated for by the addition of an electron-withdrawing CF2 group. The distances between the corresponding redox peaks of the two isomers become attenuated with an increase in the negative charge (Table 2). The formal redox potentials of the [6,6]-closed and [6,6]-open isomers for the consecutive C70ACHTUNGRE(CF2)0/ , C70ACHTUNGRE(CF2) /2 and C70ACHTUNGRE(CF2)2 /3 couples are separated by 140 mV, 100 mV, and 20 mV, respectively. This may be due to gradual smoothing of the structural differences (most importantly, the geometry of the CF2 bridge) in the highly charged states. One can expect, by analogy to the increased bond opening in the mono-anions of C70ACHTUNGRE(CF2) discussed below, that further charging may facilitate even stronger C···C elongation between the bridgehead carbon atoms in both isomers. Notably, the successive redox potentials of the two compounds that already have an open configuration in their neutral state, C70ACHTUNGRE(CF2)-II and C60ACHTUNGRE(CF2), remain constantly spaced (ca. 20 mV, see Table 2).

Relative energies and structural and electronic features of C70ACHTUNGRE(CF2) isomers: Table 3 summarises our DFT (PBE/ TZ2P) results for the relative energies and geometry of the C CF2 C fragment of the eight theoretically possible isomers of C70ACHTUNGRE(CF2). For comparison, experimental bond lengths in C70[26] are given. The most energetically preferable C70ACHTUNGRE(CF2) isomer with C2v-symmetry, the formal product of CF2 addition to the equatorial [6,6]-bond 1, is the least kinetically favourable (see Figures S2–S9 in the Supporting Information for the calculated reaction profiles). Although the respective activation energy of 58 kJ mol 1 is quite accessible in itself, it is considerably higher than the barrier heights for addition to the other bonds. Despite being [6,6]-bonds, the equatorial bonds 1 in C70 are 1.48  long, thus exhibit single-bond character.[26] Moreover, they are the longest C C bonds in the C70 molecule, with the lowest bond order (1.23) among the [6,6] bonds. Also, they are formed between the two chemically less-active carbon atoms at the triple hexagon junctions (THJs). Therefore, it is not unexpected that the insertion of the CH2 groups into the equatorial bonds to yield the [6,6]-open C2v-C70ACHTUNGRE(CH2) derivative is observed only at elevated temperatures (approximately 1100 8C).[21] Similarly, other elongated C C bonds (3, 6 and 8; 1.44–1.46 , bond orders: 1.21–1.23) are unlikely to be involved in carbene addition under mild conditions due to competition from shorter bonds. The shortest bonds, 5 (1.37 ) and 7 (1.38 ) are characterised by the highest bond orders (1.41 and 1.45, respectively). As a result, they easily undergo [2+1] cycloaddition with DCCl2 and [3+2] cycloaddition with diazomethane to result in the corresponding cyclopropane and pyrazoline derivatives, respectively.[20, 25] Analogously, CF2 addition to these bonds is characterised by EA = 18 and 19 kJ mol 1, respectively, the lowest amongst the considered set of isomeric additions. Bonds 2 and 4 constitute an intermediate case; bond 2 is slightly shorter than bond 4 (1.42 versus 1.45 ) and their bond orders (1.34 and 1.30, respectively) are in between the extreme cases discussed above. Thus, reactions that involve these bonds are relatively less probable. Addition to bond 2 should be also impeded by the low reactivity of the THJ

Table 3. Schlegel diagram of C70 (bond indices and bond lengths [] are given) and DFT relative energies, activation energy (EA) values for DCF2 addition and distances between the bridgehead carbon atoms for the various theoretically possible isomers of C70ACHTUNGRE(CF2) [in order of increasing EA, numbered according to the bond being functionalised]. Isomer

7 5 4 2 6 8 3 1

C C bond in C70 Type Length[a] []

Mulliken bond order[b]

Corresponding C C bonds in C70ACHTUNGRE(CF2) isomer DE C···C distance EA[c] ACHTUNGRE[kJmol 1] ACHTUNGRE[kJmol 1] []

II [6,6] I [6,6] ACHTUNGRE[5,6] ACHTUNGRE[6,6] ACHTUNGRE[5,6] ACHTUNGRE[5,6] ACHTUNGRE[5,6] ACHTUNGRE[6,6]

1.45 1.41 1.30 1.34 1.21 1.23 1.23 1.23

18 19 25 26 28 28 29 58

1.38 1.37 1.45 1.42 1.46 1.46 1.44 1.48

(1.40) (1.39) (1.44) (1.42) (1.45) (1.45) (1.45) (1.47)

0 17.6 2 40.8 8.9 0.3 36.9 44

2.09 1.72 2.19 2.19 2.21 2.30 2.20 2.33

[a] X-ray structural data from ref. [26]; the DFT estimated values are given in parentheses. [b] DFT (PBE/TZ2P) data. [c] When alternative inequivalent reaction paths exist, the lowest of the EA values is given, for details see the Supporting Information (Figures S2–S9).

17974

www.chemeurj.org

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2013, 19, 17969 – 17979

Isomers of C70(CF)2

FULL PAPER

carbon atom involved in this bond. However, it is known that treatment of C70 with the Seyferth reagent, PhHgCCl2Br (which releases DCCl2 upon heating), results in addition to bond 4 to yield a [5,6]-open C70ACHTUNGRE(CCl2) homofullerene, along with formation of the two isomeric C70ACHTUNGRE(CCl2) methanofullerenes (adducts at bonds 5 and 7). The ratio of the products was 1:1.2:1.3 according to HPLC data.[20, 27] Functionalisation of the fullerene cage with DCF2 differs from the reactions with its bis-chlorinated analogue because difluorocarbene more readily forms open adducts, as follows from the experimental findings reported for C60.[3, 8, 9] In case of C70, C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II show quite pronounced differences in the distance between the bridgehead carbon atoms (1.72 and 2.09 , respectively; see Table 3). These DFT results are consistent with our 19F and 13C NMR spectroscopic data and confirm that C70ACHTUNGRE(CF2)-I has a [6,6]-closed methanofullerene structure, whereas C70ACHTUNGRE(CF2)-II is of the [6,6]-open homofullerene type. Lack of bonding between the bridgehead carbon in C70ACHTUNGRE(CF2)-II is also conveniently illustrated by the electron density distribution given in Figure 7. An appreciable (though still lower than for conventional C C s-bonds) electron density can be observed along the line that connects the bridgehead carbon atoms only in the case of C70ACHTUNGRE(CF2)-I. It is noteworthy that cleavage of bond 7, the most reactive and one of the two shortest bonds in C70, was not previously observed for non-hetero derivatives. After the discovery of the structural difference we decided to study how other CX2 substituents alter the bond to which they are attached. Figure 7 shows the relaxed scans of the potential energy surfaces (PES) for the neutral isomers of C70ACHTUNGRE(CX2) [X = F, H, Cl] of types 5 and 7 along the stretching coordinate coupling the bridgehead carbon atoms. Notably, in the CF2 adducts only very shallow potential wells are observed at the equilibrium inter-atomic distances; the energy variation within a broad range of inter-atomic distances are of the order of 10 kJ mol 1. This suggests a high amplitude and a largely anharmonic CF2 opening–closure mode in the C70ACHTUNGRE(CF2) isomers. At the same time, the C70ACHTUNGRE(CCl2) and C70ACHTUNGRE(CH2) compounds of type 5 are characterised by markedly steeper PES profiles. In the isomers of type 7, the steepness is comparable to that in C70ACHTUNGRE(CF2)-II but the equilibrium inter-atomic distance is shifted to 1.65 , which may be interpreted as s bonding. In general, we see a clear trend towards the formation of closed methanofullerene compounds in the cases of C70ACHTUNGRE(CCl2) and C70ACHTUNGRE(CH2). The flatness of the PES in the C70ACHTUNGRE(CF2) isomers, as well as for C60ACHTUNGRE(CF2),[8] can be rationalised by using a simple model based on electrostatic and steric factors. One can consider the C70ACHTUNGRE(CF2) molecule as a combination of a polarisable sphere and a CF2 dipole, the strongest among other possible CX2 groups. Attraction between the dipole and the polarisable sphere brings the CF2 group closer and thus forces bond opening. Also, the CF2 carbon atom bears high effective positive charge, which induces negative charges at the bridgehead carbons and additionally contributes to their re-

Chem. Eur. J. 2013, 19, 17969 – 17979

Figure 7. a), b) PES scans for C70ACHTUNGRE(CX2), X = F, H, Cl and c) DFT-calculated electron density distribution in C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II (contour levels are given for values of 0.01, 0.05, 0.1, 0.2 and 0.3 e  3).

pulsion. The resulting s-bond cleavage is energetically unfavourable in itself but this is partly compensated by the reduction of steric strain in the cyclopropane ring. The degree of opening, however, should be limited by another steric effect: the bridgehead atoms in the sp2 state will prefer more-or-less planar coordination, which can be observed for separations of about 2.1 . The interplay of the above factors results in structural flexibility of the carbon cage. The minor differences that favour a closed configuration C70ACHTUNGRE(CF2)-I and open configuration in C70ACHTUNGRE(CF2)-II are likely associated with local curvatures of the respective sections of the carbon cage and with the ensuing differences in the energetics of the steric effects. In situ ESR spectroelectrochemistry of C70ACHTUNGRE(CF2) radical anions—the structure of C70ACHTUNGRE(CF2) anionic forms: In situ ESR spectroelectrochemical investigation of the products of

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

17975

T. V. Magdesieva, A. A. Goryunkov et al.

one-electron reduction of the C70ACHTUNGRE(CF2) isomers provides further evidence of their remarkable structural flexibility. The structural information for the radical anions can be extracted from the g-factor and hyperfine coupling (hfc) values (aF), and the influence of the negative charging on the bonding between the bridgehead carbon atom is of particular interest. As above, we complemented the experiment with DFT calculations of the PES and the hfc. As follows from Figure 8, negative charging alters the shape of the PES for both isomers. In C70ACHTUNGRE(CF2)-II, this results in additional elongation of the distance between the bridgehead carbon atoms up to 2.23  (Figure 8, bottom). DFT analysis of the net charge distribution shows that the bridgehead carbon atoms bear the highest effective net charge (calculated relative to the effective charges in the neutral molecules): 1.6–2.5 times higher than on the other carbon atoms. Apparently, this results in additional Coulomb repulsion and, consequently, elongation of the C···C distance and emergence of a deeper potential well. The behaviour of the C70ACHTUNGRE(CF2)-IC radical anion (Figure 8, top) is much trickier. Unlike the closed neutral molecule, here we see two almost isoenergetic minima separated by

a low barrier (DE  3 kJ mol 1). Thus, the radical anion can switch between the two comparably stable configurations. The somewhat deeper minimum corresponds to the [6,6]open configuration of C70ACHTUNGRE(CF2)-IC (2.17 ) and the second minimum, only 1 kJmol 1 above, is closed (1.73 ). The highest effective net charges in the [6,6]-open configuration are, as in the previous case, on the bridgehead carbon atoms, although the overall net charge distribution is more uniform. In the case of the [6,6]-closed configuration, however, the highest negative charge density is observed for the carbon atoms in the polar regions of the molecules and net charges on the bridgehead carbon atoms are much lower. The spin-density distribution is also substantially different for the [6,6]-closed and [6,6]-open configurations of the C70ACHTUNGRE(CF2)-IC isomer. This difference enables ESR-based structural assignment of the C70ACHTUNGRE(CF2)-IC radical anion. Spectroelectrochemical measurements were performed in a two-electrode cell in oDCB. The potentials were tuned to the onset of the generation of the paramagnetic radical anions C70ACHTUNGRE(CF2)C . ESR spectra for both isomers exhibit an isotropic three-line signal due to the hyperfine interaction with the pair of fluorine nuclei (Figure 9, Table 4).

Figure 9. Experimental (c) and simulated (g) ESR spectra of electrochemically generated radical anions of a) C70ACHTUNGRE(CF2)-I and b) C70ACHTUNGRE(CF2)II in Bu4NPF6 (0.1 m) in oDCB.

Figure 8. PES cross-sections along C···C stretching coordinates for neutral and radical anion forms of the C70ACHTUNGRE(CF2) isomers and their DFT optimised geometries.

17976

www.chemeurj.org

The g-factor for C70ACHTUNGRE(CF2)-IC is the same as was measured in C60ACHTUNGRE(CF2)C (2.0010).[3] The g-factor for C70ACHTUNGRE(CF2)-IIC is higher (2.0026) and quite similar to those observed for mono-functionalised C70RC radicals (2.0024–2.0028).[28] On the contrary, the g-factor for C70C is markedly lower (2.002).[29] Peak-to-peak line widths are significantly narrowed (  0.5 and 0.6 G) relative to the Ih-C60C and D5h-C70C radical anions,[29] in which small Jahn–Teller distortions and the associated dynamic effects play a role.

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2013, 19, 17969 – 17979

Isomers of C70(CF)2

FULL PAPER

Table 4. Experimental and predicted[a] ESR parameters for C70ACHTUNGRE(CF2) and C60ACHTUNGRE(CF2). Anion

t1/2 [s]

g-factor

Conclusion

Hyperfine coupling constant (aF) [G] DFT (PBE/QZ3P) Exp.[b] ACHTUNGRE[6,6]-open ACHTUNGRE[6,6]-closed

Novel isomeric difluoromethylenated derivatives of C70 with [6,6]-open and [6,6]-closed configurations 1.62 1.66 0.27 make an important addition to the narrow family of 453  6 2.0010(2) C70ACHTUNGRE(CF2)-IC 1.61 1.64 0.17 structurally characterised CF2 derivatives of fullerenes. Notably, [6,6]-open C70ACHTUNGRE(CF2) constitutes the C70ACHTUNGRE(CF2)-IIC 565  1 2.0026(2) 1.01 0.99 – first example of a non-hetero [70]fullerene derivaC60ACHTUNGRE(CF2)C 58.1  0.2 2.0010(2) 1.65 1.74 – tive in which bond opening occurs at the most reactive bond in the polar region of the cage. [a] Predicted by DFT calculations. [b] Experimental data. The synthesis of the two isomeric C70ACHTUNGRE(CF2) compounds made it possible to compare open and closed adducts of the same fullerene cage. The electronSimulation of the experimental ESR spectra based on withdrawing properties of the C70ACHTUNGRE(CF2) isomers were investiLorentz functions (Figure 9) was performed with the assumption of symmetry equivalence of the fluorine nuclei in gated by CV. We observed that open structures are better C70ACHTUNGRE(CF2)-II and by application of no constraints in C70ACHTUNGRE(CF2)acceptors, whereas in closed structures the impairment of p conjugation upon formation of a cyclopropane moiety I. The parameters obtained from the fitting procedure are nearly cancels out the acceptor effect of the CF2 group. FuraFACHTUNGRE(1 F) = 1.62 G, aF’ACHTUNGRE(1 F) = 1.6 G, Lorentzian linewidth = 0.37 G (isomer I) and aFACHTUNGRE(2 F) = 1.01 G, Lorentzian linether charging attenuates the differences. In situ ESR spectroelectrochemical investigation of the width = 0.81 G (isomer II). C70ACHTUNGRE(CF2) mono-anions supplemented with DFT calculations To interpret the ESR data, we considered the DFT-calcuproved to be an efficient tool for structural characterisation lated spin distributions and the spin-density values at the of the charged species. On the basis of these studies, we fluorine nuclei. For a better description of the spin polarisahave obtained experimental and theoretical evidence for the tion of the core s orbitals, we employed a larger built-in first example of transitions between the [6,6]-closed and quadruple-zeta core-valence basis set with a (14s8p3d2f)/ACHTUNG[6,6]-open forms in C70ACHTUNGRE(CF2)-I, driven by electrochemical TRENUG[8s4p3d2f] contraction scheme for the first-row atoms. The results shown in Table 4 demonstrate good agreement with electron transfer. Thus, the CF2 derivatives of fullerenes the experimental values and clearly support our conclusion may have interesting prospects for the design of molecular that C70ACHTUNGRE(CF2)-IC exists in the open configuration. Thus, oneswitches. electron reduction of C70ACHTUNGRE(CF2)-I triggers opening of the C C bond between the bridgehead carbon atoms. The aF value appears to be a convenient test for distinExperimental Section guishing between open and closed configurations of the radNegative-ion MALDI mass spectra were recorded with a Bruker Autoical anions of difluoromethylenated fullerenes. Indeed, the Flex II reflector time-of-flight mass spectrometer equipped with a N2 aF value correlates with the distance between the fluorine laser (l = 337 nm, 3 ns pulse) and 2-[(2E)-3-(4-tert-butylphenyl)-2-methylatom and the centres of spin localisation. In the closed conprop-2-enylidene]malononitrile (DCTB,  98 %, Sigma Aldrich) as 3 figurations, the sp -hybridised bridgehead carbon atoms lose a matrix. High-resolution MALDI mass spectra were recorded with a Thermo Scientific LTQ Orbitrap XL Hybrid Fourier Transform Mass any appreciable spin population, which yields considerable Spectrometer. HPLC analysis was performed on an Agilent 1100 series weakening of the hyperfine coupling with the fluorine liquid chromatograph fitted with a Cosmosil Buckyprep column (4.6 mm nuclei. This is the case for [6,6]-closed C70ACHTUNGRE(CF2)-IC . In the I.D.  25 cm) at 25 8C. Isolation of individual isomers was carried out on open configuration the unpaired electron is distributed over a Waters chromatograph equipped with a Cosmosil Buckyprep column the whole p system of the fullerene cage, including the (10 mm I.D.  25 cm). Toluene (99.8 %, Khimmed, Russia) and hexane (99.7 %, Khimmed, Russia) were purified by distillation. The UV/Vis bridgehead carbon atoms. As a result, the aF value is greater spectra of the toluene solutions were obtained by using a diode array dethan that for the closed form. Besides, in the closed configutector (DAD) [l = 290–950 nm with 2 nm resolution]. 19F and 13C NMR ration the distance between the fluorine atoms and the fullspectra were recorded with a Bruker Avance III spectrometer operated erene cage is increased. at 564.7 and 150.9 MHz, respectively. [D4]oDCB was used as the solvent The half-life (t1/2) of the radical anions was also measured with a small amount of TMS and hexafluorobenzene (dF = 162.9 ppm) as internal standards. in the ESR experiments. The estimated values for the Synthesis of C70ACHTUNGRE(CF2): Sodium difluorochloroacetate (10 equiv) was C70ACHTUNGRE(CF2)-IC and C70ACHTUNGRE(CF2)-IIC radical anions are approxiadded in two portions, with a 1 h interval, to a solution of C70 (1 equiv, mately 7 and 9 min, respectively (Table 4). This is an order 123.6 mg, 0.172 mmol) and [18]crown-6 (cat.) in oDCB (0.5 mg mL 1) and of magnitude longer than the lifetime of C60ACHTUNGRE(CF2)C (t1/2 = the reaction mixture was heated at reflux (180 8C). The reaction course 58.1  0.2 s, in good agreement with the literature value of was monitored by HPLC; the maximum yield of C70(CF2) mono-adducts was achieved after 3 h. Inorganic precipitate (NaCl, residual t1/2 = 51.7  0.5 s, measured with a different apparatus).[3] CF2ClCOONa) was filtered from the reaction mixture and the solvent The reason for such a difference is not yet understood and was evaporated at 90 8C under reduced pressure. The solid precipitate obneeds further investigation. tained was dissolved in toluene and the solution was passed through a column packed with silica gel. MALDI MS analysis indicated a mixture of C70ACHTUNGRE(CF2)n (n = 1–4) was formed. Two dominant mono-adducts

Chem. Eur. J. 2013, 19, 17969 – 17979

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

17977

T. V. Magdesieva, A. A. Goryunkov et al.

C70(CF2)-I (21.9 mg, 17.7 %) and C70ACHTUNGRE(CF2)-II (28.3 mg, 22.9 %) were isolated by HPLC (elution with toluene, then toluene/hexane = 3:2, v/v).

(Fc0/+) versus our RE is about 0.56 V in oDCB/Bu4NBF4. No background correction of registered voltammograms was performed.

Compound C70ACHTUNGRE(CF2)-I: HPLC (Cosmosil Buckyprep 4.6 mm I.D.  25 cm): tR = 5.75 min at a toluene flow rate of 2 mL min 1 and tR = 35.8 min at a toluene/hexane (3:2) flow rate of 1 mL min 1; 19F NMR (564.7 MHz, C6D4Cl2): d = 126.37 ppm (AB q, DdAB = 2.55 ppm, JAB = 169.3 Hz, 2 F); 13C NMR (150.9 MHz, C6D4Cl2): d = 69.4 (t, 2JACHTUNGRE(C,F) = 23 Hz, 2 C; Ccage-CF2), 102.8 (t, 1JACHTUNGRE(C,F) = 285 Hz, 1 C; CF2), 126.1, 130.7, 131.3, 131.9, 132.0, 133.0, 135.2, 141.37, 141.44, 142.8, 143.6, 144.3, 144.4, 144.5, 144.9, 145.4, 145.7, 145.9, 146.3, 146.7, 146.8, 146.9, 147.3, 148.0, 148.1, 148.15, 148.2, 148.3, 149.3, 149.4, 149.6, 150.0, 151.0, 152.9 ppm (34 signals of expected 32  2 C+4  1 C = 36 signals of sp2 carbon cage atoms; two sp2-carbon signals are masked by signals of [D4]oDCB);IR, (KBr, 4 cm 1 spectral resolution), n˜ = 578, 888, 969, 998, 1082, 1162, 1188, 1209, 1239, 1252, 1277, 1315, 1378, 1435, 1460 cm 1; UV/Vis (toluene, l = 290– 950 nm): lmax = 322 (sh), 376, 450 nm (br); UV/Vis (CH2Cl2): lmax (e): 321 (24320), 372 (24160), 445 nm (15662 mol 1 m3 cm 1); MS (MALDI): m/z (%): 890.0 [C70ACHTUNGRE(CF2)] (100), 940.0 [C70ACHTUNGRE(CF2)2] (2), 1140.1 [C70ACHTUNGRE(CF2)·DCTB] (3); HRMS (MALDI): m/z calcd for C71F2 : 889.9968; found: 889.9960.

ESR experiments: oDCB was distilled (3 ) under an argon atmosphere over CaH2. ESR spectroelectrochemical experiments were performed with a Bruker ESR 300 E spectrometer at rt under an argon atmosphere in a thin-layer quartz cell (path length  1 mm). The working electrode was a Pt net. The counter electrode consisted of a Pt wire (diameter = 0.5 mm). For the reduction of C70ACHTUNGRE(CF2)-I and C70ACHTUNGRE(CF2)-II (c = 6  10 5 m for both isomers) terminal voltages of 3.7 and 3.5 V were applied, respectively. Bu4NPF6 (0.1 m) was used as the supporting electrolyte (synthesised according to ref. [32]. For reliability, the experiments were repeated three times. Simulations were performed with the P.E.S.T. WinSim v.1.0 2002 software by using the implemented custom LBM1 algorithm.[33] For coupling constants see main text. Electrolytes were deareated by argon bubbling.

The crystallisation of C70ACHTUNGRE(CF2)-I was performed by slow mutual diffusion of saturated toluene solutions of C70ACHTUNGRE(CF2)-I and Ni(II) octaethylporphyrin [NiIIACHTUNGRE(OEP)] in a glass capillary to afford orange plate crystals (0.03  0.03  0.01 mm3). Data collection for a single crystal at 100 K was performed with a MAR-225 CCD detector by using synchrotron radiation (l = 0.83774 ) at the BESSY storage ring (BL14.2, PSF of the Free University Berlin, Germany). The structure was solved by using SHELXS97[30] and anisotropically refined with SHELXL97.[31] Crystal data for C70CF2·2NiIIACHTUNGRE(OEP)·C7H8 : Mr = 2165.77; monoclinic; space group P21/c; a = 27.734(2), b = 14.7911(5), c = 25.084(2) ; b = 106.600(4)8; V = 9861.0(11) 3 ; Z = 4; Anisotropic refinement with 24 041 reflections and 1 476 parameters yielded a conventional R1(F) = 0.094 for 22 244 reflections with I > 2s(I) and wR2(F2) = 0.240 for all reflections. CCDC-950915 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Compound C70ACHTUNGRE(CF2)-II: HPLC (Cosmosil Buckyprep 4.6 mm I.D.  25 cm) tR = 6.7 min at a flow rate of 2 mL min 1 in toluene and tR = 43.9 min at a flow rate of 1 mL min 1 in toluene/hexane = 3:2; 19F NMR (564.7 MHz, C6D4Cl2): d = 111.9 ppm (s, satellite signals: 1JACHTUNGRE(C,F) = 257.0 Hz, 3JACHTUNGRE(C,F) = 37.7 Hz, 2 F); 13C NMR (150.9 MHz, C6D4Cl2): d = 98.2 (t, 3JACHTUNGRE(C,F) = 37.4 Hz, 1 C; Cacage-CF2), 99.2 (t, 3JACHTUNGRE(C,F) = 38.5 Hz, 1 C; Cbcage-CF2), 111.6 (t, 1JACHTUNGRE(C,F) = 257 Hz, 1 C; CF2), 128.3, 129.1, 129.7, 130.9, 132.0, 135.5, 136.9, 137.0, 140.0, 140.9, 141.4, 144.70, 144.72, 144.8, 144.93, 144.94, 145.0, 145.1, 145.7, 146.2, 146.78, 146.85, 146.9, 147.2, 147.27, 147.3, 147.6, 148.4, 148.6, 149.1, 149.6, 150.1, 150.5, 151.4, 153.4 (35 signals of expected 33  2 C+2  1 C = 35 signals of sp2 carbon cage atoms);IR (KBr, 4 cm 1 spectral resolution): n˜ = 531 (w), 576 (w), 637 (vw), 671 (w), 726 (w), 801 (s), 869 (w), 991 (m), 1022 (s), 1095 (s), 1143 (m), 1187 (m), 1261 (s), 1379 (w), 1415 (m), 1430 (m), 1454 cm 1 (m); UV/Vis (toluene, l = 290–950 nm): lmax = 338, 384, 474 nm (br); UV/Vis (CH2Cl2): lmax (e) = 334 (16324), 364 (13153), 382 (16033), 466 nm (10259 mol 1 m3 cm 1); MS (MALDI): m/z (%): 890.0 [C70ACHTUNGRE(CF2)] (100), 940.0 [C70ACHTUNGRE(CF2)2] (1.3), 1140.1 [C70ACHTUNGRE(CF2)·DCTB] (7); HRMS (MALDI): m/z calcd for C71F2 : 889.9968; found: 889.9959. Voltammetric experiments: oDCB was stirred over CaH2 for 48 h under argon and then distilled under reduced pressure. The experiments were performed in a one-compartment 10 mL cell with a platinum-wire counter electrode (CE) and a Ag/AgCl/KCl (aq) reference electrode (RE) with the use of an IPC-Win potentiostat. The working electrode (WE) was either a Pt or glassy carbon (GC) disk electrode with an active surface area of 0.049 or 0.070 cm2, respectively. The concentrations of C70(CF2)-I and C70ACHTUNGRE(CF2)-II were 2  10 3 and 1  10 3 m, respectively; Bu4NBF4 (0.15 m) was used in all experiments as the supporting electrolyte. All solutions were thoroughly deoxygenated by bubbling Ar gas through the solution prior to the experiments and above the solution during the measurements. The formal potential of the ferrocene couple

17978

www.chemeurj.org

Quantum chemical calculations: Initial geometry optimisation of the C70(CF2) isomers was carried out at the AM1 level of theory with the use of the Firefly QC package,[34] which is partially based on the GAMESS (US) source code.[35] Final optimisation of molecular geometry (r.m.s. gradient 10 5–10 6 a.e./), relative energies, adiabatic electron affinities (EA), as well as spin distributions and spin-density values of the radical anions, were calculated at the DFT level with the use of the PRIRODA software[36] and employment of original TZ2P and QZ3P (for spin-density values) basis sets and a PBE exchange-correlation functional.[37] The EA values were corrected (multiplied by 0.94) according to the ratio between the experimental EA value of C70 obtained by photoelectron spectroscopy measurements[38] and that predicted by DFT (2.765  0.010 and 2.95 eV, respectively). Atomic partitions of the charge and spin densities are given according to the Hirschfeld method.[39]

Acknowledgements This work was partially supported by the Russian Foundation for Basic Research (projects No 12–03–31513, 12–03–31524, 12–03–00615, 12–03– 00858), the Ministry of Education and Science of Russia (project No MD-5540.2013.3) and the Deutsche Forschungsgemeinschaft (project No DFG Sp 265/25–1). The reported study was supported by the Supercomputing Center of Lomonosov Moscow State University.[40] We thank Marina V. Polyakova and Andreas Schank for registration of UV/Vis spectra and technical help with solvent preparation.

[1] a) J. L. Delgado, P. Bouit, S. Filippone, M. A. Herranz, N. Martin, Chem. Commun. 2010, 46, 4853 – 4865; b) A. J. Ferguson, J. L. Blackburn, N. Kopidakis, Mater. Lett. 2013, 90, 115 – 125; c) Y. Liang, Z. Xu, J. Xia, S. Tsai, Y. Wu, G. Li, C. Ray, L. Yu, Adv. Mater. 2010, 22, E135 – E138. [2] a) Medicinal Chemistry and Pharmacological Potential of Fullerenes and Carbon Nanotubes (Eds.: F. Cataldo, T.Da Ros), Springer 2008; b) P. Anilkumar, F. Lu, L. Cao, P. G. Luo, J. Liu, S. Sahu, K. N. Tackett II, Y. Wang, Y. Sun, Curr. Med. Chem. 2011, 18, 2045 – 2059. [3] A. A. Goryunkov, E. S. Kornienko, T. V. Magdesieva, A. A. Kozlov, V. A. Vorobiev, S. M. Avdoshenko, I. N. Ioffe, O. M. Nikitin, V. Y. Markov, P. A. Khavrel, A. K. Vorobiev, L. N. Sidorov, Dalton Trans. 2008, 6886 – 6893. [4] M. R. Banks, J. I. G. Cadogan, I. Gosney, A. J. Henderson, P. K. G. Hodgson, W. G. Kerr, A. Kerth, P. R. R. Langridge-Smith, J. R. A. Millar, A. R. Mount, J. A. Parkinson, A. T. Taylor, P. Thornburn, Chem. Commun. 1996, 507 – 508. [5] G. Schick, A. Hirsch, H. Mauser, T. Clark, Chem. Eur. J. 1996, 2, 935 – 943. [6] G. Schick, T. Jarrosson, Y. Rubin, Angew. Chem. 1999, 111, 2508 – 2512; Angew. Chem. Int. Ed. 1999, 38, 2360 – 2363. [7] C. H. Choi, M. Kertesz, J. Phys. Chem. A 1998, 102, 3429 – 3437.

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2013, 19, 17969 – 17979

Isomers of C70(CF)2

FULL PAPER

[8] A. S. Pimenova, A. A. Kozlov, A. A. Goryunkov, V. Y. Markov, P. A. Khavrel, S. M. Avdoshenko, V. A. Vorobiev, I. N. Ioffe, S. G. Sakharov, S. I. Troyanov, L. N. Sidorov, Dalton Trans. 2007, 5322 – 5328. [9] A. S. Pimenova, A. A. Kozlov, A. A. Goryunkov, V. Y. Markov, P. A. Khavrel, S. M. Avdoshenko, I. N. Ioffe, S. G. Sakharov, S. I. Troyanov, L. N. Sidorov, Chem. Commun. 2007, 374 – 376. [10] A. J. Gordon, R. A. Ford, The Chemists Companion: A Handbook of Practical Data, Techniques, and References, John Wiley & Sons, 1973. [11] M. Keshavarz-K, B. Knight, R. C. Haddon, F. Wudl, Tetrahedron 1996, 52, 5149 – 5159. [12] G. A. Wheaton, D. J. Burton, J. Fluorine Chem. 1977, 9, 25 – 44. [13] V. Rautenstrauch, H. J. Scholl, E. Vogel, Angew. Chem. 1968, 80, 278 – 279; Angew. Chem. Int. Ed. Engl. 1968, 7, 288 – 289. [14] E. Vogel, S. Korte, W. Grimme, H. Gunther, Angew. Chem. 1968, 80, 279 – 280; Angew. Chem. Int. Ed. Engl. 1968, 7, 289 – 290. [15] Y. Kabe, H. Ohgaki, T. Yamagaki, H. Nakanishi, W. Ando, J. Organomet. Chem. 2001, 636, 82 – 90. [16] A. M. Benito, A. D. Darwish, H. W. Kroto, M. F. Meidine, R. Taylor, D. R. M. Walton, Tetrahedron Lett. 1996, 37, 1085 – 1086. [17] A. B. Smith III, R. M. Strongin, L. Brard, G. T. Furst, W. J. Romanow, K. G. Owens, R. C. King, J. Am. Chem. Soc. 1993, 115, 5829 – 5830. [18] M. Tsuda, T. Ishida, T. Nogami, S. Kurono, M. Ohashi, Tetrahedron Lett. 1993, 34, 6911 – 6912. [19] Z. Yinghuai, J. Phys. Chem. Solids 2004, 65, 349 – 353. [20] A. F. Kiely, R. C. Haddon, M. S. Meier, J. P. Selegue, C. P. Brock, B. O. Patrick, G. Wang, Y. Chen, J. Am. Chem. Soc. 1999, 121, 7971 – 7972. [21] B. Li, C. Shu, X. Lu, L. Dunsch, Z. Chen, T. J. S. Dennis, Z. Shi, L. Jiang, T. Wang, W. Xu, C. Wang, Angew. Chem. 2010, 122, 974 – 978; Angew. Chem. Int. Ed. 2010, 49, 962 – 966. [22] a) V. P. Gubskaya, L. S. Berezhnaya, A. T. Gubaidullin, I. I. Faingold, R. A. Kotelnikova, N. P. Konovalova, V. I. Morozov, I. A. Litvinov, I. A. Nuretdinov, Org. Biomol. Chem. 2007, 5, 976 – 981; b) J. Osterodt, M. Nieger, F. Voegtle, J. Chem. Soc. Chem. Commun. 1994, 1607 – 1608. [23] a) C. B. Hbschle, S. Scheins, M. Weber, P. Luger, A. Wagner, T. Koritsnszky, S. I. Troyanov, O. V. Boltalina, I. V. Goldt, Chem. Eur. J. 2007, 13, 1910 – 1920; b) P. A. Troshin, R. N. Lyubovskaya, I. N.

Chem. Eur. J. 2013, 19, 17969 – 17979

[24]

[25]

[26] [27] [28] [29] [30]

[31] [32] [33] [34] [35]

[36] [37] [38] [39] [40]

Ioffe, N. B. Shustova, E. Kemnitz, S. I. Troyanov, Angew. Chem. 2005, 117, 238 – 241; Angew. Chem. Int. Ed., 2005, 44, 234 – 237. a) S. Stevenson, C. B. Rose, J. S. Maslenikova, J. R. Villarreal, M. A. Mackey, B. Q. Mercado, K. Chen, M. M. Olmstead, A. L. Balch, Inorg. Chem. 2012, 51, 13096 – 13102; b) M. Suzuki, Z. Slanina, N. Mizorogi, X. Lu, S. Nagase, M. M. Olmstead, A. L. Balch, T. Akasaka, J. Am. Chem. Soc. 2012, 134, 18772 – 18778. A. B. I. Smith, R. Strongin, L. Brard, G. Furst, W. Romanow, K. G. Owens, R. Goldschmidt, R. C. King, J. Am. Chem. Soc. 1995, 117, 5492 – 5502. S. I. Troyanov, Russ. J. Inorg. Chem. 2001, 46, 1612 – 1616. A. F. Kiely, M. S. Meier, B. O. Patrick, J. P. Selegue, C. P. Brock, Helv. Chim. Acta 2003, 86, 1140 – 1151. R. Borghi, L. Lunazzi, G. Placucci, P. J. Krusic, D. A. Dixon, N. Matsuzawa, M. Ata, J. Am. Chem. Soc. 1996, 118, 7608 – 7617. C. A. Reed, R. D. Bolskar, Chem. Rev. 2000, 100, 1075 – 1120. G. M. Sheldrick, SHELXS-97, Program for Solution of Crystal Structures from Diffraction Data, Universitt Gçttingen, Germany 1997. G. M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, Universitt Gçttingen, Germany 1997. S. Dmmling, E. Eichhorn, S. Schneider, B. Speiser, M. Wrde, Curr. Sep. 1996, 15, 53 – 56. D. R. Duling, J. Magnetic Res. B 1994, 104, 105 – 110. A. Granovsky, http://classic.chem.msu.su/gran/gamess/index.html. M. W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. J. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. Su, T. L. Windus, M. Dupuis, J. A. Montgomery, J. Comput. Chem. 1993, 14, 1347 – 1363. D. N. Laikov, Chem. Phys. Lett. 1997, 281, 151 – 156. J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77, 3865 – 3868. X.-B. Wang, H. K. Woo, X. Huang, M. M. Kappes, L. S. Wang, Phys. Rev. Lett. 2006, 96, 143002. F. L. Hirshfeld, Theor. Chim. Acta 1977, 44, 129 – 138. V. Sadovnichy, A. Tikhonravov, Vl. Voevodin, V. Opanasenko in Contemporary High Performance Computing: From Petascale toward Exascale (Ed.: J. S. Vetter), CRC Press, Boca Raton, USA, 2013, pp. 283 – 307. Received: July 26, 2013 Published online: November 18, 2013

 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

17979

[6,6]-Open and [6,6]-closed isomers of C70(CF2): synthesis, electrochemical and quantum chemical investigation.

Novel difluoromethylenated [70]fullerene derivatives, C70(CF2 )n (n=1-3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two ...
966KB Sizes 0 Downloads 0 Views