DOI: 10.1002/chem.201304731
Full Paper
& Photocatalysis
Visible-Light-Mediated Addition of a-Aminoalkyl Radicals to [60]Fullerene by Using Photoredox Catalysts Yoshihiro Miyake,*[a, b] Yuya Ashida,[a] Kazunari Nakajima,[a] and Yoshiaki Nishibayashi*[a]
Abstract: The functionalization of fullerene has been extensively studied and various fullerene derivatives have been synthesized. We have succeeded in the functionalization of [60]fullerene by using a-aminoalkyl radicals generated by
visible-light-mediated single-electron oxidation of a-silylamines as synthetic intermediates. In these reactions, the introduction of diarylamino groups, which are useful electron donors, has been easily achieved.
Introduction Fullerenes bearing functional groups have attracted considerable attention as structural and functional motifs for materials and biological sciences.[1] For the construction of skeletons with a fullerene moiety, a variety of methods for the functionalization of fullerenes have been developed.[1] Photoinduced reactions of [60]fullerene (C60) with tertiary amines have been studied by several groups.[2–6] In these reactions, electron transfer from amines to the photoexcited C60 triggers the formation of a-aminoalkyl radicals, and a sequential radical reaction[7, 8] leads to the corresponding C60 adducts.[2–6] Applicable substrates are quite limited to some trialkylamines and dialkylarylamines. To the best of our knowledge, there is no reported use of alkyldiarylamines for the photoreactions of C60. Recently, we reported a visible-light-mediated direct a-C H alkylation[9a] and the amination[9b] of amines, in which a-aminoalkyl radicals[10] mediated by photoredox catalysts[11] play a key role as reactive intermediates. We also found that photoredox catalysts are applicable for the generation of a-aminoalkyl radicals from a-silylamines and for the addition reaction to a,b-unsaturated carbonyl compounds.[9c, 12] These facts prompted us to investigate photoreactions of C60 with a-aminoalkyl radicals with photoredox catalysts. In fact, we developed the visiblelight-mediated addition of a-aminoalkyl radicals generated from a-silylamines to [60]fullerene, in which a variety of tertiary amines including alkyldiarylamines can be introduced into the [a] Dr. Y. Miyake, Y. Ashida, Dr. K. Nakajima, Prof. Dr. Y. Nishibayashi Institute of Engineering Innovation School of Engineering, The University of Tokyo Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan) Fax: (+ 81) 3-5841-1175 E-mail: [email protected] [email protected] [b] Dr. Y. Miyake Present address: Department of Applied Chemistry Graduate School of Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201304731. Chem. Eur. J. 2014, 20, 6120 – 6125
Scheme 1. Visible-light-mediated addition of a-aminoalkyl radicals to [60]fullerene with photoredox catalysts.
C60 moiety (Scheme 1). We believe that the method described herein provides a new efficient route for the synthesis of [60]fullerenes bearing an arylamino group as an electrondonating group, which are expected to be useful candidates for ambipolar charge-transporting materials[13] and donor–acceptor dyads.[14–16]
Results and Discussion First, we carried out the reaction of C60 with di(4-tert-butylphenyl)(trimethylsilylmethyl)amine (1 a; Table 1). When a solution of C60 and 1.5 equivalents of 1 a in the presence of 1 mol % of [3 a][ONf] (ONf: OSO2C4F9) in ortho-dichlorobenzene (ODCB) and H2O was irradiated by visible light at room temperature for 9 hours, 1-[N,N-di(4-tert-butylphenyl)aminomethyl]-1,9dihydro(C60-Ih)[5,6]fullerene (2 a) was obtained in 41 % yield (Table 1, entry 1). The formation of 2 a was confirmed by its 1H and 13C NMR spectra. The details of the molecular structure of 2 a were also determined by X-ray crystallographic studies. Reactions that used similar iridium complexes 3 b and 3 c and the [Ru(bpy)3]2 + complex (bpy = 2,2'-bipyridine) as catalysts also proceeded to give 2 a in moderate yields, but the selectivity of 2 a was lower (Table 1, entries 2, 3, and 5). In the use of the neutral iridium complex 4 and 9,10-dicyanoanthracene (DCA) as photoredox catalysts, no formation of 2 a was observed at all (Table 1, entries 4 and 6). When chlorobenzene and toluene were used as the solvents, moderate yields of 2 a were obtained (Table 1, entries 7 and 8). The addition of H2O was an important factor to promote this addition reaction. The yield of 2 a decreased without the addition of H2O (Table 1, entry 9).
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Full Paper Table 1. Photocatalytic reactions of C60 with 1 a.[a]
Table 2. Photocatalytic reactions of C60 with a-silylalkyldiarylamines 1 b–l.[a]
Entry
Photocatalyst
Solvent
Yield [%][b]
Selectivity [%][c]
Entry
a-silylamine (1)
Yield of 2 [%][b]
Selectivity [%][c]
1 2 3 4 5 6 7 8 9[e] 10[f] 11 12[g]
[3 a][ONf] [3 b][ONf] [3 c][ONf] 4 [Ru(bpy)3][ ONf]2 DCA [3 a][ONf] [3 a][ONf] [3 a][ONf] [3 a][ONf] none [3 a][ONf]
ODCB ODCB ODCB ODCB ODCB ODCB PhCl toluene ODCB ODCB ODCB ODCB
41 (32)[d] 23 28 0 20 0 20 21 27 0 0 0
87 72 74 – 56 – 69 55 61 – – –
1 2 3[d] 4 5[d] 6 7 8 9 10[d] 11[e]
R1 = R2 = Ph (1 b) R1 = R2 = 4-MeC6H4 (1 c) R1 = R2 = 4-nBuC6H4 (1 d) R1 = 4-tBuC6H4, R2 = Ph (1 e) R1 = 4-tBuC6H4, R2 = 4-PhC6H4 (1 f) R1 = 4-tBuC6H4, R2 = 4-ClC6H4 (1 g) R1 = 4-tBuC6H4, R2 = 4-MeOC6H4 (1 h) R1 = 4-tBuC6H4, R2 = 4-(pinB)C6H4 (1 i) R1 = Ph, R2 = 2-naphthyl (1 j) R1R2N = 3,6-tBu2-carbazolyl (1 k) R1R2N = phenothiazinyl (1 l)
2 b: 47 (38) 2 c: 38 (29) 2 d: 44 (38) 2 e: 42 (35) 2 f: 43 (39) 2 g: 39 (26) 2 h: 40 (32) 2 i: 46 (24) 2 j: 41 (38) 2 k: 43 (41) 2 l: 36 (27)
64 75 56 55 63 67 87 55 75 80 82
[a] All the reactions of C60 (0.14 mmol) with 1 (0.21 mmol) were carried out in the presence of [3 a][ONf] (0.0014 mmol) in ODCB (20 mL)/H2O (0.1 mL) with visible-light irradiation (l = 440 nm) at room temperature for 9 h. [b] Determined by 1H NMR spectroscopic analysis; yields of the isolated product 2 are given in the parentheses. [c] Determined by [yield of 2 determined by NMR]/[conversion of C60]. [d] For 22 h. [e] For 120 h.
[a] All the reactions of C60 (0.14 mmol) with 1 a (0.21 mmol) were carried out in the presence of a photocatalyst (0.0014 mmol) in solvent (20 mL; H2O = 0.1 mL) with visible-light irradiation (l = 440 nm) at room temperature for 9 h. [b] Determined by 1H NMR spectroscopic analysis. [c] Determined by [yield of 2 a]/[conversion of C60]. [d] Yield of the isolated product. [e] No addition of H2O. [f] Compound 5 was used in place of 1 a. [g] In the absence of light.
sponding C60 derivatives 2 k and 2 l in good yields (Table 2, entries 10 and 11). Previously, several groups have reported reactions of C60 with dialkylaryl- and trialkylamines under photoirradiation.[2–6] In fact, reactions with dialkyl- and trialkylamines 1 m and 1 n proceeded in the absence of a photocatalyst (Table 3, entries 2 When methyldi(4-tert-butylphenyl)amine (5) was used in place of 1 a, no reaction occurred at all (Table 1, entry 10). This result indicates that only the C Si bond in the amine can be activated selectively in the present reaction system.[9c, 12] Separately, we confirmed that no formation of 2 a was observed in the absence of a photocatalyst or visible light (Table 1, entries 11 and 12). Other reactions with a variety of a-silylalkyldiarylamines 1 were investigated with [3 a][ONf] as a photocatalyst (typical results are shown in Table 2). Reactions with a-silylamines 1 b– e proceeded smoothly to give the corresponding products in moderate yields (Table 2, entries 1–4). The introduction of a substituent, such as phenyl, chloro, or methoxy groups, at the para position in the one of the benzene ring of 1 a did not affect the yield of 2 much (Table 2, entries 5–7). When the reaction with the amine bearing a boronic acid ester 1 i was carried out, 2 i was obtained in 46 % yield (Table 2, entry 8). The reaction with naphthylamine (1 j) also took place smoothly to give 2 j in 41 % yield (Table 2, entry 9). Interestingly, the a-silylamines bearing a carbazolyl 1 k and phenothiazinyl moiety 1 l were applicable to this reaction system, thus giving the correChem. Eur. J. 2014, 20, 6120 – 6125
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Table 3. Photocatalytic reactions of C60 with a-silylamines 1 m and 1 n.[a]
Entry
a-silylamine (1)
Yield of 2 [%][b]
Selectivity [%][c]
1 2[d]
2 m: 36 (32) 2 m: 15 (13)
47 75
3 4[d]
2 n: 31 (27) 2 n: 15 (15)
94 88
[a] All the reactions of C60 (0.14 mmol) with 1 (0.21 mmol) were carried out in the presence of [3 a][ONf] (0.0014 mmol) in ODCB (20 mL)/H2O (0.1 mL) with visible-light irradiation (l = 440 nm) at room temperature for 9 h. [b] Determined by 1H NMR spectroscopic analysis; yields of the isolated product 2 are given in the parentheses. [c] Determined by [yield of 2 determined by NMR]/[conversion of C60]. [d] In the absence of [3 a][ONf].
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Full Paper and 4), but the presence of [3 a][ONf] in the reaction system increased the yields of 2 m and 2 n substantially (Table 3, entries 1 and 3). Photoredox catalysts such as 3 a also promoted the introduction of a variety of tertiary amines into C60 efficiently through photoinduced electron transfer (Table 3). The transformation of adduct 2 a was investigated as a synthetic application (Scheme 2). The hydrogen atom in hydrofullerenes is quite acidic,[17] and deprotonation with conventional bases has been known to occur readily.[18] The deprotonation of 2 a with KOtBu and the sequential treatment of methyl iodide afforded the corresponding 1,4-dialkylfullerene (6 a) in 49 % yield. The reaction with methyl 2-(bromomethy)acrylate also proceeded smoothly to give the 1,4-adduct 6 b in 84 % yield.
Scheme 2. Transformation of 2 a.
To obtain information on the reaction pathway, we investigated the reaction of C60 with 1 a in ODCB/D2O (Scheme 3 a). The exclusive formation of [D1]-2 a (> 99 % D-enriched at the hydrogen atom on the fullerenyl moiety) was confirmed, whereas no deuterium incorporation into 2 a was observed in the reaction of C60 with 1 a in [D4]ODCB/H2O. These results indi-
cate that the hydrogen atom on the fullerenyl moiety of 2 is derived from H2O and that the possibility of radical hydrogenatom abstraction from other species is excluded. Furthermore, when the reaction was carried out in a 1:1 mixture of H2O/D2O, the formation of 2 a was superior to that of [D1]-2 a (2 a/[D1]2 a = 71:29; Scheme 3 b). A similar kinetic isotope effect was previously observed in the protonation of C60· generated from a one-electron reduction of C60.[19, 20] In sharp contrast, when the fullerenyl anion A generated from the deprotonation of 2 a was quenched by a 1:1 mixture of H2O/D2O, the product distribution of 2 a and [D1]-2 a was almost equal (Scheme 3 c). These results suggest that the reaction of C60 with 1 in the presence of 3 a proceeds not via a fullerenyl anion A but via the radical anion, C60· . By considering the experimental results, a plausible reaction pathway is proposed in Scheme 4. The initial step is the formation of the radical anion, C60· , from a single-electron reduction of C60 by the excited photocatalyst (*cat) and subsequent protonation of C60· occurs to give B with the formation of the OH ion. The oxidation of a-silylamine 1 by the one-electron oxidized form of photocatalyst (cat + ) and sequential desilylation assisted by the OH ion occurs to give an a-aminoalkyl radical C with the formation of Me3SiOH.[12] In fact, we confirmed the formation of Me3SiOH by GC-MS analysis of the crude reaction mixture. Finally, the radical–radical coupling between B and C leads the corresponding product 2. The other reaction pathway might be assumed as follows: the direct addition of C to C60 and subsequent reduction occurs to give a fullerenyl anion, such as A, followed by the protonation of A to give 2.[9a, c] However, the results shown in Scheme 3 support that the reaction pathway through the protonation of C60· is predominant.[19, 20]
Scheme 4. Plausible pathway for the formation of 2.
Scheme 3. Deuterium isotope-labeling experiments. Chem. Eur. J. 2014, 20, 6120 – 6125
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The electronic absorption (Figure 1) and emission spectra (see Figures S1–S3 in the Supporting Information) of 2 a, 2 k, and 2 l in toluene were observed. The absorption features are similar to those of the previously reported a-aminoalkyl radical/C60 1,2-adducts (Figure 1).[2b, c, 6] The adducts, such as 2 a, 2 k, and 2 l, exhibited relatively weak and broad fluorescence, and the emission spectra have a mirror-image relationship with the absorption spectra at around 710 nm (see Figures S1– S3 in the Supporting Information).[21] The cyclic voltammetric analysis of 2 a, 2 k, and 2 l with phenyl C61 butyric acid methyl ester (PCBM) and C60 as references was also performed in ODCB with 0.1 m nBu4NBF4 as the 6122
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Full Paper Experimental Section General method 1
H NMR (270 MHz) and 13C NMR (67.8 MHz) spectra were recorded on a JEOL Excalibur 270 spectrometer in a suitable solvent. 19 F NMR (471 MHz) spectra were recorded on a JEOL JNM-ECP 500 spectrometer. Elemental analyses were performed at the Microanalytical Center at The University of Tokyo. Mass spectra were measured on a JEOL JMS-700 mass spectrometer. GC-MS analyses were carried out on a Shimadzu GC-MS QP-2010 spectrometer. Absorption and emission spectra were recorded on Shimadzu MultiSpec1500 and Shimadzu RF-5300PC spectrometers, respectively. All the reactions were carried out in a dry nitrogen atmosphere. Solvents were dried by using general methods and degassed before use. Photoirradiation was carried out with an Ushio high-pressure mercury lamp USH-250SC (250 W) with a band-pass filter of l = 440 nm (Kenko B-440 filter). Cyclic voltamograms were recorded on an ALS/Chi model 610C electrochemical analyzer with a platinum working electrode in 1,2-dichlorobenzene containing 0.1 m nBu4NBF4 as a supporting electrolyte. All the potentials were measured against an Ag/Ag + reference electrode and converted versus the ferrocene/ferrocenium + couple.
Figure 1. Electronic absorption spectra of 2 a, 2 k, and 2 l.
Table 4. Redox potentials of 2 a, 2 k, and 2 l.[a] Compound
E ox 1=2 [V]
2a 2k 2l PCBM C60
+ 0.53 + 0.76 + 0.41 – –
E red1 1=2 [V] 1.21 1.18 1.20 1.17 1.08
E red2 1=2 [V] 1.59 1.56 1.59 1.56 1.48
E red3 1=2 [V] 2.12 – – 2.07 1.94
HOMO–LUMO gap [eV] 1.74 1.94 1.61 – –
General procedure for photocatalytic reactions of fullerene with a-silylamines 1
[a] Potential in volts versus the ferrocene/ferrocenium + couple by means of cyclic voltammetry in ODCB containing nBu4NBF4 (0.1 m) as a supporting electrolyte; stick Pt, Pt wire, and Ag/Ag + were used as the working-, counter-, and reference electrodes, respectively.
electrolyte (Table 4). Compound 2 a has three reversible reduction potentials assigned to the formation of the anion, dianion, and trianion of the C60 moiety, whereas compounds 2 k and 2 l have two reversible reduction potentials. All the compounds show the first reduction waves at approximately 1.2 V, which are more negative than those of PCBM and C60. Furthermore, 2 a, 2 k, and 2 l also have one reversible oxidation wave assigned to the oxidation of the amino groups, with a very narrow HOMO–LUMO gap for all the compounds. These results demonstrate the significant potential of these adducts 2 for ambipolar charge-transporting materials.[13b]
Conclusion We have developed the efficient functionalization of [60]fullerene, in which the visible-light-mediated generation of a-aminoalkyl radicals is the key step. Our reaction system is applicable to the addition of a wide range of tertiary amines to C60.[22] We believe that the results described herein provide an efficient methodology for the introduction of the arylamino group as an electron-donating moiety into C60. Further work is currently in progress to research the electronic properties of adduct 2 and to synthesize novel materials by using this methodology. Chem. Eur. J. 2014, 20, 6120 – 6125
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A typical experimental procedure for the reaction of [60]fullerene (C60) with di(4-tert-butylphenyl)(trimethylsilylmethyl)amine (1 a) is described. Water (100 mL) and 1 a (77.3 mg, 0.210 mmol) were added to C60 (101 mg, 0.140 mmol), [3 a][ONf] (1.5 mg, 0.0014 mmol), and 1,2-dichlorobenzene (20 mL) in a Schlenk flask (50 mL, diameter = 4.0 cm) under N2. The reaction flask was placed in a water bath and illuminated with an Ushio high-pressure mercury lamp USH-250SC (250 W) with a band-pass filter of l = 440 nm at room temperature for 9 h. The solution was concentrated in vacuo. The residue was purified by column chromatography (SiO2) with cyclohexane as the eluent to give 1-[N,N-di(4-tert-butylphenyl)aminomethyl]-1,9-dihydro(C60-Ih)[5,6]fullerene (2 a) as a brown solid (46.0 mg, 0.0453 mmol, 32 %). Crystals suitable for elemental analysis and X-ray analysis were obtained by slow evaporation from toluene. 2 a: 1H NMR (C6D6/CS2): d = 7.34–7.24 (m, 8 H), 6.53 (s, 1 H), 5.59 (s, 2 H), 1.28 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 154.8, 154.0, 147.6, 147.5, 147.4, 146.9, 146.7, 146.6, 146.5, 146.41, 146.36, 146.0, 145.71, 145.67, 145.6, 144.9, 144.8, 143.6, 142.91, 142.89, 142.4, 142.3, 142.01, 141.99, 141.96, 140.6, 140.3, 136.8, 135.9, 126.7, 122.3, 68.0, 66.1, 58.0, 34.2, 31.7 ppm; HRMS (FAB, ortho-nitrophenyl octyl ether (NPOE) and meta-nitrobenzyl alcohol (NBA)) m/z calcd for C81H30N [M + H]: 1016.2378; found: 1016.2365; elemental analysis calcd (%) for C88H37N (2 a·C6H5CH3): C 95.37, H 3.37, N 1.26; found: C 95.27, H 3.51, N 1.05. 2 b: A brown solid (38 %). 1H NMR (C6D6/CS2): d = 7.34–7.30 (m, 4 H), 7.23–7.19 (m, 4 H), 6.94–6.88 (m, 2 H), 6.40 (s, 1 H), 5.55 ppm (s, 2 H); 13 C NMR (C6D6/CS2): d = 154.4, 153.7, 148.6, 147.6, 147.5, 147.3, 146.9, 146.63, 146.58, 146.45, 146.39, 146.0, 145.69, 145.67, 145.63, 145.60, 144.9, 144.8, 143.5, 143.3, 142.9, 142.4, 142.3, 142.0, 141.9, 140.6, 140.3, 136.6, 135.9, 129.9, 123.3, 122.6, 67.9, 66.2, 58.2 ppm; HRMS (FAB, NPOE) calcd for C73H13N [M]: 903.1048; found: 903.1066.
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Full Paper 2 c: A brown solid (29 %). 1H NMR (C6D6/CS2): d = 7.24 (d, 4 H, J = 8.1 Hz), 7.02 (d, 4 H, J = 8.1 Hz), 6.45 (s, 1 H), 5.54 (s, 2 H), 2.21 ppm (s, 6 H); 13C NMR (C6D6/CS2): d = 154.8, 154.0, 147.6, 147.5, 147.4, 147.1, 146.8, 146.7, 146.6, 146.5, 146.4, 146.1, 145.73, 145.71, 145.68, 145.6, 144.9, 144.8, 143.5, 143.3, 142.9, 142.44, 142.37, 142.35, 142.03, 142.01, 142.00, 140.6, 140.3, 136.7, 136.0, 132.2, 130.5, 122.6, 68.1, 66.6, 58.3, 21.0 ppm; HRMS (FAB, NPOE) calcd for C75H17N [M]: 931.1361; found: 931.1357. 2 d: A brown solid (38 %). 1H NMR (C6D6/CS2): d = 7.31–7.26 (m, 4 H), 7.07–7.02 (m, 4 H), 6.51 (s, 1 H), 5.58 (s, 2 H), 2.52 (t, 4 H, J = 7.6 Hz), 1.60–1.49 (m, 4 H), 1.37–1.24 (m, 4 H), 0.89 ppm (t, 6 H, J = 7.2 Hz); 13 C NMR (C6D6/CS2): d = 154.8, 154.0, 147.6, 147.5, 147.4, 147.0, 146.8, 146.7, 146.6, 146.5, 146.4, 146.1, 145.71, 145.68, 145.6, 144.9, 144.8, 143.5, 143.3, 142.92, 142.90, 142.41, 142.35, 142.02, 142.00, 141.98, 140.6, 140.3, 137.4, 136.7, 135.9, 129.8, 122.6, 68.0, 66.4, 58.2, 35.5, 34.3, 23.0, 14.5 ppm; HRMS (FAB, NPOE) calcd for C81H29N [M]: 1015.2300; found: 1015.2272. 2 e: A brown solid (35 %). 1H NMR (C6D6/CS2): d = 7.36–7.19 (m, 8 H), 6.91–6.85 (m, 1 H), 6.47 (s, 1 H), 5.56 (s, 2 H), 1.27 ppm (s, 9 H); 13 C NMR (C6D6/CS2): d = 154.6, 153.9, 149.0, 147.55, 147.47, 147.3, 146.9, 146.63, 146.58, 146.5, 146.44, 146.38, 146.0, 145.8, 145.67, 145.66, 145.62, 145.58, 144.9, 144.8, 143.5, 143.3, 142.87, 142.85, 142.34, 142.30, 142.0, 141.9, 140.6, 140.3, 136.7, 135.9, 129.8, 126.8, 123.7, 122.4, 121.1, 67.9, 66.1, 58.1, 34.3, 31.7 ppm; HRMS (FAB, NPOE and NBA) calcd for C77H22N [M + H]: 960.1752; found: 960.1754. 2 f: A brown solid (39 %). 1H NMR (C6D6/CS2): d = 7.47–7.41 (m, 5 H), 7.39–7.36 (m, 3 H), 7.35–7.32 (m, 2 H), 7.30–7.27 (m, 1 H), 7.26–7.21 (m, 2 H), 6.49 (s, 1 H), 5.62 (s, 2 H), 1.28 ppm (s, 9 H); 13C NMR (C6D6/ CS2): d = 154.6, 153.9, 148.6, 147.6, 147.5, 147.4, 147.2, 147.0, 146.7, 146.6, 146.5, 146.4, 146.1, 145.73, 145.68, 145.65, 145.56, 144.9, 144.8, 143.6, 142.94, 142.92, 142.38, 142.35, 142.04, 141.99, 140.8, 140.6, 140.3, 136.7, 136.0, 134.7, 129.1, 127.1, 126.91, 126.89, 124.5, 120.7, 67.9, 66.1, 58.2, 34.4, 31.7 ppm; HRMS (FAB, NPOE) calcd for C83H26N [M + H]: 1036.2065; found: 1036.2101. 2 g: A brown solid (26 %). 1H NMR (C6D6/CS2): d = 7.30 (br, 4 H), 7.13 (br, 4 H), 6.40 (s, 1 H), 5.51 (s, 2 H), 1.27 ppm (s, 9 H); 13C NMR (C6D6/ CS2): d = 154.3, 153.7, 147.9, 147.6, 147.5, 147.3, 146.8, 146.7, 146.6, 146.5, 146.4, 146.0, 145.73, 145.68, 145.6, 145.3, 144.9, 144.8, 143.6, 142.94, 142.92, 142.34, 142.33, 142.03, 141.97, 141.9, 140.6, 140.3, 136.6, 135.9, 129.7, 127.0, 126.9, 124.7, 121.2, 67.7, 66.2, 58.2, 34.4, 31.6 ppm; HRMS (FAB, NPOE) calcd for C77H20NCl [M]: 993.1284; found: 993.1249. 2 h: A brown solid (32 %). 1H NMR (C6D6/CS2): d = 7.41–7.35 (m, 2 H), 7.20–7.16 (m, 2 H), 7.10–7.04 (m, 2 H), 6.88–6.82 (m, 2 H), 6.63 (s, 1 H), 5.66 (s, 2 H), 3.73 (s, 3 H), 1.28 ppm (s, 9 H); 13C NMR (C6D6/CS2): d = 157.0, 154.6, 153.9, 147.7, 147.5, 147.4, 147.3, 146.8, 146.6, 146.5, 146.4, 146.3, 146.0, 145.62, 145.57, 145.5, 144.8, 144.7, 143.4, 143.1, 142.8, 142.3, 142.2, 141.92, 141.89, 140.8, 140.5, 140.3, 136.7, 135.9, 127.6, 126.4, 118.2, 115.3, 68.0, 66.9, 58.2, 55.3, 33.9, 31.8 ppm; HRMS (FAB, NPOE) calcd for C78H23ON [M]: 989.1780; found: 989.1760. 2 i: A brown solid (24 %). 1H NMR (C6D6/CS2): d = 7.75–7.70 (m, 2 H), 7.41–7.30 (m, 4 H), 7.23–7.19 (m, 2 H), 6.49 (s, 1 H), 5.63 (s, 2 H), 1.29 (s, 9 H), 1.21 ppm (s, 12 H); 13C NMR ([D4]ODCB): d = 154.0, 153.3, 152.0, 148.5, 147.0, 146.9, 146.7, 146.4, 146.0, 145.9, 145.8, 145.7, Chem. Eur. J. 2014, 20, 6120 – 6125
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145.4, 145.03, 144.99, 144.97, 144.4, 144.2, 142.17, 141.75, 141.68, 141.6, 141.4, 141.33, 136.5, 136.1, 135.5, 130.1, 126.5, 116.7, 83.2, 31.2, 24.7 ppm; HRMS (FAB, NPOE) calcd 1085.2526; found: 1085.2512.
144.1, 142.8, 142.18, 141.29, 139.8, 139.6, 67.4, 65.6, 57.8, 34.2, for C83H32O2NB [M]:
2 j: A brown solid (38 %). 1H NMR (C6D6/CS2): d = 7.77 (d, 1 H, J = 2.2 Hz), 7.61–7.57 (m, 3 H), 7.44 (dd, 1 H, J = 8.9 Hz and 2.4 Hz), 7.40–7.35 (m, 2 H), 7.30–7.18 (m, 4 H), 6.97–6.91 (m, 1 H), 6.41 (s, 1 H), 5.64 ppm (s, 2 H); 13C NMR (C6D6/CS2): d = 154.5, 153.8, 148.8, 147.6, 147.5, 147.3, 147.0, 146.7, 146.6, 146.5, 146.4, 146.0, 145.73, 145.71, 145.67, 145.6, 144.9, 144.8, 143.5, 142.93, 142.91, 142.4, 142.3, 142.03, 141.97, 141.96, 140.6, 140.3, 136.7, 135.8, 134.8, 130.3, 130.0, 129.7, 127.4, 127.0, 125.1, 123.5, 123.3, 122.8, 118.8, 67.9, 66.4, 58.4 ppm; HRMS (FAB, NPOE) calcd for C77H16N [M + H]: 954.1283; found: 954.1277. 2 k: A brown solid (41 %). 1H NMR (C6D6/CS2): d = 8.17 (d, 2 H, J = 1.8 Hz), 7.68 (d, 2 H, J = 8.6 Hz), 7.52 (dd, 2 H, J = 8.6 Hz and 1.8 Hz), 6.26 (s, 1 H), 5.74 (s, 2 H), 1.42 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 153.8, 153.4, 147.62, 147.60, 147.2, 146.8, 146.7, 146.6, 146.5, 146.4, 146.0, 145.9, 145.8, 145.7, 145.6, 144.9, 144.7, 143.5, 143.0, 142.9, 142.8, 142.5, 142.3, 142.2, 142.1, 141.9, 141.8, 140.6, 140.5, 140.4, 136.5, 135.8, 124.2, 124.1, 117.2, 109.9, 67.9, 58.5, 57.3, 34.8, 32.2 ppm; HRMS (FAB, NPOE) calcd for C81H27N [M]: 1013.2144; found: 1013.2164. 2 l: A brown solid (27 %). 1H NMR (C6D6/CS2): d = 7.27–7.23 (m, 2 H), 7.13–7.05 (m, 4 H), 6.88–6.82 (m, 2 H), 6.63 (s, 1 H), 5.77 ppm (s, 2 H); 13 C NMR (C6D6/CS2): d = 154.0, 153.7, 147.6, 147.3, 146.61, 146.58, 146.5, 146.41, 146.37, 146.0, 145.74, 145.71, 145.62, 145.60, 144.9, 144.7, 143.5, 142.8, 142.4, 142.31, 142.25, 141.9, 141.7, 140.4, 140.2, 136.4, 136.2, 135.6, 129.0, 128.5, 124.3, 67.9, 60.9, 58.0 ppm; HRMS (FAB, NPOE) calcd for C73H11NS [M]: 933.0612; found: 933.0648.
Reaction of 2 a with methyl iodide A solution of KOtBu (30 mL, 1.0 m, 0.030 mmol) in THF was added to 2 a (24.8 mg, 0.0244 mmol) and benzonitrile (7 mL) in a Schlenk flask (50 mL) under N2 at room temperature. After stirring for 10 min, MeI (30 mL, 0.5 mmol) was added to the reaction mixture, which was stirred for 12 h at room temperature. After the solution was concentrated in vacuo, the residue was purified by column chromatography (SiO2) with cyclohexane as the eluent to give 6 a as a brown solid (12.4 mg, 0.0120 mmol, 49 %). 1H NMR (C6D6/CS2): d = 7.31–7.20 (m, 8 H), 5.34 (d, 1 H, J = 14.9 Hz), 5.25 (d, 1 H, J = 14.9 Hz), 2.63 (s, 3 H), 1.25 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 159.0, 156.7, 153.0, 150.4, 149.3, 148.94, 148.91, 148.4, 148.1, 147.52, 147.48, 147.4, 147.30, 147.25, 147.19, 147.17, 146.6, 145.82, 145.79, 145.5, 145.4, 145.3, 145.2, 145.09, 145.07, 145.0, 144.74, 144.71, 144.67, 144.6, 144.54, 144.47, 144.46, 144.3, 144.2, 144.1, 144.0, 143.53, 143.49, 143.3, 143.04, 142.99, 142.98, 142.8, 142.7, 142.6, 142.4, 142.3, 141.2, 139.3, 139.0, 138.9, 138.0, 126.5, 122.2, 63.7, 62.2, 54.8, 34.2, 31.6, 29.1 ppm; HRMS (FAB, NPOE) calcd for C82H31N [M]: 1029.2457; found: 1029.2473.
Reaction of 2 a with methyl 2-(bromomethyl)acrylate A solution of KOtBu (30 mL, 1.0 m, 0.030 mmol) in THF was added to 2 a (25.0 mg, 0.0246 mmol) and benzonitrile (7 mL) in a Schlenk flask (50 mL) under N2 at room temperature. After stirring for 10 min, methyl 2-(bromomethyl)acrylate (60 mL, 0.5 mmol) was added to the reaction mixture, which was stirred for 1 h at room
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Full Paper temperature. After the solution was concentrated in vacuo, the residue was purified by column chromatography (SiO2) with cyclohexane/toluene (2:1) as the eluent to give 6 b as a brown solid (23.0 mg, 0.0206 mmol, 84 % ). 1H NMR (C6D6/CS2): d = 7.30–7.20 (m, 8 H), 6.44 (d, 1 H, J = 1.1 Hz), 5.51 (br, 1 H), 5.41 (d, 1 H, J = 14.9 Hz), 5.34 (d, 1 H, J = 14.9 Hz), 4.10 (d, 1 H, J = 13.0 Hz), 4.00 (d, 1 H, J = 13.0 Hz), 3.53 (s, 3 H), 1.25 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 166.9, 156.8, 156.7, 151.4, 150.7, 149.1, 148.9, 148.8, 148.0, 147.50, 147.47, 147.3, 147.24, 147.16, 147.1, 146.7, 145.81, 145.78, 145.6, 145.43, 145.37, 145.23, 145.16, 145.14, 145.06, 144.99, 144.96, 144.74, 144.71, 144.63, 144.60, 144.56, 144.5, 144.4, 144.3, 144.1, 144.0, 143.9, 143.51, 143.49, 143.4, 143.3, 143.2, 143.01, 142.97, 142.9, 142.70, 142.66, 142.4, 142.31, 142.25, 141.1, 139.3, 139.2, 138.9, 138.5, 135.6, 130.2, 126.5, 122.3, 63.7, 62.3, 59.1, 51.8, 44.2, 34.2, 31.7 ppm; HRMS (FAB, NPOE) calcd for C86H36O2N [M + H]: 1114.2746; found: 1114.2764.
Acknowledgements This work was supported by the Funding Program for Next Generation World-Leading Researchers (GR025) and a Grant-inAid for Scientific Research on Innovative Areas “Advanced Molecular Transformations by Organocatalyst” from MEXT, Japan. We also thank the Research Hub for Advanced Nano Characterization at The University of Tokyo for X-ray analysis. Keywords: aminoalkylation · fullerenes · photooxidation · radicals · redox chemistry [1] For reviews, see: a) A. Hirsch, M. Brettreich, Fullerenes: Chemistry and Reactions, Wiley-VCH, Weinheim, 2005; b) Fullerenes: Chemistry, Physics, and Technology (Eds.: K. M. Kadish, R. S. Ruoff), Wiley, New York, 2000; c) Fullerenes: Principles and Applications (Eds.: F. Langa, J.-F. Nierengarten), RSC Cambridge, 2007; d) N. Martn, Chem. Commun. 2006, 2093; e) C. Thilgen, F. Diederich, Chem. Rev. 2006, 106, 5049; f) N. Martn, M. Altable, S. Filippone, A. Martn-Domenech, Synlett 2007, 3077; g) Y. Matsuo, E. Nakamura, Chem. Rev. 2008, 108, 3016; h) M. Murata, Y. Murata, K. Komatsu, Chem. Commun. 2008, 6083; i) F. Giacalone, N. Martn, Adv. Mater. 2010, 22, 4220; j) K. Itami, Chem. Rec. 2011, 11, 226; k) Y. Matsuo, Chem. Lett. 2012, 41, 754. [2] a) B. Ma, G. E. Lawson, C. E. Bunker, A. Kitaygorodskiy, Y.-P. Sun, Chem. Phys. Lett. 1995, 247, 51; b) G. E. Lawson, A. Kitaygorodskiy, B. Ma, C. E. Bunker, Y.-P. Sun, J. Chem. Soc. Chem. Commun. 1995, 2225; c) G. E. Lawson, A. Kitaygorodskiy, Y.-P. Sun, J. Org. Chem. 1999, 64, 5913. [3] K.-F. Liou, C.-H. Cheng, Chem. Commun. 1996, 1423. [4] a) S.-H. Wu, D.-W. Zhang, G.-W. Wang, L.-H. Shu, H.-M. Wu, J.-F. Xu, X.-F. Lao, Synth. Commun. 1997, 27, 2289; b) L.-W. Guo, X. Gao, D.-W. Zhang, S.-H. Wu, H.-M. Wu, Y.-J. Li, S. R. Wilson, C. F. Richardson, D. I. Schuster, J. Org. Chem. 2000, 65, 3804. [5] L. Gan, J. Jiang, W. Zhang, Y. Su, Y. Shi, C. Huang, J. Pan, M. L, Y. Wu, J. Org. Chem. 1998, 63, 4240. [6] Y. Nakamura, M. Suzuki, K. O-kawa, T. Konno, J. Nishimura, J. Org. Chem. 2005, 70, 8472. [7] For reviews on radical reactions of C60, see: a) M. D. Tzirakis, M. Orfanopoulos in Encyclopedia of Radicals in Chemistry, Biology and Materials (Eds.: C. Chatgilialoglu, A. Studer), Wiley, Chichester, UK, 2012; b) M. D. Tzirakis, M. Orfanopoulos, Chem. Rev. 2013, 113, 5262. [8] For selected examples of transition-metal-mediated radical reactions of C60, see: a) Y. Matsuo, Y. Zhang, E. Nakamura, Org. Lett. 2008, 10, 1251; b) G.-W. Wang, C.-Z. Wang, S.-E. Zhu, Y. Murata, Chem. Commun. 2011, 47, 6111; c) S. Lu, T. Jin, M. Bao, Y. Yamamoto, J. Am. Chem. Soc. 2011, 133, 12842; and references therein.
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Received: December 3, 2013 Published online on April 2, 2014
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Full Paper
& Photocatalysis
Visible-Light-Mediated Addition of a-Aminoalkyl Radicals to [60]Fullerene by Using Photoredox Catalysts Yoshihiro Miyake,*[a, b] Yuya Ashida,[a] Kazunari Nakajima,[a] and Yoshiaki Nishibayashi*[a]
Abstract: The functionalization of fullerene has been extensively studied and various fullerene derivatives have been synthesized. We have succeeded in the functionalization of [60]fullerene by using a-aminoalkyl radicals generated by
visible-light-mediated single-electron oxidation of a-silylamines as synthetic intermediates. In these reactions, the introduction of diarylamino groups, which are useful electron donors, has been easily achieved.
Introduction Fullerenes bearing functional groups have attracted considerable attention as structural and functional motifs for materials and biological sciences.[1] For the construction of skeletons with a fullerene moiety, a variety of methods for the functionalization of fullerenes have been developed.[1] Photoinduced reactions of [60]fullerene (C60) with tertiary amines have been studied by several groups.[2–6] In these reactions, electron transfer from amines to the photoexcited C60 triggers the formation of a-aminoalkyl radicals, and a sequential radical reaction[7, 8] leads to the corresponding C60 adducts.[2–6] Applicable substrates are quite limited to some trialkylamines and dialkylarylamines. To the best of our knowledge, there is no reported use of alkyldiarylamines for the photoreactions of C60. Recently, we reported a visible-light-mediated direct a-C H alkylation[9a] and the amination[9b] of amines, in which a-aminoalkyl radicals[10] mediated by photoredox catalysts[11] play a key role as reactive intermediates. We also found that photoredox catalysts are applicable for the generation of a-aminoalkyl radicals from a-silylamines and for the addition reaction to a,b-unsaturated carbonyl compounds.[9c, 12] These facts prompted us to investigate photoreactions of C60 with a-aminoalkyl radicals with photoredox catalysts. In fact, we developed the visiblelight-mediated addition of a-aminoalkyl radicals generated from a-silylamines to [60]fullerene, in which a variety of tertiary amines including alkyldiarylamines can be introduced into the [a] Dr. Y. Miyake, Y. Ashida, Dr. K. Nakajima, Prof. Dr. Y. Nishibayashi Institute of Engineering Innovation School of Engineering, The University of Tokyo Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan) Fax: (+ 81) 3-5841-1175 E-mail: [email protected] [email protected] [b] Dr. Y. Miyake Present address: Department of Applied Chemistry Graduate School of Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201304731. Chem. Eur. J. 2014, 20, 6120 – 6125
Scheme 1. Visible-light-mediated addition of a-aminoalkyl radicals to [60]fullerene with photoredox catalysts.
C60 moiety (Scheme 1). We believe that the method described herein provides a new efficient route for the synthesis of [60]fullerenes bearing an arylamino group as an electrondonating group, which are expected to be useful candidates for ambipolar charge-transporting materials[13] and donor–acceptor dyads.[14–16]
Results and Discussion First, we carried out the reaction of C60 with di(4-tert-butylphenyl)(trimethylsilylmethyl)amine (1 a; Table 1). When a solution of C60 and 1.5 equivalents of 1 a in the presence of 1 mol % of [3 a][ONf] (ONf: OSO2C4F9) in ortho-dichlorobenzene (ODCB) and H2O was irradiated by visible light at room temperature for 9 hours, 1-[N,N-di(4-tert-butylphenyl)aminomethyl]-1,9dihydro(C60-Ih)[5,6]fullerene (2 a) was obtained in 41 % yield (Table 1, entry 1). The formation of 2 a was confirmed by its 1H and 13C NMR spectra. The details of the molecular structure of 2 a were also determined by X-ray crystallographic studies. Reactions that used similar iridium complexes 3 b and 3 c and the [Ru(bpy)3]2 + complex (bpy = 2,2'-bipyridine) as catalysts also proceeded to give 2 a in moderate yields, but the selectivity of 2 a was lower (Table 1, entries 2, 3, and 5). In the use of the neutral iridium complex 4 and 9,10-dicyanoanthracene (DCA) as photoredox catalysts, no formation of 2 a was observed at all (Table 1, entries 4 and 6). When chlorobenzene and toluene were used as the solvents, moderate yields of 2 a were obtained (Table 1, entries 7 and 8). The addition of H2O was an important factor to promote this addition reaction. The yield of 2 a decreased without the addition of H2O (Table 1, entry 9).
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Full Paper Table 1. Photocatalytic reactions of C60 with 1 a.[a]
Table 2. Photocatalytic reactions of C60 with a-silylalkyldiarylamines 1 b–l.[a]
Entry
Photocatalyst
Solvent
Yield [%][b]
Selectivity [%][c]
Entry
a-silylamine (1)
Yield of 2 [%][b]
Selectivity [%][c]
1 2 3 4 5 6 7 8 9[e] 10[f] 11 12[g]
[3 a][ONf] [3 b][ONf] [3 c][ONf] 4 [Ru(bpy)3][ ONf]2 DCA [3 a][ONf] [3 a][ONf] [3 a][ONf] [3 a][ONf] none [3 a][ONf]
ODCB ODCB ODCB ODCB ODCB ODCB PhCl toluene ODCB ODCB ODCB ODCB
41 (32)[d] 23 28 0 20 0 20 21 27 0 0 0
87 72 74 – 56 – 69 55 61 – – –
1 2 3[d] 4 5[d] 6 7 8 9 10[d] 11[e]
R1 = R2 = Ph (1 b) R1 = R2 = 4-MeC6H4 (1 c) R1 = R2 = 4-nBuC6H4 (1 d) R1 = 4-tBuC6H4, R2 = Ph (1 e) R1 = 4-tBuC6H4, R2 = 4-PhC6H4 (1 f) R1 = 4-tBuC6H4, R2 = 4-ClC6H4 (1 g) R1 = 4-tBuC6H4, R2 = 4-MeOC6H4 (1 h) R1 = 4-tBuC6H4, R2 = 4-(pinB)C6H4 (1 i) R1 = Ph, R2 = 2-naphthyl (1 j) R1R2N = 3,6-tBu2-carbazolyl (1 k) R1R2N = phenothiazinyl (1 l)
2 b: 47 (38) 2 c: 38 (29) 2 d: 44 (38) 2 e: 42 (35) 2 f: 43 (39) 2 g: 39 (26) 2 h: 40 (32) 2 i: 46 (24) 2 j: 41 (38) 2 k: 43 (41) 2 l: 36 (27)
64 75 56 55 63 67 87 55 75 80 82
[a] All the reactions of C60 (0.14 mmol) with 1 (0.21 mmol) were carried out in the presence of [3 a][ONf] (0.0014 mmol) in ODCB (20 mL)/H2O (0.1 mL) with visible-light irradiation (l = 440 nm) at room temperature for 9 h. [b] Determined by 1H NMR spectroscopic analysis; yields of the isolated product 2 are given in the parentheses. [c] Determined by [yield of 2 determined by NMR]/[conversion of C60]. [d] For 22 h. [e] For 120 h.
[a] All the reactions of C60 (0.14 mmol) with 1 a (0.21 mmol) were carried out in the presence of a photocatalyst (0.0014 mmol) in solvent (20 mL; H2O = 0.1 mL) with visible-light irradiation (l = 440 nm) at room temperature for 9 h. [b] Determined by 1H NMR spectroscopic analysis. [c] Determined by [yield of 2 a]/[conversion of C60]. [d] Yield of the isolated product. [e] No addition of H2O. [f] Compound 5 was used in place of 1 a. [g] In the absence of light.
sponding C60 derivatives 2 k and 2 l in good yields (Table 2, entries 10 and 11). Previously, several groups have reported reactions of C60 with dialkylaryl- and trialkylamines under photoirradiation.[2–6] In fact, reactions with dialkyl- and trialkylamines 1 m and 1 n proceeded in the absence of a photocatalyst (Table 3, entries 2 When methyldi(4-tert-butylphenyl)amine (5) was used in place of 1 a, no reaction occurred at all (Table 1, entry 10). This result indicates that only the C Si bond in the amine can be activated selectively in the present reaction system.[9c, 12] Separately, we confirmed that no formation of 2 a was observed in the absence of a photocatalyst or visible light (Table 1, entries 11 and 12). Other reactions with a variety of a-silylalkyldiarylamines 1 were investigated with [3 a][ONf] as a photocatalyst (typical results are shown in Table 2). Reactions with a-silylamines 1 b– e proceeded smoothly to give the corresponding products in moderate yields (Table 2, entries 1–4). The introduction of a substituent, such as phenyl, chloro, or methoxy groups, at the para position in the one of the benzene ring of 1 a did not affect the yield of 2 much (Table 2, entries 5–7). When the reaction with the amine bearing a boronic acid ester 1 i was carried out, 2 i was obtained in 46 % yield (Table 2, entry 8). The reaction with naphthylamine (1 j) also took place smoothly to give 2 j in 41 % yield (Table 2, entry 9). Interestingly, the a-silylamines bearing a carbazolyl 1 k and phenothiazinyl moiety 1 l were applicable to this reaction system, thus giving the correChem. Eur. J. 2014, 20, 6120 – 6125
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Table 3. Photocatalytic reactions of C60 with a-silylamines 1 m and 1 n.[a]
Entry
a-silylamine (1)
Yield of 2 [%][b]
Selectivity [%][c]
1 2[d]
2 m: 36 (32) 2 m: 15 (13)
47 75
3 4[d]
2 n: 31 (27) 2 n: 15 (15)
94 88
[a] All the reactions of C60 (0.14 mmol) with 1 (0.21 mmol) were carried out in the presence of [3 a][ONf] (0.0014 mmol) in ODCB (20 mL)/H2O (0.1 mL) with visible-light irradiation (l = 440 nm) at room temperature for 9 h. [b] Determined by 1H NMR spectroscopic analysis; yields of the isolated product 2 are given in the parentheses. [c] Determined by [yield of 2 determined by NMR]/[conversion of C60]. [d] In the absence of [3 a][ONf].
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Full Paper and 4), but the presence of [3 a][ONf] in the reaction system increased the yields of 2 m and 2 n substantially (Table 3, entries 1 and 3). Photoredox catalysts such as 3 a also promoted the introduction of a variety of tertiary amines into C60 efficiently through photoinduced electron transfer (Table 3). The transformation of adduct 2 a was investigated as a synthetic application (Scheme 2). The hydrogen atom in hydrofullerenes is quite acidic,[17] and deprotonation with conventional bases has been known to occur readily.[18] The deprotonation of 2 a with KOtBu and the sequential treatment of methyl iodide afforded the corresponding 1,4-dialkylfullerene (6 a) in 49 % yield. The reaction with methyl 2-(bromomethy)acrylate also proceeded smoothly to give the 1,4-adduct 6 b in 84 % yield.
Scheme 2. Transformation of 2 a.
To obtain information on the reaction pathway, we investigated the reaction of C60 with 1 a in ODCB/D2O (Scheme 3 a). The exclusive formation of [D1]-2 a (> 99 % D-enriched at the hydrogen atom on the fullerenyl moiety) was confirmed, whereas no deuterium incorporation into 2 a was observed in the reaction of C60 with 1 a in [D4]ODCB/H2O. These results indi-
cate that the hydrogen atom on the fullerenyl moiety of 2 is derived from H2O and that the possibility of radical hydrogenatom abstraction from other species is excluded. Furthermore, when the reaction was carried out in a 1:1 mixture of H2O/D2O, the formation of 2 a was superior to that of [D1]-2 a (2 a/[D1]2 a = 71:29; Scheme 3 b). A similar kinetic isotope effect was previously observed in the protonation of C60· generated from a one-electron reduction of C60.[19, 20] In sharp contrast, when the fullerenyl anion A generated from the deprotonation of 2 a was quenched by a 1:1 mixture of H2O/D2O, the product distribution of 2 a and [D1]-2 a was almost equal (Scheme 3 c). These results suggest that the reaction of C60 with 1 in the presence of 3 a proceeds not via a fullerenyl anion A but via the radical anion, C60· . By considering the experimental results, a plausible reaction pathway is proposed in Scheme 4. The initial step is the formation of the radical anion, C60· , from a single-electron reduction of C60 by the excited photocatalyst (*cat) and subsequent protonation of C60· occurs to give B with the formation of the OH ion. The oxidation of a-silylamine 1 by the one-electron oxidized form of photocatalyst (cat + ) and sequential desilylation assisted by the OH ion occurs to give an a-aminoalkyl radical C with the formation of Me3SiOH.[12] In fact, we confirmed the formation of Me3SiOH by GC-MS analysis of the crude reaction mixture. Finally, the radical–radical coupling between B and C leads the corresponding product 2. The other reaction pathway might be assumed as follows: the direct addition of C to C60 and subsequent reduction occurs to give a fullerenyl anion, such as A, followed by the protonation of A to give 2.[9a, c] However, the results shown in Scheme 3 support that the reaction pathway through the protonation of C60· is predominant.[19, 20]
Scheme 4. Plausible pathway for the formation of 2.
Scheme 3. Deuterium isotope-labeling experiments. Chem. Eur. J. 2014, 20, 6120 – 6125
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The electronic absorption (Figure 1) and emission spectra (see Figures S1–S3 in the Supporting Information) of 2 a, 2 k, and 2 l in toluene were observed. The absorption features are similar to those of the previously reported a-aminoalkyl radical/C60 1,2-adducts (Figure 1).[2b, c, 6] The adducts, such as 2 a, 2 k, and 2 l, exhibited relatively weak and broad fluorescence, and the emission spectra have a mirror-image relationship with the absorption spectra at around 710 nm (see Figures S1– S3 in the Supporting Information).[21] The cyclic voltammetric analysis of 2 a, 2 k, and 2 l with phenyl C61 butyric acid methyl ester (PCBM) and C60 as references was also performed in ODCB with 0.1 m nBu4NBF4 as the 6122
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Full Paper Experimental Section General method 1
H NMR (270 MHz) and 13C NMR (67.8 MHz) spectra were recorded on a JEOL Excalibur 270 spectrometer in a suitable solvent. 19 F NMR (471 MHz) spectra were recorded on a JEOL JNM-ECP 500 spectrometer. Elemental analyses were performed at the Microanalytical Center at The University of Tokyo. Mass spectra were measured on a JEOL JMS-700 mass spectrometer. GC-MS analyses were carried out on a Shimadzu GC-MS QP-2010 spectrometer. Absorption and emission spectra were recorded on Shimadzu MultiSpec1500 and Shimadzu RF-5300PC spectrometers, respectively. All the reactions were carried out in a dry nitrogen atmosphere. Solvents were dried by using general methods and degassed before use. Photoirradiation was carried out with an Ushio high-pressure mercury lamp USH-250SC (250 W) with a band-pass filter of l = 440 nm (Kenko B-440 filter). Cyclic voltamograms were recorded on an ALS/Chi model 610C electrochemical analyzer with a platinum working electrode in 1,2-dichlorobenzene containing 0.1 m nBu4NBF4 as a supporting electrolyte. All the potentials were measured against an Ag/Ag + reference electrode and converted versus the ferrocene/ferrocenium + couple.
Figure 1. Electronic absorption spectra of 2 a, 2 k, and 2 l.
Table 4. Redox potentials of 2 a, 2 k, and 2 l.[a] Compound
E ox 1=2 [V]
2a 2k 2l PCBM C60
+ 0.53 + 0.76 + 0.41 – –
E red1 1=2 [V] 1.21 1.18 1.20 1.17 1.08
E red2 1=2 [V] 1.59 1.56 1.59 1.56 1.48
E red3 1=2 [V] 2.12 – – 2.07 1.94
HOMO–LUMO gap [eV] 1.74 1.94 1.61 – –
General procedure for photocatalytic reactions of fullerene with a-silylamines 1
[a] Potential in volts versus the ferrocene/ferrocenium + couple by means of cyclic voltammetry in ODCB containing nBu4NBF4 (0.1 m) as a supporting electrolyte; stick Pt, Pt wire, and Ag/Ag + were used as the working-, counter-, and reference electrodes, respectively.
electrolyte (Table 4). Compound 2 a has three reversible reduction potentials assigned to the formation of the anion, dianion, and trianion of the C60 moiety, whereas compounds 2 k and 2 l have two reversible reduction potentials. All the compounds show the first reduction waves at approximately 1.2 V, which are more negative than those of PCBM and C60. Furthermore, 2 a, 2 k, and 2 l also have one reversible oxidation wave assigned to the oxidation of the amino groups, with a very narrow HOMO–LUMO gap for all the compounds. These results demonstrate the significant potential of these adducts 2 for ambipolar charge-transporting materials.[13b]
Conclusion We have developed the efficient functionalization of [60]fullerene, in which the visible-light-mediated generation of a-aminoalkyl radicals is the key step. Our reaction system is applicable to the addition of a wide range of tertiary amines to C60.[22] We believe that the results described herein provide an efficient methodology for the introduction of the arylamino group as an electron-donating moiety into C60. Further work is currently in progress to research the electronic properties of adduct 2 and to synthesize novel materials by using this methodology. Chem. Eur. J. 2014, 20, 6120 – 6125
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A typical experimental procedure for the reaction of [60]fullerene (C60) with di(4-tert-butylphenyl)(trimethylsilylmethyl)amine (1 a) is described. Water (100 mL) and 1 a (77.3 mg, 0.210 mmol) were added to C60 (101 mg, 0.140 mmol), [3 a][ONf] (1.5 mg, 0.0014 mmol), and 1,2-dichlorobenzene (20 mL) in a Schlenk flask (50 mL, diameter = 4.0 cm) under N2. The reaction flask was placed in a water bath and illuminated with an Ushio high-pressure mercury lamp USH-250SC (250 W) with a band-pass filter of l = 440 nm at room temperature for 9 h. The solution was concentrated in vacuo. The residue was purified by column chromatography (SiO2) with cyclohexane as the eluent to give 1-[N,N-di(4-tert-butylphenyl)aminomethyl]-1,9-dihydro(C60-Ih)[5,6]fullerene (2 a) as a brown solid (46.0 mg, 0.0453 mmol, 32 %). Crystals suitable for elemental analysis and X-ray analysis were obtained by slow evaporation from toluene. 2 a: 1H NMR (C6D6/CS2): d = 7.34–7.24 (m, 8 H), 6.53 (s, 1 H), 5.59 (s, 2 H), 1.28 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 154.8, 154.0, 147.6, 147.5, 147.4, 146.9, 146.7, 146.6, 146.5, 146.41, 146.36, 146.0, 145.71, 145.67, 145.6, 144.9, 144.8, 143.6, 142.91, 142.89, 142.4, 142.3, 142.01, 141.99, 141.96, 140.6, 140.3, 136.8, 135.9, 126.7, 122.3, 68.0, 66.1, 58.0, 34.2, 31.7 ppm; HRMS (FAB, ortho-nitrophenyl octyl ether (NPOE) and meta-nitrobenzyl alcohol (NBA)) m/z calcd for C81H30N [M + H]: 1016.2378; found: 1016.2365; elemental analysis calcd (%) for C88H37N (2 a·C6H5CH3): C 95.37, H 3.37, N 1.26; found: C 95.27, H 3.51, N 1.05. 2 b: A brown solid (38 %). 1H NMR (C6D6/CS2): d = 7.34–7.30 (m, 4 H), 7.23–7.19 (m, 4 H), 6.94–6.88 (m, 2 H), 6.40 (s, 1 H), 5.55 ppm (s, 2 H); 13 C NMR (C6D6/CS2): d = 154.4, 153.7, 148.6, 147.6, 147.5, 147.3, 146.9, 146.63, 146.58, 146.45, 146.39, 146.0, 145.69, 145.67, 145.63, 145.60, 144.9, 144.8, 143.5, 143.3, 142.9, 142.4, 142.3, 142.0, 141.9, 140.6, 140.3, 136.6, 135.9, 129.9, 123.3, 122.6, 67.9, 66.2, 58.2 ppm; HRMS (FAB, NPOE) calcd for C73H13N [M]: 903.1048; found: 903.1066.
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Full Paper 2 c: A brown solid (29 %). 1H NMR (C6D6/CS2): d = 7.24 (d, 4 H, J = 8.1 Hz), 7.02 (d, 4 H, J = 8.1 Hz), 6.45 (s, 1 H), 5.54 (s, 2 H), 2.21 ppm (s, 6 H); 13C NMR (C6D6/CS2): d = 154.8, 154.0, 147.6, 147.5, 147.4, 147.1, 146.8, 146.7, 146.6, 146.5, 146.4, 146.1, 145.73, 145.71, 145.68, 145.6, 144.9, 144.8, 143.5, 143.3, 142.9, 142.44, 142.37, 142.35, 142.03, 142.01, 142.00, 140.6, 140.3, 136.7, 136.0, 132.2, 130.5, 122.6, 68.1, 66.6, 58.3, 21.0 ppm; HRMS (FAB, NPOE) calcd for C75H17N [M]: 931.1361; found: 931.1357. 2 d: A brown solid (38 %). 1H NMR (C6D6/CS2): d = 7.31–7.26 (m, 4 H), 7.07–7.02 (m, 4 H), 6.51 (s, 1 H), 5.58 (s, 2 H), 2.52 (t, 4 H, J = 7.6 Hz), 1.60–1.49 (m, 4 H), 1.37–1.24 (m, 4 H), 0.89 ppm (t, 6 H, J = 7.2 Hz); 13 C NMR (C6D6/CS2): d = 154.8, 154.0, 147.6, 147.5, 147.4, 147.0, 146.8, 146.7, 146.6, 146.5, 146.4, 146.1, 145.71, 145.68, 145.6, 144.9, 144.8, 143.5, 143.3, 142.92, 142.90, 142.41, 142.35, 142.02, 142.00, 141.98, 140.6, 140.3, 137.4, 136.7, 135.9, 129.8, 122.6, 68.0, 66.4, 58.2, 35.5, 34.3, 23.0, 14.5 ppm; HRMS (FAB, NPOE) calcd for C81H29N [M]: 1015.2300; found: 1015.2272. 2 e: A brown solid (35 %). 1H NMR (C6D6/CS2): d = 7.36–7.19 (m, 8 H), 6.91–6.85 (m, 1 H), 6.47 (s, 1 H), 5.56 (s, 2 H), 1.27 ppm (s, 9 H); 13 C NMR (C6D6/CS2): d = 154.6, 153.9, 149.0, 147.55, 147.47, 147.3, 146.9, 146.63, 146.58, 146.5, 146.44, 146.38, 146.0, 145.8, 145.67, 145.66, 145.62, 145.58, 144.9, 144.8, 143.5, 143.3, 142.87, 142.85, 142.34, 142.30, 142.0, 141.9, 140.6, 140.3, 136.7, 135.9, 129.8, 126.8, 123.7, 122.4, 121.1, 67.9, 66.1, 58.1, 34.3, 31.7 ppm; HRMS (FAB, NPOE and NBA) calcd for C77H22N [M + H]: 960.1752; found: 960.1754. 2 f: A brown solid (39 %). 1H NMR (C6D6/CS2): d = 7.47–7.41 (m, 5 H), 7.39–7.36 (m, 3 H), 7.35–7.32 (m, 2 H), 7.30–7.27 (m, 1 H), 7.26–7.21 (m, 2 H), 6.49 (s, 1 H), 5.62 (s, 2 H), 1.28 ppm (s, 9 H); 13C NMR (C6D6/ CS2): d = 154.6, 153.9, 148.6, 147.6, 147.5, 147.4, 147.2, 147.0, 146.7, 146.6, 146.5, 146.4, 146.1, 145.73, 145.68, 145.65, 145.56, 144.9, 144.8, 143.6, 142.94, 142.92, 142.38, 142.35, 142.04, 141.99, 140.8, 140.6, 140.3, 136.7, 136.0, 134.7, 129.1, 127.1, 126.91, 126.89, 124.5, 120.7, 67.9, 66.1, 58.2, 34.4, 31.7 ppm; HRMS (FAB, NPOE) calcd for C83H26N [M + H]: 1036.2065; found: 1036.2101. 2 g: A brown solid (26 %). 1H NMR (C6D6/CS2): d = 7.30 (br, 4 H), 7.13 (br, 4 H), 6.40 (s, 1 H), 5.51 (s, 2 H), 1.27 ppm (s, 9 H); 13C NMR (C6D6/ CS2): d = 154.3, 153.7, 147.9, 147.6, 147.5, 147.3, 146.8, 146.7, 146.6, 146.5, 146.4, 146.0, 145.73, 145.68, 145.6, 145.3, 144.9, 144.8, 143.6, 142.94, 142.92, 142.34, 142.33, 142.03, 141.97, 141.9, 140.6, 140.3, 136.6, 135.9, 129.7, 127.0, 126.9, 124.7, 121.2, 67.7, 66.2, 58.2, 34.4, 31.6 ppm; HRMS (FAB, NPOE) calcd for C77H20NCl [M]: 993.1284; found: 993.1249. 2 h: A brown solid (32 %). 1H NMR (C6D6/CS2): d = 7.41–7.35 (m, 2 H), 7.20–7.16 (m, 2 H), 7.10–7.04 (m, 2 H), 6.88–6.82 (m, 2 H), 6.63 (s, 1 H), 5.66 (s, 2 H), 3.73 (s, 3 H), 1.28 ppm (s, 9 H); 13C NMR (C6D6/CS2): d = 157.0, 154.6, 153.9, 147.7, 147.5, 147.4, 147.3, 146.8, 146.6, 146.5, 146.4, 146.3, 146.0, 145.62, 145.57, 145.5, 144.8, 144.7, 143.4, 143.1, 142.8, 142.3, 142.2, 141.92, 141.89, 140.8, 140.5, 140.3, 136.7, 135.9, 127.6, 126.4, 118.2, 115.3, 68.0, 66.9, 58.2, 55.3, 33.9, 31.8 ppm; HRMS (FAB, NPOE) calcd for C78H23ON [M]: 989.1780; found: 989.1760. 2 i: A brown solid (24 %). 1H NMR (C6D6/CS2): d = 7.75–7.70 (m, 2 H), 7.41–7.30 (m, 4 H), 7.23–7.19 (m, 2 H), 6.49 (s, 1 H), 5.63 (s, 2 H), 1.29 (s, 9 H), 1.21 ppm (s, 12 H); 13C NMR ([D4]ODCB): d = 154.0, 153.3, 152.0, 148.5, 147.0, 146.9, 146.7, 146.4, 146.0, 145.9, 145.8, 145.7, Chem. Eur. J. 2014, 20, 6120 – 6125
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145.4, 145.03, 144.99, 144.97, 144.4, 144.2, 142.17, 141.75, 141.68, 141.6, 141.4, 141.33, 136.5, 136.1, 135.5, 130.1, 126.5, 116.7, 83.2, 31.2, 24.7 ppm; HRMS (FAB, NPOE) calcd 1085.2526; found: 1085.2512.
144.1, 142.8, 142.18, 141.29, 139.8, 139.6, 67.4, 65.6, 57.8, 34.2, for C83H32O2NB [M]:
2 j: A brown solid (38 %). 1H NMR (C6D6/CS2): d = 7.77 (d, 1 H, J = 2.2 Hz), 7.61–7.57 (m, 3 H), 7.44 (dd, 1 H, J = 8.9 Hz and 2.4 Hz), 7.40–7.35 (m, 2 H), 7.30–7.18 (m, 4 H), 6.97–6.91 (m, 1 H), 6.41 (s, 1 H), 5.64 ppm (s, 2 H); 13C NMR (C6D6/CS2): d = 154.5, 153.8, 148.8, 147.6, 147.5, 147.3, 147.0, 146.7, 146.6, 146.5, 146.4, 146.0, 145.73, 145.71, 145.67, 145.6, 144.9, 144.8, 143.5, 142.93, 142.91, 142.4, 142.3, 142.03, 141.97, 141.96, 140.6, 140.3, 136.7, 135.8, 134.8, 130.3, 130.0, 129.7, 127.4, 127.0, 125.1, 123.5, 123.3, 122.8, 118.8, 67.9, 66.4, 58.4 ppm; HRMS (FAB, NPOE) calcd for C77H16N [M + H]: 954.1283; found: 954.1277. 2 k: A brown solid (41 %). 1H NMR (C6D6/CS2): d = 8.17 (d, 2 H, J = 1.8 Hz), 7.68 (d, 2 H, J = 8.6 Hz), 7.52 (dd, 2 H, J = 8.6 Hz and 1.8 Hz), 6.26 (s, 1 H), 5.74 (s, 2 H), 1.42 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 153.8, 153.4, 147.62, 147.60, 147.2, 146.8, 146.7, 146.6, 146.5, 146.4, 146.0, 145.9, 145.8, 145.7, 145.6, 144.9, 144.7, 143.5, 143.0, 142.9, 142.8, 142.5, 142.3, 142.2, 142.1, 141.9, 141.8, 140.6, 140.5, 140.4, 136.5, 135.8, 124.2, 124.1, 117.2, 109.9, 67.9, 58.5, 57.3, 34.8, 32.2 ppm; HRMS (FAB, NPOE) calcd for C81H27N [M]: 1013.2144; found: 1013.2164. 2 l: A brown solid (27 %). 1H NMR (C6D6/CS2): d = 7.27–7.23 (m, 2 H), 7.13–7.05 (m, 4 H), 6.88–6.82 (m, 2 H), 6.63 (s, 1 H), 5.77 ppm (s, 2 H); 13 C NMR (C6D6/CS2): d = 154.0, 153.7, 147.6, 147.3, 146.61, 146.58, 146.5, 146.41, 146.37, 146.0, 145.74, 145.71, 145.62, 145.60, 144.9, 144.7, 143.5, 142.8, 142.4, 142.31, 142.25, 141.9, 141.7, 140.4, 140.2, 136.4, 136.2, 135.6, 129.0, 128.5, 124.3, 67.9, 60.9, 58.0 ppm; HRMS (FAB, NPOE) calcd for C73H11NS [M]: 933.0612; found: 933.0648.
Reaction of 2 a with methyl iodide A solution of KOtBu (30 mL, 1.0 m, 0.030 mmol) in THF was added to 2 a (24.8 mg, 0.0244 mmol) and benzonitrile (7 mL) in a Schlenk flask (50 mL) under N2 at room temperature. After stirring for 10 min, MeI (30 mL, 0.5 mmol) was added to the reaction mixture, which was stirred for 12 h at room temperature. After the solution was concentrated in vacuo, the residue was purified by column chromatography (SiO2) with cyclohexane as the eluent to give 6 a as a brown solid (12.4 mg, 0.0120 mmol, 49 %). 1H NMR (C6D6/CS2): d = 7.31–7.20 (m, 8 H), 5.34 (d, 1 H, J = 14.9 Hz), 5.25 (d, 1 H, J = 14.9 Hz), 2.63 (s, 3 H), 1.25 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 159.0, 156.7, 153.0, 150.4, 149.3, 148.94, 148.91, 148.4, 148.1, 147.52, 147.48, 147.4, 147.30, 147.25, 147.19, 147.17, 146.6, 145.82, 145.79, 145.5, 145.4, 145.3, 145.2, 145.09, 145.07, 145.0, 144.74, 144.71, 144.67, 144.6, 144.54, 144.47, 144.46, 144.3, 144.2, 144.1, 144.0, 143.53, 143.49, 143.3, 143.04, 142.99, 142.98, 142.8, 142.7, 142.6, 142.4, 142.3, 141.2, 139.3, 139.0, 138.9, 138.0, 126.5, 122.2, 63.7, 62.2, 54.8, 34.2, 31.6, 29.1 ppm; HRMS (FAB, NPOE) calcd for C82H31N [M]: 1029.2457; found: 1029.2473.
Reaction of 2 a with methyl 2-(bromomethyl)acrylate A solution of KOtBu (30 mL, 1.0 m, 0.030 mmol) in THF was added to 2 a (25.0 mg, 0.0246 mmol) and benzonitrile (7 mL) in a Schlenk flask (50 mL) under N2 at room temperature. After stirring for 10 min, methyl 2-(bromomethyl)acrylate (60 mL, 0.5 mmol) was added to the reaction mixture, which was stirred for 1 h at room
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Full Paper temperature. After the solution was concentrated in vacuo, the residue was purified by column chromatography (SiO2) with cyclohexane/toluene (2:1) as the eluent to give 6 b as a brown solid (23.0 mg, 0.0206 mmol, 84 % ). 1H NMR (C6D6/CS2): d = 7.30–7.20 (m, 8 H), 6.44 (d, 1 H, J = 1.1 Hz), 5.51 (br, 1 H), 5.41 (d, 1 H, J = 14.9 Hz), 5.34 (d, 1 H, J = 14.9 Hz), 4.10 (d, 1 H, J = 13.0 Hz), 4.00 (d, 1 H, J = 13.0 Hz), 3.53 (s, 3 H), 1.25 ppm (s, 18 H); 13C NMR (C6D6/CS2): d = 166.9, 156.8, 156.7, 151.4, 150.7, 149.1, 148.9, 148.8, 148.0, 147.50, 147.47, 147.3, 147.24, 147.16, 147.1, 146.7, 145.81, 145.78, 145.6, 145.43, 145.37, 145.23, 145.16, 145.14, 145.06, 144.99, 144.96, 144.74, 144.71, 144.63, 144.60, 144.56, 144.5, 144.4, 144.3, 144.1, 144.0, 143.9, 143.51, 143.49, 143.4, 143.3, 143.2, 143.01, 142.97, 142.9, 142.70, 142.66, 142.4, 142.31, 142.25, 141.1, 139.3, 139.2, 138.9, 138.5, 135.6, 130.2, 126.5, 122.3, 63.7, 62.3, 59.1, 51.8, 44.2, 34.2, 31.7 ppm; HRMS (FAB, NPOE) calcd for C86H36O2N [M + H]: 1114.2746; found: 1114.2764.
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Received: December 3, 2013 Published online on April 2, 2014
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