Copper-Catalyzed Aerobic Oxidative Reaction of C60 with Aliphatic

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Copper-Catalyzed Aerobic Oxidative Reaction of C60 with Aliphatic Primary Amines and CS2 Sheng-Li Wu, and Xiang Gao J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b03061 • Publication Date (Web): 29 Jan 2018 Downloaded from http://pubs.acs.org on January 29, 2018

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The Journal of Organic Chemistry

Copper-Catalyzed Aerobic Oxidative Reaction of C60 with Aliphatic Primary Amines and CS2 Sheng-Li Wu and Xiang Gao* State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, Jilin 130022, China [email protected]

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ABSTRSCT A novel type of fullerene derivatives, [60]fullerothiazolidinethiones (2), were obtained from the copper-catalyzed aerobic oxidative reaction of C60 with aliphatic primary amines and CS2 in 4:1 v/v DMF and o-DCB. The obtained products were fully characterized with the X-ray single crystal diffraction and spectroscopic methods. Control experiment with maleic anhydride, an analogue to C60, also afforded thiazolidinethione product, but via a mechanism different from that of C60 judging from the structure difference between the two types of thiazolidinethione compounds, demonstrating the unique reactivity of C60.

2


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INTRODUCTION Carbon disulfide (CS2) reacts with primary amine affording dithiocarbamic acid, which is an analogue of carbamic acid by replacing oxygen atoms with sulfur atoms and is an important intermediate in transforming the typically inert and simple CS2 into a rich variety of organosulfur compounds1 with biological activity2 and synthetic application.3 The dithiocarbamic acid is unstable, it may lose H2S to form isothiocyanate, and further reacts with another amine molecule to afford thioureas,4 or directly react with electrophiles such as alkyl halide,5 aromatic aldehyde6 or Michael acceptor7,8 to form dithiocarbamate. However, to the best of our knowledge, no reaction of dithiocarbamic acid with [60]fullerene (C60), a strong electron-deficient molecule capable of accepting up to six electrons reversibly in solution,9 has been studied so far. Due to the unique electronic and three-dimensional structure of fullerenes, the chemistry of fullerenes has attracted great interest during the last several decades, with the development of a great number of reactions and fullerene derivatives,10,11 which have shown potentials in areas such as materials science12 and medicinal chemistry.13 However, progress on fullerene thiolation is rather slow, where sophisticated reagents such as isothiocyanate and thiadiazolidinone are usually required,14‒17 while the simple and common reagent of CS2 is rarely used.18 It is noteworthy that CS2 is an excellent solvent for fullerenes,19 which has strong interaction with fullerenes as shown in the crystalline fullerene/CS2 solvates.20 Previous work on the thiolation of C60 with CS2 and amino acid esters has shown the reaction affords [60]fullerene-fused thiolactams via the isothiocyanate intermediate formed by losing H2S from dithiocarbamic acid.18 However, the sulfur atom is bound to the C60-fused heterocycle rather than to the C60 carbon cage, which would likely have less effect in modulating the property of 3



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fullerene derivatives. Herein, we report the reaction of C60 with CS2 and aliphatic primary amines, which results in [60]fullerothiazolidinethiones (2) with the sulfur atom directly bound to C60. RESULTS AND DISCUSSION Synthesis of [60]Fullerothiazolidinethiones (2). Butylamine (1a) was used for the reaction screening and the result is listed in Table 1. A 50- and 200-fold equiv of butylamine and CS2 with respect to C60 were used for the reaction. The reaction was initially evaluated in o-DCB without Cu salt (entry 1). The reaction mixture remained the characteristic purple color of C60 during the reaction, indicating that C60 did not participate in the reaction. DMF was then introduced into the system in considering that the in situ formed dithiocarbamic acid might undergo nucleophilic reaction involving ionic species5‒7 and polar solvent such as DMF was capable of facilitating the reaction of C60 with ionic species by stabilizing the ion pair.21 Interestingly, the color of the reaction mixture gradually turned to red after adding C60 into the 4:1 (v/v) DMF/o-DCB solution containing CS2 and C4H9NH2 under argon, which is the characteristic color for the anionic fullerene species, suggesting that anionic fullerene species were likely involved in the reaction and DMF was critical for the reaction. Notably, many reactions involving anionic fullerene species could be well quenched with I2 oxidation.22‒24 However, the use of I2 to quench the reaction caused the complete recovery of C60 and no fullerothiazolidinethione was obtained (entry 2). Table 1.Screening of the Reaction Conditionsa

Entry

Cu cat. (mol%)

Solvent (volume ratio) 4


Yield [%]b

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1

none

o-DCB

0

2c

none

DMF/o-DCB(4:1)

0

3

none

DMF/o-DCB(4:1)

trace

4

Cu(OAc)2•H2O (20)

DMF/o-DCB(4:1)

43

5

Cu(OAc)2•H2O (20)

o-DCB

0

6

Cu(OAc)2•H2O (20)

DMF/o-DCB(1:1)

15

7

Cu(OAc)2•H2O (20)

DMF

21

8

CuSO4•5H2O (20)

DMF/o-DCB(4:1)

22

8

CuCl2 (20)

DMF/o-DCB(4:1)

28

9

CuBr2 (20)

DMF/o-DCB(4:1)

24

10

CuCl (20)

DMF/o-DCB(4:1)

21

11

CuBr (20)

DMF/o-DCB(4:1)

22

12

CuI (20)

DMF/o-DCB(4:1)

24

13

Cu(OAc)2 (20)

DMF/o-DCB(4:1)

21

14

CuCl2•2H2O (20)

DMF/o-DCB(4:1)

26

15d

Cu(OAc)2•H2O (20)

DMF/o-DCB(4:1)

trace

a

Conditions: 690 μL (7 mmol) of butylamine, 1680 μL (28 mmol) of CS2 and 0.028 mmol of Cu cat. were put into 24 mL of DMF under argon at 30C. The mixture was kept stirring for 10 min, then 100 mg (0.14 mmol) of C60 dissolved in 6 mL of o-DCB was added. The mixture was kept stirring under argon for 5 h, followed by bubbling with 1 atm O2 for 1 h. bIsolated yield. cThe reaction was quenched with I2 oxidation. dControl experiment with addition of 2 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).

Aerobic oxidation was then performed in order to improve the reaction as it was also effective in quenching reactions involving anionic fullerene species.25‒29 A trace amount of the fullerothiazolidinethione was produced when the reaction was carried out with aerobic oxidation in 4:1 (v/v) DMF/o-DCB (entry 3). The reaction was further examined by adding Cu salt since it was 5



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capable of facilitating the aerobic oxidation.30 Impressively, [60]fullerothiazolidinethione was obtained with 43% yield when 0.2 equiv of Cu(OAc)2•H2O with respect to C60 was used in 4:1 (v/v) DMF/o-DCB (entry 4), demonstrating that the Cu-catalyzed aerobic oxidation was also critical for the reaction. The solvent was further screened by carrying out the reaction in o-DCB, 1:1 (v/v) DMF/o-DCB and DMF respectively in the presence of 0.2 equiv of Cu(OAc)2•H2O (entries 5‒7). C60 would still not participate in the reaction in o-DCB, while fullerothiazolidinethione was obtained with a yield of 15% and 21% for the reaction in 1:1 (v/v) DMF/o-DCB and DMF, respectively, suggesting that the 4:1 (v/v) DMF/o-DCB mixture was appropriate for the reaction. Experiments with other Cu salts (entries 8‒14) showed that they were all less effective compared with Cu(OAc)2•H2O. The substrate scope of the reaction was examined with different primary amines under optimized condition (entry 4 in Table 1), and the result is summarized in Table 2. The reactions of isobutylamine (1b), propylamine (1c) and hexylamine (1d) all afforded the corresponding [60]fullerothiazolidinethiones 2b-d in synthetically valuable yield. However, no product was obtained for phenylamine (1e), which was likely due to the hindered reaction of phenylamine with CS2 caused by the less nucleophilicity of the arylamine. Table 2. Substrate Scope of the Reaction

C60 + RNH2 + CS2 1

S

1) DMF/o-DCB/Ar 2) O2/Cu cat. 30 oC

N R

S

2

6


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Amines/Product: Yield

1a/2a: 43%

1b/2b: 22%

1c/2c: 25%

1d/2d: 33%

1e/2e: 0%

Structural Characterization of 2. Single crystals of 2a suitable for the X-ray diffraction were obtained by slowly diffusing hexane into the CS2 solution of 2a. Figure 1 shows the single crystal structure of 2a (CCDC 1576903) with selected bond lengths and bond angles. The N-butyl group is disordered with two orientations occupying the common nitrogen atom (fractional occupancy of 0.50 and 0.50, respectively). A thiazolidinethione heterocycle with N-butyl group is shown unambiguously with the nitrogen and sulfur atoms bonding to the C60 cage at the [6,6]-bond. The sum of the bond angles of S1‒C61‒S2, S2‒C61‒N, and N‒C61‒S1 is 360, indicating that C61 is an sp2 carbon. While the sum of bond angles of the thiazolidine pentagon is 540, indicating that the thiazolidine heterocycle is a planar ring. The bond lengths of C1‒C2 (1.597 Å), C2‒S1 (1.862 Å), S1‒C61 (1.749 Å) and N‒C1 (1.490 Å) are consistent with those of single bonds (C‒C 1.54 Å, C‒S 1.82 Å and C‒N 1.47 Å).31 The bond length of C61‒S2 is 1.634 Å, which is elongated compared to the C=S bond in CS2 (1.553 Å), but is well within the average range of C=S bond (1.67 Å).34 Notably, the C61‒N (1.345 Å) bond is significantly shortened with respect to the typical C‒N bond (1.47 Å),31 and is close to that of C=N (1.28 Å) bond,31 suggesting a conjugation over the S2, C61 and N atoms, which renders partial double bond nature to the C61‒N bond and is responsible for the planar structure of the thiazolidine pentagon. Interestingly, a close contact of 3.337 Å is shown between the thione sulfur atom and the neighboring C60 cage in the crystal packing structure (Figure 7



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S1), which is even shorter than the closest distance (3.460 Å) between the sulfur atom of CS2 and C60 in crystalline C60/CS2 solvates,20a suggesting a strong intermolecular interaction between the molecules of 2a, consistent with the fact that the compound has a much lowered solubility in most common solvents including CS2 and toluene compared with other fullerene derivatives. S2 C61

N

S1 C1 C2

Figure 1. Single crystal of 2a with 50% thermal ellipsoids. Hydrogen and solvent molecules are omitted for clarity. Selected bond lengths (Å): C1‒C2 1.597, C2‒S1 1.862, S1‒C61 1.749, C61‒N 1.345, N‒C1 1.490, C61‒S2 1.634; Selected bond angles (): C1‒C2‒S1 106.18, C2‒S1‒C61 94.92, S1‒C61‒N 111.52, C61‒N‒C1 120.78, N‒C1‒C2 106.60, S1‒C61‒S2 120.15, S2‒C61‒N 128.34. Color scheme: gray for C, blue for N, and yellow for S.

Compounds 2a-2d were further characterized by spectroscopic methods. Each compound exhibited protonated molecular ion that is well matched with the theoretical value in the HRMS spectra (Figures S2, S6, S10 and S14). Resonances due to the alkylamine protons were shown in the 1

H NMR spectra (Figures S3, S7, S11 and S15). The thione carbon atoms resonated at around 190

ppm for 2a-2d in the 13C NMR spectra (Figures S4, S8, S12 and S16). A total of less than 29 peaks

8


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of the sp2 C60 carbons were shown for each individual compound of 2a-2d, in agreement with the Cs symmetry of the molecules. Peaks of the alkylamine carbons were shown for each compound. However, signals due to the sp3 C60 carbon atoms bound to the nitrogen and sulfur atoms were rather weak, with the appearance of only the N-bound carbons in 2b and 2d at 93.1 and 91.5 ppm, consistent with the chemical shift reported for the N-bound C60 carbons.24b,32 The addition of Cr(acac)3 (chromium(III) acetylacetonate) as the relaxation agent and the use of prolonged delay time and increased number of scans under our experimental condition had little effect in improving the N- and S-bound sp3 C60 signals, which is likely associated with the weakness nature of these peaks. The UV-vis spectra of 2a-2d (Figures S5, S9, S13 and S17) exhibited similar absorption pattern, confirming a similar structure for the compounds.33 The absorption peak at around 428 nm, which is characteristic for the C60 ortho-adducts with C-bound addends,33 is absent, likely due to the effect of heteroatoms directly bonded to C60 as observed for C60 oxazoline.32a In Situ Vis-NIR Study and Mechanistic Consideration. In situ vis-NIR spectroscopy was performed for the reaction in order to obtain a better understanding of the reaction mechanism. Figure 2 shows the in situ vis-NIR spectra of the reaction. No absorption peaks appeared from 400 to 1100 nm when butylamine was mixed with CS2 under argon in the presence of 0.2 equiv of Cu(OAc)2•H2O (Figure 2a). While new absorptions gradually increased at 1074, 1036, 995 and 928 nm after C60 was added (Figures 2b-e). Such absorptions are characteristic of C60•‒,34 and were confirmed by overlapping Figure 2b with the spectrum of C60•‒ with normalizing the absorption at 1074 nm (Figure S20), demonstrating that C60•‒ is involved in the reaction. Control experiment without Cu salt was performed to examine whether Cu salt was involved in generating C60•‒ since it was shown that Cu salt could react with amino groups in copper-mediated fullerene reactions.32e,35 9



The result (Figure S21) showed that vis-NIR absorptions corresponding to C60•‒ appeared after adding C60 into the mixture of butylamine was mixed with CS2 under argon, demonstrating explicitly that the Cu salt was not involved in the formation of C60•‒, but should be responsible for the aerobic oxidation in the reaction.

1074

a b c d e

3

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1036

2

995 928

1

0 400

500

600

700

800

900

1000

1100

Wavelength(nm)

Figure 2. In situ vis-NIR spectra of (a) CS2 with butylamine and 0.2 equiv of Cu(OAc)2•H2O after mixing for 10 min; (b‒e) after adding C60 (2.8 mM) for 20, 40, 60 and 180 min, respectively. Conditions: 1-mm cuvette, under Ar. Previous work on addition of secondary amine to C60 has shown that the reaction is initiated by the single electron transfer (SET) from secondary amine to C60 under deaerated condition with the formation of C60•‒, followed by aerobic oxidative amination,26,29 where the use of polar solvent is critical as it can stabilize the ionic species. It is therefore reasonable that the formation of fullerothiazolidinethione is initiated by SET from the in situ formed dithiocarbamic acid to C60, as the dithiocarbamic acid is also a secondary amine, consistent with the in situ vis-NIR spectroscopy and rationalizing the essence of DMF for the reaction. It is notable that the SET from the starting

10


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material of primary amine to C60 is unlikely because the amine would be completely converted into dithiocarbamic acid when CS2 is in much more excess (nCS2:nRNH2 = 4:1). In addition, no aziridinofullerenes were obtained from the reaction, confirming that no reaction of C60 with primary amine occurred.35b The C60‒N bond is then formed first by subsequent oxidative amination reaction between C60•‒ and aminium radical cation, followed by the formation of the C60‒S bond via Cu-catalyzed aerobic oxidation. In principle, the dithiocarbamic acid may undergo nucleophilic addition to C60 through the anionic sulfur atom in a manner similar to the addition of anionic oxygen nucleophile.24a However, such addition would result in anionic singly bonded fullerene species that have near-IR absorptions different from that of C60•‒,36 which was not observed by the in situ spectroscopy. Control experiment with TEMPO (2 equiv) severely prohibited the formation of the product (entry 15, Table 1), implying that the reaction involved radical intermediates. Notably, the dithiocarbamic acid may decompose to isothiocyanate upon I2 treatment,37 which would likely account for the failure of the reaction when I2 was used. The proposed reaction mechanism is illustrated in Scheme 1. Scheme 1. Proposed Mechanism for the Reaction

11



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Control Experiment with Maleic Anhydride. Control experiment with maleic anhydride was performed in order to compare the reactivity of C60 with electron-deficient alkene. The reaction was carried out in CH2Cl2 under open air, and no difference was observed with or without using Cu salt. Interestingly, compound 3 was obtained from the reaction and the single crystal structure (CCDC 1582015, Figure 3) revealed that it was thiazolidinethione. The thiazolidine ring in 3 is planar caused by the partial double bond nature of the C3‒N (1.372Å) and C1‒N (1.391 Å) bonds, similar to that in 2a. However, the structure of 3 indicates that the compound is formed via the Michael addition of the sulfur atom of dithiocarbamic acid, followed by intramolecular nucleophilic addition of nitrogen at the anhydride group with ring-opening of the maleic anhydride and formation of the thiazolidine heterocycle as previous work reported,7b rather than via the addition of the dithiocarbamic acid to the double bond of maleic anhydride as the case of C60 reaction. It is notable that the reaction can be carried out directly under aerobic condition without the use of inert atmosphere, indicating that no anionic species or SET are involved, demonstrating the unique reactivity of C60. S2

C3

N

S1 C1 C2 O1

Figure 3. Single crystal of 3 with 50% thermal ellipsoids. Hydrogen and solvent molecules are omitted for clarity. Selected bond lengths (Å): C1‒C2 1.520, C2‒S1 1.819, S1‒C3 1.745, C3‒N 1.372, N‒C1 1.391, C3‒S2 1.649, C1‒O1 1.210; Selected bond angles (): C1‒C2‒S1 105.93, 12


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C2‒S1‒C3 93.33, S1‒C3‒N 111.55, C3‒N‒C1 116.86, N‒C1‒C2 112.13, S1‒C3‒S2 122.21, S2‒C3‒N 126.23. Color scheme: gray for C, blue for N, red for O, and yellow for S.

CONCLUSION Thiolation of C60 with CS2 and primary alkylamines was achieved with the generation of [60]fullerothiazolidinethiones. The reaction mechanism was studied with the in situ vis-NIR spectroscopy. The result showed that the formation of C60 monoanion via SET from the dithiocarbamic acid to C60 was the key step of the reaction, and the use of DMF and Cu-catalyzed aerobic oxidation was critical for the reaction. Control experiment with maleic anhydride further revealed the unique reactivity of C60 that is different from the electron-deficient alkene. The work extends the scope of thiolation of fullerenes.

Experimental Section General Methods. All reagents were obtained commercially and used without further purification, unless otherwise noted. Synthesis of 2a. Typically, 690 μL of butylamine (7 mmol, 50 equiv), 1680 μL of CS2 (28 mmol, 200 equiv) and 5.6 mg of Cu(OAc)2•H2O (0.028 mmol, 0.2 equiv) were put into 24 mL of DMF under argon at 30C. The mixture was kept stirring for 10 min, then 100 mg of C60 (0.14 mmol) dissolved in 6 mL of o-DCB was added. The mixture was kept stirring under argon for 5 h, followed by bubbling with 1 atm O2 for 1 h. The solvent of the reaction mixture was removed with a rotary evaporator under vacuum, and the residue was washed with methanol to remove Cu(OAc)2•H2O. The residue was dissolved in CS2 and purified over a flash chromatography silica gel column with 9:1 (v/v) CS2/CH2Cl2 solution. Compound 2a was obtained as a brown amorphous 13



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solid with an isolated yield of 43% (52 mg). Spectral Characterization of 2a. HRMS (MALDI TOF): m/z calcd for C65H10NS2+ [M + H]+ 868.0249, found 868.0229; 1H NMR (600 MHz, in CS2 with CDCl3 as the internal lock solvent) δ 4.62 (t, 2H), 2.13 (m, 2H), 1.48 (m, 2H), 1.00 (t, 3H); 13C NMR (150 MHz, in CS2 with CDCl3 as the internal lock solvent) δ 190.7, 150.1, 148.2, 147.7, 146.6, 146.3, 146.2, 145.7, 145.5, 145.4, 145.2, 144.8, 144.2, 143.8, 143.14, 143.09, 143.05, 142.9, 142.8, 142.5, 142.3, 142.2, 142.1, 142.0, 141.9, 141.6, 140.6, 139.5, 136.7, 134.1, 49.7, 29.5, 21.0, 14.1; UV-vis (in toluene): λmax/nm: 322. X-ray Single Crystal Diffraction of 2a. Black crystals of 2a suitable for X-ray diffraction were obtained by slowly diffusing hexane into the CS2 solution of 2a at room temperature. Single crystal X-ray diffraction data were collected on an instrument equipped with a CCD area detector using graphite-monochromated Mo Kα radiation (λ = 0.71070 Å) in the scan range 3.04° < θ < 26°. The structure was solved with SHELXS-97 and refined with SHELXL-97 program. Crystal data of 2a: C65.5H9NS3 (C65H9NS2 • 0.5CS2), Mw = 905.92, monoclinic, space group P21/m, a = 10.0873(8) Å, b = 13.9444(13) Å, c = 12.7124(19) Å, α = 90.00°, β = 106.462(11)°, γ = 90.00°, V = 1714.8(3) Å3, Z = 2, Dcalc= 1.754 Mg m‒3, μ = 0.277 mm‒1, T = 103.3 K, crystal size 0.25 × 0.08 × 0.08 mm; reflections collected 14234, independent reflections 3518; 2478 with I > 2σ(I); R1 = 0.0601 [I > 2σ(I)], wR2 = 0.1253 [I > 2σ(I)]; R1 = 0.0915 (all data), wR2 = 0.1407 (all data), GOF (on F2) = 1.043. Synthesis of 2b. The procedures were similar to those of preparation of 2a, except isobutylamine (700 μL, 7 mmol, 50 equiv) was used instead of butylamine. The reaction afforded 2b as a brown amorphous solid with an isolated yield of 22% (30 mg). Spectral Characterization of 2b. HRMS (MALDI TOF): m/z calcd for C65H10NS2+ [M + H]+ 14


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868.0249, found 868.0229; 1H NMR (600 MHz, in CDCl3) δ 4.63 (t, 2H), 2.78 (m, 1H), 1.19 (d, 6H); 13C NMR (150 MHz, in CDCl3) δ 193.7, 162.4, 150.2, 148.3, 147.9, 146.8, 146.5, 146.3, 145.8, 145.6, 145.5, 145.4, 144.8, 144.2, 144.0, 143.2, 143.04, 142.96, 142.5, 142.4, 142.32, 142.29, 142.2, 141.9, 141.6, 140.7, 139.4, 136.7, 134.2, 132.5, 93.1, 56.7, 28.7, 20.7; UV-vis (in toluene): λmax/nm: 322. Synthesis of 2c. The procedures were similar to those of preparation of 2a, except propylamine (580 μL, 7 mmol, 50 equiv) was used instead of butylamine. The reaction afforded 2c as a brown amorphous solid with an isolated yield of 25% (30 mg). Spectral Characterization of 2c. HRMS (MALDI TOF): m/z calcd for C64H8NS2+ [M + H]+ 854.0093, found 854.0076; 1H NMR (600 MHz, in CS2 with CDCl3 as the internal lock solvent) δ 4.57 (t, 2H), 2.18 (m, 2H), 1.06 (t, 3H); 13C NMR (150 MHz, in CS2 with CDCl3 as the internal lock solvent) δ 190.8, 150.1, 148.2, 147.7, 146.6, 146.3, 146.21, 146.19, 145.7, 145.5, 145.4, 145.2, 144.8, 144.2, 143.8, 143.13, 143.05, 142.9, 142.8, 142.5, 142.3, 142.2, 142.1, 141.9, 141.7, 140.6, 139.6, 136.7, 134.1, 51.3, 21.4, 11.8; UV-vis (in toluene): λmax/nm: 322. Synthesis of 2d. The procedures were similar to those of preparation of 2a, except hexylamine (930 μL, 7 mmol, 50 equiv) was used instead of butylamine. The reaction afforded 2d as a brown amorphous solid with an isolated yield of 33% (41 mg). Spectral Characterization of 2d. HRMS (MALDI TOF): m/z calcd for C67H14NS2+ [M + H]+ 896.0562, found 896.0542; 1H NMR (600 MHz, in CS2 with CDCl3 as the internal lock solvent) δ 4.37 (t, 2H), 1.92 (m, 2H), 1.23 (m, 2H), 1.13 (m, 2H), 0.70 (t, 3H); 13C NMR (150 MHz, in CS2 with d6-DMSO as the external lock solvent) δ 189.9, 149.9, 147.9, 147.5, 146.4, 146.0, 145.9, 145.4, 145.2, 145.1, 144.9, 144.5, 143.9, 143.5, 142.92, 142.87, 142.57, 142.55, 142.2, 142.0, 141.9, 141.8, 15



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141.6, 141.4, 140.3, 139.2, 136.4, 133.8, 91.5, 49.6, 31.4, 27.2, 27.0, 23.0, 14.3; UV-vis (in toluene): λmax/nm: 321. Control Experiment with Maleic Anhydride. Typically, 245 mg of maleic anhydride (2.5 mmol), 250 μL of butylamine (2.5 mmol) and 610 μL of CS2 (10 mmol) were put together into 20 mL of CH2Cl2. The mixture was kept stirring at 30 ºC under open air for 7 h. The reaction mixture was dried with a rotary evaporator under reduced pressure, and the residue was dissolved in CH2Cl2/hexane (1:4 v/v), and compound 3 was obtained by recrystallization from the solution as a white solid with an isolated yield of 22% (137 mg). Spectral Characterization of 3. 1H NMR (600 MHz, inCDCl3) δ 4.41 (dd, 1 H), 3.99 (t, 2 H), 3.29 (dd, 1 H), 3.05 (dd, 1 H), 1.62 (m, 2 H), 1.37 (m, 2 H), 0.95 (t, 3 H); 13C NMR (150 MHz, in CDCl3) δ 200.6, 175.3, 174.3, 45.4, 44.4, 36.7, 28.5, 19.9, 13.5. X-ray Single Crystal Diffraction of 3. White crystals of 3 suitable for X-ray diffraction were obtained by slowly diffusing hexane into the CH2Cl2 solution of 3 at room temperature. Single crystal X-ray diffraction data were collected on an instrument equipped with a CCD area detector using graphite-monochromated Mo Kα radiation (λ = 0.71070 Å) in the scan range 2.97° < θ < 25.99°. The structure was solved with SHELXS-97 and refined with SHELXL-97 program. Crystal data of 3: C9H13NO3S2, Mw = 247.32, monoclinic, space group P21/c, a = 9.7654(4) Å, b = 9.6690(4) Å, c = 12.0922(9) Å, α = 90.00°, β = 94.477(4)°, γ = 90.00°, V = 1138.28(11) Å3, Z = 4, Dcalc= 1.443Mg m‒3, μ = 0.454mm‒1, T = 103.0 K, crystal size 0.25 × 0.20 × 0.07 mm; reflections collected 8602, independent reflections 2221; 2016 with I > 2σ(I); R1 = 0.0274 [I > 2σ(I)], wR2 = 0.0637 [I > 2σ(I)]; R1 = 0.0311 (all data), wR2 = 0.0662 (all data), GOF (on F2) = 1.032. In Situ Vis-NIR Measurement. With Cu salt: butylamine (345 μL), CS2 (840 μL) and 2.8 mg 16


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of Cu(OAc)2•H2O were stirred under argon at 30 C in 20 mL of DMF for 10 min. Then 50 mg of C60 in 5 ml of o-DCB was added. Without Cu salt: butylamine (247 μL) and CS2 (604 μL) were stirred under argon at 30 C in 20 mL of DMF for 10 min. Then 36 mg of C60 in 5 ml of o-DCB mL was added. The reaction mixture was transferred into a 1-mm cuvette under argon at different time intervals, and the cuvette was sealed with a rubber septum and Parafilm for the vis-NIR measurement.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Copies of spectra of the new compounds (PDF) Crystallographic data for 2a (CIF) Crystallographic data for 3 (CIF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (21472183) and Jilin Provincial Science and Technology Department (20170101172JC). REFERENCES 1. Rudorf, W.-D. J. Sulfur Chem. 2007, 28, 295–339. 2. For example, (a) Sharma, S. K.; Wu, Y.; Steinbergs, N.; Crow-ley, M. L.; Hanson, A. S.; Casero Jr., R. A.; Woster, P. M. J. Med. Chem. 2010, 53, 5197–5212. (b) Melchini, A.; Needs, P. W.; 17



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Copper-Catalyzed Aerobic Oxidative Reaction of C60 with Aliphatic

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