A Photocatalyst-Free, SET-Mediated Photochemical Approach for the Synthesis of Dumbbell-Like Amine-Functionalized Bis-C₆₀ Fullerene through C–C Bond Formation

Abstract

A novel method for the synthesis of dumbbell-like amine-functionalized bis-C₆₀ fullerene from simple bis-α-silyl tertiary benzyl amines and C₆₀ fullerene is described. The photoreactions between bis-α-silyl tertiary benzyl amines and C₆₀ furnished single-bonded bis-aminomethyl-1,2-dihyrofullerenes and double-bonded 1,2,5-trisubstituted bis-fulleropyrrolidines through 1,3-dipolar cycloaddition reactions of azomethine ylides under mild conditions.

Key words

bis-C₆₀ fullerene - SET - photocatalyst free - 1,2-dihyrofullerenes - fulleropyrrolidines

• References and Notes

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• 23 General Procedure for Synthesis of Secondary N-Trimethylsilylmethyl-N-benzylamines 6–9: The corresponding primary amine 1–4 (1, 5823 mg; 2, 6586 mg; 3, 6801 mg; 4, 7455 mg, 54.35 mmol) was taken in acetonitrile (120 mL), and K₂CO₃ (11266 mg, 81.52 mmol) was added under argon. The reaction mixture was heated at 70 °C for 1 h and iodomethyltrimethylsilane 5 (9697 mg, 45.29 mmol) was added dropwise. The reaction mixture was stirred for 7 h at 70 °C. After completion of reaction (monitored by TLC), the mixture was concentrated in vacuo to give residues that were partitioned between water and CH₂Cl₂. The CH₂Cl₂ layers were dried and concentrated in vacuo to afford residues that were subjected to silica gel column chromatography (EtOAc/hexane = 1:1) to yield the corresponding secondary N-trimethylsilylmethyl-N-benzylamines 6 (8197 mg, 78%), 7 (9580 mg, 85%), 8 (6317 mg, 55%), and 9 (9712 mg, 80%). The spectral data matched exactly with reported data.
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• 25 General Procedure for Synthesis of Bis-α-trimethylsilyl-Substituted Tertiary Amines 13–16: The corresponding secondary amine 6–9 (6, 1160 mg; 7, 1244 mg; 8, 1268 mg; 9, 1340 mg, 6 mmol) was taken in acetonitrile (120 mL), and K₂CO₃ (1243 mg, 9 mmol) was added under argon. The reaction mixture was heated at 70 °C for 1 h and 2,2′-oxy-bis(ethane-2,1-diyl)bis(2-bromoacetate) (12; 1043 mg, 3 mmol) was added dropwise. The reaction mixture was stirred for 7 h at 70 °C. After completion of reaction (monitored by TLC), the mixture was concentrated in vacuo to give residues that were partitioned between water and CH₂Cl₂. The CH₂Cl₂ layers were dried and concentrated in vacuo to afford residues that were subjected to silica gel column chromatography (diethyl ether/hexane = 1:8) to yield the corresponding symmetrical molecules 13 (1288 mg, 75%), 14 (1442 mg, 80%), 15 (1095 mg, 60%), and 16 (1481 mg, 78%). 2,2′-Oxybis(ethane-2,1-diyl)bis(2-(benzyl((trimethylsilyl)methyl)amino)acetate): ¹H NMR: δ = 0.08 (s, 18 H), 2.23 (s, 4 H), 3.32 (s, 4 H), 3.66 (t, J = 12.30 Hz, 4 H), 3.78 (s, 4 H), 4.34 (t, J = 12.24 Hz, 4 H), 7.37–7.21 (m, 10 H); ¹³C NMR: δ = –1.5, 41.4, 45.6, 56.7, 61.3, 63.5, 126.9, 128.1, 128.7, 139.2, 170.8.
• 26 Detailed experimental procedures and characterization data are given in the Supporting Information. General Procedure for Photoreactions of C₆₀ with Bis-α-trimethylsilyl-Substituted Tertiary Benzyl Amines: Preparative photochemical reactions were conducted with a 450 W Hanovia medium vapor pressure mercury lamp surrounded by a flint glass filter (>300 nm) in a water-cooled quartz immersion well surrounded by a solution consisting of 10% EtOH–toluene of C₆₀ (201.78 mg, 0.28 mmol), and bis-α-trimethylsilyl-substituted tertiary amines 13–16 (13, 320.81 mg; 14, 336.52 mg; 15, 340.96 mg; 16, 354.44 mg, 0.56 mmol). Each solution was purged with nitrogen before and during irradiation, which was carried out for the time periods given for each substance below. The photoproducts were concentrated, and the generated residues were triturated with CHCl₃ to recover C₆₀. The triturates were concentrated in vacuo to generate residues that were subjected to silica gel column chromatography (eluants given below) to obtain the photoproducts. Photoreaction of C₆₀ with 13: In N₂-saturated conditions: 90 min irradiation, 89% conversion, column chromatography (CS₂/CHCl₃, 5:1) to yield 17 (256 mg, 49%) and 21 (22 mg, 4%). O₂-saturated conditions: 120 min irradiation, 90% conversion, column chromatography (CS₂/CHCl₃, 5:1) to yield 17 (10 mg, 2%) and 21 (286 mg, 51%). Compound 17: ¹H NMR: δ = 3.76 (t, J = 9.45 Hz, 4 H), 4.00 (s, 4 H), 4.48–4.53 (m, 8 H), 4.76 (s, 4 H), 6.90 (s, 2 H), 7.30–7.42 (m, 6 H), 7.62 (d, J = 6.60 Hz, 4 H); ¹³C NMR: δ = 41.6, 55.7, 58.0, 59.8, 64.17, 67.3, 68.4, 127.8, 128.7, 129.4, 136.0, 136.1, 138.15, 140.0, 140.2, 141.6 (2C), 141.7, 141.9, 142.0, 142.3, 142.5 (2C), 143.2, 144.4, 144.6, 145.3 (3C), 145.4, 145.8, 146.1 (2C), 146.3 (2C), 146.8, 147.2, 147.3, 154.3, 154.7, 171.1; HRMS (FAB): m/z [M + 1] calcd for C₁₄₄H₃₅N₂O₅: 1872.8212; found: 1872.9016. Compound 21: ¹H NMR: δ = 0.51 (s, 18 H), 3.57–3.68 (m, 4 H), 4.37–4.45 (m, 2 H), 4.47–4.55 (m, 2 H), 4.60 (d, J = 12.15 Hz, 2 H), 5.28 (d, J = 12.18 Hz, 2 H), 5.39 (s, 2 H), 5.51 (s, 2 H), 7.28–7.48 (m, 6 H), 7.65 (d, J = 6.30 Hz, 4 H); ¹³C NMR: δ = 0.7, 41.3, 56.2, 64.5, 70.0, 77.2, 77.6, 77.9, 127.8, 128.6, 128.9, 134.9, 135.5, 135.6, 136.3, 138.7, 139.2, 139.6, 139.7, 140.1, 141.6, 141.7, 141.8, 141.9, 142.0, 142.1 (2C), 142.2, 142.3, 142.4, 142.6, 142.7, 143.0, 143.1, 144.2, 144.3, 144.4, 144.5, 144.9, 145.1, 145.2, 145.3, 145.5, 145.8, 145.9, 146.1 (2C), 146.2, 146.6, 146.9, 147.0, 152.4, 154.7, 156.4, 156.9, 170.3; HRMS (FAB): m/z [M + 1] calcd. for C₁₅₀H₄₇N₂O₅SiO₂: 2013.1516; found: 2013.2318.