Nitration of Fullerene Derivatives under Mild Conditions

Abstract

A new family of N-(2,4-dinitrophenyl)-2-pyrazolino[60]fullerene derivatives has been synthesized by electrophilic nitration using nitronium triflate. As evidenced by CV and OSWV experiments, these species show enhanced electron-accepting ­properties (up to 90 mV) with respect to C₆₀.

fullerene - electrochemistry - electrophilic aromatic substitution

References and Notes

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13

Compound 2b: A solution of p-nitrophenylhydrazine (1.0 g, 6.5 mmol), 3,5,5-trimethylhexanal (0.82 g, 6.5 mmol) and two drops of AcOH in EtOH (50 mL) was heated under reflux for 2 h. The solid was filtered off and recrystallized in EtOH to give 2b as a red solid (1.47 g, 82%); mp 82.3-82.7 °C. ¹H NMR (200 MHz, CDCl₃): δ = 8.13 (d, J = 9.2 Hz, 2 H), 7.90 (s, 1 H), 7.19 (t, 1 H), 6.99 (d, J = 9.2 Hz, 2 H), 2.10-2.40 (m, 2 H), 1.85 (m, 1 H), 1.32 (dd, J ₁ = 3.4 Hz, J ₂ = 14.0 Hz, 1 H), 1.13 (dd, J ₁ = 6.2 Hz, J ₂ = 14.0 Hz, 1 H), 1.01 (d, J = 6.6 Hz, 3 H), 0.91 (s, 9 H). ¹³C NMR (50 MHz, CDCl₃): δ = 150.3, 145.3, 144.5, 140.4, 139.7, 126.4, 126.3, 112.0, 111.3, 50.8, 50.6, 41.6, 35.7, 31.3, 31.3, 30.1, 28.2, 27.7, 23.0, 22.8. FT-IR (ATR): 3289, 2941, 1617, 1511, 1335, 1266 cm^-1. Anal. Calcd for C₁₅H₂₃N₃O₂: C, 64.95; H, 8.36; N. 15.15. Found: C, 64.43; H, 8.13; N, 15.21.
Compound 3b: To a solution of hydrazone 2b (115 mg, 0.41 mmol) in anhyd CHCl₃ (10 mL) was added, under an Ar atmosphere, NBS (148 mg, 0.82 mmol). The mixture was kept under agitation during 2 h at r.t. The solvent was removed and an anhyd toluene (250 mL) solution of C₆₀ (300 mg) and Et₃N in excess were then added. The reaction was kept under agitation at r.t. for 1.75 h. The toluene was then evaporated under vacuum. The remaining solid was purified by column chromatography (silica gel; toluene-hexane, 2:1) to give 3b in 41% yield. ¹H NMR (200 MHz, CDCl₃): δ = 8.30 (d, J = 9.6 Hz, 2 H), 8.16 (d, J = 9.6 Hz, 2 H), 3.15 (dd, J ₁ = 5.9 Hz, J ₂ = 16.0 Hz, 1 H), 2.99 (dd, J ₁ = 8.0 Hz, J ₂ = 16.0 Hz, 1 H), 2.53 (m, 1 H), 1.65 (dd, J ₁ = 4.2 Hz, J ₂ = 14.6 Hz, 1 H), 1.37 (dd, J ₁ = 6.6 Hz, J ₂ = 14.7 Hz, 1 H), 1.33 (d, J = 6.5 Hz, 3 H), 0.99 (s, 9 H). ¹³C NMR (50 MHz, CDCl₃): δ = 150.47, 149.15, 147.94, 147.39, 146.75, 146.67, 146.56, 146.39, 146.34, 146.16, 145.76, 145.61, 145.53, 145.47, 145.34, 144.89, 144.64, 144.35, 143.74, 143.46, 143.20, 143.11, 142.64, 142.60, 142.50, 142.29, 141.82, 141.22, 141.14, 139.52, 139.44, 137.25, 136.24, 136.13, 129.28, 128.47, 125.76, 125.54, 118.58, 88.84, 84.28, 51.56, 39.37, 31.53, 31.21, 30.50, 29.96, 28.64, 23.34. FT-IR (KBr): 2941, 1597, 1535, 1335, 530 cm^-1. MALDI-TOF: m/z calcd for C₇₅H₂₁N₃O₂: 995.98; found: 995.9.

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16 Shackelford SA. Anderson MB. Christie LC. Goetzen T. Guzman MC. Hananel MA. Kornreich WD. Li H. Pathak VP. Rabinovich AK. Rajapakse RJ. Truesdale LK. Tsank SM. Vazir HN. J. Org. Chem.  2003,  68:  267 

17

Experimental Procedure: To an anhyd CH₂Cl₂ solution of the corresponding fullerene derivative 2 (1 equiv) in CH₂Cl₂, tetramethylammonium nitrate (2 equiv) was added under Ar. The solution was cooled to the desired temperature and triflic anhydride (2 equiv) was added. NO₂OTf was formed in situ and the solution was kept at this temperature until the complete disappearance of the starting material (the reaction progression was followed by TLC). The reaction was then quenched by adding a Na₂CO₃ solution (pH 8). The organic layer was separated, dried and evaporated. The remaining solid was purified by column chromatography affording the desired compounds 1a-d.
Compound 1a: reaction temperature: -5 °C for 4 h. Column chromatography (silica gel; toluene-hexane, 1:2); yield: 90%. ¹H NMR (500 MHz, CDCl₃): δ = 8.80 (d, J = 2.5 Hz, 1 H), 8.45 (dd, J ₁ = 2.5 Hz, J ₂ = 9.0 Hz, 1 H), 8.40 (sd, J = 9.0 Hz, 1 H), 2.79 (s, 3 H).¹³C NMR (125 MHz, CDCl₃): δ = 149.36, 147.79, 147.21, 146.38, 146.32, 146.08, 145.96, 145.34, 145.49, 145.29, 145.28, 145.24, 144.41, 144.23, 144.09, 143.97, 143.21, 143.07, 143.04, 142.95, 142.93, 142.84, 142.40, 142.24, 142.18, 142.05, 142.02, 141.06, 139.81, 137.31, 136.55, 127.10, 126.28, 122.22, 88.90, 83.39, 15.03. FT-IR (KBr): 2917, 2357, 1601, 1527, 1331, 526 cm^-1. UV-Vis: λ (log ε) = 255.0 (6.1), 320.0 (5.6) nm. MALDI-TOF: m/z calcd for C₆₈H₆N₄O₄: 942.94; found: 942.0.
Compound 1b: reaction temperature: -5 °C for 5 h. Column chromatography (silica gel; toluene-hexane, 1:2); yield: 85%. ¹H NMR (500 MHz, CDCl₃): δ = 8.78 (d, J = 2.4 Hz, 1 H), 8.44 (dd, J ₁ = 2.5 Hz, J ₂ = 9.0 Hz, 1 H), 8.40 (sd, J = 9.0 Hz, 1 H), 3.11 (dd, J ₁ = 4.6 Hz, J ₂ = 16.5 Hz, 1 H), 2.95 (dd, J ₁ = 8.8 Hz, J ₂ = 16.5 Hz, 1 H), 2.45 (m, 1 H), 1.54 (dd, J ₁ = 4.5 Hz, J ₂ = 14.0 Hz, 1 H), 1.33 (dd, J ₁ = 6.2 Hz, J ₂ = 14.0 Hz, 1 H), 1.27 (d, J = 6.6 Hz, 3 H), 0.99 (s, 9 H). ¹³C NMR (125 MHz, CDCl₃): δ = 151.63, 147.77, 147.20, 146.37, 146.36, 146.31, 146.31, 146.07, 146.06, 146.05, 145.96, 145.95, 145.55, 145.53, 145.51, 145.46, 145.43, 145.42, 145.32, 145.29, 145.28, 145.26, 145.25, 144.40, 144.29, 144.24, 144.10, 144.09, 144.06, 143.21, 143.01, 142.97, 142.85, 142.83, 142.75, 142.42, 142.40, 142.26, 142.24, 142.19, 142.16, 142.12, 142.10, 142.01, 142.00, 140.95, 140.90, 139.84, 139.79, 137.31, 136.45, 136.26, 126.99, 126.00, 122.19, 88.84, 83.84, 51.39, 39.25, 31.26, 30.04, 28.07, 22.98. FT-IR (KBr): 2941, 2337, 1597, 1540, 1335, 526 cm^-1. UV-Vis: λ (log ε) = 255.0 (6.2), 320.0 (5.7) nm. MALDI-TOF: m/z calcd for C₇₅H₂₀N₄O₄: 1040.98; found: 1040.1.
Compound 1c: reaction temperature: r.t. for 2 h. Column chromatography (silica gel; toluene-hexane, 2:1); yield: 65%. ¹H NMR (500 MHz, CDCl₃): δ = 8.87 (d, J = 2.5 Hz, 1 H), 8.52 (dd, J ₁ = 2.5 Hz, J ₂ = 9.0 Hz, 1 H), 8.49 (sd, J = 9.0 Hz, 1 H), 8.38 (d, J = 9.0 Hz, 2 H), 8.36 (d, J = 9.0 Hz, 2 H). ¹³C NMR (125 MHz, CDCl₃): δ = 148.61, 147.79, 147.32, 147.13, 146.46, 146.42, 146.14, 146.08, 145.60, 145.56, 145.38, 145.33, 145.16, 144.69, 144.33, 144.16, 144.15, 144.08, 143.95, 143.28, 143.07, 142.99, 142.94, 142.49, 142.32, 142.26, 142.08, 141.99, 141.95, 140.64, 140.12, 137.38, 137.21, 136.90, 129.73, 127.32, 127.13, 124.24, 122.20, 91.39, 81.42. FT-IR (KBr): 2357, 1597, 1535, 1335, 526. UV-Vis: λ (log ε) = 245.5 (6.3), 321.5 (5.9) nm. MALDI-TOF: m/z calcd for C₇₃H₇N₅O₆: 1049.87; found: 1050.2.
Compound 1d: reaction temperature: r.t. for 3 h. Column chromatography (silica gel; toluene-hexane, 1:2); yield: 47%. ¹H NMR (500 MHz, CDCl₃): δ = 8.88 (d, J = 2.5 Hz, 1 H), 8.67 (br s, 2 H), 8.53 (dd, J ₁ = 2.5 Hz, J ₂ = 9.0 Hz, 1 H), 8.48 (sd, J = 9.0 Hz, 1 H), 8.00 (br s, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 148.07, 147.58, 146.72, 146.68, 146.40, 146.35, 145.97, 145.79, 145.66, 145.59, 145.12, 144.59, 144.41, 144.16, 144.13, 143.54, 143.33, 143.25, 143.18, 142.73, 142.58, 142.53, 142.31, 142.25, 140.89, 140.40, 137.64, 137.29, 133.46, 132.90, 132.63, 128.93, 127.57, 124.26, 123.99, 122.43, 122.11, 91.81, 81.44. FT-IR (KBr): 2921, 2332, 1597, 1531, 1331, 1274, 1135, 526 cm^-1. UV-Vis: λ (log ε) = 254.5 (6.1), 319.0 (5.7) nm. MALDI-TOF: m/z calcd for C₇₅H₆F₆N₄O₄: 1140.86; found: 1141.2.

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