Supporting Information Reversible Microwave-Assisted Cycloaddition of Aziridines to Carbon Nanotubes Fulvio G. Brunetti, a,b M. Antonia Herrero, a,b Juan de M. Muñoz, b Silvia Giordani, a Angel Díaz-Ortiz, b Salvatore Filippone, c Giorgio Ruaro, d Moreno Meneghetti, d Maurizio Prato,*,a and Ester Vázquez*,b a Dipartimento di Scienze Farmaceutiche, Università di Trieste, Piazzale Europa, 1, I- 34127 Trieste, Italy. E-mail: prato@units.it b Departamento de Química Orgánica, Facultad de Químicas, Universidad de Castilla- La Mancha, 13071 Ciudad Real, Spain. E-mail: Ester.vazquez@uclm.es c Departamento de Química Orgánica I, Facultad de Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain. d Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131 Padova, Italy
Experimental section Techniques. Microwave irradiations were conducted in a CEM DISCOVER reactor, with infrared pyrometer and pressure control system, and stirring and air-cooling option. UV-Vis-NIR spectra were recorded in 1 cm quartz cuvettes on a Varian Cary 5000 spectrophotometer and on a Jasco V-530 spectrophotometer. IR spectra were recorded on a FT-IS Shimazdu spectrophotometer. The thermogravimetric analyses were performed with a TGA Q500 TA Instruments at 10 C/min under N 2. 1 H and 13 C-NMR spectra were recorded on a Varian Innova-500 spectrometer at 500 and 125 MHz respectively, in CDCl 3 using TMS as internal standard. Chemical shifts are given in ppm relative to that of tetramethylsilane. For the TEM analyses: a small amount of the functionalized SWNTs was suspended in DMF and a drop of the suspension was placed on a copper grid (3.00 mm, 200 mesh, coated with carbon film). After air-drying the sample was investigated by TEM Philips EM 208, accelerating voltage of 100 kv. Materials. Solvents were purchased from SDS and Fluka. All dry solvents were freshly distilled under argon over an appropriate drying agent before use. Chemicals were purchased from Sigma-Aldrich or Acros Organics and used as received without further purification. HiPCO SWNTs were purchased from Carbon Nanotechnologies Inc. lot # R0496 (www.cnanotech.com) and MWNT from Nanostructured & Amorphus Materials Inc. OD 20-30 nm Stock # 1240HX and use without purification. Synthesis N-(octyl)-2-carbethoxy aziridine 1 A solution of ethyl 2,3-dibromopropionate (5.00 g, 19.24 mmol) in dry THF (75 ml) was cooled with an ice-bath under nitrogen atmosphere. A solution of octylamine (3.00 ml, 19.24 mmol) and triethylamine (5.35 ml, 38.48 mmol) in 75 ml of dry THF was added dropwise over a period of 60 min. The ice-bath was removed and the mixture was
allowed to react at room temperature overnight and then filtered to remove Et 3 NHBr salt. The solvent was evaporated to dryness and purification of the product by column chromatography (hexane/acoet 10:2) gave pure aziridine 1 (3.95 g, 90%). 1 H RMN: 4.25-4.12 (m, 2H, -OCH 2 ), 2.35-2.25 (m, 2H, -NCH 2 ), 2.15 (dd, 1H, -CHH, J = 1.2-3.0 Hz), 1.99 (dd, 1H,- CH, J = 3.0, 6.4 Hz), 1.59 (q, 2H, -CH 2, J = 7.3 Hz), 1.55 (dd, 1H, -CHH, J = 1.2-6.4 Hz), 1.26-1.33 (m, 13H, [-CH 2 ] 5/ -CH 3 ), 0.87 (t, 3H, -CH 3, J = 7 Hz). 13 C RMN: 171 (CO), 61.1 (-CH 2 N), 60.9 (-O-CH 2 CH 3 ), 37.3 (-CH-COOEt), 34.5 (-CH 2 N-CH), 31.7(-CH 2 -), 29.4 (2-CH 2 -), 29.1 (-CH 2 -), 27.1 (-CH 2 -), 22.5 (-CH 2 - ), 14.1 (-CH 3 ), 14 (-CH 3 ). IR (NaCl): cm 1 3437, 2920, 2848, 1733, 1470, 1180. Fulleropyrrolidine 3 A mixture of C 60 (50.0 mg, 0.069 mmol) and aziridine 1 (17.5 mg, 0.08 mmol) in o- dichlorobenzene (O-DCB) (20 ml) was heated to reflux for 5 hours. After cooling the solution to room temperature, the product was purified by column chromatography (eluent toluene/hexane 8:2, then toluene/methanol 9:1) and then precipitated from CH 2 Cl 2 solution with methanol. C 73 H 25 NO 2 (947.97 g/mol), 7.5 mg, 0.008 mmol, yield 11.5 % 1 H-NMR: δ= 5.05 (d, 1H, -CHH, J = 9.15 Hz), 5.06 (s, 1H, -CH), 4.34-4.41 (m, 2H, -O- CH 2 -), 4.32 (d, 1H, -CHH-, J = 9.52 Hz), 3.35 3.41 (m, 1H, -N-CHH-CH 2 -), 2.93 2.98 (m, 1H, N-CHH-CH 2 -), 1.99 2.05 (m, 1H, -CH 2 -), 1.92 1.99 (m, 1H, -CH 2 -), 1.27 1.65 (m, 10H, -(CH 2 ) 5 -), 0.90 (t, 3H, -CH 3, J = 7 Hz); 13 C-RMN: 170.3, 155.1, 154.0, 151.4, 147.7, 147.6, 146.6, 146.5, 146.5, 146.3, 146.1, 146.0, 145.9, 145.7, 145.7, 145.6, 145.6, 145.5, 144.9, 144.9, 144.8, 144.8, 144.7, 143.4, 143.3, 142.9, 142.5, 142.4, 142.3, 142.2, 142.1, 142.0, 140.5, 140.5, 140.1, 139.8, 138.0, 136.9, 136.3, 135.7, 77.9, 73.1, 69.8, 65.6, 61.7, 53.1, 32.1, 29.8, 29.6, 28.5, 27.8, 23.0, 14.7,
14.4. IR (KBr): cm 1 2916, 2846, 2777, 1737, 1458, 1429, 1325, 1184, 765, 721. UV/vis (Toluene): λ max 278, 322, 431, 700 nm. MALDI-TOF MS: m/z = 947.5 [M + ] Functionalization of SWNTs under microwave irradiation in solvent-free conditions. 2a, 2b and 2c 25 mg of SWNT was suspended in CH 2 Cl 2 (2 ml) with aziridine 1 (150 mg, 0.66 mmol) in a microwave quarz vessel; after sonication for 5 minutes, the solvent was evaporated under reduced pressure, the vessel was closed and the mixture were irradiated for 1 hour at different power and temperature (see table S1a). After that time, the crude was re-suspended in 75 ml of CH 2 Cl 2 and sonicated for 5 minutes. The solution was filtered on a Millipore membrane (PTFE 0.2µm) and the collected black solid was washed with 75 ml of methanol and with 75 ml of CH 2 Cl 2 (sonicated and filtered) affording 24 mg of the f-swnts 2a. The overall sequence was repeated two times to afford f-swnts 2b and 2c. (2c solubility 1 in CH 2 Cl 2 0.11 mg ml -1 see S12, in DMF 0.13 mg ml -1 ) Functionalization of SWNT under classical conditions, 2d A suspension of SWNT (23 mg) in dry DMF (20 ml) was first sonicated for 10 minutes and then aziridine 1 (150 mg, 0.66 mmol) was added. The reaction mixture was heated at 120 C for 5 days. After cooling to room temperature, the suspension was diluted by adding 50 ml of CH 2 Cl 2, sonicated for 5 minutes and filtered on a Millipore membrane (PTFE 0.2µm). The collected black solid was washed with 75 ml of Methanol and 75 ml of CH 2 Cl 2 (sonicated and filtered) affording 26 mg of the f-swnts 2d. (See S2 and S3 for characterization data)
Functionalizacion of MWNTs under microwave irradiation in solvent-free conditions. f-mwnts, 2e 278 mg of MWNT was suspended in CH 2 Cl 2 (20 ml) with aziridine 1 (1.45 g, 6.4 mmol) in a microwave vessel; after sonication for 5 minutes, the solvent was evaporated under reduced pressure, the vessel was closed and the mixture were irradiated for 1 hour at different power and temperature (see table S1b). After that time, the crude was resuspended in 200 ml of CH 2 Cl 2 and then in 200 ml of methanol, sonicated for 5 minutes and then filtered on a Millipore membrane (PTFE 0.2µm). The collected black solid was washed several times with CH 2 Cl 2 (sonicated, and filtered) until the supernatant solution remained colourless affording 287 mg of f-mwnts 2e. (2e solubility 1 in CH 2 Cl 2 0.55 mg ml -1 see S13, in DMF 0.40 mg ml -1 ). (See S4 and S5 for characterization data) Retro-cycloaddition of f-mwnts, 2f 250 mg of f-mwnts 2e were heated to 150 C in o-dichlorobenzene (100 ml) with C 60 (70 mg, 0.1 mmol) and a catalytic amount of CuTf 2 for 48 hours. The crude was filtrated on a Teflon filter 0.2 µm and the recovered MWNTs 2f were washed with methanol (200 ml) and chloroform (200 ml) affording 230 mg. (See S6 and S7 for characterization data) The filtrate was collected, evaporated under reduced pressure and purified by silica gel column chromatography using Hexane to remove the excess of C 60 and then Toluene/ Methanol 90:10 to collect all the cycloaddition products. These products were further purified using a HPLC Semipreparative Phenomenex silica column; Toluene/Hexane 80:20, flow rate: 1 ml/min, λ = 320 nm
Retro-cycloaddition of f-swnts, 2h 50 mg of f-swnts 2g were heated to 150 C in o-dichlorobenzene (50 ml) with C 60 (40 mg, 0.05 mmol) and a catalytic amount of CuTf 2 for 48 hours. The crude was filtrated on a Teflon filter 0.2 µm and the recovered SWNTs 2h were washed with methanol (100 ml) and two times with chloroform (2x100 ml) affording 48 mg. (See S8, S9, S10 and S11 for characterization data) The filtrate was collected, evaporated under reduced pressure and purified by silica gel column chromatography using Hexane to remove the excess of C 60 and then a mixture of Toluene / Methanol 90:10 to collect all the cycloaddition products. These products were further purified using a HPLC Semipreparative Phenomenex silica column; Toluene/Hexane 80:20, flow rate: 1 ml/min, λ = 320 nm.
a) functionalization of 25 mg of CNTs. b) functionalization of 250 mg of CNTs. Ramp Hold Ramp Hold Power Temperature Power Temperature Step time time Step time time (W) (ºC) (W) (ºC) (min.) (min.) (min.) (min.) 1 50 0.3 0.3 130 1 30 0.3 0.3 130 2 30 0 1 131 2 20 0 1 131 3 50 0 0.3 140 3 30 0 0.3 140 4 30 0 1 145 4 20 0 1 145 5 50 0 60 160 5 30 0 60 160 Fig. S1 Irradiation steps used at the CEM microwave 100 Loss weight (%) 90 11.8% 80 200 400 600 800 1000 Temperature (ºC) Fig.S2. TEM pictures of 2d Fig. S3. TGA of 2d 100 Loss weight (%) 6 % 90 200 400 600 800 1000 Temperature (ºC) Fig.S4. TEM pictures of 2e Fig. S5. TGA of 2e
100 Loss weight (%) 4.7 % 90 200 400 600 800 1000 Temperature (ºC) Fig.S6. TEM pictures of 2f Fig. S7. TGA of 2f 100 Loss w eight (% ) 90 9.5 % 200 400 600 800 1000 Temperature ( o C) Fig.S8. TEM pictures of 2h Fig.S9. TGA 2h 1.0 0.8 Pristine 2h 2g 1.0 Pristine 2h 2g Intensity (a.u.) 0.6 0.4 0.2 Absorption (a.u.) 0.8 0.6 0.4 0.0 500 1000 1500 2000 2500 3000 3500 Raman shift (cm -1 ) 0.2 300 600 900 1200 1500 Wavelength (nm) Fig.S10. Raman, pristine, 2h, 2g Fig.S11. UV-VIS-NIR, pristine, 2h, 2g
Fig. S12. Solutions of SWNTs in CH 2 Cl 2. Pristine SWNTs on the left, f-swnts 2c on the right (0.11 mg/ml) Fig. S13. Solutions of MWNTs in CH 2 Cl 2. Recovered MWNTs after the retrocycloaddition on the left 2f, f-mwnts 2e on the right (0.55 mg/ml). References. 1 Christopher A. Dyke, James M. Tour Chem. Eur. J. 2004, 10, 812.