Facile Synthesis of Methanofullerenes in an Aqueous Two-Phase System under Photoirradiation Conditions

Abstract

Methanofullerenes, such as [6,6]-phenyl-C₆₁-butyric acid methyl ester {[6,6]PC₆₁BM (1a)}, were synthesized in good yields from the corresponding tosylhydrazones in an aqueous two-phase (o-dichlorobenzene–H₂O) system under photoirradiation conditions. This simple and convenient procedure was adopted for the synthesis of thienyl analogues of PC₆₁BM and its C₇₀ analogue, PC₇₁BM.

Key words

photovoltaics - fullerenes - hydrazones - methanofullerenes - PCBM

• References and Notes

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• 17 General Procedure for the Synthesis of Methanofullerenes under Photoirradiation Conditions Under Ar atmosphere, to a solution of tosylhydrazone (18.7 mg, 0.050 mmol) in ODCB (2.0 mL) was added a solution of TBAH (1.0 M in H₂O, 0.05 mL, 0.050 mmol) in H₂O (1.95 mL), and the mixture was stirred at r.t. for 0.5 h. A solution of C₆₀ (36.0 mg, 0.050 mmol) in ODCB was added to the mixture, and the mixture was stirred (800–1000 rpm by magnetic stirrer), heated in an oil bath, and irradiated with a 375 W incandescent lamp for 2 h. During the irradiation, the oil bath temperature was kept at 105–115 °C by adjusting the distance between the light source and the flask was approximately 15 cm. After the reaction, the layers were separated and the aqueous phase was extracted with toluene (2 × 5 mL). The combined organic phase was dried over MgSO₄, filtered, and concentrated to 1 mL under reduced pressure. The residue was purified by silica gel column chromatography [silica gel; 20 g, eluent; toluene for C₆₀ and monoadduct, toluene–CH₂Cl₂ (1:2) for bisadducts], and the obtained [6,6]PC₆₁BM (1a) was dissolved in a small amount of toluene and transferred to a 50 mL centrifuge tube. MeOH (ca. 30 mL) was added, and the mixture was immersed in an ultrasound bath for 1 min, the suspension was centrifuged (4000 rpm, 30 min), the supernatant was decanted, and the residue was treated with MeOH in the same manner. The product was dried in vacuo at 60 °C. [6,6]PC₆₁BM (1a, 23.5 mg, 0.026 mmol, 52%) was obtained as brown powder. Unreacted C₆₀ (7.8 mg, 0.011 mmol, 22%) and bisadducts (10.9 mg, 0.010 mmol, 20%) were isolated in the same manner. Analytical Data for 1a ¹H NMR (300 MHz, CDCl₃): δ = 7.92 (d, J = 8.7 Hz, 2 H), 7.60–7.44 (m, 3 H), 3.68 (s, 3 H), 2.94–2.88 (m, 2 H), 2.52 (t, J = 7.5 Hz, 2 H), 2.23–2.13 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 173.40, 148.79–136.71, 132.06, 128.43, 128.24, 79.87, 51.85, 51.64, 33.87, 33.67, 22.37. IR (KBr): 2921, 2849, 1735, 699, 573, 550, 526, 482, 453 cm^–1. MS (MALDI): m/z calcd for C₇₂H₁₄O₂: 910.1; found: 910.1 [M]^–.

A few pieces of research for the synthesis of methanofullerenes using flow synthesis have been reported:
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