Recyclable Polystyrene-Supported Copper Catalysts for the Aerobic Oxidative Homocoupling of Terminal Alkynes

Abstract

Polystyrene-supported copper(II) N,N,N′,N′-tetraethyldiethylenetriamine [Cu(II)–TEDETA] complexes were prepared by immobilization of TEDETA onto crosslinked polystyrene resin, followed by complexation with copper salts. The polystyrene-immobilized CuSO₄–TEDETA complex efficiently catalyzed the oxidative homocoupling of terminal alkynes under air to give the corresponding 1,3-diynes in up to 99% yield. The catalyst was easily recovered by simple filtration and reused eight times without significant loss of catalytic activity.

Key words

termial alkynes - 1,3-diynes - homocoupling - polystyrene - copper sulfate

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• 7 Preparation of Polystyrene-Supported N,N,N′,N′-Tetraethyldiethylenetriamine (PS–TEDETA) A mixture of chloromethylated polystyrene (1.0 g, 2.4 mmol/Cl), PS–TEDETA (2.47 mL, 9.6 mmol), Et₃N (1.33 mL, 9.6 mmol), and NaI (14.9 mg, 0.1 mmol) in MeCN (100 mL) was refluxed for 72 h. After cooling the mixture was filtered, and the resulting resin beads were washed sequentially with MeCN (3 × 10 mL), MeOH–H₂O (1:1, 3 × 10 mL), MeOH (3 × 10 mL), CH₂Cl₂ (3 × 10 mL), Et₂O (3 × 10 mL), and then dried in vacuo.
• 8 Preparation of Polystyrene-Supported CuSO₄–TEDETA Complex (A) A mixture of PS–TEDETA (200 mg) and CuSO₄·5H₂O (0.504 mmol) in EtOH (3 mL) was stirred at 50 °C for 6 h. After cooling the mixture was filtered, and the resulting resin beads were washed with EtOH (10 × 4 mL), dried in vacuo overnight to provide the corresponding polystyrene-supported Cu(II)–TEDETA complex (A). The loading value of copper was determined by ICP analysis: 1.16 mmol/g. Other polystyrene-supported Cu(II)–TEDETA complexes B and C were prepared following a similar procedure.
• 9 Further screening of solvents and bases under the conditions in entry 1 are shown in Table S1 in the Supporting Information. Among them, CH₂Cl₂ gave the highest yield (99% GC yield), but the color of the solution is bluer than other solvents. This result clearly indicated that the leaching of copper occurred quickly in CH₂Cl₂.
• 10 The yield was not improved significantly (88% GC yield) even when the reaction time was prolonged to 36 h.
• 11 Polystyrene–polyethylene glycol (PS–PEG) resin-supported CuSO₄–TEDETA complex was also prepared and applied to the oxidative homocoupling of ethynylbenzene 1a under the conditions in entry 8 (Table 1). The desired product 2a was obtained in 91% GC yield. However, ICP analysis indicated that 55.5% of copper was leached to the solution.
• 12 Procedure for the Oxidative Homocoupling of Terminal Alkynes A mixture of catalyst (PS–TEDETA–CuSO₄, 0.05 mmol of Cu), ethynylbenzene (1a, 0.5 mmol) and piperidine (0.5 mmol) in toluene (1.0 mL) was stirred at 60 °C for 24 h under air. After cooling, the mixture was filtered, and the residue was washed by CH₂Cl₂ (3 × 2 mL). The combined organic phases were concentrated in vacuo, and the crude products were purified by column chromatography (hexane–EtOAc = 99:1, R_f = 0.7) to give the corresponding product 2a. 1,4-Diphenylbuta-1,3-diyne (2a) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.54–7.52 (m, 4 H), 7.39–7.31 (m, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 132.5, 129.2, 128.4, 121.7, 81.5, 73.9 ppm. 1,4-Bis(p-methoxyphenyl)buta-1,3-diyne (2b) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.46 (d, J = 9.0 Hz, 4 H), 6.85 (d, J = 9.0 Hz, 4 H), 3.82 (s, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 160.2, 134.0, 114.1, 113.9, 81.2, 72.9, 55.3 ppm. 1,4-Di[(1,1′-biphenyl)-4-yl]buta-1,3-diyne (2c) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.63–7.54 (m, 12 H), 7.48–7.44 (m, 4 H), 7.40–7.36 (m, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 141.9, 140.1, 132.9, 128.9, 127.9, 127.1, 127.0, 120.6, 81.8, 74.6 ppm. 1,4-Bis(p-pentylphenyl)buta-1,3-diyne (2d) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.43 (d, J = 8.2 Hz, 4 H), 7.14 (d, J = 8.2 Hz, 4 H), 2.60 (t, J = 8.2 Hz, 4 H), 1.62–1.55 (m, 4 H), 1.32–1.28 (m, 8 H), 0.89 (t, J = 6.6 Hz, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 144.5, 132.4, 128.5, 118.9, 81.6, 73.5, 35.9, 31.4, 30.8, 22.5, 14.0 ppm. 1,4-Di(p-tolyl)buta-1,3-diyne (2e) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.41 (d, J = 8.6 Hz, 4 H), 7.14 (d, J = 8.6 Hz, 4 H), 2.36 (s, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 139.5, 132.4, 129.2, 118.7, 81.5, 73.4, 21.6 ppm. 1,4-Bis[4-(trifluoromethyl)phenyl]buta-1,3-diyne (2f) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.63 (br s, 8 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 132.8, 131.1 (d, J = 32.6 Hz, 1 C), 126.9 (q, J = 3.6 Hz, 1 C), 125.2 (d, J = 2.0 Hz, 1 C), 123.7 (d, J = 274.0 Hz, 1 C), 80.9, 75.6 ppm. 1,4-Bis(p-fluorophenyl)buta-1,3-diyne (2g) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.51 (dd, J = 8.8, 5.6 Hz, 4 H), 7.05 (dd, J = 8.8, 5.6 Hz, 4 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 163.0 (d, J = 252.9 Hz, 1 C), 134.5 (d, J = 8.6 Hz, 1 C), 117.8 (d, J = 3.9 Hz, 1 C), 115.9 (d, J = 22.1 Hz, 1 C), 80.4, 73.5 ppm. 1,4-Bis(p-carbomethoxyphenyl)buta-1,3-diyne (2h) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 8.02 (d, J = 8.8 Hz, 4 H), 7.60 (d, J = 8.8 Hz, 4 H), 3.93 (s, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 166.3, 132.5, 130.5, 129.6, 126.1, 81.8, 76.2, 52.4 ppm. 1,4-Di(m-tolyl)buta-1,3-diyne (2i) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.33–7.32 (m, 4 H),7.23–7.16 (m, 4 H), 2.33 (s, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 138.1, 132.9, 130.1, 129.6, 128.3, 121.6, 81.6, 73.6, 21.2 ppm. 1,4-Di(o-tolyl)buta-1,3-diyne (2j) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.50 (d, J = 7.2 Hz, 2 H), 7.27–7.20 (m, 4 H), 7.17–7.13 (m, 2 H),2.49 (s, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 141.6, 132.9, 129.5, 129.1, 125.6, 121.7, 81.1, 77.5, 20.7 ppm. 1,4-Bis[2-(trifluoromethyl)phenyl]buta-1,3-diyne (2k) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.69 (dd, J = 8.0, 7.6 Hz, 4 H), 7.50 (dd, J = 7.2, 6.4 Hz, 2 H), 7.47 (dd, J = 7.6, 7.2 Hz, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 135.1, 132.5 (q, J = 0.6 Hz, 1 C), 132.1, 129.1, 126.0 (q, J = 4.8 Hz, 1 C), 123.2 (d, J = 275 Hz, 1 C),119.7 (q, J = 1.9 Hz, 1 C), 78.7, 78.6 ppm. 1,4-Bis(2-fluorophenyl)buta-1,3-diyne (2l) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.54–7.50 (m, 2 H), 7.39–7.34 (m, 2 H), 7.15–7.08 (m, 4 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 163.7 (d, J = 254.9 Hz, 1 C), 134.3, 131.1 (d, J = 7.7 Hz, 1 C), 124.1 (d, J = 3.8 Hz, 1 C), 115.7 (d, J = 20.2 Hz, 1 C), 110.4 (d, J = 15.3 Hz, 1 C), 78.3, 75.8 ppm. 1,4-Di(naphthalen-1-yl)buta-1,3-diyne (2m) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 8.43 (d, J = 8.0 Hz, 2 H), 7.88 (dd, J = 7.8, 2.6 Hz, 4 H), 7.83 (dd, J = 7.0, 1.0 Hz, 2 H), 7.65–7.61 (m, 2 H), 7.57–7.53 (m, 2 H), 7.48–7.44 (m, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 133.9, 133.1, 132.1, 129.8, 128.5, 127.2, 126.7, 126.1, 125.2, 119.5, 80.9, 78.7 ppm. 1,4-Di(cyclohexenyl)buta-1,3-diyne (2n) Colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 6.26–6.24 (m, 2 H), 2.14–2.09 (m, 8 H), 1.66–1.54 (m, 8 H). ¹³C NMR (100 MHz, CDCl₃): δ = 138.1, 119.9, 82.7, 71.5, 28.7, 25.9, 22.1, 21.3 ppm. 1,6-Diphenoxyhexa-2,4-diyne (2o) White solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.30 (dd, J = 8.4, 7.6 Hz, 4 H), 7.00 (t, J = 7.6 Hz, 2 H), 6.94 (d, J = 8.4 Hz, 4 H), 4.74 (s, 4 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 157.3, 129.5, 121.7, 114.8, 74.6, 71.0, 56.1 ppm. 1,8-Bis(benzoxy)octa-3,5-diyne (2p) White solid; mp 88–89 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.06–8.04 (m, 4 H), 7.59–7.54 (m, 2 H), 7.46–7.42 (m, 4 H), 4.41 (t, J = 6.8 Hz, 4 H), 2.74 (t, J = 6.8 Hz, 4 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 166.2, 133.1, 129.7, 129.6, 128.4, 73.5, 66.6, 62.2, 19.8 ppm. IR (ATR, neat): 3063, 2920, 1715, 1450, 1386, 1265, 1116, 1021, 985, 704, 684, 677 cm^–1. ESI-HRMS: m/z calcd for C₂₂H₁₉O₄ [M⁺ + H]: 347.1283; found: 347.1284. Dibenzyldodeca-5,7-diynedioate (2q) Colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.39–7.29 (m, 10 H), 5.11 (s, 4 H), 2.48 (t, J = 7.2 Hz, 4 H), 2.32 (t, J = 6.8 Hz, 4 H), 1.89–1.82 (m, 4 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 172.7, 135.8, 128.5, 128.2, 128.1, 76.3, 66.2, 66.0, 32.9, 23.4, 18.6 ppm. IR (ATR, neat): 3033, 2942, 1731, 1455, 1212, 1148, 968, 736, 696 cm^–1. ESI-HRMS: m/z calcd for C₂₆H₂₇O₄ [M⁺ + H]: 403.1909; found: 403.1906. Deca-4,6-diyne-1,10-diol (2r) Colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 3.74 (t, J = 6.2 Hz, 4 H), 2.39 (t, J = 7.0 Hz, 4 H), 1.89 (br s, 2 H), 1.81–1.75 (m, 4 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 76.8, 65.6, 61.3, 30.9, 15.7 ppm. Hexadeca-7,9-diyne (2s) Colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 2.24 (t, J = 7.2 Hz, 4 H), 1.55–1.48 (m, 4 H), 1.42–1.22 (m, 12 H), 0.89 (t, J = 7.2 Hz, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 77.5, 65.2, 31.3, 28.5, 28.3, 22.5, 19.2, 14.0 ppm. Icosa-9,11-diyne (2t) Colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 2.24 (t, J = 7.0 Hz, 4 H), 1.56–1.48 (m, 4 H), 1.40–1.27 (m, 20 H), 0.88 (t, J = 6.8 Hz, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 77.5, 65.2, 31.8, 29.1, 29.0, 28.8, 28.3, 22.6, 19.2, 14.1 ppm.
• 13 After 9^th recycling run, ICP analysis indicated that 20% of copper content (2 mol% Cu) remained in the recovered catalyst. This suggested that 2 mol% of copper content is enough to promote the reaction. In fact, we examined the homocoupling of ethynylbenzene (1a) with PS-supported CuSO₄–TEDETA (2.0 mol% Cu), giving the desired product 2a in 91% yield.