Triazole-Based Ferrocenyl Dendrimers as a Medium for Encapsulated Palladium Nanoparticles

Abstract

Novel ferrocenyl dendrimers with 1,3,5-tris(aminothiophenol)benzeneamide core has been synthesized through click chemistry under microwave-assisted solid-support technique. The higher-generation ferrocenyl dendrimers can ‘sense’ and bind palladium nanoparticles (PdNP) by encapsulation whereas the lower-generation dendrimers stabilize the PdNP.

Key words

ferrocenyl dendrimers - click chemistry - microwave - nanoparticles - palladium

• References and Notes

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• 15 General Procedure for the S-Alkylation A mixture of propargyloxybenzyl chloride derivatives 6 and 9 (1.0 mmol, 1 equiv), 2-aminothiophenol (1.2 mmol, 1.2 equiv), and TBAB (5 mg), KOH (1.5 mmol, 1.5 equiv), in a mixture of toluene–H₂O (1:1, 40 mL), was refluxed for 4 h. The toluene layer was separated, washed with 5% KOH solution (2 × 10 mL), H₂O (20 mL), and then dried over Na₂SO₄. Toluene was evaporated under vacuum, and the residue obtained was purified by column chromatography with hexane–CHCl₃ as eluent to give the corresponding propargyloxybenzyl-2-aminothiophenol.
• 16 3,5-Bis(propargyloxy)benzyl-2-aminothiophenol (10) Colorless liquid; yield 86%; R_f  = 0.45 (hexane–CHCl₃ = 3:7). ¹H NMR (300 MHz, CDCl₃): δ = 2.52 (t, J = 2.4 Hz, 2 H), 3.82 (s, 2 H), 4.25 (br s, 2 H), 4.57 (d, J = 2.4 Hz, 4 H), 6.37 (d, J = 2.4 Hz, 2 H), 6.47 (t, J = 2.4 Hz, 1 H), 6.63 (dt, J = 7.5, 1.5 Hz, 1 H), 6.70 (dd, J = 9.0 Hz, 1.2 Hz, 1 H), 7.11 (dt, J = 9.0 Hz, 1.8 Hz, 1 H), 7.23 (dd, J = 7.8 Hz, 1.5 Hz, 1 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 39.7, 55.9, 75.6, 78.4, 101.5, 108.4, 114.9, 117.2, 118.5, 130.1, 136.6, 140.8, 148.7, 158.5 ppm. MS–FAB: m/z = 323 [M⁺]. Anal. Calcd (%) for C₁₉H₁₇NO₂S: C, 70.56; H, 5.30; N, 4.33. Found: C, 70.49; H, 5.25; N, 4.31.
• 17 General Procedure for the Amide-Core-Based Propargylated Dendritic Wedge A solution of the benzene-1,3,5-tricarboxylic acid chloride (1.0 mmol) in dry CH₂Cl₂ (100 mL) and a solution of the propargyloxy benzyl-2-aminothiophenol derivative 10 or 11 (3.0 mmol) and Et₃N (3.1 mmol) in dry CH₂Cl₂ (100 mL) were simultaneously added dropwise to a well-stirred solution of dry CH₂Cl₂ (500 mL) during 6 h. After the addition was complete, the reaction mixture was stirred for another 6 h. The solvent was removed under reduced pressure, and the residue obtained was then dissolved in CH₂Cl₂ (300 mL), washed with H₂O (2 × 100 mL) to remove Et₃N·HCl and then dried over Na₂SO₄. CH₂Cl₂ was evaporated under vacuum, and the residue obtained was purified by column chromatography with CHCl₃–MeOH as eluent to give the corresponding amide-core-based propargylated dendritic wedge.
• 18 Dendritic Wedge 13 Pale yellow solid; yield 71%; R_f  = 0.54 (CHCl₃–MeOH = 99:1); mp 79 °C. ¹H NMR (300 MHz, CDCl₃): δ = 2.34 (t, J = 2.4 Hz, 3 H), 2.45 (t, J = 2.4 Hz, 6 H), 3.90 (s, 6 H), 4.49 (d, J = 2.4 Hz, 12 H), 4.55 (d, J = 2.4 Hz, 6 H), 6.36 (s, 6 H), 7.13 (dt, J = 7.5, 0.9 Hz, 3 H), 7.44 (dt, J = 7.8 Hz, 1.2 Hz, 3 H), 7.52 (dd, J = 7.5 Hz, 1.2 Hz, 3 H), 8.47 (d, J = 7.8 Hz, 3 H), 8.70 (d, J = 1.5 Hz, 3 H), 9.31 (s, 3 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 41.8, 56.9, 60.2, 75.3, 75.9, 78.3, 79.0, 108.8, 120.8, 123.5, 125.0, 130.3, 130.6, 131.1, 131.4, 133.8, 135.8, 136.3, 139.9, 151.5, 163.1, 168.7 ppm. MS–FAB: m/z = 1287 [M⁺]. Anal.Calcd (%) for C₇₅H₅₇N₃O₁₂S₃: C, 69.91; H, 4.46; N, 3.26. Found: C, 69.85; H, 4.40; N, 3.21.
• 19 General Procedure for the Microwave-Assisted Solid-Support Click Chemistry A mixture of azide 5 (2 equiv, 2.0 mmol)/ 5 (6 equiv, 6.0 mmol/ 5 (9 equiv, 9.0 mmol)/ 8 (6 equiv, 6.0 mmol)/ 8 (9 equiv, 9.0 mmol) and alkyne dendron 6/12/13/12/13 (1 equiv, 1.0 mmol) each in Na₂SO₄ (0.5 g) in the presence of CuSO₄·5H₂O (5 mol%) and NaAsc (10 mol%) was kept under microwave irradiation (80 W) for 1 min. The crude residue was treated with H₂O (150 mL) for 10 min in order to resume all the Cu(I) trapped in the dendrimer as Cu(NH₃)₆ ⁺ and then extracted with CHCl₃ (2 × 150 mL). The organic layer was separated, washed with brine (1 × 150 mL), dried over Na₂SO₄, and evaporated to give the crude triazole, which was purified by column chromatography (SiO₂), using the eluent as mentioned under each compound.
• 20 Ferrocenyl Dendrimer 1 Pale yellow solid; yield 96%; R_f  = 0.52 (CHCl₃–MeOH, 25:3); mp 111–113 °C. ¹H NMR (300 MHz, CDCl₃): δ = 3.78 (s, 6 H), 4.14, 4.16, 4.18 (s, 54 H, Cp), 4.73 (s, 12 H), 5.18 (s, 12 H), 6.17 (s, 6 H), 7.13 (t, J = 7.5 Hz, 3 H), 7.37 (t, J = 7.2 Hz, 3 H), 7.47 (s, 6 H), 7.54 (t, J = 8.1 Hz, 3 H), 8.38 (s, 3 H), 8.41–8.47 (m, 6 H), 9.41 (s, 3 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 50.0, 61.8 [68.9, 69.0 (2 C), Cp], 80.9, 107.4, 121.0, 122.3, 122.5, 124.3, 125.1, 128.8, 130.2, 135.4, 135.9, 139.9, 140.0, 143.4, 159.3, 163.0 ppm. MS (MALDI-TOF): m/z = 2595 [M⁺ + Na]. Anal. Calcd (%) for C₁₃₂H₁₁₇Fe₆N₂₁O₉S₃: C, 61.62; H, 4.58; N, 11.43. Found: C, 61.53; H, 4.54; N, 11.52.
• 21 Ferrocenyl Dendrimer 2 Pale yellow solid; yield 84%; R_f  = 0.65 (CHCl₃–MeOH, 25:1); mp 116–118 °C. ¹H NMR (300 MHz, CDCl₃): δ = 3.75 (s, 6 H), 4.12, 4.17, 4.18 (s, 81 H, Cp), 4.78 (s, 12 H), 4.87 (s, 6 H), 5.10 (s, 6 H), 5.17 (s, 12 H), 6.24 (s, 6 H), 7.11 (t, J = 7.5 Hz, 3 H), 7.36 (t, J = 7.8 Hz, 3 H), 7.43 (d, J = 7.8 Hz, 3 H), 7.53 (s, 6 H), 7.61 (s, 3 H), 8.32 (d, J = 8.4 Hz, 3 H), 8.43 (s, 3 H), 9.43 (s, 3 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 49.8, 50.0, 62.9 [68.9, 69.0 (2 C), Cp], 81.2, 81.6, 108.1, 122.9, 123.3, 124.3, 125.1, 128.9, 130.1, 130.2, 133.6, 135.6, 136.1, 136.6, 139.9, 143.4, 143.6, 152.0, 163.1 ppm. MS (MALDI-TOF): m/z = 3481 [M⁺ + Na]. Anal. Calcd (%) for C₁₇₄H₁₅₆Fe₉N₃₀O₁₂S₃: C, 60.43; H, 4.53; N, 12.15. Found: C, 60.47; H, 4.50; N, 12.01.
• 22 Ferrocenyl Dendrimer 3 Pale yellow solid; yield 87%; R_f  = 0.50 (CHCl₃–MeOH, 20:3); mp 135–137 °C. ¹H NMR (300 MHz, CDCl₃): δ = 3.71 (s, 6 H), 4.13, 4.24, (s, 108 H, Cp), 4.67 (s, 12 H), 4.88–4.95 (m, 24 H), 5.22–5.32 (m, 36 H), 6.13 (s, 6 H), 6.39–6.46 (m, 21 H), 7.04 (s, 6 H), 7.24 (s, 3 H), 7.51 (s, 18 H), 8.28 (s, 3 H), 8.37 (s, 3 H), 9.39 (s, 3 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 50.1, 61.9, 61.88 [68.9, 69.0 (2 C), Cp], 80.9, 107.4, 107.8, 109.7, 115.5, 120.4, 122.7, 123.1, 122.8, 129.0, 131.0, 135.4, 137.8, 139.3, 144.1, 143.2, 143.5, 159.5, 159.7 ppm. MS (MALDI-TOF): m/z = 5490 [M⁺ + Na]. Anal. Calcd (%) for C₂₇₆H₂₄₉Fe₁₂N₅₇O₂₁S₃: C, 60.64; H, 4.59; N, 14.60. Found: C, 60.51; H, 4.50; N, 14.48.
• 23 Ferrocenyl Dendrimer 4 Pale yellow solid; yield 77%; R_f  = 0.72 (CHCl₃–MeOH, 5:1); mp 163–164 °C. ¹H NMR (300 MHz, CDCl₃): δ = 3.65 (s, 6 H), 4.13, 4.23 (s, 162 H, Cp), 4.94 (s, 54 H), 5.22 (s, 54 H), 6.43 (s, 33 H), 7.02–7.14 (m, 6 H), 7.28–7.30 (m, 3 H), 7.57 (s, 18 H), 7.61 (s, 9 H), 8.46–8.51 (m, 6 H), 9.51 (s, 3 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 50.1, 53.8, 54.6, 58.5, 61.7, 61.9 [68.8, 68.9, 69.0, 69.1, Cp], 80.8, 80.9, 100.9, 101.8, 107.4, 107.7, 122.6, 123.3, 123.5, 124.7, 125.2, 128.9, 130.3, 131.3, 133.6, 134.3, 135.3, 135.4, 136.1, 137.0, 137.4, 139.6, 140.0, 134.2, 143.4, 143.8, 159.3, 159.7, 159.8, 163.1 ppm. MS (MALDI-TOF): m/z = 7821 [M⁺ + Na]. Anal. Calcd (%) for C₃₉₀H₃₅₄Fe₁₈N₈₄O₃₀S₃: C, 60.06; H, 4.58; N, 15.09. Found: C, 60.07; H, 4.44; N, 15.00.
• 24 General Procedure for the Preparation of the PdNP A solution of ferrocenyl dendrimers (1 mmol, 1 equiv) in CHCl₃ (3 mL) was placed in a round-bottom flask under an inert atmosphere. A solution of PdCl₂ (6 mmol, 9 mmol, 12 mmol, 18 mmol, 1 equiv per triazole) in a mixture of CHCl₃–MeOH (1:10, 0.5:5 mL) was added to this solution and stirred continuously r.t. for 3 h. The solution was stirred for 5 min and NaBH₄ (10 mmol, 10 equiv per Pd) was added dropwise, and the yellow solution turned to golden brown indicating the formation of PdNP.