Synlett 2013; 24(5): 575-580
DOI: 10.1055/s-0032-1318236
letter
© Georg Thieme Verlag Stuttgart · New York

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

Perumal Rajakumar*
a   Department of Organic Chemistry University of Madras, Guindy Campus Chennai – 600025, Tamil Nadu, India   Fax: +91(44)22352492   Email: perumalrajakumar@gmail.com
,
Ramasamy Anandhan
a   Department of Organic Chemistry University of Madras, Guindy Campus Chennai – 600025, Tamil Nadu, India   Fax: +91(44)22352492   Email: perumalrajakumar@gmail.com
,
Sampath Malathi
b   Department of Inorganic Chemistry, University of Madras, Guindy Campus Chennai – 600025, Tamil Nadu, India
,
Sengottuvelan Balasubramanian
b   Department of Inorganic Chemistry, University of Madras, Guindy Campus Chennai – 600025, Tamil Nadu, India
› Author Affiliations
Further Information

Publication History

Received: 10 December 2012

Accepted after revision: 28 January 2013

Publication Date:
12 February 2013 (online)


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.

 
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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%; Rf  = 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%; Rf  = 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%; Rf  = 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%; Rf  = 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%; Rf  = 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%; Rf  = 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.