Synthesis of an Isocyanate-Functionalized Terpyridine as Building Block for Metallo-Supramolecular Polymers

Abstract

An amino-pentyl-functionalized terpyridine was converted to the corresponding isocyanate, which could be crystallized and studied by X-ray diffraction. The isocyanate-functionalized terpyridine was utilized as a reactive building block for the formation of a metal-coordinating polymer by reacting it under mild ­conditions with a hydroxy functionalized poly(THF). GPC characterization and UV-titration proved successful functionalization and complexation. Secondly, the isocyanate building block was successfully utilized for the formation of a metal coordinating ­compound with two different binding moieties as was proven by ¹H NMR spectroscopy.

Key words

terpyridines - ligands - polymers - coupling - supramolecular chemistry

References

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14

4′-(5-Isocyanatopentyloxy)-[2,2′;6′,2′′]terpyridine ( 2). To a stirred solution of di-tert-butyltricarbonate (40 mg, 0.15 mmol) in CH₂Cl₂ (8 mL) at r.t., a solution of 1 (40 mg, 0.12 mmol) was added over a period of 5 min. After 15 min stirring, the solvent was evaporated and the oily residue dissolved in pentane (at r.t.) in order to obtain a sat. solution. Crystallization at -25 °C yielded 2 as colorless crystals (31 mg, 73%). Mp 68 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.55-1.78 (m, 4 H, H _{γ , δ}), 1.89 (tt, J = 6.2, 6.5 Hz, 2 H, H _β), 3.36 (t, J = 6.5 Hz, 2 H, H _ε), 4.25 (t, J = 6.2 Hz, 2 H, H _α), 7.33 (ddd, J = 1.5, 4.8, 7.2 Hz, 2 H, H _{5,5 ′′}), 7.85 (ddd, J = 1.5, 7.2, 8.0 Hz, 2 H, H _{4,4 ′′}), 8.01 (s, 2 H, H _{3 ′ ,5 ′}), 8.62 (ddd, J = 1.0, 1.5, 8.0 Hz, 2 H, H _{3,3 ′′}), 8.69 (ddd, J = 1.0, 1.5, 4.8 Hz, 2 H, H _{6,6 ′′}). ¹³C NMR (300 MHz, CDCl₃): δ = 23.2 (C _γ), 28.4 (C _δ), 30.9 (C _β), 42.9 (C _ε), 67.8 (C _α), 107.3 (C _{5,5 ′′}), 121.3 (C _{4,4 ′′}), 123.8 (C _{3,3 ′′}), 136.8 (C _{3 ′ ,5 ′}), 149.0 (C _{6,6 ′′}), 156.1 (C _{2,2 ′′}), 157.1 (C _{2 ′ ,6 ′}), 167.2 (C _{4 ′}). MALDI-TOF MS (matrix: dithranol): m/z = 335 (MH⁺). EIMS (70 eV): m/z = 361 (MH⁺), 695 (di-terpyridine urea + H⁺). Anal. Calcd for C₂₁H₂₀N₄O₂ (360.41): C, 69.98; H, 5.59; N, 15.55. Found: C, 70.23; H, 5.34; N, 15.29. Crystallographic data (C₂₁H₂₀N₄O₂): triclinic, space group P-1, a = 9.5475 (11), b = 10.3815 (11), c = 11.2582 (13) Å, α = 69.366 (2)°, β = 66.798 (2)°, γ = 74.549 (3)°.

15

CCDC 234779 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystalographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)[phone]; email: [e-mail]].

17

Poly(THF)-terpyridine ( 3). Polymerization of tetra-hydrydrofuran (THF) was performed by the addition of methyl triflate (200 µL, 0.84 mmol) to dry THF (50 mL) at r.t. After 45 min stirring, the polymerization was quenched by the addition of 50 mL H₂O followed by precipitation of the reaction mixture in H₂O (200 mL). The poly(THF) was obtained as a white solid (6.1 g, 63%). GPC [CHCl₃: Et₃N: i-PrOH (93:5:2), column at 50 °C]: RI-detector: M_n = 11,600 Da; PDI = 1.20.
To a solution of this (dried) poly(THF) (1.0 g, 0.086 mmol) in CHCl₃ (25 mL), isocyanato-terpyridine 2 (150 mg, 0.45 mmol) and two drops of dibutyltindilaurate were added. After 16 h stirring at r.t., the solvent was evaporated and the polymer was precipitated from THF into H₂O resulting in the functionalized poly(THF) as a white solid (610 mg, 61%). ¹H NMR (400 MHz, CDCl₃): δ = 1.38-1.95 (m, 280 H, H_{β , γ , δ}, OCH₂CH _{2 ,pTHF}), 3.12-3.69 (m, 275 H, H _α, OCH ₂ CH_2,pTHF, OCH ₃ ), 4.25 (t, J = 6.0 Hz, 2 H, H_ε), 4.62 (t, J = 5.5 Hz, 1 H, NH), 7.32 (br s, 2 H, H_{5,5 ′′}), 7.85 (ddd, J = 1.7, 7.1, 7.1 Hz, 2 H, H_{4,4 ′′}), 8.00 (s, 2 H, H_{3 ′ ,5 ′}), 8.62 (d, J = 7.7 Hz, 2 H, H_{3,3 ′′}), 8.68 (d, J = 4.4 Hz, 2 H, H_{6,6 ′′}). M_n,NMR = 9,700 Da.
GPC [CHCl₃: Et₃N:i-PrOH (93:5:2), column at 50 °C]: RI-detector: M_n = 11,900 Da, PDI = 1.21, UV-detector (290 nm): M_n = 12,100; PDI = 1.19.

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To a solution of tpy-poly(THF) 3 (3.5 mg, 0.36 µmol) in CHCl₃ (3 mL), 10 µL aliquots of iron(II)chloride (32.3 mg, 0.255 mmol) in MeOH (100 mL) were added. After each aliquot, an UV-vis spectrum was recorded.

20

[5-([2,2";6",2""]Terpyridin-4"-yloxy)-pentyl]-carbamic acid 4-(3,6-di-pyridin-2-yl-pyridazin-4-yl)-butyl ester ( 5). Isocyanato-terpyridine 2 (100 mg, 0.28 mmol) and two drops of dibutyltindilaurate were added to a solution of 3,6-di(2-pyridyl)-4-(1-hydroxybutyl)pyridazine 4 (74 mg, 0.22 mmol) in CHCl₃ (25 mL). After 16 h stirring at r.t., the solvent was evaporated and the crude product was purified by column chromatography (Al₂O₃, eluent: 1% MeOH in CHCl₃) resulting in a white compound (113 mg, 77%). Mp 130-131 °C. ¹H NMR (400 MHz, CDCl₃): δ = 1.55-1.78 (m, 8 H, H _{tpy, γ , δ} + H _{dpp, β , γ}), 1.89 (t, J = 6.0 Hz, 2 H, H _{tpy, β}), 3.04-3.25 (m, 4 H, H _{dpp, α} + H _{tpy, ε}), 4.04 (t, J = 6.0 Hz, 2 H, H _{dpp, δ}), 4.21 (t, J = 6.0 Hz, 2 H, H _{tpy, α}), 4.80 (t, J = 4.9 Hz, 1 H, NH), 7.31 (ddd, J = 1.1, 4.9, 7.7 Hz, 2 H, H _{tpy,5,5 ′′}), 7.38 (ddd, J = 1.1, 3.8, 7.7 Hz, 2 H, H _{dpp,5,5 ′′}), 7.80-7.95 (m, 4 H, H _{tpy,4,4 ′′} +H _{dpp,4,4 ′′}), 7.98 (s, 2 H, H _{tpy,3 ′ ,5 ′}), 8.12 (d, J = 7.7 Hz, 1H, H _dpp,3), 8.49 (s, 1 H, H _{dpd,5 ′}), 8.59-8.75 (m, 7 H, H _{tpy,3,3 ′′} + H _{dpp,3 ′′} + H _{tpy,6,6 ′′} + H _{dpp,6,6 ′′}). ¹³C NMR (400 MHz, CDCl₃): δ = 23.1 (C _{tpy, γ}), 26.0 (C _{dpp, γ}), 28.5 (C _{tpy, δ}), 29.5 (C _{tpy, β}), 31.4 (C _{dpp, α}), 31.8 (C _{dpp, β}), 40.7 (C _{tpy, ε}), 64.1 (C _{dpp, δ}), 67.8 (C _{tpy, α}), 107.2 (C _{tpy,5,5 ′′}), 121.2 (C _{tpy,4,4 ′′}), 121.6 (C _{dpp,3 ′′}), 123.5 (C _dpp,5), 123.7 (C _{tpy,3,3 ′′}), 124.6 (C _{dpp,3,5 ′′}), 125.5 (C _{dpp,5 ′}), 136.7 (C _{tpy,3 ′ ,5 ′} + C _dpp,4), 137.0 (C _{dpp,4 ′′}), 142.1 (C _{dpp,4 ′}), 148.4 (C _dpp,6), 148.8 (C _{tpy,6,6 ′′}), 149.2 (C _{dpp,6 ′′}), 153.3 (C _{dpp,2 ′′}), 155.8 (C _dpp,2), 156.1 (C _{dpp,6 ′}), 156.6 (C _{dpp,3 ′}), 156.8 (C _{tpy,2,2 ′′}), 157.1 (C _{tpy,2 ′ ,6 ′}), 158.8 (NCO), 167.0 (C _{tpy,4 ′}). MALDI-TOF MS (matrix: dithranol): m/z = 667 (MH⁺), 689 (MNa⁺). Anal. Calcd for C₂₁H₂₀N₄O₂·H₂O (666.79 + 18.02): C, 68.40; H, 5.89; N, 16.36. Found: C, 68.47; H, 5.86; N, 16.48.