A Novel and Versatile Access to Task-Specific Ionic Liquids Based on 1,2,3-Triazolium Salts

Sven Hanelt; Jürgen Liebscher

doi:10.1055/s-2008-1042915

LETTER

A Novel and Versatile Access to Task-Specific Ionic Liquids Based on 1,2,3-Triazolium Salts

Sven Hanelt, Jürgen Liebscher*
Institute of Chemistry, Humboldt-University Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany
Fax: +49(30)20937552; e-Mail: Liebscher@chemie.hu-berlin.de;

Abstract

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Abstract

Novel task-specific ionic liquids based on 1,2,3-triazolium salts were prepared in a straightforward two-step procedure. Azides and alkynes were transformed into 1,4-disubstituted 1,2,3-triazoles by Cu-catalyzed click reaction. Subsequent alkylation afforded 1,3,4-trisubstituted 1,2,3-triazoles as ionic liquids. Useful functionalities, such as organocatalysts, fluorophors or linkers can be incorporated into the ionic liquids in this way.

Key words

ionic liquids - alkylation - heterocycles - click reaction - 1,2,3-triazolium salts

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References and Notes

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Preparation of 3; General Procedure: The azide 1 (20 mmol) was dissolved in the appropriate solvent (50 mL) and CuI (see Table [1] ) was added. The flask was flushed with argon and the mixture was kept under argon until the workup procedure (balloon) was followed. DIPEA (see Table [1] ) and the alkyne 2 (10 mmol) were added one after the other, the latter in portions under stirring. If the alkyne was a solid or a sticky liquid, the solvent quantity of 50 mL was shared for dissolving the azide and the alkyne. After a short time an exothermic reaction started and the pace of the addition of the alkyne was adjusted accordingly. Cooling by a water-bath might be advisable. After complete addition of the alkyne stirring was continued at r.t. The mixture was diluted with CHCl₃ (50 mL) and filtered. The filtrate was evaporated and the residue was purified by column chromatography (Kieselgel 60; MeOH-CHCl₃, 1:19). If DMF was used as solvent, the reaction mixture was diluted with CHCl₃ (250 mL), filtered and the filtrate was washed with H₂O (3 × 150 mL) and dried with Na₂SO₄ before volatile compounds were removed under vacuum. Eventually the washing procedure had to be repeated.
Preparation of 5; General Procedure: A solution of the 1,2,3-triazole 3 (20 mL) and the alkylating reagent 4 (see Table [1] ) in anhyd MeCN (30 mL) was refluxed (see Table [1] ). All volatile compounds were removed under vacuum with a rotary evaporator leaving behind the ionic liquid as an oil or a sticky oil.
Compound 3a: ¹H NMR (300.13 MHz, CDCl₃): δ = 0.87 (t, J = 7.2 Hz, 3 H, CH₂CH₂CH₂CH ₃), 1.32 (sext, J = 7.4 Hz, 2 H, CH₂CH₂CH ₂CH₃), 1.58 (m, 2 H, CH₂CH ₂CH₂CH₃), 2.68 (t, J = 7.8 Hz, 2 H, CH ₂CH₂CH₂CH₃), 5.46 (s, 2 H, CH ₂NNN), 7.19 (s, 1 H, CH), 7.27 (m, 5 H, Ph). ¹³C NMR (75.47 MHz, CDCl₃): δ = 13.7 (CH₂CH₂CH₂ CH₃), 22.1 (CH₂CH₂ CH₂CH₃), 25.3 (CH₂ CH₂CH₂CH₃), 31.3 (CH₂CH₂CH₂CH₃), 53.8 (PhCH₂), 120.5 (CH_triazole), 127.8 (CH_o), 128.4 (CH_m), 128.9 (CH_p), 134.8 (C_Ph), 148.8 (C_triazole).
Compound 3e: [α]_D ²⁵ -80.3 (c 0.02, CHCl₃). ¹H NMR (300.13 MHz, CDCl₃): δ = 1.96 (m, 4 H, NCbzCHCH ₂CH ₂), 3.48 (m, 2 H, NCbzCH₂), 4.30 (m, 1 H, NCbzCH), 5.00 (m, 2 H, PhCH₂NNN), 5.17 (m, 2 H, COOCH₂), 5.34 (s, 1 H, NCOOCH ₂Ph), 5.42 (s, 1 H, NCOOCH ₂Ph), 7.23 (m, 10 H, 2 × Ph), 7.56 (s, 1 H, CH_triazole). ¹³C NMR (75.47 MHz, CDCl₃): δ = 23.5 (NCbzCH₂ CH₂), 30.0 (NCbzCHCH₂), 46.4 (NCbzCH₂), 53.7 (PhCH₂NNN), 57.9 (COOCH₂), 58.7 (NCbzCH), 66.5 (PhCH₂OCON), 123.3 (CH_triazole), 127.2-128.7 (CH_Ph), 134.2 (NNNCH₂ C), 136.3 (NCOOCH₂ C), 142.6 (CHCOOCH₂ C), 154.2 (NCOOCH₂Ph), 172.2 (CHCOOCH₂).
Compound 3g: [α]_D ²⁵ -260.7 (c 0.033, CHCl₃). H NMR (300.13 MHz, CDCl₃): δ = 0.83 (t, J = 6.5 Hz, 3 H, CH₂CH₂CH₂CH₂CH ₃), 1.27 (m, 5 H, CH₂CH₂CH ₂CH ₂CH₃ + NCbzCHCHH), 1.61 (m, 3 H, NCbzCHCHHCH ₂), 1.89 (m, 2 H, CH₂CH ₂CH₂CH₂CH₃), 2.60 (m, 2 H, CH ₂CH₂CH₂CH₂CH₃), 3.15 (m, 1 H, NCbzCHH), 3.33 (m, 1 H, NCbzCHH), 4.10 (m, 1 H, NCbzCH), 4.48 (m, 2 H, CHCH ₂NNN), 5.13 (m, 2 H, PhCH ₂), 6.88 (s, 0.7 H, CH _triazole), 7.10 (s, 0.3 H, CH _triazole), 7.31 (m, 5 H, Ph).¹³C NMR (75.47 MHz, CDCl₃): δ = 13.8 (CH₂CH₂CH₂CH₂ CH₃), 22.2 (CH₂CH₂CH₂ CH₂CH₃), 23.1 (NCbzCHCHH), 25.3 (CH₂CH₂CH₂CH₂CH₃), 27.8 (CH₂ CH₂CH₂CH₂CH₃), 28.9 (NCbzCHCH₂ CH₂), 31.1 (CH₂CH₂ CH₂CH₂CH₃), 46.8 (NCbzCH₂), 51.5 (CH₂NNN), 57.1 (CHCH₂NNN), 66.9 (PhCH₂), 121.2 (CH_triazole), 127.7-128.4 (CH_Ph), 136.3 (C_Ph), 148.3 (C_triazole), 154.5 (NCOO).
Compound 5a: ¹H NMR (400.13 MHz, CD₃CN): δ = 0.92 (t, J = 7.6 Hz, 3 H, CH₂CH₂CH₂CH ₃), 1.40 (sext, J = 7.4 Hz, 2 H, CH₂CH₂CH ₂CH₃), 1.65 (m, 2 H, CH₂CH ₂CH₂CH₃), 2.81 (t, J = 7.2 Hz, 2 H, CH ₂CH₂CH₂CH₃), 4.12 (s, 3 H, N⁺Me), 5.82 (s, 2 H, CH₂NNN), 7.46 (m, 5 H, Ph), 8.70 (s, 1 H, CH). Signals at δ = 2.81 and 4.12 ppm showed a weak cross peak with each other in the NOESY spectrum. ¹³C NMR (100.61 MHz, CD₃CN): δ = 13.5 (CH₂CH₂CH₂ CH₃), 22.2 (CH₂CH₂ CH₂CH₃), 23.4 (CH₂ CH₂CH₂CH₃), 29.0 (CH₂CH₂CH₂CH₃), 38.5 (N⁺Me), 57.1 (PhCH₂), 117.9 (CH_triazole), 128.8 (CH_o), 129.6 (CH_m), 130.0 (CH_p), 133.0 (C_Ph), 145.5 (C_triazole).
Compound 5e: [α]_D ²⁵ -36.1 (c 0.024, CHCl₃)^{. 1}H NMR (300.13 MHz, CDCl₃): δ = 1.87 (m, 4 H, NCbzCHCH ₂CH ₂), 3.40 (m, 2 H, NCbzCH₂), 4.06 (s, 3 H, N⁺Me), 4.21 (m, 1 H, NCbzCH), 4.89 (m, 2 H, PhCH₂NNN), 5.45 (m, 2 H, COOCH₂), 5.34 (s, 1 H, NCOOCH₂Ph), 5.42 (s, 1 H, NCOOCH₂Ph), 7.27 (m, 10 H, 2 × Ph), 8.87 (s, 1 H, CH_triazole). ¹³C NMR (75.47 MHz, CDCl₃): δ = 23.1 (NCbzCH₂ CH₂), 29.9 (NCbzCHCH₂), 39.3 (N⁺Me), 46.3 (NCbzCH₂), 54.2 (PhCH₂NNN), 57.0 (COOCH₂), 58.6 (NCbzCH), 66.5 (PhCH₂OCON), 123.3 (CH_triazole), 127.0-130.6 (CH_Ph), 135.9 (NNNCH₂ C), 138.3 (NCOOCH₂ C), 142.3 (CHCOOCH₂ C), 153.9 (NCOOCH₂Ph), 171.5 (CHCOOCH₂).
Compound 5g: [α]_D ²⁵ -72.9 (c 0.02, CHCl₃). ¹H NMR (300.13 MHz, CD₃CN): δ = 0.87 (t, J = 6.5 Hz, 3 H, CH₂CH₂CH₂CH₂CH ₃), 1.31 (m, 5 H, CH₂CH₂CH ₂CH ₂CH₃ + NCbzCHCHH), 1.58 (m, 3 H, NCbzCHCHHCH ₂), 1.87 (m, 2 H, CH₂CH ₂CH₂CH₂CH₃), 2.39 (m, 2 H, CH ₂CH₂CH₂CH₂CH₃), 3.16 (m, 1 H, NCbzCHH), 3.34 (m, 1 H, NCbzCHH), 3.90 (m, 1 H, NCbzCH), 4.07 (s, 3 H, N⁺Me), 4.51 (m, 2 H, CHCH ₂NNN), 5.12 (m, 2 H, PhCH ₂), 7.35 (m, 5 H, Ph), 8.55 (s, 1 H, CH_triazole). ¹³C NMR (75.47 MHz, CD₃CN): δ = 14.0 (CH₂CH₂CH₂CH₂ CH₃), 22.6 (CH₂CH₂CH₂ CH₂CH₃), 23.5 (NCbzCHCHH), 25.7 (CH₂CH₂CH₂CH₂CH₃), 27.1 (CH₂ CH₂CH₂CH₂CH₃), 28.6 (NCbzCHCH₂ CH₂), 31.2 (CH₂CH₂ CH₂CH₂CH₃), 38.3 (N⁺Me), 47.3 (NCbzCH₂), 51.6 (CH₂NNN), 57.6 (CHCH₂NNN), 67.0 (PhCH₂), 118.1 (CH_triazole), 128.1-129.7 (CH_Ph), 137.8 (C_Ph), 146.8 (C_triazole), 155.6 (NCOO).

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