Synlett 2018; 29(10): 1314-1318
DOI: 10.1055/s-0036-1591848
letter
© Georg Thieme Verlag Stuttgart · New York

An Effective Synthesis of N,N-Diphenyl Carbazolium Salts

Sinai Aharonovich
a  Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Technion City, Haifa, 32000, Israel   Email: charles@technion.ac.il
,
Nansi Gjineci
a  Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Technion City, Haifa, 32000, Israel   Email: charles@technion.ac.il
,
Dario R. Dekel
b  Wolfson Department of Chemical Engineering, Technion – Israel Institute of Technology, Technion City, Haifa, 32000, Israel
,
a  Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Technion City, Haifa, 32000, Israel   Email: charles@technion.ac.il
› Author Affiliations
This work was funded by the Ministry of National Infrastructure, Energy and Water Resources of Israel (grant 216-11-048); the Ministry of Science, Technology & Space of Israel through the M.era-NET Transnational Call 2015, NEXTGAME project grant 3-12948; and the European Union's Horizon 2020 research and innovation program under grant agreement No 721065.
Further Information

Publication History

Received: 29 September 2017

Accepted after revision: 07 November 2017

Publication Date:
20 December 2017 (eFirst)

Published as part of the Special Section 9th EuCheMS ­Organic Division Young Investigator Workshop

Abstract

Tetraaryl ammonium salts are a synthetic challenge, since there is no general method for the arylation of triaryl amines. Contrary to other quaternary ammonium salts, tetraaryl ammonium salts should be very chemically stable. The ipso carbons are not very electrophilic, since the positive charge is distributed throughout the pi systems and they have no acidic β hydrogens. Here we demonstrate a simple approach to N,N-diphenyl carbazolium salts using only three synthetic steps, allowing for an easy production of these salts in large amounts and in a relatively short time. In addition, we study the Cu(I) catalyzed multi-arylation of 2,2’-diaminobiphenyl, focusing on the regioselectivity of each step. Finally, we characterize, for the first time, the solid state structure of a tetraaryl ammonium salt.

Supporting Information

 
  • References and Notes

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  • 34 Representative Experimental Procedures and Characterization Data 2,2′-Diaminobiphenyl (A) In a 3 L beaker flask, glacial acetic acid (190 mL) is added to a stirred solution of 2,2′-dinitro biphenyl (13.00 g, 53.23 mmol) in absolute ethanol (1.9 L), followed by portionwise addition of zinc powder (75.00 g, 1147 mmol) during 2 min. Once the exothermic reaction subsides (10 min) the beaker is left stirring for additional 5 min after which it is allowed to reach RT. The yellow-green reaction mixture is filtered, the unreacted zinc powder is washed with small amounts of ethanol, and the filtrate is concentrated to a thick syrup, which is dissolved in 16% hydrochloric acid (80 mL). The aqueous phase is extracted with CHCl3 (5 × 20 mL), until no color is observed in the organic phase, and then added slowly to 25% NH4OH (1 L), for liberation of the amine and complexation of zinc(II). The free amine is extracted with CHCl3 (4 × 100 mL), and the organic phase is washed with water (40 mL) and dried over Na2SO4. After the solvent is removed in vacuo, A is obtained as a light brown oil which solidifies to an off-white solid (9.23 g, 94%). 2-Amino,2′-(N,N-diphenylamino)biphenyl (B) In a 250 mL flame-dried Schlenk flask, A (9.00 g, 48.9 mmol) is deoxygenated (see Supporting Information). Xylenes (135 mL) are transferred via a syringe, and to the resulting solution KOtBu (12.09 g, 107.7 mmol) is added under argon. The mixture is stirred for 10 min at RT, during which a brown-yellow color develops. PhI (20.93 g, 102.6 mmol) is injected to the Schlenk flask under argon, followed by addition of CuI (1.86 g, 9.77 mmol) and o-phenanthroline (1.76 g, 9.77 mmol). The mixture is stirred at 125 °C for 3.5 h, after which it is allowed to reach RT. The mixture is filtered, and the filtration cake washed with small amounts of CHCl3 (ca. 70 mL). The solids are dissolved in 25% NH4OH (200 mL), and the dark green-blue aqueous phase is extracted with CHCl3 (2 × 30 mL) which is added to the filtrate. The filtrate is concentrated to a dark paste, which is dissolved in CHCl3 (200 mL) and extracted with small amounts of 25% NH4OH, until the aqueous phase is free from the copper complexes color. The organic phase is then extracted with 0.1 M HCl (3 × 250 mL) for separation of the unreacted A and phenanthroline, which can be recycled. The organic phase is washed with aq sat. NaHCO3, water, dried over Na2SO4, filtered, and the solvent is removed in vacuo to give a dark paste, consisting of a mixture of B and F (ca. 7:3 mol ratio), which is used for the next step without further purification. Samples of pure B and F are obtained by column chromatography of this mixture. Analytical Data of Compound B Red-brown solid, 60%; Rf = 0.57 (CHCl3). 1H NMR (400 MHz, CDCl3): δ = 7.66, (d, J = 8.0 Hz, 1 H), 7.59, (d, J = 8.0 Hz, 1 H), 7.53 (dt, J = 8.0, 1.3 Hz, 1 H), 7.43 (t, J = 8.0 Hz, 1 H), 7.25 (t, J = 8.0 Hz, 4 H, Ph-m), 7.12 (t, J = 8.0 Hz, 2 H, Ph-p), 7.07–7.02 (m, 6 H), 6.75 (t, J = 8.0 Hz, 1 H), 6.58 (d, J = 8.0 Hz, 1 H), 3.38 (br s, 2 H, NH2). 13C NMR (75 MHz, CDCl3): δ = 147.34 (C(Ph)–N, 2 C), 146.04 (C–N, 1 C), 143.35 (C–N, 1 C), 136.82 (C–C, 1 C), 132.46 (C–H(biphenyl), 1 C), 130.10 (C–H(biphenyl), 1 C), 128.86 (C–H (biphenyl), 1 C), 128.62 (C–H(biphenyl), 1 C), 128.50 (C–H(Ph), 4 C), 127.89 (C–H(biphenyl), 1 C), 125.25 (C–H(bi­phenyl), 1 C), 125.10 (C–C, 1 C), 122.02 (C–H(Ph), 4 C), 121.36 (C–H(Ph), 2 C), 118.03 (C–H(biphenyl), 1 C), 115.26 (C–H(biphenyl), 1 C). APCI-HRMS: m/z calcd for C24H21N2 [M + H]+: 337.1699; found: 337.1719 (–5.8 ppm). N,N-Diphenylcarbazolium Hexafluorophosphate (C) In a 100 mL Erlenmeyer beaker, a mixture of B and F (4.36 g) is dissolved in glacial acetic acid (53 mL). The solution is cooled to 0–5 °C using an ice bath, and the solidified acetic acid solution was crushed by a steel spatula. A solution of NaNO2 (4.15 g, 60.2 mmol) in water (5.5 mL) is added, and the resulting dark slurry stirred mechanically (using a spatula) for 20 min. Urea prills (3.32 g, 55.3 mmol) are then added, and the mixture stirred mechanically (using a spatula) for 1 h at 40 °C, during which a black tar appears. The reaction mixture is concentrated under reduced pressure and the residue dissolved in CHCl3 (50 mL), filtered, and the filtration cake washed with small amounts of CHCl3. The solvent is removed in vacuo, and the dark residue partitioned between diethyl ether (40 mL) and water (10 mL). The organic phase is further extracted with water (5 mL), and the volume of the united aqueous phase reduced to ca. 6 mL in vacuo, and extracted with small amounts of diethyl ether until no color is seen in the organic phase. Removal of water and acetic acid from the yellow aqueous phase by reduced pressure azeotropic distillation with toluene and freeze-drying affords the acetate salt as a highly hygroscopic yellow solid, which still contains acetic acid and water. Pure C is obtained by addition of 75% (w/v) NH4PF6 solution (5 mL) to the concentrated solution of acetate. The resulted light yellow precipitate is collected, washed with small amounts of water, and dried under reduced pressure. Analytical Data of Compound C Yellow solid, 857 mg, 22% from B; 1H NMR (400 MHz, CD3CN): δ = 8.21 (d, J = 8.0 Hz, 2 H, biphenyl), 7.81 (t, J = 8.0 Hz, 2 H), 7.73 (d, J = 8.0 Hz, 2 H), 7.67–7.62 (m, 4 H), 7.56 (t, J = 8.0 Hz, 4 H, m-Ph), 7.47 (d, J = 8.0 Hz, 4 H, o-Ph). 13C NMR (75 MHz, CD3CN): δ = 151.31 (2 C), 147.74 (2 C), 133.40 (C–H(biphenyl), 2 C), 132.53 (C–H(biphenyl), 2 C), 132.19 (C–H(biphenyl), 2 C), 131.88 (C–H (Ph), 4 C), 131.52 (C–C(biphenyl), 2 C), 124.53 (C–H(biphenyl), 2 C), 123.55 (C–H(Ph), 4 C). 19F NMR (377 MHz, CD3CN): δ = –72.82 (d, J1= 707 Hz, P–F). ESI-HRMS: m/z calcd for C24H18N [M – PF6]+: 320.1439; found: 320.1420 (–5.9 ppm).