Synthesis of Functional Carbo-benzenes with Functional Properties: The C₂ Tether Key

Abstract

Beyond demonstration of conceptual relevance and synthetic feasibility of aryl/alkyl-substituted representatives, carbo-benzene molecules started to gain prospects of broader impact through the emergence of alkynyl derivatives. This is first illustrated by examples of di- and hexaalkynyl-carbo-benzenes, a carbo-naphthalene, a carbo-biphenyl, and two carbo-terphenyls. A focus is then given to dialkynyl derivatives by reference to the peripherally C₂-extruded parents. In the centro­symmetric quadrupolar series, the C₂ expansion or ethynylogation effect is more particularly considered for 9H-fluoren-2-yl, tris(O-n-­alkyl)pyrogallyl, indol-3-yl, 4-anilinyl, and tetraphenyl-carbo-phenyl substituents on the following respective properties: two-photon absorption, chemical stability, columnar mesogenicity, on-surface photo­induced charge separation vs single-molecule conductance, and reduction potential. Topical results and prospects of application are discussed on the basis of crystallographic, spectroscopic, and electrochemical analyses vs DFT-calculated nuclear and electronic structures. For the sake of the discussion consistency, complementary experimental and computational results are disclosed in the dianilinyl series. Overall, it is shown that combined advances in strategy, protocols, and substrate scope of acetylenic synthesis remain crucial for the development of yet poorly explored but promising types of molecular materials.

1 Introduction

2 Hexaalkynyl-carbo-benzene

3 ortho-Dialkynyl-carbo-benzene

4 para-Dialkynyl-carbo-benzenes

4.1 Bistrimethylsilylethynyl-carbo-benzene

4.2 Bisfluorenylethynyl-carbo-benzene

4.3 Bistrialkoxyarylethynyl-carbo-benzenes

4.4 Bisindolylethynyl-carbo-benzene

4.5 Bisanilinylethynyl-carbo-benzene

5 Carbo-oligo(phenyleneethynylene)s

6 Conclusions

Key words

alkyne - C₂ tether - carbo-benzene - carbo-mer - π-conjugation

• References and Notes


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• 31 Experimental Procedure and Characterization of 27b First StepBis(benzonitrile)palladium(II)chloride (41.3 mg, 0.107 mmol) and CuI (9.6 mg, 0.074 mmol) were placed into a Schlenk tube under argon and dissolved in 4 mL of dry 1,4-dioxane. The mixture was then treated with tri-tert-butylphosphine (0.22 mL, 1 M solution in toluene, 0.22 mmol) at r.t. After the solution turned black, distilled diisopropylamine (0.65 mL, 4.99 mmol), 4-bromo-N,N-bis(trimethylsilyl)aniline (1.0 mL, 3.54 mmol) and trimethylsilylacetylene (0.65 mL, 4.60 mmol) were added. The resulting mixture was heated at 50 °C for 2 h, and then cooled down to r.t. before addition of EtOAc, filtering through Celite®, and concentration under reduced pressure to afford 29 as a black sticky liquid (1.42 g), which was used without further purification.Second StepA solution of the crude product 29 (1.42 g) in methanol (20 mL) was cooled down to 0 °C, before treatment with K₂CO₃ (884 mg, 6.40 mmol). The resulting mixture was stirred for 1 h at 0 °C before addition of distilled water (20 mL). Then, the methanol was removed under reduced pressure. The remaining aqueous layer was extracted with Et₂O, and the combined organic layers were washed with brine, dried over anhydrous MgSO₄, and concentrated under reduced pressure to afford 27b as a spectroscopically pure brown viscous liquid (920 mg, 3.50 mmol, 98% yield over 2 steps). Analytical Data ¹H NMR (400 MHz, 298 K, (CD₃)₂CO): δ = 0.10 (s, 18 H, -Si(CH₃)₃), 3.7 (s, 1 H, ≡CH) 6.96 (d, ³ J _HH = 8.0 Hz, 2 H, o-C₆H₄–), 7.39 (d, ³ J _HH = 8.0 Hz, 2 H, m-C₆H₄–) ppm. ¹³C{¹H} NMR (100 MHz, 298 K, (CD₃)₂CO): δ = 1 .31 (–Si(CH₃)₃), 77.66 (–C≡C–H), 83.37 (–C≡C–H), 117.54 (ipso-C₆H₄), 130.28 (o-C₆H₄), 132.77 (m-C₆H₄), 149.08 (p-C ₆H₄) ppm.
• 32 Experimental Preparation and Characterization of 1p First StepA solution of 27b (638 mg, 2 .44 mmol) in dry THF (15 mL) was treated at –78 °C with lithium bis(trimethylsilyl)amide (2.8 mL, 1 M solution in THF, 2.8 mmol). The resulting mixture was stirred for 1 h at –78 °C before dropwise addition of a solution of 16 (706 mg, 1.04 mmol) in dry THF (60 mL) at the same temperature. The resulting mixture was allowed to warm up to r.t. under stirring over 18 h. After treatment with a saturated aqueous solution of NH₄Cl and extractions of the aqueous layer with Et₂O, the combined organic layers were washed with brine, dried over anhydrous MgSO₄, and concentrated under reduced pressure to afford the diol 28b as an orange solid (1.48 g), which was used without further purification.Second StepA solution of the crude 28b (1.48 g) in dry DCM (330 mL) was treated at –78 °C with SnCl₂ (2.43 g, 12.8 mmol) and HCl·Et₂O (12.4 mL, 2 M solution in Et₂O, 24.8 mmol). The resulting mixture was allowed to warm up to –15 °C under stirring over 3.5 h, and then kept for 10 min. at r.t. before addition of NaOH (25 mL, 2 M aqueous solution, 50 mmol). The resulting mixture was stirred at r.t. for 16 h. After treatment with a saturated aqueous solution of Na₂CO₃ and extractions of the aqueous layer with DCM, the combined organic layers were dried over anhydrous MgSO₄ before filtration through Celite^® and concentration under reduced pressure. Washings of the crude solid with pentane and Et₂O afforded the expected carbo-benzene 1p as a dark violet solid (160 mg, 0.21 mmol, 20% yield over 2 steps).Analytical Data ¹H NMR (400 MHz, 298 K, (D₈-THF)): δ = 5.38 (br s, 4 H, –NH₂), 6.83 (³ J _HH = 8.0 Hz, 4 H, m-C₆ H ₄–NH₂), 7.70 (t, ³ J _HH = 8.0 Hz, 4 H, p-C₆H₅), 7,80 (d, ³ J _HH = 8.0 Hz, 4 H, o-C₆ H ₄–NH₂), 7.98 (t, ³ J _HH = 8.0 Hz, 8 H, m-C₆H₅), 9.47 (t, ³ J _HH = 8.0 Hz, 8 H, o-C₆H₅) ppm. ¹³C{¹H} NMR (100 MHz, 298 K, (D₈-THF)): δ = 87.00–113.90 (–C≡C– and >C≡C≡C≡C<), 115,16 (m-C₆H₄–NH₂), 119,85, 120,81 (>C(C₆H₄–NH₂)– and >C(C₆H₅)–), 130.00–130.84 (o, m, p-C₆H₅), 134.85 (o-C₆H₄–NH₂), 140.33, 152.07 (p-C₆H₄–NH₂ and p-C₆H₅) ppm. MS (MALDI-TOF/DCTB): m/z (%) = 756.2 (100) [M]⁺.HRMS (MALDI-TOF/DCTB): m/z [M]⁺ calcd for C₅₈H₃₂N₂: 756.2565; found: 756.2602; [M + Na]⁺ calcd for C₅₈H₃₂N₂Na: 779.2463; found: 779.2437. UV-vis (THF): λ_max(ε) = 493 nm (131000 L/mol/cm). Voltammetry: reduction: E (V/SCE) = –0.67 (rev), –1.09 (rev), –1.56 (irrev), oxidation: 0.74 (irrev).
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