Synthesis of Bifluorenylidene- and Cycloocta[1,2,3-jk:6,5,4-j′k′]difluorene-Extended Tetrathiafulvalenes: Novel Multi-Redox Systems

Abstract

Herein, we present the synthesis of a novel 9,9′-bifluorenylidene-extended tetrathiafulvalene (TTF) as an E/Z isomeric mixture that was found to readily undergo an oxidative dimerization to furnish a TTF vinylogue with the two dithiafulvene units connected to an eight-membered ring fused to a bifluorenylidene core. This compound exhibited multiredox behavior and was found to take six charge states under cyclic voltammetry conditions: –2, –1, 0, +1, +2, +3. The dication corresponds to a cycloocta[1,2,3-jk:6,5,4-j′k′]difluorene with two appended 1,3-dithiolium rings.

Key words

bifluorenylidene - C–C bond formation - chromophores - olefination - polycyclic aromatic hydrocarbons - tetrathiafulvalenes

Publication History

Received: 15 June 2024

Accepted after revision: 24 July 2024

Accepted Manuscript online:
25 July 2024

Article published online:
14 August 2024

• References and Notes

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• 10 (E/Z)-4 Phosphonate 12 (575.6 mg, 1.731 mmol) was added to a 50-mL Schlenk flask containing dry THF (10 mL). Dialdehyde 11 (166.0 mg, 431.8 μmol) was added to a second 100-mL Schlenk flask containing dry THF (25 mL). Both flasks were cooled to –78 °C, and a 1 M solution of LiHMDS in toluene (1.7 mL, 1.7 mmol) was slowly added to the flask containing 12, resulting in a bright-yellow coloration. The contents of the two flasks were stirred for 20 min, before the contents of the flask containing the deprotonated phosphonate 12 were cannulated into the second flask. The resulting mixture was allowed to reach rt for 20 h, and the reaction was then quenched by washing with sat. aq NH₄Cl (50 mL). The two phases were separated, and the aqueous phase was extracted with CH₂Cl₂ (2 × 30 mL). The combined organic phases were dried (MgSO₄), filtered, and concentrated in vacuo. The residue was purified by flash column chromatography [silica gel, CH₂Cl₂–heptane (2:3)] to give a mixture of the E/Z isomers as a dark blackish-green powder; yield: 128.3 mg (37%; E/Z = 5:1); R_f = 0.31 (CH₂Cl₂–heptane, 2:3). IR (ATR, film): 3046.5w, 2973.1m, 2921.8m, 2865.7w, 1667.7w, 1561.0s, 1492.3m, 1444.2s, 1420.4w, 1402.0m, 1373.7w, 1350.0w, 1258.5m, 1055.1w, 966.1w, 889.8w, 813.0m, 781.7w, 765.3s, 749.0s, 738.2m, 605.6w cm^–1. HRMS (MALDI-FT-ICR): m/z [M^•+] Calcd for C₄₂H₃₆S₈: 796.05827; found: 796.05412. (E)-4 ¹H NMR (500 MHz, CD₂Cl₂): δ = 7.72–7.68 (m, 4 H), 7.49 (dd, J = 7.6, 7.6 Hz, 2 H), 7.42 (d, J = 7.8 Hz, 2 H,), 7.25–7.19 (m, 2 H), 7.06 (ddd, J = 7.4, 7.0, 1.2 Hz, 2 H), 7.01 (d, J = 7.8 Hz, 2 H), 6.04 (s, 2 H), 2.98–2.59 (m, 8 H), 1.37 (t, J = 7.3 Hz, 6 H), 1.20 (t, J = 7.3 Hz, 6 H). ¹³C NMR (126 MHz, CD₂Cl₂): δ = 142.76, 140.56, 139.40, 138.70, 136.03, 135.69, 134.51, 129.70, 128.51, 128.38, 128.24, 126.85, 125.69, 124.85, 119.57, 118.77, 118.40, 30.79, 30.61, 15.44, 15.38. (Z)-4 ¹H NMR (500 MHz, CD₂Cl₂): δ = 8.42 (d, J = 7.9 Hz, 2 H), 7.75 (d, J = 7.5 Hz, 2 H), 7.64 (dd, J = 7.4, 1.0 Hz, 2 H), 7.47–7.44 (m, 2 H), 7.31 (ddd, J = 7.4, 7.4, 1.0 Hz, 2 H), 7.25–7.19 (m, 4 H), 5.45 (s, 2 H), 2.98–2.59 (m, 8 H), 1.33–1.23 (m, 12 H). ¹³C NMR (126 MHz, CD₂Cl₂): δ = 141.59, 141.39, 140.10, 139.75, 134.99, 134.57, 134.27, 129.54, 128.72, 127.32, 127.03, 125.40, 120.23, 117.87, 114.68, 30.83, 15.52, 15.25.
• 11 5: I₂ (35.5 mg) was added to a solution of compound 4 (E/Z) (41.3 mg, 51.1 μmol) in CH₂Cl₂ (10 mL), and the mixture was stirred for 5 min. The reaction was then quenched with sat. aq Na₂S₂O₃ (25 mL), and the mixture was stirred for another 5 min. The two phases were separated, and the aqueous phase was extracted with CH₂Cl₂ (10 mL). The combined organic phases were dried (MgSO₄), filtered, and concentrated in vacuo. The residue was purified by column chromatography [silica gel, CH₂Cl₂–heptane (3:2)] to give a black–yellow powder; yield: 14.3 mg (35%); R_f = 0.45 (CH₂Cl₂–heptane, 1:1). IR (ATR, film): 3047.92, 2957.0m, 2922.0s, 2852.8m, 1597.3w, 1563.0m, 1534.6m, 1487.9m, 1444.1m, 1419.8m, 1400.4m, 1374.2m, 1349.0m, 1257.5m, 1053.9w, 965.9w, 886.4w, 767.6s, 752.4s, 736.8m, 705.9m, 662.3w, 609.3w, 582.8w, 468.6w cm^–1. ¹H NMR (500 MHz, CD₂Cl₂): δ = 8.14 (d, J = 8.0 Hz, 2 H), 7.79 (dd, J = 7.6, 1.2 Hz, 2 H), 7.76 (dd, J = 7.5, 1.2 Hz, 2 H), 7.73 (d, J = 7.5 Hz, 2 H), 7.43 (dd, J = 7.5, 7.5 Hz, 2 H), 7.28 (ddd, J = 7.5, 7.4, 1.0 Hz, 2 H), 7.03 (ddd, J = 7.6, 7.2, 1.2 Hz, 2 H), 2.73 (q, J = 7.3 Hz, 4 H), 2.67 (q, J = 7.4 Hz, 4 H), 1.18 (t, J = 7.4 Hz, 6 H), 1.14 (t, J = 7.3 Hz, 6 H). ¹³C NMR (126 MHz, C₆D₆): δ = 142.52, 141.06, 140.75, 139.36, 139.01, 138.23, 135.82, 129.98, 129.71, 129.07, 128.57, 127.67, 127.51, 127.35, 126.15, 119.76, 119.63, 30.63, 30.61, 15.27, 15.25. HRMS (MALDI-FT-ICR): m/z [M^•+] Calcd for C₄₂H₃₄S₈: 794.04207; found: 794.04303
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