Fulvalene Derivatives Containing a Tetrabenzofluorene Unit: New Nonplanar Fulvalenes with High Electron Affinity

Abstract

17H-Tetrabenzo[a,c,g,i]fluoren-17-one possessing a nonplanar, helicene-like structure was efficiently prepared by aerial oxidation of 17H-tetrabenzo[a,c,g,i]fluorene under mild basic conditions. A quinone methide and an unsymmetrical fulvalene containing a tetrabenzofluorene unit were synthesized from the ketone. Treatment of 17-bromotetrabenzo[a,c,g,i]fluorene with a base afforded a symmetric fulvalene as an air-sensitive blue solid. Electrochemical analyses revealed that these compounds have high electron affinities.

Key words

conjugation - nonplanar π-systems - tetrabenzofluorenes - fulvalenes - electron acceptors - polycycles

• References and Notes

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• 9 17H-Tetrabenzo[a,c,g,i]fluoren-17-one (4) Dark-red prisms; yield: 256 mg (70%); mp 284.0–286 °C (Lit.2 295 °C). IR (KBr): 3072w, 3057w, 1697s, 1425m, 1095m, 748s, 729s, 718s cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 7.64–7.84 (m, 8 H), 8.31 (d, J = 8.2 Hz, 2 H), 8.69 (d, J = 7.9 Hz, 2 H), 8.78 (d, J = 8.6 Hz, 2 H), 9.23 (d, J = 8.6 Hz, 2 H). ¹³C NMR (125.8 MHz, CDCl₃): δ = 122.75, 123.95, 124.85, 125.88, 126.46, 126.58, 126.95, 127.63, 128.46, 128.55, 128.94, 131.60, 134.71, 146.93, 197.44. MS (EI): m/z (%): 380 [M⁺] (100), 352 [M–CO]⁺ (35), 350 (38). UV/Vis (CH₂Cl₂): λ_max (ε, M⁻¹·cm⁻¹) = 321 (29500), 336 (33500), 423 (2320), 530 (900) nm. 3,5-Di-tert-butyl-4-(17H-tetrabenzo[a,c,g,i]fluoren-17-ylidene)cyclohexa-2,5-dien-1-one (5) Black-red prisms; yield: 15 mg (10%); mp 293–294 °C. FT-IR (KBr): 719s, 747s, 870m, 1256m, 1364m, 1456w, 1620s (C=O), 2859w, 2947m, 3077w cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 1.18 (s, 18 H), 7.61–7.66 (m, 6 H), 7.73 (t, J = 7.8 Hz, 2 H), 7.90 (s, 2 H), 8.22 (t, J = 8.3 Hz, 2 H), 8.48 (d, J = 8.3 Hz, 2 H), 8.74 (t, J = 8.3 Hz, 2 H), 8.77 (d, J = 8.3 Hz, 2 H). MS (EI): m/z (%): 570 [M + 2]⁺ (100), 569 [M + 1]⁺ (10), 568 [M⁺] (20). HRMS (ESI): m/z [M + 1]⁺ calcd for C₄₃H₃₇O: 569.2839; found: 569.2851. UV/Vis (CH₂Cl₂): λ (ε, M⁻¹·cm⁻¹) = 301 (26500), 358 (27000), 452 (20500), 529 (6300) nm. ¹³C NMR spectra for 5–7 could not be recorded because of the low solubilities of these compounds. 17-(9H-Fluoren-9-ylidene)-17H-tetrabenzo[a,c,g,i]fluorene (6) Black-violet prisms; yield: 7 mg (5%); mp >300 °C. FT-IR (KBr): 733s, 1429w, 1447m, 3034w, 3064w cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 6.90 (t, J = 7.2 Hz, 2 H), 7.09 (t, J = 7.2 Hz, 2 H), 7.15 (t, J = 7.6 Hz, 2 H), 7.38 (t, J = 7.6 Hz, 2 H), 7.42 (d, J = 7.6 Hz, 2 H), 7.56 (t, J = 7.6 Hz, 2 H), 7.65 (d, J = 7.7 Hz, 2 H), 7.69 (t, J = 7.6 Hz, 2 H), 7.93 (d, J = 8.3 Hz, 2 H), 8.33 (d, J = 8.3 Hz, 2 H), 8.59 (d, J = 8.1 Hz, 2 H), 8.68 (d, J = 8.1 Hz, 2 H). HRMS (ESI): m/z [M⁺] calcd for C₄₂H₂₄: 528.1881; found: 528.1873. UV/Vis (CH₂Cl₂): λ (ε, M⁻¹·cm⁻¹) = 303 (29600), 342 (13100), 359 (12100), 545 (13600) nm. 17-Bromo-17H-tetrabenzo[a,c,g,i]fluorene (12) Dark-red prisms; yield: 267 mg (60%); mp 255–256 °C. FT-IR (KBr): 1125, 1157, 1435, 1447, 3069 cm^–1. ¹H NMR (270 MHz, CDCl₃): δ = 6.58 (s, 1 H), 7.62–7.81 (m, 4 H), 8.43 (d, J = 7.6 Hz, 4 H), 8.64 (d, J = 7.9 Hz, 4 H), 8.81 (t, J = 7.6 Hz, 4 H). ¹³C NMR (125.8 MHz, CDCl₃): δ = 44.35, 123.35, 123.78, 124.81, 125.48, 126.80 (2C), 127.01, 127.71, 127.79, 128.05, 131.00, 132.48, 136.40, 140.04. The structure was confirmed by the X-ray crystallographic analysis; see Figure S3 in the Supporting Information. 17,17′-Bi(17H-tetrabenzo[a,c,g,i]fluorenylidene) (7) Dark-blue leaflets; yield: 40 mg (50%); mp >300 °C. IR (KBr): 1495, 1564, 1607, 2851, 2920, 2957, 3038, 3073 cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 6.72 (t, J = 7.7 Hz, 4 H), 7.64–7.71 (m, 12 H), 7.96 (d, J = 8.2 Hz, 4 H), 8.42 (d, J = 8.2 Hz, 4 H), 8.49 (d, J = 7.9 Hz, 4 H), 8.63 (d, J = 7.9 Hz, 4 H). MS (EI): m/z 728. HRMS (ESI): m/z [M⁺] calcd for C₅₈H₃₂: 728.2499; found: 728.2505. UV/Vis (CH₂Cl₂): λ (ε, M⁻¹·cm⁻¹) = 312 (29500), 370 (17400), 495 (3300), 641 (14800) nm.
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