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Synlett 2010(9): 1333-1336  
DOI: 10.1055/s-0029-1219905
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of Thiosulfonate-Bridged Bromofluorene Endcapping Reagents

Vasco D. B. Bonifácio*a,b, Jorge Morgadoc,d, Ullrich Scherfb
a REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
Fax: +351(21)2948550; e-Mail: vasco.bonifacio@dq.fct.unl.pt;
b Macromolecular Chemistry Group and Institute for Polymer Technology, University of Wuppertal, Gaußstr. 20, 42119 Wuppertal, Germany
c Instituto Superior Técnico, Departamento de Engenharia Química e Biológica, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
d Instituto de Telecomunicações, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
Further Information

Publication History

Received 9 March 2010
Publication Date:
22 April 2010 (online)

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Abstract

A simple and versatile synthesis of thiosulfonate-bridged bromofluorene end-capping reagents is reported. The novel fluorene-based π-electron-poor aromatic building block was used as end-capping reagent in the synthesis of a polyfluorene-based molecular wire.

Key words

fluorine - halogenation - thiosulfonates - Yamamoto homocoupling - oligomerization

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Complete reduction was monitored by TLC.

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6,6-Di- n -octyl-6 H -fluorene[4,5- cde ][1,2]dithiine (3)
9,9-Di-n-octalyfluorene (2, 29.5 g, 0.0756 mol) was stirred with n-BuLi (1.6 M in hexane, 192 mL, 0.302 mol) and TMEDA (48 mL, 0.302 mol) at 60 ˚C for 3 h. The resulting dark red solution was cooled down to -78 ˚C and diluted with THF (250 mL). Sulfur (24.0 g, 0.755 mol) was added, and the resulting orange mixture allowed to reach r.t. and stirred for additional 12 h. This mixture was then washed with a 1 M aq NaOH solution (this washing completely removes intensively smelling byproducts) and H2O. The organic layer was separated and the aqueous layer further extracted with Et2O. The organic layers were combined, dried with anhyd MgSO4, filtered, and the solvent removed in vacuo. Purification of the resulting dark red oil by column chromatography(hexane) gave a yellow oil that solidified upon standing (20.7 g, 60% yield); mp 43-45 ˚C(hexane). IR (thin film): 2924, 2852, 1464, 1409, 786, 735 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.21 (2 H, t, J = 7.6 Hz), 7.11 (2 H, d, J = 8.0 Hz), 7.05 (2 H, d, J = 7.6 Hz), 1.93-1.89 (4 H, m), 1.27-1.08 (20 H, m), 0.84 (6 H, t, J = 7.0 Hz), 0.73 (4 H, m). ¹³C NMR (100.6 MHz, CDCl3): δ = 150.79, 137.41, 129.30, 125.47, 124.08, 122.00, 56.65, 39.21, 31.76, 29.95, 29.17, 24.01, 22.58, 14.03. Anal. Calcd for (C29H40S2): C, 76.93; H, 8.90; S, 14.16. Found: C, 75.76; H, 9.52; S, 13.60.
Thiosulfonate-Bridged Fluorene (4)
A CH2Cl2 solution (100 mL) of 3 (2.32 g, 5.94 mmol), NBS (2.11 g, 11.87 mmol), and silica gel (24 g, 2.0 g mmol-¹ NBS) were stirred at r.t. for 13 h. The orange mixture obtained was filtered, extracted with CH2Cl2 and the organic phase washed with H2O. The organic layers were combined, dried with anhyd MgSO4, filtered, and the solvent removed under vacuo. After purification by column chromatography (hexane) a light yellow oil was obtained (1.9 g, 66% yield). IR (thin film): 2920, 2848, 1392, 1323, 1155, 1136, 1119 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.81 (1 H, d, J = 8.0 Hz), 7.63 (1 H, d, J = 8.0 Hz), 7.58 (1 H, t, J = 8.0 Hz), 7.44 (1 H, d, J = 8.0 Hz), 7.36 (1 H, d, J = 8.0 Hz), 7.26 (1 H, d, J = 8.0 Hz), 2.05-2.01 (4 H, m), 1.22-1.07 (20 H, m), 0.82 (6 H, t, J = 8.0 Hz), 0.70 (4 H, m). ¹³C NMR (100.6 MHz, CDCl3): δ = 152.08, 151.54, 137.15, 135.19, 132.35, 129.54, 128.83, 125.95, 124.77, 122.13, 117.61, 56.63, 39.20, 31.75, 29.94, 29.16, 24.01, 22.57, 14.03. Anal. Calcd for (C29H40S2O2): C, 71.85; H, 8.32; S, 13.23. Found: C, 71.74; H, 8.41; S, 13.24.
Thiosulfonate-Bridged Monobromofluorene (5)
Compound 4 (1.0 g, 2.06 mmol), Br2 (0.22 mL, 9.75 mmol) and concd H2SO4 (15 mL) were stirred at r.t. overnight. The red mixture obtained was quenched with H2, and extracted with CH2Cl2. The organic layers were combined, dried with anhyd MgSO4, filtered, and the solvent removed under vacuo. After recrystallization from hexane white crystals were obtained (1.0 g, 86% yield); mp 75-76 ˚C(hexane). IR (thin film): 2921, 2849, 1393, 1323, 1157, 1138, 1120 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.84 (1 H, dd, J = 8.0, 4.0 Hz), 7.64-7.62 (3 H, m), 7.25 (1 H, d, J = 8.0 Hz), 2.04-2.00 (4 H, m), 1.22-1.07 (20 H, m), 0.83 (6 H, t, J = 8.0 Hz), 0.69 (4 H, m). ¹³C NMR (100.6 MHz, CDCl3): δ = 152.47, 150.74, 136.72, 134.91, 134.15, 132.91, 129.71, 128.21, 127.29, 123.23, 118.35, 118.01, 57.71, 39.12, 31.67, 29.76, 29.08, 23.95, 22.52, 13.99. Anal. Calcd for (C29H39BrO2S2): C, 61.80; H, 6.97; S, 11.38. Found: C, 61.49; H, 7.68; S, 11.05.
Thiosulfonate-Endcapped Oligofluorene (TS-OF)
A Schlenk flask was charged with 2,7-dibromo-9,9-
di-n-octylfluorene (500 mg, 0.91 mmol), Ni(cod)2 (599 mg, 2.18 mmol), and 2,2′-bipyridyl (340.4 mg, 2.18 mmol) under argon. 1,5-Cyclooctadiene (COD, 170 µL, 1.365 mmol) and THF (25 mL) were subsequently added and the mixture heated up to 60 ˚C for 3 h. After this period the thiosulfonate endcapping reagent 5 (154 mg, 0.273 mmol) was added and the mixture heated for additional 3 h. The solution was poured into aq 2 N HCl and extracted with CHCl3. The organic layer was washed with a sat. EDTA solution, dried over anhyd MgSO, and the solvent evaporated to dryness. The residue obtained was Soxhlet-extracted with MeOH (1 d) and EtOAc (3 d), redissolved in CHCl3 and reprecipitated into cold MeOH (1:100) to yield the endcapped oligo-fluorene TS-OF (245 mg, 70% yield). The copolymer showed thermal stability up to 350 ˚C by to thermo-gravimetric analysis (TGA). GPC (THF): Mn = 4300, Mw = 9190, PD = 2.13 (after extraction). UV/Vis (CHCl3): λmax,abs = 360 nm, photoluminescence: λmax,PL = 415 nm. IR (thin film): 2923, 2852, 1506, 1455, 1248, 1177, 1048, 812 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.83 (br s, ArH), 7.67 (br s, ArH), 7.38 (br s, ArH), 2.04 (4 H, br s), 1.13 (20 H, br s), 0.81 (6 H, br s). Anal. Calcd for (C319H438O4S4; 4465, n = 9): C, 85.81; H, 9.89; S, 2.87. Found: C, 84.04; H, 10.33; S, 2.64.