Synthesis of Thiosulfonate-Bridged Bromofluorene Endcapping Reagents

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.

fluorine - halogenation - thiosulfonates - Yamamoto homocoupling - oligomerization

References and Notes

For an interesting perspective on molecular electronics, see:

<A NAME="RG08410ST-1A">1a</A> Miller JS. Adv. Mater.  1990,  2:  378 

<A NAME="RG08410ST-1B">1b</A> Miller JS. Adv. Mater.  1990,  2:  495 

<A NAME="RG08410ST-1C">1c</A> Miller JS. Adv. Mater.  1990,  2:  603 

<A NAME="RG08410ST-2">2</A> Ofir Y. Samanta B. Rotello VM. Chem. Soc. Rev.  2008,  37:  1814 

<A NAME="RG08410ST-3A">3a</A> Tour JM. Jones L. Pearson V. Lamba JJS. Burgin TP. Whitesides GM. Allara DL. Parikh AN. Atre SV. J. Am. Chem. Soc.  1995,  117:  9529 

<A NAME="RG08410ST-3B">3b</A> Stuhr-Hansen N. Christensen JB. Harrit N. Bjørnholm T. J. Org. Chem.  2003,  68:  1275 

<A NAME="RG08410ST-4A">4a</A> Römbke P. Schier A. Wiesbrock F. Schmidbaur H. Inorg. Chim. Acta  2003,  347:  123 

<A NAME="RG08410ST-4B">4b</A> Römbke P. Schier A. Schmidbaur H. J. Chem. Soc., Dalton Trans.  2001,  2482 

<A NAME="RG08410ST-5">5</A> Burdinski D. Blees MH. Chem. Mat.  2007,  19:  3933 

<A NAME="RG08410ST-6">6</A> Stachel H.-D. Eckl E. Immerz-Winkler E. Kreiner C. Weigand W. Robl C. Wünsch R. Dick S. Drescher N. Helv. Chim. Acta  2002,  85:  4453 

<A NAME="RG08410ST-7A">7a</A> Aucott SM. Milton HL. Robertson SD. Slawin AMZ. Walker GD. Woollins JD. Chem. Eur. J.  2004,  10:  1666 

<A NAME="RG08410ST-7B">7b</A> Aucott SM. Kilian P. Robertson SD. Slawin AMZ. Woollins JD. Chem. Eur. J.  2006,  12:  895 

<A NAME="RG08410ST-8">8</A> Aucott SM. Kilian P. Milton HL. Robertson SD. Slawin AMZ. Woollins JD. Inorg. Chem.  2005,  44:  2710 

<A NAME="RG08410ST-9">9</A> Bo Z, and Yaquin F. inventors; CN  1629113. 

<A NAME="RG08410ST-10">10</A> Ashe AJ. Kampf JW. Savla PM. Heteroat. Chem.  1994,  5:  113 

<A NAME="RG08410ST-11">11</A> Nakano K. Hidehira Y. Takahashi K. Hiyama T. Nozaki K. Angew. Chem. Int. Ed.  2005,  44:  7136 

<A NAME="RG08410ST-12">12</A> Grainger RS. Patel B. Kariuki BM. Angew. Chem. Int. Ed.  2009,  48:  4832 

<A NAME="RG08410ST-13">13</A> Oxelbark J. Thunberg L. Anderson A. Allenmark S. Acta Chem. Scand.  1999,  53:  710 

<A NAME="RG08410ST-14A">14a</A> Armarego WLF. Turner EE. J. Chem. Soc.  1956,  1665 

<A NAME="RG08410ST-14B">14b</A> Stender K.-W. Klar G. Knittel D. Z. Naturforsch., B  1985,  40:  774 

<A NAME="RG08410ST-15">15</A> A similar but less constrained ring system has been reported. Thieno[2,3,4,5-lmn][9,10]dithiaphenantherene-9,9-dioxide was obtained in low yield using MCPBA. See: Kimura T. Ishikawa Y. Ogawa S. Nishio T. Iida I. Furukawa N. Tetrahedron Lett.  1992,  33:  6355 

<A NAME="RG08410ST-16">16</A> Wang L. Jing H. Bu X. Chang T. Jin L. Liang Y. Catal. Commun.  2007,  8:  80 

<A NAME="RG08410ST-17">17</A>

Complete reduction was monitored by TLC.

For examples of cyclic aromatic disulfides and their properties, see:

<A NAME="RG08410ST-18A">18a</A> Goodings EP. Mitchard DA. Owen G. J. Chem. Soc., Perkin Trans. 1  1972,  1310 

<A NAME="RG08410ST-18B">18b</A> Chiang L.-Y. Meinwald J. Tetrahedron Lett.  1980,  21:  4565 

<A NAME="RG08410ST-18C">18c</A> Miller EW. Bian SX. Chang CJ. J. Am. Chem. Soc.  2007,  129:  3458 

<A NAME="RG08410ST-19A">19a</A> Cossu S. Delogu G. Lucchi O. Fabbri D. Fois MP. Synth. Commun.  1989,  19:  3431 

<A NAME="RG08410ST-19B">19b</A> Zhu-Ohlbach Q. Gleiter R. Rominger F. Schmidt H.-L. Reda T. Eur. J. Org. Chem.  1998,  2409 

<A NAME="RG08410ST-20">20</A> Scherf U. List EJW. Adv. Mater.  2002,  14:  477 

<A NAME="RG08410ST-21">21</A> Søndergaard R. Strobel S. Bundgaard E. Norrman K. Hansen AG. Albert E. Csaba G. Lugli P. Tornow M. Krebs FC. J. Mater. Chem.  2009,  19:  3899 

<A NAME="RG08410ST-22">22</A> Methanethiosulfonate has been shown to influence the Ca^²+ release in the sarcoplasmic reticulum by selective activation of ryanodine receptors (RyRs), a key Ca^²+ regulatory channel, see: Pessah IN. Pest. Manag. Sci.  2001,  57:  941 

<A NAME="RG08410ST-23">23</A>

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): M_n = 4300, M_w = 9190, PD = 2.13 (after extraction). UV/Vis (CHCl₃): λ_max,abs = 360 nm, photoluminescence: λ_max,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.