6752 J. Am. Chem. Soc., Vol. 122, No. 28, 2000
Hicks and Nodwell
the counter electrode was a Pt wire, and the reference electrode was
an acetonitrile-based Ag wire/AgNO3 solution. All cell solutions
contained approximately 1 mmol of analyte and 0.1 M Bu4NBF4
electrolyte in dry, deoxygenated dichloromethane. Peak potentials are
reported referenced to standard calomel electrode (SCE), using ferrocene
as an added (∼0.5 mmol) internal standard. The redox couple of
ferrocene was taken to be 0.470 V vs SCE in dichloromethane.14
Generation of 2-Mesitylenesulfenyl Chloride, MesSCl. In a typical
preparation, mesitylenethiol (2.52 g, 16.6 mmol) in 5 mL of dry THF
was added dropwise to a slurry of N-chlorosuccinimide (2.22 g, 16.6
mmol) in 10 mL of THF. The resulting bright yellow solution was
stirred for 1 h, upon which the solution turned bright orange. The THF
was removed under vacuum, and the resulting orange solid was
redissolved in 20 mL of dry hexanes. The resulting succinimide
precipitate was filtered off to afford solutions of 2-mesitylenesulfenyl
was refluxed for 24 h. The solvent was removed and the residue
recrystallized from acetone/MeOH to yield 6 (0.36 g, 0.66 mmol, 69%)
as bright yellow crystals, mp 164 °C. UV-vis (CH2Cl2) λmax 386 nm
(ꢀ ) 30.9 × 103). 1H NMR (CDCl3) δ 6.95 (s, 4H), 6.82 (m, 6H), 2.50
(s, 12H), 2.27 (s, 6H). 13C NMR (CDCl3) δ 142.81, 139.51, 137.28,
137.04, 135.65, 129.43, 128.64, 123.83, 123.41, 21.79, 21.09 ppm. MS
(FAB, m/z) 548 (M+, 100%). Anal. Calcd for C30H28S5: C, 65.65; H,
5.14; S, 29.21%. Found: C, 65.69; H, 5.21; S, 29.08%.
5,5′′′-Bis(mesitylthio)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (7). A 20
mL toluene solution containing 3 (0.551 g, 1.76 mmol), 5,5′-bis-
(tributylstannyl)-2,2′-bithiophene (0.625 g, 0.840 mmol), and Pd(PPh3)4
(0.121 g, 5.95 mol %) was refluxed for 24 h. The solvent volume was
reduced to 5 mL, and 100 mL of hexanes was added, causing an orange
precipitate to form. This solid was recrystallized from toluene to yield
7 (0.23 g, 0.365 mmol, 43.4%) as a bright orange microcrystalline solid,
mp 219-220 °C. UV-vis (CH2Cl2) λmax 420 nm (ꢀ ) 16.2 × 103). 1H
1
chloride in quantitative yield by NMR. H NMR (CDCl3) δ 6.98 (s,
2H), 2.61 (s, 6H), 2.29 ppm (s, 3H). 13C NMR (CDCl3) δ 145.5, 143.3,
129.4, 128.9, 21.5, 21.4 ppm.
NMR (CDCl3) δ 6.94-6.77 (m, 12H), 2.50 (s, 12H), 2.27 (s, 6H). 13
C
NMR (360 MHz, CDCl3) δ 142.82, 139.55, 137.23, 137.19, 135.99,
135.54, 129.45, 128.63, 124.08, 123.98, 123.55, 21.80, 21.10. MS (EI,
m/z) 630 (M+, 33%). Anal. Calcd for C34H30S6: C, 64.72; H, 4.79; S,
30.49%. Found: C, 64.48; H, 4.79; S, 29.77%.
2,5-Dibromo-3,4-ethylenedioxythiophene (9). This compound was
prepared by modification of the literature procedure.53 EDOT 8 (5.0 g,
35.2 mmol) was dissolved in a mixture of THF (20 mL) and glacial
acetic acid (20 mL). To this was added solid NBS in small portions.
After stirring at room temperature for 2 h, the deep red solution was
poured onto 100 mL of water, effecting precipitation of 9 quantitatively
as a light yellow solid. 1H NMR (DMSO-d6) δ 4.07 (s). This compound
was used without further purification.
2-Bromo-5-(mesitylthio)-thiophene (3). A solution of 2,5-dibromo-
thiophene (5.0 g, 20.7 mmol) in THF (20 mL) cooled to -78 °C was
treated dropwise with n-BuLi (13.5 mL, 21.7 mmol). The resulting
cloudy colorless solution was stirred for 1.5 h at -78 °C. A solution
of MesSCl (20.7 mmol) in hexanes (15 mL) was added, and the reaction
was stirred for 30 min at -78 °C and then allowed to warm to room
temperature. The solvent was evaporated, and the residue was redis-
solved in dichloromethane (50 mL). This solution was washed with
water (3 × 30 mL), and the organic phase was dried over MgSO4 and
concentrated to yield a brownish oil which crystallized upon standing.
Recrystallization from EtOH produced 3 (3.6 g, 11.8 mmol, 57%) as
1
very pale purple needles, mp 47-48 °C. H NMR (CDCl3) δ 6.94 (s,
2-Bromo-5-mesitylthio-3,4-ethylenedioxythiophene (10). A solu-
tion of 9 (4.99 g, 16.6 mmol) in THF (20 mL) was cooled to -78 °C,
and BuLi (10.88 mL, 17.4 mmol) was added dropwise. Upon the
addition, the dark brown solution turned deep purple. This mixture was
stirred at -78 °C for 1.5 h. A solution of MesSCl (16.6 mmol) in 20
mL of hexanes was then added slowly, giving a clear red solution.
The solution was stirred at -78 °C for 30 min, then warmed to room
temperature, and stirred for an additional 30 min. The mixture was
washed with distilled water (3 × 50 mL), and the organic layer was
dried with MgSO4 and concentrated, causing 12 to crystallize as a red
2H), 6.81 (d, J ) 4 Hz, 1H), 6.69 (d, J ) 4 Hz, 1H), 2.49 (s, 6H), 2.26
(s, 3H). 13C NMR (CDCl3) δ 142.72, 139.59, 138.61, 129.91, 129.43,
128.67, 110.99, 21.75, 21.06. MS (FAB, m/z) 312 (M+, 79Br, 90%)
314 (M+, 81Br, 100%). Anal. Calcd for C13H13BrS2: C, 49.84; H, 4.18;
S, 20.47%. Found: C, 49.99; H, 4.20; S, 20.51%.
2,5-Bis(mesitylthio)thiophene (4). A 20 mL THF solution contain-
ing thiophene (1.0 mL, 12.5 mmol) and TMEDA (3.02 g, 26.0 mmol)
was treated with nBuLi (16.3 mL, 26.0 mmol) and then refluxed for 30
min. The solution was then cooled to 0 °C, and a freshly prepared
solution of MesSCl (26.0 mmol) in hexanes (40 mL) was added
dropwise. The resulting solution was stirred overnight and then washed
with H2O (3 × 75 mL), followed by saturated aqueous CuSO4 solution
(3 × 75 mL). The organic phase was dried over MgSO4 and evaporated
to yield a blood-red oil. This was chromatographed (silica, 5:1 hexanes:
EtOAc) to give crude 2 which was recrystallized from hexanes/EtOH
as slightly brown crystals (2.16 g, 5.61 mmol, 45%) mp 93-94 °C.
UV-vis (CH2Cl2) λmax 302 nm (ꢀ ) 13.0 × 103). 1H NMR (CDCl3) δ
6.90 (s, 4H) 6.65 (s, 2H) 2.45 (s, 12H) 2.25 (s, 6H). 13C NMR (CDCl3)
δ 142.66, 139.18, 137.45, 129.31, 128.85, 21.83, 21.05. MS (FAB,
m/z) 384.1 (M+, 100%). Anal. Calcd for C22H24S3: C, 68.7; H, 6.29;
S, 25.01%. Found: C, 68.13; H, 6.26; S, 25.41%.
5,5′-Bis(mesitylthio)-2,2′-bithiophene (5). A solution of 3 (0.61 g,
1.95 mmol) in dry THF (20 mL) was cooled to -78 °C and treated
slowly with nBuLi (1.28 mL, 2.05 mmol). Upon addition of the nBuLi,
the slightly purple solution immediately turned dull yellow. The solution
was stirred for 1.5 h, and solid CuCl2 (0.262 g, 1.95 mmol) was added.
The brown solution was then allowed to warm to room temperature,
stirred for 10 min, and then heated to 50 °C for 2 h. The black solution
was cooled to room temperature and was passed quickly through a
silica frit, eluting with CHCl3 to yield a deep purple solution. The CHCl3
was removed and the solid purple residue was recrystallized from
benzene/MeOH to yield 5 (0.30 g, 0.642 mmol, 66%) as purple crystals,
mp ) 145-147 °C. UV-vis (CH2Cl2) λmax 358 nm (ꢀ ) 24.5 × 103).
1H NMR (CDCl3) δ 6.93 (s, 4H), 6.76 (d, J ) 4 Hz 2H), 6.73 (d, J )
4 Hz, 2H), 2.48 (s, 12H), 2.26 (s, 6H). 13C NMR (CDCl3) δ 142.76,
139.42, 137.45, 136.59, 129.40, 128.67, 123.19, 21.78, 21.08. MS (FAB,
m/z) 466 (M+, 100%). Anal. Calcd for C26H26S4: C, 66.91; H, 5.62; S,
27.48%. Found: C, 66.49; H, 5.62; S 27.26%.
1
solid (4.5 g, 12.1 mmol, 73%), mp 95-96 °C. H NMR (CDCl3) δ
6.91 (s, 2H), 4.23 (s, 4H), 2.52 (s, 6H), 2.24 (s, 3H). 13C NMR (CDCl3)
δ 142.74, 141.22, 139.43, 139.28, 139.20, 129.35, 109.42, 87.29, 64.84,
64.80, 22.05, 21.06. MS, (CI m/z) 370 (M+, 79Br, 63%), 371 (M + 1,
79Br, 86%), 372 (M+, 81Br, 74%), 373 (M + 1, 81Br, 81%). Anal. Calcd
for C15H15O2S2Br: C, 48.52; H, 4.07; S, 17.27%. Found; C, 48.27; H,
4.14; S, 17.53%.
2,5-Bis(tributylstannyl)-3,4-ethylenedioxythiophene (11). A solu-
tion of EDOT 8 (1.0 g, 7.03 mmol) in dry THF (20 mL) was treated
with nBuLi (9.0 mL, 14.4 mmol). Immediately a white precipitate
formed, and the reaction mixture was refluxed gently for 45 min. The
solution was then cooled to room temperature, and tributyltin chloride
(3.91 mL, 14.4 mmol) was added to the solution purely via syringe.
The solution turned from white to dark red, and a precipitate formed.
The solution was then refluxed for 18 h. The THF was removed under
vacuum, and the remaining red residue was dissolved in hexanes. The
resulting solution was filtered, washed with hexanes, and concentrated
to yield a mixture of 8 and 2-tributylstannyl-3,4-ethylenedioxythiophene
in a 5:1 ratio by 1H NMR. Attempts to separate the mixture by column
chromatography or distillation led to decomposition of the product. 1H
NMR (CDCl3) δ 6.56 (s), 4.14 (s), 4.11 (s), 1.58 (m), 1.33 (m), 1.10
(m), 0.896 (m). The listed 1H peaks in italics are assigned to the
monostannylated product.
2,5-Bis(mesitylthio)-3,4-ethylenedioxythiophene (12). nBuLi (4.40
mL, 7.1 mmol) was added dropwise to a solution of EDOT 8 (0.5 g,
3.5 mmol) in THF (20 mL) at room temperature, and the solution was
then stirred for 1.5 h. To this was added a solution of freshly prepared
MesSCl (7.7 mmol) in hexanes (20 mL). The resulting dark red solution
was stirred at 0 °C for 1.5 h. The solution was washed with 3 × 50
mL of water, and the organic phase was dried over MgSO4 and then
concentrated to give a red oil. This was filtered through a silica frit,
eluting with hexanes, and the filtrate was chromatographed (5:1 hexanes:
2,5′′-Bis(mesitylthio)- 2,2′:5′,2′′-terthiophene (6). A 20 mL toluene
solution containing 3 (0.67 g, 2.14 mmol), 2,5-bis(tributylstannyl)-
thiophene (0.638 g, 0.963 mmol), and Pd(PPh3)4 (0.125 g, 5.1 mol %)