for 3 h. The mixture was extracted with toluene (3×100 mL).
The extracts were washed with 5% HCl (2×250 mL) and
4,4∞-Dibromo-2,5-dioctyl-3,3∞-dithienyl sulfide, 22
A mixture of 21 (5 g, 10.7 mmol) and 6 (10.4 g, 43.0 mmol)
was treated with n-BuLi followed by 7 (8.40 g, 26.9 mmol)
according to the procedure described above for the preparation
of 19. The product was purified by flash column chromatogra-
phy (silica gel; hexanes) to give 1 (3.6 g) and 22 (2.3 g, 37.5%
based on 21) as a light yellow liquid. 1H NMR (CDCl ) d
0.87 (t, 6H, J=7 Hz, C8), 1.2–1.4 (m, 20H), 1.5–1.7 (m, 4H,
water (2×500 mL) and dried over MgSO . The solvent was
4
removed under reduced pressure and the residue was distilled
under reduced pressure to afford 20 (31 g, 44%) as light yellow
oil, bp 140–150 °C/0.8 mmHg. 1H NMR (CDCl ) d 0.88 (t, 6H,
3
J=7 Hz, C8 and C8∞ CH ), 1.27 (m, 20H), 1.64 (p, 4H, J=
3
7 Hz, C2 and C2∞ CH ), 2.73 (t, 4H, J=7 Hz, C1 and C1∞
CH ), 6.55 (s, 2H, thienyl C–H). IR (neat) 3060, 2960, 2920,
3
2
2
C2), 2.78 (t, 2H, J=7 Hz, C1–thienyl C2), 2.94 (t, 2H, J=
2
840, 1490, 1390, 810, 740 cm−1.
7
Hz, C1–thienyl C5), 6.40 (d, 1H, thienyl C2), 7.28 (d, 1H,
thienyl C5). IR (neat) 3105, 2960, 2920, 2840, 1520, 1380,
(
B) Dialkylation of thiophene. A 2.5 M solution of n-BuLi
1140, 1030, 922, 851, 778 cm−1.
in hexanes (90.0 mL, 225 mmol) was added dropwise to a
solution of thiophene (8.41 g, 100 mmol) and TMEDA (26.2 g,
25 mmol) in hexanes (200 mL). The mixture was heated at
1
,3-Dimethyldithieno[3,4-b53∞,4∞-d]thiophene, 3
2
reflux, stirred for 4 h and 1-bromooctane (38.6 g, 200 mmol)
was added. The mixture was stirred at reflux for 20 h and
A 2.5 M solution of n-BuLi in hexanes (6.0 mL, 15 mmol)
was added dropwise to the solution of 19 (2.87 g, 7.48 mmol)
poured into a saturated solution of NaHCO (500 mL). The
in Et O (15 mL) in an externally-cooled dropping funnel at
3
2
organic layer was separated, washed with a saturated solution
−78 °C, and stirred for 45 min. The mixture was added to a
of NaHCO (2×500 mL) and H O (2×250 mL), dried over
vigorously stirred suspension of CuCl (2.7 g, 20 mmol) in
3
2
2
MgSO , and the solvent and other impurities were removed
Et O (50 mL) at −50 °C. The mixture was stirred for 2 h, and
4
2
under reduced pressure. The residue was purified by flash
MeOH (20 mL) and H O (20 mL) was added. The mixture
was extracted with hexanes (4×50 mL) and combined extracts
2
column chromatography (silica gel; hexanes) to give 19 (25.6 g,
8
3%) as a light yellow liquid.
were washed with H O (4×50 mL), dried over MgSO , and
2
4
the solvent was removed under reduced pressure. The residue
was purified by flash column chromatography (silica gel;
hexanes) followed by recrystallization from hexanes to give 3
3
,4-Dibromo-2,5-dimethylthiophene, 18
(
(
(
0.30 g, 16%) as a light yellow crystalline solid. 1H NMR
A solution of Br (37.3 g, 235 mmol) in CHCl (30 mL) was
added dropwise to a solution of 2,5-dimethylthiophene, 17
2
3
CDCl ) d 2.37 (s, 3H, CH –C3), 2.63 (s, 3H, CH –C1), 7.00
3
3
3
d, 1H, J=2.6 Hz, C5), 7.33 (d, 1H, J=2.6 Hz, C7). IR (neat)
(
25.0 g, 223 mmol) in CHCl (30 mL) at 0 °C. The mixture
3
3
130, 2920, 2850, 1500, 1450, 1360, 1140, 850, 780 cm−1.
was stirred for 4 h and saturated aqueous NaHCO was
added (100 mL). The organic layer was separated, and the
3
Analysis for C H S , Calcd: C, 53.58; H, 3.60; S, 42.82.
Found: C, 53.47; H, 3.64; S, 42.53%.
1
0 8 3
aqueous layer was extracted with CHCl (100 mL). The com-
3
bined extracts were dried over MgSO and solvent was
4
removed under reduced pressure to give a crude product. This
1
,3-Dioctyldithieno[3,4-b53∞,4∞-d]thiophene, 4
crude product was distilled under reduced pressure to afford
Compound 22 (0.34 g, 0.59 mmol) was treated with n-BuLi
and CuCl according to the procedure given above for the
preparation of 3. The product was purified by flash column
chromatography (silica gel; hexanes) to give 4 (103 mg, 40%)
as a light yellow liquid. 1H NMR (CDCl ) d 0.88 (t, 6H, J=
7
3
-bromo-2,5-dimethylthiophene (20 g) and 18 (10 g,
1
(
5%), bp 70–75 °C/2.5 mmHg, mp 38–40 °C. 1H NMR
CDCl ) d 2.40 (s, 6H, CH ). IR (neat) 2950, 2910, 2820, 1500,
2
3
3
1
340, 1250, 1120, 1000, 820 cm−1.
3
Hz, C8), 1.2–1.45 (m, 20H), 1.72 (p, 4H, J=7 Hz, C2), 2.71
3
,4-Dibromo-2,5-dioctylthiophene, 21
(t, 2H, J=7 Hz, C1), 2.99 (t, 2H, J=7 Hz, C1∞), 6.99 (d, 1H,
J=2.6 Hz, C5), 7.30 (d, 1H, J=2.6 Hz, C7). IR (neat) 3130,
2960, 2920, 2850, 1500, 1450, 1360, 1140, 850, 780 cm−1.
Compound 20 (3.1 g) was treated with Br (2 equiv.) according
2
to the method described for the synthesis of 18. The product
Analysis for C H S , Calcd: C, 68.54; H, 8.63; S, 22.83.
24 36 3
was purified by flash column chromatography (silica gel;
hexanes) to afford 21 as a colorless liquid (44% yield). 1H
NMR (CDCl ) d 0.88 (t, 6H, J=7 Hz, C8 and C8∞ CH ),
Found: C, 68.46; H, 8.57; S, 22.68%.
3
3
1
2
1
.2–1.4 (m, 20H), 1.62 (p, 4H, J=7 Hz, C2 and C2∞ CH ),
Chemical polymerization of 1,3-dioctyldithieno[3,4-b53∞,4∞-d]
thiophene
2
.77 (t, 4H, J=7 Hz, C1 and C1∞ CH ). IR (neat), 2920, 2860,
2
460, 1340, 1250, 1120, 1000, 820 cm−1.
A dispersion of anhydrous FeCl (0.15 g, 0.95 mmol) in dry
CHCl (15 mL) was added to a solution of 4 (0.10 g,
0.24 mmol) in CHCl (12 mL) and the mixture was stirred for
1
purple solid precipitated. The precipitate was extracted in a
Soxhlet extractor with MeOH for 1 d, followed by extraction
with acetone for 1 d and with CHCl for 1 d. Flash column
chromatography (silica gel; hexanes–CH Cl ) of the fraction
extracted with CHCl gave 15 mg of a red solid, and by
changing the eluent to CH Cl , a further 25 mg was recovered.
1
(broad, 4H), 1.5–1.1 (broad, 22H), 0.8 (broad, 6H). IR (neat)
2
3
3
4
,4∞-Dibromo-2,5-dimethyl-3,3∞-dithienyl sulfide, 19
3
d. MeOH (20 mL) was added to the mixture and a dark
A 2.5 M solution of n-BuLi in hexanes (43.0 mL, 108 mmol)
was added dropwise to a solution of 18 (5.6 g, 21 mmol) and
bis(phenylsulfonyl) sulfide (20 g, 83 mmol) in Et O (100 mL)
2
at −78 °C. The mixture was stirred for 45 min and 6 (16.4 g,
3
5
.20 mmol) was added in small portions. The mixture was
2 2
stirred at −78 °C for 2 h, ethanol was added, and the mixture
was warmed to room temperature. The mixture was washed
with H O (3×100 mL), dried over MgSO and the solvent
3
2
2
H NMR (CDCl ) d 2.88 (broad, 2H), 2.62 (broad, 2H), 1.6
3
2
4
was removed under reduced pressure. The residue was purified
by flash column chromatography (silica gel; hexanes) to give
950, 2920, 2850, 1700, 1470 1280, 1220, 1180 cm−1.
7
(4.6 g) and 19 (2.9 g, 35% based on 18) as a light yellow
liquid. 1H NMR (CDCl ) d 2.40 (s, 3H, CH –thienyl C2),
3
3
Acknowledgement
2
.54 (s, 3H, CH –thienyl C5), 6.49 (d, 1H, thienyl C2∞), 7.289
3
(
d, 1H, thienyl C5∞). IR (neat) 3105, 2916, 2850, 1520, 1480,
This research was supported by a National Science Foundation
CAREER Award to D.M.C.
1
320, 1140, 1030, 922, 851, 778 cm−1.
1
724
J. Mater. Chem., 1999, 9, 1719–1725