M. Landman, H. Görls, S. Lotz
FULL PAPER
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standard on a Bruker ARX-300 spectrometer. Ϫ Infrared spectra
were recorded on a FT-IR spectrophotometer using dichlor-
omethane as solvent unless otherwise specified. Ϫ Mass spectra
were recorded at ca. 70 eV on a Finnigan Mat 8200 instrument,
using the electron impact method.
(q, J ϭ 7.0 Hz, 2 H, OCH2CH3), 2.47 (s, 3 H, Me3), 2.41 (d, J ϭ
1.2, 3 H, Me6), 1.71 (t, 3J ϭ 7.0, 3 H, OCH2CH3). Ϫ 13C NMR
(CDCl3, 75.1 MHz): δ ϭ 318.7 (carbene carbon), 222.8, 216.8
(CO), 150.1 (C2), 144.7 (C4), 142.6 (C5), 130.8 (C3), 129.5 (C6),
128.2 (C7), 76.4 (OCH2CH3), 18.6 (Me3), 15.6 (OCH2CH3), 14.7
(Me6). Ϫ MS (EI); m/z: 416 [Mϩ], 388 [Mϩ Ϫ CO], 360 [Mϩ
2 CO], 332 [Mϩ Ϫ 3 CO], 304 [Mϩ Ϫ 4 CO], 276 [Mϩ Ϫ 5 CO].
Ϫ
All reactions were performed in an inert atmosphere of either nitro-
gen or argon by using standard Schlenk techniques and vacuum-
line methods. Solvents were dried and distilled under nitrogen prior
to use. Ϫ Column chromatography was carried out under nitrogen
using either silica gel (particle size 0.063Ϫ0.200 nm) or neutral alu-
minium oxide as resin. Ϫ Most chemicals were used directly with-
out prior purification. The following compounds were prepared us-
ing known literature methods: 3,6-dimethylthieno[3,2-b]thi-
ophene,[14] 2,3,5-tribromothiophene,[11] 3-bromothiophene,[12] ethyl
(3-thienylthio)acetate,[10] ethyl (2-formyl-3-thienylthio)acetate,[13]
2: Yield 1.25 g (47%), C24H16O12S2Cr2 (664.5): calcd. C 43.38, H
2.43; found C 43.61, H 2.62. Ϫ IR (νCO; CH2Cl2) ϭ 2053 (m), 1986
(w), 1941 (vs) cmϪ1. Ϫ 1H NMR (CDCl3, 300.135 MHz): δ ϭ 5.19
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3
(q, J ϭ 7.1 Hz, 4 H, OCH2CH3), 2.47 (s, 6 H, Me3), 1.74 (t, J ϭ
7.1 Hz, 6 H, OCH2CH3). Ϫ 13C NMR (CDCl3, 75.1 MHz): δ ϭ
223.6, 216.3 (CO), 167.7 (C2), 149.8 (C4), 131.9 (C3), 76.6
(OCH2CH3), 17.6 (Me3), 15.5 (OCH2CH3). Ϫ MS (EI); m/z: 636
[Mϩ Ϫ CO], 552 [Mϩ Ϫ 4 CO], 524 [Mϩ Ϫ 5 CO].
thieno[3,2-b]thiophene carboxylic acid, thieno[3,2-b]thiophene[12]
,
and triethyloxonium tetrafluoroborate.[20]
3: Yield 0.23 g (12%), C19H16O8S2Cr (488.5): calcd. C 46.72, H
3.31; found C 46.86, H 3.45. Ϫ IR (νCO; CH2Cl2) ϭ 2057 (m), 1984
(w), 1940 (vs) cmϪ1. Ϫ 1H NMR (CDCl3, 300.135 MHz): δ ϭ 5.20
Revised Synthesis of Thieno[3,2-b]thiophene: Synthesis of 2,3,5-trib-
romothiophene was effected according to the method described by
Brandsma and Verkruijsse,[11] and involved the reaction of bromine
(180.00 mL; 3.50 mol) and thiophene (80.00 mL, 1.00 mol) in a
48% aqueous HBr/diethyl ether solution (400 mL/100 mL) at elev-
ated temperatures (75°C). The target product (97%) and HBr were
formed. Reduction of 2,3,5-tribromothiophene (321.00 g, 1.00 mol)
to obtain 3-bromothiophene (55%),[12] was performed using zinc
dust (196.00 g, 3.00 mol) in 175 mL of acetic acid. Reaction of 3-
bromothiophene (90.50 g, 0.55 mol) with elemental sulfur (17.60 g,
0.55 mol), followed by the addition of ethyl bromoacetate
(61.4 mL, 0.55 mol), afforded ethyl (3-thienothio)acetate (73%). On
reacting this acetate-substituted thiophene (26.60 g, 0.13 mol) with
phosphorus oxychloride (30.00 g, 0.19 mol) in N,N-dimethylforma-
mide (14.00 g, 0.19 mol) afforded ethyl(2-formyl-3-thienothio)acet-
ate (85%) in a Vilsmeier formylation reaction.[13] Cyclization and
the subsequent decarboxylation of this compound yielded thi-
eno[3,2-b]thiophene.[10]
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3
(q, J ϭ 6.9 Hz, 2 H, OCH2CH3ϪM), 4.35 (q, J ϭ 7.2 Hz, 2 H,
OCH2CH3ϪO), 2.70 (s, 3 H, Me3), 2.43 (s, 3 H, Me6), 1.72 (t, 3J ϭ
6.9 Hz,
3 ϭ 7.2 Hz, 3 H,
H, OCH2CH3ϪM), 1.38 (t, 3J
OCH2CH3ϪO). Ϫ 13C NMR (CDCl3, 75.1 MHz): δ ϭ 317.9 (car-
bene carbon), 223.3, 216.7 (CO), 163.6 (C2), 163.1 (C7), 142.7 (C4),
142.0 (C5), 130.6 (C3), 129.7 (C6), 76.4 (OCH2CH3ϪM), 61.4
(OCH2CH3ϪO), 17.7 (Me3), 15.6 (OCH2CH3ϪM), 15.0 (Me6),
14.4 (OCH2CH3ϪO). Ϫ MS (EI); m/z: 488 [Mϩ], 460 [Mϩ Ϫ CO],
432 [Mϩ Ϫ 2 CO], 404 [Mϩ Ϫ 3 CO], 376 [Mϩ Ϫ 4 CO], 348 [Mϩ
Ϫ 5 CO].
Tungsten Carbene Complexes 4, 5, and 6: 3,6-Dimethylthieno[3,2-
b]thiophene (0.34 g, 2.00 mmol) was dissolved in 30 mL of hexane.
TMEDA (0.60 mL, 4.00 mmol) and n-butyl lithium (2.80 mL, 4.40
mmol) were added to this solution at room temperature. The same
procedure was followed as for the chromium analog with the addi-
tion of W(CO)6 (1.40 g, 4.00 mmol). For alkylation triethyloxon-
ium tetrafluoroborate (0.74 g, 4.00 mmol) was used. On purifica-
tion using column chromatography, three bands separated. The elu-
ent used involved hexane/dichloromethane mixtures of various
compositions. While the first product was isolated using pure hex-
ane as eluent, a 1:1 mixture was used to isolate the third product.
The first monocarbene complex 4 was isolated as an orange solid.
The second purple complex was characterized as the biscarbene
complex 5, while the third red-orange band was identified as 6.
Chromium Carbene Complexes 1, 2, and 3: 3,6-Dimethylthieno[3,2-
b]thiophene (0.67 g, 4.00 mmol) was dissolved in 50 mL of hexane.
TMEDA (1.20 mL, 8.00 mmol) and n-butyl lithium (5.5 mL, 8.8
mmol) were added at room temperature. The mixture was refluxed
for 45 minutes and then cooled to 0 °C. After the addition of 50 mL
of THF, Cr(CO)6 (1.76 g, 8.00 mmol) was added and the suspen-
sion stirred for an hour. The color of the reaction changed to dark
brown. After completion of the reaction, the solvent was removed
in vacuo. The residue was dissolved in 20 mL of dichloromethane.
Triethyloxonium tetrafluoroborate (1.50 g, 8.10 mmol) was dis-
solved in 20 mL of dichloromethane and this was added to the
cooled reaction mixture (Ϫ20 °C). An immediate color change to
a purple solution was observed. Stirring was maintained for a fur-
ther hour while the temperature was allowed to reach room temper-
ature. The mixture was then filtered, the solvent removed, and the
remainder purified on a silica gel column. Three products were
isolated, starting with pure hexane as eluent and gradually increas-
ing the polarity of the solvent by adding dichloromethane. The first
was the orange monocarbene complex 1. The second purple com-
plex was the biscarbene complex 2, while the third red-orange com-
pound was characterized as 3. This complex was isolated using a
hexane/dichloromethane mixture (1:1) as eluent.
4: Yield 0.45 g (41%), m.p.187Ϫ189 °C. Ϫ C16H12O6S2W (548.3):
calcd. C 35.05, H 2.21; found C 35.23, H 2.40. Ϫ IR (νCO
;
CH2Cl2) ϭ 2063 (m), 1989 (w), 1933 (vs) cmϪ1. Ϫ 1H NMR
(CDCl3, 300.135 MHz): δ ϭ 7.22 (q, J ϭ 1.1 Hz, 1 H, H7), 5.02
4
(q, 3J ϭ 7.1 Hz, 2 H, OCH2CH3), 2.48 (s, 3 H, Me3), 2.41 (d, J ϭ
4
1.1 Hz, 3 H, Me6), 1.69 (t, J ϭ 7.1 Hz, 3 H, OCH2CH3). Ϫ 13C
3
NMR (CDCl3, 75.1 MHz): δ ϭ 292.6 (carbene carbon), 201.9,
197.8 (CO), 150.2 (C2), 144.1 (C4), 144.1 (C5), 132.1 (C3), 131.0
(C6), 128.8 (C7), 79.0 (OCH2CH3), 18.9 (Me3), 15.4 (OCH2CH3),
14.6 (Me6). Ϫ MS (EI); m/z: 548 [Mϩ], 520 [Mϩ Ϫ CO], 492 [Mϩ
Ϫ 2 CO], 464 [Mϩ Ϫ 3 CO], 436 [Mϩ Ϫ 4 CO], 408 [Mϩ Ϫ 5 CO].
5: Yield 0.67 g (36%), C24H16O12S2W2 (928.3): calcd. C 31.05, H
1.74; found C 31.14, H 1.82. Ϫ IR (νCO; CH2Cl2) ϭ 2062 (m), 1983
(w), 1938 (vs) cmϪ1. Ϫ 1H NMR (CDCl3, 300.135 MHz): δ ϭ 5.04
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3
1: Yield 0.55 g (33%), m.p.173Ϫ177 °C. Ϫ C16H12CrO6S2 (416.4): (q, J ϭ 7.1 Hz, 4 H, OCH2CH3), 2.48 (s, 6 H, Me3), 1.72 (t, J ϭ
calcd. C 46.15, H 2.91; found C 46.36, H 3.05. Ϫ IR (νCO
;
7.1 Hz, 6 H, OCH2CH3). Ϫ 13C NMR (CDCl3, 75.1 MHz): δ ϭ
CH2Cl2) ϭ 2055 (m), 1979 (w), 1938 (vs) cmϪ1. Ϫ 1H NMR 202.2, 197.3 (CO), 164.9 (C2), 149.3 (C4), 123.5 (C3), 79.6
(CDCl3, 300.135 MHz): δ ϭ 7.18 (q, J ϭ 1.2 Hz, 1 H, H7), 5.19 (OCH2CH3), 18.4 (Me3), 15.3 (OCH2CH3). Ϫ MS (EI); m/z: 932
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Eur. J. Inorg. Chem. 2001, 233Ϫ238