Fluorinated molecules relevant to conducting polymer research

Article abstract of DOI:10.1016/S0022-1139(02)00289-0

The synthesis of versatile fluorine compounds for conducting polymer research on fluorinated materials is presented. 1,2,4,5-Tetrafluorobenzene was converted to 1,2,4,5-tetrafluorobenzaldehyde (1) and protected as an acetal. This gave the acetals 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)benzene (2a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)benzene (2b). Compounds 2a and 2b were converted into the semiprotected 2,3,5,6-tetrafluoroterephthaldehydes: 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)-6-formylbenzene (3a) and 1,2,4,5- tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)-6-formylbenzene (3b). While 3a was easily deprotected to give 2,3,5,6-tetrafluoroterephthaldehyde (4) compound 3b proved very resilient to hydrolysis and gave a 1:1 mixture of 4 and 1,2,4,5-tetrafluoro-3,6-bis(5,5-dimethyl-1,3-dioxan-2-yl)benzene (5). Compound 4 was reduced to 1,2,4,5-tetrafluoro-3,6-dihydroxymethylbenzene (6) and converted into 1,2,4,5-tetrafluoro-3,6-dibromomethylbenzene (7). Compound 7 was finally converted into 1,2,4,5-tetrafluoro-3,6-bis(diethylphosponylmethyl)benzene (8). Compounds 4 and 8 are versatile fluorinated molecules that can be used to replace their hydrogen counterparts in many molecules and materials. To illustrate this compounds 4 and 8 were oligomerised to give partially fluorinated polyphenylenevinylene (9).

Full text of DOI:10.1016/S0022-1139(02)00289-0

Journal of Fluorine Chemistry 120 (2003) 77–84
Fluorinated molecules relevant to conducting polymer research
Frederik C. Krebs*, Thomas Jensen
The Danish Polymer Centre, RISØ National Laboratory, P.O. Box 49, DK-4000 Roskilde, Denmark
Received 23 August 2002; received in revised form 7 November 2002; accepted 12 November 2002
Abstract
The synthesis of versatile fluorine compounds for conducting polymer research on fluorinated materials is presented. 1,2,4,5-Tetra-
fluorobenzene was converted to 1,2,4,5-tetrafluorobenzaldehyde (1) and protected as an acetal. This gave the acetals 1,2,4,5-tetrafluoro-3-
(1,3-dioxol-2-yl)benzene (2a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)benzene (2b). Compounds 2a and 2b were converted
into the semiprotected 2,3,5,6-tetrafluoroterephthaldehydes: 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)-6-formylbenzene (3a) and 1,2,4,5-tetra-
fluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)-6-formylbenzene (3b). While 3a was easily deprotected to give 2,3,5,6-tetrafluoroterephthaldehyde
(4) compound 3b proved very resilient to hydrolysis and gave a 1:1 mixture of 4 and 1,2,4,5-tetrafluoro-3,6-bis(5,5-dimethyl-1,3-dioxan-2-
yl)benzene (5). Compound 4 was reduced to 1,2,4,5-tetrafluoro-3,6-dihydroxymethylbenzene (6) and converted into 1,2,4,5-tetrafluoro-3,6-
dibromomethylbenzene (7). Compound 7 was finally converted into 1,2,4,5-tetrafluoro-3,6-bis(diethylphosponylmethyl)benzene (8).
Compounds 4 and 8 are versatile fluorinated molecules that can be used to replace their hydrogen counterparts in many molecules and
materials. To illustrate this compounds 4 and 8 were oligomerised to give partially fluorinated polyphenylenevinylene (9).
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Versatile tetrafluorobenzene derivatives; Fluorinated monomers; Fluorinated polyphenylenevinylene; Fluorinated conducting polymers
1. Introduction
In this paper, we describe the synthesis of a series of
versatile fluorinated molecules pertaining to fundamental
studies of fluoroorganic compounds. The range of com-
pounds presented are particularly relevant to conducting
polymer research. We have exemplified their use in the
synthesis of fluorinated oligophenylenevinylene. Structural
drawings are shown in Scheme 1.
The literature on the subject of conducting polymers has
expanded dramatically within the past 10 years. Particular
interest has been devoted to the realisation of polymer based
applications [1–3]. Of crucial importance to the proper
function and application of these materials are the position
of the electronic energy levels [4,5]. In this respect fluorine
is particularly attractive due to the strong inductive effect
where it is possible to lower the position of the valence band
without large alterations in the magnitude of the optical
bandgap. Furthermore, large changes in the emission proper-
ties upon fluorine substitution have been observed for dye
molecules [6,12] and for polytetrafluorophenylenevinylene
(FPPV) itself where excellent photoluminescence in a light
emitting diode application with low turn-on voltage has been
reported [7]. Many of the synthetic procedures however
require readily accessible fluorinated materials and detailed
reports on versatile synthetic procedures leading to fluorine
containing materials are not as preponderant as for the
hydrogen containing analogues.
2. Results and discussion
2.1. Synthesis
Polyparaphenylenevinylene (PPV) [8] the conducting
polymer that has proved the most applicable both in terms
of device construction and fundamental studies in conduct-
ing polymer physics involving theory and experiment. Stu-
dies on variations in the PPV backbone and molecular
structure are numerous and include reports of a partially
halogenated and fluorinated backbone [9,10], the incorpora-
tion of tetrafluorophenylene in a copolymer [11] and the use
of the tetrafluorophenylenevinylene oligomers to efficiently
organise block copolymers with application to electrolumi-
nescent devices [12]. We decided to synthesise versatile
fluorinated molecules that were suitable for these tasks
* Corresponding author. Tel.: þ45-46-77-47-99; fax: þ45-46-77-47-91.
E-mail address: frederik.krebs@risoe.dk (F.C. Krebs).
0022-1139/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 2 ) 0 0 2 8 9 - 0

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F.C. Krebs, T. Jensen / Journal of Fluorine Chemistry 120 (2003) 77–84
Scheme 1.
starting from simple 1,2,4,5-tetrafluorobenzene as outlined
in Scheme 2 employing simple lithiation using nBuLi in
THF at dry ice temperatures. The formation of the aldehyde
is very sluggish when using traditional carbanion formyla-
tion reagents (DMF, N-methylformamide). We found that
excess ethyl formate was the only reagent that gave the
aldehyde in moderate yield. The aldehyde was subsequently
protected with ethylene glycol by a standard procedure
employing azeotropic distillation of water from toluene
under acid catalysis giving 2a. The acetal was easily distilled
and could be subjected to a further lithiation following the
same procedure as above. The semiprotected dialdehyde
3a was crystallised to high purity and easily deprotected in
warm aqueous trifluoroacetic acid giving the desired fluori-
nated terephthaldehyde, 4. The molecules presented in
Scheme 2 allow for easy access to unsymmetrical substitu-
tion in the 3,6 positions of the 1,2,4,5-tetrafluorobenzene
skeleton.
Crystals of compound 4 had a slightly yellow colour even
when purified by repeated crystallisation. In comparison
terephthaldehyde is colourless and the crystal structure of 4
showed a very similar molecular geometry [13] as shown in
Fig. 1.
Compound 4 could be reduced with borane-dimethylsul-
fide to give the dialcohol 6 as shown in Scheme 3. The
conversion of compound 6 into the dibromide 7 using
thionylbromide or CBr4/Ph3P proved unfruitful. Phosphor-
oustribromide was found suitable for the reaction.
However, during the reaction a considerable amount of
an insoluble orange material was formed and further after
removal of excess phosphoroustribromide (by distillation
at low pressure) it proved difficult to properly isolate 7
in a pure form. The product could be crystallised from
Fig. 1. A stereoview showing the molecular geometry of 4.
tetrachloroethylene or CCl4 but the impurities were not
efficiently alleviated and this made further reaction difficult.
The impurities could be efficiently removed by passing the
product mixture dissolved in chloroform through a large
excess of silica. The yellow impurities were filtered off in
this manner and only the clear colourless chloroform phase
was collected and subsequently concentrated to give pure 7.
Compound 7 was converted to the diethylphosphonate ester,
8, under standard Arbuzov conditions by reflux in excess
triethylphosphite. Interestingly 8 was found to be able to
crystallise with or without a water molecule as observed by
crystal structure solution. The molecular geometry of 8 is
shown in Fig. 2.
The use of compounds 6 [14], 7 [15] and the methyl
analogue of 8 [11,12,16] have been reported in the literature
but little synthetic details were given and we therefore
present full synthetic detail and analytical data here.
The synthesis of the partially fluorinated PPV oligomer
was achieved by reacting the dialdehyde 4 and the dipho-
sphonate ester 8 using NaH as base and dry THF as solvent.
The synthesis of the oligomer is shown in Scheme 4.
Compound 9 was obtained as a yellow solid. The material
was poorly soluble in THF at 40 8C where the molecular
weight determination using solvent exclusion chromatogra-
phy (SEC) was attempted. The molecular weight obtained
from the SEC experiment using polystyrene standards was
found to be approximately 1000 g molÀ1 indicating that the
soluble part of the material consist of oligomers. It has to be
kept in mind that 9 is likely to have a stiff geometry in
Scheme 2.

F.C. Krebs, T. Jensen / Journal of Fluorine Chemistry 120 (2003) 77–84
79
Scheme 3.
Fig. 2. A stereoview of 8 showing the molecular geometry of the bisphosphonate ester.
insolubility of the product our results do show that the
formation of oligomers is possible by this reaction.
2.2. Acetal formation
We initially employed neopentylglycol as the protecting
diol for the acetal formation shown in Scheme 5. There were
some complications that were easily avoided by the use of
ethylene glycol as the protecting diol.
Scheme 4.
Firstly, when using benzene as the solvent for the azeo-
tropic distillation along with an excess of neopentylglycol
we obtained, aside from the desired acetal, 2b, also con-
siderable amounts of the very unexpected 1,2,4,5-tetra-
fluoro-3-bis(3-hydroxy-2,2-dimethylpropyloxy)methylben-
zene, 2c. The molecular structure of 2c was confirmed by
solving the X-ray structure as shown in Fig. 3. It was found
that using toluene as the solvent under vigorous reflux and
solution and that the molecular weight based on the stan-
dards is not an absolute but a relative measure depending on
the hydrodynamic volume of the standards and the sample.
MALDI-TOF showed the presence of molecular weights up
to 2200 g molÀ1 corresponding to the bisphosphonate ter-
minated undecamer. While the true yield and polymeric
nature of the product was difficult to establish due to the
Scheme 5.

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F.C. Krebs, T. Jensen / Journal of Fluorine Chemistry 120 (2003) 77–84
Fig. 3. The molecular structure of the unexpected acetal 2c as a stereoview (above) and a sterioview of the acetal 2b showing the molecular geometry in the
crystal (below). The geometry explains the 1H NMR spectrum where two different methyl proton signals are seen and a strong geminal coupling of the
methylene protons next to oxygen.
only a small excess of neopentylglycol avoided this pro-
blem. The reaction was complete in less than 1 h.
3. Conclusion
We have presented a versatile synthetic approach giving
access to multigram quantities of symmetrically and asym-
metrically 3,6-disubstituted 1,2,4,5-tetrafluorobenzene deri-
vatives. We identified important problems in the acetal
formation and deprotection of the formyl derivatives and
showed by crystal structure solution the nature of the by-
products that formed when using neopentylglycol as the
protecting diol. Furthermore the neopentylglycol acetals
were difficult to deprotect. The problems were easily and
effectively avoided simply using ethyleneglycol as protecting
diol. Our work is particularly relevant to fluorinated materials
with emphasis on conducting polymers and oligomers. We
succeeded in applying the precursors for the synthesis of
partially fluorinated oligoparaphenylenevinylene.
2.3. Deprotection
The deprotection, however, proved very difficult as out-
lined in Scheme 5 where a 1:1 mixture of the desired aldehyde
4 and the doubly protected aldehyde 5 was obtained. In order
to find an explanation for the resilience of neopentylglycol
derived acetals to strongly acidic aqueous conditions the
crystal structure was solved to determine the geometry of
the acetal 2b. The molecular structure is shown in Fig. 3
showing how the steric effect of the fluorine atoms forces the
angle formed between the plane of the benzene ring and the
mean plane of the dioxane ring to be near 908.
Unfortunately there have been no previous reports on the
crystal structure of an acetal made from an aromatic alde-
hyde and neopentylglycol. Further, only 24 structures (at
present) containing an acetal of an aromatic aldehyde with a
2,2-disubstituted 1,3-propanediol have been reported mak-
ing a statistically justified comparison difficult though the
data does indicate that a torsion angle of around 908 as
observed here is preferred. From this point of view, it would
seem that the reason for the difficulty encountered in the
hydrolysis is not a steric one. A likely reason is the inductive
electron withdrawing effect of the fluorine atoms that desta-
bilises any protonated and formally positively charged
intermediate.
4. Experimental
All chemicals were reagent grade. NMR spectra were
recorded on a 250 MHz instrument at 300 K unless other-
1
wise stated. TMS was used as reference in the H NMR
spectra and C6F6 in a sealed capillary was used as a standard
for the 19F NMR spectra. Melting points are uncorrected.
SEC was performed using THF as the eluent at 40 8C using
polystyrene standards for calibration. MALDI-TOF was
performed with negative ion detection.

F.C. Krebs, T. Jensen / Journal of Fluorine Chemistry 120 (2003) 77–84
81
4.1. 1,2,4,5-Tetrafluoro-3-(1,3-dioxol-2-yl)benzene (2a)
4.3. 1,2,4,5-Tetrafluoro-3-bis(3-hydroxy-2,2-dimethyl-
propyloxy)methylbenzene (2c)
A dry 2-l three necked flask under argon containing dry
THF (1000 ml) was cooled to À78 8C. nBuLi (340 ml,
1.6 M, 0.54 mol) was added and the mixture cooled to
À78 8C. 1,2,4,5-Tetrafluorobenzene (80 g, 0.53 mol) was
added slowly. The reaction is exothermic and the tempera-
ture was kept below À50 8C. The colour remained light
yellow until the end of the addition where the mixture
became colourless and a white precipitate formed. After
1 h ethyl formate (80 g, excess) was added in one portion.
The precipitate dissolved and the mixture was allowed to
reach room temperature. The mixture was washed with
saturated NaHCO3(aq) (200 ml). The organic phase was
separated, dried with MgSO4, filtered and the solvent was
removed in vacuo. The residue was transferred to a 1000 ml
conical flask containing ethylene glycol (65.4 g, excess) and
toluene (500 ml). para-Toluenesulfonic acid (0.6 g, catalyst)
was added and the mixture refluxed with a water separator.
The reaction was complete in 2 h. After cooling the mixture
was washed with saturated NaHCO3(aq) (200 ml), dried
with MgSO4 and evaporated to give an oil that was distilled
at 65 8C/1 mmHg. This gave 2a as a colourless oil that
crystallise upon standing in 75% yield (89 g). The mp 37–
38 8C; 1H NMR (250 MHz, CDCl3, TMS): d 3.98–4.06
(2H, m), 4.18–4.27 (2H, m), 6.24 (1H, s), 7.01–7.14 (1H,
m); 13C NMR (63 MHz, CDCl3, TMS): d ¼ 66:7 (s), 97.5
(m), 107.4 (t, J ¼ 23 Hz), 118.6 (t, J ¼ 12 Hz), 145.7 (dm,
J ¼ 257 Hz), 146.4 (dm, J ¼ 249 Hz); 19F NMR (235 MHz,
CDCl3, 330 K, C6F6): d ¼ À141:2 (2F, m), À135.8 (2F, m).
Anal. calcd. for C9H6F4O2: C, 48.66; H, 2.72. Found: C,
48.47; H, 2.48.
The raw aldehyde was prepared as described for 2a above.
The raw aldehyde was extracted with benzene (750 ml) and
dried using MgSO4. 2,2-Dimethylpropane-1,3-diol (60 g,
excess) and para-toluenesulphonic acid (0.5 g, catalyst)
was added and the mixture was refluxed gently with a water
separator for 72 h. The mixture was cooled and NaOH(aq)
(200 ml, 1 M) was added. The mixture was further washed
with water (3 Â 1 l). The organic phase was dried using
MgSO4 and evaporated to give an oil that was distilled. The
fraction boiling at temperatures up to 190 8C/17 mmHg was
mainly 2b. The remaining compound was distilled with an
oil pump and the fraction boiling at 152–154 8C/1 mmHg
was collected as a material that solidifies. This gave 2c as a
colourless material in 12% yield (14.7 g). The mp 70–71 8C;
1H NMR (250 MHz, CDCl3, 300 K, TMS): d ¼ 0:91 (6H, s),
0.92 (6H, s), 2.35 (2H, bs), 3.32–3.57, (8H, m), 5.73 (1H, s),
7.00–7.14 (1H, m); 13C NMR (63 MHz, CDCl3, 330 K,
TMS): d ¼ 21:58 (s), 21.63 (s), 36.3 (s), 69.5 (s), 74.4
(s), 97.2 (m), 106.2 (t, J ¼ 14 Hz), 117.8 (m), 144.4 (dm,
J ¼ 251), 145.9 (dm, J ¼ 248 Hz); 19F NMR (235 MHz,
CDCl3, 330 K, C6F6): d ¼ À139:7 (2F, m), À135.1 (2F, m).
Anal. calcd. for C17H24F4O4: C, 55.43; H, 6.57. Found: C,
55.53; H, 6.52.
4.4. 1,2,4,5-Tetrafluoro-3-(1,3-dioxol-2-yl)-6-
formylbenzene (3a)
Compound 2a (95 g, 0.43 mol) was dissolved in dry THF
(1000 ml) and cooled to À78 8C. nBuLi (280 ml, 1.6 M,
0.45 mol) was added quickly while keeping the temperature
below À25 8C. When the temperature stopped rising ethyl
formate (64.6 g, excess) was added and the mixture became
light yellow. After the addition the mixture was allowed to
reach room temperature and saturated aqueous NaHCO3
(200 ml) was added to give a two phase system. The organic
phase was separated, dried with MgSO4 and the solvent was
removed using a rotary evaporator. The crude product was
recrystallised from n-heptane (1000 ml). This gave 3a as a
colourless material in 76% yield (81 g). The mp 76–78 8C; 1H
NMR (250 MHz, CDCl3, 300 K, TMS): d ¼ 4:01À4:22 (4H,
m), 6.21 (1H, s), 10.27 (1H, s); 13C NMR (63 MHz, CDCl3,
330 K, TMS): d ¼ 66:9 (s), 97.1 (s), 116.2 (t, J ¼ 10 Hz),
123.8 (t, J ¼ 13 Hz), 145.8 (dm, J ¼ 250 Hz), 147.2 (dm,
J ¼ 257 Hz), 182.9 (s); 19F NMR (235 MHz, CDCl3, 330 K,
C6F6): d ¼ À142:2 (2F, m), À139.9 (2F, m). Anal. calcd. for
C10H6F4O3: C, 48.01; H, 2.42. Found: C, 48.26; H, 2.22.
4.2. 1,2,4,5-Tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-
yl)benzene (2b)
The raw aldehyde solution in toluene was prepared as
described for 2a above. 2,2-Dimethylpropane-1,3-diol
(37 g, excess) and para-toluenesulfonic acid (0.5 g, catalyst)
was added and the mixture was refluxed vigorously with a
water separator for 1 h. The water separation is very fast
initially. The mixture was cooled and NaOH(aq) (200 ml,
1 M) was added and the mixture further washed with water
(3 Â 1 l). The organic phase was dried using MgSO4 and
evaporated to give an oil that was distilled at 142–143 8C/
17 mmHg. This gave 2b as a colourless material in 75%
yield (67 g). The mp 50–51 8C; 1H NMR (250 MHz, CDCl3,
300 K, TMS): d ¼ 0:81 (3H, s), 1.37 (3H, s), 3.62 (2H, d,
J ¼ 11 Hz), 3.77 (2H, d, J ¼ 10 Hz), 5.80 (1H, s), 6.99–7.13
(1H, m); 13C NMR (63 MHz, CDCl3, 330 K, TMS):
d ¼ 22:3 (s), 23.4 (s), 31.1 (s), 78.6 (s), 95.7 (m), 107.2
(t, J ¼ 23 Hz), 118.4(t, J ¼ 14 Hz), 145.4(dm, J ¼ 253 Hz),
146.7 (dm, J ¼ 252 Hz); 19F NMR (235 MHz, CDCl3,
330 K, C6F6): d ¼ À139:4 (2F, m), À135.8 (2F, m). Anal.
calcd. for C12H12F4O2: C, 54.55; H, 4.58. Found: C, 54.52;
H, 4.49.
4.5. 1,2,4,5-Tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)-
6-formylbenzene (3b)
Compound 2b (67 g, 0.26 mol) was dissolved in dry THF
(500 ml) under Ar and cooled to À78 8C. nBuLi (1.7 M,
160 ml, 0.27 mol) was added in three equal portions allowing

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F.C. Krebs, T. Jensen / Journal of Fluorine Chemistry 120 (2003) 77–84
the temperature to decrease below À60 8C between succes-
sive portions. The reaction is exothermic and the colour
changes to light red. After stirring for 15 min ethyl formate
(150 ml, excess) was added in one portion and the mixture
allowed to reach room temperature. NH4Cl(aq) (2 M,
500 ml) was added and the organic phase separated, washed
with water, dried and evaporated to give a solid. The solid
was recrystallised from heptane (250 ml) by extended heat-
ing. After crystallisation the product was filtered, washed
with light petrol and dried overnight in the vacuum oven at
50 8C. This gave 3b as colourless needle shaped crystals in
73% yield (56 g). The mp 116–117 8C; 1H NMR (250 MHz,
CDCl3, 300 K, TMS): d ¼ 0:80 (3H, s), 1.34 (3H, s), 3.61
(2H, d, J ¼ 11 Hz), 3.77 (2H, d, J ¼ 11), 5.80 (1H, s), 10.28
(1H, s); 13C NMR (63 MHz, CDCl3, 330 K, TMS): d ¼ 22:3
(s), 23.4 (s), 31.2 (s), 78.6 (s), 95.3 (m), 116.1 (t, J ¼ 10 Hz),
123.1 (t, J ¼ 14 Hz), 145.5 (dm, J ¼ 252 Hz), 147.2 (dm,
J ¼ 256 Hz); 19F NMR (235 MHz, CDCl3, 330 K, C6F6):
d ¼ À142:0 (2F, m), À137.7 (2F, m). Anal. calcd. for
C13H12F4O3: C, 53.43; H, 4.14. Found: C, 53.59; H, 4.18.
(4H, d, J ¼ 11), 5.78 (2H, s); 13C NMR (63 MHz, CDCl3,
330 K, TMS): d ¼ 22:4 (s), 23.5 (s), 31.1 (s), 78.6 (s),
95.6 (m), 145.4 (dm, J ¼ 247 Hz); 19F NMR (235 MHz,
CDCl3, 330 K, C6F6): d ¼ À139:4 (4F, s). Anal. calcd.
for C18H22F4O4: C, 57.14; H, 5.86. Found: C, 57.34; H,
5.91.
4.8. 1,2,4,5-Tetrafluoro-3,6-dihydroxymethylbenzene (6)
Compound 4 (40 g, 0.20 mol) was dissolved in dry
THF (1000 ml) under Ar and cooled to 0 8C. The mixture
was light yellow. (CH3)2SÁBH3 was added slowly keeping the
temperature below 5 8C. During the addition of (CH3)2SÁBH3
the mixture became colourless. After the addition the mix-
ture was kept at 0 8C for 15 min and then allowed to reach
RT. Methanol (750 ml) was added carefully due to the
vigorous development of H2. When the development of
H2 had ceased (approximately 45 min) the solvent was
removed using a rotary evaporator. The product was recrys-
tallised from toluene (600 ml). This gave 6 as a colourless
material in 83% yield (34 g). The mp 126–127 8C; 1H NMR
(250 MHz, Me2SO, 300 K, TMS): d ¼ 4:58 (4H, d,
J ¼ 5 Hz), 5.53 (2H, t, J ¼ 6 Hz); 13C NMR (63 MHz,
Me2SO, 300 K, TMS): d ¼ 38:5À40:5 (m), 50.86–50.93
(m), 118.9–119.5 (m), 144.2 (dm, J ¼ 252 Hz); 19F NMR
(235 MHz, Me2SO, 330 K, C6F6): d ¼ À141:8 (4F, s). Anal.
calcd. for C8H6F4O2: C, 45.73; H, 2.88. Found: C, 45.71;
H, 2.73.
4.6. 2,3,5,6-Tetrafluoroterephthaldehyde (4)
Trifluoroacetic acid (200 ml, excess) was placed in a
conical flask. Compound 3a (83 g, 0.33 mol) was added
slowly giving a yellow mixture, followed by water (1000 ml)
and hydrochloric acid (200 ml, 37%). A precipitate form
during the addition. After 20 min stirring at 55 8C the
mixture was allowed to reach RT. The solution was extracted
with chloroform (3 Â 500 ml) and the organic phase was
isolated. The organic phase was washed with water (500 ml)
and the solvent was removed in vacuo to give a light yellow
and solid product. The product was recrystallised from
chloroform (600 ml). This gave 4 as light yellow and
needled shaped crystals in 72% yield (49 g). The mp
131–132 8C; 1H NMR (250 MHz, CDCl3, 300 K, TMS):
d ¼ 10:33 (2H, s); 13C NMR (63 MHz, CDCl3, 300 K,
TMS): d ¼ 119:6 (s), 147.2 (dm, J ¼ 265 Hz), 182.1–182.2
(m); 19F NMR (235 MHz, CDCl3, 330 K, C6F6): d ¼ À140:8
(4F, s). Anal. calcd. for C8H2F4O2: C, 46.62; H, 0.98. Found:
C, 46.79; H, 0.79.
4.9. 1,2,4,5-Tetrafluoro-3,6-dibromomethylbenzene (7)
Compound 6 (34 g, 0.16 mol) was heated gently with
PBr3 (75 ml, 97%, excess) for 1 h. The mixture was distilled
at a pressure of 17 mmHg by heating on an oil bath kept at
100 8C. During the reflux an orange sticky precipate formed.
When the distillation of the excess PBr3 had ceased the
contents of the distillation flask were cooled and the system
repressurised with argon (CAUTION! letting air into the
system at this point occasionally lead to ignition. We ascribe
this to the formation of low oxidation states of phosphor
during the reaction). The residue was dissolved in chloro-
form (1 l) and silica (500 g) was added slowly (CAUTION!
the mixture reacts with the silica providing considerable
amounts of HBr). When the reaction had subsided the slurry
was poured onto a column containing silica (250 g). The
column was washed with chloroform (4 Â 500 ml) collect-
ing only the clear fractions of CHCl3. The solvent was
removed using the rotary evaporator leaving 7 as a colour-
less material which was recrystallised from CCl4 (400 ml).
This gave 7 as a colourless material in 63% yield (34 g). The
mp 125–126 8C; 1H NMR (250 MHz, CDCl3, 300 K, TMS):
d ¼ 4:51 (4H, s); 13C NMR (63 MHz, CDCl3, 330 K, TMS):
d ¼ 16:8 (m), 118.0 (m), 145.3 (dm, J ¼ 254 Hz); 19F NMR
(235 MHz, CDCl3, 330 K, C6F6): d ¼ À139:0 (4F, s). Anal.
calcd. for C8H4Br2F4: C, 28.60; H, 1.20. Found: C, 28.35;
H, 1.07.
4.7. 1,2,4,5-Tetrafluoro-3,6-bis(5,5-dimethyl-1,3-dioxan-
2-yl)benzene (5)
Compound 3b (10 g, 34 mmol) was dissolved in trifluor-
oacetic acid (100 ml) and heated to reflux. Water (25 ml)
was added and the mixture was refluxed for 1 h. Water
(175 ml) was added and the mixture refluxed for 1 h during
which a solid starts to precipitate. The mixture was cooled
and filtered. The solid was washed with water, dried and
recrystallised from heptane (compound 4 (3 g, 43%) could
be recovered from the liquor by evaporation). This gave 5 as
colourless needle shaped crystals in 47% yield (6.1 g). The
mp 169–170 8C; 1H NMR (250 MHz, CDCl3, 300 K, TMS):
d ¼ 0:80 (6H, s), 1.36 (6H, s), 3.60 (4H, d, J ¼ 11), 3.77

F.C. Krebs, T. Jensen / Journal of Fluorine Chemistry 120 (2003) 77–84
83
4.10. 1,2,4,5-Tetrafluoro-3,6-
bis(diethylphosponylmethyl)benzene (8)
browntoyellow. Thesolventwasremovedinvacuo.Thisgave
compound9asayellowpowder. Thepowderwaswashedwith
CH2Cl2 (200 ml) and CH3OH (200 ml). This gave 9 as a
yellow material in 58% yield (0.26 g).
Compound 7 (10 g, 30 mmol) was added to boiling
triethylphosphite (100 ml, excess) and Ar was bubbled
through the mixture. During the additon the mixture became
light green. The mixture was kept at the boiling point
for 15 min and then cooled to room temperature. The last
traces of the mixture of triethylphosphate, ethyldiethylpho-
sphonate and triethylphosphate was removed with an oil
pump. The residue crystallised giving a colourless product.
The product was recrystallised from n-heptane (150 ml).
This gave 8 as a colourless material in 82% yield (11 g). The
4.12. Crystallography
General crystallographic data for 2b, 2c, 4 and 8 can be
found in Table 1. The crystals were mounted on a glass
capillary using ApiezonTM grease and transferred to the cold
stream on the diffractometer.
An almost complete sphere of reciprocal space was
covered by a combination of several sets of exposure frames;
each set with a different j angle for the crystal and each
frame covering a scan of 0.38 in o. Data collection, integra-
tion of frame data and conversion to intensities corrected for
Lorenz, polarization and absorption effects were performed
using the programs SMART [17], SAINT [17] and SADABS
[18]. Structure solution, refinement of the structures, struc-
ture analysis and production of crystallographic illustrations
was carried out using the programs SHELXS97 [19],
SHELXL97 [19] and SHELXTL [20]. The structure was
checked for higher symmetry and none was found [21].
The H atoms were included in their calculated positions.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplemen-
tary publication no. CCDC-191096, CCDC-191097, CCDC-
191098 and CCDC-191099. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: þ44-1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk).
1
mp 41–42 8C; H NMR (250 MHz, CDCl3, 300 K, TMS):
d ¼ 1:22 (12H, t, J ¼ 7), 3.18 (4H, d, J ¼ 20 Hz), 4.01–4.07
(8H, m); 13C NMR (63 MHz, CDCl3, 330 K, TMS):
d ¼ 16:0 (m), 21.4 (d, J ¼ 142 Hz), 62.5 (m), 110.6 (m),
144.7 (dm, J ¼ 243 Hz); 19F NMR (235 MHz, CDCl3,
330 K, C6F6): d ¼ À139:0 (4F, s). Anal. calcd. for
C16H24F4O6P2: C, 42.68; H, 5.37. Found: C, 42.68; H, 5.34.
4.11. Poly-(2,3,5,6-tetrafluoro-1,4-phenylene-1,
2-vinylene) (9)
Compound 8 (1.13 g, 2.5 mmol) was placed in a conical
flaskanddissolvedinTHF(500 ml). NaH(60%, 0.5 g,excess,
washed with n-hexane) was added and the mixture was stirred
for20 min. Subsequentlycompound4(0.52 g, 2.5 mmol)was
added.Thisturnedthecolourofthemixturefromdarkgreento
brownwithblueflourescence. Themixturewasrefluxedunder
argonovernight. AfterwardsCH3OH(500 ml)andHCl(3 ml,
37%) was added changing the colour of the mixture from
Table 1
Crystallographic data for the compounds 2b, 2c, 4 and 8
Compounds
2b
2c
4
8
Formula
C12H12F4O2
264.22
C17H24F4O4
368.36
C8H2F4O2
206.10
C16H24F4O6P2ÁH2O
468.31
Formula wt.
Crystal system
Space group
Type of radiation
Z
Monoclinic
P21/c
Triclinic
P-1
Monoclinic
P21/n
Triclinic
P-1
Mo Ka
8
Mo Ka
2
Mo Ka
2
Mo Ka
2
˚
a (A)
23.356(4)
5.5606(9)
19.572(3)
90
6.0397(14)
11.300(3)
13.802(3)
68.329(4)
82.626(4)
89.237(5)
867.6(4)
1.410
7.6258(11)
5.6926(9)
8.2861(13)
90
7.9527(14)
9.5390(17)
14.899(3)
93.421(3)
98.848(3)
106.888(3)
1062.1(3)
1.464
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
113.649(3)
90
103.594(3)
90
3
˚
V (A )
2328.4(7)
1.507
349.63(9)
1.958
r (g cm3)
Crystal dimensions (mm)
0.83 Â 0.75 Â 0.50
0.143
0.25 Â 0.16 Â 0.10
0.126
0.75 Â 0.70 Â 0.25
0.208
0.76 Â 0.50 Â 0.25
0.274
m (cmÀ1
T (K)
)
120(2)
28199
120(2)
11470
120(2)
4179
120(2)
13506
Number of reflections
Unique reflections ðI > 2sÞ
R(F), Rw(F2) all data
4018
4756
951
5591
0.0551, 0.1678
0.0817, 0.2678
0.0385, 0.0971
0.0383, 0.1194

84
F.C. Krebs, T. Jensen / Journal of Fluorine Chemistry 120 (2003) 77–84
[6] F.C. Krebs, H. Spanggaard, J. Org. Chem. 67 (2002) 7185–7192.
Acknowledgements
[7] L.H. Gan, Y.M. Wang, Y. Xu, N.K. Goh, Y.Y. Gan, Macromolecules
34 (2001) 7409–7413.
This work was supported by the Danish Technical
Research Council (STVF).
[8] J.D. Capistran, D.R. Gagnon, S. Anton, R.W. Lens, E.F. Karasz,
A.C.S. Polym. Preprints 25 (1984) 282.
[9] I.-N. Kang, D.-H. Hwang, H.-K. Shim, Synth. Met. 69 (1995)
547–548.
References
[10] R. Riehn, J. Morgado, R. Iqbal, S.C. Moratti, A.B. Holmes, S. Volta,
F. Cacialli, Synth. Met. 124 (2001) 67–69.
[11] A.M. Sarker, B. Strehmel, D.C. Neckers, Macromolecules 32 (1999)
7409–7413.
¨
[12] F. Cacialli, W.J. Feast, R.H. Friend, M. de Jong, P.W. Lovenich, W.R.
[1] (a) P.K.H. Ho, J.-S. Kim, H. Burroughes, S.F.Y. Becker, T.M.
Brown, F. Caclalli, R.H. Friend, Nature 404 (2000) 408;
(b) Y. Yang, Mater. Res. Soc. Bull. 22 (1997) 16–24;
(c) H.E.A. Huitema, G.H. Gelinck, J.B.P.H. Van der Putten, K.E.
Kuijk, C.M. Hart, E. Cantatore, P.T. Herwig, A.J.J.M. van Breemen,
D.M. de Leeuw, Nature 414 (2001) 599.
Salaneck, Polymer 43 (2002) 3555–3561.
[13] D. Britton, J. Chem. Cryst. 28 (1998) 601.
[14] J. Forrester, R.V.H. Jones, L. Newton, P.N. Preston, Tetrahedron 57
(2001) 2871–2884.
[2] (a) H.E. Katz, A.J. Lovinger, J. Johnson, C. Kloc, T. Siegrist, W. Li,
Y.-Y. Lin, A. Dodabalapur, Nature 404 (2000) 478–480;
(b) C.J. Drury, C.M.J. Mutsaers, C.M. Hart, M. Matters, D.M. de
Leeuw, Appl. Phys. Lett. 73 (1998) 108–110;
[15] (a) R. Filler, G.L. Cantrell, D. Wolanin, S.M. Naqvi, J. Fluorine
Chem. 30 (1985) 399–414;
(b) A.K. Barbour, M.W. Buxton, P.L. Coe, R. Stephens, J.C. Tatlow,
J. Chem. Soc. (1961) 808–817.;
(c) H. Sirringhaus, N. Tessler, R.H. Friend, Science 393 (1998) 619–
620.
¨
[3] (a) J.H. Schon, C. Kloc, E. Bucher, B. Batlogg, Nature 403 (2000)
(c) W.-Q. Liu, B.P. Roques, C. Garbay, Tetrahedron Lett. 38 (1997)
1389–1392.
[16] B. Strehmel, A.M. Sarker, J.H. Malpert, V. Strehmel, H. Seifert,
D.C.J. Neckers, Am. Chem. Soc. 121 (1999) 1226–1236.
[17] Siemens, SMART and SAINT, Area-Detector Control and Integra-
tion Software, Siemens Analytical X-ray Instruments Inc., Madison,
WI, USA, 1995.
408–410;
¨
(b) M. Granstrom, K. Petritsch, A.C. Arias, A. Lux, M.R.
Andersson, R.H. Friend, Nature 395 (1998) 257–260.
[4] (a) C.C. Wu, C.I. Wu, J.C. Sturm, A. Kahn, Appl. Phys. Lett. 70
(1997) 1348–1350;
[18] G.M. Sheldrick, Empirical Absorption Program (SADABS), Siemens
SMART Platform.
(b) I.H. Campbell, S. Rubin, T.A. Zawodzinski, J.D. Kress, R.L.
Martin, D.L. Smith, N.N. Barashkov, J.P. Ferraris, Phys. Rev. B 54
(1996) 14321–14324;
[19] G.M. Sheldrick, SHELX-97, Program for Structure Solution and
Refinement, 1997.
(c) E.L. Bruner, N. Koch, A.R. Span, S.L. Bernasek, A. Kahn, J.
Schwartz, J. Am. Chem. Soc. 124 (2002) 3192–3193.
´
[5] (a) J.L. Bredas, A.J. Heeger, Chem. Phys. Lett. 217 (1994) 506–512;
[20] G.M. Sheldrick, SHELXTL95, Siemens Analytical X-ray Instru-
ments Inc., Madison, WI, USA, 1995.
[21] A.L. Spek, Acta Cryst. A46 (1990) C–31.
(b) F.C. Krebs, M. Jørgensen, Macromolecules 35 (2002) 7200–7206.