Dithienophosphole-capped π-conjugated oligomers

Article abstract of DOI:10.1039/c0nj00026d

The synthesis of a 2-monobrominated dithieno[3,2-b:2′,3′-d] phosphole has opened the access to a series of highly luminescent π-conjugated oligomers that link two dithienophosphole units via a variety of aromatic spacers. The nature of the linking mode wa

Full text of DOI:10.1039/c0nj00026d

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www.rsc.org/njc | New Journal of Chemistry
Dithienophosphole-capped p-conjugated oligomerswzy
Stefan Durben, Thomas Linder and Thomas Baumgartner*
Received (in Montpellier, France) 15th January 2010, Accepted 2nd March 2010
DOI: 10.1039/c0nj00026d
The synthesis of a 2-monobrominated dithieno[3,2-b:20,30-d]phosphole has opened the access
to a series of highly luminescent p-conjugated oligomers that link two dithienophosphole
units via a variety of aromatic spacers. The nature of the linking mode was found to
have a significant impact on the photophysical properties of the system as a whole, either
considerably improving the molar absorptivity of the new extended chromophores, or providing
luminescent materials with red-shifted emission features and substantial photoluminescence
quantum yields.
to systematically address a variety of important features
Introduction
targeted toward certain applications.5 Our studies have
shown that dithienophosphole is an exceptionally strong
chromophore with impressive quantum yields ranging from
50–90%. We were further able to fine tune the properties of
molecular building blocks (i.e., emission colors and semi-
conducting behavior),6 as well as to access polymeric materials
with desirable photophysical properties and processability
features.7
The intriguing optical and electronic properties of organic
p-conjugated materials have led to the significant growth and
considerable importance of organic electronics in recent years.
The intrinsic semiconducting properties of these materials
make them excellent candidates for a variety of optoelectronic
applications, such as Organic Light-Emitting Diodes
(OLEDs), Organic Photovoltaic Cells (OPVs), and Organic
Field-Effect Transistors (OFETs), among others.1 The inherent
benefits of using organic components include an almost
infinite pool of synthons that can be incorporated in these
materials, allowing for the possibility of tailoring the materials
properties towards specific applications. Although purely
organic components have proven to be quite a useful resource
for the synthesis of organic electronic materials, inorganic main
group components have recently started to draw an increasing
amount of attention in this context. Particularly, organoboron-,2
organosilicon-,3 and organophosphorus-based4 p-conjugated
materials have proven to be very valuable for this purpose.
Due to their unique nature, in terms of electronics and
chemistry, inorganic components provide unprecedented (with
purely organic based materials) opportunities to significantly
tune the materials’ electronics. Whereas boron provides
an empty p-orbital that can effectively overlap with a
p-conjugated scaffold, silicon and phosphorus have shown a
peculiar interaction involving the p-conjugated scaffold—the
p*-orbital in particular—and the antibonding s*-orbitals of
exocyclic Si/P–C bonds that both lower the LUMO levels of
the materials significantly.2–4 These electronic effects are much
more pronounced than those of purely organic units and
illustrate the highly valuable nature of the main group
approach toward organic electronics.
In this contribution we now report the synthesis and
advanced characterization of a series of p-conjugated oligomers
that showcase two dithienophosphole units as ‘end-caps’ linked
by different aromatic spacers. We were interested, if the
unprecedented photophysical properties of dithienophosphole-
based materials can be enhanced through the presence of two
units within the same material. Furthermore, we wanted to
investigate how the linking mode of the two dithienophosphole
units affects the photophysical properties of the materials as
a whole.
Results and discussion
Synthesis and characterization of 2-bromodithieno[3,2-b:20,30-d]-
phosphole oxide
To be able to install the dithienophosphole moiety as an end
cap, mono-functionalization of the scaffold was deemed
necessary. Recently, a 2-iododithieno[3,2-b:20,30-d]phosphole
oxide has been reported by our group as precursor for highly
luminescent
dithienophosphole-containing
terpyridinyl
complexes,8 representing the first example of monofunctionalized
dithienophosphole building blocks. Starting point for the
work presented here is the corresponding bromo-derivative 2
(BrS2PO), which was prepared by rapid addition of one
equivalent N-bromosuccinimide (NBS) to dithienophosphole
oxide 1 (S2PO) in dimethylformamide solution at 0 1C
(Scheme 1). Under these conditions, the reaction proceeds
extremely fast, meaning that the conversion is complete
immediately after addition of the brominating reagent.
Unfortunately, dibromination in the 2- and 6-positions6b
seems to be favored over the desired monobromination. In
an attempt to optimize the reaction it was found that traces of
2,6-dibrominated product 3 (Br2S2PO) started to form upon
In this context we have established the dithieno[3,2-b:20,30-d]-
phosphole system over the past seven years or so and were able
Department of Chemistry, University of Calgary, 2500 University Dr.
NW, Calgary AB, T2N 1N4, Canada.
E-mail: thomas.baumgartner@ucalgary.ca; Fax: +1 403-289-9488
w This article is part of a themed issue on Main Group chemistry.
z In memory of Pascal Le Floch, an esteemed member of the phos-
phorus family.
y CCDC reference number 761478 (2). For crystallographic data in
CIF format see DOI: 10.1039/c0nj00026d
ꢀc
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Scheme 1 Synthesis of monobrominated dithienophosphole 2.
addition of only 0.3 equivalents of NBS, indicating that the
reactivity of 2-bromodithienophosphole oxide 2 towards NBS
is significantly higher than that of non-halogenated oxide 1.
The previously reported 2-iododithieno[3,2-b:20,30-d]phosphole
could be conveniently separated from the product mixture
with cold dichloromethane.8 Similar procedures with a variety
of solvents were attempted for the purification of 2, however,
due to the similar solubility of mono- and dibrominated
species 2 and 3, none of these methods were successful. For
the same reason, crystallization from a variety of different
solvent mixtures did not provide pure product. Column
chromatography on silica gel with chloroform/ethyl acetate
(1/1) was established to be the most successful method for the
separation of non-, mono- and dibrominated product. Due to
the polar nature of phosphole oxides, retention factors for 1–3
are low (Rf = 0.4–0.5). Even though tedious, the effort leads
to pure compound 2 in moderate yields (61%). Typically,
B10% of starting material 1 and B15% of dibromide 3 are
also recovered. The formation of 2 is supported by a significant
change in the 1H NMR spectrum, clearly showing the presence
of an asymmetric species. To a lesser extent, the 31P NMR
resonance also supports the monobrominated product with
a chemical shift of d31P 18.9 ppm, which lies in between
the resonance frequencies for 1 (d31P 18.7 ppm) and 3
(d31P 19.1 ppm).
cell. All bond lengths of the dithienophosphole scaffold are in
very good agreement to previously reported dithienophosphole
oxides.5b,6b The monobromination seems to have only minor
influence on the annelated framework. In the crystal packing
(Fig. 1, bottom), however, the presence of the bromine results in
short intermolecular bromine–oxygen contacts of 2.97 A that
had been observed in the packing of a dibrominated dithieno-
phosphole before.9 In addition, the crystal structure exhibits
coplanar face-to-face interactions between the dithienophosphole
backbone of neighboring molecules (3.75 A), and the phenyl
substituents of neighboring molecules (3.60 A), respectively.
The photophysical properties of the new monobrominated
dithienophosphole were determined in dilute methylene
chloride solution (c = 10ꢁ5 M) and show, in comparison to
Single crystals of 2, suitable for X-ray crystallography, could
be obtained from a concentrated acetone solution (Table 1). The
solid state structure (Fig. 1, top) of the monobrominated
dithienophosphole exhibits a planar dithienophosphole scaffold,
indicating a high degree of p-conjugation. As a result of
the monofunctionalization, the pyramidal phosphorus atom
becomes a stereocenter. Both enantiomers are present in the unit
Table 1 Crystal data and data collection details for 2
Empirical formula
Formula weight
Crystal system
Space group
a/A
C14H8BrOPS2
734.41
Monoclinic
P21/c
19.5034(6)
8.3637(2)
18.1644(6)
105.2595(11)
2858.52(15)
4
b/A
c/A
b1
V/A3
Z
Dcalc/g cmꢁ3
T/K
F(000)
1.706
293
1456
3.267
Fig. 1 Molecular structure of 2 (top) and packing (bottom) in the
solid state (50% probability level, hydrogens are omitted for clarity).
Selected bond lengths [A]: P1–C3 1.805(5), P1–C6 1.814(5), P1–C9
1.806(5), BR1–C1 1.859(5), C1–C2 1.362(6), C2–C3 1.419(6), C3–C4
1.369(6), C4–C5 1.454(6), C5–C6 1.389(7), C6–C7 1.409(7), C7–C8
1.367(8), P2–C23 1.807(5), P2–C26 1.812(5), P2–C29 1.789(5),
BR2–C21 1.858(5), C21–C22 1.376(7), C22–C23 1.410(7), C23–C24
1.379(6), C24–C25 1.445(7), C25–C26 1.380(7), C26–C27 1.423(7),
C27–C28 1.356(8).
m/mmꢁ1
Reflections collected
Unique reflections
Observed reflections
R indices (all data)
10 482
6410
5391
Rint = 0.0292
R1 = 0.0698
wR2 = 0.1743
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Table 2 Photophysical data and calculated frontier orbital energies for 1–5
emaxa/L molꢁ1 cmꢁ1
lexb/nm
lemb/nm
fPL
EHOMOd/eV
ELUMOd/eV
DEbgd/eV
c
Compound
labsa/nm
1
2
362
374
384
428
397
416
430
465
6650
7800
9450
19 550
25 650
75 800
38 400
41 900
365
382
397
432
402
421
437
458
453
465
473
498
481
489
500
544
0.57
0.54
0.57
0.32
0.47
0.21
0.19
0.80
—
—
—
ꢁ5.32
ꢁ5.28
ꢁ5.34
ꢁ5.23
ꢁ5.06
—
—
—
—
—
—
3.04
2.56/2.64
3.15
3.05
2.64
36b
4a
4b
4c
4d
5
ꢁ2.28
ꢁ2.72/ꢁ2.64
ꢁ2.19
ꢁ2.18
ꢁ2.42
a
b
c
UV/VIS absorption in CH2Cl2. Fluorescence excitation and emission maxima in CH2Cl2. Photoluminescence quantum yields in CH2Cl2
d
solution, relative to quinine sulfate (1–4) or fluorescein (5). Calculated energies, B3LYP/6-31G*.
1, red-shifted excitation and emission features due to a
decrease of the LUMO energy as a result of the electron
withdrawing nature of the halogen atom (Table 2).6b The
excitation and emission wavelengths of 2 (lex = 382 nm,
lem = 465 nm) are red-shifted from the starting material 1
(lex = 365 nm, lem = 453 nm) by 17 nm and 12 nm,
respectively. Upon introduction of a second bromine in the
6-position (3, lex = 397 nm, lem = 473 nm),6b the excitation
and emission bands experience a further bathochromic shift by
15 nm and 8 nm, respectively, which represents an almost
linear dependence of the photophysical features on the degree
of bromination. Monobrominated compound 2 shows a high
photoluminescence quantum yield (fPL = 54%), comparable
to those previously reported for 1 (fPL = 57%) and 3
(fPL = 57%). The UV/VIS absorption spectra (Fig. 2) follow
the same quasi-linear trend for the absorption wavelengths of
the p–p*-transition with increasing degree of bromination
(1: labs = 362 nm; 2: labs = 374 nm;3: labs = 384 nm).
An increase of the absorption coefficient was observed with
increasing numberꢁo1f bromine atoms present (1: e(362) =
6650 L molꢁ1 cm ; 2: e(374) = 7800 L molꢁ1 cmꢁ1; 3:
e(384) = 9450 L molꢁ1 cmꢁ1). Participation of bromine lone
pairs in the p-conjugation, or an increased cross-section could
explain this behavior.
Synthesis and characterization of cross-coupled oligomers
The monobrominated dithienophosphole oxide 2 was sub-
sequently used as starting material for the synthesis of a series
of p-conjugated oligomers via an established Suzuki–Miyaura
cross-coupling protocol (Scheme 2). In previous studies,5b,6b,7b,8
Fig. 2 UV/VIS absorption (top) and normalized emission spectra
the oxidized phosphorus center proved to be very tolerant to
subsequent cross-coupling reactions, as it prevents coordination
of the phosphorus to palladium, which is commonly used as
catalyst for a variety of carbon–carbon bond forming
reactions, such as Heck–Cassar–Sonogashira-, Suzuki–
Miyaura- or Stille-reactions.10 In order to investigate the
effects of different conjugation-pathways and -lengths, a series
of oligomers with benzene-derived linkers 4a–d was targeted.
In addition, the effect of a heteroarene-bridge was examined in
compound 5. Suzuki–Miyaura coupling of 2 with the corres-
(bottom) of 1–3 in CH2Cl2 solution.
compounds show slightly downfield shifted 31P NMR
resonances (d31P 19.2–19.6 ppm) compared to that of 2
(d31P 18.9). In the case of the hydrocarbon linked systems
1
4a–d, the highly diagnostic H NMR signal for the proton in
the 3-position of the dithienophosphole scaffold experiences
a characteristic downfield shift (d1H 7.37–7.42 ppm) when
compared to the corresponding signal in the starting material 2
(d1H 7.12 ppm). This effect is far less pronounced in the
bithiophene-linked oligomer 5 (d1H 7.19 ppm), potentially
due to some sulfur–hydrogen interactions.
ponding diboronic acids in
a biphasic (toluene/water)
mixture6b,10 afforded the short chains 4a–d as yellow to orange
solids in moderate yields. The bithiophene-bridged compound
5 was obtained as dark orange solid in moderate yield from
the reaction of 2 with 2,20-bithiophene-5,50-diboronic acid
bis(pinacole) ester11 in tetrahydrofuran solution. All coupled
All cross-coupled oligomers feature two phosphorus
stereocenters, giving rise to three possible diastereomers in
statistical distribution. Even though all diastereomers must be
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Scheme 2 Synthesis of dithienophosphole-capped oligomers.
present, it was impossible to separately characterize them,
since only a single set of NMR-signals was observed in each
case. The 1,3- and 1,4-benzene bridged compounds 4a,b were
purified by column chromatography, but no separation of the
diastereomers was observed. The separation of the diastereomers
would have been desirable in order to increase the chance of
crystallizing the oligomers but none of the materials formed
single crystals suitable for X-ray crystallography. The latter,
on the other hand, is a beneficial feature, as crystallinity
and resulting solid-state quenching effects often reduce the
applicability of these compounds in optoelectronic devices.1
Upon extension of the p-conjugated system, all photo-
physical features are significantly red-shifted from those of
starting material 2 (Table 2). The smallest bathochromic
shift is observed with the 1,3-benzene-bridged oligomer 4b
(lex = 402 nm, lem = 481 nm), due to the somewhat disrupted
conjugation path through the 1,3-benzene link. Surprisingly,
the 4,40-biphenyl-linked chain 4c shows only slightly
red-shifted excitation and emission features (lex = 421 nm,
lem = 489 nm) compared to 4b. This is probably due to the
non-coplanar structure of biphenyl, leading to a disrupted
conjugation path and electronic decoupling into two separate
fluorophores. The 1,4-benzene- and the 2,7-fluorene-bridged
compounds 4a and 4d show almost identical maxima of
excitation and emission (4a: lex = 432 nm, lem = 498 nm;
4d: lex = 437 nm, lem = 500 nm), giving rise to the assumption
that a comparable effective conjugation length is present in
both molecules. In the case of the bithiophene-bridged
molecule 5, excitation and emission features are most
significantly red-shifted (lex = 458 nm, lem = 544 nm),
probably due to a more planar structure and electron donating
nature of the electron-rich linker (Fig. 3).
Fig. 3 UV/VIS absorption (top) and normalized emission spectra
(bottom) of 4a–d and 5 in CH2Cl2 solution.
Compounds 4d and 5 showed significantly increased molar
UV/VIS absorption maxima are in very good agreement
with the excitation data. The extinction coefficients rise in the
order 4a o 4b o 4d o 5 o 4c (Table 2). The fact that 4b has a
higher absorption coefficient than 4a was surprising, however,
theoretical calculations showed a two-fold degenerate LUMO
in 4b (Fig. 4) that very likely leads to a significant increase
absorptivities (4d: e(430)
= 38 400 L ; 5:
molꢁ1 cmꢁ1
e(465) = 41 900 L molꢁ1 cmꢁ1) compared to 4a and b due
to their extended p-conjugated system and high planarity. The
highest absorptivity was observed in compound 4c (e(416) =
75 800 L molꢁ1 cmꢁ1), which can be explained by the
non-coplanar nature of the biphenyl linker, resulting in the
(De 6100
L ) of the absorption coefficient.
molꢁ1 cmꢁ1
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Fig. 4 Frontier orbital diagrams of 4a (left) and 4b (right).
formation of two separate chromophores in one molecule. The
photoluminescence quantum yields for the hydrocarbon-
linked compounds 4a–d are moderate to good (Table 2),
probably due to some degree of rotational freedom between
the dithienophosphole end groups and the linker. The
bithiophene-bridged oligomer 5 shows a very high photo-
luminescence quantum efficiency (fPL = 80%), which is very
likely caused by the fixated coplanar structure of the
thiophene units.
path in the spacer. In accordance with previous studies,4c–f,5,6c,8
the phosphorus centers exclusively contribute to the LUMO,
offering the unique possibility of tuning the LUMO energies
by functionalization of the phosphorus centers. Compounds
4a–d show consistently low-lying HOMO energies (EHOMO
=
ꢁ5.34 to ꢁ5.23 eV), illustrating the stabilizing effect of
moderately electron-poor spacers. In contrast to that, a
destabilized HOMO-level (EHOMO = ꢁ5.06 eV) is observed
in 5, due to the electron-rich linker. The LUMO energies of
4a,c,d are also similar (ELUMO = ꢁ2.28 to ꢁ2.18 eV).
Compound 4b, however, shows a significantly stabilized
LUMO energy as an effect of the degeneration. The bithiophene-
bridged oligomer 5 shows a low-lying LUMO compared to
4a,c,d due to the presence of electron-deficient end-groups
attached to a linker with high electron-density, i.e. an acceptor–
donor–acceptor (A–D–A) architecture.
In order to gain a deeper understanding of the electronic
structure of the oligomers, DFT calculations at the B3LYP/
6-31G* level of theory were performed.12 All oligomers show
coplanar or only slightly twisted structures with, 4b excepted,
frontier orbitals extending over the entire conjugated
backbone. The frontier orbitals of compound 4a are shown
as an example (Fig. 4). As mentioned above, the 1,3-benzene
linked derivative 4b shows a two-fold degeneration (DE o 0.1 eV)
of the LUMO orbital (Fig. 4), resulting in an increased molar
absorptivity compared to 4a, despite a disrupted conjugation
As shown in our previous studies,5,6 functionalization of the
phosphorus centers results in a fine tuning of the band gaps by
shifting the energy of the LUMO. In an attempt to illustrate
ꢀc
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this effect, the reduction of the phosphorus centers of
compounds 4a and 4b was investigated via the established
protocols.6b Upon treatment of the phosphole oxides with an
excess of BH3, both 4a and 4b exhibited a visibly increased
emission intensity with unchanged emission color upon
irradiation with a hand-held UV-lamp, very likely due to the
formation of a phosphole–borane adduct, which has been
previously reported for the inverse systems.6b
used as received. 2,20-Bithiophene-5,50-diboronic acid bis(pinacol)
ester11 and dithieno(3,2-b:20,30-d)phosphole oxide5b were
1
prepared according to literature methods. H NMR, 13C NMR
and 31P NMR spectra were recorded on a Bruker DMX-300 or
Bruker Avance(-II, -III) 400 spectrometer. Chemical shifts are
reported in ppm, referenced to external 85% H3PO4 (31P) or
solvent signal (1H, 13C). 13C and 31P NMR spectra were
measured with proton decoupling. Elemental analysis was
performed at the Department of Chemistry at the University
of Calgary. It should be noted that some samples showed low
carbon values even after column chromatography, indicating
inherent problems with the measurement of these samples.
Mass spectrometry was performed using a Finnigan SSQ700
or Bruker Daltonics AutoFlex III system. Optical spectro-
scopy was performed with dichloromethane solutions using a
Jasco FP-6600 spectrometer and UV-Vis-NIR Cary 5000
spectrometer. Theoretical calculations have been carried out
at the B3LYP/6-31G* level by using the GAUSSIAN 03 suite
of programs.12 This level of the theory has provided satisfactory
results for phosphole–thiophene oligomers before.4–6,8 The
geometries were fully optimized and at the resulting structures
second derivatives were calculated.
Subsequently, an excess of triethylamine was added, which
led to a visible blue shift of the emission for both investigated
oligomers upon irradiation with UV-light. 31P NMR spectro-
scopy of the crude product mixture of the reduction of 4a gave
a single and very weak signal at d31P ꢁ20.3 ppm, indicating
successful reduction to the phosphole. However, due to the
extremely low solubility of the reduced oligomers in various
solvents, purification attempts were unsuccessful and the
reduced species could not be isolated.
Conclusions
In conclusion, we have succeeded in synthesizing and isolating
a
valuable monobrominated dithienophosphole building
block, whose photophysical properties align nicely with those
of the non- and dibrominated relatives. Subsequent cross-
coupling reactions with a series of aryl linkers, exhibiting
different architectures, provided some detailed insights
into the modification of the photophysical properties of
‘dithienophosphole-rich’ conjugated materials. Our studies
have indicated that proper choice of the linker components
allows for selectively addressing the molar absorptivity, or the
emission colors/quantum yields of the materials. Linkers that
disrupt the conjugation were found to separate the oligomers
into two independent chromophores with dramatically
X-Ray crystallography
Diffraction data were collected on a Nonius Kappa CCD
diffractometer using monochromated MoKa radiation
(l = 0.71073 A) at ꢁ100 1C. The data sets were corrected
for Lorentz and polarization effects and empirical absorption
correction was applied to the net intensities. The structure was
solved by direct methods and refined using SHELX.13 After
full-matrix least-square refinement of the nonhydrogen atoms
with anisotropic thermal parameters, the hydrogen atoms were
placed in calculated positions using a riding model.
improved absorption coefficients of over 75 000 L molꢁ1 cmꢁ1
,
whereas linkers that promote conjugation over the whole
scaffold provide for significantly red-shifted emission colors.
Depending on the rigidity of the linker, remarkable photo-
luminescence quantum yields of up to 80% can be obtained
for materials with an orange emission.
Syntheses
2-Bromodithieno[3,2-b:20,30-d]phosphole oxide 2. To a solution
of dithieno[3,2-b:20,30-d]phosphole oxide (2.57 g, 8.91 mmol) in
120 mL dimethylformamide (DMF), a solution of NBS (1.56 g,
8.91 mmol) in 25 mL DMF was dropwise (quickly) added at
0 1C. Immediately after addition, the mixture was poured on
500 mL of water. The yellow suspension was extracted with
chloroform (3 ꢂ 100 mL). The combined organic phases were
dried over magnesium sulfate and evaporated at reduced
pressure to leave a yellow solid, which was purified by column
chromatography on silica using chloroform/ethyl acetate (1/1) as
eluent to give monobrominated product 2 (2.00 g, 61%) as
yellow solid (found: C, 45.5; H, 2.1. C14H8OPS2 requires C,
We are currently addressing the solubility issue of the
extended oligomers by introducing additional solubilizing
groups to the scaffold in order to investigate the fine tuning
of the photophysical properties of the materials through
phosphorus chemistry and to install improved processability
features within these highly luminescent materials for a
potential application in light-emitting devices.
45.7; H, 2.2%); 1H NMR (300 MHz; CDCl3) 7.12 (1H, d, 3JH,P
=
Experimental section
3
2.5 Hz, 3-H), 7.16 (1H, dd, JH,P = 2.3 Hz, JH,H = 4.9 Hz,
3
General procedures
4
5-H), 7.32 (1H, dd, JH,P = 3.3 Hz, JH,H = 4.9 Hz, 6-H),
3
Reactions were carried out in dry glassware under inert gas
atmosphere of purified nitrogen using Schlenk techniques.
Solvents were dried using an MBraun solvent purification
system. N-Bromosuccinimide (NBS), 1,3-phenyldiboronic
acid, 1,4-phenyldiboronic acid, 4,40-biphenyldiboronic acid,
9,9-dihexylfluorene-2,7-diboronic acid, caesium fluoride,
sodium carbonate and tetrakis(triphenylphosphine)palladium(0)
were purchased from Alfa Aesar, Sigma Aldrich or Strem and
7.39–7.49 (2H, m, m-Ph), 7.51–7.61 (1H, m, p-Ph), 7.67–7.77
(2H, m, o-Ph); 31P{1H} NMR (121.5 MHz, CDCl3) 18.9;
3
13C{1H} NMR (100.6 MHz; CDCl3) 114.8 (d, JC,P
=
18.1 Hz, Ar-Br), 126.1 (d, JC,P = 14.9 Hz, Ar), 128.4 (d,
JC,P = 13.8 Hz, Ph), 128.9 (d, JC,P = 15.1 Hz, Ar), 129.0
1
(d, JC,P = 101.8 Hz, ipso-Ph), 129.0 (d, JC,P = 13.2 Hz, Ph),
4
130.8 (d, JC,P = 11.5 Hz, Ar), 132.7 (d, JC,P = 3.0 Hz, p-Ph),
1
1
137.7 (d, JC,P = 98.5 Hz, ipso-Ar), 138.8 (d, JC,P = 95.5 Hz,
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ipso-Ar), 145.4 (d, JC,P = 24.6 Hz, Ar), 145.8 (d, JC,P
=
(d, JC,P = 23.1 Hz, Ar), 145.9 (d, JC,P = 24.5 Hz, Ar), 147.2
(d, JC,P = 14.4 Hz, Ar). It should be noted that the high-field
peak of the signal at 129.4 ppm overlaps with the signal at
129.0 ppm, resulting in a shoulder rather than a distinct peak.
HRMS: m/z 649.9821 (M+. C34H20O2P2S4 requires 649.9821).
22.2 Hz, Ar).
Compound 4a (1,4-benzene-bridged oligomer). 1,4-Phenyl-
diboronic acid (83 mg, 0.5 mmol), [Pd(PPh3)4] (60 mg,
0.04 mmol) and BrS2PO (400 mg, 1.1 mmol) were dissolved
in 25 mL toluene and an aqueous solution of Na2CO3 (1 M,
10 mL) added. The emulsion was refluxed at 110 1C for 48 h.
After cooling, the mixture was poured on 100 mL saturated
NH4Cl solution. The aqueous phase was extracted with
chloroform (3 ꢂ 60 mL). The combined organic phases were
dried over magnesium sulfate and evaporated at reduced
pressure to leave an orange solid, which was purified by
column chromatography on silica using chloroform/ethyl
acetate (1/1) as eluent to give product 4a (150 mg, 46%) as
orange-yellow solid (found: C, 61.3; H, 3.4. C34H20O2P2S4
requires C, 62.8; H, 3.1%); 1H NMR (400 MHz; CD2Cl2) 7.18
(2H, dd, 3JH,P = 2.4 Hz, 3JH,H = 4.9 Hz, 5,50-H, S2PO), 7.38
(2H, dd, 4JH,P = 3.3 Hz, 3JH,H = 4.9 Hz, 6,60-H, S2PO), 7.41
Compound 4c (4,40-biphenyl-bridged oligomer). 4,40-Biphenyl-
diboronic acid (150 mg, 0.6 mmol), [Pd(PPh3)4] (75 mg,
0.07 mmol) and BrS2PO (478 mg, 1.3 mmol) were dissolved in
35 mL toluene and an aqueous solution of Na2CO3 (1 M, 15 mL)
added. The emulsion was refluxed at 110 1C for 72 h. After
cooling, the mixture was poured on 150 mL water. The aqueous
phase was extracted with chloroform (5 ꢂ 60 mL). The combined
organic phases were dried over magnesium sulfate and evaporated
at reduced pressure to leave an orange-brown solid, which was
washed repeatedly with hot hexanes and acetone to give product
1
4c (185 mg, 41%) as light orange solid. H NMR (300 MHz;
4
3
CDCl3) 7.18 (2H, dd, JH,P = 2.4 Hz, JH,H = 4.9 Hz, 5,50-H,
3
3
S2PO), 7.32 (2H, dd, JH,P = 3.3 Hz, JH,H = 4.9 Hz, 6,60-H,
3
3
(2H, d, JH,P = 2.7 Hz, 3,30-H, S2PO), 7.42–7.48 (4H, m,
S2PO), 7.39 (2H, d, JH,P = 2.7 Hz, 3,30-H, S2PO), 7.42–7.50
m-Ph), 7.53–7.59 (2H, m, p-Ph), 7.61 (4H, s, Ph-bridge),
7.70–7.79 (4H, m, o-Ph); 31P{1H} NMR (121.5 MHz, CDCl3)
(4H, m, m-Ph), 7.52–7.59 (2H, m, p-Ph), 7.63 (8H, br s,
3
Ph2-bridge), 7.79 (4H, br dd, JH,H = 7.0 Hz, JH,P
3
=
19.6; 13C{1H} NMR (100.6 MHz; CD2Cl2) 122.2 (d, JC,P
=
13.5 Hz, o-Ph); 31P{1H} NMR (121.5 MHz, CDCl3) 19.2;
14.2 Hz, Ar), 126.4 (d, JC,P = 14.6 Hz, Ar), 126.7 (s, C-H, Ph-
bridge), 129.5 (d, JC,P = 12.8 Hz, Ph), 129.6 (d, JC,P = 14.8
13C{1H} NMR (100.6 MHz; DMSO-d6) 122.4 (d, JC,P
14.4 Hz, Ar), 125.8 (s, C-H, biphenyl), 126.1 (d, JC,P
=
=
Hz, Ph), 129.8 (d, 1JC,P = 72.4 Hz, ipso-Ph), 131.4 (d, JC,P
=
14.5 Hz, Ar), 127.1 (s, C-H, biphenyl), 129.1 (d, JC,P = 12.7 Hz,
1
11.4 Hz, Ar), 133.0 (d, JC,P = 2.7 Hz, p-Ph), 133.8 (s, C-C,
1
Ph-bridge), 139.2 (d, JC,P = 111.8 Hz, ipso-Ar), 141.0 (d,
1JC,P = 110.6 Hz, ipso-Ar), 145.0 (d, JC,P = 22.9 Hz, Ar),
146.4 (d, JC,P = 24.0 Hz, Ar), 148.0 (d, JC,P = 14.1 Hz, Ar);
HRMS: m/z 649.9850 (M+. C34H20O2P2S4 requires 649.9821).
Ph), 130.2 (d, JC,P = 106.9 Hz, ipso-Ph), 130.5 (d, JC,P =
11.3 Hz, Ar), 130.8 (d, JC,P = 14.7 Hz, Ph), 132.1 (s, C-C,
1
biphenyl), 132.6 (d, JC,P = 2.7 Hz, p-Ph), 138.2 (d, JC,P
=
=
1
109.2 Hz, ipso-Ar), 138.6 (s, C-C, biphenyl), 139.9 (d, JC,P
109.2 Hz, ipso-Ar), 143.2 (d, JC,P = 23.0 Hz, Ar), 144.7 (d,
JC,P = 24.0 Hz, Ar), 147.0 (d, JC,P = 14.2 Hz, Ar).
Compound 4b (1,3-benzene-briged oligomer). 1,3-Phenyl-
diboronic acid (80 mg, 0.5 mmol), [Pd(PPh3)4] (58 mg,
0.04 mmol) and BrS2PO (370 mg, 1.0 mmol) were dissolved
in 20 mL toluene and an aqueous solution of Na2CO3 (1 M,
10 mL) added. The emulsion was refluxed at 110 1C for 48 h.
After cooling, the mixture was poured on 100 mL saturated
NH4Cl solution. The aqueous phase was extracted with
chloroform (3 ꢂ 50 mL). The combined organic phases were
dried over magnesium sulfate and evaporated at reduced
pressure to leave an orange solid, which was purified by
column chromatography on silica using chloroform/ethyl
acetate (1/1) as eluent to give product 4b (132 mg, 42%) as
yellow solid (found: C, 61.2; H, 3.3. C34H20O2P2S4 requires C,
Compound 4d (9,9-dihexylfluorene-bridged oligomer). 9,9-
Dihexylfluorene-2,7-diboronic acid (296 mg, 0.7 mmol),
[Pd(PPh3)4] (85 mg, 0.07 mmol) and BrS2PO (540 mg,
1.5 mmol) were dissolved in 30 mL toluene and an aqueous
solution of Na2CO3 (1 M, 15 mL) added. The emulsion was
refluxed at 110 1C for 48 h. After cooling, the mixture was
poured on 100 mL water. The aqueous phase was extracted
with chloroform (3 ꢂ 60 mL). The combined organic phases
were dried over magnesium sulfate and evaporated at reduced
pressure to leave an orange solid, which was washed repeatedly
with hexanes and diethyl ether to give product 4d (318 mg,
50%) as orange solid (found: C, 69.1; H, 5.1. C53H48O2P2S4
requires C, 70.2; H, 5.3%); 1H NMR (400 MHz; CDCl3) 0.75
1
62.8; H, 3.1%); H NMR (400 MHz; CDCl3) 7.16 (2H, dd,
3JH,P = 2.4 Hz, 3JH,H = 4.9 Hz, 5,50-H, S2PO), 7.31 (2H, dd,
3
(6H, t, JH,H = 7.0 Hz, CH3), 0.96–1.34 (16H, m, CH2), 1.99
(4H, t, 3JH,H = 8.0 Hz, a-CH2), 7.19 (2H, dd, 4JH,P = 2.4 Hz,
3
4JH,P = 3.3 Hz, JH,H = 4.9 Hz, 6,60-H, S2PO), 7.37 (2H, d,
3JH,P = 2.5 Hz, 3,30-H, S2PO), 7.38–7.49 (7H, complex area,
m-Ph and Ph-bridge), 7.50–7.59 (2H, m, p-Ph), 7.66 (1H, t,
4JH,H = 1.5 Hz, Ph-bridge), 7.77 (4H, br dd, 3JH,H = 7.9 Hz,
3JH,P = 13.3 Hz, o-Ph); 31P{1H} NMR (121.5 MHz, CDCl3)
3JH,H = 4.9 Hz, 5,50-H, S2PO), 7.32 (2H, dd, 3JH,P = 3.3 Hz,
3
3JH,H = 4.9 Hz, 6,60-H, S2PO), 7.42 (2H, d, JH,P = 2.7 Hz,
3,30-H, S2PO), 7.44–7.52 (6H, m, m-Ph and 1,8-H, fluorene),
7.52–7.60 (4H, m, p-Ph and 3,6-H, fluorene), 7.69 (2H, br d,
3
19.6; 13C{1H} NMR (100.6 MHz; CDCl3) 122.0 (d, JC,P
=
4,5-H, fluorene), 7.82 (4H, br dd, JH,H = 7.0 Hz, JH,P =
3
14.2 Hz, Ar), 122.8 (s, Ph-bridge), 122.9 (s, Ph-bridge), 125.5
13.5 Hz, o-Ph); 31P{1H} NMR (121.5 MHz, CDCl3) 19.6;
13C{1H} NMR (100.6 MHz; CDCl3) 14.0 (s, CH3), 22.5 (s,
CH2), 23.7 (s, CH2), 29.6 (s, CH2), 31.4 (s, CH2), 40.3
(s, a-CH2), 55.4 (s, 9-C, fluorene), 119.9 (s, C-H,
fluorene), 120.5 (s, C-H, fluorene), 121.3 (d, JC,P = 14.2 Hz,
Ar), 124.9 (s, C-H, fluorene), 126.1 (d, JC,P = 14.7 Hz, Ar),
(s, Ph-bridge), 126.1 (d, JC,P = 14.6 Hz, Ar), 128.8 (d, JC,P
15.1 Hz, Ph), 129.0 (d, JC,P = 13.2 Hz, Ph), 129.4 (d, 1JC,P
=
=
106.0 Hz, ipso-Ph), 130.8 (d, JC,P = 11.4 Hz, Ar), 132.5 (d,
C,P = 2.8 Hz, p-Ph), 134.2 (s, C-C, Ph-bridge), 138.3 (d, 1JC,P
112.5 Hz, ipso-Ar), 140.0 (d, 1JC,P = 111.3 Hz, ipso-Ar), 144.6
J
=
ꢀc
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128.4 (d, JC,P = 15.1 Hz, Ph), 129.0 (d, JC,P = 13.0 Hz, Ph),
129.7 (d, 1JC,P = 108.0 Hz, ipso-Ph), 130.9 (d, JC,P = 11.3 Hz,
Ar), 132.5 (s, C-C, fluorene), 132.5 (d, JC,P = 2.7 Hz, p-Ph),
2 (a) M. J. D. Bosdet and W. E. Piers, Can. J. Chem., 2009, 87, 8;
(b) M. Elbing and G. C. Bazan, Angew. Chem., Int. Ed., 2008, 47,
834; (c) S. Yamaguchi and A. Wakamiya, Pure Appl. Chem., 2006,
78, 1413; (d) F. Jakle, Coord. Chem. Rev., 2006, 250, 1107;
¨
1
1
138.2 (d, JC,P = 112.4 Hz, ipso-Ar), 140.1 (d, JC,P
111.6 Hz, ipso-Ar), 140.7 (s, C-C, fluorene), 143.8 (d, JC,P
=
=
(e) C. D. Entwistle and T. B. Marder, Chem. Mater., 2004, 16,
4574.
3 (a) A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz and
A. B. Holmes, Chem. Rev., 2009, 109, 897; (b) M. Shimizu,
H. Tatsumi, K. Mochida, K. Oda and T. Hiyama, Chem.–Asian
J., 2008, 3, 1238; (c) S. Yamaguchi, C. Xu and T. Okamoto, Pure
Appl. Chem., 2006, 78, 721; (d) S. Yamaguchi and K. Tamao,
23.0 Hz, Ar), 146.2 (d, JC,P = 24.2 Hz, Ar), 149.1 (d,
JC,P = 14.4 Hz, Ar), 152.0 (s, C-C, fluorene); HR-MALDI/
TOF-MS: m/z 929.1938 (M+
+ Na. C53H48NaO2P2S4
requires 929.1964).
Chem. Lett., 2005, 34, 2; (e) M. Hissler, P. W. Dyer and R. Re
Coord. Chem. Rev., 2003, 244, 1.
4 (a) T. Baumgartner and R. Re
´
au,
Compound
5
(5,50-bithiophene-bridged oligomer). 2,20-
´
au, Chem. Rev., 2006, 106, 4681
Bithiophene-5,50-diboronic acid bis(pinacol) ester (321 mg,
0.8 mmol), [Pd(PPh3)4] (90 mg, 0.06 mmol), caesium fluoride
(770 mg, 5.1 mmol) and BrS2PO (620 mg, 1.7 mmol) were
dissolved in 50 mL tetrahydrofuran and refluxed at 70 1C for
72 h. After cooling, the mixture was reduced to dryness and
the residue taken up in 150 mL chloroform. The solution
was extracted with saturated NH4Cl solution and water.
The organic phase was dried over magnesium sulfate and
evaporated at reduced pressure to leave an orange solid, which
was repeatedly washed with cold diethyl ether to give product
5 (330 mg, 58%) as orange-red solid (found: C, 57.9; H, 3.1.
C36H20O2P2S6 requires C, 58.5; H, 2.7%); 1H NMR
(300 MHz; CDCl3) 7.08 (4H, br s, bridge), 7.17 (2H, dd,
(Chem. Rev., 2007, 107, 303) Correction; (b) M. G. Hobbs and
T. Baumgartner, Eur. J. Inorg. Chem., 2007, 3611; (c) Y. Matano
and H. Imahori, Org. Biomol. Chem., 2009, 7, 1258; (d) J. Crassous
and R. Reau, Dalton Trans., 2008, 6865; (e) A. Fukazawa,
´
Y. Ichihashi, Y. Kosaka and S. Yamaguchi, Chem.–Asian
J., 2009, 4, 1729; (f) A. Saito, T. Miyajima, M. Nakashima,
T. Fukushima, H. Kaji, Y. Matano and H. Imahori,
Chem.–Eur. J., 2009, 15, 10000; (g) T. Agou, Md. D. Hossain,
T. Kawashima, K. Kamada and K. Ohta, Chem. Commun., 2009,
6762.
5 (a) T. Baumgartner, T. Neumann and B. Wirges, Angew. Chem.,
2004, 116, 6323 (Angew. Chem., Int. Ed., 2004, 43,
6197); (b) T. Baumgartner, W. Bergmans, T. Ka
T. Neumann, M. Nieger and L. Nyulaszi, Chem.–Eur. J., 2005,
11, 4687.
6 (a) T. Neumann, Y. Dienes and T. Baumgartner, Org. Lett., 2006,
8, 495; (b) Y. Dienes, S. Durben, T. Karpati, T. Neumann,
U. Englert, L. Nyulaszi and T. Baumgartner, Chem.–Eur. J.,
2007, 13, 7487; (c) Y. Dienes, M. Eggenstein, T. Karpati,
T. C. Sutherland, L. Nyulaszi and T. Baumgartner, Chem.–Eur.
rpati,
´ ´
´
3
3JH,P = 2.4 Hz, JH,H = 4.9 Hz, 5,50-H, S2PO), 7.19 (2H, d,
´
´
´
3JH,P = 2.7 Hz, 3,30-H, S2PO), 7.31 (2H, dd, 4JH,P = 3.4 Hz,
3JH,H = 4.9 Hz, 6,60-H, S2PO), 7.41–7.50 (4H, m, m-Ph),
´
´
´
3
7.52–7.60 (2H, m, p-Ph), 7.77 (4H, br dd, JH,H = 7.0 Hz,
J., 2008, 14, 9878; (d) Y. Ren, Y. Dienes, S. Hettel, M. Parvez,
B. Hoge and T. Baumgartner, Organometallics, 2009, 28, 734;
(e) C. Romero-Nieto, S. Merino, J. Rodrıguez-Lopez and
´ ´
3JH,P = 13.5 Hz, o-Ph); 31P{1H} NMR (121.5 MHz, CDCl3)
19.4; 13C{1H} NMR (100.6 MHz; CDCl3) 121.9 (d, JC,P
=
T. Baumgartner, Chem.–Eur. J., 2009, 15, 4135.
14.4 Hz, Ar), 124.8 (s, C-H, bridge), 125.1 (s, C-H, bridge),
7 (a) S. Durben, Y. Dienes and T. Baumgartner, Org. Lett., 2006, 8,
5893; (b) S. Durben, D. Nickel, R. A. Krueger and
T. Baumgartner, J. Polym. Sci., Part A: Polym. Chem., 2008, 46,
8179; (c) C. Romero-Nieto, S. Durben, I. M. Kormos and
T. Baumgartner, Adv. Funct. Mater., 2009, 19, 3625.
8 D. R. Bai, C. Romero-Nieto and T. Baumgartner, Dalton Trans.,
2010, 39, 1250.
9 Y. Dienes, U. Englert and T. Baumgartner, Z. Anorg. Allg. Chem.,
2009, 635, 238.
126.2 (d, JC,P = 14.6 Hz, Ar), 128.7 (d, JC,P = 14.7 Hz, Ph),
1
129.0 (d, JC,P = 13.1 Hz, Ph), 129.4 (d, JC,P = 103.1 Hz,
ipso-Ph), 130.9 (d, JC,P = 11.4 Hz, Ar), 132.6 (d, JC,P = 2.8 Hz,
p-Ph), 135.2 (s, C-C, bridge), 136.4 (s, C-C, bridge), 138.4
1
1
(d, JC,P = 112.6 Hz, ipso-Ar), 140.0 (d, JC,P = 110.9 Hz,
ipso-Ar), 140.6 (d, JC,P = 15.4 Hz, Ar), 143.7 (d, JC,P
=
22.8 Hz, Ar), 145.8 (d, JC,P = 24.3 Hz, Ar); HR-MALDI/
TOF-MS: m/z 760.9165 (M+
10 Metal-Catalyzed Cross-Coupling Reactions, ed. A. de Meijere and
F. Diederich, Wiley-VCH, Weinheim, 2nd edn, 2004.
11 H. Usta, G. Lu, A. Facchetti and T. J. Marks, J. Am. Chem. Soc.,
2006, 128, 9034.
+ Na. C36H20NaO2P2S6
requires 760.9155).
12 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Jr. Montgomery,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam,
S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador,
J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels,
M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox,
T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez and J. A. Pople, GAUSSIAN 03,
Revision E.01, Gaussian Inc., Wallingford, CT, 2007.
Acknowledgements
Financial support by Natural Sciences and Engineering
Research Council (NSERC) of Canada and by the Canada
Foundation for Innovation (CFI) is gratefully acknowledged.
We thank Alberta Ingenuity for a student scholarship (S.D.)
and for a New Faculty Award (T.B.). The authors thank
Prof. Todd Sutherland (University of Calgary) for helpful
discussions and Prof. Dr Jun Okuda (RWTH Aachen
University) for his support.
Notes and references
1 (a) Handbook of Conducting Polymers, ed. T. A. Skotheim and
J. R. Reynolds, CRC Press, Boca Raton, FL, 3rd edn, 2006;
(b) Organic Light Emitting Devices, ed. K. Mullen and U. Scherf,
¨
Wiley-VCH, Weinheim, 2005; (c) Handbook of Oligo- and
Polythiophenes, ed. D. Fichou, Wiley-VCH, Weinheim, 1998.
13 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
2008, 64, 112.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1592 | New J. Chem., 2010, 34, 1585–1592