Synthesis and properties of branched oligo(2-thienyl)- and oligo(2,2′-bithien-5-yl)-substituted pyridine derivatives

Article abstract of DOI:10.1002/adsc.201300613

Starting from easily accessible precursors we describe the preparation of a series of branched oligo(2-thienyl)- and oligo(2,2′-bithienyl)- substituted pyridine derivatives. With palladium-catalyzed cross-coupling reactions of pyridyl nonaflates/triflates as key steps we synthesized 2,6-di(2-thienyl)pyridines bridged by thiophene or benzene rings. By selective bromination of 2,6-di(2-thienyl)pyridine and 2,4,6-tri(2-thienyl)pyridine and subsequent coupling reactions an access to oligo(2,2′-bithien-5-yl)- substituted pyridine derivatives was gained. The constitution and solid state conformation of 2,6-bis(2,2'-bithien-5-yl)pyridine was determined by X-ray analysis. This series of new pyridine-thiophene conjugates was systematically investigated by UV/vis spectroscopy. Large Stokes shifts in the neutral and protonated form were observed. The electrochemical oxidation of two typical compounds was studied, however, these oxidations were irreversible forming a polymeric film at the anode. As a selected example, a thiophene-bridged 2,6-di(2-thienyl)pyridine derivative was also investigated by scanning tunneling microscopy showing an interesting self-assembly into a highly ordered monolayer on highly oriented pyrolytic graphite. Copyright

Full text of DOI:10.1002/adsc.201300613

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DOI: 10.1002/adsc.201300613
Synthesis and Properties of Branched Oligo(2-thienyl)- and
Oligo(2,2’-bithien-5-yl)-Substituted Pyridine Derivatives
Mrinal K. Bera,a,b Shivajirao L. Gholap,a Paul Hommes,a Katja Neuthe,a
Daniel Trawny,a Jꢀrgen P. Rabe,c Dieter Lentz,+a Reinhold Zimmer,a
and Hans-Ulrich Reissiga,*
a
Institut fꢀr Chemie und Biochemie, Freie Universitꢁt Berlin, Takustr. 3, 14195 Berlin, Germany
Fax : (+49)-30-83-855-367; e-mail: hans.reissig@chemie.fu-berlin.de
Current address: Department of Chemistry, Kamaun University, SSJ Campus Almora, Almora 263601, Uttarkhand, India
Institut fꢀr Physik, Humboldt Universitꢁt zu Berlin, Newtonstraße 15, 12489 Berlin, Germany
b
c
+
Responsible for the X-ray crystal structure determination.
Received: July 11, 2013; Published online: November 19, 2013
Dedicated to Professor Goverdhan Mehta on the occasion of his 70th birthday.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300613.
Abstract: Starting from easily accessible precursors Large Stokes shifts in the neutral and protonated
we describe the preparation of a series of branched form were observed. The electrochemical oxidation
oligo(2-thienyl)- and oligo(2,2’-bithienyl)-substituted of two typical compounds was studied, however,
pyridine derivatives. With palladium-catalyzed cross- these oxidations were irreversible forming a polymer-
coupling reactions of pyridyl nonaflates/triflates as ic film at the anode. As a selected example, a thio-
key steps we synthesized 2,6-di(2-thienyl)pyridines phene-bridged 2,6-di(2-thienyl)pyridine derivative
bridged by thiophene or benzene rings. By selective was also investigated by scanning tunneling micros-
bromination of 2,6-di(2-thienyl)pyridine and 2,4,6- copy showing an interesting self-assembly into
tri(2-thienyl)pyridine and subsequent coupling reac- a highly ordered monolayer on highly oriented pyro-
tions an access to oligo(2,2’-bithien-5-yl)-substituted lytic graphite.
pyridine derivatives was gained. The constitution and
solid state conformation of 2,6-bis(2,2ꢂ-bithien-5-yl)-
pyridine was determined by X-ray analysis. This Keywords: electrochemistry; palladium-catalyzed
series of new pyridine-thiophene conjugates was sys- couplings; pyridines; scanning tunneling microscopy;
tematically investigated by UV/vis spectroscopy. thiophenes; UV/vis spectroscopy
Introduction
simple reaction sequences.[1] Since redox and photoac-
tive compounds with sequential thienyl substituents
Recently we reported that highly functionalized 2- are of high interest as materials for organic electron-
thienyl-substituted pyridine derivatives such as 1[1] are ics,[5–7] we continued our previous studies on the syn-
smoothly available even on a gram scale by our flexi- thesis of per(2-thienyl)-substituted pyridines[1,8] and
ble
multi-component
synthesis
of
pyridines prepared a series of new extended and branched
(Scheme 1).[2] The two differentiated oxygen function- oligo(2-thienyl)-substituted pyridine derivatives and
alities of this precursor could be used to introduce ad- studied the physical properties of selected examples.
ditional functional groups or substituents. Nonaflate
1b is a perfect starting material for palladium-cata-
lyzed coupling reactions allowing the introduction of Results and Discussion
a third 2-thienyl group at C-4.[3] Alternatively, the
nonafloxy (or trifloxy) group can be used for reduc- Compound 1b and thiophene-2,5-diboronic acid (5)
tive removal of the oxygen functionalities.[4] Playing underwent a double Suzuki coupling[9] under standard
with these options we prepared precursors 2 and 3 in conditions to efficiently furnish the expected inter-
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undergo a regioselective bromination at C-5, which
allows subsequent Stille couplings[11] in this position.
Indeed, this turned out to be smoothly applicable to
compounds such as 1b functionalized with a methoxy
and a nonafloxy substituent. Bromination with NBS
furnished dibromide 15 (Scheme 3) which was directly
converted into compound 17 by a three-fold Stille
coupling with commercially available 2-tri(n-butyl-
stannyl)thiophene (16) in good overall yield. Routine
removal of the methoxy group via intermediates 18
and 19 finally provided the desired 2,6-di(2,2’-bithien-
5-yl)-4-(2-thienyl)pyridine (20).
As a further target we envisioned the preparation
of a compound very similar to 20 but lacking the 4-(2-
thienyl) group at the pyridine core by employing 2,6-
di(2-thienyl)pyridine (2) as precursor. Its bromination
and subsequent substitution occurred without prob-
lems furnishing the desired compound 22 in two
good-yielding steps. This sequence again demonstrates
Scheme 1. 2,6-(2-Thienyl)-substituted
blocks 1a, 1b and products 2–4.
pyridine
building
mediate
6
containing seven heterocyclic rings the high reliability of the bromination/Stille coupling
(Scheme 2). Dealkylation of the hetaryl ether moiety sequence.
with sodium ethanethiolate[10] provided compound 7
Compound 22 was crystallized from dichlorome-
which was subsequently converted into bistriflate 8 in thane to obtain a pale yellow crystal suitable for an
very good overall yield. In the final step the trifloxy X-ray analysis (Figure 1). As expected the heterocy-
group was removed using palladium acetate and tri- clic rings are slightly out of plane with torsion angles
ethylammonium formate as reducing components.[4] between two thiophene rings of À37.48 and À8.58, re-
Hence, the first desired oligo(2-thienyl)-substituted spectively. The torsion angles of the inner thiophene
pyridine derivative 9 bridged by a 2,5-thiophene unit rings and the pyridine core are À15.38 and À27.68.
was easily obtained in a four-step sequence. Analo- Hence the arrangement in the solid state is surprising-
gously, compound 1b and benzene-1,4-diboronic acid ly unsymmetrical. One of the terminal thiophene
(10) furnished the desired 1,4-phenylene-bridged in- rings is disordered with respect to a 1808 rotation
termediate 11 with good efficacy (Scheme 2). Depro- around the carbon-carbon single bond (see Figure S1
tection to 12 and triflation to 13 were executed as in the Supporting Information). In the major orienta-
above and the final reductive removal of the trifloxy tion (70%) the thiophene sulfur atom S-4 is in a trans
groups afforded the expected product 14 with two position to the sulfur atom S-3 of the attached thio-
2,6-(2-thienyl)pyridine moieties in good overall yield. phene ring.
We next planned to extend the range of our polyhe-
We also performed the bromination sequence start-
terocyclic compounds by adding more thiophene rings ing with 2,4,6-tri(2-thienyl)pyridine (3) (Scheme 4).
to the already existing thiophene substituents. It is Surprisingly, under standard bromination conditions
well known that 2-substituted thiophene derivatives we obtained a tetrabrominated product which turned
Scheme 2. Preparation of bridged oligo(2-thienyl)-substituted pyridine derivatives 9 and 14. Reagents and conditions:
a) Pd
ACHTUNGTRENNUNG
ture, 6–12 h; d) PdACHTUNGTRENNUNG
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Synthesis and Properties of Branched Oligo(2-thienyl)- and Oligo(2,2’-bithien-5-yl)-Substituted Pyridines
Scheme 3. Preparation of bis(2,2’-bithien-5-yl)-substituted pyridine derivatives 20 and 22. Reagents and conditions: a) NBS
(2.5–3.0 equiv.), DMF, À208C to room temperature, 12 h; b) 2 tri(n-butylstannyl)thiophene (16), Pd
ACHTUNGTRENNUNG
2 h; c) NaSEt, DMF, sealed tube, 908C, 1 h; d) NaH, NfF, THF, room temperature, overnight; e) Pd
HCO2H, DMF, sealed tube, 908C, 2 h.
ACHTUNGTRENNUNG
out to be compound 23. Apparently, the more elec- was achieved either by the Stille protocol (59% yield)
tron-rich character of the tri(2-thienyl)-substituted or with a Suzuki reaction employing thiophene-2-bor-
pyridine core facilitates an electrophilic bromination onic acid (27) which gave a better yield of 76%.
at C-3 of the pyridine ring. Immediate reaction of
With these straightforward sequences we could pre-
compound 23 with stannane 16 resulted in a four-fold pare a series of novel branched oligo(2-thienyl)-sub-
Stille coupling leading to compound 24 containing stituted pyridine derivatives employing palladium-cat-
À
seven thiophene substituents. The overall yield of this alyzed C C bond forming steps as the key reaction.
sequence with more than 95% per newly formed C C The efficacy of these couplings in the presence of
À
bond is impressive and underscores the efficacy of a high number of sulfur-containing heterocycles is
palladium-catalyzed coupling processes. Bromination quite impressive. Selected compounds of our series
of the central pyridine ring of 3 could be avoided by were studied by physical methods.
careful control of the reaction conditions. With
2.5 equivalents of NBS at À208C dibromo derivative
25 was isolated in good yield whereas the desired tri- Absorption and Fluorescence Spectra
bromo compound 26 was obtained in 80% yield when
four equivalents of the brominating reagent were In our earlier reports[1,8] on oligo- and per
ACTHUNRTGNE(GNU thienyl)-
used. The subsequent Stille couplings of 25 with stan- substituted pyridine derivatives we already observed
nane 16 provided the expected product 20 in good remarkable UV/vis and fluorescence spectra with
yield. The conversion of tribromo compound 26 into fairly large Stokes shifts and a strong influence exhib-
the desired tri(2,2’-bithienyl)-substituted pyridine 28 ited by the protonation of the pyridine nitrogen. As
anticipated the newly synthesized bridged oligo(2-
thienyl)-substituted pyridines 6, 9 and 14 as well as
the oligo(2,2’-bithien-5-yl)-substituted derivatives 20,
22, 24 and 28 also showed similar interesting photo-
physical properties. Their UV/vis absorption and fluo-
rescence spectra were studied in solution with chloro-
form and a mixture of chloroform and trifluoroacetic
acid (99:1) as solvents. The respective spectra are de-
picted exemplarily for compound 22 in Figure 2 and
for 28 in Figure 3.
The determined extinction coefficients as well as
the observed lmax values for the absorption and the
fluorescence after excitation at maximum absorption
wavelengths are summarized in Table 1.
Figure 1. Molecular structure of 22 (ORTEP3 for Win-
dows,[12] 50% probability level), hydrogen atoms omitted for
clarity. The numbers represent the torsion angles.
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Scheme 4. Bromination of precursor 3 and subsequent coupling to oligo(2-thienyl)pyridine derivatives 20, 24 and 28. Re-
agents and conditions: a) DMF, À208C to room temperature, 5–24 h; b) 2-tri(n-butylstannyl)thiophene (16), Pd(PPh3)4,
DMF, 120 or 908C, 2 h; c) thiophene-2-boronic acid (27), Pd(PPh3)4, K2CO3, DMF, 808C, 3 h.
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
All studied compounds show a broad absorption dines 6, 9 and 14 as well as for compound 22 is ob-
ranging from about 260 up to 400 nm with lmax values served between 400 and 440 nm. The 2,2’-bithien-5-yl-
between 300 and 340 nm for the bridged 2-thienyl- substituted pyridines 20, 24 and 28 show respective
substituted pyridines. Expectedly the increased lmax values again at longer wavelengths between 440
number of thiophene moieties contained in the 2,2’- and 467 nm. This results in Stokes shifts between 4700
bithien-5-yl-substituted pyridines results in lmax values and 5900 cmÀ1 for the 2,2’-bithien-5-yl-substituted pyr-
at longer wavelengths as they show the most intensive idines 20, 22, 24, 28 and the thiophene-bridged com-
absorption between 350 and 370 nm. The strongest pound 9. For the other bridged 2-thienyl-substituted
emission for the bridged 2-thienyl-substituted pyri- pyridines significantly higher values of 8200 cmÀ1 for
Figure 2. UV (dashed lines) and fluorescence spectra (solid
lines) of 2,6-di(2,2’-bithien-5-yl)pyridine 22 in CHCl3 (1) and
in CHCl3/TFA (99:1) (2).
Figure 3. UV (dashed lines) and fluorescence spectra (solid
lines) of 2,4,6-tri(2,2’-bithien-5-yl)pyridine 28 in CHCl3 (1)
and in CHCl3/TFA (99:1) (2).
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Synthesis and Properties of Branched Oligo(2-thienyl)- and Oligo(2,2’-bithien-5-yl)-Substituted Pyridines
Table 1. Absorption and emission data of selected oligo(2-thienyl)-substituted pyridine derivatives.
2-Thienylpyridine
CHCl3
Emission[b] Stokes
CHCl3/TFA (99:1)
Emission[b] Stokes
Absorption[a]
Absorption[a]
lmax [nm], (log e)
lmax [nm]
shift
lmax [nm], (log e)
lmax [nm]
shift
[cmÀ1]
[cmÀ1]
299 (4.61), 349 (sh)
(4.55)
407 (4.69), 298 (sh)
(4.44)
443
417
10900
5400
530
5700
5400
340 (4.69), 303 (sh)
(4.63), 266 (sh)
(4.54)
396 (4.82), 286 (sh)
(4.56)
503
474
302 (4.72), 344 (sh)
(4.21)
340 (4.55), 394 (sh)
(4.45)
401
8200
8300
349 (4.56), 385 (sh)
(4.39)
440, 463
(sh)
352 (4.50), 476 (sh)
(4.49)
10700
(3300)
5900
4700
565
550
465 (4.48), 362 (sh)
(4.12), 297 (sh)
(3.95)
353 (4.50)
368 (4.63)
424
3200
3900
476 (4.53), 350 (sh)
(4.25), 303 (sh)
(4.22)
467, 454
(sh)
5800
5800
583
571
451, 465
(sh)
468 (4.73), 342 (sh)
(4.37)
367 (4.81)
3900
[a]
Absorption; recorded at c=10À5 mol·LÀ1 in 1-cm cuvettes.
[b]
Emission after excitation at max. absorption wavelength; recorded at c=10À5–10À6 mol·LÀ1 in 1-cm cuvettes.
14 and 10900 cmÀ1 for 6 are observed. After protona- served at about 400 nm for the bridged 2-thienyl-sub-
tion of the pyridine moieties with trifluoroacetic acid stituted pyridines and in the range of 465 and 475 nm
the absorption and emission lmax values are considera- for the 2,2’-bithien-5-yl-substituted pyridines respec-
bly red-shifted.[13,14] The strongest absorption is ob- tively. The emission lmax values are shifted to between
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470 and 530 nm for the bridged 2-thienyl-substituted we observed immediate film formation at the anode
pyridines and range from 550 to 580 nm for the 2,2’- during oxidation as already noticed for compounds
bithien-5-yl-substituted derivatives. The Stokes shifts previously reported.[8,15] Continuous cycling leads to
of the protonated species are also fairly large, ranging the disappearance of the oxidation signal (see the
from 5400 to 8300 cmÀ1 for the bridged 2-thienyl-sub- Supporting Information), indicating the formation of
stituted pyridines 6, 9 and 14, and from 3200 to the new polymeric species, a behaviour well known
3900 cmÀ1 for the 2,2’-bithien-5-yl-substituted pyri- from related compounds and 1,3,5-(trisaryl)ben-
dines 22, 24 and 28. The protonated species of 20 ex- zenes.[16] These films produced were insoluble in typi-
hibits two lmax values with almost identical intensities cal solvents such as THF, DMSO, chloroform, aceto-
(at 352 and 476 nm) in its absorption spectrum and nitrile, and ethanol.
a lmax of 565 nm in the emission spectrum, resulting in
Stokes shifts of 10700 and 3300 cmÀ1, respectively.
Scanning Tunneling Microscopy
Electrochemistry
Due to our continuous interest in multivalent hetero-
cyclic compounds[17] we also studied bispyridyl-substi-
The 2,4,6-tris(2,2’-bithienyl)-substituted pyridines 24 tuted thiophene derivative 6 with respect to its ability
and 28 were investigated electrochemically using to form self-assembled monolayers at the interface
cyclic voltammetry in chloroform (also see Figures S2 between the basal plane of highly oriented pyrolytic
and S3 in the Supporting Information). The com- graphite (HOPG) and 1-phenyloctane.[18] Scanning
pounds were expected to show similar electrochemi- tunneling microscopy (STM) of a saturated solution
cal behaviour as the previously reported[8] (2-thienyl)- of 6 in this solvent reveals molecular self-assembly
substituted pyridines. Compound 24 is irreversibly into two-dimensional crystals with a unit cell size of
oxidized in two steps at 1.335 and 1.571 V vs. NHE, A=(4.97Æ0.29) nm2 (Figure 5), which fits to two op-
whereas derivative 28 shows only one oxidation at positely oriented molecules per unit cell and interdigi-
1.290 V vs. NHE (Figure 4). Due to the enhanced tation between the molecules. In our proposed molec-
electron-donating effect of the 2,2’-bithienyl groups ular model the bright areas in the STM image corre-
the oxidation potentials are slightly shifted towards spond to high tunneling current, indicating the posi-
less positive potentials compared to 2,4,6-tris(2-thie- tions of the p-systems.[19] The dark lines between the
nyl)pyridine which was oxidized at 1.36 and 1.86 V.[8] molecules correspond to low tunneling current and
Compound 28 shows the strongest shift to less posi- designate the gap which is caused by the molecular ar-
tive potentials, whereas compound 24 with an addi- rangement. The molecular orbitals were calculated
tional 3-thiophene moiety is less easily oxidized. This with the DMol3 interface of Accelrys Materials
may be due to a higher deviation from planarity due Studio using the local-density approximation method
to steric hindrance of the substituents in 2-, 3- and 4- (LDA) and Perdew Wang correlation (PWC).[20] The
positions of the pyridine core. For both compounds implemented space-filling models are based on stan-
dard van-der-Waals parameters. Our STM measure-
ments show that fully conjugated polyheterocycles
with thienyl moieties such as 6 are interesting candi-
dates to achieve highly ordered two-dimensional ar-
rangements on HOPG. The behaviour of these or-
dered structures and structure-property relationships
will be further investigated and compared with relat-
ed compounds.
Conclusions
In summary, we have continued our earlier studies,
searching for new oligo-2-thienylated pyridines as
candidates for organic electronic applications.[1,8]
Starting with precursors available from our highly
flexible three-component reaction[1,2] and using
straightforward transformations, we successfully pre-
Figure 4. Linear scan voltammograms of 24 and 28 obtained
pared a series of new bridged 2-thienylpyridine conju-
gates and oligo(2,2’-bithien-5-yl)-substituted pyridines
showing interesting photophysical properties. As ex-
in the range of 0–2.2 V vs. NHE on a platinum electrode;
sweep rate n=100 mVsÀ1, 0.300 mM and 0.200 mM in 0.1M
Bu4NPF6 in chloroform.
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Synthesis and Properties of Branched Oligo(2-thienyl)- and Oligo(2,2’-bithien-5-yl)-Substituted Pyridines
Figure 5. STM current image of compound 6 at the interface between a solution in 1-phenyloctane and the basal plane of
HOPG as well as the proposed molecular model in detail. Unit cell size: a=(2.88Æ0.17) nm, b=(1.86Æ0.11) nm, a=(75Æ
3)8, A=(4.97Æ0.29) nm2. Tunneling parameters were sample bias Us =À1.05 V and tunneling current It =73 pA.
pected, the prepared compounds show fluorescence
after excitation with UV/vis light. Exemplarily, the
oxidation potentials of the (2,2’-bithien-5-yl)-substi-
tuted pyridines 24 and 28 were determined by cyclic
voltammetry, resulting in irreversible oxidation and
the formation of polymeric films. In addition, as re-
vealed by STM, the bridged 2-thienylpyridine conju-
gate 6 showed a remarkable self-assembly into
a highly ordered monolayer on HOPG.
(AC 500, AVIII 700) and JEOL (Eclipse 500) instruments.
Chemical shifts are reported relative to solvent residual
peaks or TMS. Integrals are in accordance with assignments,
and coupling constants are given in Hz. All 13C NMR spec-
tra are proton-decoupled. 13C NMR signals of Nf-groups
[CF3ACHTNUTRGNE(NUG CF2)3] are not given since unambiguous assignment is
not possible due to strong splitting by coupling with the 19F
nuclei. IR spectra were measured with a Jasco FT/IR-4100
spectrometer. HR-MS analyses were performed with
a Varian Ionspec QFT-7 (ESI-FT ICRMS) or an Agilent
6210 (ESI-TOF) instrument. Elemental analyses were car-
ried out with CHN-Analyzer 2400 (Perkin–Elmer), Vario
EL or Vario EL III instruments. Melting points were mea-
sured with a Reichert apparatus (Thermovar) and are uncor-
rected. UV/vis spectra were measured with a UV/vis spec-
trophotometer Scinco S-3150 PDA. Fluorescence spectra
were measured with a spectrofluorometer Jasco FP-6500.
Experimental Section
General Methods
Reactions were performed under an atmosphere of argon in
flame-dried flasks. Solvents and liquid reagents were added
by syringe. THF and CH2Cl2 were transferred from a MB
SPS-800-dry solvent system into the reaction vessels. Dry
DMF was purchased from Acros Organics and stored in the
presence of molecular sieve under an atmosphere of argon.
Et3N was distilled from CaH2 and stored over KOH under
argon. Pyridine was stored over KOH under argon. All
other reagents were purchased from commercial suppliers
and used without further purification. Thin layer chromatog-
raphy (TLC) analyses were performed on TLC plates pur-
chased from Merck (silica gel 60, fluorescence indicator
F254, 0.25 mm layer thickness). Products were purified by
flash chromatography on silica gel 60 (230–400 mesh, Ma-
cherey-Nagel). NMR spectra were recorded with Bruker
X-Ray Crystallography
Single crystals of 22 were obtained by crystallization from
a dichloromethane solution. Data were collected using
a Bruker AXS SMART diffractometer at 173 K. The struc-
ture was solved using direct methods and refined by least
squares refinement applying a disorder model for one of the
thiophene moieties. Crystal data for 22: C21H13NS4, M=
407.56, monoclinic, a=7.330(3) ꢄ, b=8.228(3) ꢄ, c=
15.279(6) ꢄ, a=90.008, b=99.262(8)8, g=90.008, V=
909.5(6) ꢄ3, T=173(2) K, space group P21, Z=2, MoKa,
9754 reflections measured, 5444 independent reflections
(Rint =0.0290). R1 =0.0502 (I> 2s(I)), wR(F2)=0.1146 (all
data). The goodness of fit on F2 was 1.060. Flack parame-
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Mrinal K. Bera et al.
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ter=À0.06(8). CCDC 948665 contains the supplementary
crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Typical Procedure 2: 4,4’-(Thiophene-2,5-diyl)bisACHTUNGTRENNUNG[2,6-
di(2-thiophenyl)pyridin-3-ol] (7)
To a solution of compound 6 (120 mg, 0.19 mmol) in dry
DMF (3 mL) was added NaSEt (162 mg, 1.93 mmol) and the
resulting mixture was heated in an ACE-sealed tube at 908C
for 2 h. The mixture was diluted with Et2O (10 mL),
quenched with water (10 mL) and the layers were separated.
After cooling to 08C the aqueous layer was slowly acidified
(litmus paper indication) with 10% aqueous HCl and ex-
tracted with EtOAc (3ꢅ25 mL). The combined organic
layers were washed with brine, dried with Na2SO4 and the
solvent was evaporated under reduced pressure to obtain 7
as a brownish solid which was used without further purifica-
tion for the next step; yield: 80 mg (70%).
Electrochemistry
The cyclic voltammetry data were recorded on an Autolab
PGSTAT302N potentiostat. Cyclovoltammetric measure-
ments were performed in MeCN containing 0.1M tetra-n-
butylammonium hexafluorophosphate as conducting salt in
a 3-electrode compartment at a scan rate of 100 mVsÀ1. The
working electrode was a platinum disc electrode (ø=
0.2 mm), the counter electrode was a platinum wire elec-
trode, and an Ag/AgCl electrode with 1M LiCl in ethanol
as electrolyte was used as reference electrode. Before all
measurements, the electrolyte was purged with nitrogen for
20 min and the reference electrode was calibrated against
ferrocene. The potentiostat and all electrodes were pur-
chased from Metrohm.
Typical Procedure 3: 4,4’-(Thiophene-2,5-diyl)bisACHTUNGTRENNUNG[2,6-
di(2-thiophenyl)pyridine-3,4-diyl] Bistriflate (8)
To a solution of crude pyridinol 7 (80 mg, 0.13 mmol) in dry
CH2Cl2 (5 mL) were added pyridine (0.10 mL, 1.20 mmol)
and DMAP (3 mg, 0.03 mmol) at room temperature. After
15 min stirring, the mixture was cooled to 08C and Tf2O
(0.20 mL, 1.19 mmol) was added. The temperature was al-
lowed to rise to room temperature and the mixture was
stirred for 6 h. The reaction was quenched with water
(5 mL) and the product was extracted with CH2Cl2 (3ꢅ
15 mL). The combined organic layers were washed with
brine, dried with Na2SO4 and the solvent was evaporated.
The crude product was purified by column chromatography
on silica gel (15–25% EtOAc in hexanes) to provide bistri-
flate 8 as a light yellow solid; yield: 95 mg (83%); mp 210–
2158C. 1H NMR (CDCl3, 500 MHz): d=7.16 (dd, J=5.1,
3.8 Hz, 2H, Thio), 7.19 (dd, J=5.1, 3.8 Hz, 2H, Thio), 7.50
(dd, J=5.0, 1.1 Hz, 2H, Thio), 7.58 (dd, J=5.0, 1.1 Hz, 2H,
Thio), 7.65, 7.67 (2 s, 2 H each, Thio, Py), 7.73 (dd, J=3.8,
1.0 Hz, 2H, Thio), 7.84 (br d, J=3.8 Hz, 2H, Thio);
13C NMR (CDCl3, 126 MHz): d=117.7 (d, Py), 126.7, 128.2,
128.5, 129.5, 129.7, 130.2, 130.8, 137.6, 137.7, 138.7 (7 d, 3s,
Thio), 139.5, 142.5, 147.3, 151.9 (4s, Py), the signal for the
CF3 group was not detected; IR (ATR): n=3095–2855
Scanning Tunneling Microscopy
STM imaging was carried out at room temperature at the in-
terface between freshly cleaved highly oriented pyrolytic
graphite (HOPG) substrate and an almost saturated solution
in 1-phenyloctane (Aldrich)[21] by employing a home-made
set-up at a scan speed between 10 and 50 lines/s. After visu-
alization of the HOPG lattice, a drop of an almost saturated
solution was applied to the basal plane of HOPG. The STM
images were corrected with respect to the hexagonal HOPG
lattice underneath by exploiting SPIP software.[22] In this
way, the unit cell of the crystalline adsorbate could be deter-
mined with a high degree of precision.
The syntheses of compounds 1b, 2 and 3 have previously
been described.[1]
Typical Procedure 1: 2,5-Bis[3-methoxy-2,6-di(2-thio-
phenyl)pyridin-4-yl)]thiophene (6)
A mixture of pyridyl nonaflate 1b (510 mg, 0.89 mmol),
PdACHTUNGTRENNUNG(PPh3)4 (103 mg, 0.09 mmol), K2CO3 (92 mg, 0.67 mmol),
(=C H, C H), 1585–1420 (C=C) cmÀ1; HR-MS: m/z=
862.9033, calcd. for C32H17F6N2O6S7 [M+H]+: 862.9030.
À
À
and thiophene-2,5-diboronic acid (5) (115 mg, 0.67 mmol) in
DMF (10 mL) was heated at 708C for 24 h under an argon
atmosphere. The mixture was cooled to room temperature,
diluted with brine (10 mL) and extracted with Et2O (3ꢅ
25 mL). The combined organic phases were dried with
Na2SO4 and concentrated to dryness. The residue was puri-
fied by column chromatography on silica gel (25–50%
EtOAc in hexanes) to give 6 as a dark yellow solid; yield:
Typical Procedure 4: 2,5-Bis
pyridin-4-yl]thiophene (9)
ACHTUNGERTN[NUNG 2,6-di(2-thiophenyl)-
A mixture of bistriflate 8 (70 mg, 0.08 mmol), PdACHTUNGTRENNUNG(OAc)2
(5 mg, 0.02 mmol), dppp (9 mg, 0.02 mmol), Et3N (0.20 mL,
1.4 mmol) and formic acid (0.05 mL, 1.3 mmol) in dry DMF
(3 mL) was placed in an ACE-sealed tube and heated at
908C for 2 h. The mixture was diluted with Et2O (10 mL)
and quenched with water (10 mL). The layers were separat-
ed and the aqueous phase was extracted with Et2O (2ꢅ
15 mL). The combined organic layers were washed with
brine and dried with Na2SO4. The solvent was evaporated
and the crude product was subjected to column chromatog-
raphy on silica gel (5–10% EtOAc in hexanes) to afford
compound 9 as a pale yellow solid; yield: 30 mg (66%); mp
1
182 mg (65%); mp 165–1708C. H NMR (CDCl3, 500 MHz):
d=3.77 (s, 6H, OMe), 7.14 (dd, J=5.0, 3.6 Hz, 2H, Thio),
7.19 (dd, J=5.1, 3.8 Hz, 2H, Thio), 7.41 (dd, J=5.1, 1.0 Hz,
2H, Thio), 7.49 (dd, J=5.0, 1.0 Hz, 2H, Thio), 7.64 (dd, J=
3.6, 1.0 Hz, 2H, Thio), 7.76, 7.78 (2 s, 2 H each, Py, Thio),
8.11 (dd, J=3.8, 1.0 Hz, 2H, Thio); 13C NMR (CDCl3,
126 MHz): d=60.3 (q, OMe), 115.4 (d, Py), 124.6, 127.8,
127.9, 128.1, 128.3, 128.6, 128.7, 136.1, 139.2, 140.9 (7 d, 3s,
Thio), 144.4, 146.3, 147.5, 148.2 (4s, Py); IR (ATR): n=
3105–2970 (=C H, C H), 1590–1400 (C=C) cmÀ1; HR-MS:
m/z=627.0308, calcd. for C32H23N2O2S5 [M+H]+: 627.0358;
anal. calcd. for C32H22N2O2S5 (626.8): C 61.31, H 3.54, N
4.47, S 25.58; found: C 61.22, H 3.39, N 4.46, S 25.44.
>2308C. H NMR (CDCl3, 500 MHz): d=7.15 (dd, J=5.1,
1
À
À
3.8 Hz, 4H, Thio), 7.44 (dd, J=5.1, 1.0 Hz, 4H, Thio), 7.61
(s, 2H, Thio), 7.68 (s, 4H, Py), 7.73 (dd, J=3.8, 1.0 Hz, 4H,
Thio); 13C NMR (CDCl3, 126 MHz): d=112.9 (d, Py), 125.2,
3470
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Adv. Synth. Catal. 2013, 355, 3463 – 3474

Synthesis and Properties of Branched Oligo(2-thienyl)- and Oligo(2,2’-bithien-5-yl)-Substituted Pyridines
126.6, 128.1, 128.2, 142.3, 142.7 (4 d, 2s, Thio), 144.5, 153.0
1,4-BisACHTNUTRGNE[UNG 2,6-di(2-thiophenyl)pyridin-4-yl]benzene (14)
À
À
(2s, Py); IR (ATR): n=3025–2865 (=C H, C H), 1475–
1360 (C=C) cmÀ1
; HR-MS: m/z=567.0140, calcd. for
According to typical procedure 4, a mixture of the bistriflate
13 (50 mg, 0.06 mmol), Pd(OAc)2 (4 mg, 0.02 mmol), dppp
C30H19N2S5 [M+H]+: 567.0146.
AHCTUNGTRENNUNG
(7 mg, 0.02 mmol), Et3N (0.20 mL, 1.4 mmol), and formic
acid (0.05 mL, 1.3 mmol) in DMF (2 mL) was heated in an
ACE-sealed tube at 908C for 2 h to afford after purification
by column chromatography on silica gel (5–10% EtOAc in
hexanes) pyridine derivative 14 as a colorless solid; yield:
1,4-Bis[3-methoxy-2,6-di(2-thiophenyl)pyridin-4-yl]-
benzene (11)
1
According to typical procedure 1, a mixture of nonaflate 1b
(350 mg, 0.61 mmol), benzene 1,4-diboronic acid (10)
(75 mg, 0.45 mmol), K2CO3 (62 mg, 0.45 mmol) and
19 mg (56%); mp 123–1248C. H NMR (CDCl3, 500 MHz):
d=7.16 (dd, J=5.0, 3.6 Hz, 4H, Thio), 7.45 (dd, J=5.0.
1.0 Hz, 4H, Thio), 7.74 (s, 4H, Py), 7.74 (dd, J=3.6, 1.0 Hz,
4H, Thio), 7.87 (s, 4H, Ar); 13C NMR (CDCl3, 126 MHz):
d=114.8 (d, Py), 124.9, 127.7, 127.9*, 139.2, 144.6 (3 d, 2s,
Thio, Ar), 149.1, 152.7 (2s, Py), * intensity of the peak cor-
PdACHTUNGTRENNUNG(PPh3)4 (35 mg, 0.03 mmol) in dry DMF (8 mL) upon stir-
ring at 708C for 24 h and after purification by column chro-
matography on silica gel (25–50% EtOAc in hexanes) pro-
vided compound 11 as a pale yellow solid; yield: 157 mg
À
responds to 2C atoms; IR (ATR): n=3015–2900 (=C H,
1
C H), 1585–1435 (C=C) cmÀ1; HR-MS: m/z=561.0587,
(82%); mp >2308C. H NMR (CDCl3, 500 MHz): d=3.52
À
calcd. for C32H21N2S4 [M+H]+: 561.0582.
(s, 6H, OMe), 7.12 (dd, J=5.1, 3.8 Hz, 2H, Thio), 7.18 (dd,
J=5.1, 3.8 Hz, 2H, Thio), 7.41 (dd, J=5.1, 1.1 Hz, 2H,
Thio), 7.47 (dd, J=5.1, 1.0 Hz, 2H, Thio), 7.56 (s, 2H, Py),
7.61 (dd, J=3.8, 1.0 Hz, 2H, Thio), 7.85 (s, 4H, Ar), 8.15
(dd, J=3.8, 1.1 Hz, 2H, Thio) ppm. 13C NMR (CDCl3,
126 MHz): d=60.2 (q, OMe), 118.5 (d, Py), 124.5, 127.7,
127.8, 128.1, 128.5, 128.6, 129.2, 136.6, 140.9, 143.1 (7 d, 3 s,
Thio, Ar), 144.6, 146.2, 148.1, 148.8 (4 s, Py) ppm. IR
Typical Procedure 5: 2,6-Di([2,2’-bithiophen]-5-yl)-3-
methoxy-4-(thiophen-2-yl)pyridine (17)
A solution of N-bromosuccinimide (173 mg, 0.97 mmol) in
dry DMF (3 mL) was added dropwise under argon to
a
cooled solution (À208C) of nonaflate 1b (185 mg,
À
À
(ATR): n=3105–2930 (=C H, C H), 1585–1455 (C=C)
cmÀ1; HRMS: m/z=621.0805, calcd. for C34H25N2O2S4 [M+
H]+: 621.0793.
0.32 mmol) in dry DMF (3 mL). The mixture was warmed
up to room temperature and stirred overnight. When the
starting material was fully consumed (TLC monitoring), 2-
tri(n-butylstannyl)thiophene
(16)
(588 mg,
0.50 mL,
1.57 mmol) and Pd(PPh3)4 (56 mg, 0.05 mmol) were added
AHCTUNGTRENNUNG
4,4’-(1,4-Phenylene)bisACTHNURTGNEU[GN 2,6-di(2-thiophenyl)pyridin-3-
ol] (12)
and the resulting mixture was heated at 1208C for 2 h. The
reaction was quenched with water (10 mL) and extracted
with Et2O (2ꢅ25 mL). The combined organic layers were
washed with brine, dried with Na2SO4 and the solvent was
evaporated to dryness. The crude product was purified
through column chromatography on silica gel (10–25%
EtOAc in hexanes) to afford compound 17 as a greenish
yellow solid; yield: 104 mg (63%, two steps); mp 120–
According to typical procedure 2, a mixture of pyridine de-
rivative 11 (150 mg, 0.24 mmol) and NaSEt (203 mg,
2.42 mmol) in DMF (5 mL) was heated in an ACE-sealed
tube at 908C for 2 h to provide compound 12 as a dark
brownish oil which was used without further purification in
the next step; yield: 95 mg (67%).
1
1238C. H NMR (CDCl3, 500 MHz): d=3.69 (s, 3H, OMe),
7.04–7.07 (m, 2H, Thio), 7.16–7.18 (m, 2H, Thio), 7.22–7.26
(m, 3H, Thio), 7.29 (br d, J=3.4 Hz, 1H, Thio), 7.33 (br d,
J=3.6 Hz, 1H, Thio), 7.46 (d, J=3.9 Hz, 1H, Thio), 7.51 (br
d, J=5.1 Hz, 1H, Thio), 7.64 (s, 1H, Py), 7.70 (br d, J=
3.3 Hz, 1H, Thio), 7.98 (d, J=3.9 Hz, 1H, Thio) ppm.
13C NMR (CDCl3, 126 MHz): d=60.2 (q, OMe), 115.5 (d,
Py), 124.1, 124.2, 124.5, 124.6, 124.7, 124.8, 125.1, 127.6,
128.0*, 128.1, 128.8, 129.3, 136.1, 136.4, 137.6, 137.7, 139.5,
139.7, 140.2 (12 d, 7s, Thio), 143.0, 146.3, 147.6, 147.8 (4s,
Py), * intensity of the peak corresponds to 2C atoms; IR
4,4’-(1,4-Phenylene)bis
4,3-diyl] Bistriflate (13)
ACHTUNGTRNE[NUNG 2,6-di(2-thiophenyl)pyridine-
According to typical procedure 3, a mixture of pyridinol de-
rivative 12 (95 mg, 0.16 mmol), pyridine (0.15 mL,
1.9 mmol), DMAP (4 mg, 0.03 mmol) and Tf2O (0.30 mL,
1.78 mmol) in dry CH2Cl2 (10 mL) upon stirring over night
at room temperature and after purification by column chro-
matography on silica gel (10–20% EtOAc in hexanes) pro-
vided the corresponding bistriflate 13 as a brown amorphous
À
À
(ATR): n=3105–2990 (=C H, C H), 1585–1445 (C=C)
cmÀ1; HR-MS: m/z=519.9996, calcd. for C26H18NOS5 [M+
H]+: 519.9986; anal. calcd. for C26H17NOS5 (519.7): C 60.08,
H 3.30, N 2.69, S 30.85; found: C 60.22, H 3.10, N 2.59, S
31.11.
1
solid; yield: 103 mg (75%); mp >2308C. H NMR (CDCl3,
500 MHz): d=7.15 (dd, J=5.1, 3.8 Hz, 2H, Thio), 7.19 (dd,
J=5.1, 3.8 Hz, 2H, Thio), 7.50 (dd, J=5.1, 1.0 Hz, 2H,
Thio), 7.57 (s, 2H, Py), 7.58 (dd, J=5.1, 1.0 Hz, 2H, Thio),
7.71 (dd, J=3.8, 1.0 Hz, 2H, Thio), 7.81 (s, 4H, Ar), 7.85 (br
d, J=3.6 Hz, 2H, Thio); 13C NMR (CDCl3, 126 MHz): d=
118.7 (d, Py), 126.5, 128.1, 128.4, 129.4, 129.5, 129.9*, 130.0,
136.1, 138.4, 139.6 (7 d, 3 s, Thio, Ar), 142.8, 144.9, 146.9,
151.8 (d, 4 s, Py); a signal for the CF3 group was not ob-
served; 19F NMR (CDCl3, 470 MHz): d=À74.1 (s, CF3); IR
2,6-Di[(2,2’-bithiophen)-5-yl]-4-(thiophen-2-yl)pyri-
din-3-ol (18)
According to typical procedure 2, a mixture of pyridine de-
rivative 17 (90 mg, 0.17 mmol) and NaSEt (73 mg,
0.87 mmol) in DMF (3 mL) was heated in an ACE-sealed
tube at 908C for 1 h to provide compound 18 as a brown oil
À
À
(ATR): n=3105–2990 (=C H, C H), 1550–1425 (C=C)
cmÀ1; HR-MS: m/z=856.9491, calcd. for C34H19F6N2O6S6
[M+H]+: 856.9466.
Adv. Synth. Catal. 2013, 355, 3463 – 3474
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
3471

Mrinal K. Bera et al.
FULL PAPERS
which was used as obtained in the next step; yield: 48 mg
(55%).
MS: m/z=489.9889, calcd. for C25H16NS5 [M+H]+:
489.9881.
2,6-Bis(5-bromothiophen-2-yl)pyridine (21)
2,6-Di[(2,2’-bithiophen)-5-yl]-4-(thiophen-2-yl)pyri-
din-3-yl Nonaflate (19)
A solution of N-bromosuccinimide (247 mg, 1.39 mmol) in
dry DMF (5 mL) was added dropwise under argon to
The crude pyridinol derivative 18 (45 mg, 0.09 mmol) was
dissolved in dry THF (5 mL) and NaH (21 mg, 0.89 mmol)
was added under an argon atmosphere. Nonafluorobutane-
sulfonyl fluoride (0.15 mL, 0.83 mmol) was added dropwise.
The mixture was stirred overnight at room temperature and
then diluted with Et2O (25 mL) and quenched by slow addi-
tion of ice-water. The layers were separated and the aque-
ous phase was extracted with Et2O (3ꢅ25 mL). The com-
bined organic layers were dried with Na2SO4 and concen-
trated to dryness. The residue was purified by column chro-
matography on silica gel (5–15% EtOAc in hexanes) to
afford nonaflate 19 as a light yellow oil; yield: 49 mg (69%).
1H NMR (CDCl3, 500 MHz): d=7.05 (dd, J=5.1, 3.6 Hz,
1H, Thio), 7.07 (dd, J=5.0, 3.6 Hz, 1H, Thio), 7.19 (d, J=
3.9 Hz, 1H, Thio), 7.20 (dd, J=5.0, 3.6 Hz, 1H, Thio), 7.23
(d, J=3.9 Hz, 1H, Thio), 7.27 (dd, J=5.1, 1.0 Hz, 1H,
Thio), 7.29 (dd, J=5.1, 1.0 Hz, 1H, Thio), 7.32 (dd, J=3.6,
2.7 Hz, 1H, Thio), 7.35 (dd, J=3.6, 1.0 Hz, 1H, Thio), 7.52
(s, 1H, Py), 7.52 (br d, J=3.4 Hz, 1H, Thio), 7.55–7.57 (m,
2H, Thio), 7.71 (br d, J=3.9 Hz, 1H, Thio); 13C NMR
(CDCl3, 126 MHz): d=117.8 (d, Py), 124.5, 124.6, 124.7,
124.8, 125.3, 125.4, 127.1, 128.0, 128.1, 128.2, 128.9, 130.1,
130.3, 135.3, 137.1, 137.2, 138.1, 138.3, 138.8, 141.0 (13 d, 7s,
Thio), 141.4, 141.8, 146.9, 151.3 (4s, Py); 19F NMR (CDCl3,
470 MHz): d=À80.6 (t, J=9.4 Hz, 3F, CF3), À110.6, À120.5,
À125.7 (3 mc, 2F each, CF2); IR (ATR): n=2960–2875
a
cooled solution (À208C) of compound
2 (135 mg,
0.56 mmol) in dry DMF (5 mL). The mixture was warmed
up to room temperature and stirred for 12 h. The reaction
mixture was diluted with CH2Cl2 (10 mL) and quenched
with water (10 mL). The layers were separated, the aqueous
phase was extracted with CH2Cl2 (2ꢅ20 mL) and the com-
bined organic layers were washed with brine and dried with
Na2SO4. The solvent was evaporated and the crude product
was purified by chromatography (SiO2, 25–50% EtOAc in
hexanes) to afford compound 21 as a light yellow solid;
yield: 196 mg (87%); mp 188–1928C. 1H NMR (CDCl3,
500 MHz): d=7.05 (d, J=3.9 Hz, 2H, Thio), 7.32 (d, J=
3.9 Hz, 2H, Thio), 7.40 (d, J=7.8 Hz, 2H, Py), 7.67 (t, J=
7.8 Hz, 1H, Py); 13C NMR (CDCl3, 126 MHz): d=114.9,
115.4 (2 d, Py, Thio), 123.9, 130.1, 136.8, 145.3, 150.6 (2 d,
À
À
3s, Py, Thio); IR (ATR): n=3060–2850 (=C H, C H),
1555–1415 (C=C) cmÀ1; HR-MS: m/z=399.8445, calcd. for
C13H8Br2NS2 [M+H]+: 399.8459.
Typical Procedure 6; 2,6-Di[(2,2’-bithiophen)-5-yl]-
pyridine (22)
A mixture of dibromide 21 (180 mg, 0.45 mmol), 2-tri(n-bu-
tylstannyl)thiophene (16) (0.70 mL, 2.20 mmol) and
PdACHTNURTGNEUG(N PPh3)4 (51 mg, 0.04 mmol) in dry DMF (5 mL) was
heated at 1208C for 2 h under an argon atmosphere. The re-
action was quenched by adding water (10 mL) and the prod-
uct was extracted with Et2O (3ꢅ25 mL). The combined or-
ganic layers were washed with brine, dried with Na2SO4 and
the solvent was evaporated to dryness. The crude product
was purified by column chromatography on silica gel (10–
25% EtOAc in hexanes) to afford compound 22 as brown
crystals; yield: 138 mg (76%); a sample was recrystallized
from CH2Cl2 to provide crystals suitable for X-ray structure
analysis; mp 145–1488C. 1H NMR (CDCl3, 500 MHz): d=
7.05 (dd, J=5.1, 3.7 Hz, 2H, Thio), 7.18 (d, J=3.8 Hz, 2H,
Thio), 7.25 (dd, J=5.1, 1.0 Hz, 2H, Thio), 7.31 (dd, J=3.6,
1.0 Hz, 2H, Thio), 7.44 (d, J=8.0 Hz, 2H, Py), 7.51 (d, J=
3.8 Hz, 2H, Thio), 7.64 (t, J=8.0 Hz, 1H, Py); 13C NMR
(CDCl3, 126 MHz): d=116.5 (d, Py), 124.2, 124.5, 124.8,
125.4, 128.0, 137.2 (6d, Py, Thio), 137.6, 139.7, 143.4, 151.9
(=C H, C H), 1555–1430 (C=C) cmÀ1; HR-MS: m/z=
787.9164, calcd. for C29H15F9NO3S6 [M+H]+: 787.9227.
À
À
2,6-Di[(2,2’-bithiophen)-5-yl]-4-(thiophen-2-yl)pyri-
dine (20)
Method A: According to typical procedure 4, a mixture of
pyridyl nonaflate 19 (40 mg, 0.05 mmol), PdACTHNURGTNEUNG(OAc)2 (3 mg,
0.01 mmol), dppp (6 mg, 0.01 mmol), Et3N (0.20 mL,
1.44 mmol), and formic acid (0.05 mL, 1.3 mmol) in DMF
(3 mL) was heated in an ACE-sealed tube at 908C for 2 h to
afford after purification by column chromatography on
silica gel (5–10% EtOAc in hexanes) pyridine derivative 20
as a light yellow oil; yield: 20 mg (82%).
À
À
Method B: According to typical procedure 5, a mixture of
dibromide 25 (25 mg, 0.05 mmol), 2-tri(n-butylstannyl)thio-
phene (16) (96 mg, 0.08 mL, 0.26 mmol), PdACTHNUTRGNE(UNG PPh3)4 (6 mg,
(4s, Py, Thio); IR (ATR): n=3100–2925 (=C H, C H),
1580–1435 (C=C) cmÀ1; HR-MS: m/z=408.0017, calcd. for
C21H14NS4 [M+H]+: 408.0004.
0.005 mmol) in DMF (1 mL) upon heating at 908C for 2 h
and after purification by column chromatography (SiO2, 5–
10% EtOAc in hexanes) provided compound 20 as a light
2,4,6-Tri[(2,2’-bithiophen)-5-yl]-3-(thiophen-2-yl)-
pyridine (24)
1
yellow oil; yield: 18 mg (74%). H NMR (CDCl3, 500 MHz):
d=7.05 (dd, J=5.1, 3.6 Hz, 2H, Thio), 7.17 (dd, J=5.2,
3.8 Hz, 1H, Thio), 7.20 (d, J=4.0 Hz, 2H, Thio), 7.25–7.26
(m, 2H, Thio), 7.31 (br d, J=3.6 Hz, 2H, Thio), 7.45 (br d,
J=5.1 Hz, 1H, Thio), 7.57–7.58 (m, 3H, Thio), 7.62 (s, 2H,
Py); 13C NMR (CDCl3, 126 MHz): d=112.9 (d, Py), 124.3,
124.5, 124.9, 125.6, 125.7, 127.2, 128.0, 128.5, 137.6, 139.9,
141.3, 142.9 (8 d, 4s, Thio), 143.2, 152.6 (2s, Py); IR (ATR):
A solution of N-bromosuccinimide (205 mg, 1.15 mmol) in
dry DMF (3 mL) was added dropwise to a cooled solution
(À208C) of compound 3 (75 mg, 0.23 mmol) in dry DMF
(3 mL). The mixture was warmed up to room temperature
and stirred for 24 h. After full consumption of the starting
material (TLC monitoring), 2-tri(n-butylstannyl)thiophene
(16) (470 mg, 0.40 mL, 1.26 mmol) was injected slowly and
n=3030–2905 (=C H, C H), 1550–1435 (C=C) cmÀ1; HR-
PdACTHUNGTERNU(NG PPh3)4 (53 mg, 0.05 mmol) was added and the resulting
À
À
3472
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ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2013, 355, 3463 – 3474

Synthesis and Properties of Branched Oligo(2-thienyl)- and Oligo(2,2’-bithien-5-yl)-Substituted Pyridines
mixture was heated at 1208C for 2 h. The mixture was dilut-
ed with Et2O (10 mL) and quenched with water (10 mL).
The layers were separated and the aqueous phase was ex-
tracted with Et2O (2ꢅ25 mL). The combined organic layers
were washed with brine, dried with Na2SO4 and the solvent
was evaporated. The crude product was purified by column
chromatography on silica gel (5–20% EtOAc in hexanes) to
give compound 24 as a greenish yellow solid; yield: 130 mg
(86%, two steps); mp 118–1228C. 1H NMR (C6D6,
500 MHz): d=6.55 (d, J=4.0 Hz, 1H, Thio), 6.59–6.61 (m,
2H, Thio), 6.65 (dd, J=5.1, 3.6 Hz, 1H, Thio), 6.67–6.69 (m,
3H, Thio), 6.73 (dd, J=5.1, 1.1 Hz, 1H, Thio), 6.76–6.80 (m,
4H, Thio), 6.95 (dd, J=3.6, 1.0 Hz, 1H, Thio), 7.01–7.03 (m,
2H, Thio), 7.06 (d, J=3.9 Hz, 1H, Thio), 7.07–7.08 (m, 1H,
Thio), 7.26 (d, J=3.8 Hz, 1H, Thio), 7.47 (s, 1H, Py);
13C NMR (C6D6, 126 MHz): d=115.7 (d, Py), 121.5, 123.7,
124.2, 124.3, 124.55, 124.56, 124.58, 124.7, 124.8, 124.9, 126.2,
127.71, 127.73, 127.9, 128.1, 128.2, 129.30, 129.32, 130.2,
136.9, 137.5, 137.6, 138.3, 138.8, 140.1, 140.6*, 143.0 (17d,
10s, Thio), 143.7, 144.6, 151.7, 152.4 (4s, Py), *intensity of
the peak corresponds to 2C atoms; IR (ATR): n=3070–
was purified by column chromatography on silica gel (10%
EtOAc in hexanes) to afford tribromo compound 26 as a col-
1
orless solid; yield: 54 mg (80%); mp 145–1488C. H NMR
(CDCl3, 700 MHz): d=7.06 (d, J=4.2 Hz, 2H, Thio), 7.11
(d, J=4.2 Hz, 1H, Thio), 7.28 (d, J=4.2 Hz, 1H, Thio), 7.34
(d, J=4.2 Hz, 2H, Thio), 7.41 (s, 2H, Py); 13C NMR
(CDCl3, 176 MHz): d=112.0, 114.6, 116.0 (3d, Thio, Py),
124.8, 125.8 (2d, Thio), 130.9, 131.3 (2s, Thio), 142.2, 145.6,
152.0 (3s, Py, Thio), only 10C atoms with different chemical
À
shifts could be detected; IR (ATR): n=2960–2865 (=C H),
1465–1360 (C=C) cmÀ1; HR-MS: m/z=559.7457, calcd. for
C17H9Br3NS3 [M+H]+: 559.7442.
2,4,6-Tri[(2,2’-bithiophen)-5-yl]pyridine (28)
According to typical procedure 1, a mixture of tribromide
26 (25 mg, 0.044 mmol), PdACHTNUGRTNEUNG(PPh3)4 (6 mg, 0.005 mmol),
K2CO3 (31 mg, 0.22 mmol), and thiophene-2-boronic acid
(27) (29 mg, 0.22 mmol) in DMF (1.1 mL) was heated at
808C for 3 h under an argon atmosphere. The mixture was
cooled to room temperature, diluted with brine (10 mL) and
extracted with Et2O (3ꢅ20 mL). The combined organic
phases were dried with Na2SO4 and concentrated to dryness.
The residue was purified by column chromatography on
silica gel (5–10% EtOAc in hexanes) to give 28 as a light
2865 (=C H, C H), 1615–1470 (C=C) cmÀ1; HR-MS: m/z=
653.9696, calcd. for C33H20NS7 [M+H]+: 653.9635.
À
À
2,6-Bis(5-bromothiophen-2-yl)-4-(thiophen-2-yl)-
pyridine (25)
1
yellow solid; yield: 19 mg (76%); mp 240–2448C. H NMR
(CDCl3, 700 MHz): d=7.04–7.08 (m, 3H, Thio), 7.21 (d, J=
3.5 Hz, 2H, Thio), 7.22 (d, J=3.5 Hz, 1H, Thio), 7.25–7.27
(m, 2H, Thio), 7.28 (dd, J=3.5, 1.4 Hz, 1H, Thio), 7.29 (dd,
J=5.6, 1.4 Hz, 1H, Thio), 7.32 (dd, J=3.5, 1.4 Hz, 2H,
Thio), 7.50 (d, J=3.5 Hz, 1H, Thio), 7.59 (d, J=3.5 Hz, 2H,
Thio), 7.60 (s, 2H, Py); 13C NMR (CDCl3, 176 MHz): d=
112.4, 124.2, 124.4, 124.5, 124.7, 124.8, 125.3, 125.6, 126.2,
127.9, 128.0 (11d, Thio, Py), 136.8, 137.5, 139.2, 139.5, 139.9,
142.4, 143.0, 152.5 (8s, Thio, Py); IR (ATR): n=2960–2865
A solution of N-bromosuccinimide (45 mg, 0.25 mmol) in
dry DMF (0.5 mL) was added dropwise under argon to
a
cooled solution (À208C) of compound
3 (33 mg,
0.10 mmol) in dry DMF (0.5 mL). The mixture was warmed
up to room temperature and stirred for 6 h. The reaction
mixture was diluted with CH2Cl2 (10 mL) and quenched
with water (5 mL). The layers were separated, the aqueous
phase was extracted with CH2Cl2 (2ꢅ10 mL), the combined
organic layers were washed with brine and dried with
Na2SO4. The solvent was evaporated and the crude product
was purified by chromatography on silica gel (10% EtOAc
in hexanes) to afford dibromo compound 25 (yield: 35 mg,
72%) and tribromo compound 26 (yield: 4 mg, 7%), both as
colorless solids.
(=C H), 1465–1360 (C=C) cmÀ1; HR-MS: m/z=571.9773,
À
calcd. for C29H18NS6 [M+H]+: 571.9758.
Supporting Information
1H NMR, 13C NMR, and 19F NMR spectra of all new com-
pounds; UV/vis and emission spectra of 6, 9, 14, 20, 22, 24
and 28; cyclic voltammogramms of 24 and 28 are given in
the Supporting Information.
1
Data of 25: mp 235–2408C. H NMR (CDCl3, 500 MHz):
d=7.08 (d, J=3.9 Hz, 2H, Thio), 7.17 (dd, J=5.1, 3.7 Hz,
1H, Thio), 7.39 (d, J=3.9 Hz, 2H, Thio), 7.45 (dd, J=5.1,
1.1 Hz, 1H, Thio), 7.55 (dd, J=3.7, 1.1 Hz, 1H, Thio), 7.57
(s, 2H, Py); 13C NMR (CDCl3, 126 MHz): d=112.7, 115.9,
124.9, 125.7, 127.5, 128.5 (6d, Py, Thio), 130.9, 141.0, 143.3
(3 s, Thio,), 145.9, 152.0 (2s, Py); IR (ATR): n=2960–2870
Acknowledgements
(=C H, C H), 1520–1355 (C=C) cmÀ1; HR-MS: m/z=
483.8333, calcd. for C17H10Br2NS3 [M+H]+: 483.8337.
À
À
Support of this work by the Deutsche Forschungsgemein-
schaft (SFB 765), the Alexander von Humboldt Foundation
(fellowships for M. K. B. and S. L. G.), the Evonik Founda-
tion (fellowship to D. T.) and Bayer HealthCare is most
gratefully acknowledged.
2,4,6-Tris(5-bromothiophen-2-yl)pyridine (26)
A solution of N-bromosuccinimide (88 mg, 0.49 mmol) in
dry DMF (1 mL) was added dropwise under argon to
a
cooled solution (À208C) of compound
3 (40 mg,
0.12 mmol) in dry DMF (1 mL). The mixture was warmed References
up to room temperature and stirred for 5 h. The reaction
mixture was diluted with CH2Cl2 (10 mL) and quenched
with water (5 mL). The layers were separated, the aqueous
phase was extracted with CH2Cl2 (2ꢅ10 mL), the combined
organic layers were washed with brine and dried with
Na2SO4. The solvent was evaporated and the crude product
[1] M. K. Bera, P. Hommes, H.-U. Reissig, Chem. Eur. J.
2011, 17, 11838–11843.
[2] a) For a review, see: T. Lechel, H.-U. Reissig, Pure
Appl. Chem. 2010, 82, 1835–1845; b) O. Flçgel, J. Dash,
I. Brꢀdgam, H. Hartl, H.-U. Reissig, Chem. Eur. J.
Adv. Synth. Catal. 2013, 355, 3463 – 3474
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
3473

Mrinal K. Bera et al.
FULL PAPERS
2004, 10, 4283–4290; c) J. Dash, T. Lechel, H.-U. Reis-
sig, Org. Lett. 2007, 9, 5541–5544; d) T. Lechel, J. Dash,
I. Brꢀdgam, H.-U. Reissig, Eur. J. Org. Chem. 2008,
3647–3655; e) C. Eidamshaus, H.-U. Reissig, Adv.
Synth. Catal. 2009, 351, 1162–1166; f) T. Lechel, J.
Dash, P. Hommes, D. Lentz, H.-U. Reissig, J. Org.
Chem. 2010, 75, 726–732; g) T. Lechel, J. Dash, C. Ei-
damshaus, I. Brꢀdgam, D. Lentz, H.-U. Reissig, Org.
Biomol. Chem. 2010, 8, 3007–3014; h) M. K. Bera, H.-
U. Reissig, Synthesis 2010, 2129–2138; i) C. Eidamshaus,
R. Kumar, M. K. Bera, H.-U. Reissig, Beilstein J. Org.
Chem. 2011, 7, 962–975.
453–478; n) M. Haemori, K. Itaka, J. Yamaguchi, A.
Kumagai, S. Yaginuma, H. Fukumoto, Y. Matsumoto,
T. Yamamoto, H. Koinuma, Thin Solid Films 2012, 520,
4445–4448; o) H.-j. Jiang, J.-l. Zhang, J. Sun, W. Huang,
Polymer 2012, 53, 5684–5690; p) K. Cao, X. Sun, Q.
Zhang, Y. Liu, Macromol. Chem. Phys. 2012, 213, 917–
923; q) L. Fillaud, G. Trippꢉ-Allard, J. C. Lacroix, Org.
Lett. 2013, 15, 1028–1031; r) G.-O. Buica, E.-M. Ungur-
eanu, L. Birzan, A. C. Razus, L.-R. Mandoc (Popescu),
J. Electroanal. Chem. 2013, 693, 67–72; s) F. Algi, Tetra-
hedron 2013, 69, 3523–3529.
[8] S. L. Gholap, P. Hommes, K. Neuthe, H.-U. Reissig,
[3] For a review summarizing the advantages of alkenyl
and aryl nonaflates in transition metal-catalyzed reac-
tions, see: J. Hçgermeier, H.-U. Reissig, Adv. Synth.
Catal. 2009, 351, 2747–2763.
[4] a) For the reduction of nonaflates, see: L. R. Subrama-
nian, A. Garcia Martinez, A. Herrera Fernandez, R.
Martinez Alvarez, Synthesis 1984, 481–485; b) for the
applied reaction conditions, see: S. Cacchi, P. G. Ciatti-
ni, E. Morera, G. Ortar, Tetrahedron Lett. 1986, 27,
5541–5544.
[5] a) Functional Organic Materials, (Eds.: T. J. J. Mꢀller,
U. H. F. Bunz), Wiley-VCH, Weinheim, 2007; b) Hand-
book of Thiophene Based Materials, (Eds.: I. F. Pere-
pichka, D. F. Perepichka), J. Wiley & Sons, Hoboken,
2009.
[6] Selected reviews: a) J. Roncali, Chem. Rev. 1997, 97,
173–206; b) I. F. Perepichka, D. F. Perepichka, H.
Meng, F. Wudl, Adv. Mater. 2005, 17, 2281–2305; c) I.
Osaka, R. D. McCullogh, Acc. Chem. Res. 2008, 41,
1202–1214; d) A. Mishra, C.-Q. Ma, P. Bꢁuerle, Chem.
Rev. 2009, 109, 1141; e) F. Zhang, D. Wu, Y. Xua, X.
Feng, J. Mater. Chem. 2011, 21, 17590–17600.
Org. Lett. 2013, 15, 318–321.
[9] a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–
2483; b) A. Suzuki, J. Organomet. Chem. 2002, 653, 83–
90; c) A. Suzuki, in: Handbook of Organopalladium
Chemistry for Organic Synthesis, (Eds.: E.-i. Negishi,
A. de Meijere), John Wiley & Sons, New York, 2002,
pp 249–262.
[10] I. G. Feutrill, R. N. Mirrington, Tetrahedron Lett. 1970,
1327–1328.
[11] a) J. K. Stille, Angew. Chem. 1986, 98, 504–519; Angew.
Chem. Int. Ed. Engl. 1986, 25, 508–524; b) T. N. Mitch-
ell, Synthesis 1992, 803–815; c) P. Espinet, A. M. Echa-
varren, Angew. Chem. 2004, 116, 4808–4839; Angew.
Chem. Int. Ed. 2004, 43, 4704–4734.
[12] L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565.
[13] In comparison to the corresponding neutral com-
pounds, a strong decrease in the fluorescence intensity
was observed for the protonated species.
[14] For related pH-sensitive fluorescence phenomena, see:
a) P. N. W. Baxter, J. Org. Chem. 2004, 69, 1813–1821,
and ref.[19] cited therein; b) Y. Liu, F. Zhang, C. He, D.
Wu, X. Zhuang, M. Xue, Y. Liu, X. Feng, Chem.
Commun. 2012, 48, 4166–4168; c) S. V. Rocha, N. S.
Finney, Org. Lett. 2010, 12, 2598–2601.
[7] For selected recent examples on 2,2’-bithienyl-substitut-
ed pyridines and other hetaromatic moieties, see:
a) J. S. Bair, R. G. Harrison, J. Org. Chem. 2007, 72,
6653–6661; b) A. Kumagai, H. Fukumoto, T. Yamamo-
to, J. Phys. Chem. B 2007, 111, 8020–8026; c) T. J.
OꢂSullivan, B. Djukic, P. A. Dube, M. T. Lemaire, Can.
J. Chem. 2009, 87, 533–538; d) C. Hertzog-Ronen, E.
Borzin, Y. Gerchikov, N. Tessler, Y. Eichen, Chem. Eur.
J. 2009, 15, 10380–10386; e) J.-i. Nishida, T. Masuko, Y.
Cui, K. Hara, H. Shibuya, M. Ihara, T. Hosoyama, R.
Goto, S. Mori, Y. Yamashita, J. Phys. Chem. C 2010,
114, 17920–17925; f) A. Bolduc, S. Dufresne, G. S.
Hanan, W. G. Skene, Can. J. Chem. 2010, 88, 236–246;
g) S. Steinberger, A. Mishra, E. Reinold, C. M. Mꢀller,
C. Uhrich, M. Pfeiffer, P. Bꢁuerle, Org. Lett. 2011, 13,
90–93; h) M. Melucci, M. Zambianchi, L. Favaretto, V.
Palermo, E. Treossi, M. Montalti, S. Bonacchi, M.
Cavallini, Chem. Commun. 2011, 47, 1689–1691; i) M.
Kondo, J.-i. Miyake, K. Tada, N. Kawatsuki, Chem.
[15] A photograph of the deposited film is included in the
Supporting Information (Figure S4).
[16] For example, see: a) O. A. Semenikhin, M. M. D. Hos-
sain, M. S. Workentin, J. Phys. Chem. B 2006, 110,
20189–20196; b) K. R. Idzik, P. Ledwon, R. Beckert, S.
Golba, J. Frydel, M. Lapkowski, Electrochim. Acta
2010, 55, 7419–7426, and references cited therein.
[17] For a recent review on multivalency, see: C. Fasting,
C. A. Schalley, M. Weber, O. Seitz, S. Hecht, B.
Koksch, J. Dernedde, C. Graf, E.-W. Knapp, R. Haag,
Angew. Chem. 2012, 124, 10622–10650; Angew. Chem.
Int. Ed. 2012, 51, 10472–10498.
[18] For related studies, see: a) L. Vandromme, H.-U. Reis-
sig, S. Grçper, J. P. Rabe, Eur. J. Org. Chem. 2008,
2049–2055; b) T. Lechel, M. Gerhard, D. Trawny, B.
Brusilowskij, L. Schefzig, R. Zimmer, J. P. Rabe, D.
Lentz, C. A. Schalley, H.-U. Reissig, Chem. Eur. J.
2011, 17, 7480–7491.
ˇ
Lett. 2011, 40, 264–265; j) J. Svoboda, P. Stenclovꢆ, F.
Uhlꢇk, J. Zednꢇk, J. Vohlꢇdal, Tetrahedron 2011, 67, 75–
79; k) M. Krompiec, I. Grudzka, M. Filapek, Ł. Skꢈrka,
S. Krompiec, M. Łapkowski, M. Kania, W. Danikie-
wicz, Electrochim. Acta 2011, 56, 8108–8114; l) S.-i.
Kato, S. Shimizu, H. Taguchi, A. Kobayashi, S. Tobita,
Y. Nakamura, J. Org. Chem. 2012, 77, 3222–3232;
m) for a review on thienyl-substituted terpyridines, see:
J. Husson, M. Knorr, J. Heterocycl. Chem. 2012, 49,
[19] R. Lazzaroni, A. Calderone, J. L. Brꢉdas, J. P. Rabe, J.
Chem. Phys. 1997, 107, 99–105.
[20] J. P. Perdew, Y. Wang, Phys. Rev. B 1992, 45, 13244–
13249.
[21] J. P. Rabe, S. Buchholz, Science 1991, 253, 424–427.
[22] Scanning Probe Image Processor (Image Metrology A/
S, Kgs. Lyngby, Denmark).
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Adv. Synth. Catal. 2013, 355, 3463 – 3474