Alkynylated diazadioxaacenes: Syntheses and properties

Article abstract of DOI:10.1021/jo400092r

We report the successful synthesis of a series of ethynylated dioxadiazaacenes and investigate their properties. We developed a modular Cu-based catalytic procedure to build up [1,4]dioxino[2,3-b]pyrazine motifs starting from only a few building blocks. TIPS-acetylene-substituted benzene-1,2-diol and naphthalene-2,3-diol were reacted with 2,3- dichloropyrazine, 2,3-dichloroquinoxaline, and 2,3-dichlorobenzoquinoxaline to give a set of six novel and well-soluble dioxadiazaacenes. Different reaction conditions for the coupling were tested. Copper catalysis is most effective and gave the best yield of dioxadiazaacenes. The resulting azaoxaacenes were characterized in terms of optical and electronic properties and crystal packing.

Full text of DOI:10.1021/jo400092r

Article
pubs.acs.org/joc
Alkynylated Diazadioxaacenes: Syntheses and Properties
Manuel Schaffroth, Benjamin D. Lindner, Vladislav Vasilenko, Frank Rominger, and U. H. F. Bunz*
Organisch-Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg
̈
S
* Supporting Information
ABSTRACT: We report the successful synthesis of a series of ethynylated dioxa-
diazaacenes and investigate their properties. We developed a modular Cu-based catalytic
procedure to build up [1,4]dioxino[2,3-b]pyrazine motifs starting from only a few building
blocks. TIPS-acetylene-substituted benzene-1,2-diol and naphthalene-2,3-diol were reacted
with 2,3-dichloropyrazine, 2,3-dichloroquinoxaline, and 2,3-dichlorobenzoquinoxaline to
give a set of six novel and well-soluble dioxadiazaacenes. Different reaction conditions for
the coupling were tested. Copper catalysis is most effective and gave the best yield of
dioxadiazaacenes. The resulting azaoxaacenes were characterized in terms of optical and
electronic properties and crystal packing.
Scheme 1. Synthesis of 9,10-Diaza-11,12-dioxatetracene
INTRODUCTION
■
Here we describe Pd- or Cu-catalyzed synthesis and photo-
physical, electrochemical, and structural characterization of a
series of hitherto (almost) unknown heteroacene-derivatives
featuring a [1,4]dioxino[2,3-b]pyrazine motif (Figure 1).
Here, as an extension of known derivatives of acenes, we
introduce a simple and efficient modular synthesis of
azaoxatetracenes, -pentacenes, and -hexacenes and systemati-
cally evaluate their structural, electronic, and electrochemical
properties.
Figure 1. [1,4]Dioxino[2,3-b]pyrazine motif of the synthesized
diazadioxaacenes.
RESULTS AND DISCUSSION
■
The synthesis of the target dioxadiazaacenes was planned by
coupling diols such as 6 and 9 to halogenated pyrazine/
quinoxaline derivatives. Diols 6 and 9 are unknown but can be
made from the literature known dihalides 4 and 7 by Pd-
catalyzed coupling to TIPS-acetylene to give the ethers 5 and 8,
respectively (Scheme 2).11,12 Demethylation by BBr3 at low
temperature affords the diols 6 and 9 in overall yields of 60%
for 6 and 40% for 9.13 The diols are (surprisingly) persistent at
room temperature under laboratory conditions and can be
stored for long periods of time in a freezer.
Acenes as a class of compounds have garnered great attention
for a variety of reasons including access to new structural motifs
(graphene segments) and precursors of organic dyes due to
their remarkable electronic properties.1 Pentacene itself is a
charge-carrier superstar but recently also pyrazine- or pyridine-
carrying derivatives of pentacene (tetraazapentacene)2−4 and
also N,N′-dihydrodiazapentacenes5 have been shown to be
attractive charge-transporting materials. However, the potential
evaluation of materials as effectors in organic electronic devices
critically rests on their synthetic accessibility so that there is a
constant pressure to make and evaluate new classes of
compounds or perform “chemical mutagenesis” on the
structures of known ones. One of the less investigated but
potentially attractive classes of acene types are the diazadiox-
aacenes (Figure 1). To our knowledge, there are only a few
derivatives of the larger diazadioxaacenes known, mainly 9,10-
diaza-11,12-dioxatetracene 3 (Scheme 1).6−9 These, however,
are not very soluble and were not studied concerning their
structural, optical, and electronic or electrochemical properties.
Very recently, a related TIPS-triphenodioxazine compound was
demonstrated to be a promising organic semiconductor.10
To test the coupling reactions, we treated 6 with
dichloroquinoxaline (2) under different reaction conditions
(Scheme 3). In a first experiment, we added base (Cs2CO3)
and heated using microwave irridiation. The desired product 10
was formed in 21% yield after chromatography and
crystallization. The yield of 10 increased to 37% upon addition
of a Pd catalyst and a Buchwald-type ligand (RuPhos).14
However, using copper iodide in the presence of picolinic acid
Received: January 15, 2013
Published: February 8, 2013
© 2013 American Chemical Society
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and K3PO4 as base is cheaper and worked even better,
furnishing the coupling product 10 in 45% yield after
chromatography.15,16 Therefore, we selected this optimized
method to perform all of the other coupling reactions.
Scheme 2. Synthesis of the Dihydroxyarenes 6 and 9
In Scheme 4 we have applied the optimized conditions and
coupled 6 and 9 in a modular fashion to 11, 2, and 15 to obtain
the target molecules 12−14, 16, and 17 in satisfactory to good
yields after chromatography and crystallization. In the solid
state, these acene types are colorless to slightly greenish and
show a blue to green fluorescence. In n-hexane all of them are
blue fluorescent. The heteroacenes 16 and 17 show a distinct
positive solvatochromism from blue to bright green (Figure 2).
Scheme 3. Synthesis of the Diazadioxaacene 10 and
Optimization of the Reaction Conditions
Figure 2. Photographs of the fluorescence of solutions (2 × 10−6 M)
of 17 in different solvents (hand-held black light with an excitation of
λmax = 365 nm).
Optical Properties. Figure 3 displays the absorption
spectra of the representative coupling products 10, 14, 16,
and 17. In 10 and 16, the dihydroxybenzene derivative 6 was
the coupling partner, while for 14 and 17 catechol 9 served as
the module. The absorption maximum of each compound is
determined by the presence of the largest uninterrupted acene,
i.e., the dioxine bridge is somewhat of a conjugative block, even
though the whole system is formally conjugated. This is
Scheme 4. Synthesis of the Diazadioxaacenes 12−16
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Figure 3. Normalized absorption spectra of 10 and 16 (left) and 14 and 17 (right) taken in n-hexane (solid line) and as a thin film (dashed line).
reminiscent of the isoelectronic N,N′-dihydrooligoazaacenes,
which show a similar behavior. As a consequence, 16 and 17
have roughly the same λmax in absorption and emission. While
the diazadioxaacenes display a significant stokes shift (see Table
1), the compounds with the quinoxaline moiety 10 and 14
compound 17 (Figure 4). This effect is due to the apparent
interaction of the molecules in the solid state. The broad and
featureless emission suggests that an excimer is formed. The
fluorescence quantum yields were the highest for the
quinoxaline containing compounds 10 and 14, but the lowest
for the products 16 and 17 having a benzoquinoxaline subunit.
For the fluorescence lifetimes this order is inverted.
Solvatochromism. The absorption maximum of 17 did not
change very much when screened from n-hexane to methanol.
In contrast, the emission spectrum was quite sensitive to the
solvent polarity (Figure 5, left). The plot (Figure 5, right)
indicates that no specific interactions exist between the solvent
and the dye, except for the polarizability as modeled by the
Lippert−Mataga equation.17 Only the value for methanol did
not fit well to the plot, as the Lippert−Mataga model works
best for aprotic solvents, where hydrogen bonding can be
excluded.
MO Calculations and Aromaticity. If one looks at the
diazadioxaacenes, there are two aromatic systems bridged by a
formally antiaromatic 8π-system, the dioxine motif. These
systems resemble the N,N′-dihydroazaacenes, which have been
investigated in depth.18−20 We have performed NICS(1)zz
calculations on 10, 12−14, 16, and 17 (Figure 6).21−24 The
geometry optimization was performed by TURBOMOLE
employing B3LYP def2-TZVP, and a single-point energy
calculation (Gaussian09, B3LYP 6-311++G**) followed.25,26
The contributing 8π-dioxine rings all display positive NICS
values, which range from 13.5 ppm for the largest computa-
tionally investigated acene to 17.6 ppm for the smallest, while
all of the other rings show large negative NICS values. These
heteroacenes are aromatic but have a somewhat diminished
aromaticity as compared to that of the fully conjugated
hydrocarbon congeners, similar to the situation described by
Table 1. Photophysical Properties Recorded for the
a
Diazadioxaacenes in Solution
Stokes
b
abs λmax em λmax
shift
Φf
0.1
τf
ε
compd
(nm)
(nm)
(cm−1
)
(ns) (L mol−1 cm−1
)
12
10
16
13
14
17
299
364
387
355
369
389
351
366
408
369
370
411
4955
150
0.35
0.39
0.16
0.32
0.51
0.13
c
80000
13000
15800
32200
29300
24700
2.36
5.28
4.18
2.59
5.25
1330
1068
74
1376
a
b
All data were acquired in n-hexane as solvent. Fluorescene lifetimes
c
were measured in solution. Compound 12 has almost no absorption
at the wavelength of the excitation laser (376 nm). Thus, no reliable
data could be obtained.
show almost no Stokes shifts. As an exception, 12 has a large
Stokes shift of 4955 cm−1, as it features no absorption
maximum greater than 299 nm, although the absorption onset
is at 350 nm (see the Supporting Information).
There is a small but significant red shift (≤5 nm) between
the absorption spectra in solution and in thin film, but for 17 it
extends to 33 nm. As the absorption peaks of 17 in thin film
match peaks of the solution spectrum with lower intensity (at
369 and 389 nm), this red shift might refer to those vibronic
fine structures. In contrast, the emission maxima show a
substantial red shift, which reaches nearly 100 nm for
Figure 4. Normalized emission spectra of 10 and 16 (left) and 14 and 17 (right) taken in n-hexane (solid line) and as thin film (dashed line).
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Figure 5. Normalized emission spectra of 17 in different solvents (left) and the corresponding Lippert−Mataga plot (right). For the calculation of
the orientation polarizability Δf we used following formula: Δf = (ε − 1)/(2ε + 1) − (n2 − 1)/(2n2 + 1), where ε is the relative permittivity and n
the refractive index of the solvent.
Figure 6. NICS(1)zz calculations (TURBOMOLE, B3LYP def2-TZVP//Gaussian09, B3LYP 6-311++G**).
Figure 7. FMOs: LUMOs (top row) and HOMOs (bottom row) (calculated by TURBOMOLE, B3LYP def2-TZVP//Gaussian09, B3LYP 6-311+
+G**; for the citation see the Supporting Information).
us for the N,N′-dihydroazaacenes.27 The synthesized diazadiox-
aacenes are stable and persistent, and do not experience any
type of apparent destabilization by the presence of the 8π-
system.
This separation of the molecules into two electronically
separated “halves” is also obvious when looking at the FMOs
(Figure 7). In most cases, the HOMOs and LUMOs are
concentrated on one side of the molecule. The HOMOs are
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mostly located on the side carrying the TIPS-ethynyl moiety,
only for 16 is it located on the pyrazine side and for 17 it is
delocalized on both sides. The LUMOs of 12 and 13 are also
located on the TIPS-ethynyl side, while for 14 it is delocalized
and for the other compounds it is situated on the pyrazine side.
Without going into detail, a prerequisite for a substantial
transfer integral and so a high charge carrier mobility, the
HOMO (for hole transport) or the LUMO (for electron
transport), respectively, should be delocalized as widely as
possible. Thus, 14 features the only appropriate LUMO and 17
the best HOMO distribution of the whole set. These candidates
might be interesting for possible applications in organic
electronics.
reduction potentials and their calculated (B3LYP 6-311+G**)
LUMO levels fit well into the master curve we have recently
developed19 to connect calculated LUMO levels with reduction
potentials as measured by cyclic voltammetry (see Figure 8).
Another important necessary criterion for good device
performance is a low LUMO energy for n-channel transport
or a high HOMO energy for p-channel transport. In Table 2,
Table 2. Calculated and Experimental HOMO−LUMO Gaps
(Gas Phase) for the Synthesized Diazadioxaacenes and
Pentacene for Comparison
Figure 8. Comparison of the first reduction potentials to the calculated
LUMO positions (TURBOMOLE, B3LYP def2-TZVP//Gaussian09,
B3LYP 6-311+G**). The red line is taken from the master curve
developed by Bunz et al.19 connecting first reduction potentials with
calculated LUMO levels. The blue spots are the values for the
corresponding diazadioxaacenes.
a
a
b
HOMO
(eV)
LUMO
(eV)
calcd gap exptl gap
gapcalc −
compd
12
(eV)
(eV)
gapexp (eV)
0.68
−6.31
−6.29
−6.04
−5.97
−5.94
−5.88
−4.93
−1.98
−2.21
−2.51
−2.26
−2.34
−2.56
−2.74
4.34
(339 nm)
3.66
10
4.08
3.53
3.71
3.60
3.31
2.20
(365 nm)
3.40
0.68
0.45
0.30
0.22
0.21
Solid-State Structures. We obtained crystal structures of
all six diazadioxaacenes (Figure 9). As expected, the measured
bond lengths and angles fit well to those obtained from DFT
calculations in the gas phase (TURBOMOLE, B3LYP def2-
TZVP). Remarkably, the structures are very planar, with 14
showing the greatest angulation between the two aromatic
moieties of 9.6° at the dioxine ring (Figure 10, bottom right).
Because of crystal packing effects, the ethynyl units are often
bent in TIPS-ethynylated acenes and heteroacenes.19,28 In 14,
16, and 17, the bending of the alkynes is particularly obvious.
The packing of the azaoxaacenes is different for each.
Compound 12 forms one-dimensional stacks but does not
show much overlap of the acene backbone becaue of the TIPS
substituents. So does 10, but with more overlap and units of
two molecules, inversely superimposed. Compound 16 forms a
herringbone motif with plane distances of 3.32, 3.51, 3.36 Å and
3.40 Å, respectively (Figure 10). These plane distances might
be small enough for an efficient charge transport. Compound
13 forms dimers at the pyrazine units with a CH−N bond
length of 2.69 Å. The dimers are arranged in a herringbone
motif with only small overlap. The kinked 14 forms a brickwall
motif, while 17 features a herringbone motif. One stack shows
inversely superimposed pairs of molecules with plane distances
of 3.36 and 3.37 Å, and the other moiety has equally oriented
molecules with a plane distance of 3.39 Å. In addition to spread
out FMOs and appropriate energy levels, a good overlap of the
molecules in the solid phase is critical to an efficient charge
transport as it should increase the overlap integral.29
Azaoxaacenes 14, 16, and 17 fulfill this condition to a good
degree and will be investigated in TFT-type devices.
16
(402 nm)
3.08
13
(364 nm)
3.41
14
(367 nm)
3.38
17
(400 nm)
3.10
pentacene
a
Calculated by TURBOMOLE, B3LYP def2-TZVP//Gaussian09,
b
B3LYP 6-311++G**. Acquired from the intersection of the
absorption and emission spectra.
the calculated energies and band gaps are shown and compared
to experimental gaps acquired from the intersection of the
absorption and emission spectra. The calculated gaps of the
naphtho compounds 13, 14, and 17 fit quite well to the values
obtained by experiment, while for the benzo compounds 12,
10, and 16 the values differ up to 0.68 eV. Overall, the LUMO
energies are relatively high; therefore, these materials might not
work well as electron-transport materials. However, the high-
lying HOMO energies are suggestive that the diazadioxaacenes
might be worth checking as hole transport materials, as in 17
the HOMO is only 1 eV lower in energy than that of
pentacene.
Electrochemistry. Cyclic voltammetry shows that the
coupling products display one reversible reduction potential
versus ferrocene at −2.25 V (13), −2.20 V (14), −2.02 V (16),
and −2.02 V (17). Reduction potentials of 10 and 12 were too
near to the decomposition limit of the solvent to be
determined. From these data, one can see that reduction of
the pyrazine-containing subunit defines the reduction potential.
Compound 13 displaying a pyrazine unit is less easily reduced
than 16 or 17, which incorporate a benzoquinoxaline unit.
These results underscore the “split” nature of the diazadiox-
aacenes, which is determined by the separating oxygen bridges.
For 17 we were also able to determine the first oxidation
potential with a value of 0.64 V vs ferrocene. The measured
CONCLUSION
■
We have produced a series of hitherto unknown, substituted,
stable, and soluble diazadioxaacenes by a modular coupling
process of aromatic ortho-diols to dichloropyrazines, -quinoxa-
lines, and -benzoquinoxalines. The best method for their
modular synthesis is the cheap, copper-catalyzed, base-
promoted reaction developed by Buchwald et al. superior to
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Figure 9. Crystal structures of 12, 10, 16, 13, 14, and 17.
Figure 10. Herringbone motif of 16 (top, left), dimer of 13 (top, right), the herringbone motif of 17 (bottom, left), and brickwall motif of kinked 14
(bottom, right). Where necessary for a better overview, the ethynyl side chains were hidden.
either that uses only base- or even Pd-catalyzed processes.15
The obtained heteroacenes are persistent and stable under
laboratory conditions and display promising crystal packings.
Despite the formally antiaromatic dioxine ring, they overall
exhibit aromaticity, albeit somewhat reduced. The diminished
conjugation at the dioxine ring often causes a localization of the
FMOs on one-half of the molecules, and consequently
relatively high LUMO and low HOMO energies result. In
contrast to the fully conjugated N-heteroacenes, these
molecules could prove to work as a p-channel material. Here,
especially 17 might be a promising candidate due to its spread
out HOMO distribution, high HOMO level (oxidized at 0.64 V
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mg, 508 μmol, 4 mol %), and CuI (96.7 mg, 508 μmol, 4 mol %) were
dissolved in dry NEt3 (65 mL) and NH(i-Pr)3 (25 mL). The mixture
was degassed three times (freeze−thaw method). After slow addition
of TIPS-acetylene (6.95 g, 8.55 mL, 38.1 mmol, 3 equiv), the solution
was stirred under reflux for 16 h. The mixture was filtered through
Celite, extracted with CH2Cl2, and washed with water twice and with a
saturated solution of NH4Cl. The organic phase was dried over
Na2SO4 and concentrated. Flash chromatography (petroleum ether/
ethyl acetate 500:1 to 100:1) gave 8 as a colorless solid (5.48 g, 9.98
vs ferrocene), and good crystal packing. In the future, we will
investigate larger diazadioxaacenes in organic thin film
transistors.
EXPERIMENTAL SECTION
■
Quantum yields were measured relative to quinine sulfate in dilute
sulfuric acid. Time-correlated single photon counting lifetime
measurements were made with a pulsed laser diode. Computational
studies were carried out using DFT calculations on a Turbomole 6.3.1
or a Gaussian09 platform. Geometry optimization was found by
B3LYP functional and def2-TZVP basis set. Using this geometry,
FMO energies were assigned on single point approach by employing
B3LYP/6-311++G**. Electrochemical measurements were performed
using 0.1 M n-Bu4NPF6 in dry THF or DCM as electrolyte solution.
Potentials were determined using cyclic voltammetry at 40 mV s−1
using a platinum working electrode and a platinum/titanium wire
auxiliary electrode. Ferrocene was used as an internal reference.
1,4-Diiodo-2,3-dimethoxybenzene (4). Compound 4 was
synthesized according to the procedure described by Zhu and
1
mmol, 79%): Rf = 0.82 (PE/EA = 9:1); mp 39 °C; H NMR (300
MHz, CDCl3, 25 °C) δ = 1.19−1.23 (m, 42H), 4.05 (s, 6H), 7.48−
7.53 (m, 2H), 8.25−8.30 (m, 2H); 13C {1H} NMR (75 MHz, CDCl3,
25 °C) δ = 11.5, 18.8, 61.5, 100.3, 102.8, 115.0, 125.9, 126.4, 131.1,
155.2; IR ν = 2941, 2890, 2864, 2144, 1457, 1376, 1246, 1043, 1016,
995, 956, 881, 766, 712, 677, 574, 504, 458; HR-MS (ESI-FT-ICR) m/
z calcd for C34H53O2Si2 [M + H]+ 549.35786, found 549.35791.
1,4-Bis[[tri(prop-2-yl)silyl]ethynyl]naphthalene-2,3-diol (9).
Under an atmosphere of nitrogen, 8 (549 g, 1.00 mmol) was
dissolved in dry CH2Cl2 (5 mL) at −78 °C. After slow addition of
BBr3 (501 mg, 190 μL, 2.00 mmol, 2 equiv), the solution was stirred at
−78 °C for 45 min and afterward under warming to rt for 1 h. Then
ice−water was added, and the mixture was stirred for 1 h. After
extraction with CH2Cl2, the organic phase was washed with water
twice, dried over Na2SO4, and concentrated. Flash chromatography
(petroleum ether/ethyl acetate 200:1) gave 6 as a colorless solid (251
mg, 482 μmol, 48%): Rf = 0.53 (PE/EA = 9:1); mp 137 °C under
Swager:11 Rf = 0.65 (PE/EA = 9:1); H NMR (300 MHz, CDCl3,
1
25 °C) δ = 3.87 (s, 6H), 7.24 (s, 2H).
[(2,3-Dimethoxybenzene-1,4-diyl)diethyne-2,1-diyl]bis[tri-
(prop-2-yl)silane] (5). Under an atmosphere of argon, 4 (4.00 g, 10.3
mmol), piperidine (4.39 g, 5.09 mL, 51.5 mmol, 5 equiv),
Pd(PPh3)2Cl2 (361 mg, 515 μmol, 5 mol %), and CuI (98.1 mg,
515 μmol, 5 mol %) were dissolved in dry THF (50 mL), and the
mixture was degassed three times (freeze−thaw method). After slow
addition of TIPS-acetylene (5.64 g, 6.94 mL, 30.9 mmol, 3 equiv) the
solution was stirred under reflux for 18 h. The mixture was filtered
through Celite and concentrated. Flash chromatography (petroleum
ether/CH2Cl2 10:1) gave 5 as a colorless liquid (4.73 g, 9.47 mmol,
92%): Rf = 0.64 (PE/EA = 20:1); 1H NMR (600 MHz, CDCl3, 25 °C)
δ = 1.10−1.17 (m, 42H), 3.95 (s, 6H), 7.08 (s, 2H); 13C {1H} NMR
(150 MHz, CDCl3, 25 °C) δ = 11.4, 18.7, 61.1, 97.1, 102.4, 119.2,
128.3, 154.7; IR ν = 2941, 2890, 2863, 2155, 1459, 1401, 1230, 1066,
1030, 995, 922, 881, 818, 779, 676, 656, 589, 479, 457, 446; HR-MS
(ESI-FT-ICR) m/z calcd for C30H51O2Si2 [M + H]+ 499.34221, found
499.34227.
1
decompostion; H NMR (600 MHz, CDCl3, 25 °C) δ = 1.18−1.23
(m, 42H), 6.17 (s, 2H), 7.43−7.47 (m, 2H), 8.07−8.11 (m, 2H); 13C
{1H} NMR (150 MHz, CDCl3, 25 °C) δ = 11.3, 18.8, 98.8, 104.9,
105.4, 125.2, 125.6, 128.4, 146.5; IR ν = 3504, 3458, 2941, 2863, 2148,
1513, 1460, 1442, 1381, 1287, 1254, 1221, 1194, 1153, 1019, 996, 943,
881, 860, 761, 670, 573, 507, 467, 435, 415, 405; HR-MS (ESI-FT-
ICR) m/z calcd for C32H49O2Si2 [M + H]+ 521.32656, found
521.32662.
1,4-Bis[[tri(prop-2-yl)silyl]ethynyl][1,4]benzodioxino[2,3-b]-
quinoxaline (10). (i) Under an atmosphere of argon, 6 (50.0 mg, 106
μmol), 2 (21.1 mg, 106 μmol, 1 equiv), and Cs2CO3 (104 mg, 318
μmol, 3 equiv) were dissolved in dry THF (2 mL) in a 10 mL
microwave tube. In the microwave reactor, the mixture was stirred at
150 °C for 2 h. The mixture was purified by flash chromatography
(petroleum ether/ethyl acetate 200:1) to obtain 10 as a colorless solid
(13.0 mg, 21.8 μmol, 21%).
(ii) Under an atmosphere of argon, 6 (50.0 mg, 106 μmol), 2 (21.1
mg, 106 μmol, 1 equiv), Pd(RuPhos)(NH2EtPh)Cl (3.86 mg, 5.30
μmol, 5 mol %), RuPhos (2.47 mg, 5.30 μmol, 5 mol %), and Cs2CO3
(104 mg, 318 μmol, 3 equiv) were dissolved in dry THF (2 mL) in a
10 mL microwave tube. In the microwave reactor, the mixture was
stirred at 150 °C for 2 h. The mixture was purified by flash
chromatography (petroleum ether/ethyl acetate 200:1) to obtain 10 as
a colorless solid (23.5 mg, 39.4 μmol, 37%).
(iii) Under an atmosphere of nitrogen, 6 (50.0 mg, 106 μmol), 2
(21.1 mg, 106 μmol, 1 equiv), CuI (2.02 mg, 10.6 μmol, 10 mol %),
picolinic acid (2.61 mg, 21.2 μmol, 20 mol %), and K3PO4 (90.0 mg,
424 μmol, 4 equiv) were dissolved in dry DMSO (2 mL). The mixture
was stirred at 90 °C for 24 h. After dilution with diethyl ether and
washing with water, the organic phase was dried over Na2SO4 and
concentrated. The mixture was purified by flash chromatography
(petroleum ether/ethyl acetate 300:1) to obtain 10 as a colorless solid
(28.5 mg, 47.7 μmol, 45%): Rf = 0.64 (PE/EA = 9:1); mp 146 °C; 1H
NMR (300 MHz, CDCl3, 25 °C) δ = 1.14−1.22 (m, 42H), 7.10 (s,
2H), 7.54−7.62 (m, 2H), 7.79−7.86 (m, 2H); 13C {1H} NMR (75
MHz, CDCl3, 25 °C) δ = 11.3, 18.7, 99.5, 100.6, 113.1, 127.6, 128.3,
128.8, 139.5, 141.9, 144.1; IR ν = 2942, 2890, 2864, 2157, 1420, 1372,
1330, 1231, 1167, 1141, 1052, 1019, 995, 881, 794, 759, 748, 675, 658,
616, 580, 447; UV−vis λmax (hexane) 364 nm; ε(364 nm)= 13000
L·mol−1·cm−1; fluorescence λmax (hexane) 366 nm; HR-MS (ESI-FT-
ICR) m/z calcd for C36H49N2O2Si2 [M + H]+ 597.33271, found
597.33395.
3,6-Bis[[tri(prop-2-yl)silyl]ethynyl]benzene-1,2-diol (6).
Under an atmosphere of nitrogen, 5 (4.72 g, 9.46 mmol) was
dissolved in dry CH2Cl2 (50 mL) at −78 °C. After slow addition of
BBr3 (3.56 g, 1.35 mL, 14.2 mmol, 1.5 equiv) the solution was stirred
under warming to rt for 1.5 h. Then ice−water was added, and the
mixture was stirred for 30 min. After extraction with CH2Cl2, the
organic phase was washed with water twice, dried over Na2SO4, and
concentrated. Flash chromatography (petroleum ether/ethyl acetate
100:1) gave 6 as a colorless solid (2.88 g, 6.12 mmol, 65%): Rf = 0.58
(PE/EA = 9:1); mp 122 °C; 1H NMR (600 MHz, CDCl3, 25 °C) δ =
1.12−1.16 (m, 42H), 5.74 (s, 2H), 6.87 (s, 2H); 13C {1H} NMR (150
MHz, CDCl3, 25 °C) δ = 11.2, 18.7, 99.7, 100.7, 111.1, 123.0, 144.8;
IR ν = 3502, 2942, 2863, 2146, 1614, 1452, 1303, 1230, 1205, 997,
945, 882, 803, 785, 678, 640, 626, 578, 531, 499, 460, 446, 404; HR-
MS (ESI-FT-ICR) m/z calcd for C28H46NaO2Si2 [M + Na]+
493.29285, found 493.29274.
1,4-Dibromo-2,3-dimethoxynaphthalene (7). 2,3-Dimethoxy-
naphthalene (1.00g, 5.31 mmol) was dissolved in glacial acetic acid (7
mL). After slow addition of a solution of Br2 (1.69 g, 0.54 mL, 10.6
mmol, 2 equiv) in glacial acetic acid (3 mL), the solution was stirred in
the dark at rt for 24 h. Then a saturated solution of Na2S2O3 was
added, and the mixture was extracted with CH2Cl2. The organic phase
was washed with a saturated solution of NaHCO3 and twice with
water, dried over Na2SO4, and concentrated. Flash chromatography
(petroleum ether/ethyl acetate 100:1) gave 7 as a colorless solid (1.48
1
g, 4.28 mmol, 81%): Rf = 0.57 (PE/EA = 9:1); H NMR (300 MHz,
CDCl3, 25 °C) δ = 4.01 (s, 6H), 7.52−7.61 (m, 2H), 8.20−8.28 (m,
2H).
[(2,3-Dimethoxynaphthalene-1,4-diyl)diethyne-2,1-diyl]bis-
[tri(prop-2-yl)silane] (8). Under an atmosphere of nitrogen, 7 (4.39
g, 12.7 mmol), Pd(PPh3)4 (294 mg, 254 μmol, 2 mol %), PPh3 (133
6,9-Bis[[tri(prop-2-yl)silyl]ethynyl][1,4]benzodioxino[2,3-b]-
pyrazine (12). Under an atmosphere of argon, 6 (150 mg, 319 μmol),
3148
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The Journal of Organic Chemistry
Article
11 (47.5 mg, 319 μmol, 1 equiv), CuI (6.08 mg, 31.9 μmol, 10 mol %),
picolinic acid (7.85 mg, 63.8 μmol, 20 mol %), and K3PO4 (272 mg,
1.28 mmol, 4 equiv) were dissolved in a mixture of dry
dimethoxyethan (2 mL) and dry toluene (2 mL) in a 10 mL
microwave tube. In the microwave reactor the mixture was stirred at
160 °C for 4 h. After dilution with diethyl ether and washing with
water, the organic phase was dried over MgSO4 and concentrated. The
mixture was purified by flash chromatography (petroleum ether/ethyl
acetate 250:1) to obtain 12 as a colorless solid (130 mg, 237 μmol,
9:1); mp 280 °C dec; 1H NMR (500 MHz, CDCl3, 25 °C) δ = 1.19−
1.23 (m, 42H), 7.13 (s, 2H), 7.50−7.55 (m, 2H), 7.98−8.03 (m, 2H),
8.34 (s, 2H); 13C {1H} NMR (125 MHz, CDCl3, 25 °C) δ = 11.4,
18.7, 99.4, 100.8, 113.2, 125.7, 126.5, 128.1, 128.3, 133.3, 136.8, 141.6,
144.1; IR ν = 2942, 2890, 2864, 2154, 1433, 1395, 1362, 1279, 1169,
1053, 1017, 876, 768, 744, 675, 660, 627, 596, 470, 433; UV−vis λmax
(hexane) 387 nm; ε(387 nm)= 15800 L·mol−1·cm−1; fluorescence λmax
(hexane) 408 nm; HR-MS (ESI-FT-ICR) m/z calcd for
C40H51N2O2Si2 [M + H]+ 647.34836, found 647.35257. Anal. Calcd
for C40H50N2O2Si2: C, 74.25; H, 7.79; N, 4.33. Found: C, 74.07; H,
7.67; N, 4.14.
5,16-Bis[[tri(prop-2-yl)silyl]ethynyl]benzo[g]naphtho-
[2′,3′:5,6][1,4]dioxino[2,3-b]quinoxaline (17). Under an atmos-
phere of nitrogen, 9 (156 mg, 300 μmol), 15 (74.7 mg, 300 μmol, 1
equiv), CuI (5.71 mg, 30.0 μmol, 10 mol %), picolinic acid (7.39 mg,
60.0 μmol, 20 mol %), and K3PO4 (255 mg, 1.20 mmol, 4 equiv) were
dissolved in dry DMSO (4 mL). The mixture was stirred at 90 °C for
48 h. After dilution with diethyl ether and washing with water, the
organic phase was dried over Na2SO4 and concentrated. The mixture
was purified by flash chromatography (petroleum ether/ethyl acetate
500:1) to obtain 17 as a yellow solid (152 mg, 218 μmol, 73%): Rf =
0.71 (PE/EA = 9:1); mp 374 °C dec; 1H NMR (400 MHz, CDCl3, 25
°C) δ = 1.25−1.32 (m, 42H), 7.48−7.54 (m, 2H), 7.55−7.61 (m, 2H),
7.99−8.05 (m, 2H), 8.28−8.34 (m, 2H), 8.40 (s, 2H); 13C {1H} NMR
(100 MHz, CDCl3, 25 °C) δ = 11.5, 18.9, 97.7, 106.4, 108.7, 125.8,
126.2, 126.5, 127.3, 128.2, 130.6, 133.3, 136.8, 141.6, 143.7; IR ν =
2941, 2890, 2864, 2164, 2137, 1425, 1396, 1361, 1346, 1280, 1168,
1139, 1106, 1037, 989, 877, 761, 740, 672, 660, 583, 499, 489, 471,
461, 432, 420, 408; UV−vis λmax (hexane) 389 nm; ε(389 nm) =
24700 L·mol−1·cm−1; fluorescence λmax (hexane): 411 nm; HR-MS
(ESI-FT-ICR) m/z calcd for C44H53N2O2Si2 [M + H]+ 697.36401,
found 697.36422.
1
74%): Rf = 0.55 (PE/EA = 9:1); mp 155 °C; H NMR (400 MHz,
CDCl3, 25 °C) δ = 1.13−1.20 (m, 42H), 7.04 (s, 2H), 7.83 (s, 2H);
13C {1H} NMR (100 MHz, CDCl3, 25 °C) δ = 11.3, 18.7, 99.5, 100.3,
113.0, 128.3, 137.8, 142.4, 146.0; IR ν = 2942, 2890, 2864, 2157, 1581,
1462, 1410, 1388, 1303, 1189, 1162, 1037, 1001, 881, 816, 783, 695,
675, 660, 627, 585, 506, 470, 460, 417, 405; UV−vis λmax (hexane) 299
nm; ε(299 nm)= 80000 L·mol−1·cm−1; fluorescence λmax (hexane) 351
nm; HR-MS (ESI-FT-ICR) m/z calcd for C32H47N2O2Si2 [M + H]+
547.31706, found 547.31779.
6, 11-Bis[[tri(prop-2-yl)silyl]ethynyl]naphtho-
[2′,3′:5,6][1,4]dioxino[2,3-b]pyrazine (13). Under an atmosphere
of argon, 9 (100 mg, 192 μmol), 11 (28.6 mg, 192 μmol, 1 equiv), CuI
(3.66 mg, 19.2 μmol, 10 mol %), picolinic acid (4.73 mg, 38.4 μmol,
20 mol %), and K3PO4 (163 mg, 768 μmol, 4 equiv) were dissolved in
a mixture of dry dimethoxyethane (2 mL) and dry toluene (2 mL) in a
10 mL microwave tube. In the microwave reactor, the mixture was
stirred at 160 °C for 2 h. After dilution with diethyl ether and washing
with water, the organic phase was dried over MgSO4, and
concentrated. The mixture was purified by flash chromatography
(petroleum ether/ethyl acetate 250:1) to obtain 12 as a colorless solid
1
(130 mg, 237 μmol, 43%): Rf = 0.57 (PE/EA = 9:1); mp 176 °C; H
NMR (600 MHz, CDCl3, 25 °C) δ = 1.19−1.30 (m, 42H), 7.51−7.55
(m, 2H), 7.90 (s, 2H), 8.22−8.27 (m, 2H); 13C {1H} NMR (150
MHz, CDCl3, 25 °C) δ = 11.4, 18.8, 97.7, 105.9, 108.5, 126.1, 127.2,
130.6, 137.8, 142.4, 144.5; IR ν = 2941, 2890, 2863, 2162, 2140, 1598,
1460, 1430, 1403, 1367, 1351, 1337, 1304, 1248, 1191, 1166, 1032,
1016, 993, 960, 881, 850, 761, 746, 676, 664, 652, 605, 581, 496, 470,
460, 418; UV−vis λmax (hexane) 355 nm; ε(355 nm) = 32200
L·mol−1·cm−1; fluorescence λmax (hexane) 369 nm; HR-MS (ESI-FT-
ICR) m/z calcd for C36H49N2O2Si2 [M + H]+ 597.33271, found
597.33393.
ASSOCIATED CONTENT
* Supporting Information
■
S
Copies of NMR spectra, full scaled absortion and emission
spectra, further information about the computational calcu-
lations, and X-ray data (cif). This material is available free of
charge via the Internet at http://pubs.acs.org.
7,12-Bis[[tri(prop-2-yl)silyl]ethynyl]naphtho[2′,3′:5,6][1,4]-
dioxino[2,3-b]quinoxaline (14). Under an atmosphere of nitrogen,
9 (156 mg, 300 μmol), 2 (59.7 mg, 300 μmol, 1 equiv), CuI (5.71 mg,
30.0 μmol, 10 mol %), picolinic acid (7.39 mg, 60.0 μmol, 20 mol %),
and K3PO4 (255 mg, 1.20 mmol, 4 equiv) were dissolved in dry
DMSO (4 mL). The mixture was stirred at 90 °C for 24 h. After
dilution with diethyl ether and washing with water, the organic phase
was dried over Na2SO4 and concentrated. The mixture was purified by
flash chromatography (petroleum ether/ethyl acetate 500:1) to obtain
14 as a yellow solid (57.6 mg, 89.0 μmol, 30%): Rf = 0.65 (PE/EA =
9:1); mp 225 °C dec; 1H NMR (600 MHz, CDCl3, 25 °C) δ = 1.24−
1.32 (m, 42H), 7.53−7.58 (m, 2H), 7.59−7.63 (m, 2H), 7.86−7.90
(m, 2H), 8.26−8.31 (m, 2H); 13C {1H} NMR (150 MHz, CDCl3, 25
°C) δ = 11.4, 18.8, 97.7, 106.2, 108.6, 126.2, 127.2, 127.7, 128.8, 130.6,
139.5, 141.9, 143.6; IR ν = 2941, 2891, 2864, 2155, 2137, 1415, 1395,
1371, 1338, 1329, 1254, 1232, 1039, 985, 882, 766, 758, 713, 675, 659,
605, 447; UV−vis λmax (hexane) 369 nm; ε(369 nm)= 29300
L·mol−1·cm−1; fluorescence λmax (hexane): 670 nm; HR-MS (ESI-FT-
ICR) m/z calcd for C40H51N2O2Si2 [M + H]+ 647.34836, found
647.34969.
1,4-Bis[[tri(prop-2-yl)silyl]ethynyl][1,4]benzodioxino[2,3-b]-
benzo[g]quinoxaline (16). Under an atmosphere of nitrogen, 6
(150 mg, 319 μmol), 15 (79.5 mg, 319 μmol, 1 equiv), CuI (6.08 mg,
31.9 μmol, 10 mol %), picolinic acid (7.85 mg, 63.8 μmol, 20 mol %),
and K3PO4 (272 mg, 1.28 mmol, 4 equiv) were dissolved in dry
DMSO (4 mL). The mixture was stirred at 90 °C for 48 h. After
dilution with diethyl ether and washing with water, the organic phase
was dried over Na2SO4 and concentrated. The mixture was purified by
flash chromatography (petroleum ether/ethyl acetate 500:1) to obtain
16 as a yellow solid (96.1 mg, 149 μmol, 47%): Rf = 0.69 (PE/EA =
AUTHOR INFORMATION
Corresponding Author
*E-mail: uwe.bunz@oci.uni-heidelberg.de.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the Struktur and Innovation Fonds of the State of
■
Baden-Wurttemberg for generous support.
̈
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