New push-pull chromophores featuring TCAQ (11,11,12,12-Tetracyano-9,10- anthraquinodimethane) and other dicyanovinyl acceptors

Article abstract of DOI:10.1002/ejoc.200700970

Stable, highly colored push-pull chromophores with NMe₂ donor and C=C(CN)₂ acceptor moieties, featuring intense intramolecular charge-transfer (CT) bands in the UV/Vis spectra, are reported. In an attempt to prepare the quinoid pushpull systems 2, chromophores 10 and 11, with a central cyclohexene spacer, were obtained and characterized by X-ray analysis. A series of donor-substituted TCAQ (11,11,12,12-tetracyano-9,10-anthraquinodimethane) derivatives were synthesized, using the Knoevenagel condensation between appropriately functionalized anthraquinones and malononitrile, mediated by the Lehnert reagent (TiCl₄/pyridine), as the key step. HCl addition to triple bonds was observed when this transformation was applied to alkynylated anthraquinones. Electrochemical studies by cyclic voltammetry (CV) and rotating-disk voltammetry (RDV) showed that introduction of donor substituents into the TCAQ core of 25, 26, and 31 shifts the first reduction potential to more negative values, while chromophores bearing guanidine moieties (27, 28) displayed a specific and complex redox behavior. Both electrochemical and UV/Vis data provide good evidence that D-A conjugation is more efficient through olefinic (in 10) than through acetylenic (in 37) spacers. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200700970

FULL PAPER
DOI: 10.1002/ejoc.200700970
New Push-Pull Chromophores Featuring TCAQ (11,11,12,12-Tetracyano-
9,10-anthraquinodimethane) and Other Dicyanovinyl Acceptors
[a]
[b]
[b]
ˇ [a]
Filip Bures, W. Bernd Schweizer, Corinne Boudon, Jean-Paul Gisselbrecht,
Maurice Gross,[b] and François Diederich*[a]
Keywords: Donor–acceptor chromophores / 11,11,12,12-Tetracyano-9,10-anthraquinodimethane (TCAQ) / Charge trans-
fer / Electrochemistry / Pi conjugation / Quinodimethanes
Stable, highly colored push-pull chromophores with NMe2
donor and C=C(CN)2 acceptor moieties, featuring intense in-
tramolecular charge-transfer (CT) bands in the UV/Vis spec-
tra, are reported. In an attempt to prepare the quinoid push-
when this transformation was applied to alkynylated anthra-
quinones. Electrochemical studies by cyclic voltammetry
(CV) and rotating-disk voltammetry (RDV) showed that in-
troduction of donor substituents into the TCAQ core of 25,
pull systems 2, chromophores 10 and 11, with a central cyclo- 26, and 31 shifts the first reduction potential to more negative
hexene spacer, were obtained and characterized by X-ray
analysis. A series of donor-substituted TCAQ (11,11,12,12-
tetracyano-9,10-anthraquinodimethane) derivatives were
synthesized, using the Knoevenagel condensation between
appropriately functionalized anthraquinones and malono-
nitrile, mediated by the Lehnert reagent (TiCl4/pyridine), as
the key step. HCl addition to triple bonds was observed
values, while chromophores bearing guanidine moieties (27,
28) displayed a specific and complex redox behavior. Both
electrochemical and UV/Vis data provide good evidence that
D–A conjugation is more efficient through olefinic (in 10)
than through acetylenic (in 37) spacers.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
comprehensive study, we identified a strong dependence of
ground-state D–A conjugation from the length of the π
spacer. More efficient D–A conjugation leads to larger op-
tical gaps.[7,9] Smaller optical gaps, i.e. more bathochrom-
ically shifted CT bands, are obtained by reducing the effi-
ciency of D–A conjugation through introduction of ex-
tended spacers, such as alkenes or alkynes.[7,9] At strong D–
A conjugation, the HOMO (highest occupied molecular or-
bital) of the donor is lowered and the LUMO (lowest unoc-
cupied molecular orbital) of the acceptor raised, yielding a
large optical (and electrochemical) gap. In the case of
weaker D–A conjugation, i.e. when donor and acceptor are
separated by larger spacers, the energy levels of HOMO and
LUMO resemble those in the free components and a
smaller optical gap (bathochromically shifted CT band) is
measured. At the same time, the insertion of large π spacers
was found to strongly enhance third-order optical nonline-
arities of the push-pull chromophores.[4]
On the other hand, literature reports that D–π–A com-
pounds with π spacers, that gain aromaticity (“proaro-
matic” spacers) upon CT excitation,[1] yield low-energy CT
transitions and large first molecular hyperpolarizabilities
β.[10] In 1968, Gompper et al. described the first such chro-
mophore 1, with a strong 1,3-dithio-2-ylidene donor and a
strong dicyanomethylene acceptor,[11] and since then, a vari-
ety of D–π–A systems with quinoid π spacers and low-en-
ergy CT transitions have been prepared.[10a,12]
Introduction
Push-pull chromophores, with the electron donor and ac-
ceptor separated by π-conjugating linkers (D–π–A), have
been investigated for decades.[1] Nevertheless, they continue
to attract growing interest in view of their promising opto-
electronic properties, in particular their second-order[2] and
third-order[2a,3,4] nonlinear optical (NLO) behavior, and
their potential for application as advanced functional mate-
rials in molecular devices.
We have prepared several families of new push-pull chro-
mophores featuring intense, bathochromically shifted intra-
molecular charge-transfer (CT) bands, high third-order op-
tical nonlinearities,[4] and interesting redox properties.[5]
They comprise donor–acceptor-substituted tetraethynyl-
ethenes (TEEs, 3,4-diethynylhex-3-ene-1,5-diynes)[4,6] and
D–π–A systems featuring new potent electron acceptors,
such as donor-substituted cyanoethynylethenes (CEEs)[7]
and 1,1,4,4-tetracyano-1,3-butadienes (TCBDs).[8] In a
[a] Laboratorium für Organische Chemie, ETH-Zürich,
Hönggerberg, HCI, 8093 Zürich, Switzerland
Fax: +41-1-632-1109
E-mail: diederich@org.chem.ethz.ch
[b] Laboratoire d’Electrochimie et de Chimie Physique du Corps
Solide, Institut de Chimie, UMR 7177, C.N.R.S., Université
Louis Pasteur,
4, rue Blaise Pascal, 67000 Strasbourg, France
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
994
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New Push-Pull Chromophores Featuring TCAQ
We have now started an experimental program aimed at ylamino)phenyl]boronic acid,[20] afforded donor-substituted
merging these two approaches towards achieving low-en- cyclohexanones 6 and 7, respectively. Al2O3-catalyzed
ergy CT absorptions and high NLO efficacies. Here, we de- Knoevenagel condensation[21] with malononitrile smoothly
scribe our attempts to prepare the new quinoid push-pull provided 8 and 9 in good yields. Oxidation of the central
systems 2 (n = 0, 1). We also report on the synthesis and cyclohexane moiety was accomplished using 2,3-dichloro-
electronic properties of a series of donor-substituted 5,6-dicyano-1,4-benzoquinone (DDQ) at 20 °C.[18] Surpris-
11,11,12,12-tetracyano-9,10-anthraquinodimethane
ingly, only the blue, stable cyclohexene derivatives 10 and
(TCAQ)[13,14] derivatives with the general structure 3 (Fig- 11, instead of the quinoid chromophores 2 (n = 0, 1), were
ure 1). While several such compounds are known,[15] the formed and isolated (Scheme 1). All further attempts to
number of systematic investigations of D–π–A systems with prepare 2 also failed: various oxidation conditions [excess
TCAQ as acceptor remains limited.
of DDQ or reflux,[18] MnO2,[22a] ceric ammonium nitrate
(CAN),[22b] NH4NO3/trifluoroacetic anhydride (TFAA)[22c]
]
only yielded insoluble polymers, presumably featuring
poly(p-xylylene) backbones similar to those obtained from
homopolymerization of other quinodimethane-type mono-
mers.[23]
X-ray analysis [see Supporting Information (SI)] con-
firmed the proposed structures of 10 and 11, with their in-
completely oxidized central cyclohexene ring (Figure 2). In
compound 10, the entire π-conjugated chromophore, in-
cluding the two N,N-dimethylanilino (DMA) rings, is
planar, with a maximum out-of-plane deviation of 0.28 Å
(N31). The crystal packing shows a layered structure with
a distance of 3.27 Å between the mean planes of molecules
in neighboring layers (shortest interatomic distance
C6···C14 3.39 Å). In contrast, the DMA rings in 11 are
forced out of the mean plane passing through the divinylcy-
Figure 1. Quinoid push-pull chromophores 1,[11b] 2, and 3.
Results and Discussion
Attempted Synthesis of Push-Pull Chromophores 2
On the way to 2 (n = 0, 1), dibromoolefination of com- clohexene ring to avoid repulsive intramolecular contacts,
mercially available 1,4-dioxaspiro[4.5]decan-8-one furnished as already seen in previous work.[9] The DMA ring adjacent
4 (Scheme 1).[16] Removal of the acetal protecting group[17] to the bulkier CH2 group is turned out somewhat more
and subsequent Sonogashira[18] or Suzuki[19] cross-coupling (torsional angle C1–C2–C9–C10 46°) than the other DMA
on 5, using 4-ethynyl-N,N-dimethylaniline or [4-(dimeth- ring (C1–C2–C3–C4 41°).
Scheme 1. Synthesis of push-pull chromophores 10 and 11. (a) CBr4, PPh3, benzene, ∆, 12 h, 68%; (b) CH3COOH, H2O, 75 °C, 2 h,
99%; (c) for 6: 4-ethynyl-N,N-dimethylaniline, [PdCl2(PPh3)2], CuI, Et3N, 20 °C, 48 h, 89%; for 7: 4-(dimethylamino)phenylboronic acid,
[PdCl2(PPh3)2], Na2CO3, THF, H2O, 70 °C, 12 h, 87%; (d) (CN)2CH2, Al2O3, CH2Cl2, ∆, 1 h, 93% (8, 9); (e) DDQ, toluene, 20 °C, 1 h,
42% (10), 50% (11). DDQ = 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.
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F. Diederich et al.
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Figure 2. ORTEP representations of compounds 10 (a) and 11 (b). Vibrational ellipsoids obtained at 202–203 K are shown at the 50%
probability level (for further information, see SI).
Synthesis of TCAQ-Based D–A Chromophores
yields.[25] Treatment of 12 or 13 with N,N,NЈ,NЈ-tetrameth-
ylurea in the presence of phosphoryl chloride (POCl3)[26]
TCAQ and derivatives are conveniently accessible by afforded the N,N,NЈ,NЈ-tetramethylguanidine derivatives 16
Knoevenagel condensation of anthracene-9,10-dione deriv- and 17, respectively. Diazotation of 12, followed by substi-
atives with malononitrile, mediated by TiCl4/pyridine tution with iodide, afforded 2-iodoanthracene-9,10-dione
(Lehnert reagent).[24] Therefore, our efforts were focused on (18).[27] A similar transformation of 13 furnished an insepa-
the preparation of various donor-substituted anthracene- rable mixture of products. On the other hand, diazotization
9,10-diones, starting from commercially available 2-amino- with tert-butyl nitrite, followed by Sandmeyer reaction with
and 2,6-diaminoanthracene-9,10-diones 12 and 13 CuBr2, gave 2,6-dibromoanthracene-9,10-dione (19).[28]
(Scheme 2). N-Methylation using MeI/KOH/Me2SO readily Facile Sonogashira or Suzuki cross-coupling on 18 afforded
furnished anthraquinones 14 and 15, respectively, in good DMA-substituted anthraquinones 20 and 21, respectively,
Scheme 2. Synthesis of donor-substituted anthracene-9,10-diones. (a) KOH, Me2SO, 20 °C, 30 min, then CH3I, 20 °C, 10 min, 95% (14),
87% (15); (b) N,N,NЈ,NЈ-tetramethylurea, POCl3, benzene, 20 °C, 12 h, then 12 or 13, ∆, 6 h, 52% (16), 23% (17); (c) 18: THF, H2O,
HCl, 40 °C, 24 h, then NaNO2/H2O, 0 °C, 10 min and KI/H2O, 0 °C, 15 min Ǟ 20 °C, 30 min Ǟ 60 °C, 30 min, 81%; 19: tBuONO,
CuBr2, CH3CN, 65 °C, 2 h, 91%; (d) 20: [4-(dimethylamino)phenyl]boronic acid, [PdCl2(PPh3)2], Na2CO3, THF, H2O, 60 °C, 1 h, 96 %;
21/22: 4-ethynyl-N,N-dimethylaniline, [PdCl2(PPh3)2], CuI, Et3N/Et2NH, 20 °C/∆, 5 min/12 h, 97% (21), 45% (22); 23: 4-ethynyl-N,N-
dihexylaniline, [PdCl2(PPh3)2], CuI, Et2NH, ∆, 12 h, 76%.
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New Push-Pull Chromophores Featuring TCAQ
in nearly quantitative yields. Also, dibromo derivative 19 ing 2-iodinated (29) and 2,6-dibrominated (30)[13c] TCAQs.
underwent smoothly a twofold Sonogashira cross-coupling However, Sonogashira or Suzuki cross-coupling reactions
furnishing 22. Due to the low solubility of 22, its N,N-di- of 29 and 30 were not successful and, therefore, the prod-
hexyl analogue 23 was synthesized as well (Scheme 2).
ucts with triple-bond linkers were not synthesized. On the
The Knoevenagel reaction with malononitrile, mediated other hand starting from the tetrabromide 35, fourfold
by the Lehnert reagent, was first carried out on unsubsti- Sonogashira coupling could be successfully applied to the
tuted anthracene-9,10-dione, yielding TCAQ (24) in 89% synthesis of the new extended D–π–D system 36, which was
yield. The other, donor-substituted anthraquinones were obtained as a red solid in low yield (9%; Scheme 4).
treated with malononitrile under the above condition as
X-ray crystal structures were obtained for the two
well. Whereas anthraquinones 14–17 and 20 afforded the anthraquinones 17 and 20 and the two TCAQ derivatives
expected products 25–28 and 31, respectively, derivatives 25 and 32, confirming the proposed structures (Figure 3).
bearing a triple-bond linker between the DMA and the
anthraquinone moieties (21–23) were hydrochlorinated,
yielding products 32–34 (Scheme 3). The regioselectivity of
the HCl addition is controlled by the potency of the DMA
moiety to stabilize a carbocationic intermediate. The (Z)
configuration of 32 was proven by X-ray analysis (see be-
low). Modification of the reaction conditions did also not
lead to the desired alkynes; dehydrohalogenations proved
to be difficult as well. In an alternative approach, the Knoe-
venagel condensation was carried out on 18 and 19, provid-
Scheme 3. TiCl4-mediated Knoevenagel condensation. Reaction
conditions: reflux, 36–96 h.
Figure 3. ORTEP representations of the compounds (a) 17 (223 K),
(b) 20 (203 K), (c) 25 (223 K; mean dihedral angle between the
plane through the cyanovinyl group and the planes through the two
phenyl rings 37Ϯ2°, dihedral angle between the two phenyl ring
planes 34°), and (d) 32 (203 K; mean dihedral angle between the
plane through the cyanovinyl group and the planes through the two
phenyl rings 42Ϯ2°, dihedral angle between the two phenyl ring
planes 34°). Vibrational ellipsoids are shown at the 50% probability
level (for further information, see SI).
Scheme 4. Synthesis of D–π–D system 36. (a) CBr4, PPh3, ben-
zene, 20 °C, 24 h, 96%; (b) 4-ethynyl-N,N-dimethylaniline,
[PdCl2(PPh3)2], CuI, benzene, Et2NH, 20 °C, 48 h, 9%.
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The crystal structure of 20 contains two symmetrically inde- Table 1. Electrochemical data obtained by cyclic voltammetry (CV)
at a scan rate of 0.1 Vs–1 and rotating disk voltammetry (RDV) in
pendent molecules which arrange in a herringbone pattern
with an interplanar angle of 42°. The C=O dipoles of two
CH2Cl2 + 0.1  nBu4NPF6 (vs. Fc+/Fc).
Compound
Cyclic voltametry
Rotating disk voltametry
neighboring, symmetry-independent molecules undergo fa-
vorable orthogonal C=O···C=O interactions (distance O···C
3.3 Å, angle C···C=O 108°).[29] The structures of 25 and
32 show the typical, saddle-like out-of-plane defor-
mation,[15c,30] reported for TCAQ derivatives, which is in-
duced by steric hindrance between the C(CN)2 moieties and
the tricyclic central core. The chloroethene derivative 32 is
(Z)-configured, as expected for an anti-HCl addition to the
intermediate alkyne. On the basis of spectral similarity
(NMR, UV, IR), we also assume this double-bond configu-
ration for compounds 33 and 34. An (E) configuration
would lead to sterically repulsive interactions between
DMA and C(CN2) moieties. It should also be noted that
the (Z) geometry in 32 induces a favorable Cl···CN interac-
tions (angle C–Cl···N 103°, distance Cl···N 3.62 Å), also re-
ferred to as halogen bonding.[31]
E° [V][a] ∆Ep [mV][b] Ep [V][c]
E1/2 [V][d]
Slope [mV][e]
[f]
10
+0.48
–1.31
100
–1.35
65
65
–1.75[f]
–1.81[g]
–2.29
+0.70
100
80
11
+0.32
+0.33
50
–1.71[h]
–1.45
24
25
–0.81
+0.93
–0.90
100
110
170
–0.84 (2 e–) 90
+0.92 (1 e–) 75
–0.97 (2 e–) 90
26
27
+1.00
+0.88
0.85 (1 e–) 60
–0.98
90
–1.00 (2 e–) 50
+0.72
+0.44
–0.73
–0.88
–1.05
–1.42
–0.86
–0.95
–1.40
–1.58
+0.51
–0.82
70
100
60
60
70
110
80
130
75
–0.80 (1 e–)
–0.99 (2 e–)
–1.14 (1 e–)
–1.53 (1 e–)
28
Electrochemistry
Electrode
inhibition
Electrochemical investigations were carried out by cyclic
voltammetry (CV) and rotating disk voltammetry (RDV) in
CH2Cl2 + 0.1  nBu4NPF6, using the ferricinium/ferrocene
(Fc+/Fc) couple as internal reference (Table 1). TCAQ (24)
had previously been studied by Aumüller and Hünig[13a]
and Gerson and co-workers.[14c] In contrast to 7,7,8,8-tetra-
cyanoquinodimethane (TCNQ),[32] TCAQ is reduced in a
single reversible two-electron step. The peak characteristics
in acetonitrile clearly demonstrate that a potential inversion
for the two overlapping one-electron transfers occurs.
Under our experimental conditions, namely in dichloro-
methane, the peak characteristics are in agreement with a
normal ordering of the two overlapping one-electron re-
duction steps, indicative of two almost independent redox
centers, as suggested by Gerson and co-workers.
For most compounds, well-resolved voltammograms
could be observed. However, for some species such as 27
and 28, electrode inhibition required electrode polishing be-
tween each scan. The reduction of TCAQ derivatives 24–
28 and 32–34 occurs in a single, unresolved reversible two-
electron step. The peak characteristics show that the peak
potentials are scan-rate-independent and that the peak-po-
tential difference for the first reduction step ranges from 90
to 100 mV. This indicates that the two reversible one-elec-
tron transfers are separated by about 80 mV. The difference
in redox behavior between TCNQ (2 distinct one-electron
reductions) and TCAQ (unresolved two-electron step) re-
flects differences in the electronic communication between
the two dicyanovinyl redox centers. Whereas this communi-
cation is high in planar TCNQ, it is much reduced in TCAQ
derivatives due to nonplanarity of the chromophore (see the
31
32
33
34
36
+0.52 (1 e–) 70
–0.85 (2 e–) 75
+0.43 (1 e–) 50
–0.83 (2 e–) 60
100
+0.46
+0.45
+0.43
–0.79
–0.79
100
90
–0.82 (2 e–) 50
+0.41 (2 e–) 60
–0.84 (2 e–) 60
–0.77
+0.59
160
115
+0.27
–1.73
+0.43
–1.24
–1.74
+0.17
100
[i]
37[j]
+0.40
–1.18
–1.68
70
70
[a] E° = (Epc + Epa)/2, where Epc and Epa correspond to the cath-
odic and anodic peak potentials, respectively. [b] ∆Ep = Eox – Ered
,
where the subscripts ox and red refer to the conjugated oxidation
and reduction steps, respectively. [c] Ep = Irreversible peak poten-
tial. [d] E1/2 = Half-wave potential. [e] Slope of the linearized plot
of E vs. log[I/(Ilim – I)], where Ilim is the limiting current and I the
current. [f] Adsorption peak. [g] Strong adsorption post wave. [h]
Reversible at scan rates higher than 2 Vs–1. [i] Unresolved spread
out reduction wave. [j] Taken from ref.[9]
The observed reduction potentials are dependent of the
X-ray crystal structures of 25 and 32 in Figure 3) and, most nature of the substituents. NMe2 substituents directly at-
importantly, the reduction in π conjugation between the tached to the TCAQ core (25, 26) are stronger electron-
two redox centers as a result of double benzene-ring fusion donating (negative potential shift of the first reduction wave
to the quinodimethane scaffold.
of 90 mV per substituent) than DMA residues (31; negative
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New Push-Pull Chromophores Featuring TCAQ
potential shift of only 10 mV). In contrast, upon introduc- and ethynediyl in 37. Ground-state D–A conjugation is sub-
tion of the chlorovinyl spacers in 32–34, the first reduction stantially stronger in 10, with the olefinic spacer, than in
step becomes facilitated (shift to more positive potential by 37, with the acetylenic spacer. The DMA moiety in 10 is
20–40 mV as compared to TCAQ). DMA and DHA moie- more difficult to oxidize (+0.48 V) than in 37 (+0.43 V)
ties in 31–34 undergo reversible one-electron oxidations be- and, accordingly, the dicyanovinyl acceptor in 10 is also
tween +0.43 and +0.51 V, as previously observed.[5]
more difficult to reduce (–1.31 V) than in 37 (–1.24 V). The
The guanidine derivatives 27 and 28 show a specific re- electrochemical gap ∆(Eox,1 – Ered,1) in 10 is –1.79 V
dox behavior. Indeed, 27 gives four well-resolved reversible whereas it amounts to –1.67 V in 37. Obviously, some
electron transfers at –0.73, –0.88, –1.05, and –1.42 V, (minor) influence of the bridging ethanediyl fragment in the
respectively. The first, third, and fourth reduction step in- cyclohexene ring on the redox potentials for 10 cannot be
volve a one-electron transfer, whereas the second reduction excluded.
involves a two-electron transfer which may occur on the
two C=C(CN)2 moieties. For the disubstituted species 28,
the rotating disk voltammograms are not well resolved due
to adsorption phenomena; nevertheless, four reductions are
UV/Vis Spectroscopy
observed by cyclic voltammetry.
UV/Vis spectroscopic data of the new chromophores
Finally, in view of the actual debate about the efficiency were recorded in CH2Cl2 and are summarized in Table 2.
of double and triple bonds in transmitting conjugative ef- The more effective D–A conjugation in ethenediyl-linked
fects,[33] a comparison between the chromophores 10 10, as compared to ethynediyl-linked 37, is also apparent
(Scheme 1) and previously reported 37 (below Table 1)[9] from the higher energy of the intramolecular CT band and
seems worthwhile. The two D–π–A systems contain iden- the larger optical gap in the UV/Vis spectra: λmax = 528 nm
tical donor and acceptor moieties and differ only by the (2.35 eV) and λend = 699 nm (1.77 eV) for 10 and λmax
central section of the π linker, namely (Z)-ethenediyl in 10 534 nm (2.32 eV) and λend = 740 nm (1.68 eV) for 37.
=
Figure 4. UV/Vis spectra of the TCAQ derivatives 24–28 and 31 in CH2Cl2.
Figure 5. UV/Vis spectra of TCAQ derivatives 32–34 and D–π–D system 36 in CH2Cl2.
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Table 2. Longest-wavelength absorptions and end-absorptions in bonds were hydrochlorinated. X-ray crystal structures con-
CH2Cl2 determined by UV/Vis spectroscopy.
firmed the saddle or butterfly conformation of TCAQ de-
rivatives 25 and 32 as well as the configuration of the (Z)-
ethenediyl linker in 32. The UV/Vis spectra of the stable
colored compounds feature intense CT bands with maxima
in the range from 528 to 531 nm for 10 and 11 and from
480 to 580 nm for donor-substituted TCAQs 25–36, respec-
tively. Very weak CT absorptions are observed for guani-
dine derivatives 27 and 28 which also show a rather com-
plex redox behavior, featuring four reversible reduction
steps. The electrochemical reductions of TCAQs 24–28 and
32–34 were observed in a single, unresolved reversible two-
electron step. Introduction of NMe2 and DMA chromo-
phores (25, 26, 31) shifts the first reduction potential to
more negative values, whereas the potential is shifted to
more positive values in chromophores 32–34 bearing chlo-
rovinyl spacers. This is in agreement with previous findings
that introduction of larger spacers reduces the efficiency of
D–A conjugation but also reflects the electronic effects of
both substituents (NMe2 vs. Cl). The comparison of elec-
trochemical and UV/Vis data between 10, with a central
ethenediyl, and previously prepared 37, with a central
ethynediyl spacer, suggests that ground-state D–A conjuga-
tion across the olefinic spacer is more efficient – a finding
of interest in view of the ongoing debate on the efficiency
of olefinic versus acetylenic π conjugation. The third-order
optical nonlinearities of the new chromophores are now in-
vestigated.
Compound
λmax [nm (eV)]
λend [nm (eV)]
10
11
24
25
26
27
28
31
32
33
34
36
37[b]
528 (2.35)
531 (2.33)
347 (3.57)
553 (2.24)
588 (2.11)[a]
524 (2.37)
480 (2.58)
571 (2.17)
549 (2.26)
544 (2.28)
580 (2.14)
486 (2.55)
534 (2.32)
699 (1.77)
665 (1.86)
406 (3.05)
664 (1.87)
669 (1.85)
679 (1.83)
610 (2.03)
748 (1.66)
710 (1.75)
734 (1.69)
766 (1.62)
576 (2.15)
740 (1.68)
[a] Peak fitting by Gaussian deconvolution of the broad absorption
band of 26 gave a hidden peak maximum (observed as shoulder on
the broad absorption) at λmax = 588 nm (2.11 eV). [b] Taken from
ref.[9]
All TCAQ derivatives feature strong absorptions in the
range between 250 and 380 nm, which are transitions in-
volving the anthraquinodimethane core [compare the spec-
trum of TCAQ (24) in Figure 4]. In tetra(DMA-ethynyl)-
substituted 36, additional strong bands at λmax = 486 and
576 nm are observed, reflecting an intramolecular CT from
the peripheral donors into the tetraalkynylated anthraquin-
odimethane core (Figure 5).
Bathochromically shifted intramolecular CT bands are
observed for all donor-substituted TCAQ derivatives (Fig-
ure 4), including the chlorovinyl derivatives 32–34 (Fig-
ure 5); they all form highly colored solids. The most intense
CT bands are seen in the spectrum of bis(Me2N)-substi-
tuted TCAQ 26, which also features the longest-wavelength
absorption of all push-pull systems (λmax = 588 nm). The
CT character of the longest-wavelenght absorption of all
push-pull chromophores was confirmed by protonation/
neutralization experiments (SI). Upon protonation of the
Me2N groups with trifluoroacetic acid (TFA), all CH2Cl2
solutions turned from intensely colored to nearly colorless
and the longest-wavelength absorption bands disappeared
almost completely. Full regeneration of the original CT
bands occurred upon neutralization with Et3N.
Experimental Section
Materials and General Methods: Reagents and solvents were pur-
chased at reagent grade from Acros, Aldrich, and Fluka, and used
as received. THF was freshly distilled from Na/benzophenone un-
der N2. Evaporation and concentration in vacuo was performed
at water-aspirator pressure. All reactions were performed under a
positive pressure of N2. Column chromatography (CC) and plug
filtrations were carried out with SiO2 60 (particle size 0.040–
0.063 mm, 230–400 mesh; Fluka) and distilled technical solvents.
Thin-layer chromatography (TLC) was conducted on aluminum
sheets coated with SiO2 60 F254 obtained from Macherey–Nagel;
visualization with a UV lamp (254 or 366 nm). Melting points
(M.p.) were measured with a Büchi B-540 melting-point apparatus
in open capillaries and are uncorrected, “dec.” refers to decomposi-
tion. 1H and 13C NMR spectra were measured with a Varian Gem-
ini 300 spectrometer at 20 °C. Chemical shifts are reported in ppm
Conclusions
1
relative to the signal of Me4Si. Residual solvent signals in the H
and 13C NMR spectra were used as an internal reference. Coupling
A series of thermally stable D–A chromophores, featur-
ing dialkylamino donors and dicyanovinyl acceptors, were constants (J) are given in Hz. The apparent resonance multiplicity
is described as s (singlet), br. s (broad singlet), d (doublet), dd
(doublet of doublet), t (triplet), q (quartet), and m (multiplet).
Anthraquinone protons are marked as AQ. Infrared spectra (IR)
were recorded with a Perkin–Elmer Spectrum BX instrument. UV/
Vis spectra were recorded with a Varian Cary-5 spectrophotometer.
The spectra were measured in CH2Cl2 in a quartz cuvette (1 cm).
The absorption wavelengths are reported in nm with the molar ex-
tinction coefficient ε (mol–1 dm3 cm–1) in parentheses; shoulders are
indicated as sh. High-resolution (HR) EI-MS spectra were mea-
sured with a Hitachi–Perkin–Elmer VG-Tribrid spectrometer. HR
prepared and their properties investigated. The initially tar-
geted quinodimethane systems 2 were not obtained, due to
ready polymerization, and the blue chromophores 10 and
11, with a central cyclohexene spacer, were isolated and
characterized instead. A variety of donor-substituted
TCAQ derivatives were synthesized by Knoevenagel con-
densation of the appropriately substituted anthracene-9,10-
diones and malononitrile, mediated by the Lehnert reagent.
However, this reagent (TiCl4/pyridine; used in excess) was
found to be incompatible with alkyne linkers since the triple FT-MALDI spectra were measured with an IonSpec Ultima Fou-
1000
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 994–1004

New Push-Pull Chromophores Featuring TCAQ
rier transform (FT) instrument with [(2E)-3-(4-tert-butylphenyl)-2-
methylprop-2-enylidene]malononitrile (DCTB) or 3-hydroxypico-
linic acid (3-HPA) as matrix. The most important signals are re-
ported in m/z units with M as the molecular ion. [4-(Dimeth-
ylamino)phenyl]boronic acid was synthesized from 4-bromo-N,N-
dimethylaniline, according to a literature procedure, in 61%
yield.[20] 4-Ethynyl-N,N-dimethylaniline and 4-ethynyl-N,N-dihex-
ylaniline were prepared from 4-iodo-N,N-dimethylaniline or 4-
iodo-N,N-dihexylaniline and trimethylsilylacetylene by Sonoga-
shira cross-coupling and final Me3Si group removal (K2CO3,
MeOH) in 92% and 78% overall yields, respectively. Compounds
4 (68%),[16] 5 (99%),[17] 14 (95%),[25] 15 (87%),[25] 18 (81%),[27] 19
(91%),[28] 24 (89%),[15b] 25 (91%),[13b] 26 (66%),[13c] 30 (61%),[13c]
and 35 (96%)[18,34] were prepared according to literature procedures
in the indicated yields.
9.0 Hz, 4 H, Ar), 7.02 (d, 3JH,H = 9.0 Hz, 4 H, Ar) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 30.47, 40.62, 41.77, 111.75, 130.16,
130.42, 130.94, 138.13, 148.97, 212.37 ppm. IR (neat): ν = 2886,
˜
2797, 1709, 1606, 1516, 1442, 1337, 1225, 1190, 1164, 1129, 1061,
946, 821, 744 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 282 nm
(28500 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA): m/z calcd.
for [C23H29N2O+] 349.2274; found 349.2268 [MH+].
2-(4-{1,5-Bis[4-(dimethylamino)phenyl]penta-1,4-diyn-3-ylidene}-
cyclohexylidene)malononitrile (8): Ketone 6 (50 mg, 0.126 mmol),
malononitrile (9 mg, 0.139 mmol), and Al2O3 (10 mg, 0.098 mmol,
activity II–III) in CH2Cl2 (10 mL) were heated to reflux for 1 h.
The mixture was filtered, concentrated in vacuo, and subjected to
CC (SiO2; CH2Cl2) yielding 8 (52 mg, 93%) as a brown solid. Rf =
0.79 (SiO2; CH2Cl2); m.p. 247–248 °C. 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 2.83–2.94 (m, 8 H, CH2), 2.98 (s, 12 H, NCH3),
6.66 (d, 3JH,H = 9.0 Hz, 4 H, Ar), 7.35 (d, 3JH,H = 9.0 Hz, 4 H, Ar)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 31.11, 33.97, 40.27,
83.51, 84.04, 94.02, 102.98, 109.25, 111.82, 111.87, 132.68, 148.37,
Electrochemistry: Electrochemical measurements were carried out
in CH2Cl2 containing 0.1  nBu4NPF6 in a classical three-electrode
cell by cyclic voltammetry (CV) and rotating disk voltammetry
(RDV). The working electrode was a glassy carbon disk (3 mm in
diameter), the auxiliary electrode a platinum wire, and the reference
electrode either an aq. Ag/AgCl reference electrode or a platinum
wire used as pseudo-reference electrode. The cell was connected to
an Autolab PGSTAT20 potentiostat (Eco Chemie, Holland) driven
by a GPSE software running on a personal computer. All poten-
tials are given versus Fc+/Fc used as internal reference and uncor-
rected from ohmic drop.
150.53, 182.97 ppm. IR (neat): ν = 2905, 2228, 2186, 1610, 1528,
˜
1443, 1377, 1355, 1229, 1196, 1188, 1106, 983, 813, 799,
744 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 336 (40100), 293 nm
(32400 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA): m/z calcd.
for [C30H29N4+] 445.2387; found 445.2380 [MH+].
2-(4-{Bis[4-(dimethylamino)phenyl]methylene}cyclohexylidene)-
malononitrile (9): The title compound was prepared from ketone 7
(100 mg, 0.287 mmol), according to the method described for 8.
X-ray Analysis: CCDC-640603 (10), -640604 (11), -640608 (17), Yield 106 mg (93%) as a yellow solid. Rf = 0.44 (SiO2; CH2Cl2);
1
-640605 (20), -640606 (25), and -640607 (32) contain the supple-
mentary crystallographic data for the new compounds reported in
this paper. These data can be obtained free of charge from The
m.p. 199–200 °C. H NMR (300 MHz, CDCl3, 25 °C): δ = 2.61 (t,
3JH,H = 6.9 Hz, 4 H, CH2), 2.77 (t, 3JH,H = 6.9 Hz, 4 H, CH2), 2.95
3
3
(s, 12 H, NCH3), 6.66 (d, JH,H = 9.0 Hz, 4 H, Ar), 6.97 (d, JH,H
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ = 9.0 Hz, 4 H, Ar) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
data_request.cif. See also SI.
32.06, 35.57, 40.57, 82.83, 111.71, 128.59, 130.25, 130.41, 139.26,
149.14, 184.57 (1 C missing) ppm. IR (neat): ν = 2887, 2795, 2230,
˜
4-{1,5-Bis[4-(dimethylamino)phenyl]penta-1,4-diyn-3-ylidene}cyclo-
hexanone (6): 4-Ethynyl-N,N-dimethylaniline (455 mg, 3.135 mmol)
in triethylamine (50 mL), [PdCl2(PPh3)2] (53 mg, 0.075 mmol) and
CuI (28 mg, 0.149 mmol) were added to a degassed solution of the
dibromo olefin 5 (400 mg, 1.493 mmol). The mixture was stirred
under N2 at 20 °C for 48 h. The solvent was evaporated in vacuo
and the residue purified by CC [SiO2; CH2Cl2/hexane (2:1) to
CH2Cl2]. Yield 527 mg (89%) as a brown solid. Rf = 0.22 (SiO2;
CH2Cl2/hexane, 2:1); m.p. 181–182 °C. 1H NMR (300 MHz,
1607, 1517, 1441, 1343, 1218, 1190, 1165, 1124, 1055, 941,
826, 811, 749 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 281 nm
(35200 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA):m/z calcd.
for [C26H29N4+] 397.2387; found 397.2381 [MH+].
2-(4-{1,5-Bis[4-(dimethylamino)phenyl]penta-1,4-diyn-3-ylidene}-
cyclohex-2-enylidene)malononitrile (10): To a solution of 8 (55 mg,
0.124 mmol) in dry toluene (20 mL), DDQ (42 mg, 0.186 mmol)
was added. The violet mixture was stirred at 20 °C for 1 h, concen-
trated in vacuo, and subjected to CC (SiO2; CH2Cl2) yielding 10
(23 mg, 42%). Metallic solid. Rf = 0.82 (SiO2; CH2Cl2); m.p. Ͼ
3
CDCl3, 25 °C): δ = 2.52 (t, JH,H = 6.9 Hz, 4 H, CH2), 2.98 (s, 12
3
3
H, NCH3), 3.02 (t, JH,H = 6.9 Hz, 4 H, CH2), 6.63 (d, JH,H
=
1
9.0 Hz, 4 H, Ar), 7.37 (d, 3JH,H = 9.0 Hz, 4 H, Ar) ppm. 13C NMR
400 °C. H NMR (300 MHz, CDCl3, 25 °C): δ = 2.90–3.00 (m, 4
3
(75 MHz, CDCl3, 25 °C): δ = 29.49, 39.49, 40.27, 83.69, 93.43, H, CH2), 3.02 (s, 6 H, NCH3), 3.03 (s, 6 H, NCH3), 6.66 (d, JH,H
3
102.45, 109.73, 111.68, 132.54, 149.98, 150.10, 211.11 ppm. IR
= 9.0 Hz, 4 H, Ar), 6.75 (d, JH,H = 9.5 Hz, 1 H, CH), 7.42 (d,
3
(neat): ν = 2896, 2191, 1706, 1606, 1520, 1445, 1363, 1346, 1102, 3JH,H = 9.0 Hz, 4 H, Ar), 7.62 (d, JH,H = 9.5 Hz, 1 H, CH) ppm.
˜
1067, 943, 812 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 338 nm (sh, 13C NMR (75 MHz, CDCl3, 25 °C): δ = 25.67, 28.57, 40.17, 78.59,
46300 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA): m/z calcd.
84.38, 86.84, 99.22, 102.55, 108.42, 108.48, 2ϫ 111.59, 111.99,
112.43, 113.28, 122.92, 133.02, 133.21, 140.90, 141.20, 150.49,
for [C27H29N2O+] 397.2274; found 397.2274 [MH+].
150.63, 167.69 ppm. IR (neat): ν = 2850, 2162, 16001, 1520, 1486,
˜
4-{Bis[4-(dimethylamino)phenyl]methylene}cyclohexanone (7):
[PdCl2(PPh3)2] (43 mg, 0.061 mmol) and Na2CO3 (193 mg,
1.818 mmol) were added to a degassed solution of the dibromo
olefin 5 (163 mg, 0.606 mmol) and [4-(dimethylamino)phenyl]bo-
ronic acid (300 mg, 1.818 mmol) in THF/H2O (10 mL, 4:1). The
mixture was stirred under N2 at 70 °C for 12 h, diluted with H2O,
and extracted with EtOAc (2ϫ50 mL). The combined organic lay-
ers were dried (MgSO4) and concentrated in vacuo. Subsequent CC
(SiO2; CH2Cl2) afforded 7 (184 mg, 87%) as a yellow solid. Rf =
1351, 1305, 1218, 1184, 1097, 940, 810 cm–1. UV/Vis (CH2Cl2):
λmax (ε) = 528 (35200), 311 nm (sh, 36900 mol–1 dm3 cm–1). HR-FT-
MALDI-MS (3-HPA):m/z calcd. for [C30H26N4+] 442.2152; found
442.2157 [M+].
2-(4-{Bis[4-(dimethylamino)phenyl]methylene}cyclohex-2-enylidene)-
malononitrile (11): The title compound was synthesized from 9
(100 mg, 0.252 mmol), according to the method described for 10.
Yield 49 mg (50%) as a metallic solid. Rf = 0.6 (SiO2; CH2Cl2);
1
0.23 (SiO2; CH2Cl2); m.p. 145–146 °C. 1H NMR (300 MHz, m.p. 150–151 °C. H NMR (300 MHz, CDCl3, 25 °C): δ = 2.81 (s,
3
CDCl3, 25 °C): δ = 2.44 (t, JH,H = 6.9 Hz, 4 H, CH2), 2.69 (t,
4 H, CH2), 3.02 (s, 6 H, NCH3), 3.03 (s, 6 H, NCH3), 6.55 (d, 3JH,H
3
3
3JH,H = 6.9 Hz, 4 H, CH2), 2.94 (s, 12 H, NCH3), 6.66 (d, JH,H
=
= 9.5 Hz, 1 H, CH), 6.64 (d, JH,H = 9.0 Hz, 4 H, Ar), 6.99 (d,
Eur. J. Org. Chem. 2008, 994–1004
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1001

F. Diederich et al.
= 9.0 Hz, 4 H, Ar), 7.83 (dd, JH,H = 9.0, JH,H = 2.0 Hz, 2 H,
FULL PAPER
3JH,H = 9.0 Hz, 2 H, Ar), 7.01 (d, JH,H = 9.5 Hz, 1 H, CH), 7.07
3
3
4
3
3
4
(d, JH,H = 9.0 Hz, 2 H, Ar) ppm. 13C NMR (75 MHz, CDCl3, AQ), 8.26 (d, JH,H = 9.0 Hz, 2 H, AQ), 8.37 (d, JH,H = 2.0 Hz, 2
25 °C): δ = 29.41, 29.84, 40.30, 73.93, 110.92, 113.25, 114.07,
119.78, 126.90, 127.94, 128.56, 132.30, 133.30, 147.54, 150.32, 111.65, 130.24, 130.84, 133.11, 133.21, 135.71 (low solubility, 7 C
150.78, 153.16, 169.04 ppm. IR (neat): ν = 2887, 2212, 1609, 1521, missing) ppm. IR (neat): ν = 2893, 2194, 1663, 1606, 1580, 1523,
H, AQ) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 40.19,
˜
˜
1440, 1352, 1334, 1304, 1223, 1188, 1167, 1124, 1056, 947, 1363, 1332, 1305, 1279, 1229, 1200, 1168, 1062, 815, 742, 712 cm–1.
812 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 531 (sh, 28500); 323 (sh,
14300), 287 nm (20600 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-
HPA): m/z calcd. for [C26H26N4+] 394.2152; found 394.2146 [M+].
UV/Vis (CH2Cl2): λmax (ε) = 467 (20400), 375 (35400), 332 (34700),
289 (34200), 275 nm (35700 mol–1 dm3 cm–1). HR-FT-MALDI-MS
(3-HPA): m/z calcd. for [C34H26N2O2+] 494.1989; found 494.1982
[M+].
2-[4-(Dimethylamino)phenyl]anthracene-9,10-dione (20): [PdCl2-
(PPh3)2] (64 mg, 0.09 mmol) and Na2CO3 (160 mg, 1.5 mmol) were
added to a degassed solution of 18 (300 mg, 0.898 mmol) and [4-
(dimethylamino)phenyl]boronic acid (248 mg, 1.5 mmol) in THF/
H2O (30 mL, 4:1). The mixture was stirred under N2 at 60 °C for
1 h, diluted with H2O, and extracted with CH2Cl2 (2ϫ50 mL). The
combined organic layers were dried (MgSO4) and concentrated in
vacuo. Subsequent CC [SiO2; CH2Cl2/hexane (1:1) to CH2Cl2] af-
forded 20 (282 mg, 96 %) as an orange solid. Rf = 0.45 (SiO2;
CH2Cl2/hexane, 1:1); m.p. 233–234 °C. 1H NMR (300 MHz,
2,6-Bis{[4-(dihexylamino)phenyl]ethynyl}anthracene-9,10-dione (23):
The title compounds was synthesized from 18 (204 mg, 0.558
mmol) and 4-ethynyl-N,N-dihexylaniline (350 mg, 1.226 mmol) in
a similar manner to 22. Yield 264 mg (61 %). Rf = 0.45 (SiO2;
CH2Cl2/hexane, 1:1); m.p. 160–161 °C. 1H NMR (300 MHz,
3
CDCl3, 25 °C): δ = 0.91 (t, JH,H = 6.5 Hz, 12 H, Hex), 1.30–1.38
3
(m, 24 H, Hex), 1.54–1.64 (m, 8 H, Hex), 3.28 (t, JH,H = 7.5 Hz,
3
3
8 H, Hex), 6.56 (d, JH,H = 9.0 Hz, 4 H, Ar), 7.37 (d, JH,H
=
3
4
9.0 Hz, 4 H, Ar), 7.78 (dd, JH,H = 9.0, JH,H = 2.0 Hz, 2 H, AQ),
3
4
3
8.23 (d, JH,H = 9.0 Hz, 2 H, AQ), 8.32 (d, JH,H = 2.0 Hz, 2 H,
AQ) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 14.17, 22.79,
26.88, 27.26, 31.78, 51.00, 86.89, 97.11, 107.35, 111.06, 127.17,
129.35, 130.81, 131.14, 133.29, 133.42, 135.53, 148.38, 181.99 ppm.
CDCl3, 25 °C): δ = 3.04 (s, 6 H, NCH3), 6.81 (d, JH,H = 9.0 Hz,
3
2 H, Ar), 7.68 (d, JH,H = 9.0 Hz, 2 H, Ar), 7.75–7.85 (m, 2 H,
3
4
AQ), 7.97 (dd, JH,H = 9.0, JH,H = 2.0 Hz, 1 H, AQ), 8.29–8.35
(m, 3 H, AQ), 8.49 (d, JH,H = 2.0 Hz, 1 H, AQ) ppm. 13C NMR
4
IR (neat): ν = 2924, 2192, 1660, 1607, 1580, 1529, 1402, 1364, 1333,
˜
(75 MHz, CDCl3, 25 °C): δ = 40.35, 112.38, 123.80, 125.86, 126.99,
127.05, 127.92, 130.64, 133.55, 133.66, 133.74, 133.90, 146.63,
1282, 1199, 1169, 849, 810, 741, 712 cm–1. UV/Vis (CH2Cl2): λmax
(ε) = 489 (23300), 385 (40400), 337 (38400), 295 (36300), 274 nm
(37700 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA): m/z calcd.
for [C54H67N2O2+] 775.5197; found 775.5209 [MH+].
150.73, 182.61, 183.37 (3 C missing) ppm. IR (neat): ν = 2895,
˜
1665, 1584, 1532, 1368, 1326, 1294, 1219, 1107, 1060, 951, 933,
911, 858, 818, 807, 731, 706, 696, 632 cm–1. UV/Vis (CH2Cl2): λmax
(ε) = 470 (8300), 362 (11900), 323 (17600), 255 nm (sh,
35500 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA): m/z calcd.
for [C22H17NO2+] 327.1254; found 327.1249 [M+].
TiCl4/Pyridine-Catalyzed Knoevenagel Condensation. General
Method: Malononitrile (59.4 mg, 0.9 mmol), TiCl4 (0.18 mL,
0.9 mmol), and pyridine (0.15 mL, 1.8 mmol) were added to an an-
thracene-9,10-dione derivative (0.3 mmol) in CHCl3 (50 mL), and
the mixture was heated to reflux for the indicated time. Every 12 h,
identical amounts of malononitrile, TiCl4, and pyridine were
added. The mixture was poured on ice/water and extracted with
CHCl3 (3 ϫ 100 mL). The combined organic layers were dried
(MgSO4), concentrated in vacuo, washed with Et2O to remove ex-
cess of malononitrile, and subjected to CC.
2-{[4-(Dimethylamino)phenyl]ethynyl}anthracene-9,10-dione (21): 4-
Ethynyl-N,N-dimethylaniline (232 mg, 1.6 mmol) was added to a
degassed solution of 18 (500 mg, 1.496 mmol), [PdCl2(PPh3)2]
(53 mg, 0.076 mmol), CuI (29 mg, 0.15 mmol), and Et3N (0.5 mL)
in THF (10 mL). The deep red mixture was stirred at 20 °C for
5 min, then concentrated in vacuo. CC [SiO2; CH2Cl2/hexane (1:1)
to CH2Cl2] furnished 21 (510 mg, 97%) as a red solid. Rf = 0.4
(SiO2; CH2Cl2/hexane, 1:1); m.p. 209–210 °C. 1H NMR (300 MHz,
2-[9,10-Bis(dicyanomethylene)-9,10-dihydroanthracen-2-yl]-1,1,3,3-
tetramethylguanidine (27): The title compound was prepared from
16 (100 mg, 0.311 mmol), according to the general method. The
mixture was heated to reflux for 96 h, poured on ice/water, neutral-
ized with NaHCO3, and extracted with CH2Cl2 (3ϫ100 mL). Sub-
sequent CC (SiO2; acetone) afforded 27 (93 mg, 72%) as a dark
solid. Rf = 0.35 (SiO2; acetone); m.p. 126–127 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 2.84 (s, 12 H, NCH3), 6.88 (d, 3JH,H
= 9.0, 4JH,H = 2.0 Hz, 1 H, AQ), 7.35 (d, 4JH,H = 2.0 Hz, 1 H, AQ),
3
CDCl3, 25 °C): δ = 3.02 (s, 6 H, NCH3), 6.68 (d, JH,H = 9.0 Hz,
3
2 H, Ar), 7.45 (d, JH,H = 9.0 Hz, 2 H, Ar), 7.75–7.86 (m, 3 H,
3
AQ), 8.26 (d, JH,H = 9.0 Hz, 1 H, AQ), 8.30–8.35 (m, 2 H, AQ),
4
8.37 (d, JH,H = 2.0 Hz, 1 H, AQ) ppm. 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 40.02, 86.84, 96.62, 108.57, 111.62, 127.11,
127.16, 127.23, 129.51, 130.67, 131.36, 133.13, 133.30, 133.37,
133.56, 133.92, 134.10, 135.83, 150.52, 182.42, 182.76 ppm. IR
(neat): ν = 2894, 2186, 1670, 1661, 1612, 1585, 1529, 1369, 1335,
˜
1317, 1281, 1237, 1198, 1168, 1068, 931, 861, 806, 707, 633 cm–1.
UV/Vis (CH2Cl2): λmax (ε) = 462 (10700), 362 (17300), 326 (26500),
286 (26800), 264 nm (33800 mol–1 dm3 cm–1). HR-FT-MALDI-MS
(3-HPA): m/z calcd. for [C24H17NO2+] 351.1254; found 351.1257
[M+].
3
7.62–7.70 (m, 2 H, AQ), 8.09 (d, JH,H = 9.0 Hz, 1 H, AQ), 8.13–
8.16 (m, 1 H, AQ), 8.22–8.25 (m, 1 H, AQ) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 39.92, 82.02, 113.35, 113.38, 114.24,
114.38, 118.95, 124.44, 127.14, 127.20, 129.29, 130.21, 140.00,
131.47, 131.83, 132.04, 157.60, 159.98, 161.42, 161.79 (2 C missing)
ppm. IR (neat): ν = 2931, 2220, 1502, 1457, 1388, 1335, 1279, 1140,
˜
2,6-Bis{[4-(dimethylamino)phenyl]ethynyl}anthracene-9,10-dione
(22): [PdCl2(PPh3)2] (58 mg, 0.082 mmol) and CuI (16 mg,
0.082 mmol) were added to a degassed solution of 19 (300 mg,
0.817 mmol) and 4-ethynyl-N,N-dimethylaniline (261 mg,
1.803 mmol) in Et2NH (50 mL). The mixture was heated to reflux
under N2 for 12 h and afterwards concentrated in vacuo. Subse-
quent CC [SiO2; CH2Cl2/hexane (1:1) to CH2Cl2] afforded 22
(182 mg, 45%) as a dark red solid. Rf = 0.13 (SiO2; CH2Cl2/hexane,
1021, 835, 766, 697 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 524 (6830),
349 (sh, 20900), 285 nm (23400 mol–1 dm3 cm–1). HR-FT-MALDI-
MS (3-HPA): m/z calcd. for [C25H20N7+] 418.1775; found 418.1782
[MH+].
2Ј,2Ј-[9,10-Bis(dicyanomethylene)-9,10-dihydroanthracene-2,6-di-
yl]bis(1,1,3,3-tetramethylguanidine) (28): The title compound was
prepared from 17 (100 mg, 0.230 mmol), according to the general
method. The mixture was heated to reflux for 96 h, poured on ice/
water, neutralized with NaHCO3, and extracted with CH2Cl2
1
1:1); m.p. Ͼ 400 °C. H NMR (300 MHz, CDCl3, 25 °C): δ = 3.03
3
3
(s, 12 H, NCH3), 6.68 (d, JH,H = 9.0 Hz, 4 H, Ar), 7.46 (d, JH,H
1002
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 994–1004

New Push-Pull Chromophores Featuring TCAQ
(3ϫ100 mL). Subsequent CC (Al2O3; CH2Cl2/acetone, 5:1) af-
forded 28 (25 mg, 21%) as a dark orange solid. Rf = 0.65 (Al2O3;
(16900), 416 (29000), 353 (44700), 320 nm (43600 mol–1 dm3 cm–1).
+
HR-FT-MALDI-MS (3-HPA): m/z calcd. for [C40H28Cl2N6
]
CH2Cl2/acetone, 5:1); m.p. 129–130 °C. 1H NMR (300 MHz, 662.1747; found 662.1736 [M+].
3
CDCl3, 25 °C): δ = 2.83 (s, 24 H, NCH3), 6.83 (dd, JH,H = 9.0,
2,2Ј-(2,6-Bis{(Z)-2-chloro-2-[4-(dihexylamino)phenyl]vinyl}-
anthracene-9,10-diylidene)dimalononitrile (34): The title compound
was prepared from 23 (100 mg, 0.13 mmol), according to the gene-
ral method. The mixture was heated to reflux for 48 h. Yield 83 mg
(68%), dark green solid. Rf = 0.9 (SiO2; CH2Cl2); m.p. 77–78 °C.
4
4JH,H = 2.0 Hz, 2 H, AQ), 7.36 (d, JH,H = 2.0 Hz, 2 H, AQ), 8.00
3
(d, JH,H = 9.0 Hz, 2 H, AQ) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 39.89, 111.48, 114.59, 114.75, 118.85, 121.09, 123.76,
128.96, 132.61, 157.24, 161.20, 161.81 ppm. IR (neat): ν = 2931,
˜
2091, 1634, 1505, 1463, 1390, 1321, 1292, 1142, 1023, 834 cm–1.
UV/Vis (CH2Cl2): λmax (ε) = 480 (3800), 395 (5200), 347 (6600),
285 nm (9400 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA): m/z
calcd. for [C30H31N10+] 531.2728; found 531.2730 [MH+].
3
1H NMR (300 MHz, CDCl3, 25 °C): δ = 0.91 (t, JH,H = 6.5 Hz,
12 H, Hex), 1.30–1.40 (m, 24 H, Hex), 1.53–1.66 (m, 8 H, Hex),
3
3
3.32 (t, JH,H = 7.5 Hz, 8 H, Hex), 6.63 (d, JH,H = 9.0 Hz, 4 H,
3
Ar), 6.95 (s, 2 H, CH), 7.60 (d, JH,H = 9.0 Hz, 4 H, Ar), 8.00 (dd,
3JH,H = 9.0, JH,H = 2.0 Hz, 2 H, AQ), 8.21 (d, JH,H = 9.0 Hz, 2
4
3
2,2Ј-{2-[4-(Dimethylamino)phenyl]anthracene-9,10-diylidene}-
dimalononitrile (31): The title compound was prepared from 20
(100 mg, 0.31 mmol), according to the general method. The mix-
ture was heated to reflux for 48 h. Yield 124 mg (96%), dark green
solid. Rf = 0.7 (SiO2; CH2Cl2); m.p. 316–317 °C. 1H NMR
H, AQ), 8.59 (d, JH,H = 2.0 Hz, 2 H, AQ) ppm. 13C NMR
4
(75 MHz, CDCl3, 25 °C): δ = 14.16, 22.77, 26.86, 27.27, 31.77,
51.10, 81.78, 110.87, 113.19, 113.45, 118.13, 123.89, 127.36, 127.50,
127.52, 128.17, 130.51; 132.32, 138.07, 140.82, 149.11, 159.94 ppm.
IR (neat): ν = 2925, 2222, 1578, 1547, 1515, 1366, 1294, 1254, 1183,
3
˜
(300 MHz, CDCl3, 25 °C): δ = 3.06 (s, 6 H, NCH3), 6.81 (d, JH,H
1117, 807 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 580 (18400), 438
(30200), 357 (47300), 327 nm (43700 mol–1 dm3 cm–1). HR-FT-
MALDI-MS (3-HPA): m/z calcd. for [C60H69Cl2N6+] 943.4955;
found 943.4938 [MH+].
3
= 9.0 Hz, 2 H, Ar), 7.61 (d, JH,H = 9.0 Hz, 2 H, Ar), 7.70–7.75
3
4
(m, 2 H, AQ), 7.87 (dd, JH,H = 9.0, JH,H = 2.0 Hz, 1 H, AQ),
4
8.21–8.30 (m, 3 H, AQ), 8.39 (d, JH,H = 2.0 Hz, 1 H, AQ) ppm.
13C NMR (75 MHz, CDCl3, 25 °C): δ = 40.12, 81.13, 82.74, 112.49,
113.15, 113.40, 113.50, 124.60, 124.85, 126.18, 127.45, 128.10, 4,4Ј,4ЈЈ,4ЈЈЈ-[3,3Ј-(Anthracene-9,10-diylidene)bis(penta-1,4-diyne-
128.17, 128.76, 130.11, 130.48, 130.64, 132.11, 132.34, 145.59, 1,5-diyl-3-ylidene)]tetrakis(N,N-dimethylaniline) (36): To a degassed
151.13, 160.03, 160.91 ppm (2 C missing). IR (neat): ν = 2852, solution of 35 (260 mg, 0.5 mmol), 4-ethynyl-N,N-dimethylaniline
˜
2217, 1581, 1531, 1464, 1367, 1330, 1277, 1201, 1171, 1125, 950,
896, 814, 775, 731, 692 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 571
(7000), 422 (9800), 345 (27300), 308 (27400), 287 nm
(31400 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA): m/z calcd.
for [C28H18N5+] 422.1400; found 422.1400 [MH+].
(508 mg, 3.5 mmol), and Et2NH (0.3 mL, 3.0 mmol) in anhydrous
benzene (15 mL), [PdCl2(PPh3)2] (17.5 mg, 0.05 mmol) and CuI
(4 mg, 0.02 mmol) were added. The mixture was stirred under N2
at 20 °C for 2 d, concentrated in vacuo, and subjected to CC (SiO2;
CH2Cl2/hexane, 1:1 to 3:1). Yield 35 mg (9%), red solid. Rf = 0.1
(SiO2; CH2Cl2); m.p. 170–171 °C. 1H NMR (300 MHz, CDCl3,
(Z)-2,2Ј-(2-{2-Chloro-2-[4-(dimethylamino)phenyl]vinyl}anthracene-
9,10-diylidene)dimalononitrile (32): The title compound was pre-
pared from 21 (100 mg, 0.29 mmol), according to the general
method. The mixture was heated to reflux for 72 h. Yield 121 mg
(88%), dark blue solid. Rf = 0.75 (SiO2; CH2Cl2); m.p. 290–291 °C.
1H NMR (300 MHz, CDCl3, 25 °C): δ = 3.05 (s, 6 H, NCH3), 6.71
3
25 °C): δ = 2.99 (s, 24 H, NCH3), 6.64 (d, JH,H = 9.0 Hz, 8 H,
Ar), 7.34–7.37 (m, 4 H, AQ), 7.40 (d, J = 9.0 Hz, 8 H, Ar), 8.47–
8.50 (m, 4 H, AQ) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
40.26, 88.25, 94.78, 101.41, 110.28, 111.68, 126.27, 127.22, 132.71,
134.87, 142.46, 149.95 ppm. IR (neat): ν = 2850, 2165, 1601, 1516,
˜
1440, 1343, 1190, 1165, 1111, 1061, 944, 810, 764, 676 cm–1. UV/
Vis (CH2Cl2): λmax (ε) = 486 (29900), 400 (38700), 308 (sh, 46400),
250 nm (36800 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-HPA):
m/z calcd. for [C56H48N4+] 776.3874; found 776.3869 [M+].
3
3
(d, JH,H = 9.0 Hz, 2 H, Ar), 7.63 (d, JH,H = 9.0 Hz, 2 H, Ar),
3
4
7.71–7.76 (m, 2 H, AQ), 8.02 (dd, JH,H = 9.0, JH,H = 2.0 Hz, 1
H, AQ), 8.20–8.28 (m, 3 H, AQ), 8.61 (d, 4JH,H = 2.0 Hz, 1 H, AQ)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 40.38, 82.14, 83.37,
111.71, 113.109, 113.38, 113.54, 118.93, 125.28, 127.73, 127.78,
127.83, 128.29, 130.53, 130.57, 130.63, 132.52, 132.63, 132.94,
133.66, 138.44, 141.11, 151.58, 159.99, 160.67 ppm (3 C missing).
Supporting Information (see also the footnote on the first page of
this article): Experimental procedures and spectral characterization
of the compounds 16, 17, 25, 26, 29, and 30. X-ray crystallography
data of the compounds 10, 11, 17, 20, 25, and 32. Representative
CV diagrams as well as UV/Vis spectra.
IR (neat): ν = 2811, 2222, 1574, 1537, 1520, 1341, 1327, 1169, 813,
˜
767, 695 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 549 (8400), 351 (sh,
37000), 296 nm (27500 mol–1 dm3 cm–1). HR-FT-MALDI-MS (3-
HPA): m/z calcd. for [C30H19ClN5+] 484.1324; found 484.1321
[MH+].
Acknowledgments
This research was supported by the ETH Research Council and the
Fonds der Chemischen Industrie (Germany). F. B. is indebted to
the Ministry of Education, Youth, and Sport of the Czech
Republic.
2,2Ј-(2,6-Bis{(Z)-2-chloro-2-[4-(dimethylamino)phenyl]vinyl}-
anthracene-9,10-diylidene)dimalononitrile (33): The title compound
was prepared from 22 (50 mg, 0.1 mmol), according to the general
method. The mixture was heated to reflux for 96 h. Yield 53 mg
(79%), dark solid. Rf = 0.7 (SiO2; CH2Cl2); m.p. 302–303 °C. 1H
NMR (300 MHz, CDCl3, 25 °C): δ = 3.04 (s, 12 H, NCH3), 6.71
[1] R. Gompper, H.-U. Wagner, Angew. Chem. 1988, 100, 1492–
1511; Angew. Chem. Int. Ed. Engl. 1988, 27, 1437–1455.
[2] a) S. Barlow, S. R. Marder, in Functional Organic Materials
(Eds: T. J. J. Müller, U. H. F. Bunz), Wiley-VCH, Weinheim,
2007, pp. 393–437; b) J. J. Wolf, R. Wortmann, Adv. Phys. Org.
Chem. 1999, 32, 121–217; c) Nonlinear Optics of Organic Mole-
cules and Polymers (Eds: H. S. Nalwa, S. Miyata), CRC Press,
Boca Raton, FL, 1997.
3
3
(d, JH,H = 9.0 Hz, 4 H, Ar), 6.98 (s, 2 H, CH), 7.63 (d, JH,H
=
3
4
9.0 Hz, 4 H, Ar), 8.02 (dd, JH,H = 9.0, JH,H = 2.0 Hz, 2 H, AQ),
3
4
8.23 (d, JH,H = 9.0 Hz, 2 H, AQ), 8.61 (d, JH,H = 2.0 Hz, 2 H,
AQ) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 40.26, 81.96,
111.44, 113.15, 113.38, 118.77, 125.09, 127.38, 127.50, 127.72,
127.98, 130.50, 132.45, 137.98, 140.70, 151.20, 159.90 ppm. IR
(neat): ν = 2893, 2223, 1575, 1519, 1346, 1315, 1190, 1164, 1118,
˜
[3] a) R. R. Tykwinski, U. Gubler, R. E. Martin, F. Diederich, C.
Bosshard, P. Günter, J. Phys. Chem. B 1998, 102, 4451–4465;
911, 815, 803, 696, 625 cm–1. UV/Vis (CH2Cl2): λmax (ε) = 544
Eur. J. Org. Chem. 2008, 994–1004
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1003

F. Diederich et al.
FULL PAPER
b) J. L. Brédas, C. Adant, P. Tackx, A. Persoons, B. M. Pierce,
Chem. Rev. 1994, 94, 243–278.
[17] T. Satoh, T. Kawashima, S. Takahashi, K. Sakai, Tetrahedron
2003, 59, 9599–9607.
[4] a) J. C. May, I. Biaggio, F. Bures, F. Diederich, Appl. Phys.
[18] R. Neidlein, M. Winter, Synthesis 1998, 1362–1366.
Lett. 2007, 90, 251106/1–251106/3; b) J. C. May, J. H. Lim, I. [19] A. Bauer, M. W. Miller, S. F. Vice, S. W. McCombie, Synlett
Biaggio, N. N. P. Moonen, T. Michinobu, F. Diederich, Opt.
Lett. 2005, 30, 3057–3059.
2001, 2, 254–256.
[20] Y. Kobayashi, M. Ito, Eur. J. Org. Chem. 2000, 3393–3397.
[21] F. Texier-Boullet, A. Foucaud, Tetrahedron Lett. 1982, 23,
4927–4928.
[5] J.-P. Gisselbrecht, N. N. P. Moonen, C. Boudon, M. B. Nielsen,
F. Diederich, M. Gross, Eur. J. Org. Chem. 2004, 2959–2972.
[6] R. R. Tykwinski, M. Schreiber, V. Gramlich, P. Seiler, F. Died-
erich, Adv. Mater. 1996, 8, 226–231.
[7] N. N. P. Moonen, W. C. Pomerantz, R. Gist, C. Boudon, J.-
P. Gisselbrecht, T. Kawai, A. Kishioka, M. Gross, M. Irie, F.
Diederich, Chem. Eur. J. 2005, 11, 3325–3341.
[8] T. Michinobu, C. Boudon, J.-P. Gisselbrecht, P. Seiler, B.
Frank, N. N. P. Moonen, M. Gross, F. Diederich, Chem. Eur.
J. 2006, 12, 1889–1905.
[9] F. Bures, W. B. Schweizer, J. C. May, J.-P. Gisselbrecht, M.
Gross, I. Biaggio, F. Diederich, Chem. Eur. J. 2007, 13, 5378–
5387.
[10] a) R. Andreu, M. J. Blesa, L. Carrasquer, J. Garín, J. Orduna,
B. Villacampa, R. Alcalá, J. Casado, M. C. R. Delgado, J. T. L.
Navarrete, M. Allain, J. Am. Chem. Soc. 2005, 127, 8835–8845;
b) S. R. Marder, L.-T. Cheng, B. G. Tiemann, A. C. Friedli, M.
Blanchard-Desce, J. W. Perry, J. Skindhøj, Science 1994, 263,
511–514.
[22] a) T. Itoh, S. Nomura, N. Saitoh, T. Uno, M. Kubo, K. Sada,
K. Inoue, M. Miyata, Macromolecules 2004, 37, 7938–7944; b)
M. Essers, G. Haufe, J. Chem. Soc. Perkin Trans. 1 2002, 2719–
2728; c) J. V. Crivello, J. Org. Chem. 1981, 46, 3056–3060.
[23] a) T. Itoh, S. Nomura, M. Ohtake, T. Yoshida, T. Uno, M.
Kubo, A. Kajiwara, K. Sada, M. Miyata, Macromolecules
2004, 37, 8230–8238; b) S. Nomura, T. Itoh, H. Nakasho, T.
Uno, M. Kubo, K. Sada, K. Inoue, M. Miyata, J. Am. Chem.
Soc. 2004, 126, 2035–2041; c) T. Itoh, S. Nomura, T. Uno, M.
Kubo, K. Sada, M. Miyata, Angew. Chem. 2002, 114, 4482–
4485; Angew. Chem. Int. Ed. 2002, 41, 4306–4309; d) S. Ichi-
kawa, T. Uno, M. Kubo, T. Itoh, Polym. Bull. 2001, 46, 249–
255; e) T. Itoh, H. Okuno, T. Hishida, A. Inokuchi, N. Kamei,
T. Sato, M. Kubo, S. Iwatsuki, Tetrahedron 1997, 53, 15247–
15261.
[24] a) W. Lehnert, Synthesis 1974, 667–669; b) W. Lehnert, Tetra-
hedron Lett. 1970, 11, 4723–4724.
[11] a) R. Gompper, H.-U. Wagner, E. Kutter, Chem. Ber. 1968,
101, 4144–4151; b) R. Gompper, H.-U. Wagner, E. Kutter,
Chem. Ber. 1968, 101, 4123–4143.
[12] a) A. S. Batsanov, M. R. Bryce, M. A. Coffin, A. Green, R. E.
Hester, J. A. K. Howard, I. K. Lednev, N. Martin, A. J. Moore,
J. N. Moore, E. Ortí, L. Sánchez, M. Savirón, P. M. Viruela,
R. Viruela, T.-Q. Ye, Chem. Eur. J. 1998, 4, 2580–2592; b) S.
Inoue, Y. Aso, T. Otsubo, Chem. Commun. 1997, 1105–1106;
c) T. Kawase, N. Nishigaki, H. Kurata, M. Oda, Eur. J. Org.
Chem. 2004, 3090–3096.
[13] a) A. Aumüller, S. Hünig, Liebigs Ann. Chem. 1984, 618–621;
b) Y. Nishizawa, T. Suzuki, Y. Yamashita, T. Miyashi, T. Mu-
kai, Nippon Kagaku Kaishi 1985, 5, 904–909; Chem. Abstr.
1986, 104, 68550; c) Y. Yamashita, T. Suzuki, T. Mukai, Nippon
Kagaku Kaishi 1986, 3, 268–275; Chem. Abstr. 1987, 106,
67197.
[14] a) R. Gomez, C. Seonane, J. L. Segura, Chem. Soc. Rev. 2007,
36, 1305–1322; b) N. A. Macias-Ruvalcaba, D. H. Evans, J.
Phys. Chem. B 2006, 110, 5155–5160; c) A. M. Kini, D. O.
Cowan, F. Gerson, R. Möckel, J. Am. Chem. Soc. 1985, 107,
556–562.
[25] S. Arai, S. Kato, M. Hida, Bull. Chem. Soc. Jpn. 1985, 58,
1458–1463.
[26] a) E. Winkelmann, W. Raether, Arzneim.-Forsch. 1979, 29,
1504–1507; b) P. F. Fabio, T. L. Fields, Y. Lin, E. J. Burden, S.
Carvajal, K. C. Murdock, S. A. Lang Jr, J. Med. Chem. 1978,
21, 273–276.
[27] R. A. I. Abou-Elkhair, T. L. Netzel, Nucleosides, Nucleotides
Nucleic Acids 2005, 24, 85–110.
[28] a) S. K. Lee, W. J. Yang, J. J. Choi, C. H. Kim, S.-J. Jeon, B. R.
Cho, Org. Lett. 2005, 7, 323–326; b) P. Hodge, G. A. Power,
M. A. Rabjohns, Chem. Commun. 1997, 73–74.
[29] R. Paulini, K. Müller, F. Diederich, Angew. Chem. 2005, 117,
1820–1839; Angew. Chem. Int. Ed. 2005, 44, 1788–1805.
[30] E. Torres, C. A. Panetta, R. M. Metzger, J. Org. Chem. 1987,
52, 2944–2945.
[31] P. Metrangolo, H. Neukirch, T. Pilati, G. Resnati, Acc. Chem.
Res. 2005, 38, 386–395.
[32] C. Diaz, A. Arancibia, Polyhedron 2000, 19, 137–145. In
CH2Cl2 (+ 0.1  nBu4NPF6, vs. SCE), TCNQ undergoes two
reversible one-electron reduction steps at 0.25 and –0.31 V.
[33] a) D. W. Rogers, N. Matsunaga, A. A. A. Zavitsas, F. J. McLaf-
ferty, J. F. Liebman, Org. Lett. 2003, 5, 2373–2375; b) P. D.
Jarowski, M. D. Wodrich, C. S. Wannere, P. v. R. Schleyer,
K. N. Houk, J. Am. Chem. Soc. 2004, 126, 15036–15037.
[34] P. M. Donovan, L. T. Scott, J. Am. Chem. Soc. 2004, 126,
3108–3112.
[15] a) J. Segura, R. Gómez, R. Blanco, E. Reinold, P. Bäuerle,
Chem. Mater. 2006, 18, 2834–2847; b) F. Giacalone, J. L. Seg-
ura, N. Martín, M. Catellani, S. Luzzati, N. Lupsac, Org. Lett.
2003, 5, 1669–1672; c) D. F. Perepichka, M. R. Bryce, A. S.
Batsanov, J. A. K. Howard, A. O. Cuello, M. Gray, V. M. Rot-
ello, J. Org. Chem. 2001, 66, 4517–4524.
Received: October 16, 2007
Published Online: December 20, 2007
[16] J. B. Lambert, S. M. Ciro, J. Org. Chem. 1996, 61, 1940–1945.
1004
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Eur. J. Org. Chem. 2008, 994–1004