Synthesis, crystal structures, and photophysical properties of triphenylamine-based multicyano derivatives

Article abstract of DOI:10.1021/jo101456v

A new series of intramolecular charge transfer (ICT) molecules were synthesized by attaching various strong electron-withdrawing groups to a triphenylamine backbone. Relationships between chemical structures and optoelectronic properties of these compound

Full text of DOI:10.1021/jo101456v

pubs.acs.org/joc
Synthesis, Crystal Structures, and Photophysical Properties of
Triphenylamine-Based Multicyano Derivatives
Xianglin Tang,† Weimin Liu,† Jiasheng Wu,† Chun-Sing Lee,*,‡ Juanjuan You,† and
Pengfei Wang*,†
†Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics
and Chemistry, Chinese Academy of Sciences, Beijing, 100190, China, and ‡Center of Super-Diamond and
Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong,
Hong Kong SAR, China
apcslee@cityu.edu.hk; wangpf@mail.ipc.ac.cn
Received July 30, 2010
A new series of intramolecular charge transfer (ICT) molecules were synthesized by attaching various
strong electron-withdrawing groups to a triphenylamine backbone. Relationships between chemical
structures and optoelectronic properties of these compounds were investigated with X-ray diffrac-
tion, cyclic voltammetry, absorption spectroscopy, and density functional theory calculations. It is
shown that the compounds exhibit intensive ICT interactions leading to substantial extension of their
absorption spectral response, which may be potentially used for efficient solar cells.
Introduction
for their high absorption coefficients, tunable functional groups,
and simple synthetic procedures.5
Electron-rich triphenylamine-based derivatives have been
widely investigated and applied in organic field-effect tran-
sistors,1 organic light-emitting diodes (OLED),2 as well as second-
order nonlinear optical devices.3 In the past few years, organic
solar cells based on triphenylamine derivatives have been devel-
oped.4 On the other hand, dye-sensitized solar cells based on
metal-free organic dyes have attracted considerable attention
One possible solution for extending the absorption spec-
tral response of organic dyes consisting of electron accepting
and donating parts is to increase the conjugation length
bridging these parts. However, intermolecular aggregation
of dyes with long chain length can reduce their energy con-
version efficiency.6 Another option is to introduce stronger
electron-withdrawing groups to get a D-π-A structure within
the molecule.7 With this approach, absorption spectra of
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DOI: 10.1021/jo101456v
r
Published on Web 10/12/2010
J. Org. Chem. 2010, 75, 7273–7278 7273
2010 American Chemical Society

Tang et al.
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these compounds can be easily tuned via controlling the
extent of intramolecular charge transfer (ICT).
Results and Discussion
Synthesis. Aldehyde 6 was synthesized according to a pre-
viously reported method.10 Dicyanovinyl derivative 1 was
synthesized by condensation of 6 with malonodinitrile.11 The
reaction was carried out in ethanol at room temperature with
triethylamine as catalyst and produced 1in 80% yield (Scheme 1).
2 was synthesized straightforwardly in high yield by reacting
triphenylamine with an excess of tetracyanoethylene (TCNE)
in DMF.3
Common acceptors in these dyes are mostly weak electron-
withdrawing groups such as cyanoacrylic acid and rhodanine-
3-acetic acid.8 It is well-known that the cyano group is one of
the strongest electron-withdrawing groups. Stronger electron-
accepting effects can be further obtained by introducing
several cyano groups into a conjugated system. For example,
tetracyanoethene (TCNE) and 7,7,8,8-tetracyanoquinodi-
methane (TCNQ) as stable strong electron acceptors are
widely used in many fields.9 In this context, we designed and
synthesized a new series of ICT compounds by incorporating
the triphenylamine moiety (electron donor) with different
multicyano groups (electron acceptor) (3-5, Chart 1). To explore
the relationship between chemical structures and properties
of these compounds, we also synthesized other compounds
(1 and 2, Chart 1) for comparison. Properties of all these tri-
phenylamine-based derivatives (1-5) were investigated with
X-ray diffraction, cyclic voltammetry, absorption spectroscopy,
and density functional theory calculations.
Compounds 3-5 were obtained from the same intermedi-
ate 8. According to a reported route,12 compound 8 has to be
synthesized by using palladium chemistry with diphenyl-
amine as starting material in four steps. Here the procedure
was simplified and compound 8 can be obtained in excellent
yield via three simple steps without any palladium catalyst
from triphenylamine. First, triphenylamine underwent for-
mylation to form 6. Then, a Wittig reaction of 6 with CBr4
and PPh3 led to dibromoalkene 7 at room temperature in 1 h.
Finally, treatment of 7 with n-BuLi generated a bromo-
alkyne intermediate, which via dehydrohalogenation gave the
alkyne 8 upon aqueous workup. [2 þ 2] cycloaddition13 of
alkyne 8 with TCNE and 7,7,8,8-tetracyanoquinodimethane
(TCNQ) yielded the terminal compounds 3 and 5, respec-
tively (Table 1). In both cases, the reaction proceeded at
room temperature in dichloromethane for 5 h and provided
the products with nearly unity yields. Cyanoalkyne 9 was
obtained in 85% yields by treatment of alkyne 8 with
successively n-BuLi and PhOCN at low temperature. Addi-
tion of the electron-withdrawing group lowered the reactiv-
ity of compound 9. The corresponding reaction of 9 with
TCNE required much longer time than alkyne 8, and gave
compound 4 with 60% yield. All new compounds were
isolated as deep colored solids and found to be stable under
ambient conditions. Identities and structures of the com-
pounds were confirmed with NMR and mass spectrometry.
X-ray Structures. Single crystals of 3, 4, and 5 suitable
for X-ray crystallographic analysis were obtained by slow
diffusion of hexane into CH2Cl2 solution of the compounds
at ambient temperature. Common features in compounds 3
to 5 were observed. First, the N atom in the triphenylamine
group has an sp2 geometry.14 The three central C-N single
bonds are nearly coplanar with the benzene ring bearing the
acceptors, while the other two benzene rings are twisted. On
the other hand, due to strong repulsion arising from the steric
CHART 1. Structures of Compounds 1-5
SCHEME 1. Synthesis of Compounds 1-5
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TABLE 1. Crystallographic Data of 3-5 and Theoretical Calculation
Data for 1-5
θexpa [deg]
θcalb [deg]
δHc [ppm]
˚
δr [A]
1
2
3
4
5
0.5
15.5
44.1
26.8
56.0
7.72
7.95
7.33
7.53
7.10
0.034
0.046
0.032
32.1
26.3
50.9
aThe torsion angle between cyanovinyl moiety and donor rings
determined from crystal structure. bThe torsion angle determined from
theoretical calculation. c1H NMR chemical shifts of the protons in the
ortho position to the acceptor (400 MHz) in CDCl3.
hindrance of cyano groups, intense distortions were ob-
served in all the acceptor moieties. In particular, rotation
of the two vinyl groups around the central single bond
disturbs the planarity of the butadiene. For example, torsion
angles of respectively 41°, 54°, and 22° in the single bonds
were observed in 3-5. However, the torsion angle between
the vinyl moieties and the benzene rings changes with an
opposite trend. The measured θ values for 3(C(20)-C(19)-
C(16)-C(17)), 4(C(20)-C(19)-C(16)-C(17)), and 5(C(20)-
C(19)-C(16)-C(17)) (for atom labels, see Figure 1) are
respectively 32°, 26°, and 51°. The more planar structure
indicates more conjugation between the vinyl groups and
the donor moieties.
Charge transfer from the donor to the acceptor parts is
accompanied by bond length alternation in the bridging
benzene ring. The amount of bond length variation reflects
the extent of CT in the ground state, and can be expressed by
the quinoid character (δr)15 (eq 1, see Figure 1 for the definition
of bonds a, a0, b, b0, c, and c0).
δr ¼ ð½ða þ a0Þ=2 - ðb þ b0Þ=2ꢀ þ ½ðc þ c0Þ=2 - ðb þ b0Þ=2ꢀÞ=2
ð1Þ
The δr value is 0 for a single benzene molecule. Upon intro-
duction of donor and/or acceptor moieties, bond length
variations in the ring would lead to changes in the δr value.
The δr value in fully quinoid rings varies between 0.08 and
0.10. For the bridging benzene ring in 5, the δr value ob-
tained from the X-ray data is 0.032. In 3 and 4, higher values
(8) (a) Marinado, T.; Hagberg, D. P.; Hedlund, M.; Edvinsson, T.;
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Hagberg, D. P.; Sun, L.; Hagfeldt, A.; Albinsson, B. J. Phys. Chem. C 2009,
113, 3881.
FIGURE 1. Molecular structures of 3, 4, and 5 with ellipsoids
shown at the 30% probability level (hydrogen atoms are omitted
for clarity).
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of 0.034 and 0.046 were observed, respectively, due to increased
coplanarity between the vinyl groups and the attached benzene
rings. These values indicate efficient ICT interaction in the
ground state.
Changes in electron distribution resulting from the CT
would also influence the chemical shifts of the protons in the
bridging benzene ring. Downfield shifts of the protons in the
ortho position to the acceptor moiety increase from 7.10 for
5 to 7.33 and 7.53 respectively for 3 and 4. The trend in
chemical shifts of the protons is consistent with that of the δr
values. The chemical shifts of the nearby protons may indi-
cate the efficiency of ground-state ICT interaction.16 Taking
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J. Org. Chem. Vol. 75, No. 21, 2010 7275

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FIGURE 3. Absorption spectra of compounds 1 (black), 2 (red),
3 (green), 4 (blue), and 5 (purple) in CH2Cl2 at 298 K.
FIGURE 2. Cyclic voltammograms of compounds 1-5 in CH2Cl2.
All solutions contained tetrabutylammonium hexafluorophosphate
(TBAPF6, 0.1 M) as the supporting electrolyte, scan rate is 100 mV
s-1, using glassy carbon as the working electrode, Pt wire as the
counter electrode, and Ag/AgNO3/DMF as the reference electrode.
TABLE 2. Cyclic Voltammetric Data (in 0.10 M Bu4NPF6/CH2Cl2,
vs Fcþ/Fc, Scan rate 100 mV/s) and Optical Gap Determined from the
Optical Absorption Edge (in CH2Cl2) for Compounds 1-5
Eox [V]
Ered [V]
ΔEopc [eV]
ΔEeld [V]
1
2
3
0.95
0.97
0.85
-1.79a
-1.05
-0.62
-1.27b
-0.24
-0.84b
-0.49
-0.79b
2.47
1.84
1.44
2.74
2.02
1.47
4
5
0.93
0.64
1.31
1.09
1.17
1.13
aIrreversible process. bSecond reduction potentials. Optical gap
estimated from the absorption edge. dElectrochemical gap ΔEel
Eox,1 - Ered,1
c
=
.
FIGURE 4. Linear correlation between the optical gap Egap and the
electrochemical gap Δ(Eox,1 - Ered,1) for compounds 1-5.
account of the X-ray and NMR data, the extent of ICT
increases in the order of 5 < 3 < 4.
potential of the anodic peak reflects the efficiency of ground
state ICT directly. The oxidation potentials of 3 and 4 shift to
0.85 and 0.93 V, respectively, relative to that of 5 (0.64 V).
Furthermore, the oxidation processes occur at slightly more
positive potentials for 1 (0.95 V) and 2 (0.97 V). The anodic shift
resulting from efficient intramolecular CT is presumably a
consequence of the trade-off between acceptor strength and
the coplanarity between the donor and the acceptor moieties.
UV-Vis Spectroscopy. Absorption spectra of all com-
pounds recorded in CH2Cl2 show their first absorption band
in the 270-330 nm region and subsequent bands of lower
energy. On the basis of the spectrum of triphenylamine, the
first absorption band can be attributed to a π-π* transition.
The other bands can be assigned to ICT transitions between
triphenylamine and different acceptors. The origin of the
ICT bands is further confirmed by the solvatochromic effects
as shown in the Supporting Information.18 While the spectra
of 1 and 2 show only one intense ICT band with their
maximum shifting from 440 to 530 nm, an additional weak
and broad ICT band at longer wavelengths can be observed
in 3, 4, and 5 due to the additional cyanovinyl group (Figure 3).
In addition, the TCNQ moiety in 5 may result in a more
complex absorption band, which is obviously different
Electrochemical Experiments. As shown in Figure 2, cyclic
voltammograms of compounds 1-5 have been measured in
CH2Cl2 with 0.1 M tetrabutylammonium hexafluorophos-
phate as the supporting electrolyte. Compound 1 undergoes
an irreversible reduction, whereas compound 2 shows one
reversible reductive step. Two reversible reduction processes
were observed in 3 to 5 indicating formation of stable anions
and dianions. As expected, increasing the number of cyano
groups in the acceptor moieties leads to enhancement of the
acceptor strength and thus anodic shift of the first reduction
potential. For example, the first reduction potential shifts
toward more positive values from -1.79 V for 1 to -1.05,
-0.62, -0.49 V respectively for 2, 3, and 5 (Table 2). The
value of 4 is even comparable to that of TCNQ (-0.25 vs
-0.24 V). However, the second reduction in 5 (-0.79 V) is
easier than that in 3 (-1.27 V) and 4 (-0.84 V), which can be
explained by the more conjugative acceptor moiety in 5. As
for oxidation, the diphenylamino groups in all compounds show
quasi-reversible processes due to the unprotected para-position
of the phenyl groups.3a,17 Electron density transfer from donor
to acceptor hinders the oxidation of donor, and thereby the
(17) Tsai, M.-H.; Lin, H.-W.; Su, H.-C.; Ke, T.-H.; Wu, C.-c.; Fang,
F.-C.; Liao, Y.-L.; Wong, K.-T.; Wu, C.-I. Adv. Mater. 2006, 18, 1216.
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7276 J. Org. Chem. Vol. 75, No. 21, 2010

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FIGURE 5. Spatial distributions of the calculated HOMOs and LUMOs of 1-5.
from that of compound 1-4. It is found that there exists a
shoulder peak centered at 400 nm in compound 5, which
can be ascribed to the characteristic peak of TCNQ.19
Furthermore, the optical gaps estimated from the absorp-
tion edge of the UV-vis spectra show a linear correlation
(R = 0.995) with the electrochemical gaps Δ(Eox,1 - Ered,1),
indicating that the same orbitals are involved in both
optical and electrochemical band gaps for 1-5 (Figure 4).20
Although the X-ray crystal structures and electrochemical
results indicate that 5 has the lowest extent of ICT inter-
action in the ground state, the absorption maximum (750 nm)
for 5 is the longest in the whole series. This is in agreement
with recent studies that bathochromic shift of the ICT
band in the UV-vis spectrum is generally not a good indi-
cator for the extent of ICT interaction.21 Interestingly, as
shown in Figure 3, the UV-vis spectra of 3, 4, and 5
feature very broad absorption bands, and the broadest
absorption bands of 5 may result from the longest con-
jugated system. This suggests that these ICT molecules can
absorb photons over a wide spectral range.
optimizations show good correlations with the experimental
data obtained from single crystal structures for 3, 4, and 5.
For 4, the calculated angle (26.8°) is in good agreement with
the experimental value (26.3°). On the other hand, the cal-
culated angles in 3 and 5 are slightly larger than the corre-
sponding experimental values. In contrast, DFT calculations
indicated smaller dihedral angles in 1 and 2 when compared
to that in 4, which suggest that 1 and 2 should have more
planar conformations. The small discrepancy between the
experimental and the theoretical results may be caused by
the absence of intermolecular interactions in the latter. The
calculated HOMOs and LUMOs of 1-5 are illustrated in
Figure 5. The density in the HOMOs of all the compounds is
mainly concentrated on the electron-donating triphenyl-
amine moiety with low coefficients on the electron-withdraw-
ing cyanovinyl group. The distributions of HOMOs in all
compounds directly show the ICT interactions. The LUMOs
are mainly located on the electron-withdrawing groups. The
separation between HOMO and LUMO indicates that sub-
stantial charge transfer from the donor moiety to the acceptor
moiety when molecules are excited.
Theoretical Basis. To investigate the geometric and elec-
tronic properties of compounds 1-5, quantum calculations
using the Gaussian 03 program have been performed.22
The calculations were optimized by using the restricted
B3LYP/6-31G(D,P) functions at a density functional theory
(DFT) level. The calculated dihedral angles between the
planes of acceptor moieties and the conjugated benzene rings
are listed in Table 1. As expected, the results of geometry
Conclusions
A new series of triphenylamine-based multicyano deriva-
tives have been synthesized in high yields. The electronic
properties and the efficiency of the ICT interactions were
considered from their crystallography, NMR chemical shifts
of hydrogen atoms, and electrochemical data. The electro-
chemical analysis of the effect of the number of cyano groups
shows that increasing the number of cyano groups leads to an
increase of the acceptor strength. Through analysis of the
physicochemical properties of the new chromophores, it was
observed that the extent of intramolecular charge transfer
can be enhanced by using a stronger acceptor and/or a more
planar structure between the cyanovinyl moiety and the
donor ring. Both the X-ray crystallographic analysis and
theoretical calculations reveal that the acceptors in these new
chromophores 3-5 are highly distorted. Comparing with
1 and 2, additional strong intramolecular charge transfer
bands in the near-infrared region were observed in 3-5.
As a result, 3-5 have board absorption spectra responses
over the solar spectrum. These results suggest that the
present approach of molecular engineering might pave a
potential route for developing materials suitable for applica-
tions in solar energy conversion.
(19) Ong, W.; McCarley, R. L. Org. Lett. 2005, 7, 1287.
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Muller, I. B.; Langer, N.; Jarowski, P. D.; Gescheidt, G.; Diederich, F.
Chem.—Eur. J. 2009, 15, 4111.
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(b) Spitler, E. L.; Monson, J. M.; Haley, M. M. J. Org. Chem. 2008, 73, 2211.
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Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
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Experimental Section
Synthesis of Compounds 3 and 5. To a solution of compound
8 (200 mg, 0.74 mmol) in CH2Cl2 (10 mL) was added TCNE
(100 mg, 0.78 mmol) or TCNQ (150 mg, 0.74 mmol). The
mixture was stirred for 5 h at room temperature. After evapora-
tion of the solvent in vacuo, the solid was dissolved in a minimal
amount of CH2Cl2, then n-hexane was added until precipitation
started. Crystallization at 0 °C afforded the desired pure pro-
ducts. Compound 3 was isolated pure in 90% yield as dark blue
glassy solid. In the case of 5, pure product was obtained in 88%
yield as dark green glassy solid.
2-(4-(Diphenylamino)phenyl)buta-1,3-diene-1,1,4,4-tetracarbo-
nitrile (3). Mp 184-185 °C; H NMR (400 MHz, CDCl3) δ
7.01 (d, 2H, J = 9 Hz), 7.19 (m, 6H), 7.33 (d, 2H, J = 9 Hz),
7.36 (m, 4H), 8.01 (s,1H); 13C NMR (CDCl3, 100 MHz) δ 83.7,
97.9, 108.0, 109.0, 111.7, 112.3, 112.9, 119.3, 121.5, 126.3,
126.8, 130.1, 131.6, 145.2, 153.8, 155.1, 160.1; EI-HR-MS m/z
calcd for C26H15N5þ 397.1327, found 397.1330.
2-(4-(3,3-Dicyano-1-(4-(diphenylamino)phenyl)allylidene)cy-
clohexa-2,5-dienylidene)malononitrile (5). Mp 258-260 °C; 1HNMR
(400 MHz, CDCl3) δ 7.06 (d, 2H, J = 8.8 Hz), 7.10 (d, 2H, J = 8.8
Hz), 7.17 (m, 6H), 7.33 (m, 6H), 7.56 (s, 2H), 8.17 (s, 1H); 13C NMR
(CDCl3, 100 MHz) δ 79.8, 89.9, 92.2, 110.5, 111.7, 113.6, 114.1,
121.2, 125.2, 126.2, 127.4, 129.9, 131.4, 133.1, 137.5, 146.1, 146.3,
150.9, 151.7, 152.9, 154.5; EI-HR-MS m/z calcd for
Synthesis of 4-(2,2-Dibromovinyl)-N,N-diphenylbenzenamine
(7). 4-(Diphenylamino)benzaldehyde 6 (1.36 g, 5.0 mmol) was
added to a solution of CBr4 (3.31 g, 10.0 mmol) and PPh3 (5.25 g,
20.0 mmol) in anhydrous dichloromethane (50 mL). After the
solution was stirred for 60 min at room temperature, the re-
action was quenched with water (50 mL) and extracted with
dichloromethane (3 ꢁ 50 mL). The combined organic layers
were washed with water and brine, then dried over Mg2SO4.
After the solvent was removed under a reduced pressure, the
crude residue was purified by column chromatography on SiO2
with ethyl acetate-petroleum ether (1:1) to afford the desired
product 7 (1.5 g, 71%) as light yellow solid. Mp 122-123 °C; 1H
NMR (400 MHz, CDCl3) δ 6.99 (d, 2H, J = 8.7 Hz), 7.06 (m,
6H), 7.27 (m, 4H), 7.38 (s, 1H), 7.43 (d, 2H, J=8.7 Hz); 13C
NMR (CDCl3, 100 MHz) δ 87.1, 122.0, 123.8, 125.2, 128.5,
129.6, 136.4, 147.3, 148.3; HR-EI-MS m/z calcd for C20H15-
N79Br81Brþ 428.9551, found 428.9545.
Synthesis of (4-Ethynylphenyl)diphenylamine (8). n-BuLi
(27.50 mmol, 10 mL of a 2.75 M solution in hexane) was
added dropwise to a stirred solution of 7 (2.0 g, 4.7 mmol) in
anhydrous THF (30.0 mL) under a nitrogen atmosphere at
-78 °C. The solution was stirred at -78 °C for 1 h then
warmed to room temperature. The reaction mixture was
quenched with brine and extracted with ethyl acetate. The
combined organic layers were washed with water and brine,
then dried over Mg2SO4. The solvent was removed under a
reduced pressure. Purification by column chromatography on
SiO2 eluting with ethyl acetate-petroleum ether (1:99) af-
forded the desired product 8 (1.2 g, 95%) as a light yellow
solid. Mp 108-109 °C; spectroscopic data were consistent
with those reported previously23 for this compound; EI-MS
m/z C20H15Nþ 269.
Synthesis of 3-(4-(Diphenylamino)phenyl)propiolonitrile (9).
To a solution of compound 8 (800 mg, 2.9 mmol) dissolved at
-78 °C under nitrogen atmosphere in anhydrous THF (15.0
mL) was added n-BuLi (13.8 mmol, 5.0 mL of a 2.75 M solution
in hexane) dropwise. After 10 min of stirring at -78 °C, PhOCN
(1.3 g, 11 mmol) in THF (5.0 mL) was added slowly. The
solution was stirred for 30 min at -78 °C and warmed to room
temperature. The reaction mixture was quenched with brine and
extracted with ethyl acetate. The organic solution was washed
with water and brine, then dried over Mg2SO4. After removal of
the solvent under a reduced pressure, the residue was chroma-
tographed on SiO2 (eluent 1:50 ethyl acetate/petroleum ether) to
give 9 (800 mg, 90%) as a yellow solid. Mp 139-140 °C;
1H NMR (400 MHz, CDCl3) δ 6.92 (d, 2H, J = 8.8 Hz), 7.15
(m, 6H), 7.33 (m, 4H), 7.38 (d, 2H, J = 8.8 Hz); 13C NMR
(CDCl3, 100 MHz) δ 62.8, 84.6, 106.3, 107.9, 119.9, 125.2, 126.2,
1
C
32H19N5þ 473.1640, found 473.1643.
Synthesis of 3-(4-(Diphenylamino)phenyl)buta-1,3-diene-1,1,-
2,4,4-pentacarbonitrile (4). To a solution of compound 9 (800
mg, 2.72 mmol) in CH2Cl2 (40 mL) was added TCNE (350 mg,
2.73 mmol). The mixture was stirred for 48 h at room tempera-
ture. After evaporation of the solvent in vacuo, the residue was
chromatographed on SiO2 (eluent 1:4 petroleum/CH2Cl2) to
give a green product. The solid was dissolved in a minimal
amount of CH2Cl2, then n-hexane was added until precipitation
started. Crystallization at 0 °C afforded 4 (650 mg, 56%) as
a green solid. Mp 208-209 °C; 1HNMR (400 MHz, CDCl3) δ
6.96 (d, 2H, J = 9.2 Hz), 7.23 (d, 4H, J = 7.4 Hz), 7.31 (m, 2H),
7.43 (t, 4H, J = 7.4 Hz), 7.53 (d, 2H, J = 9.2 Hz); 13C NMR
(CDCl3, 100 MHz) δ 79.1, 105.3, 108.2, 108.9, 111.1, 112.3,
112.7, 118.4, 119.2, 127.1, 127.4, 130.4, 132.0, 138.6, 144.1,
þ
153.8, 154.9; EI-HR-MS m/z calcd for C27H14N6 422.1280,
found 422.1277.
Acknowledgment. This work is financially supported by
the National Natural Science Foundation of China (Grant
Nos. 60778033 and 20903110), the National High Technol-
ogy Research and Development Program of China (863
Program) (Grant No. 2008AA03A327), and the National
Basic Research Development Program of China (973 Program)
(Grant Nos. 2006CB933000 and 2009CB623703).
þ
129.9, 134.8, 146.1, 151.1; EI-HR-MS m/z calcd for C21H14N2
294.1157, found 294.1160.
Supporting Information Available: 1H NMR and 13C NMR
spectra for the new compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
(23) Onitsuka, K.; Ohara, N.; Takei, F.; Takahashi, S. Dalton Trans.
2006, 3693.
7278 J. Org. Chem. Vol. 75, No. 21, 2010