Facile Synthesis of 9,10,19,20-Tetraarylporphycenes

Article abstract of DOI:10.1002/ejoc.201402770

A simple route was developed for the synthesis of 9,10,19,20-tetraarylporphycenes by combining both McMurry and oxidative synthetic strategies and using readily available precursors. The desired 5,6-diaryldipyrroethenes, which were prepared in multigram quantities over two steps, were used to prepare 9,10,19,20-tetraarylporphycenes under mild acid-catalyzed conditions. As 5,6-diaryldipyrroethene precursors can easily be prepared in multigram quantities, this method is useful for the preparation of meso-tetrarylporphycenes that contain different aryl substituents. The molecular structures of these macrocycles were determined by HRMS analysis as well as 1D and 2D NMR studies. The tetraarylporphycenes exhibited a strong Soret band at approximately 380 nm and three Q bands in the region of 580-655 nm. The tetraarylprophycenes are reasonably fluorescent and stable under redox conditions. A simple, rapid method was developed for the synthesis of meso-tetraarylporphycenes by employing a McMurry coupling followed by an oxidation reaction as the key steps. This synthetic strategy uses readily available precursors to afford 9,10,19,20-tetraarylporphycenes. The absorption, fluorescence, and electrochemical properties of these macrocycles were also studied.

Full text of DOI:10.1002/ejoc.201402770

FULL PAPER
DOI: 10.1002/ejoc.201402770
Facile Synthesis of 9,10,19,20-Tetraarylporphycenes
Emandi Ganapathi,[a] Tamal Chatterjee,[a] and Mangalampalli Ravikanth*[a]
Keywords: Macrocycles / Nitrogen heterocycles / C–C coupling / Fluorescence / Electrochemistry
A simple route was developed for the synthesis of 9,10,19,20-
is useful for the preparation of meso-tetrarylporphycenes that
tetraarylporphycenes by combining both McMurry and oxi- contain different aryl substituents. The molecular structures
dative synthetic strategies and using readily available pre- of these macrocycles were determined by HRMS analysis as
cursors. The desired 5,6-diaryldipyrroethenes, which were
prepared in multigram quantities over two steps, were used
to prepare 9,10,19,20-tetraarylporphycenes under mild acid-
catalyzed conditions. As 5,6-diaryldipyrroethene precursors
can easily be prepared in multigram quantities, this method
well as 1D and 2D NMR studies. The tetraarylporphycenes
exhibited a strong Soret band at approximately 380 nm and
three Q bands in the region of 580–655 nm. The tetraaryl-
prophycenes are reasonably fluorescent and stable under
redox conditions.
pyrrole under McMurry coupling conditions followed
by oxidation.[2] A perusal of the literature reveals that por-
Introduction
Porphycene is a tetrapyrrolic planar 18π-electron aro- phycenes that contain alkyl substituents at the β-pyrrole
matic macrocycle, which consists of two 2,2Ј-bipyrrole sub- and meso carbon atoms were readily prepared by following
units that are linked by two double bonds.[1] Porphycene, the standard McMurry coupling strategy over a sequence
which was prepared by Vogel and co-workers in 1986,[2] is steps,[6] but there is no report available for the synthesis of
a constitutional isomer of porphyrin and possesses unique a porphycene that contains meso-aryl substituents by using
optical properties such as a strong absorption in the far red this strategy.
region of the visible spectrum,[1,3] which differentiates it
Srinivasan and co-workers[7] reported the first examples
from porphyrins. Because of these optical properties, por- of 9,10,19,20-tetraarylporphycenes by adopting a new syn-
phycenes have been examined as possible photosensitizers thetic method (see Scheme 1). They first prepared the ap-
for photodynamic therapy.[4] Porphycenes, like porphyrins, propriate benzoin or benzil compounds, which were then
are divalent and have a high tendency to form metal com- converted into 1,2-diphenylethane-1,2-diol through
a
plexes.[1] The synthetic approaches for porphycenes have NaBH4 reduction. The diol was treated with mesyl chloride
been well established in the literature and were reviewed by (MsCl) to give the mesylated product, which was then
Sessler and co-workers in 2008.[1] It has been shown that treated with pyrrole to obtain 5,6-diaryldipyrroethane.[7] In
substituents at the β-pyrrole[5] and meso positions can sig- the final step, the 5,6-diaryldipyrroethane was subjected to
nificantly modulate the physico-chemical properties of the an acid-catalyzed oxidative coupling by treatment with
porphycene macrocycle. In general, porphycenes have been para-toluenesulfonic acid (p-TSA) followed by an oxidation
prepared by the reductive dimerization of diformyl-2,2Ј-bi- by treatment with 2,3-dichloro-5,6-dicyano-para-benzo-
Scheme 1. Reported synthesis of 9,10,19,20-tetraarylporphycenes (TEA = triethylamine).
[a] Department of Chemistry, Indian Institute of Technology,
quinone (DDQ) to yield 9,10,19,20-tetraarylporphycene in
approximately 5% yield. By following this strategy, Sriniva-
san and co-workers[7] reported two examples of 9,10,19,20-
tetraarylporphycene derivatives. There are major draw-
Bombay, Powai, Mumbai 400076, India
E-mail: ravikanth@chem.iitb.ac.in
http://www.chem.iitb.ac.in/people/Faculty/prof/mr.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402770.
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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E. Ganapathi, T. Chatterjee, M. Ravikanth
FULL PAPER
backs, however, to this strategy. The synthesis of the key 8.05 ppm. There were also signals that corresponded to the
precursor 5,6-diaryldipyrroethane is one inconvenience, and meso-aryl protons. The dipyrroethenes showed one well-de-
the longer reaction times that are required for some reac- fined absorption band at approximately 350 nm, which had
tion steps also limit the versatility of this strategy for the a shoulder on the higher energy side. Compounds 13–18 are
preparation of the desired 9,10,19,20-tetraarylporphycenes. fluorescent in solution and in the solid state.
We have developed an alternate facile approach for the syn-
Single crystals of compounds 14 and 15 were obtained
thesis of 9,10,19,20-tetraarylporphycenes that combines by slow diffusion of an n-hexane into a chloroform solution
both McMurry and oxidative synthetic strategies and uses over a period of one week. Diaryldipyrroethenes 14 and 15
readily available precursors that can be easily prepared in crystallized into the monoclinic space group P21/c, and
multigram quantities. Our strategy involves three simple their crystallographic data are summarized in the Table 1.
steps, and the method is versatile for the synthesis of the The ORTEP plots of compounds 14 and 15 are presented in
desired 9,10,19,20-tetraarylporphycenes.
Figure 1. In these dipyrroethenes, we considered the double
bond between the two pyrrole rings as the mean plane and
the deviation of the two pyrrole nitrogen atoms from this
mean plane as approximately 0.85 Å. In both compounds
14 and 15, the dihedral angle between the meso-aryl rings
and double bond of the dipyrroethene is approximately
120°, and the dihedral angle between the pyrrole rings and
double bond of the dipyrroethene is approximately 125°.
Results and Discussion
The synthesis of the desired 9,10,19,20-tetraarylporphyc-
enes 1–6 was carried out in three steps by starting from
commercially available pyrrole and acid chlorides as shown
in Scheme 2. Pyrrole (1 equiv.) was benzoylated at the
2-position by treating it with 1 equiv. of the substituted
benzoyl chloride in CH2Cl2 in the presence of 1.2 equiv. of
AlCl3 at room temperature for 4 h followed by workup and
column chromatographic purification to afford benzoylated
pyrroles 7–12 as white solids in yields of 60–75%. The 2-
benzoylated pyrroles 7–12 were subjected to McMurry cou-
pling conditions in the presence of Zn-CuI/TiCl4 in tetra-
hydrofuran (THF), and the mixture was heated at reflux for
12 h. The progress of the reaction was followed by TLC
analysis, whereupon the crude reaction mixture showed a
less polar, new fluorescent spot and the disappearance of
the spot from the 2-benzoylated pyrrole. The crude com-
pounds were subjected to chromatography on a silica gel
column to afford pure 5,6-diaryldipyrroethenes 13–18 as
yellow fluorescent solids in yields of 44–54%. Dipyrroeth-
enes 13–18 were characterized by HRMS and NMR spec-
troscopy as well as by X-ray crystallography for compounds
14 and 15. The HRMS data for compounds 13–18 showed
a molecular ion peak that confirmed the composition of
Table 1. Crystallographic data for compounds 14 and 15.
Parameters
14
15
Formula
Mw
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C24H22N2
338.44
150
0.71073
monoclinic
P21/c
9.397(5)
20.072(5)
9.826(5)
90
C24H22N2O2
370.44
100
0.71075
monoclinic
P21/c
9.340(4)
19.040(7)
10.970(4)
90
β [°]
97.995(5)
90
1835.3(14)
4
0.072
1.225
97.836(6)
90
1932.6(13)
4
0.082
1.273
γ [°]
V [Å3]
Z
μ [mm–1]
ρcalcd. [gcm–3]
F(000)
720.0
784.0
2θ range [°]
e data
R1, wR2 [I Ͼ 2σ(I)]
R1, wR2 (all data)
Goodness-of-fit
Largest diff. peak/hole [eÅ–3]
2.03–25.00
3233
0.0491, 0.1341 0.0510, 0.1250
0.0551, 0.1466 0.0685, 0.1127
1.103
0.466/–0.281
3.89–25.36
3506
1
dipyrroethenes 13–18. In the H NMR spectra of 13–18,
the six protons of the two pyrrole rings appeared as three
sets of signals in the δ = 5.80–6.80 ppm region, and the
NH proton appeared as broad singlet at approximately δ =
0.963
0.196/–0.216
Scheme 2. Alternate method for the synthesis of 9,10,19,20-tetraarylporphycenes.
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Facile Synthesis of 9,10,19,20-Tetraarylporphycenes
The torsion angle between the two pyrrole units and the NOESY spectrum, the doublet at δ = 7.72 ppm, which we
two meso-aryl groups is 15° and 17°, respectively. Overall identified as the c-type meso-aryl protons showed an NOE
the molecule is significantly distorted.
correlation with the multiplet at δ = 7.38–7.36 ppm as well
as with the doublet at δ = 8.43 ppm. The multiplet at δ =
7.38–7.36 ppm was identfied as the d- and e-type protons
of the meso-aryl groups, and the doublet at δ = 8.43 ppm
was recognized as the b-type pyrrole protons. The b-type
pyrrole protons at δ = 8.43 ppm showed a cross-peak corre-
lation with the doublet at δ = 9.43 ppm, which we identified
as the a-type pyrrole protons. The broad signal at δ =
5.98 ppm was the result of the two inner NH protons. Thus,
the macrocycle had a very simple NMR spectrum. Further-
more, porphycene 1 was also characterized by crystal struc-
ture analysis, and the structure was identical with the pre-
viously reported[7] structure of porphycene 1 (see Figures
S46–S47 in Supporting Information).
Figure 1. Single-crystal X-ray structures of compounds 14 and 15:
(a) top view and (b) side view. In the side view, hydrogen atoms are
omitted for clarity.
In the final synthetic step, 5,6-diaryldipyrroethenes 13–
18 were subjected to a condensation reaction by using p-
TSA in CH2Cl2 at room temperature under nitrogen for
1.5 h followed by an oxidation by treatment with DDQ at
room temperature in air for 1 h. TLC analysis showed one
significant, rapidly moving red fluorescent spot under UV
light, which indicated the formation of the desired macro-
cycles. The crude compounds were purified by chromatog-
raphy on a silica gel column to afford the desired
9,10,19,20-tetraarylporphycenes 1–6 as purple solids in
yields of 4–7%. Porphycenes 1–6 were readily soluble in
common organic solvents, and their compositions were con-
firmed by HRMS analysis. The molecular structures of
compounds 1–6 were deduced by 1D and 2D NMR spec-
Figure 2. NOESY spectrum of compound 1.
1
troscopy. The signals of H NMR spectra were identified
by NOESY analysis as shown for compound 1 in Figure 2.
The signals in the NMR spectrum were assigned on the
basis of the integration values, coupling constants, and
Absorption, Fluorescence, and Electrochemical Properties
The properties of porphycenes 1–6 were studied by ab-
cross-peak correlations in the NOESY spectrum (see Fig- sorption, fluorescence, and electrochemical experiments.
1
ure 2). In the H NMR spectrum, the macrocycle showed The relevant data for the absorption and fluorescence prop-
only five sets of signals in the region of δ = 7.0 to 10.0 ppm, erties of 1–6 in CHCl3 are shown in Table 2, and the repre-
because of the symmetric nature of the molecule, and these sentative absorption and fluorescence spectra of porphy-
signals correlated with each other in NOESY spectrum. cene 1 are shown in Figure 3. Upon inspection of Figure 3
The doublets at δ = 9.43 and 8.43 ppm with a coupling and the data in Table 2, we found that meso-tetraarylpor-
constant of approximately 4.4 Hz were identified as the pyr- phycenes 1–6 generally show a strong Soret band at approx-
role protons, as these signals correlated with each other in imately 380 nm and three weak Q bands in the region of
the NOESY spectrum. The doublet at δ = 7.72 ppm with a 580–655 nm. Porphycenes 1–6 did not show any significant
coupling constant of 7.7 Hz and the multiplet at δ = 7.38– shifts to their peak maxima upon changing the meso-aryl
7.36 ppm were recognized as the meso-aryl protons. In the group. The fluorescence properties of porphycenes 1–6 were
Table 2. Photophysical data of compounds 1–6 (1ϫ10–6 m) recorded in CHCl3.
Soret band [nm][a]
Q bands [nm][a]
λem [nm]
Φf
τ [ns]
1
2
3
4
5
6
381 (5.1)
383 (5.0)
382 (5.0)
380 (4.9)
379 (4.9)
380 (5.0)
585 (4.1), 624 (4.3), 653 (4.4)
586 (4.2), 626 (4.4), 654 (4.5)
585 (4.1), 626 (4.3), 655 (4.5)
578 (4.0), 619 (4.2), 650 (4.4)
580 (4.0), 623 (4.2), 653 (4.3)
580 (4.1), 621 (4.3), 650 (4.4)
665, 724 (sh)
668, 725 (sh)
667, 724 (sh)
656, 716 (sh)
660, 720 (sh)
658, 717 (sh)
0.23
0.21
0.21
0.18
0.16
0.18
3.91
3.68
3.59
3.01
2.95
3.06
[a] Values in parentheses correspond to logε.
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E. Ganapathi, T. Chatterjee, M. Ravikanth
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studied by both steady-state and time-resolved fluorescence duction at –0.98 V. The redox potentials were sensitive to
techniques. Porphycenes 1–6 are reasonably fluorescent the nature of the substituent present in the meso-phenyl
with a strong fluorescence band at approximately 660 nm groups. However, compared to the isomer 5,10,15,20-
along with a shoulder band at approximately 720 nm. The tetraphenylporphyrin (H2TPP), porphycenes 1–6 are diffi-
quantum yields are dependent on the type of aryl substitu- cult to oxidize but much easier to reduce, which supports
ent present at the meso position. The quantum yields of the electron-deficient nature of porphycenes. The HOMO–
porphycenes 1–6 were in the range of 0.16–0.23. The fluo- LUMO gap of porphycenes 1–6 were in the range of 1.81–
rescence decays of porphycenes 1–6 were fitted to single ex- 1.87 eV, which is smaller than that of H2TPP (2.23 eV).
ponential decay, and the representative fluorescence decay Thus, electrochemical studies indicate that porphycenes 1–
profile for porphycene 1 in CHCl3 is shown in Figure 4. The 6 are highly stable under redox conditions.
lifetimes of the singlet state of porphycenes 1–6 were in the
range of 2.95–3.91 ns. The electrochemical properties of
porphycenes 1–6 were measured by cyclic voltammetry and
differential pulse voltammetry at a scan rate of 50 mVs–1
with tetrabutylammonium perchlorate (TBAP) as the sup-
porting electrolyte in CH2Cl2. The representative cyclic vol-
tammogram along with the differential pulse voltammog-
ram for porphycene 1 is shown in Figure 5, and the data
are presented in Table 3. All porphycenes 1–6 showed one
Figure 5. Overlay of cyclic voltammogram (thick line) and differen-
reversible oxidation, one reversible reduction, and one
quasi-reversible reduction. For example, porphycene 1
showed one reversible oxidation at 1.18 V, one reversible
reduction at –0.63 V, and the second quasi-reversible re-
tial pulse voltammogram (dotted line) of compound 1 recorded in
CH2Cl2 by using TBAP (0.1 m) as the supporting electrolyte at a
scan rate of 50 mVs–1.
Table 3. Electrochemical data of compounds 1–6 recorded in
CH2Cl2 containing TBAP (0.1 m) as the supporting electrolyte re-
corded at scan rate 50 mVs–1.
Oxidation
E1/2/V vs. SCE
II
Reduction
E1/2/V vs. SCE
I
II
HOMO–LUMO gap
Eox [V]
Ered [V] Ered [V]
ΔEred–ox [V]
1
2
3
4
5
6
1.18
1.28
1.29
1.29
1.30
1.41
1.03
–0.63
–0.59
–0.54
–0.52
–0.51
–0.46
–1.23
–0.98
–0.88
–0.84
–0.82
–0.80
–0.72
–1.55
1.81
1.87
1.83
1.81
1.81
1.87
2.26
Figure 3. Comparison of normalized absorption (thick line) and
emission (dotted line) spectra of tetraphenylporphycene
1
H2TPP
(1ϫ10–6 m) in CHCl3.
Conclusions
In summary, we synthesized the meso-tetraarylpor-
phycenes by using readily available precursors under simple
reaction conditions. This straightforward method allows for
the preparation of different types of meso-tetraarylpor-
phycenes and is complementary to the earlier reported ap-
proach. The meso-tetraraylporphycenes strongly absorb and
emit in the visible region and are stable under redox condi-
tions. The meso-tetraarylporphycenes have tremendous po-
tential for applications in various fields from materials to
medicine, and we are currently exploring the possibility to
prepare water soluble meso-tetraraylporphycenes.
Experimental Section
Figure 4. Fluorescence decay profile and the corresponding
weighted residual distribution fit for the fluorescence decay of
tetraphenylporphycene 1 in CHCl3. The employed excitation wave-
length was approximately 380 nm, and the emission was detected
at the emission peak maxima (655–665 nm) of tetraphenylpor-
phycene 1 in CHCl3.
General Methods: All chemicals that were used in the synthesis were
reagent grade, and solvents were dried by routine procedures imme-
diately before use. Column chromatography was performed on sil-
ica gel (60–120 mesh). The 1H and 13C NMR spectroscopic data
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Eur. J. Org. Chem. 2014, 6701–6706

Facile Synthesis of 9,10,19,20-Tetraarylporphycenes
were recorded by using CDCl3 as the solvent and tetramethylsilane
[Si(CH3)4] as the internal standard. The fluorescence quantum
yields (Φf) were estimated from the emission and absorption spec-
tra by using a comparative method at the excitation wavelength of
380 nm with tetraphenylporphycene[7] (Φf = 0.23) as the standard.
Cyclic voltammetric (CV) studies were carried out by using a three-
electrode configuration that consisted of glassy carbon (working
electrode), platinum wire (auxiliary electrode), and saturated calo-
mel (SCE, reference electrode) electrodes. The experiments were
done in dry CH2Cl2 with tetrabutylammonium perchlorate (0.1 m)
as the supporting electrolyte. Half-wave potentials were measured
by DPV (differential pulse voltammetry) and also calculated man-
ually by taking the average of the cathodic and anodic peak poten-
tials. All potentials were calibrated versus a saturated calomel elec-
trode by the addition of ferrocene (Fc) as an internal standard,
taking E1/2 (Fc/Fc+) = 0.42 V vs. SCE.[8] The HRMS spectra were
recorded by using ESI and a quadrupole analyzer.
311.1543; found 311.1551. C22H18N2 (310.40): calcd. C 85.13, H
5.85, N 9.03; found C 85.17, H 5.93, N 9.06.
1
Compound 14: (1.06 g, 54% yield). H NMR (400 MHz, CDCl3): δ
= 8.01 (br. s, 2 H, NH), 6.99 (d, J = 8.3 Hz, 4 H, Ar), 6.89 (d, J =
8.3 Hz, 4 H, Ar), 6.67 (dd, J = 3.8 Hz, J = 1.8 Hz, 2 H, Py), 6.17
(dd, J = 3.8 Hz, J = 1.8 Hz, 2 H, Py), 5.93 (dd, J = 3.9 Hz, J =
1.7 Hz, 2 H, Py), 2.46 (s, 6 H, CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 154.1, 137.7, 136.5, 133.1, 125.6, 119.3, 112.3, 108.8,
107.3, 36.4 ppm. HRMS: calcd. for C24H23N2 [M + 1]+ 339.1856;
found 339.1860. C24H22N2 (338.45): calcd. C 85.17, H 6.55, N 8.28;
found C 85.16, H 6.54, N 8.25.
1
Compound 15: (1.09 g, 51% yield). H NMR (400 MHz, CDCl3): δ
= 8.02 (br. s, 2 H, NH), 7.03 (d, J = 8.2 Hz, 4 H, Ar), 6.67 (dd, J
= 3.9 Hz, J = 1.5 Hz, 2 H, Py), 6.65 (d, J = 8.2 Hz, 4 H, Ar), 6.15
(dd, J = 3.9 Hz, J = 1.5 Hz, 2 H, Py), 5.94 (dd, J = 3.9 Hz, J =
1.6 Hz, 2 H, Py), 3.74 (s, 6 H, OCH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 158.2, 134.8, 133.6, 132.7, 128.4, 118.5, 113.1, 111.6,
108.9, 55.3 ppm. HRMS: calcd. for C24H22N2O2Na [M + Na]+
393.1573; found 393.1578. C24H22N2O2 (370.45): calcd. C 77.81, H
5.99, N 7.56; found C 77.87, H 6.04, N 7.61.
X-ray Crystallography Method: Single crystals of suitable size for
the X-ray diffractometer were selected under a microscope and
mounted on the tip of a glass fiber, which was positioned on a
copper pin. The X-ray crystal structure data for compounds 14
and 15 were collected with a Bruker Kappa CCD diffractometer,
employing graphite-monochromated Mo-Kα radiation at 200 K
and the θ – 2θ scan mode. The space groups for compounds 14
and 15 were determined on the basis of systematic absences and
intensity statistics, and the structures of compounds 14 and 15 were
solved by direct methods using SIR92 or SIR97 and refined with
SHELXL-97.[9] An empirical absorption correction by multi-scans
was applied. All non-hydrogen atoms were refined by anisotropic
displacement factors. Hydrogen atoms were placed in ideal posi-
tions and fixed by relative isotropic displacement parameters.
1
Compound 16: (1.02 g, 44% yield). H NMR (400 MHz, CDCl3): δ
= 8.04 (br. s, 2 H, NH), 7.05 (d, J = 7.5 Hz, 4 H, Ar), 6.89 (d, J =
7.4 Hz, 4 H, Ar), 6.59 (dd, J = 4.2 Hz, J = 1.8 Hz, 2 H, Py), 6.15
(dd, J = 4.2 Hz, J = 1.8 Hz, 2 H, Py), 5.92 (dd, J = 4.1 Hz, J =
1.6 Hz, 2 H, Py) ppm. 13C NMR (100 MHz, CDCl3): δ = 138.57,
133.4, 131.9, 131.1, 130.2, 129.9, 129.1, 128.5, 128.3, 126.2, 120.3,
111.0 ppm. HRMS: calcd. for C22H17N4O4 [M + 1]+ 401.1253;
found 401.1249. C22H16N4O4 (400.39): calcd. C 66.00, H 4.03, N
13.99; found C 66.09, H 4.12, N 14.06.
1
Compound 17: (1.21 g, 45% yield). H NMR (400 MHz, CDCl3): δ
= 8.08 (br. s, 2 H, NH), 7.13 (d, J = 7.8 Hz, 4 H, Ar), 6.95 (d, J =
7.8 Hz, 4 H, Ar), 6.69 (dd, J = 3.8 Hz, J = 1.7 Hz, 2 H, Py), 6.13
(dd, J = 3.8 Hz, J = 1.7 Hz, 2 H, Py), 5.82 (dd, J = 3.9 Hz, J =
1.8 Hz, 2 H, Py) ppm. 13C NMR (100 MHz, CDCl3): δ = 137.2,
132.5, 132.0, 131.7, 130.9, 130.7, 126.8, 126.3, 120.1, 111.3 ppm.
CCDC-990254 (for 15) and -990255 (for 14) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
HRMS: calcd. for C22H17N2Br2 [M
+
1]+ 469.9811; found
General Method for the Synthesis of 5,6-Diaryldipyrroethenes 13–
18: Activated zinc powder (35.1 mmol) and copper(I) chloride
(1.16 mmol) in THF (80 mL) were combined in a three-neck round-
bottomed flask, and the system was purged with nitrogen for
10 min. The mixture was cooled to 0 °C, and TiCl4 (17.55 mmol)
was slowly added as the temperature was maintained at 0 °C. The
suspension was warmed to room temperature, stirred for 30 min,
and then heated at reflux for 3 h. The mixture was once again
cooled to 0 °C, and a solution of the appropriate 2-arylated pyrrole
7–12 (5.85 mmol) in THF (25 mL) was added slowly. The reaction
mixture was heated at reflux for 12 h until the starting material was
completely consumed, as monitored by TLC analysis. The reaction
mixture was quenched by the addition of a 10% aqueous NaHCO3
solution, and the resulting mixture was extracted with diethyl ether.
The combined organic layers were dried with anhydrous Na2SO4
and concentrated by using a rotary evaporator under vacuum. The
crude compound was purified by chromatography on a silica gel
column (petroleum ether/ethyl acetate) to afford the desired 5,6-
diaryldipyrroethene 13–18 as a light green solid.
469.9807. C22H16Br2N2 (468.19): calcd. C 56.44, H 3.44, N 5.98;
found C 56.40, H 3.38, N 5.90.
1
Compound 18: (0.96 g, 48% yield). H NMR (400 MHz, CDCl3): δ
= 8.10 (br. s, 2 H, NH), 7.45 (d, J = 8.1 Hz, 2 H, Ar), 7.33 (d, J =
8.0 Hz, 2 H, Ar), 7.24 (dd, J = 8.1 Hz, J = 1.9 Hz, 2 H, Ar), 7.04
(dd, J = 8.1 Hz, J = 1.8 Hz, 2 H, Ar), 6.70 (d, J = 4.1 Hz, 2 H, Py),
6.18 (d, J = 4.1 Hz, 2 H, Py), 5.92 (d, J = 4.0 Hz, 2 H, Py) ppm. 13
C
NMR (100 MHz, CDCl3): δ = 140.6, 104.5, 130.9, 130.2, 130.1,
128.3, 124.9, 120.2, 119.0, 118.9, 116.1, 115.9, 111.5 ppm. HRMS:
calcd. for C22H17N2F2 [M + 1]+ 348.1432; found 348.1438.
C22H16F2N2 (346.38): calcd. C 76.29, H 4.66, N 8.09; found C
76.33, H 4.70, N 8.15.
General Procedure for the Synthesis of Tetraarylporphycenes 1–6:
5,6-Diaryldipyrroethene 13–18 (0.65 mmol) was dissolved in dry
dichloromethane (300 mL) in a 500 mL one-neck round-bottomed
flask, and the mixture was stirred under nitrogen for 15 min. The
condensation reaction was initiated by the addition of a catalytic
amount of p-TSA (0.13 mmol), and the reaction mixture was
stirred at room temperature for 1.5 h under nitrogen. DDQ
(0.65 mmol) was added, and the mixture was stirred at room tem-
perature for an additional 1 h in the air. The solvent was removed
1
Compound 13: (0.94 g, 52% yield). H NMR (400 MHz, CDCl3): δ
= 8.09 (br. s, 2 H, NH), 7.09–7.07 (m, 6 H, Ar), 6.93 (d, J = 7.9 Hz,
4 H, Ar), 6.72 [dd, J = 4.1 Hz, J = 1.6 Hz, 2 H, Py (pyrrole)], 6.19
(dd, J = 4.1 Hz, J = 1.6 Hz, 2 H, Py), 5.95 (dd, J = 4.0 Hz, J = under reduced pressure, and the resulting crude compound was
1.5 Hz, 2 H, Py) ppm. 13C NMR (100 MHz, CDCl3): δ = 141.6, purified by chromatography on a silica gel column (petroleum
133.1, 131.5, 130.8, 129.6, 129.3, 128.1, 127.6, 126.7, 126.3, 111.9,
ether/ dichloromethane, 90:10) to afford the desired tetraaryl-
110.4, 109.8, 106.6 ppm. HRMS: calcd. for C22H19N2 [M + 1]+ porphycene 1–6 as a purple solid in a yield of 5–7%.
Eur. J. Org. Chem. 2014, 6701–6706
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6705

E. Ganapathi, T. Chatterjee, M. Ravikanth
Compound 1: (27 mg, 7% yield). 1H NMR (400 MHz, CDCl3): δ = NMR for all the compounds, and spectral and electrochemical data
FULL PAPER
9.43 (d, J = 4.4 Hz, 4 H, Py), 8.43 (d, J = 4.4 Hz, 4 H, Py), 7.72
(d, J = 7.7 Hz, 8 H, Ph), 7.38–7.36 (m, 12 H, Ph), 5.98 (br. s, 2 H,
NH) ppm. 13C NMR (100 MHz, CDCl3): δ = 142.3, 134.7, 127.8,
126.8, 120.2 ppm. UV/Vis (CHCl3): λmax [log(ε/m–1 cm–1)] = 381
[5.1], 585 [4.1], 624 [4.3], 653 [4.4] nm; λem = 665, 724 (sh) nm.
HRMS: calcd. for C44H31N4 [M + 1]+ 615.2543; found 615.2537.
C44H30N4 (614.75): calcd. C 85.97, H 4.92, N 9.11; found C 85.92,
H 4.88, N 9.05.
for selected compounds.
Acknowledgments
The authors thank the Department of Science and Technology
(DST), New Delhi for financial support. E. G. thanks the Univer-
sity Grants Commission (UGC), New Delhi for a fellowship.
Compound 2: (26 mg, 6% yield). 1H NMR (400 MHz, CDCl3): δ =
9.42 (d, J = 4.4 Hz, 4 H, Py), 8.44 (d, J = 4.3 Hz, 4 H, Py), 7.61
(d, J = 7.8 Hz, 8 H, Ar), 7.21 (d, J = 7.8 Hz, 8 H, Ar), 6.12 (br. s,
2 H, NH), 2.53 (s, 12 H, CH3) ppm. 13C NMR (100 MHz, CDCl3):
δ = 139.5, 137.4, 134.7, 127.5, 120.2, 29.8 ppm. UV/Vis (CHCl3):
λmax [log(ε/m–1 cm–1)] = 383 [5.0], 586 [4.2], 626 [4.4], 654 [4.5] nm;
λem = 668, 725 (sh) nm. HRMS: calcd. for C48H39N4 [M + 1]+
671.3169; found 671.3172. C48H38N4 (670.86): calcd. C 85.94, H
5.71, N 8.35; found C 85.99, H 5.75, N 8.38.
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Compound 3: (28 mg, 6% yield). 1H NMR (400 MHz, CDCl3): δ =
9.42 (d, J = 4.5 Hz, 4 H, Py), 8.43 (d, J = 4.5 Hz, 4 H, Py), 7.72
(d, J = 7.6 Hz, 8 H, Ar), 7.15 (d, J = 7.6 Hz, 8 H, Ar), 5.99 (br. s,
2 H, NH), 3.90 (s, 12 H, OCH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 144.7, 135.7, 135.1, 132.1, 124.8, 117.8, 55.4 ppm. UV/
Vis (CHCl3): λmax [log(ε/m–1 cm–1)] = 382 [5.0], 585 [4.1], 624 [4.3],
655 [4.5] nm; λem
= 667, 724 (sh) nm. HRMS: calcd. for
C48H39N4O4 [M + 1]+ 735.2978; found 735.2971. C48H38N4O4
(734.85): calcd. C 78.45, H 5.21, N 7.62; found C 78.49, H 5.26, N
7.69.
Compound 4: (26 mg, 5% yield). 1H NMR (400 MHz, CDCl3): δ =
9.48 (d, J = 4.1 Hz, 4 H, Py), 8.48 (d, J = 4.1 Hz, 4 H, Py), 7.61
(d, J = 8.1 Hz, 8 H, Ar), 7.14 (d, J = 8.1 Hz, 8 H, Ar), 5.82
(br. s, 2 H, NH) ppm. 13C NMR (100 MHz, CDCl3): δ =
141.3, 138.0, 134.4, 128.9, 125.5, 117.7 ppm. UV/Vis (CHCl3): λmax
[log(ε/m–1 cm–1)] = 380 [4.9], 578 [4.0], 619 [4.2], 650 [4.4] nm; λem
= 656, 716 (sh) nm. HRMS: calcd. for C44H27N8O8 [M + 1]+
795.1945; found 795.193. C44H26N8O8 (794.74): calcd. C 66.50, H
3.30, N 14.10; found C 66.42, H 3.20, N 14.07.
Compound 5: (30 mg, 5% yield). 1H NMR (400 MHz, CDCl3): δ =
9.43 (d, J = 3.9 Hz, 4 H, Py), 8.40 (d, J = 3.9 Hz, 4 H, Py), 7.70
(d, J = 7.8 Hz, 8 H, Ar), 7.16 (d, J = 7.9 Hz, 8 H, Ar), 5.93
(br. s, 2 H, NH) ppm. 13C NMR (100 MHz, CDCl3): δ =
141.8, 139.0, 136.5, 127.7, 124.8, 123.9 ppm. UV/Vis (CHCl3): λmax
[log(ε/m–1 cm–1)] = 379 [4.9], 580 [4.0], 623 [4.2], 653 [4.3] nm; λem
= 660, 720 (sh) nm. HRMS: calcd. for C44H27N4Br4 [M + 1]+
930.8926; found 930.8916. C44H26Br4N4 (930.33): calcd. C 56.81,
H 2.82, N 6.02; found C 56.90, H 2.93, N 6.10.
Compound 6: (27 mg, 6% yield). 1H NMR (400 MHz, CDCl3): δ =
9.48 (d, J = 4.2 Hz, 4 H, Py), 8.49 (d, J = 4.2 Hz, 4 H, Py),
7.55–7.32 (m, 12 H, Ar), 7.16–7.14 (m, 4 H, Ar), 5.82 (br. s, 2 H,
NH) ppm. 13C NMR (100 MHz, CDCl3): δ = 143.4, 141.1,
135.9, 135.1, 129.2, 127.9, 127.3, 117.8 ppm. UV/Vis (CHCl3): λmax
[log(ε/m–1 cm–1)] = 380 [5.0], 580 [4.1], 621 [4.3], 650 [4.4] nm; λem
= 658, 717 (sh) nm. HRMS: calcd. for C44H27N4F4 [M + 1]+
687.2166; found 687.2159. C44H26F4N4 (686.71): calcd. C 76.96, H
3.82, N 8.16; found C 76.90, H 3.77, N 8.09.
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1997.
Supporting Information (see footnote on the first page of this arti-
Received: June 23, 2014
Published Online: September 5, 2014
cle): The characterization data including HR-MS, 1H NMR, 13C
6706
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Eur. J. Org. Chem. 2014, 6701–6706