Core-modified phthalocyanine analogues with a seven-membered ring unit in place of a five-membered ring unit

Article abstract of DOI:10.1016/j.tetlet.2011.11.092

A variety of phthalocyanine analogues with a seven-membered ring unit in place of a five-membered ring unit were synthesized from aromatic dicarbonitriles bearing cyano groups at 1,4-separate positions. Based on the spectroscopic analyses and theoretical

Full text of DOI:10.1016/j.tetlet.2011.11.092

Tetrahedron Letters 53 (2012) 579–581
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Core-modified phthalocyanine analogues with a seven-membered ring unit
in place of a five-membered ring unit
⇑
⇑
Soji Shimizu , Kaoru Uemura, Hua Zhu, Nagao Kobayashi
Department of Chemistry, Graduate School of Science, Tohoku University, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A variety of phthalocyanine analogues with a seven-membered ring unit in place of a five-membered ring
unit were synthesized from aromatic dicarbonitriles bearing cyano groups at 1,4-separate positions.
Based on the spectroscopic analyses and theoretical calculations, tetraazachlorine-like electronic struc-
tures of these novel compounds stemming from severe twist of the conjugation system at the seven-
membered ring unit have been revealed.
Received 25 October 2011
Revised 17 November 2011
Accepted 18 November 2011
Available online 26 November 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Phthalocyanine
Electronic absorption
Magnetic circular dichroism
Aromaticity
Phthalocyanine 1 has been broadly utilized as blue and green
dyes and pigments, and has recently attracted much attention as
functional molecules in a variety of areas of photo-energy conver-
sion and molecular electronics because of their intense absorption
4,5-Phenanthrenedicarbonitrile 4 and 2,20-bipyridyl-3,30-dicar-
bonitrile 5 were synthesized according to the literature proce-
dures.8,9 Mixed-condensation reactions of these nitriles with
4,5-di-p-tert-butylphenyloxyphthalonitrile in the presence of
nickel acetate and ammonium molybdate in quinoline at 330 °C
provided core-modified analogues with a seven-membered ring
unit (7 and 8) in 1.7% and 2.1% yields, respectively, together with
phthalocyanine 6 (Scheme 1).10,11 The HR-ESI-MS exhibits molecu-
lar ion peaks and theoretical distribution patterns corresponding to
of the UV/vis light and planar macrocyclic 18p-conjugation sys-
tems.1,2 Core-modification, that is replacement of isoindole units
with other hetero-aromatic ring units, is a potentially promising
modification method, but has been rarely investigated mainly
due to synthetic difficulties.3 Recently we succeeded in the synthe-
ses of core-modified phthalocyanine analogues with six- or seven-
membered ring units in place of five-membered ring units of the
isoindole moieties (Chart 1) by using aromatic dicarbonitriles,
which possess cyano groups at 1,3- or 1,4-separate positions, and
significant changes of their electronic structures from those of reg-
ular phthalocyanines were also revealed.4,5 The absorption spectra
and electrochemical analyses revealed that the electronic structure
of 2 is typical of low-symmetrically benzene-fused phthalocya-
nines,6 whereas 3 exhibits a rather tetraazachlorine-like electronic
structure7 due to an unusual twist of the structure at the seven-
membered ring unit. Among these core-modified phthalocyanine
analogues, the unique electronic structure of 3 has motivated us
to change the external ring unit from a biphenyl unit to a phenan-
threne unit or a bipyridine unit by using 4,5-phenanthrenedicarbo-
nitrile 4 or 2,20-bipyridyl-3,30-dicarbonitrile 5 in order to obtain
insight into the effects of peripheral conjugation or external coor-
dination on the electronic structures of 3.
the structures of
C
C
7
and
100H93N8NiO6 = 1559.6572 [M++H], 8: m/z = 1559.6290, calcd for
96H90N10NiO6Na = 1559.6296 [M++Na]). The 1H NMR spectrum
-benzo proton peaks as a singlet at 8.45,
8 (7: m/z = 1559.6566, calcd for
of 7 in CD2Cl2 exhibits
a
8.38, and 8.06 ppm and phenanthrene proton peaks at 8.01 (dou-
blet), 7.90 (singlet), 7.58 (triplet), and 6.84 (doublet) ppm. This
peak pattern reflects a twofold molecular symmetry of 7. A similar
twofold molecular symmetry of 8 was also inferred from the 1H
NMR spectrum of 8 in CD2Cl2, which exhibits three
a-benzo pro-
tons peaks at 8.37, 8.09, and 7.98 ppm and three bipyridyl proton
⇑
Corresponding authors. Tel./fax: +81 22 795 7719.
E-mail addresses: ssoji@m.tohoku.ac.jp (S. Shimizu), nagaok@m.tohoku.ac.jp (N.
Kobayashi).
Chart 1. Phthalocyanine and core-modified phthalocyanine analogues.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.11.092

580
S. Shimizu et al. / Tetrahedron Letters 53 (2012) 579–581
Scheme 1. Syntheses of phthalocyanine analogues bearing a seven-membered ring unit (7 and 8).
peaks at 8.83 and 7.22 ppm with the integration ratio of 1:2. The
significant up-field shift of the 3- and 6-phenanthrene protons
and the 4- and 40-bipyridyl protons from the corresponding proton
peaks of 4 and 5 is indicative of twisted conformations for 7 and 8,
in which hydrogen atoms at these positions lie above and below
for 8. Similar potential differences between the first oxidation
and reduction (1.48 V for 7 and 1.52 V for 8) are consistent with
the similar Q band energies of these compounds. The negative
shifts of the redox potentials of 7 from those of 35 and 8 can be
interpreted in terms of destabilization of both the HOMO and
LUMO of 7 upon fusion of a benzene ring to the structure of 3.
Optimized structures of 7 and 8 based on DFT calculations at
B3LYP/6–31G(d) level exhibit significant twist of these molecules
at the seven-membered ring units, which is in good agreement
with the proposed conformations from the NMR measurements.
Dihedral angles between the phenanthrene and bipyridyl moieties
from the rest of the molecules are 72° and 77°, respectively,
whereas the torsion angles of these moieties are 18° for 7 and
37° for 8 (Fig. 2). Almost perpendicular orientation of the seven-
membered ring units in 7 and 8 can rationalize very small MO coef-
ficients at the seven-membered ring units in the frontier orbitals
(Fig. 3), which can also be observed in the case of 3.5 The slightly
higher energies of the frontier MOs in 7 compared to those of 3
and 8 well reproduce the observed negative shift of the redox
potentials of this compound in the cyclic voltammetry measure-
ments. As a result of the lowering of the molecular symmetry
and changes in the main conjugation pathway from phthalocya-
nines, both compounds exhibit a large energy difference between
the LUMO and LUMO+1. Time-dependent (TD) DFT calculations
on 7 and 8 at B3LYP/6–31G(d) level, thus, predict split theoretical
Q bands comprising transitions from the HOMO to the LUMO and
the LUMO+1 at 698 and 594 nm for 7 and at 700 and 597 nm for
8 (Table 1). These theoretical absorption spectra are in good agree-
ment with the observed electronic absorption and MCD spectra.
The peripheral bipyridyl moiety in 8 can be used as an outer
coordination site for transition metals to provide metal-linked di-
mer or trimer systems.13 A preliminary study using a ruthenium
the macrocyclic 18p-conjugation systems.
Compounds 7 and 8 exhibit similar split Q bands in the longer
and shorter wavelength regions compared to the single Q band
of phthalocyanine 6 at 675 nm (791 and 618 nm for 7 and 791
and 624 nm for 8, Fig. 1). The shapes of these absorption spectra
are also similar to that of 3.5 Corresponding to the split Q bands,
Faraday B terms at 819 (minus) and 619 (plus) nm for 7 and at
820 (minus) and 624 (plus) nm for 8 are observed in the magnetic
circular dichroism (MCD) spectra, which is indicative of the pres-
ence of non-degenerate excited states of 7 and 8 and a larger en-
ergy difference of the frontier HOMOs than that of the frontier
LUMOs.12 These electronic absorption and MCD spectral features
suggest tetrazachlorine-like electronic structures for 7 and 8.7
The cyclic voltammograms reveal one reversible oxidation at
0.08 V for 7 and 0.27 V for 8 (vs Fc+/Fc) and two reversible reduc-
tions at ꢀ1.40 V and ꢀ1.78 V for 7 and at ꢀ1.25 V and ꢀ1.65 V
Figure 1. Absorption (bottom) and MCD (top) spectra of 7 (black line) and 8 (blue
line) in CHCl3.
Figure 2. Optimized structures of 7 (left) and 8 (right) (B3LYP/6–31G(d)).

S. Shimizu et al. / Tetrahedron Letters 53 (2012) 579–581
581
ming from their tetraazachlorine-like electronic structures. The
peripheral coordination site of 8 can potentially be used to con-
struct coordination oligomers without changing the spectroscopic
properties, and research along this direction is currently being
investigated.
Acknowledgments
This work was partly supported by a Grant-in-Aid for Scientific
Research (C) (No. 23550040) and (B) (No. 23350095) from Japan
Society for the Promotion of Science (JSPS) and a Grant-in-Aid for
Scientific Research on Innovative Areas (No. 20108007, ‘pi-Space’)
from the Ministry of Education, Culture, Sports, Science, and Tech-
nology (MEXT).
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.11.092.
References and notes
Figure 3. Partial molecular orbital diagrams of 7 (left) and 8 (right) (B3LYP/6–
31G(d) level).
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3. Fernandez-Lazaro, F.; Torres, T.; Hauschel, B.; Hanack, M. Chem. Rev. 1998, 98,
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Table 1
Selected transition energies and wave functions of 7 and 8 based on the TDDFT
method (B3LYP/6–31G(d))
4. (a) Shimizu, S.; Zhu, H.; Kobayashi, N. Chem. Eur. J. 2010, 16, 11151; (b) Zhu, H.;
Shimizu, S.; Kobayashi, N. Angew. Chem., Int. Ed. 2010, 49, 8000.
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b
Compd Energy
(nm)
fa
Wave function
7
698
594
0.32 +0.594|173 172> +0.122|174 166> +. . .
0.24 +0.583|174 172> ꢀ0.122|173 166>
+0.142|175 172> +0.110|177 172> +. . .
0.32 +0.593|167 166> +0.105|168 161> +. . .
0.24 +0.588|168 166> +0.105|169 165>
+0.172|169 166> +. . .
8
700
597
8. Ege, G.; Beisiege, E. Synthesis 1974, 22.
a
Oscillator strength.
9. Baxter, P. N. W.; Connor, J. A.; Povey, D. C.; Wallis, J. D. J. Chem. Soc., Chem.
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b
Wave functions based on the eigenvectors predicted by TDDFT. The |172> and
|166> represent the HOMO of 7 and 8, respectively. Eigenvectors greater than 0.10
10. Selected data for 7. 1H NMR (600 MHz, CD2Cl2, 298 K): d = 8.45 (s, 2H;
a
-benzo),
8.38 (s, 2H;
a-benzo), 8.06 (s, 2H; a-benzo), 8.01 (d, J = 7.2 Hz, 2H; phenan
are included.
threne), 7.90 (s, 2H; phenanthrene), 7.58 (t, J = 7.8 Hz, 2H; phenanthrene), 7.36
(m, 8H; phenyloxy), 7.27 (d, J = 9.0 Hz, 4H; phenyloxy), 7.02 (m, 8H;
phenyloxy), 6.98 (d, J = 9.0 Hz, 4H; phenyloxy), 6.84 (d, J = 6.0 Hz, 2H;
phenanthrene), 1.33 (s, 18H; t-butyl), 1.32 (s, 18H; t-butyl), and 1.24 ppm (s,
ion has revealed the formation of a trimer system based on MALDI-
TOF-MS. Although coordination of the ruthenium ion reduces the
torsion angle of the bipyridyl moiety, significant changes in the
absorption spectra were not observed (see Supplementary data),
which can be rationalized from the fact that 7 and 8, which have
different torsion angles, still exhibit similar spectral features.
In summary, two novel core-modified phthalocyanine ana-
logues with a seven-membered ring unit were successfully synthe-
sized from aromatic dicarbonitriles bearing cyano groups at 1,
4-separate positions. In spite of the difference in the peripheral
ring units and the torsion angles of these moieties, all the com-
pounds exhibit similar spectral and electrochemical features stem-
18H; t-butyl); UV/vis (CHCl3): kmax [nm] (e) = 309 (43000), 353 (33000), 618
(41000), and 791 (47000 Mꢀ1 cmꢀ1); HR-ESI-TOF-MS: m/z (%): 1559.6566
(100); Calcd for C100H93N8O6Ni [M++H]; 1559.6572.
11. Selected data for 8: 1H NMR (600 MHz, CD2Cl2, 298 K): d = 8.83 (br s, 2H;
pyridyl), 8.37 (s, 2H;
a-benzo), 8.09 (s, 2H; a-benzo), 7.98 (s, 2H; a-benzo),
7.36 (d, J = 8.4 Hz, 4H; phenyloxy), 7.31 (m, 8H; phenyloxy), 7.22 (m, 4H;
pyridyl), 7.10 (d, J = 8.4 Hz, 4H; phenyloxy), 7.06 (d, J = 9.0 Hz, 4H; phenyloxy),
6.88 (d, J = 7.8 Hz, 4H; phenyloxy), 1.33 (s, 18H; t-butyl), 1.31 (s, 18H; t-butyl),
and 1.28 ppm (s, 18H; t-butyl); UV/vis (CHCl3): kmax [nm] (e) = 354 (37000),
623 (41000), and 791 (51000 Mꢀ1 cmꢀ1); HR-ESI-TOF-MS: m/z (%): 1559.6290
(100); Calcd for C96H90N10O6NiNa [M++Na]; 1559.6296.
12. Mack, J.; Stillman, M. J.; Kobayashi, N. Coord. Chem. Rev. 2007, 251, 429.
13. Okujima, T.; Mifuji, A.; Nakamura, J.; Yamada, H.; Uno, H.; Ono, N. Org. Lett.
2009, 11, 4088.