Hexaazaphenalene derivatives: One-pot synthesis, hydrogen-bonded chiral helix, and fluorescence properties

Article abstract of DOI:10.1021/ol102200v

Symmetric hexaazaphenalenes (R = phenyl and tert-butyl) have been synthesized by one-pot condensations of corresponding amidine hydrochlorides with tricyanomethanide. The hexaazaphenalenes are linked with each other by a N-H???N hydrogen-bonding interaction in the crystalline states. Interestingly, a planar and achiral tert-butylated derivative was crystallized in a chiral space group with assembly of one-handed helical hydrogen-bonded chains. Hexaazaphenalenyl anions were isolated as air- and water-stable tetraethyl ammonium salts.

Full text of DOI:10.1021/ol102200v

ORGANIC
LETTERS
2010
Vol. 12, No. 21
5036-5039
Hexaazaphenalene Derivatives: One-Pot
Synthesis, Hydrogen-Bonded Chiral
Helix, and Fluorescence Properties
Shuichi Suzuki,†,‡ Kozo Fukui,‡ Akira Fuyuhiro,† Kazunobu Sato,‡ Takeji Takui,‡
Kazuhiro Nakasuji,† and Yasushi Morita*,†
Department of Chemistry, Graduate School of Science, Osaka UniVersity, Toyonaka,
Osaka 560-0043, Japan, and Department of Chemistry, Graduate School of Science,
Osaka City UniVersity, Sumiyoshi-ku, Osaka 558-8585, Japan
morita@chem.sci.osaka-u.ac.jp
Received September 14, 2010
ABSTRACT
Symmetric hexaazaphenalenes (R ) phenyl and tert-butyl) have been synthesized by one-pot condensations of corresponding amidine
hydrochlorides with tricyanomethanide. The hexaazaphenalenes are linked with each other by a N-H···N hydrogen-bonding interaction in the
crystalline states. Interestingly, a planar and achiral tert-butylated derivative was crystallized in a chiral space group with assembly of one-
handed helical hydrogen-bonded chains. Hexaazaphenalenyl anions were isolated as air- and water-stable tetraethyl ammonium salts.
Recently, phenalenyl 11,2 has attracted great attention as a
basic molecular system for creating functional materials with
high conductivity,3 two photon absorption,4 ambipolar field-
effect transistor (FET) properties,5 as well as electrode-active
properties in the secondary battery.6 Furthermore, incorpora-
tion of nitrogen atoms into the phenalenyl skeleton affords
an azaphenalenyl system and has a substantial effect on its
electronic structure, providing new spin-delocalized radi-
cals,7-9 metal complex ligands,10 and hydrogen-bonded (H-
bonded) electron-donor molecules.11
† Osaka University.
‡ Osaka City University.
(1) (a) Reid, D. H. Chem. Ind. (London) 1956, 1504–1505. (b) Pettit,
R. Chem. Ind. (London) 1956, 1306–1307. (c) Pettit, R. J. Am. Chem. Soc.
1960, 82, 1972–1975. (d) Reid, D. H. Quart. ReV. 1965, 19, 274–302. (e)
Suzuki, S.; Morita, Y.; Fukui, K.; Sato, K.; Shiomi, D.; Takui, T.; Nakasuji,
K. J. Am. Chem. Soc. 2006, 128, 2530–2531. (f) Nishida, S.; Morita, Y.;
Ueda, A.; Kobayashi, T.; Fukui, K.; Ogasawara, K.; Sato, K.; Takui, T.;
(5) Chikamatsu, M.; Mikami, T.; Chisaka, J.; Yoshida, Y.; Azumi, R.;
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2007, 91, 043506.
Nakasuji, K. J. Am. Chem. Soc. 2008, 130, 14954–14955
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(2) Recent overview of the phealenyl chemistry: Morita, Y.; Nishida,
S. Phenalenyls, Cyclopentadienyls, and Other Carbon-Centered Radicals.
In Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron
Compounds; Hicks, R., Ed.; John Wiley & Sons Ltd.: West Sussex, 2010;
Chapter 3, pp 81-145.
(6) (a) Morita, Y.; Nishida, S.; Kawai, J.; Fukui, K.; Nakazawa, S.; Sato,
K.; Shiomi, D.; Takui, T.; Nakasuji, K. Org. Lett. 2002, 4, 1985–1988. (b)
Morita, Y.; Nishida, S.; Kawai, J.; Takui, T.; Nakasuji, K. Pure Appl. Chem.
2008, 80, 507–517. (c) Morita, Y.; Okafuji, T.; Sato, M. Jpn. Kokai Tokkyo
Koho JP 2007-227186 A 20070906, 2007.
(3) (a) Pal, S. K.; Itkis, M. E.; Tham, F. S.; Reed, R. W.; Oakley, R. T.;
Haddon, R. C. Science 2005, 309, 281–284. (b) Kubo, T.; Goto, Y.; Uruichi,
M.; Yakushi, K.; Nakano, M.; Fuyuhiro, A.; Morita, Y.; Nakasuji, K. Chem.
Asian J. 2007, 2, 1370–1379.
(7) Morita, Y.; Aoki, T.; Fukui, K.; Nakazawa, S.; Tamaki, K.; Suzuki,
S.; Fuyuhiro, A.; Yamamoto, K.; Sato, K.; Shiomi, D.; Naito, A.; Takui,
T.; Nakasuji, K. Angew. Chem., Int. Ed. 2002, 41, 1793–1796
.
(8) Morita, Y.; Suzuki, S.; Fukui, K.; Nakazawa, S.; Kitagawa, H.;
Kishida, H.; Okamoto, H.; Naito, A.; Sekine, A.; Ohashi, Y.; Shiro, M.;
Sasaki, K.; Shiomi, D.; Sato, K.; Takui, T.; Nakasuji, K. Nat. Mater. 2008,
(4) Kubo, T.; Shimizu, A.; Sakamoto, M.; Uruichi, M.; Yakushi, K.;
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10.1021/ol102200v  2010 American Chemical Society
Published on Web 10/08/2010

The phenalenyl radical derivatives form unique dimer
structures, π- or σ-dimers, in the crystalline states and even
in a solution state.1e,2,12 Thus, the azaphenalenyl radicals give
an intriguing opportunity to discuss bonding interactions in
the aggregate states from both experimental and theoretical
sides.2,12 Hexaazaphenalenyl (HAP) 2 is a highly symmetric
heterocycle with a six-nitrogen incorporation in all R-sites
of the phenalenyl system, which possesses a unique direc-
tionality of the lone-pair electrons at six nitrogen sites,
realizing the radially extended mode in multiple H-bonds
and metal-coordination bonds (Figure 1).10 Furthermore,
the flexible and easily accessible synthetic method opens a
new chance to execute the creation of functional materials
using HAP derivatives. Crystal structures and fluorescence
properties of the newly synthesized HAP systems are also
reported.
Tomlin reported the synthesis of triphenyl hexaazaphe-
nalene H+·2b- by a condensation with benzamide and 4,6-
diamino-5-cyano-2-phenylpyrimidine.13 It is known that the
pyrimidine derivative is prepared from benzamidine hydro-
chloride (3b) with tricyanomethanide 4.14,15 The amidine 3b
is considered as a synthetic equivalent of benzamide. Thus,
we have conceived a one-pot synthetic method by using 3b
and succeeded in the synthesis of H+·2b- via the following
method: heating a mixture of 3b and 4 at 190 °C and then
additional heating in N,N-dimethylacetamide (DMA) at 180
°C (Scheme 1). Unfortunately, the isolated yield was quite
Scheme 1.
One-Pot Synthetic Procedures of H+·2b- and H+·2c-
Figure 1. Structures of phenalenyl derivatives 1 and 2. The arrows
show radially extended mode of coordination and H-bonding
interactions.
quantum chemical calculation indicates that large positive
spin densities of HAP radical 2• reside on the R-sites, being
similar to that of the parent phenalenyl radicals.2 Thus, from
the viewpoint of difference in bond energy between C-C
and N-N, the HAP radical 2• is of great interest in evaluating
intermolecular bonding natures.
low (4% based on 4) probably because of the poor solubilities
in common solvents under the isolation procedure. Therefore,
we next tried to synthesize a tert-butyl derivative H+·2c-
that might have a high solubility. By the optimized conden-
sation condition between 3c with 4, we have succeeded in
the one-pot synthesis of H+·2c- in 25% yield (Scheme 1).16,17
The obtained H+·2c- is soluble to common organic solvents
We succeeded in the synthesis of HAP anion 2a-
according to Tomlin’s method with some modifications and
isolated it as crystals for the first time.10,13 It turned out that
π-π stacking and radially extended hydrogen/coordination
bonds were constructed by the HAP anions in the crystal of
potassium salts and copper complex of 2a-.10 The experi-
mental and theoretical results encouraged us to design and
synthesize new HAP derivatives with substituents and
functional groups for the creation of diverse assembled
structures and developments of exotic electronic properties
intrinsic to the phenalenyl system.2 Here, we have reported
one-pot syntheses of symmetric HAP, H+·2b-, and H+·2c-,
from commercially available compounds. We consider that
1
such as dichloromethane and ethyl acetate. In H NMR, a
broad signal was observed at 13.1 ppm in dimethylsufoxide-
d6 (DMSO-d6) and 9.3 ppm in chloroform-d (CDCl3).16 We
assumed that the signal was assigned to the NH proton of
H+·2c-. Fortunately, single crystals of H+·2b-and
H+·2c-suitable for X-ray crystal structure analysis were
obtained by vapor diffusion methods with water and DMSO.
In the crystal of H+·2b-, the HAP skeleton possesses a
planar structure, similar to the parent HAP anion
H+·2a-(Figure 2a).10,18 The two substituted phenyl groups
(14) Trofimenko, S.; Little, E. L., Jr.; Mower, H. F. J. Org. Chem. 1962,
(9) (a) Zheng, S.; Lan, J.; Khan, S. I.; Rubin, Y. J. Am. Chem. Soc.
2003, 125, 5786–5791. (b) Zheng, S.; Thompson, J. D.; Tontcheva, A.;
27, 433–438.
(15) Graboyes, H.; Jaffe, G. E.; Pachter, I. J.; Rosenbloom, J. P.; Villani,
Khan, S. I.; Rubin, Y. Org. Lett. 2005, 7, 1861–1863
(10) Suzuki, S.; Morita, Y.; Fukui, K.; Sato, K.; Shiomi, D.; Takui, T.;
Nakasuji, K. Inorg. Chem. 2005, 44, 8197–8198
(11) Murata, T.; Morita, Y.; Fukui, K.; Tamaki, T.; Yamochi, H.; Sato,
G.; Nakasuji, K. Bull. Chem. Soc. Jpn. 2006, 79, 894–913
.
A. J.; Wilson, J. W.; Weinstock, J. J. Med. Chem. 1968, 11, 568–573.
(16) Selected compound data of H+·2c-: colorless solid; 1H NMR (300
MHz, DMSO-d6) δ 13.09 (bs, 1H), 1.41 (s, 27H); 1H NMR (300 MHz,
CDCl3) δ 9.31 (bs, 1H), 1.52 (s, 9H), 1.50 (s, 18H); HRMS (EI) C19H28N6
(M+) calcd 340.2374, found 340.2393. Anal. Calcd for C19H28N6: C, 67.03;
H, 8.29; N, 24.68. Found: C, 66.83; H, 8.17; N, 24.57.
.
.
(12) (a) Tian, Y.-H.; Kertesz, M. J. Am. Chem. Soc. 2010, 132, 10648–
10649. (b) Mota, F.; Miller, J. S.; Novoa, J. J. J. Am. Chem. Soc. 2009,
131, 7699–7707. (c) Small, D.; Zaitsev, V.; Jung, Y.; Rosokha, S. V.; Head-
Gordon, M.; Kochi, J. K. J. Am. Chem. Soc. 2004, 126, 13850–13858. (d)
Tian, Y.-H.; Huang, J.; Kertesz, M. Phys. Chem. Chem. Phys. 2010, 12,
(17) The multistep synthesis of H+·2c-and its crystal structure have been
recently reported. See: Jiang, Y.; Zhang, H.; Wan, X.; Xue, X.; Liu, Y.;
Song, H.; Yu, A.; Chen, Y. Z. Naturforsch., B: Chem. Sci. 2008, 63, 1425–
1430
.
5084–5093
.
(18) Crystallographic data for H+·2b-: space group P21/a (No. 14), a
) 9.588(4), b ) 18.682(9), c ) 11.326(7) Å; ꢀ ) 108.987(19)°; V )
(13) Tomlin, C. D. S. Diss. Abstr. 1965, 26, 105; Chem. Abstr. 1965,,
63, 16354g.
1918.4(16) Å3; T ) 200 K, R1 ) 0.0377, Rw ) 0.1090, GOF ) 1.067
.
Org. Lett., Vol. 12, No. 21, 2010
5037

axis.20 CD spectra of two kinds of the solid-state (KBr
pellets) samples originating in two pieces of single crystals
picked up show significant Cotton effects with a mirror image
of each other (Figure 4).21 To our knowledge, this is rare
Figure 2.
ORTEP presentations of for H+·2b- (50% ellipsoid
probability). (a) Molecular structure. (b) Packing diagram. Hydrogen
atoms are omitted for clarity. The red dashed lines denote
H-bonding interactions between 1,3-positions of the HAP skeleton.
are nearly coplanar to the HAP skeleton (phenyl-HAP angles,
5.2° and 8.4°), and the other is twisted (31.6°). A HAP
molecule H+·2b-is linked to the neighboring HAP molecules
with nearly perpendicular arrangements by H-bonding in-
teraction between 1,3-positions (N···N distance, 2.86 Å)
(Figure 2b). In addition, the H-bonding chain structures are
assembled by π-π interactions between phenyl groups and
HAP moiety (ca. 3.2-3.5 Å).
Figure 4. Solid-state CD spectra (KBr pellets) for two crystalline
samples of H+·2c-. The solid and the dashed lines denote different
single crystals picked up from the same batch.
Crystal structure of H+·2c- shows that the HAP skeleton
also possesses a planar structure, and the molecule has C2
symmetry due to disordering in one of the tert-butyl groups
and amino proton (Figure 3a).19 In addition, H+·2c- is linked
event for the construction of H-bonded chiral helix composed
of achiral rigid and π-conjugated planar molecules.22
We also obtained the anion species 2b- and 2c- by
treatment with sodium hydroxide and tetraethylammoium
chloride. The ammonium salts Et4N+·2b- and Et4N+·2c- are
stable under air and water condition, similar to K+·2a-.10,23
The triphenyl derivative Et4N+·2b- is slightly soluble to
common organic solvents, whereas the tert-butyl derivative
Et4N+·2c- is very soluble. In 1H NMR of Et4N+·2c-, a signal
assigned to tert-butyl protons was observed at 1.35 ppm in
DMSO-d6 and 1.47 ppm at CDCl3, which show magnetic
field shifts slightly higher than those of H+·2c-(1.41 ppm in
DMSO-d6, 1.52 and 1.50 ppm in CDCl3).16,23 X-ray crystal
structure analysis of Et4N+·2c- showed that the structure of
Figure 3.
ORTEP presentations for H+·2c- (50% ellipsoid prob-
ability). (a) Molecular structure. One of the tert-butyl groups is
disordered. Disordered methyl groups, H-atoms, and amino protons
are omitted for clarity. (b) Perspective view along to the c axis
packing diagram. tert-Butyl groups and H-atoms are omitted for
clarity. The red dashed lines denote H-bonding interactions with
one-handed helicities between 1,6-positions of the HAP skeleton.
The dark and the light colored molecular frameworks are located
in the upper and lower of the H-bonding chains.
(20) Unfortunately, the absolute configuration could not be identified
because the refinement of flack parameter was not possible in the X-ray
crystal structure analysis.
(21) A single crystal (ca. 0.01 mg) was picked up, ground with KBr
(15 mg), and pressed for preparing a pellet, and the CD spectrum was
measured. Then, another single crystal that was similar in size to the first
one was picked up, and the CD spectrum was measured in the same manner.
In the case using many crystals of H+·2c- for the CD measurement, the
Cotton effect was not observed, which indicates that formation of an almost
1:1 mixture of the right- and left-handed H-bonded helices and chirality
enrichment did not occur under the crystallization process.
to the neighboring molecules with nearly perpendicular
arrangements by H-bonding interaction between 1,6-positions
(N···N distance 3.09 Å). Interestingly, the H-bonding chain
structures of H+·2c-form a one-handed helix along the c
(22) Recent reviews: (a) Matsuura, T.; Kojima, H. J. Photochem.
Photobiol. C 2005, 6, 7–24. (b) Steed, J. W.; Atwood, J. L. Supramolecular
Chemistry, 2nd ed.; John Wiley & Sons Ltd.: West Sussex, 2009; pp
687-691.
(23) Selected compound data of Et4N+·2c-: 1H NMR (300 MHz, DMSO-
d6) δ 3.20 (q, J ) 7.2 Hz, 8H), 1.35 (s, 27H), 1.16 (tt, JH-H ) 7.2 Hz and
1
JN-H ) 1.8 Hz, 12H); H NMR (300 MHz, CDCl3) δ 2.92 (q, J ) 7.3 Hz,
(19) Crystallographic data for H+·2c-: space group P3121 (No. 152), a
) 10.4770(16), c ) 15.328(3) Å; V ) 1457.1(4) Å3; T ) 200 K, R )
0.0671, Rw ) 0. 2081, GOF ) 1.126.
8H), 1.47 (s, 27H), 1.15 (m, JH-H ) 7.3 Hz and JN-H ) 1.9 Hz, 12H). Anal.
Calcd for C19H27N6·C8H20N·(CH2Cl2)0.9: C, 61.36; H, 9.01; N, 17.95. Found:
C, 61.28; H, 8.99; N, 17.99.
5038
Org. Lett., Vol. 12, No. 21, 2010

Figure 5. (a) ORTEP presentations of molecular structure for
Et4N+·2c- (50% ellipsoid probability). CH2Cl2 existing as crystal
solvent is omitted for clarity. (b) IR spectra (KBr pellets) for
H+·2c-(solid line) and Et4N+·2c-(dashed line).
Figure 6. UV-vis and fluorescence (inset: λex ) 300 nm) spectra
of H+·2c-(line) and Et4N+·2c-(dashed line). The fluorescence
intensities of these compounds were compared at the same
absorbance of the excitation wavelength.
2c- possessed a high planarity (Figure 5a).24 Additionally,
bond equalization was observed in carbon-nitrogen bonds
(1.33-1.36 Å) on the HAP skeleton. These results are
experimental evidence of charge delocalization on the whole
HAP skeleton.
was not observed in usual conditions of CV measurements
for the corresponding hydrocarbon phenalenyl system, which
indicated a substantial decrease in the calculated LUMO
energy of the HAP anion system.10
In summary, we have succeeded in the one-pot syntheses
of symmetric HAP derivative, H+·2b- and H+·2c-, by the
condensations of the corresponding amidine hydrochroride
with tricyanomethanide. Syntheses of other HAP derivatives
and neutral radicals are underway. We believe that the
present synthetic method of HAP derivatives is very useful
for further development of HAP chemistry.
In the IR spectra, CdN stretching vibrations were observed
at 1592 cm-1 for Et4N+·2b-and 1602 cm-1 for Et4N+·2c-.
Those were similar to K+·2a- (1599 cm-1).10 In contrast,
two peaks were observed in the IR spectra of the hexaaza-
phenalene species, 1638 and 1596 cm-1 for H+·2b-, 1644
and 1607 cm-1 for H+·2c- (Figure 5b, and see Supporting
Information). These observations were consistent with the
result of bond equalization proved by the X-ray crystal
structure analysis of Et4N+·2c-. In UV spectra of H+·2c-
and Et4N+·2c-, no absorption bands were observed in the
wavelength region above 350 nm (Figure 6). In the fluores-
cent spectra, the fluorescence of H+·2c- was observed at 350
nm, whereas that of Et4N+·2c- was quite weak (Figure 6).
A cyclic voltammogram (CV) of Et4N+·2c- gave an
irreversible oxidation wave at around +1.1 V vs Fc/Fc+,
being assigned to the redox potential between 2c- and 2c•
(see Supporting Information). These observations were
consistent with the result of parent derivative 2a-.10 Fur-
thermore, the CV measurement of Et4N+·2c-gave a quasi-
reversible reduction wave at around -2.0 V (see Supporting
Information), being assigned to the redox potential between
2c- and 2c·2- (or more reduced state). The reduction wave
Acknowledgment. We thank Prof. Dr. H. Miyake and
Prof. Dr. H. Tsukube (Osaka City University) for CD
measurements. This work was partially supported by Grants-
in-Aid for Scientific Research on Innovative Areas (No.
20110006 and Quantum Cybernetics) and Elements Science
and Technology Project from Ministry of Education, Culture,
Sports, Science, and Technology, Japan, and also by Core
Research for Evolutional Science and Technology (CREST-
JST).
Supporting Information Available: Detailed synthetic
procedure, IR spectra, UV and fluorescence spectra, and
cyclic voltammogram. This material is available free of
charge via the Internet at http://pubs.acs.org.
(24) Crystallographic data for Et4N+·2c-·CH2Cl2: monoclinic, space
group P21/c (No. 14), a ) 12.412(7), b ) 19.626(11), c ) 13.146(8) Å; ꢀ
) 106.484(6)°; V ) 3070.7(30) Å3; T ) 200 K, R ) 0.0852, Rw ) 0.2245,
GOF ) 1.068.
OL102200V
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5039