Bis(azafulvene) as a versatile building block for giant cyclopolypyrroles: X-ray crystal structure of [64]hexadecaphyrin(1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0)

Full text of DOI:10.1021/ja005588o

J. Am. Chem. Soc. 2000, 122, 12405-12406
12405
Scheme 1
Bis(azafulvene) as a Versatile Building Block for
Giant Cyclopolypyrroles: X-ray Crystal Structure of
[64]Hexadecaphyrin(1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0)
Jun-ichiro Setsune* and Satoshi Maeda
Department of Chemistry, Faculty of Science
and Graduate School of Science and Technology
Kobe UniVersity, Nada-ku, Kobe 657-8501, Japan
ReceiVed September 8, 2000
The figure-eight structure of [40]decaphyrin(1.0.1.0.0.1.0.1.0.0)
indicated that fully conjugated porphyrinoids need not be
topographically flat.1 We have recently proceeded one step further
to demonstrate that giant porphyrinoids with 12- and 16-pyrrole
units have a cylindrical cavity.2 The promise of these giant
porphyrinoids for use in molecular recognition and catalysis
accelerates study on the synthetic methodology.3 Acid-catalyzed
MacDonald-type condensation has been one of the most important
methods and afforded [32]octaphyrin(1.0.1.0.1.0.1.0) and [40]-
decaphyrin(1.0.1.0.0.1.0.1.0.0).1,4 Very recently [32]octaphyrin
(1.0.0.0.1.0.0.0) has been formed by oxidative ring closure of
linear oligopyrroles with R-free pyrrolic units at both ends.5 On
the other hand, condensation of R-free pyrrole derivatives with
aldehydes analogous to the Rothemund porphyrin synthesis
gave [24]hexaphyrin(1.0.1.0.1.0) known as rosarin,6 [26]hexa-
phyrin(1.1.1.1.1.1),7 [32]octaphyrin(1.0.1.0.1.0.1.0),2 [48]-
dodecaphyrin(1.0.1.0.1.0.1.0.1.0.1.0),2 and [64]hexadecaphyrin-
(1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0).2 Although the Rothemund-type
reaction of 2,2′-bipyrrole does afford cyclopolypyrroles with
world-record ring sizes, the chromatographic separation of a
mixture of bipyrrole-based homologues is not easy. Thus, this
work is intended to explore a facile synthetic method for even
larger cyclopolypyrroles by using modified MacDonald-type
reactions which would give a mixture of tetrapyrrole-based
homologues.
the reaction was run for 24 h, 6 and 8 were produced in 24 and
20% yield, respectively. The formation of 6 as a major product
indicates that tetrapyrrole-based cyclooligomers should be de-
composed and recyclized to bipyrrole-based cyclooligomers under
the acidic reaction conditions. This reaction was further compli-
cated by the acid-catalyzed decomposition of 2 to benzaldehyde
and 1. 1H NMR monitoring indicated that 2 (0.02 mmol) did not
react with 1 (0.02 mmol) in CDCl3 (0.5 mL) in 3 h when 5%
decomposition of 2 to give benzaldehyde has occurred. Addition
of CD3CO2D (2 µL) not only triggered the condensation reaction
between 1 and 2 but also enhanced decomposition of 2 to give
benzaldehyde in 20% yield in 30 min. Therefore, the MacDonald-
type condensation of 1 and 2 should be accompanied by the
Rothemund-type condensation of 1 and benzaldehyde under the
above reaction conditions. Since water is responsible for acid-
catalyzed redistribution among cyclooligomers of different ring
size before DDQ oxidation, a new bipyrrole building block which
eliminates undesired formation of water should be preferred.
Addition of phenyllithium (5 equiv) to 5,5′-diformyl-3,3′,4,4′-
tetraethyl-2,2′-bipyrrole in THF would generate the tetraanion that
was quenched with water to give 95% yield of 2. When the
tetraanion was quenched with acetic anhydride (5 equiv) instead
of water, a yellow compound 3 was obtained in 55% yield. The
13C NMR signal due to the methine carbon connecting pyrrole
and phenyl group indicates change in hybridization from sp3 in 2
(68.2 ppm) to sp2 in 3 (131.5 ppm). The resonances due to the
pyrrole ring carbons undergo great downfield shifts from 120.4,
122.5, 122.8, and 128.0 ppm in 2 to 168.8, 141.7, 147.6, and
154.8 ppm in 3. These data are consistent with the bis(azafulvene)
structure of 3. The ROESY spectrum of 3 demonstrated trans
stereochemistry of the phenyl groups with respect to the pyrrole-
â-ethyl groups.8 The polar electronic structure characteristic of
fulvene in 3 would induce facile electrophilic addition to 1 without
the undesired equilibria caused by water.
The condensation reaction of 3,3′,4,4′-tetraethyl-2,2′-bipyrrole
(1, 0.2 mmol) and 5,5′-bis(phenylhydroxymethyl)-3,3′,4,4′-tetra-
ethyl-2,2′-bipyrrole (2, 0.2 mmol) was carried out for 1 h in a
solvent mixture of AcOH (2.5 mL) and CH2Cl2 (2.5 mL)
containing 2 equiv of Zn(OAc)2‚2H2O. Oxidative workup with
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) gave a mixture
of 2,3,6,7,11,12,15,16,20,21,24,25-dodecaethyl-9,18,27-triphenyl-
rosarin (6)2 and 2,3,6,7,11,12,15,16,20,21,24,25,29,30,33,34-
hexadecaethyl-9,18,27,36-tetraphenyl[32]octaphyrin-
(1.0.1.0.1.0.1.0) (8)2 in 11 and 14% yield, respectively. When
(1) Sessler, J. L.; Weghorn, S. J.; Lynch, V.; Johnson, M. R. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1507-1510.
(2) Setsune, J.; Katakami, Y.; Iizuna, N. J. Am. Chem. Soc. 1999, 121,
8957-8958.
(3) (a) Sessler, J. L. J. Porphyrins Phthalocyanins 2000, 4, 331-336. (b)
Lash, T. D. Angew. Chem., Int. Ed. Engl. 2000, 39, 1763-1767. (c) Sessler,
J. L.; Gebauer, A.; Weghorn, S. J. The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 2,
p 55. (d) Sessler, J. L.; Weghorn, S. J. Expanded, Contracted & Isomeric
Porphyrins; Pergamon: Oxford, U.K., 1997. (e) Jasat, A.; Dolphin, D. Chem.
ReV. 1997, 97, 2267-2340.
(4) (a) Bro¨ring, M.; Jendrny, J.; Zander, L.; Schmickler, H.; Lex, J.; Wu,
Y. D.; Nendel, M.; Chen, J. G.; Plattner, D. A.; Houk, K. N.; Vogel, E. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2515-2517. (b) Vogel, E.; Broring, M.; Fink,
J.; Rosen, D.; Schmickler, H.; Lex, J.; Chan, K. W. K.; Wu, Y. D.; Plattner,
D. A.; Nendel, M.; Houk, K. N. Angew. Chem., Int. Ed. Engl. 1995, 34, 2511-
2514.
When a mixture of 1 and 3 is reacted in the AcOH- CH2-
Cl2-Zn(OAc)2‚2H2O system for 1 h, 8 was obtained in 20% yield
with no trace of 6. In addition to 8, blue fractions showing UV-
vis maxima at 674, 674, 708, and 728 nm were obtained in 6, 7,
4, and 3% yield, respectively, by chromatographic separation using
silica gel and polydivinylbenzene gel. The ESI-TOF MS data of
these four fractions (m/z 1982.2708, 2643.6856, 3304.1440, and
3965.5523 for monocations) are in good agreement with the theory
for [48]dodecaphyrin(1.0.1.0.1.0.1.0.1.0.1.0) (12, M + 1 )
1982.2603), [64]hexadecaphyrin(1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0)
(5) Sessler, J. L.; Seidel, D.; Lynch, V. J. Am. Chem. Soc. 1999, 121,
11257-11258.
(6) Sessler, J. L.; Weghorn, S. J.; Morishima, T.; Rosingana, M.; Lynch,
V.; Lee, V. J. Am. Chem. Soc. 1992, 114, 8306-8307
(7) Neves, M. G. P. M. S.; Martins, R. M.; Tome, A. C.; Silvestre, A. J.
D.; Silva, A. M. S.; Felix, V.; Drew, M. G. B.; Cavaleiro, J. A. S. Chem.
Commun. 1999, 385-386.
(8) A cross-peak was observed between the methylene protons at 2.65 ppm
and the methine proton at 6.98 ppm in the ROESY spectrum.
10.1021/ja005588o CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/28/2000

12406 J. Am. Chem. Soc., Vol. 122, No. 49, 2000
Communications to the Editor
units (pyrrole-C(Ph)dpyrrole) are mostly coplanar and the phenyl
groups are almost perpendicular to them.
Very recently some reports have appeared on the giant
porphyrinoids which contain eight to twelve pyrroles and/or
related heterocycles.11 Compared with these, the tetracosaphyrin
24 is a remarkably large compound and its cavity with a diameter
more than 20 Å exceeds the molecular size of γ-cyclodextrin itself
(ca. 17 Å). It is of great importance that the reaction between
2,2′-diaza-3,3′-bifulvene and 2,2′-bipyrrole provides a series of
cyclopolypyrroles with ring sizes varied by a tetrapyrrole unit
with the meso-phenyl group. Special meso-aryl groups such as
pentafluorophenyl and 2,6-dichlorophenyl are not necessary. The
high reactivity of bis(azafulvene) and the elimination of water-
driven equilibria are the key features in our synthesis of giant
porphyrinoids. Furthermore, it is promising that bis(azafulvene)
has wide application as a powerful building block in porphyrinoid
chemistry.12
Figure 1. X-ray structure of 16 with its atom-numbering scheme. Thirty-
two ethyl groups at the pyrrole-â positions and eight phenyl groups at
the meso positions are omitted for clarity. A front view of a space filling
model (left) and a side view of a ball-and-stick model (right) are shown.
Selected distances (Å) and angles (deg): N1-C1, 1.337(6); N1-C4,
1.383(5); C1-C2, 1.403(6); C2-C3, 1.385(6); C3-C4, 1.443(7); C4-
C5, 1.401(6); C5-C6, 1.398(6); N2-C6, 1.402(5); N2-C9, 1.329(5);
C6-C7, 1.436(6); C7-C8, 1.378(6); C8-C9, 1.424(6); C1-N1-C4,
110.2(4); C6-N2-C9, 107.6(4); C4-C5-C6, 124.3(4); N1-C4-C5-
C6, 8.5(7); C4-C5-C6 N2, 7.8(7); N2-C9-C10-N3, 52.6(6); N4-
C18-C19-N5, 171.0(4); N6-C27-C28-N7, 93.4(5); N8-C36-C1*-
N1*, 145.0(4).
Acknowledgment. This work was supported by a Grant-in-Aid for
Scientific Research on Priority Area (No. 12023231) from the Ministry
of Education, Science, Sports, and Culture, Japan and Photonics Material
Laboratory of the Graduate School of Science and Technology of Kobe
University. We are grateful to Ms. M. Nishinaka (Kobe University) for
microanalysis.
Supporting Information Available: Experimental details on the
synthesis and characterization of compounds 2, 3, 12, 16, 20, and 24, as
well as tables of crystallographic data, atomic coordinates, bond lengths,
bond angles, thermal parameters, and ORTEP drawings of X-ray structure
for 16 (PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
(16,
M
+
2
)
2643.6826),
[80]icosaphyrin-
(1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0) (20, M + 2 ) 3304.1023),
and [96]tetracosaphyrin(1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0)
(24, M + 3 ) 3965.5212), respectively. While MS signals
associated with higher homologues were detected in the first
fraction of GPC,9 those with an odd number of bipyrrole units
have never been detected. This indicates that acid-catalyzed
redistribution of cyclooligomers is not taking place under the
present reaction conditions. Bis(azafulvene) 3 is so reactive that
addition to 1 took place without catalyst in CH2Cl2 in 1 h to give
8, 12, 16, 20, and 24 in 23, 3, 4, 3, and 2% yield, respectively.
The X-ray crystallography of 16 shows the square pillar
structure with a tetragonal cut end of 18.8 × 16.3 Å (see Figure
1).10 The height (14.4 Å) of the pillar corresponds to the b-axis
of the unit cell. The molecules are stacked precisely face to face
to make a channel along the b-axis in the crystal packing. The
JA005588O
(10) Recrystallization from benzene/acetone gave crystals of 16. Crystal
data: C184H208N16, M ) 2643.66, monoclinic, space group C2/c, a ) 34.611-
(3) Å, b ) 14.3764(14) Å, c ) 34.408(4) Å, â ) 94.085(2)°, V ) 17077(3)
Å3, Z ) 4, Dcalc ) 1.028 g/cm3, µ(Mo KR) ) 0.060 mm-1, T ) 299 K, crystal
size 0.30 × 0.30 × 0.30 mm3. A total of 17212 unique reflections were
collected (2 < 2θ < 55°) using graphite-monochromated Mo KR radiation.
R1 ) 0.097, wR2 ) 0.244 for 5816 reflections with I > 2.00σ(I); R1 ) 0.245,
wR2 ) 0.329 for all data. GOF (on F2) ) 0.928.
(11) (a) Kozaki, M.; Parakka, J. P.; Cava, M. P. J. Org. Chem. 1996, 61,
3657-3661. (b) Kral, V.; Sessler, J. L.; Zimmerman, S.; Seidel, D.; Lynch,
V.; Andrioletti, B. Angew. Chem., Int. Ed. Engl. 2000, 39, 1055-1058. (c)
Michels, M.; Zander, L.; Wytko, J. Abstracts of the 24th International
Symposium on Macrocyclic Chemistry; Barcelona, July 1999. (d) Shin, J.-Y.;
Minezawa, N.; Furuta, H.; Osuka, A. Abstracts of the 1st International
Conference on Porphyrins and Phthalocyanines; POST562, Dijon, June 2000.
(e) Arumugam, N.; Jang, Y.-S.; Lee, C.-H. Org. Lett. 2000, 2, 3115-3117.
(12) (a) Sessler, J. L.; Gebauer, A.; Vogel, E. The Porphyrin Handbook;
Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: New York,
2000; Vol. 2, p 1. (b) Lash, T. D. The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 2,
p 125. (c) Paolesse R. The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 2, p 201.
molecule has a C2 axis of symmetry and large N-C(R-pyrrole)
-
C(R-pyrrole)-N torsion angles (52.5°, 171.0°, 93.4°, and 145.0°)
in the bipyrrole units are observed, while the dipyrrylmethene
(9) The observed MS signals at m/z 4623, 5283, 5944, and 6604 are
associated with 28-, 32-, 36-, and 40-phyrins, respectively.