A self-assembled porphyrin-based dimeric capsule constructed by a Pd(II)-pyridine interaction which shows efficient guest inclusion

Article abstract of DOI:10.1021/ol006620m

(matrix presented) Novel self-assembled molecular capsules were constructed from two moles of pyridine-containing porphyrin derivatives and four moles of Pd(II) complexes utilizing a pyridine-Pd(II) interaction. The ¹H NMR spectral studies esta

Full text of DOI:10.1021/ol006620m

ORGANIC
LETTERS
2000
Vol. 2, No. 23
3707-3710
A Self-Assembled Porphyrin-Based
Dimeric Capsule Constructed by a
Pd(II)−Pyridine Interaction Which Shows
Efficient Guest Inclusion
,†
,†
Atsushi Ikeda,* Masatsugu Ayabe,† Seiji Shinkai,* Shigeru Sakamoto,‡ and
Kentaro Yamaguchi‡
Department of Chemistry & Biochemistry, Graduate School of Engineering,
Kyushu UniVersity, Fukuoka 812-8581, Japan, and Chemical Analysis Center,
Chiba UniVersity, Chiba 263-8522, Japan
seijitcm@mbox.nc.kyushu-u.ac.jp
Received September 19, 2000
ABSTRACT
Novel self-assembled molecular capsules were constructed from two moles of pyridine-containing porphyrin derivatives and four moles of
Pd(II) complexes utilizing a pyridine−Pd(II) interaction. The 1H NMR spectral studies established that these self-assembled molecular capsules
5 and 6 have a highly symmetrical D4h structure as well as a large inside cavity. It was shown that molecular capsule 6 can include a large
bipyridine guest by a two-point simultaneous pyridine−Zn(II) interaction.
A great deal of effort has been devoted toward multipor-
phyrin arrays such as molecular wires,1 molecular switches,2
photosynthetic systems,3 photosensitizers for DNA cleavage,4
and photocurrent generation.5 A combination of these excel-
lent devices with host-guest chemistry has a large future
potential but is much less developed so far. A few cyclic
host compounds composed of covalently linked multipor-
phyrins have been synthesized, and some of them can include
guest molecules such as pyridine derivatives6,7 and fullerenes.8
The findings suggest that molecular capsules with a three-
dimensional cavity would have larger association constants
and kinetically slower exchange rates for specific guest
molecules than cyclic compounds with a two-dimensional
cavity, but the syntheses of such molecular capsules are
† Kyushu University.
‡ Chiba University.
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R. W.; Lindsey, J. S. J. Am. Chem. Soc. 1994, 116, 9759-9760. (c) Aratani,
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10.1021/ol006620m CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/21/2000

frequently very troublesome. Here, it occurred to us that the
utilization of coordination bonds has been somewhat ne-
glected, given that Fujita et al.9 and Stang et al.10 have shown
a number of attractive examples in which coordination bonds
are employed for the construction of self-assembled su-
pramolecular architectures.11 We previously found that two
homooxacalix[3]arenes dimerize with three cis-Pd(II) com-
plexes into a molecular capsule according to a self-assembled
manner.12,13 The spectroscopic studies have shown that the
molecular capsule thus formed can specifically include [60]-
fullerene, the selectivity of [60]fullerene vs [70]fullerene
being nearly “perfect”.12,14 Utilizing this class of concept,
several self-assembled multiporphyrin arrays were recently
reported in organic solvents.15 However, most of the preced-
ing examples are two-dimensional macrocycles without a
sufficient inclusion cavity, whereas the examples for three-
demensional molecular capsules have been very limited.16,17
If such a novel molecular capsule with “porphyrin walls” is
successfully constructed, it follows that a guest is shielded
inside the cavity while electrons are injected only via these
“porphyrin walls”. With this object in mind, we here report
novel self-assembled molecular capsules constructed from
porphyrin 1 or 2 through the pyridyl-Pd(II) interaction. Very
interestingly, we have found that these molecular capsules
can include bipyridine derivatives with relatively large
association constants.
hyde with pyrrole in propionic acid. Compound 2 was
obtained in 99% yield by the reaction of 1 with Zn(OAc)2.
1
These compounds were identified by IR, H NMR, and
MALDI-TOF mass ([M + H]+ ) 1651.9 and 1713.8 for 1
and 2, respectively) spectral evidence and elemental analyses.
1
As shown in Figure 1b, the simple H NMR splitting
pattern was obtained when 1 and 3 were mixed in a 1:2 ratio
Figure 1. Partial 1H NMR spectra of (a) 1 (2.2 mM) and (b) [1]:[3]
) 1:2 (2.2 mM/4.4 mM): CDCl3, 27 °C, 600 MHz.
in CDCl3. When the ratio was higher or lower than this value,
the 1H NMR spectra gave additional peaks and became very
1
complicated. Careful examination of Figure 1b and the H-
1H COSY spectrum reveals that all peaks of 1‚3 complex
can be assigned to one kind of signals, supporting the 2:4
1/3 complex (5) with a D4h symmetrical structure but not
the 1:2 complex with a C2V symmetrical structure ais
inconceivable because the rigid tetraphenylporphyrin skeleton
of 1 suppresses the pyridyl groups to get close to each other
and thus prevents 1 from the formation of the intramolecular
bonds with two cis-Pd(II) complexes. Meanwhile, a solution
of 2 in CDCl3 gave a very complicated and very broadened
1H NMR spectrum, suggesting that the pyridyl groups act
as axial ligands to bind Zn(II) intermolecularly.19 When 3
was added, 2 gave a 1H NMR spectral splitting pattern very
(11) Fox, O. D.; Drew, M. G. B., Wilkinson, E. J. S.; Beer, P. D. Chem.
Commun. 2000, 391-392.
Compound 1 was obtained18 in 22% yield by the reaction
of 3-methoxy-4-n-octyloxy-5-pyridin-4-ylethynyl benzalde-
(12) Ikeda, A.; Yoshimura, M.; Tani, F.; Naruta, Y.; Shinkai, S. Chem.
Lett. 1998, 587-588.
(13) Ikeda, A.; Yoshimura, M.; Udzu, H.; Fukuhara, C.; Shinkai, S. J.
Am. Chem. Soc. 1999, 121, 4296-4297.
(14) Ikeda, A.; Udzu, H.; Yoshimura, M.; Shinkai, S. Tetrahedron 2000,
56, 1825-1832.
(15) (a) Drain, C. M.; Lehn, J. M. J. Chem. Soc., Chem. Commun. 1994,
2313-2314. (b) Stang, P. J.; Fan, J.; Olenyuk, B. Chem. Commun. 1997,
1453-1454. (c) Fan, J.; Whiteford, J. A.; Olenyuk, B.; D. Levin, M. D.;
Stang, P. J.; Fleischer, E. B. J. Am. Chem. Soc. 1999, 121, 2741-2752.
(16) Slone, R. V.; Hupp, J. T. Inorg. Chem. 1997, 36, 5422-5423.
(17) Fujita, N.; Fujita, M.; Sakamoto, S.; Yamaguchi, K. Abstracts, XI
International Symposium on Supramolecular Chemistry, Fukuoka, Japan,
2000; PD-37.
(6) Sanders et al. have reported that a large number of multiporphyrin
hosts can include pyridine guests by a multipoint simultaneous pyridine-
Zn(II) interaction: (a) Anderson, S.; Anderson, H. L.; Sanders, J. K. M. J.
Chem. Soc., Perkin Trans. 1 1995, 2255-2267. (b) Vidal-Ferran, A.; Clyde-
Watson, Z.; Bampos, N.; Sanders, J. K. M. J. Org. Chem. 1997, 62, 240-
241. (c) Nakash, M.; Clyde-Watson, Z.; Feeder, N.; Davies, J. E.; Teat, S.
J.; Sanders, J. K. M. J. Am. Chem. Soc. 2000, 122, 5286-5293 and
references therein.
(7) Ambroise, A.; Li, J.; Lianhe Yu, Lindsey, J. S. Org. Lett. 2000, 2,
2563-2566.
(8) Tashiro, K.; Aida, T.; Zheng, J. Y.; Kinbara, K.; Saigo, K.; Sakamoto,
S.; Yamaguchi, K. J. Am. Chem. Soc. 1999, 121, 5645-5647.
(9) (a) Fujita, M.; Yazaki, J.; Ogura, K. J. Am. Chem. Soc. 1990, 112,
5645-5647. (b) Fujita, M.; Nagao, S.; Ogura, K. J. Am. Chem. Soc. 1995,
117, 1649-1650.
(18) Synthetic details and characterization data relating to 1 and 2 can
be found in the Supporting Information.
(19) Supramolecular complexes consisting of tripyridine derivatives and
tris{Zn(II) porphyrin} derivatives were reported. However, they cannot
include the guest molecules in their cavities utilizing Zn(II)-metal
coordination: (a) Felluga, F.; Tecilla, P.; Hillier, L.; Hunter, C. A.; Licini,
G.; Scrimin, P. Chem. Commun. 2000, 1087-1088. (b) Ikeda, A.; Sonoda,
K.; Shinkai, S. Chem. Lett. 2000, 1220-1221.
(10) (a) Stang, P. J.; Cao, D. H. J. Am. Chem. Soc. 1994, 116, 4981-
4982. (b) Stang, P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc.
1995, 117, 6273-6283.
3708
Org. Lett., Vol. 2, No. 23, 2000

Here, we evaluated whether these novel molecular capsules
are capable of including some guest molecules. NMR
spectroscopic studies have provided clear evidence that 6
can form complex with 4,4′-trimethylenedipyridine (4). The
1H NMR spectrum of 6 in the presence of 4 is shown in
Figure 4. The proton signals for free 6 and 6‚4 complex
1
Figure 4. Partial H NMR spectra of (a) 4 (0.8 mM), (b) [6]:[4]
) 2:1 (0.8 mM/0.4 mM), and (c) [6]:[4] ) 1:1 (0.8 mM/0.8 mM):
CDCl3, 27 °C, 600 MHz. Open and filled circles denote the signals
for free 4 and 6 and those for 6‚4 complex, respectively.
appear separately. The peak separation implies that the
complexation-decomplexation exchange rate is slower than
1
the H NMR time-scale. The stoichiometry of 6‚4 complex
Figure 2. Schematic illustration of 1:2 and 2:4 complexes.
was estimated to be 1:1 from the peak intensities. These
results consistently support the view that 4 resides in the
cavity of 6.21 Large upfield shift is observed for the R- and
â-protons in the pyridyl groups of 4 (1.91 and 4.69 ppm,
respectively). These changes are ascribed to the strong
shielding effect of the porphyrin π-systems on the R- and
â-protons of the included 4.
similar to that of 2:4 1/3 complex (Figure 3b), which can be
also assigned to the molecular capsule 6.
The formation of molecular capsule 6 was also supported
by coldspray ionization mass spectrometery (CIS-MS).20
When a CH2Cl2 solution containing 2 and 3 in a 1:2 ratio
was subjected to the CIS-MS measurement, strong peaks
appeared at 967, 1190, and 1525, which are assignable to [6
Figure 5 shows the influence of added 4 on the absorption
spectral change in 6 (25 °C, CHCl3). It is seen from Figure
- 6+
- 5+
- 4+
- 6CF3SO3 ] , [6 - 5CF3SO3 ] , and [6 - 4CF3SO3 ] ,
respectively.
Figure 3. Partial 1H NMR spectra of (a) 2 (1.5 mM) and (b) [2]:[3]
) 1:2 (1.5 mM/3.0 mM): CDCl3, 27 °C, 600 MHz.
Figure 5. Absorption spectral change in 6 (2.0 × 10-6 M): [4] )
0-5.0 × 10-6 M. Insert: ∆A436 vs [4] plot in CHCl3 at 25 °C.
Org. Lett., Vol. 2, No. 23, 2000
3709

5 that the λmax for the Soret band (431 nm) shifts to longer
wavelength (436 nm) with a tight isosbestic point (433 nm
in the Soret band region). The result supports the view that
two pyridine units in 4 simultaneously coordinate to Zn(II)
in 6. From a plot of ∆A436 vs [4] (inserted in Figure 5), one
can obtain K ) 2.6 × 106 M-1 for the formation of the 1:1
complex from 4 and 6 (the formation of 6‚4 complex is 65%
at [4] ) [6] ) 2.0 × 10-6 M). Since the K for the formation
of the 1:1 complex from pyridine and ZnTPP (TPP )
tetraphenylporphyrin) (estimated under the similar measure-
ment conditions) is 1.1 × 103 M-1, one can regard that the
two-point simultaneous binding dramatically enhances the
K value. Moreover, the formation of 6‚4 complex was also
supported by coldspray ionization mass spectrometry. When
a CH2Cl2 solution containing 4 and 6 in a 1:1 ratio was
subjected to the CIS-MS measurement, strong peaks appeared
at 1000, 1223, and 1574, which are assignable to [6‚4 - 6
CF3SO3-]6+, [6‚4 - 5 CF3SO3-]5+, and [6‚4 - 4 CF3SO3-]4+,
respectively.
In conclusion, two porphyrin-based building blocks (1 or
2) intermolecularly bind four cis-Pd(II) complexes, resulting
in a novel molecular capsule according to a self-assembled
manner. Owing to rigid acetylene spacers between meso-
phenyl moieties and pyridyl moieties in 2, molecular capsule
6 can hold an unusually large cavity enough to bind large
bipyridine guest 4. These results show that porphyrins can
act as powerful building blocks for constructing molecular
capsules in a self-assembled manner. The further applications
of these systems to porphyrin-mediated molecular recogni-
tion, redox reactions, photochemical reactions, etc. are
currently under investigation in these laboratories.
Acknowledgment. The present work is supported by the
Sumitomo Foundation and by a Grant-in-Aid for COE
Research “Design and Control of Advanced Molecular
Assembly Systems” from the Ministry of Education, Science
and Culture, Japan (No. 08CE2005).
Supporting Information Available: Synthetic scheme
1
and assignment of the H NMR spectra of 1, 2, 5, 6, and
(20) Sakamoto, S.; Fujita, M.; Kim, K.; Yamaguchi, K. Tetrahedron
2000, 56, 955-964.
(21) Although 4 is capable of coordination to Pd(II) to decomposed the
capsular structure, it favorably interacts with porphyrin-Zn(II) for the steric
suitability.
6‚4 complex. This material is available free of charge via
the Internet at http://pubs.acs.org.
OL006620M
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Org. Lett., Vol. 2, No. 23, 2000