Porphyrin polygons: A new synthetic strategy for cyclic porphyrin oligomers utilizing a porphyrin double decker structure

Article abstract of DOI:10.1246/cl.2001.1266

A novel synthetic scheme for constructing cyclic porphyrin oligomers is presented: bisporphyrin derivative 1 reacts with La(acac)₃ in 1,2,4-trichlorobenzene to yield porphyrin polygons, such as cyclic dimer 1₂·2La(III) and cyclic tri

Full text of DOI:10.1246/cl.2001.1266

1266
Chemistry Letters 2001
Porphyrin Polygons: A New Synthetic Strategy for Cyclic Porphyrin Oligomers
Utilizing a Porphyrin Double Decker Structure
Masato Ikeda, Atsushi Sugasaki, Yohei Kubo, Kazunori Sugiyasu, Masayuki Takeuchi,* and Seiji Shinkai*
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Fukuoka 812-8581
(Received August 24 , 2001; CL-010830)
A novel synthetic scheme for constructing cyclic porphyrin
Compound 1 was prepared from 5,10,15-tris(4-n-
buthoxyphenyl)-20-[4-(trimethylsilylethynyl)phenyl]porphyrin
according to Scheme 2 and identified by 1H NMR and MALDI-
TOFMS (MALDI = Matrix-Assisted Laser Desorption
Ionization) spectral evidence and elemental analysis.11 A solu-
tion of 1 (3.5 mmol dm–3 (condition A) or 7.0 mmol dm–3 (con-
dition B)) and three equivalents of La(acac)3 (acac = acetylacet-
onato) in 5 mL of 1,2,4-trichrolobenzene was heated at reflux
temperature. The time course of the reaction between La(acac)3
and 1 was monitored by GPC and MALDI-TOFMS. The reac-
tion was terminated after 24 h and 14 h in condition A and con-
dition B, respectively. Further addition of La(acac)3 to this
reaction mixture caused no GPC chromatogram change, indi-
cating that unreacted freebase porphyrin no longer exists in the
mixture and resultant oligomers have cyclic structures (vide
infra). The typical GPC chromatograms are shown in Figure 1.
oligomers is presented: bisporphyrin derivative 1 reacts with
La(acac)3 in 1,2,4-trichlorobenzene to yield porphyrin polygons,
such as cyclic dimer 12·2La(III) and cyclic trimer 13·3La(III).
The design of porphyrin arrays toward artificial photosyn-
thetic systems, molecular photonic devices, molecular containers
or capsules is a hot challenging research area.1–7 Such polymeric
or oligomeric porphyrins have been prepared by either covalent
linkage of monomeric porphyrins or programmed self-assem-
bling methods. The pursuit of new schemes for preparing por-
phyrin arrays with defined structures which frequently lead to
new photochemical and electrochemical properties has been paid
much attention by many research groups.1–7 For example,
Sanders et al. demonstrated that template synthesis is a powerful
scheme for cyclic porphyrin oligomers.1a Linear porphyrin
arrays have been synthesized by Anderson et al.1b–d and Osuka et
al.,1g–i independently. Recently, Hunter et al. showed an elegant
self assembling approach toward cyclic oligomeric porphyrin
rings utilizing a pyridine-appended cobalt porphyrin.1e–f Lindsey
et al. reported that porphyrin arrays with double- and triple-deck-
er porphyrin complexes are useful as novel candidates for a
multibit information storage system because of their unique elec-
trochemical characteristics.7 Here we describe a new synthetic
strategy for constructing cyclic porphyrin oligomers utilizing
La(III) metal and porphyrin ligands complexation. It has been
known that La(III) results in a double decker structure with por-
phyrins bearing four meso-aryl substituents by a simple treatment
(e.g., refluxing of a reaction mixture).8,9 It thus occurred to us
that the reaction of La(III) with covalently-linked bisporphyrin
should produce linear or cyclic oligomeric porphyrin arrays
(Scheme 1).10 This system is undoubtedly advantageous in pro-
ducing porphyrin arrays because (i) the orientation of two por-
phyrin planes in a double decker complex is controlled by the
inherent coordination geometry of La(III) and (ii) since the por-
phyrin ligands in the La(III) bis(porphyrinate)s can rotate in
NMR time scale,8–10 the porphyrin corners can adopt various
angles, which is suitable for the polygon formation. These char-
acteristics of La(III) coordination to porphyrin ligands have
enabled us, for the first time, to synthesize a large variety of
cyclic porphyrin oligomers from bisporphyrin 1. As far as we are
aware, this is the first example for the molecular design of double
decker porphyrin-based cyclic porphyrin arrays.
The peaks which could be assigned to dimeric species
(retention time 33.6 min) and trimeric species (retention time
31.0 min) in Figure 1A were isolated by size exclusion chro-
matography (Bio-beads SX-1, THF) and the samples were sub-
jected to analysis by GPC and MALDI TOF MS spectroscopies
(Figure 1). MALDI TOF MS spectra shows that these peaks
are assignable to the cyclic structures, 12·2La(III) (m/z 3688.36)
and 13·3La(III) (m/z 5532.1), respectively.12 The trimer frac-
tion showed a small, additional peak assignable to cyclic
tetramer 14·4La(III) (m/z 7376.6 ([M]+ = 7376.06)), which was
estimated to less than 10 mol% from GPC analysis (Figure 1D).
The measurements of MALDI TOF MS for condition A estab-
lished that the relative intensities of the peaks attributed to 1
(retention time 35.0 min), 12·2La(III) and 13·3La(III) is in a
1.0:2.5:1.0 ratio, respectively, in addition to a very small
tetramer peak. Condition B featuring the higher feed concen-
tration of 1 also yielded cyclic dimer, trimer and tetramer in a
2.6:1.0:1.0 ratio in addition to the peaks attributable to pen-
tamer and hexamer. It is seen from Figure 1 and 1H NMR spec-
tra (vide infra) that no linear oligomeric porphyrin array
remains both in the end of the reactions of condition A and con-
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2000
1267
Arnold, Synlett, 2000, 296.
dition B. Presumably, once linear 1n·(n – 1)La(III) (n ≥ 2) is
produced, the following intramolecular reaction between La(III)
and freebase porphyrin to yield cyclic porphyrin arrays occurs
in preference to the intermolecular reaction to yield linear por-
phyrin arrays under these reaction conditions.
4
R. Shediac, M. H. B. Gray, H. T. Uyeda, R. C. Johnson, J. T.
Hupp, P. J. Angiolillo, and M. J. Therien, J. Am. Chem. Soc., 122,
7017 (2000) and references cited therein.
5
6
7
K. Sugiura, Y. Fujimoto, and Y. Sakata, Chem. Commun., 2000,
1105.
A. Ikeda, M. Ayabe, S. Shinkai, S. Sakamoto, and K. Yamaguchi,
Org. Lett., 2, 3707 (2000).
a) J. Li, D. Gryko, R. B. Dabke, J. R. Diers, D. F. Bocian, W. G.
Kuhr, and J. S. Lindsey, J. Org. Chem., 65, 7379 (2000). b) A.
Ambroise, R. W. Wagner, P. D. Rao, J. A. Riggs, P. Hascoat, J. R.
Diers, J. Seth, R. K. Lammi, D. F. Bocian, D. Holten, and J. S.
Lindsey, Chem. Mater., 13, 1023 (2001) and references cited therein.
a) W. Buchler, M. K.-Botulinski, J. Löttler, and B. Scharbert,
New. J. Chem., 16, 545 (1992). b) J. W. Buchler and D. K. P. Ng,
“The Porphyrin Handbook,” ed. by K. M. Kadish, K. M. Smith,
and R. Guilard, Academic Press, San Diego (2000), Vol. 3, Chap.
20 and references cited therein.
We characterized cyclic dimer 12·2La(III) and trimer
1
13·3La(III) complexes by UV–vis and H NMR spectroscopies.
The λmax of the Soret band in 12·2La(III) is slightly blue-shifted
compared with that of 1 and the Q band is significantly broad-
ened, which are characteristic of La(III) bis(porphyrinate)s.8,9
The λmax values of 13·3La(III) appear at 424, 518, 560, and 610
8
9
1
nm, which are comparable with those of 12·2La(III). In the H
NMR spectra of 12·2La(III),12 it is confirmed that there is no pyr-
role N–H proton assignable to freebase porphyrin (δ –2.54 ppm)
and no mono-porphyrinated La(III)(acac)X species, whose proton
signals should appear in higher magnetic field. These findings
together with mass spectral evidence support our assertion that
both the dimer and the trimer have the cyclic structures.
M. Ikeda, M. Takeuchi S. Shinkai, F. Tani, and Y. Naruta, Bull.
Chem. Soc. Jpn., 74, 739 (2001).
10 We have tried to synthesize cyclic porphyrin oligomers by the
reaction of 1 with Ce(acac)3, because it is also known that
Ce(acac)3 results in a double decker structure with porphyrins.
The reaction between Ce(acac)3 and 1, however, did not proceed
at all under these reaction conditions. See recent references on Ce
bis(porphyrinate) double decker complexes; a) M Takeuchi, T.
Imada, and S. Shinkai, Angew. Chem. Int. Ed., 37, 2096 (1998). b)
M. Takeuchi, T. Imada, and S. Shinkai, Tetrahedron Lett., 39,
7897 (1998). c) M. Ikeda, M. Takeuchi, A. Sugasaki, A.
Robertson, T. Imada, and S. Shinkai, Supramol. Chem., 12, 321
(2000). d) M. Ikeda, T. Tanida, M. Takeuchi, and S. Shinkai, Org.
Lett., 2, 1803 (2000). e) A. Sugasaki, M. Ikeda, M. Takeuchi, and
S. Shinkai, Angew. Chem. Int. Ed., 39, 3839 (2000). f) K. Tashiro,
K. Konishi, and T. Aida, Angew. Chem., Int. Ed. Engl. 36, 856
(1997). g) K. Tashiro, T. Fujiwara, K. Konishi, and T. Aida,
Chem. Commun., 1998, 1121. h) K. Tashiro, K. Konishi, and T.
Aida, J. Am. Chem. Soc., 122, 7921 (2000).
In conclusion, we have demonstrated a new synthetic strat-
egy for constructing cyclic porphyrin arrays utilizing porphyrin
dimerization with La(III). In this scheme, one can easily obtain
porphyrin polygons, which should show multiple redox states.
Electrochemical studies using these porphyrin oligomers are
now in progress in our research group.
References and Notes
1
a) S. Anderson, H. L. Anderson, and J. K. M. Sanders, Acc. Chem.
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A. Osuka, J. Synth. Org. Chem., Jpn., 57, 749 (1999). i) N.
Aratani, A. Osuka, Y. H. Kim, D. H. Jeong, and D. Kim, Angew.
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J., 6, 3254 (2000) and references cited therein. l) A. Tsuda and A.
Osuka, Science, 293, 79 (2001).
11 1: Mp >300 °C, MALDI-TOFMS (CHCA) m/z 1709.23 ([M+H]+
=1709.14). 1H NMR (250 MHz, CDCl3, TMS, 25 °C) δ –2.54 (s,
4H), 1.08–1.14 (m, 18H), 1.65–1.68 (m, 12H), 1.96–2.01 (m,
12H), 4.24–4.26 (m, 12H), 7.25–7.28 (m, 12H), 8.01 (d, J = 7.80
Hz, 4H), 8.09–8.12 (m, 12H), 8.23 (d, J = 7.74 Hz, 4H), and
8.85–8.98 (m, 16H).
12 For 12·2La(III): Yield 35%, MALDI-TOFMS (CHCA) m/z
3688.36 ([M+H]+ = 3689.04), 1H NMR (600 MHz, THF-d8, TMS,
25 °C) δ 1.24–1.33 (m, 60H), 1.67–1.73 (m, 24H), 4.26–4.29 (m,
24H), 6.92–6.93 (m, 12H), 7.02–7.05 (m, 4H), 7.21–7.23 (m,
16H), 7.46–7.47 (m, 16H), 8.11–8.32 (m, 32H), and 8.76 (m,
16H). For 13·3La(III): MALDI TOF MS (CHCA) m/z 5532.1 (M+
= 5532.04). NMR spectrum of 13·3La(III) gives serious line-
broadened proton signals, especially for aromatic protons.
2
3
M. G. H. Vicente, L. Jaquinod, and K. M. Smith, Chem.
Commun., 1999, 1771.
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