Directly linked dehydropurpurin-porphyrin dyads from Ag(I)-promoted oxidation of meso-phenylethynyl substituted zinc(II) porphyrins

Article abstract of DOI:10.1039/b106050n

Ag(I)-promoted oxidation of (5,15-diaryl-10-phenylethynylporphyrinato)zinc(n) complexes in CHCl₃ gave directly linked 12,13-dehydropurpurin-porphyrin dyads, the structures of which were revealed by X-ray analysis.

Full text of DOI:10.1039/b106050n

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Directly linked dehydropurpurin–porphyrin dyads from
Ag( )-promoted oxidation of meso-phenylethynyl substituted zinc(II
I
)
porphyrins
Aiko Nakano, Naoki Aratani, Hiroyuki Furuta and Atsuhiro Osuka*
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502,
Japan. E-mail: osuka@kuchem.kyoto-u.ac.jp
Received (in Cambridge, UK) 9th July 2001, Accepted 21st August 2001
First published as an Advance Article on the web 13th September 2001
Ag(
I
)-promoted oxidation of (5,15-diaryl-10-phenylethynyl-
9.07 ppm, a meso-proton at 10.31 ppm, and a set of protons due
to the two equivalent 3,5-dioctyloxyphenyl substituents, while
the peripheral b-protons in the dehydropurpurin macrocycle
appeared as a singlet at 7.56 ppm (Ha); three sets of mutually
coupled pairs of doublets were observed of which the most
high-field shifted signal appearing at 4.77 ppm was assigned to
Hb because of its location in the shielding region of the
neighboring porphyrin. In order to obtain an X-ray crystal
structure, a similar hybrid dimer 2b–Zn was prepared from 1b
in 19% yield and was converted into the bis-Cu(II) complex 2b–
Cu. Fig. 1 shows the X-ray crystal structure of 2b–Cu,9 which
provides firm evidence for the directly-linked porphyrin–
12,13-dehydropurpurin dyad. Whereas the meso-arylethynyl
substituent in the dehydropurpurin moiety is intact, that in the
porphyrin is condensed with the unsubstituted porphyrin side to
form an exocyclic five-membered ring. The dehydropurpurin
macrocycle is nearly flat with a mean plane deviation of 0.119
Å and is directly linked with the porphyrin ring with a dihedral
angle of 90.8°. This orthogonal structure well explains the
observed 1H NMR spectra mentioned above. It is of interest that
the two phenyl rings [designated as Ph1 and Ph2 in Fig. 1(a)] are
nearly coplanar with the dehydropurpurin macrocycle with
dihedral angles of 20.7 and 15.6°, respectively. The mechanism
of this dimerization is not fully understood but may be
considered to be initiated by one-electron oxidation of the
zinc(II)-phenylethynylporphyrin with AgPF6 followed by nu-
cleophilic attack of another neutral porphyrin with its meso-
position against the ethynyl-carbon adjacent to the meso-
position.
porphyrinato)zinc(II) complexes in CHCl3 gave directly
linked 12,13-dehydropurpurin–porphyrin dyads, the struc-
tures of which were revealed by X-ray analysis.
5,15-Diaryl metalloporphyrins without b-pyrrolic substituents
have been shown to be reactive in direct coupling at the meso-
and/or b-positions under one-electron oxidizing conditions.1
Along this line, we reported efficient synthetic routes to meso–
meso singly-linked diporphyrins,2 meso–b singly-linked di-
porphyrins,3 meso–b doubly-linked diporphyrins,4 and meso–
meso, b–b, b–b triply-linked diporphyrins5 through the
oxidation of metalloporphyrins. The observed metal-dependent
coupling regioselectivities are likely to be correlated with the
electronic properties of the cation radical intermediates, espe-
cially whether the SOMO is derived from the A2u or A1u orbital.
In this respect, meso-ethynylated metalloporphyrins are of
particular interest since their HOMO orbitals are indicated to be
extending over the meso-ethynyl substituent.6,7 Here, we report
that Ag(
nyl-substituted zinc(II
dehydropurpurin–porphyrin dyads.
I
)-promoted oxidation of 5,15-diaryl-10-phenylethy-
porphyrins gave directly-linked
)
Treatment of 1a–Zn with 1.0 equiv. of AgPF6 in CHCl3 at
room temperature for 6 h followed by separations over size-
exclusion and silica-gel columns provided a dimer of 1a–Zn in
34% yield. The molecular weight of the dimer was revealed to
be m/z = 2273 (calc. for C144H174N8O8Zn2, 2271) by the FAB-
MS measurement but its 1H NMR spectrum was compatible not
with the structure of symmetric meso–meso coupling product 38
1
but with that of 2a–Zn. The H NMR spectrum revealed the
Although tetrapyrrolic macrocycles with an exocyclic five
membered ring are quite ubiquitous both in nature10 and
synthetic studies,11 the 12,13-dehydropurpurin structure is quite
presence of a symmetric 5-substituted porphyrin subunit by
featuring four 2H-equivalent b-protons at 10.31, 9.43, 9.23 and
Scheme 1 Reaction of 1 and AgPF6.
1920
Chem. Commun., 2001, 1920–1921
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b106050n

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nm for 2a–Zn and 415 nm for 2a–H2 can be assigned to Soret
bands of the porphyrin, and the broad bands at 471 and 498 nm
for 2a–Zn and 482 nm for 2a–H2 can be assigned to Soret-like
bands of the dehydropurpurin. In addition, broad Q-like bands
are observed at 645 nm for 2a–Zn and at 674 nm for 2a–H2.
Neither 2a–Zn nor 2a–H2 exhibits fluorescence, probably
reflecting strong electronic interaction between the two macro-
cycles. These findings may suggest the potential use of such
dyads as energy- and electron-transfer functional units. Related
detailed studies will be reported elsewhere.
This work was supported by a Grant-in-Aids for Scientific
Research from the Ministry of Education, Science, Sports and
Culture of Japan and by CREST (Core Research for Evolutional
Science and Technology) of the Japan Science and Technology
Corporation (JST).
Notes and references
† Spectral data for 2a–Zn; dH(500 MHz, CDCl3): 10.31 (d, J = 4.5 Hz, 2H,
b-H), 10.31 (s, 1H, meso-H), 9.43 (d, J 4.5 Hz, 2H, b-H), 9.23 (d, J 4.5 Hz,
2H, b-H), 9.07 (d, J 4.5 Hz, 2H, b-H), 9.00 (d, J 4.5 Hz, 1H, b-H), 8.94 (d,
J 4.5 Hz, 1H, b-H), 8.31 (d, J 4.5 Hz, 1H, b-H), 8.07 (d, J 5.0 Hz, 1H, b-H),
7.88 (d, J 7.0 Hz, 2H, Ph), 7.67 (s, 1H, b-H), 7.50 (t, J 7.0 Hz, 2H, Ph), 7.45
(t, J 7.0 Hz, 1H, Ph), 7.42 (s, 2H, Ar), 7.38 (s, 2H, Ar), 7.26 (d, J 2.0 Hz,
2H, Ar), 7.06 (d, J 8.0 Hz, 2H, Ph), 6.93 (d, J 4.5 Hz, 1H, b-H), 6.85 (t, J
2.5 Hz, 1H, Ar), 6.84 (t, J 2.5 Hz, 2H, Ar), 6.74 (t, J 8.0 Hz, 1H, Ph), 6.63
(d, J 2.0 Hz, 2H, Ar), 6.61 (t, J 8.0 Hz, 2H, Ph), 6.36 (t, J 2.0 Hz, 1H, Ar),
4.77 (d, J 5.0 Hz, 1H, b-H), 4.18 (t, J 6.5 Hz, 4H, octyl), 4.11 (t, J 6.5 Hz,
4H, octyl), 4.06 (t, J 6.0 Hz, 4H, octyl), 3.70 (m, 4H, octyl), 1.92 (m, 4H,
octyl), 1.84 (m, 4H, octyl), 1.79 (m, 4H, octyl), 1.55–1.12 (m, 84H, octyl),
0.89 (t, J 8.0 Hz, 6H, octyl), 0.84 (t, J 8.0 Hz, 6H, octyl), 0.79 (t, J 8.0 Hz,
6H, octyl) and 0.75 (t, J 8.0 Hz, 6H, octyl). Mass (FAB): found 2273, calc.
for C144H174N8O8Zn2, 2271. UV–VIS (THF): lmax (log e) = 421 (5.58),
471 (4.88), 498 (5.00), 552 (4.65) and 645 (3.94) nm.
1 N. Aratani and A. Osuka, Bull. Chem. Soc. Jpn., 2001, 74, 1361.
2 A. Osuka and H. Shimidzu, Angew. Chem., Int. Ed. Engl., 1997, 36, 135;
N. Aratani, A. Osuka, Y. H. Kim, D. H. Jeong and D. Kim, Angew.
Chem., Int. Ed., 2000, 39, 1458; Y. H. Kim, D. H. Jeong, D. Kim, S. C.
Jeoung, H. S. Cho, S. K. Kim, N. Aratani and A. Osuka, J. Am. Chem.
Soc., 2001, 123, 76.
Fig. 1 Molecular structure of 2b–Cu: (a) top view and (b) side view;
solvents and hydrogen atoms are omitted for clarity. Bond lengths of C(6)–
C(7) and C(6)–porphyrin meso-carbon are 1.38(1) and 1.50(1) Å,
respectively.
3 T. Ogawa, Y. Nishimoto, N. Yoshida, N. Ono and A. Osuka, Angew.
Chem., Int. Ed., 1999, 38, 176.
4 A. Tsuda, A. Nakano, H. Furuta, H. Yamochi and A. Osuka, Angew.
Chem., Int. Ed., 2000, 39, 558.
5 A. Tsuda, H. Furuta and A. Osuka, Angew. Chem., Int. Ed., 2000, 39,
2549; A. Tsuda and A. Osuka, Science, 2001, 293, 79.
6 D. P. Arnold, G. A. Heath and D. A. James, J. Porphyrins
Phthalocyanines, 1999, 3, 5; S. M. LeCours, S. G. DiMagno and M. J.
Therien, J. Am. Chem. Soc., 1996, 118, 11854; H. L. Anderson, Chem.
Commun., 1999, 2323.
7 A. Nakano, H. Shimidzu and A. Osuka, Tetrahedron Lett., 1998, 39,
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2001, 105, 4822.
rare in the literature,12 and there is much less information on this
1
macrocycle. The H NMR spectrum of 2a–H2 revealed the
inner NH protons at 3.09 and 5.04 ppm for the dehydropurpurin
ring, hence suggesting that its ring current is weaker compared
with those in structurally related porphyrins and pheophor-
bides.
Fig. 2 shows the absorption spectra of 2a–Zn† and 2a–
H2 taken in THF. It is conceivable that the direct connection
leads to the strong electronic interaction between the two
macrocycles and causes broadening of the absorption bands.
Nevertheless, it seems likely that relatively sharp bands at 421
8 The dimer was independently prepared from meso–meso linked
diporphyrin through meso,meso-dibromination followed by bis-phenyl-
ethynylation: A. Nakano, A. Osuka, T. Yamazaki, Y. Nishimura, S.
Akimoto, I. Yamazaki, A. Itaya, M. Murakami and H. Miyasaka, Chem.
Eur. J., 2001, 7, 3134.
9 Crystal data for 2b–Cu: red prism, C84H54N8Cu2·C7H8, Mw = 1394.64,
¯
triclinic, space group P1, a = 13.204(1), b = 24.665, c = 11.0879(9)
Å, a = 99.737(2), b = 106.210(3), g = 83.472(5)°, V = 3409.1(5) Å3,
Z = 2, m(Mo-Ka) = 6.81 cm21, Dc = 1.359 g cm23, T = 296(1) K.
Final R = 0.060, Rw = 0.066 for 8332 reflections with I > 3s(I).
CCDC reference number 168237. See http://www.rsc.org/suppdata/cc/
b1/b106050n/ for crystallographic data in CIF or other electronic
format.
10 Chlorophylls, ed. H. Scheer, CRC Press, Boca Raton, FL, 1991.
11 M. D. G. H. Vicente, in The Porphyrin Handbook, ed. K. M. Kadish, K.
M. Smith and R. Guilard, Academic Press, San Diego, CA, 2000, vol. 1,
pp. 149–199.
12 C. Bauder, R. Ocampo and H. J. Callot, Tetrahedron, 1992, 48, 5135; H.
Klement, M. Helfrich, U. Oster, S. Schoch and W. Rüdiger, Eur. J.
Biochem., 1999, 265, 862.
Fig. 2 Absorption spectra of 2a–Zn (——) and 2a–H2 (- - - - - - ) in
THF.
Chem. Commun., 2001, 1920–1921
1921