A linear multiporphyrinic [2]-rotaxane via amide bond formation

Article abstract of DOI:10.1021/ol006137b

(matrix presented) A linear multiporphyrinic [2]-rotaxane has been synthesized using the transition metal-templating method for threading a gold(III)-incorporating macrocycle onto a rodlike, phenanthroline-derived chelate bearing carboxylate end groups. S

Full text of DOI:10.1021/ol006137b

ORGANIC
LETTERS
2000
Vol. 2, No. 20
3051-3054
A Linear Multiporphyrinic [2]-Rotaxane
via Amide Bond Formation
Mar´ıa-Jesu´s Blanco, Jean-Claude Chambron,* Vale´rie Heitz, and
Jean-Pierre Sauvage*
Laboratoire de Chimie Organo-Mine´rale, UMR 7513 du C.N.R.S., UniVersite´ Louis
Pasteur, Institut Le Bel, 4, rue Blaise Pascal, 67000 Strasbourg, France
chambron@chimie.u-strasbg.fr
Received May 31, 2000
ABSTRACT
A linear multiporphyrinic [2]-rotaxane has been synthesized using the transition metal-templating method for threading a gold(III)-incorporating
macrocycle onto a rodlike, phenanthroline-derived chelate bearing carboxylate end groups. Stoppering has been performed by reacting the
resulting prerotaxane with the amino derivative of a zinc tetraarylporphyrin under EDC−HOBt activation. A 34% yield has been realized for this
one-pot, double amide bond formation.
Rotaxanes have become very accessible compounds thanks
to the many efficient template syntheses that have been
discovered in the past decade.1 Interest in these compounds
has switched from synthetic exercise to the development of
functional molecular systems that take advantage of the
mechanical bond between the ring and the dumbbell com-
ponents.2 In particular, rotaxanes based on porphyrins (as
stoppers and as elements of the macrocycle) have shown
remarkable photochemical properties.3 The molecules de-
veloped in our group are usually synthesized using transition
metal-controlled threading of the macrocycle onto a stringlike
fragment prior to in situ generation of the porphyrin
stoppers.4 Both organic precursors incorporate a 2,9-di-
phenyl-1,10-phenanthroline chelate, to enforce a tetrahedral
coordination sphere on the metal center. As a result of the
(1) For recent references, see: (a) Rowan, A. E.; Aarts, P. P. M.;
Figure 1. Schematic representations of copper(I) complexes of
Koutstaal, K. W. M. Chem. Commun. 1998, 611. (b) Kolchinski, A. G.;
[2]-rotaxanes based on oblique (a) and linear (b) Zn(II) (green
diamonds) bisporphyrin dumbbells and incorporating a gold(III)
(red diamond) porphyrin in the ring. The bold lines represent the
coordinating sites and the blue disk is a CuI atom.
Alcock, N. W.; Roesner, R. A.; Busch, D. H. Chem. Commun. 1998, 1437.
(c) Loeb, S. J.; Wisner, J. A. Chem. Commun. 1998, 2757. (d) Hu¨bner, G.
M.; Gla¨ser, J.; Seel, C.; Vo¨gtle, F. Angew. Chem., Int. Ed. 1999, 38, 383.
(e) Tuncel, D.; Steinke, J. H. G. Chem. Commun. 1999, 1509. (f) Chichak,
K.; Walsh, M. C.; Branda, N. R.; Chem. Commun. 2000, 847. (g) Buston,
J. E. H.; Young, J. R.; Anderson, H. L. Chem. Commun. 2000, 905.
10.1021/ol006137b CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/14/2000

Figure 2. Chemical structure of the copper(I) complex [1Cu]2+ of [2]-rotaxane 1+.
2,9-disubstitution of the phenanthroline nuclei, the porphyrin
stoppers display oblique orientations with respect to each
other, as shown schematically in Figure 1a. This geometrical
property was essential in the design of reaction center
mimics.5
In this Letter, we report on the synthesis of a zinc(II)
porphyrin-stoppered [2]-rotaxane built from a linear thread
component in order to maximize the distance between the
stoppers and a gold(III) porphyrin-incorporating macrocycle,
as shown schematically in Figure 1b.
The structural formula of the CuI complex [1Cu]2+ of
[2]-rotaxane 1+ of this study is depicted in Figure 2. This
molecule was designed according to the following features:
(i) The linear arrangement of the porphyrin termini is
achieved by connecting them through a sequence of spacers
to the positions 3 and 8 of the threading phenanthroline
chelate. (ii) 2,9-Dimethyl substitution of the same chelate
allows one to strictly control the coordination geometry of
the metal template (CuI). (iii) Amide bonds were chosen as
connections between the phenylene spacers attached respec-
tively to the porphyrin stoppers and to the central chelating
piece of the molecular thread for the rigidity imparted by
their partial double bond character.
Synthetic routes to the key intermediates phenanthroline
8 and porphyrin 11 are shown in Figures 3 and 4, respec-
tively. Macrocycle 12PF6 (Figure 4) was prepared as
Figure 3. Synthesis of the rod component 8‚HCl.
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Org. Lett., Vol. 2, No. 20, 2000

Figure 4. The porphyrin intermediates of [2]-rotaxane 1+.
described in ref 4. Phenanthroline 8 was synthesized as
follows. Double Suzuki cross-coupling of 3,8-dibromo-1,10-
phenanthroline 26 with p-(5,5-dimethyl-1,3-dioxan-2-yl)-
phenylpinacylborate 37 ([Pd(PPh3)4], toluene, reflux) using
Ba(OH)2 as a base to minimize the competitive deboronation
reaction8 afforded 4 in 92% yield. Dimethylation leading to
Figure 5. Copper(I)-templated strategy and synthetic steps for the
preparation of [2]-rotaxane 1+, using schematic representations for
the different compounds (see legend of Figure 1 for the key).
6 was carried out in a stepwise manner.9 Addition at 0 °C
of a 3-fold excess of MeLi to 4 followed by hydrolysis and
MnO2 oxidation provided the monomethylated phenanthro-
line derivative 5, which was treated similarly, affording, after
purification, the disubstituted compound 6 in 87% overall
yield. HCl cleavage of the acetal groups produced dialdehyde
7 in 89% yield. The target diacid 8 was obtained in 89%
yield as the hydrochloride salt by KMnO4 oxidation in
acetone followed by HCl precipitation. 5,10,15-Tris(3,5-di-
tert-butylphenyl)-20-(4-nitrophenyl)porphyrin 9 was prepared
(2) (a) Bissell, R. A.; Co´rdova, E.; Kaifer, A. E.; Stoddart, J. F. Nature
1994, 369, 133. (b) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake,
M.; Nakashima, N. J. Am. Chem. Soc. 1997, 119, 7605. (c) Lane, A. S.;
Leigh, D. A.; Murphy, A. J. Am. Chem. Soc. 1997, 119, 10547. (d) Ashton,
P. R.; Ballardini, R.; Balzani, V.; Baxter, I.; Credi, A.; Fyfe, M. C. T.;
Gandolfi, M. T.; Go´mez-Lo´pez, M.; Mart´ınez-D´ıaz, M.-V.; Piersanti, A.;
Spencer, N.; Stoddart, J. F.; Venturi, M.; White, A. J. P.; Williams, D. J.
J. Am. Chem. Soc. 1998, 120, 11932. (e) Armaroli, N.; Balzani, V.; Collin,
J.-P.; Gavin˜a, P.; Sauvage, J.-P.; Ventura, B. J. Am. Chem. Soc. 1999, 121,
4397.
(3) Andersson, M.; Linke, M.; Chambron, J.-C.; Davidsson, J.; Heitz,
V.; Sauvage, J.-P.; Hammarstro¨m, L. J. Am. Chem. Soc. 2000, 122, 3526.
(4) Linke, M.; Chambron, J.-C.; Heitz, V.; Sauvage, J.-P. Chem. Commun.
1998, 2469.
(7) Bruce, J.; Chambron, J.-C.; Ko¨lle, P.; Sauvage, J.-P. Manuscript in
preparation.
(8) Watanabe, T.; Miyaura, N.; Suzuki, A. Synlett 1992, 207.
(9) Dietrich-Buchecker, C.; Jime´nez, M. C.; Sauvage, J.-P. Tetrahedron
Lett. 1999, 40, 3395.
(5) Chambron, J.-C.; Chardon-Noblat, S.; Harriman, A.; Heitz, V.;
Sauvage, J.-P. Pure Appl. Chem. 1993, 65, 2343.
(6) Saitoh, Y.; Koizumi, T.-a.; Osakada, K.; Yamamoto, T. Can. J. Chem.
1997, 75, 1336.
Org. Lett., Vol. 2, No. 20, 2000
3053

by following the method of Adler and Longo,10 by reaction
of 4-nitrobenzaldehyde, 3,5-di-tert-butylbenzaldehyde,11 and
pyrrole in refluxing propionic acid, and isolated in 12% yield
after chromatography. Reduction of 9 with SnCl2 in the
presence of HCl in EtOH at 70 °C afforded the aminopor-
phyrin derivative 10 in 90% yield. Its zinc complex (11) was
obtained in 97% yield by reaction with Zn(OAc)2‚2H2O in
refluxing CHCl3/MeOH.
Figure 5 shows the strategy for rotaxane construction and
the synthetic route that has been followed to prepare
[2]-rotaxane 1PF6. Effective copper(I)-templated threading
to form prerotaxane 13 was observed only upon reaction of
the dicarboxylate form of 8, generated by treating 8‚HCl with
Et3N (330 mol %), with the copper complex of macrocycle
12PF6, prepared by reaction of 12PF6 with Cu(CH3CN)4PF6
in stoichiometric amounts. The stoppering reaction was
performed by coupling zinc aminoporphyrin 11 with in situ
activated prerotaxane 13. 1-Hydroxybenzotriazole (HOBt)12
and 1-ethyl-3-(3-dimethylamino)propylcarbodiimide (EDC)13
were used as mild coupling reagents for the formation of
the activated ester. Accordingly, to a solution of 13 at 0 °C
were sequentially added EDC (250 mol %), HOBt (400 mol
%), and zinc aminoporphyrin 11 (210 mol %). After 2 days
at room temperature, anion exchange with KPF6, and
chromatographic purification, copper(I)-complexed [2]-ro-
taxane [1Cu](PF6)2 was obtained in 34% yield. The true
rotaxane species 1PF6 was obtained by reaction of the CuI
complex with excess of KCN.
Photoinduced electron-transfer properties of [2]-rotaxane
1+, its copper complex 1Cu+, and those of related compounds
are under investigation and will be reported in due course.
Acknowledgment. We thank Jean-Daniel Sauer for the
1
high-field H NMR spectra and Raymond Hueber for the
FAB mass spectrometry measurements. M.J.B. is grateful
to the European Community for a grant (TMR Contract
FMRX-CT96-0031).
(10) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour,
J.; Korsakoff, L. J. Org. Chem. 1967, 32, 476.
(11) Chardon-Noblat, S.; Sauvage, J.-P. Tetrahedron 1991, 47, 5123.
(12) Ko¨nig, W.; Geiger, R. Chem. Ber. 1970, 103, 788.
OL006137B
(13) (a) Sheehan, J. C.; Ledis, S. L. J. Am. Chem. Soc. 1973, 95, 875.
(b) Chen, F. M. F.; Benoiton, N. L. Synthesis 1979, 709.
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