Published on Web 02/01/2003
The Bis-Barium Complex of a Butterfly Crown Ether as a
Phototunable Supramolecular Catalyst
Roberta Cacciapaglia,* Stefano Di Stefano, and Luigi Mandolini*
Contribution from the Dipartimento di Chimica and ICCOM CNRsSezione di Roma, UniVersita`
La Sapienza, Box 34-ROMA 62, 00185 Roma, Italy
Abstract: Reversible phototuning of the catalytic efficiency of the bis-barium complex of azobis(benzo-
18-crown-6) in the basic ethanolysis of anilide derivatives has been achieved by light-induced cis a trans
interconversion of the azobenzene spacer unit of the catalyst. The geometry of the productive catalyst-
substrate complex is more favorable when the concave cis form of the catalyst is involved. Continuous
photoregulation of the catalytic activity at any intermediate value between the “HIGH” and “LOW” levels
was achieved by proper adjustment of the excitation wavelength or the irradiation time. The complete and
relatively fast interconvertibility of photostationary states allowed the activity of the catalyst to be repeatedly
photoswitched “HIGH” and “LOW” in the course of the same run.
Introduction
bind to the catalyst through a distal carboxylate anchoring group,
as schematically depicted in Figure 1.
This work deals with the bis-barium complex of the azobis-
Light-induced changes in molecular geometry, e.g., cis a
trans isomerization of suitable photochromics, have been widely
used to control the shape and, consequently, the properties and
(benzo-18-crown-6) ether 1, whose catalytic properties can be
1
functions of molecules, macromolecules, and biomaterials.
Among the various functions which are worth triggering by
external stimuli, catalysis plays an important role. Fairly
numerous reports are available on the photoregulation of the
catalytic activity of enzymes and related systems chemically
2
modified with photoisomerizable units. However, surprisingly
little work has been carried out on the photocontrol of catalysis
by artificial systems. A pioneering report on photocontrol of
the catalytic activity of an azobenzene-capped â-cyclodextrin
3
dates back to 1981, and a few years later Balzani et al. clearly
defined the essential machinery of a photocoreceptiVe catalyst:
i.e., a photochemical molecular device capable of performing
4
the function of a photoswitchable supramolecular catalyst. Yet,
to the best of our knowledge, only one more paper on the subject
5
has been published ever since.
6
Recently, we have shown that dinuclear alkaline-earth (Ba,
Sr) metal ion complexes of bis-crown ether ligands selectively
catalyze the basic ethanolysis of esters and anilides, which can
reversibly activated-deactivated by light-induced changes in
molecular geometry. The azobenzene unit is a well-known
*
To whom correspondence should be addressed.
7
photochromic, whose use in the construction of molecular
(
(
1) Molecular Switches; Feringa, B., Ed.; Wiley-VCH: Weinheim, Germany,
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3,9
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1
65-218.
(
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wood: Midsamer Norton, Avon, U.K., 1991; p 199.
9
4-96.
(
4) Balzani, V.; Moggi, L.; Scandola, F. In Supramolecular Photochemistry;
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Y.; Ogawa, T.; Manabe, O. J. Am. Chem. Soc. 1980, 102, 5860-5865. (d)
Shinkai, S.; Nakaji, T.; Ogawa, T.; Shigematsu, K.; Manabe, O. J. Am.
Chem. Soc. 1981, 103, 111-115. (e) Shinkai, S.; Shigematsu, K.; Kusano,
Y.; Manabe, O. J. Chem. Soc., Perkin Trans. 1 1981, 3279-3283. (f)
Shinkai, S.; Ogawa, T.; Kusano, Y.; Manabe, O.; Kikukawa, K.; Goto, T.;
Matsuda, T. J. Am. Chem. Soc. 1982, 104, 1960-1967.
(
(
4
48.
6) (a) Cacciapaglia, R.; Di Stefano, S.; Kelderman, E.; Mandolini, L. Angew.
Chem., Int. Ed. Engl. 1999, 38, 348-351. (b) Cacciapaglia, R.; Di Stefano,
S.; Mandolini, L. J. Org. Chem. 2001, 66, 5926-5928. (c) Cacciapaglia,
R.; Di Stefano, S.; Mandolini, L. J. Org. Chem. 2002, 67, 521-525.
2224
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J. AM. CHEM. SOC. 2003, 125, 2224-2227
10.1021/ja029331x CCC: $25.00 © 2003 American Chemical Society