ISMSC 2007 - Università degli Studi di Pavia

Synthetic Strategies and Structural Aspects of Metal-Mediated Multi-
Porphyrin Assemblies
Elisabetta Iengo, † Ennio Zangrando, Enzo Alessio
Department of Chemistry, University of Trieste, 34127 Trieste, Italy.
†
Current address: University of Cambridge, Chemical Laboratories, Lensfield Road, Cambridge
CB2 1EW, UK.
Porphyrins play a major role as active chromophores in artificial systems mimicking the natural
photoinduced processes. The formation of coordination bonds between peripheral donor sites
on the porphyrins and external metal fragments has proved to be an efficient alternative to
covalent synthesis for the construction of multi-porphyrin assemblies, whose complexity and
beauty gradually approach those of the multichromophore systems found in Nature.
In a modular approach, relatively simple metal-mediated porphyrin adducts, owing to their
thermodynamic and kinetic stability, can be exploited as building blocks in the construction of
higher order architectures. Thus multichromophore systems become accessible on demand,
with a limited synthetic effort.
The collection of solid state
structures that will be
reported demonstrates that
the flexibility of the
porphyrins and of the metal
junctions, combined with
the conformational freedom
of the coordination bonds,
may lead to assemblies
with hardly predictable
architectures. Examples in
which X-ray structural determination was essential for establishing the real composition and
geometry of the multiporphyrin assemblies, such as the slipped-cofacial porphyrin macrocycle
shown in the figure, will be highlighted.
Some recent references of our contributions to this field are given below [1-4].
[1] F. Scandola, C. Chiorboli, A. Prodi, E. Iengo, E. Alessio, Coord. Chem. Rev., 2006, 250,
1471-1496.
[2] E. Iengo, F. Scandola, E. Alessio, Struct. Bond., 2006, 121, 105-144.
[3] E. Iengo, E. Zangrando, E. Alessio, Acc. Chem. Res., 2006, 39, 841-851.
[4] A. Prodi, C. Chiorboli, F. Scandola, E. Iengo, E. Alessio, ChemPhysChem, 2006, 7, 1514-
1519.
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Cyclodextrin-based Supramolecular Architectures and Dynamics
Akira Harada, Hiroyasu Yamaguchi, Yoshinori Takashima, Yasushi Okumura
Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
E-mail: harada@chem.sci.osaka-u.ac.jp
Cyclodextrins (CDs) have been extensively used as
host molecules for small molecules. We found that
CDs form inclusion complexes with some polymers
selectively to give pseudo-polyrotaxanes.[1]
Recently, we found that CD rings pass through
some groups unidirectionally (Figure1) [2]. In
addition, we found that the threading process could
be monitored by using a CD with a PEG chain by
way of a cinnamoyl group in the presence of a
competitive guest. (Figure 2) [3]
When each end of the polymer chain of the
pseudo-polyrotaxane is blocked by large
stopper groups, polyrotaxanes were obtained.
[4] One or two CD rings could be moved by
using an STM tip along a polymer chain. [5]
When neighbouring CD units were linked by
short binding agents, followed by removing
bulky stopper groups at both ends of the
polymer chain, tubular polymers were obtained.
[6] The molecular tube includes long molecules
like 1,6-diphenylhexatriene to give highly
fluorescent inclusion complexes.
When a guest part was attached to a
cyclodextrin host, they formed intramolecular or
intermolecular complexes to give
supramolecular assemblies. When a cinnamoyl
group was attached to one of 6-OH groups by
an ester linkage, they formed a cyclic trimer
(cyclic daisy chain). When a cinnamoyl group
was attached by an amide bond, they formed a
Figure 1. Unidirectional threading
Figure 2. Conformational switching
Figure 3. α-,β-CD alternating copolymer
IL 4
cyclic dimer. When a cinnamoyl group was attached to one of the secondary hydroxyl groups,
they formed linear oligomers, when the t-Boc group was attached to the cinnamoyl group, they
formed longer helical supramolecular polymers. In addition we have prepared α−,β-CDalternating
supramolecular polymers and [2]rotaxane polymers.[7] Supramolecular catalytic
system [8], stimuli-resposive systems[9], and supramolecular sensors have been developed.
[1] Chem. Commun., 1990, 1332. Macromolecules, 23, 2823 (1990).
[2] J. Am. Chem. Soc., 2005,127, 12186: J. Phys. Condens. Matter 2006, 18, S1809; Chem.Euro. J., in
press.; J. Am. Chem. Soc., 2000, 122, 3797.
[3] J. Am. Chem. Soc., 2006, 128, 8994; Macromolecules, in press.
[4] Nature, 356, 325 (1992). J. Am. Chem. Soc., 1994, 116, 3192.
[5] J. Am. Chem. Soc. ,2000, 122, 5411; 2003, 125, 5080
[6] Nature, 364, 516 (1993), 370, 126 (1994).
[7] J. Am. Chem. Soc., 2000, 122, 9876; 2004, 126, 11418; 2005, 127, 2034; 2005, 127, 2984.
[8] J. Am. Chem. Soc., 2004, 126, 13588; Macromolecules, in press.
[9] J. Am. Chem. Soc., 2006, 128, 2226; Angew. Chem., Intl. Ed., 2006, 4605.