ISMSC 2007 - Università degli Studi di Pavia

PSB 11
Dual binding properties of polycyclic receptors incorporating 5,12-dioxocyclam
units: the interplay between amines and amides
Michel Meyer, Guy-Yves Vollmer, Laurent Frémond, Enrique Espinosa, Roger Guilard
Institut de Chimie Moléculaire de l'Université de Bourgogne (UMR CNRS 5260), 9, avenue Alain
Savary, BP 47870, 21078 Dijon, France
The quest for new macropolycyclic receptors that could serve as functional catalysts or as
biomimetic models of biological systems is stimulating continuous endeavor aimed to design
new synthetic strategies. A trans "autodiprotected" tetraazamacrocycle with 5,12-disposed
carbonyl groups was found to provide a convenient entry into a new class of highly
preorganized ligands possessing well defined but tunable metal-ion binding cavities. Provided
that 5,12-dioxocyclam (L 1 ) reacts with the appropriate biselectrophile, macrobicyclic and
macrotricyclic cages of spheroïdal (A 1 -A 3 ) and cylindrical (T 1 -T 3 ) topologies are obtained.
O
R
N HN
O
NH
N
R
L 1 R = H
L 2 R = CH 3
X
Br Br
X = N or CH
O
X
N
N
N
X
HN
N
NH
O
HN
NH
O
O
O
HN
NH
O
N
N
X
A 1 X = CH (o-xylyl)
A 2 X = CH (m-xylyl)
A 3 X = N
T 1 X = CH (m-xylyl)
T 2 X = CH (p-xylyl)
T 3 X = N (m-pyridyl)
The peculiar acid-base properties of these amide-based ligands will be discussed in light of
structural, spectroscopic and potentiometric data [1,2]. Reorganization of intramolecular
hydrogen bond networks will be invoked to rationalize both the slow protonation kinetics
exhibited by the strapped dioxocyclams A 1 -A 3 and the unprecedented allosteric regulation and
cooperative protonation displayed by the barrel-shaped tricyclic receptors T 1 -T 3 .
Abstraction of the amide protons by a weak base affords remarkably stable and inert copper(II)
complexes which are able to switch from an amidate to an iminolate binding mode upon
acidification [3]. Moreover, selective metalation of T 1 enables to isolate both the mono- and the
dicopper species. Selected structural and spectroscopic properties, including metal-metal
interactions in the dinuclear species, will also be presented.
[1] M. Meyer, L. Frémond, A. Tabard, E. Espinosa, G. Y. Vollmer, R. Guilard and Y. Dory, New
J. Chem., 2005, 29, 99.
[2] M. Meyer, L. Frémond, E. Espinosa, S. Brandès, G. Y. Vollmer and R. Guilard, New J.
Chem., 2005, 29, 1121.
[3] M. Meyer, L. Frémond, E. Espinosa, R. Guilard, Z. Ou and K. M. Kadish, Inorg. Chem.,
2004, 43, 5572.
PSB 12
Synthesis and Characterization of the First Paramagnetic [1]Rotaxane
Michela Fanì, Paola Franchi, Elisabetta Mezzina, Marco Lucarini
Dipartimento di Chimica Organica “A. Mangini”, Università di Bologna, Via San Giacomo 11, I-
40126 Bologna, Italy
Nitroxide radicals are of great importance and interest in many fields of chemistry and related
sciences whose properties can be exploited in many technological field., i.e. in biomedicine as spin
traps,[1] in chemical synthesis,[2] and in the assembly of organic radical centers to control
magnetic interaction in multispin molecular systems.[3]
Design and dynamics control of new supramolecular host-guest complexes bearing unpaired
electrons represent one of our research fields.[4]
When a guest part is covalently attached to a cyclic host, it may form intramolecular and
intermolecular complexes. Among the cyclic hosts cyclodextrins (CDs) are known to form a wide
variety of inclusion complexes in aqueous solution. When covalently derivatized at 6 position
(small anular edge) or at 2/3 position (large anular face) with a substituent of proper size and
lenght, the CD can form either intramolecular (self-inclusion) or intermolecular complexes with the
substituent, where the substituent is inserted in the anular cavity of the host. If the substituent
involved in a self-inclusion complex is blocked into the CD with a bulky paramagnetic group acting
as a stopper, a [1]rotaxane structure derives in which one side of the guest (the so-called ‘dumbell’
of rotaxane) results covalently linked to the cyclic host.
In the present work we report the synthesis and the
OH OTs
SH
S
β-CD 6-TsO-β-CD 6-SH-β-CD (2) 3a
a, Y=CH 2
b, Y=CH 2
c, Y=CH 2CH2
d
I
TsCl Thiourea a
O
O
NO
Br Y O
Br Y N H
N
H
S
O N
O N O
O
N
b, c, d
3b, 3c, 3d
O
characterization of a paramagnetic [1]rotaxane starting
from a derivative of a β-cyclodextrin monosubstituted at
C6 position, i.e. mono-6-deoxy-6-mercapto-β-CD (2).
Reaction of 2 with different linear halides a-d containing
at one side a persistent radical centre consisting of a
2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) moiety, in
basic aqueous medium, allows the preparation of the
corresponding monoderivatized CDs.
Self-complexation of the linear component into the CD
allows the rotaxanation reaction to occur only in the case
of compound 3a. In the other cases (3b-3d) the new bond
is formed only outside the cyclic host. The self-included
structure of the paramagnetic [1]rotaxane 3a was
obtained by ESI-MS, 1D and 2D NMR and EPR spectra.
EPR kinetic measurements have evidenced the
enhanced persistency of the new rotaxaned radicals.
[1] R. P. Mason, Free Radical Bio. Med. 2004, 36, 1214-1223.
[2] C. J. Hawker, A. W. Bosman and E. Harth, Chem. Rev. 2001, 101, 3661-3688. C. J. Hawker,
Acc. Chem. Res. 1997, 30, 373-382. A. Studer, Chem.-Eur. J. 2001, 7, 1159-1164. F. Minisci,
F. Recupero, G. F. Pedulli, and M. Lucarini, J. Mol. Cat. A 2003, 204-205, 63-90.
[3] D. B. Amabilino and J. Veciana in Magnetism, Molecules to Materials II, Vol. II (Ed.: J. S.
Miller, M. Drillon), Wiley-VCH, Weinheim, 2001, pp. 1-60.
[4] E. Mezzina, M. Fanì, F. Ferroni, P. Franchi, M. Menna and M. Lucarini, J. Org. Chem. 2006,
71, 3773-3777.