Synthesis of [5]rotaxanes containing bi- and tridentate coordination sites in the axis.

Autor: Collin JP; Laboratoire de Chimie Organo-Minérale, Institut de Chimie, LC3 UMR 7177 du CNRS, Université de Strasbourg, 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France. jpcollin@chimie.u-strasbg.fr, Durot S, Keller M, Sauvage JP, Trolez Y, Cetina M, Rissanen K
Jazyk: angličtina
Zdroj: Chemistry (Weinheim an der Bergstrasse, Germany) [Chemistry] 2011 Jan 17; Vol. 17 (3), pp. 947-57. Date of Electronic Publication: 2010 Nov 16.
DOI: 10.1002/chem.201002220
Abstrakt: A new example of a linear [5]rotaxane has been synthesized by using the traditional "gathering-and-threading" approach but based on an unusual axle incorporating a symmetrical bis(bidentate) chelating fragment built on a 4,7-phenanthroline core. The stoppering reaction is particularly noteworthy since, instead of using a trivial bulky stopper as precursor to the blocking group, two semistoppered copper-complexed [2]pseudorotaxanes (namely [2]semirotaxanes) are used, which leads to the desired [5]rotaxane in good yield. The efficiency of the method relies on the use of "click" chemistry, with its very mild conditions, and on the protection by a transition-metal (copper(I)) of the various coordinating groups present in the fragments to be interconnected (terpy and bidentate chelating groups), thus inhibiting potential detrimental side reactions during the copper-catalyzed stoppering reaction. Since the external fragments and the central core of the system contain tri- and bidentate chelating units, respectively, the axle of the final [5]rotaxane incorporates two types of coordinating units: two external terpy groups (terpy: 2,2':6',2''-terpyridine) and two central bidentate ligands. Such a situation enables the system to tidy two different metals centers, and to localize them in a priori well-defined positions. This is what was observed when mixing the free ligand with a mixture of Zn(2+) and Li(+) : the zinc(II) ions were unambiguously shown to occupy the external sites, whereas the Li(+) cations were found in the central part of the [5]rotaxane. An X-ray diffraction study carried out on a [3]pseudorotaxane, the axis of which is similar to the central part of the [5]rotaxane axle, demonstrates that Zn(2+) is clearly five-coordinate, the fifth ligand being a counterion, even when the coordination site of the pseudorotaxane is designed for four-coordinate metals, which is in marked contrast with copper(I) or Li(+) .
(Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)
Databáze: MEDLINE
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