Construction of Interlocking and Threaded Rings Using Two Different Transition Metals as Templating and Connecting Centers: Catenanes and Rotaxanes Incorporating Ru(terpy)2-Units in Their Framework
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Abstract
This work describes a new method for the preparation of metal-containing catenanes and rotaxanes, using pure coordination chemistry, by stepwise reaction of organic fragments with two different transition metals. The key organic compound contains two terpyridine (terpy) ligands and one diphenylphenanthroline (dpp) moiety and was prepared in high yield by alkylation of 2,9-bis(hydroxyphenyl)-1,10-phenanthroline with 5-(3-methanosulfonyl-1-propyl)-5''-methyl-2,2':6',2''-terpyridine. Reaction of this polyfunctional ligand with 1 equiv of a dpp-containing 30-membered macrocycle and Cu(I) as a template led to a threaded Cu(dpp)2+-type precursor complex (P). Due to the high affinity of Cu(I) for the dpp ligands, the reaction is selective, and no competition of the terpy units for the metal takes place. Thus, this threaded complex contains two free terpy moieties suitable for a further coordination reaction. Ru(II) was used to build the stoppers or to clip the free ligands due to the high stability of Ru(terpy)22+ complexes. Compound P reacts with Ru(DMSO)4Cl2 in 1,2-dichloroethane−EtOH at 70 °C under high dilution conditions to give the desired catenate in 43% yield. A Cu coordinated rotaxane was obtained by stoppering the free ends of precursor P with 2 equiv of Ru(terpy)(acetone)3(BF4)2. In both cases the intertwined geometry of the dpp units is maintained after Ru(II) coordination. The complexes were characterized by spectroscopic methods, FAB-MS, and cyclic voltammetry. The high stability of the Ru complexes allows for the selective removal of Cu(I). Thus, reaction of the Cu-complexed rotaxane or the catenate with KCN in MeCN−H2O led to the corresponding rotaxane or catenane, respectively, in which the intertwined topography has been destroyed upon liberation of the dpp ligands. This approach opens a new way for the preparation of multicomponent species with promising photochemical properties.
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