Metallo catenanes

Dietrich-Buchecker, C.O., Sauvage, J.P. Une nouvelle famille de molecules les metallo-catenanes, Tetrahedron Lett. 24 (1983), 5091-5094. 

The above section describes the pioneering work which opened the route to the synthesis of interlocked rings, i.e., catenanes. The displayed X-ray stuctures of the prototypical free [2]catenane and of some metallo catenanes allow one to visualize the interlocking of the coordinating macrocycles, the intramolecular interactions responsible for the overall structures, and to understand their particular behavior (such as electrochemical properties, enhancement of basicity, etc.) due to their topography and to their topology. 

Dietrich-Buchecker, C.O., Sauvage, JP., and Kitzinger, JP. (1983) Une nouvelle famille de molecules Les metallo-catenanes. Tetrahedron Lett, 24, 5095-5098. Sauvage, J.P. (1990) Interlacing molecular threads on transition metals Catenands, catenates, and knots, Acc. Chem, Res. 23, 319-327. Dietrich-Buchecker, C.O. and Sauvage, JP. (1992) Supramoleculcur chemistry, Kluwer, Amsterdam, 259-277. 

Hydrophobic forces are also important in the assemblies of metallo-supramolecular catenanes. One of the most interesting examples is formed when one of the unpolar bipyridine ligands of one macrocycle is included spontaneously in the other macrocycle s internal cavity [39]. Here, the benzene unit of the one macrocycle serves as a guest molecule for the other macrocycle, and the cyclization is favored by n-n interactions. In addition, the minimization of hydrophobic surfaces in polar medium constitutes the second driving force for the catenane formation. The quantitative formation of the [2]catenanes 31a and 31b based on this principle are depicted in Figure 13. Formation of catenane 31b was found to be reversible. Even at room temperature, two monomeric ring structures equilibrate quickly due to the labile nature of Pd-N bond and interlocked molecular ring system 31b is formed. 

Metallo-Rotaxanes and Catenanes as Redox Switches Towards Molecular Machines and Motors... 

Fig. 3 The equilibrium-controlled self-assembly of a metallo-organic [2]catenane. (From Ref. [12].)...

Figure 3.34 (a) The eight components and (b) the crystal structure of a catenane consisting of two metallo-macrocycles. The void with one cyclic species is an ideal size/shape fit for another copy of itself to fill. 

In 1995, Hamilton et al. described one of the first examples of a combinatorial approach to synthetic receptors using reversible coordination around a metal ion [20]. In the same year Harding et al. described the guest-induced amplification of a metallo-macrocycle 4 and metaUo-[2]catenane 5 from a mixture (Scheme 1.4) [20, 21]. Although not described as such, these examples employed the basic principles of DCC-template-stabilized selection of effective synthetic receptors from among an equihbrating library of potential receptors. 

The metallo-carbene catalysts for ring-closing metathesis (RCM) reactions are ideal for this purpose. As a result of the mild reaction conditions and lack of competition with the coordination chemistry of the intermediate helical complex, the RCM strategy is particularly well adapted to the synthesis of copper(I)-complexed catenanes. A natural extension of this work was the preparation of a trefoil knot following the strategy depicted in Figure 11. 

HenkeUs JJ, Ronson TK, Harding LP, Hardie MJ (2011) M3L2 metallo-cryptophanes [2]catenane tmd simple cages. Chem Commun 47 6560-6562... 

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