Catenane metal-containing

J.-P. Sauvage, Transition Metal-Containing Rotaxanes and Catenanes in Motion Toward Molecular Machines and Motors , Acc Chem. Res. 1998,31, 611-619. 

Fujimoto and coworkers used a self-assembled Janus [2]-pseudorotaxane406 to obtain a Janus[2]rotaxane 407 (Figure 8.2.4) [33]. A quadruply stranded alkaline earth metal containing helical catenate, a charge-neutral heterotopic homodinuclear [2]catenane, was reported by Castro et al. [34]. 

Another fascinating approach to catenanes via self-assembly involves metal-coordination which templates or directs the assembly of catenane frameworks. After brief discussions on the recent examples of metal-containing catenanes and related topologically interesting molecules (Sections 4.2.1-4.2.3), the focus will be on the self-assembly of Pd(II)-linked catenanes (Sections 4.2.4 and 4.2.5). 

Balzani, V., Venturi, M., Credi, A. Molecular Devices and Machines. A Jorney into the Nanoworld, Wiley-VCH, Weinheim, 2003 b) Feringa, B.L. (ed.), Molecular Switches, Wiley-VCH, Weinheim, 2001 c) Raehm, L., Sauvage, J.-P. Molecular machines and motors based on transition metal-containing catenanes and rotaxanes, Struct. Bond. 99 (2001), 55-78. 

In the following two chapters, we will explore two further major categories of discrete, non-metal-containing, supramolecular assemblies - namely, rotaxanes and the catenanes. 

Figure 4 A linear mechanically linked polymer based on the Sauvage metal-containing catenanes...

Molecular Machines and Motors Based on Transition Metal-Containing Catenanes and Rotaxanes... 

Raehm L (2001) Molecular Machines and Motors Based on Transition Metal-Containing Catenanes and Rotaxanes 99 55-78 Rakke T, see Kjekshus A (1974) 19 45-83 Rakke T, see Kjekshus A (1974) 19 85-104... 

Sauvage. J.-P. Transition metal-containing rotaxanes and catenanes in motion Toward molecular machines and motors. Acc. Chem. Res. 1998, 31. 611-619. 

Sauvage. J.-P. Transition-metal-containing rotaxanes and catenanes Toward molecular machines and motors. Acc. Chem. Res. 1998. 31. 611-619 and references therein. McArdle, C.P. Irwin, M.J. Jennings, M.C. Vittal. J.J. Puddephate. R.J. Self-assembly of gold(I) rings and reversible formation of organometallic [2]catenanes. Chem. Eur. J. 2002. 8. 723-734. 

A great variety of possibilities were realized to have the metal as part of a linear or crosslinked macromolecule (Figure 3). One possibility is the covalent incorporation of a metal into homochain or heterochain polymers. Coordinative bonds between a metal and another element can occur in various combinations. Recently, the supramolecular organization under formation of metal containing coordination polymers were described. Different bonds were realized in stacking of metal chelates. In addition, metal containing catenanes and dendrimers are mentioned in this subchapter. 

TRANSITION METAL-CONTAINING CATENANES AND ROTAXANES CONTROL OF ELECTRONIC AND MOLECULAR MOTIONS... 

Self-assembly of [2]catenanes containing metals in their backbones 99ACR53. 

Fujita, M. Self-assembled macrocycles, cages and catenanes containing transition metals in their backbones. In Comprehensive Supramolecular Chemistry Sauvage, J.-P., Hosseini, M. W., Eds. Elsevier Oxford, 1996, Vol. 9, pp 253-282. 

Several examples of catenanes and rotaxanes have been constructed and investigated on solid surfaces.1 la,d f 12 13 26 If the interlocked molecular components contain electroactive units and the surface is that of an electrode, electrochemical techniques represent a powerful tool to study the behavior of the surface-immobilized ensemble. Catenanes and rotaxanes are usually deposited on solid surfaces by employing the Langmuir-Blodgett technique27 or the self-assembled monolayer (SAM) approach.28 The molecular components can either be already interlocked prior to attachment to the surface or become so in consequence of surface immobilization in the latter setting, the solid surface plays the dual role of a stopper and an interface (electrode). In most instances, the investigated compounds are deposited on macroscopic surfaces, such as those of metal or semiconductor electrodes 26 less common is the case of systems anchored on nanocrystals.29... 

In this chapter, we will focus on transition metal-based catenanes and rotaxanes. We will restrict ourselves to compounds that are set in motion by an electrochemical signal. Indeed, the electrochemical techniques represent privileged methods for piloting these machines since they contain electroactive transition metal centers or complexes. In addition to triggering the motions, electrochemistry allows to investigate the dynamic properties of the compounds. 

Wozniak and coworkers described recently the first heterodinuclear bismacrocyclic transition metal complex 34 + (Fig. 14.5) that exhibits potential-driven intramolecular motion of the interlocked crown ether unit.25 26 Although the system contains transition metals, the main interaction between the various subunits, which also allowed to construct catenane 34+, is an acceptor-donor interaction of the charge transfer type. 

From the results summarized in Table 1 we can conclude that the self-assembly of Pd(II)-linked catenanes is predictable. When the component rings have a cavity with an appropriate interplane distance (ca. 3.5 A), catenanes are obtained efficiently (e.g. from ligands 12, 22, 24, 26+27, or 29+30). If, however, the cavity is too large or too small, catenanes are not assembled (e.g. from 26, 27, 35, or 36). Thus two conditions must be satisfied if metal-incorporating catenanes are to be obtained by self-assembly. Firstly, component rings should contain reversible coordinate bonds. Second, both component rings should have interplane separation of approximately 3.5 A in the cavity. 

---