Transition Metal-Incorporating Catenanes

Fujita, M. Transition metal-incorporating catenanes. In Molecular Catenanes, Rotaxanes and Knots Sauvage, J.-P., Dietrich-Buchecker, C., Eds. Wiley-VCH Verlag Weinheim, Germany, 1999, pp 57-76. 

In this and the following sections self-assembling catenanes incorporating (en)Pd(II) units in their backbones are emphasized [21]. Discussion will be focused on the rational design, self-assembly, mechanistic aspect, and chemical manipulation of the transition metal-linked catenanes. 

Fig. 17 Two strategies for the transition metal-templated synthesis of a [2]catenane made with Zn and Au porphyrin-incorporating interlocked macrocycles. The thick lines represent chelating fragments, the black disk symbolises copper(I), the empty diamonds are Zn(II) porphyrins, and the hatched diamonds are Au(III) porphyrins...

Let us start the discussion with a metal ion template, which was introduced by Sauvage and his coworkers in the mid-1980s (Fig. 2, top left). A Cu(I) ion with its preferred tetrahedral coordination geometry is capable of binding two phenanthroline units. If one of the phenan-throlines is incorporated in a macrocycle, which later will become the wheel, the second ligand is drawn into the cavity by the copper ion and can be easily equipped with two stoppers. The rotaxane precursor can then be dernetallated by treatment with cyanide ions to yield the desired rotaxane. Similarly, catenanes and other mechanically bound molecules can be synthesized. Also, other transition metals were used, some of which had an octahedral coordination geometry and were reacted with terpyridine instead of phenanthroline units. 

Macromolecules incorporating repeating units connected by covalent bonds are widespread in nature [1], Synthetic procedures for the construction of their artificial counterparts are well established [2], Furthermore, the properties of these unnatural macromolecules are now rather well understood and, indeed, polymeric materials have found applications in numerous branches of science and technology [2], In recent years, synthetic chemists have learned how to introduce mechanical bonds (Fig. 1) into small molecules. Mechanically interlocked rings, as well as wheels mechanically trapped onto axles, can be constructed efficiently to afford molecular compounds, named catenanes and rotaxanes, respectively.t Metal coordination [18-32], donor/acceptor interactions [33-43], hydrogen bonds [44-64] and/or hydrophobic interactions [65-78] between appropriate components have all been employed to template the formation of these exotic molecules. Making the transition from simple catenanes and rotaxanes to their macromolecular counterparts—namely, polycatenanes and polyrotaxanes. 

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