Non‐Rusty [2]Catenanes with Huge Rings and Their Polymers

Abstract

We describe the design and synthetic realisation of [2]catenanes characterised by having huge rings that can rotate freely and shift laterally within the constraints of concatenation. The synthetic strategy, which is based on using a carbonate group as a covalent template and oxidative dimerization of alkynes to achieve ring formation, is versatile with respect to ring size and the presence of functional groups. The monocyclic constitutional isomer of the catenane is available by a simple exchange of steps in the sequence. EPR spectroscopy revealed that in solution the catenanes adopt all possible co‐conformations in equal abundances. The thermotropic liquid crystallinity of the [2]catenanes and their corresponding non‐intertwined macrocycles proves intermolecular ordering in the bulk phase. The [2]catenanes were polymerized through ester formation and through acyclic diene metathesis. All of the poly[2]catenanes have rather low degrees of polymerisation (<Pn> ≈︁ 10), possibly because cyclisation occurs. For the preparation of [n]catenanes having n > 3, we propose fusing the rings of [2]catenanes so that the crucial steps of threading and cyclisation need only occur during the synthesis of the smallest catenane. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

On sublinks and their connections within the graphs of the mechanically bound molecules

“…Obviously, we all use such an approach even subconsciously each time when we plan to make even very easy chemical compounds. Syntheses of [2]-rotaxanes 1 are good examples of retro-synthetic methodology in the field of mechanically built structures. There are the following general methods known: (1) threading-followed-bystoppering, 14 (2) "clipping," 15 and (3) slippage.…”

“…On the other hand, the numbers M or L either reflect directly or are quite close to the real numbers of the mechanical bonds. In the cases of bis- [2]-(5) and bis-[3]-(6) catenanes 9b MB = M and are 2 and 4, respectively. However, the situation in 7 is additionally complicated due to the fusion of macrocycles (Figure 2).…”

“…There are at least twenty one possibilities to represent 18 as the sum of sublinks ( Table 2). Some of the most obvious are: (1) four [2]catenanes, which are connected with each other via the mechanical bonds in the cyclic way; (2) (Figure 9). The complete analysis of all links with at least two mechanical bonds met here, are summarized in Table 2.…”

“…As only one example, [2]-catenane 2 is taken for such purpose (Figure 10) and the derivative structures 4, 28 -35 are constructed via the building either new mechanical or covalent bonds. I applied two conditions for such combinations: (1) only two 2 are combined; (2) one ring of one 2 can build only one either mechanical or covalent bond to only one ring of the second 2.…”

Classification of the Mechanical Bonds

“…The mechanically bound compounds (Balzani et al, 2009;Bogdan et al, 2006;Coronado et al, 2009;Crowley et al, 2009;Faiz et al, 2009;Godt, 2004;Harada et al, 2009;Saha et al, 2007;Sauvage et al, 1999;Stoddart, 2009) attract from year to year more and more attention not only because of their idealistically appealing structures which require sophisticated synthetic macrocyclisation methods (Wang et al, 2004;Wu et al, 2007), but also because of their feasible applications in nano-technologies (Collier et al, 1999;Green et al, 2007), material sciences (Ma et al, 2010;Tian et al, 2006) and even in bio-imaging (Gassensmith et al, 2009). The main force which contributes to the connectivity in such molecules is the mechanical bond.…”