Interlocking rings

Our definitions of the stereoisomeric center, line, and plane all stipulate the existence of bonds between the ligating element and its ligands. The exclusive use of these elements limits our analysis to classical stereochemistry and thus does not encompass the so-called topological isomerism (47) of interlocked rings—catenanes (48)—or of knots. As there is no bond between the rings of the catenanes we cannot expect to handle such compounds with a system based on connectedness. At the present stage of development, this limitation in scope... 

According to Sauvage [48a] ...compounds containing interlocking rings or... 

Catenanes and rotaxanes represent examples of interlocked architectures. A catenane consists of two interlocked rings (it is called in this case a [2]catenane),... 

As already said, catenanes are minimally composed of two interlocked rings. If it is arranged during the template-directed synthesis to have two identical units, that is, recognition sites, located within two different macrocycles, then the resulting... 

Electrochemical techniques can also give interesting information in the case of catenanes of higher complexity, as shown by the results obtained by investigating a series of catenanes made of up to seven interlocked rings.20 The three basic components of these catenanes are the tetracationic cyclophanes 124+ and 154+, and macrocycle 16 containing three electron donor DMN units (Fig. 13.16). For space reasons, only the electrochemical behavior of catenanes 174 1, 188+, 194+, and 204+ (Fig. 13.17), compared to those of their molecular components, is reported. 

I was introduced to interlocked rings in 1956 by M.S. Newman, a seminar speaker at Harvard. In informal discussion after the talk he described the proposal of a graduate student at Ohio State, L. Friedman, for a many-step synthesis of a catenane. The final reaction was cleavage of the two bonds connecting the linked and chemically bound rings. 

The synthesis of interlocking ring molecular systems and knots combines both sets of motivation but it also adds an aesthetic dimension to the chemical problem. Indeed the search for aesthetically attractive molecules has been a goal since the very origin of chemistry. 

Figure 12. Three-dimensional template synthesis of interlocked ring systems induced by a transition metal. The metal center m disposes the two f-f fragments perpendicular to one another. Functions f and g react to form the links.

Almost a century has elapsed between Willstatters visionary speculation about a molecule made of two interlocked rings - a catenane - and the todays outspreading molecular chemistry concerned with topology. 

A laboratory preparation of the simplest of these catenation compounds. two interlocking rings, has been carried out at AT T Bell Laboratories. They started wilh the dimethyl ester of a 34-carbon paraffinic dicarboxylic acid, CH ,OOC-(CH )j2-COOCHi, which was reacted in a suspension of metallic sodium in xylene with acelic acid to condense the terminal ester groups to form an aceloin ring compound. 

In the introduction we mentioned extravagant interlocked structures of higher complexity such as doubly intertwined catenane and molecular composite knots of Sauvage et al. and multicatenanes made up of 4 to 7 interlocked rings obtained by Stoddart et al. In this section, we will discuss assemblies made up of amide-based catenanes, rotaxanes and knots. Here we use the term assembly to describe covalent or... 

The first molecular motor elaborated and studied in our group was a catenane containing two different interlocking rings. Its principle is explained in Figure 17.1861... 

The reactions of cyclic olefins by the four-center reaction scheme to form larger ring cyclic polyolefins and interlocked ring systems (catenanes) have also been proposed S9-67). These can be classified as Type V reactions. 

Independent interpretation of mass spectroscopic data by Wolovsky 66> and Ben-Efraim, Batich, and Wasserman 6 ) indicate that cyclic olefins subjected to disproportionation conditions form interlocking rings (catenanes) as well as cyclopolyolefins. The proposed scheme involves four-center transition state and Mobius-Strip approach... 

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