New [2]rotaxanes were prepared by the threading and the slipping procedure, the latter having the advantage of not needing templating interactions. As a consequence, the first [2]rotaxane consisting of a tetraamide macrocycle and a pure hydrocarbon thread was synthesized (see 12a in Scheme 2). Sterically matching wheels and axles being the basic requirement of a successful slipping approach to rotaxanes, mono‐ and bishomologous wheels 5b,c with larger diameters than the parent 5a were synthesized and mechanically connected to amide axles 10a – c which were stoppered with blocking groups of different spatial demand (Scheme 1). The deslipping kinetics of the resulting rotaxanes 8a – c and 9a,b were measured and compared; it emerges that even slight increases in the wheel size require larger stoppers to stabilize the mechanical bond. Moreover, when the deslipping rate of 8a (amide wheel and amide axle) was determined in either DMF or THF, a strong dependence on the solvent polarity, which is caused by a differing extent of intramolecular H‐bonds between the wheel and the axle, was observed. As expected, no such dependence was detected for rotaxane 12a (amide wheel and hydrocarbon axle) whose components cannot interact via H‐bonds. The comparison of the sterically matching pairs of macrocycles and blocking groups, found by a systematic fitting based on the results of slipping and deslipping experiments, with other rotaxane types bearing similar stoppers allows conclusions concerning the relative cavity size of wheels of various structure.

A new pathway for the supramolecular synthesis of oligocatenanes is developed. It is based on a combination of most suitable macrocyclic structural units, obtained from tert-butyl-substituted isophthalic acid and terephthalic acid building blocks. These structural parts guarantee, on the one hand, the solubility of the catenanes and their intermediates, and, on the other hand, the preferred formation of larger ring sizes of the macrocycles to be intertwined. Acting as monotopic and ditopic concave templates, the tetra-and octalactam macrocycles were submitted to threading procedures to yield higher-order catenanes of the amide type. By repetition of the threading steps, it was possible to isolate multiply mechanically connected [n]catenanes up to n 4 composed of various macrocyclic units.

Abstract

Template-assisted reactions make use of the self-organization of two (or more) molecules, one being the host, the other acting as a guest [l]. By that means the reactants adopt a conformation that facilitates the formation of a generally macrocyclic product. Although the term 'template effect' was introduced in the early sixties [2], only the enormous impetus of supramolecular chemistry [3] within the last two decades has led to the chemical breakthrough of this elegant strategy. The application of the template effect not only raises yields, but also often enables the preparation of otherwise unobtainable products.The progress in synthesis of catenanes, rotaxanes, and knots is exemplary for the effect of templates. Early syntheses of these molecules with mechanical bonds used statistical or multistep procedures [4]. Yields were very low and thus catenanes and rotaxanes had the standing of laboratory curiosities. The pioneering work of Sauvage et al. [5] and Stoddart et al. [6] introduced the template strategy to the synthesis of mechanically interlocked molecules by using ionic coordination (I) and ionic n-n donor-acceptor complexes (II) combined with hydrogen bonding, respectively (Figure 1). In 1992 Hunter et al. [7a] and Vogtle et al. [8]established, independently of each other, a third, yet nonionic template effect founded on hydrogen-bonding and 7t-n interactions (111), the same interactions that are involved in many biological processes.The synthesis of molecules with mechanical bonds via the nonionic template strategy is all the more fascinating if one considers naturally occurring DNA catenanes [9] or proteins forming knotted structures [lo]. Starting from simple twoand one-step syntheses of catenanes by the use of neutral templates, it took only a few years to develop not only amide-based rotaxanes, but also nanoscale assemblies of several mechanically bound building blocks, topologically chiral 'pretzelanes' and cycloenantiomeric rotaxanes as will be described in the following section of this progress report.

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