Pre rotaxanes

The illustration of the process is provided in Figure 2.30.13d At first, pre-rotaxane 82 was generated in a manner similar to that of Figure 2.25. The prerotaxane was subsequently combined with 4,4/-dimethyl-3,3/-dihexyl-2,2/-dipyrrylmethane 83 (10 equiv), and 3,5-di-ter -butylbenzaldehyde 84 (8 equiv) using trifluoroacetic acid catalysis, followed by oxidation of the porphyrinogen intermediates with chloranil 85 to afford bis-copper(I)-complexed [3]-rotaxane 86 in 35% yield. Remarkably, a copper(I)-complexed [5]-rotaxane (87) could be isolated from the reaction mixture in 8% yield. 

The notion of pre-rotaxane was introduced by Schill to describe the ultimate precursor to a rotaxane in a long sequence of reactions see ref. [16] pp. 151-4 a pseudorotaxane is a threaded species whose axis does not bear any stopper. 

Tripincer template-directed cyclization of a dienic pyridine precursor leads to the formation of the 69-membered ring trimeric heterocycle 112 (Figure 2.6). Decomplexation of the tripincer from the product is realized with NaCl [72]. The synthesis of a [2]rotaxane by M-RCM using a similar pincer-pyridine complex for pre-assembly was also reported by Leigh et al. [73]. 

Figure 2.39. Preparation of poly([2]-rotaxane) 118 by electropolymerization of Co(II)-comple-xed pre[2]-rotaxane 117, formed by cobalt(II)-templated threading of macrocycle 58 onto the dpp-based thread 114. Cu(I) turned out to be ineffective as template for the electropolymerization process. The Cu(I)-complexed polymer (119) was obtained by successive demetallation-remetallation processes.

Since these studies, many other rotaxanes incorporating cyclodextrins or their substituted derivatives have been reported, including other metal-containing systems. The latter include a series of a-cyclodextrin rotaxanes formed by the reaction of labile [Fe(CN)50H2J ions with pre-threaded l,l"-(a,(o-alkanediyl)-bis(4,4 -bipyridinium) dicationic moieties (incorporating methylene chains between 8- and 12-members long). " ... 

Figure 54 Schematic representation of the formation of compartmentai [3]- and [5]-rotaxanes (136) and (149). (i) Condensation of two pre([2]-rotaxane) units (A) to afford compartmentaJ [3]-rotaxane (C) (iii) condensation of two pre([3J-rotaxane) units (B) to afford compartmental [5]-rotaxane (D) [59, 117].

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