Chloride Anion Templated Synthesis and Crystal Structure of a Handcuff Catenane

Abstract

Catenanes and rotaxanes are highly attractive synthetic targets in supramolecular chemistry due, in part, to their potential uses as molecular machines [1] or as selective hosts for ionic and molecular guests. [2] The preparation of higherorder interlocked architectures provides a much greater synthetic challenge than the construction of the prototypical [2]catenanes and [2]rotaxanes, but can allow for functionality not open to simpler systems. Indeed, impressive examples of such species have been assembled using cationic [3,4] and neutral [5] templates. In contrast, the use of anion templation to generate interlocked structures, whilst having been demonstrated by us [6] and others, [7] remains in its infancy. In particular, almost all reports of anion templation of interlocked molecules involve the construction of either [2]catenane or [2]rotaxane structures. [8,9] A "handcuff" catenane is an example of a higher-order interlocked architecture where two covalently linked macrocycles have a single macrocycle passing through both rings ( Figure 1). To the best of our knowledge, only two examples of such species-constructed using cationic templation-have been described in the chemical literature to date. [10,11] Here, we detail the preparation and characterization of a novel chloride anion templated handcuff catenane, along with its crystal structure-this being the first handcuff catenane crystal structure to be determined.The synthetic strategy undertaken to prepare the target handcuff catenane is illustrated in Figure 2. Two identical Nmethyl pyridinium molecules thread, by anion templation, through a handcuff-like bis(macrocycle), where each macrocycle contains an isophthalamide group able to hydrogen bond to the chloride anion. Pseudorotaxane formation is also supported by p-p stacking between the electron-rich hydroquinone groups of the bis(macrocycle) and electron-poor pyridinium rings of the threading components. Subsequent cyclization will lead to the formation of the desired handcuff catenane.The actual detail of the synthesis of novel bis(macrocycle) 4 and handcuff catenane 6 2+ (Cl À ) 2 is shown in Schemes 1 and 2. The bis(macrocycle) was synthesized by reacting 2 equivalents of bis(amine) 1 with tetraacid chloride 2 [12] in the presence of 2 equivalents of the N-methyl pyridinium template 3 + Cl À and NEt 3 in dry CH 2 Cl 2 . [13] After aqueous workup and silica gel chromatography, 4 was isolated in a 15 % yield. [14] Subsequently, 4 was suspended in dry CH 2 Cl 2 , and two equivalents of the bis(vinyl) precursor 5 + Cl À [6b] added, which led to the solubilization of the bis(macrocycle) indicating that the prerequisite pseudorotaxane complex was formed. Addition of 10 % (by wt) Grubbs secondgeneration catalyst, followed by stirring at room temperature for 16 hours under a nitrogen atmosphere allowed ringclosing metathesis (RCM) to occur. After solvent removal, preparative silica gel thin layer chromatography (TLC) was undertaken, whereupon a new yellow band was separated from the crude reaction mixtu...

Progress in the synthesis and exploitation of catenanes since the Millennium

“…This higher order catenane was constructed by Grubbs' catalyzed linear cross metathesis of two equivalents of a methyl pyridinium chloride precursor threaded through a bis-isophthalamide "handcuff" bis-macrocycle. 67 The solid-state structural determination of this species represents the first example of a crystal structure of such a catenane topology. The dianion sulfate has also been shown to be a highly efficient template for catenane formation: double cyclization of a 45 pyridinium nicotinamide thread around a sulfate anion produced a [2]catenane in 80% yield, which after sulfate removal was found to selectively bind the templating oxodianion ( Figure 23).…”

Rotaxane and Catenane Host Structures for Sensing Charged Guest Species

“…22 More recently, we have demonstrated alternative routes toward anion-templated interlocked structures: using an amide condensation strategy, rotaxanes 3 and 4 were formed by templating the formation of the macrocycle in the presence of pyridinium chloride axle 2 in yields of 56% and 60%. 23 Chloride anion templation has also been applied to the synthesis of catenanes 24 and more complex architectures, such as a hand-cuff catenane, 25 Janus [2]rotaxane, 26 and [3]-rotaxanes, 27,28 while bromide, 29 sulfate 30 and nitrate 31 have also been utilized as the templating anions for mechanical bond formation.…”

I19, the small-molecule single-crystal diffraction beamline at Diamond Light Source

“…Catenanes consist of two or more interlocked macrocycles and recently I19 data was used to solve, for the first time, the crystal structure of a 'handcuff' catenane where two covalently linked macrocycles have a third, single, macrocycle passing through the other two rings (see Fig. 5) (Evans et al, 2011).…”