Rotaxane or Pseudorotaxane? That Is the Question!

Abstract

A series of secondary dialkylammonium ions (RCH2)2NH2 + have been prepared, and their binding properties toward the macrocyclic polyether dibenzo[24]crown-8 (DB24C8) evaluated. By using this information, a route to a kinetically stable rotaxane-like entitystabilized by noncovalent bonding interactions between the DB24C8 macroring and the ammonium centerwas established, in which the crown ether slips over a dialkylammonium ion's stopper groups (R). However, we have found that the kinetic stability of this rotaxane-like entity is extremely dependent on the nature of the solvent in which it is dissolved, suggesting that pseudorotaxanes lie in the fuzzy domain between two sets of extremes, wherein a beadlike macrocycle and a dumbbell-like component may either (1) exist as a rotaxane or (2) be completely disassociated from one another.

Polymer architectures assisted by dynamic covalent bonds: synthesis and properties of boronate-functionalized polyrotaxane and graft polyrotaxane

“…Compound 6 decomposes promptly (entry 1), 7 dissociated slowly (entry 2) and 8 dissociates at a rate too slow to measure (entry 3). The boronate moiety of 7 behaves as an end-capping group whose size is complementary to the DB24C8 cavity, [41][42][43][44] to prevent dissociation. On the other hand, the addition of triethylamine (Et 3 N) prompted the dissociation of 7 and 8 in comparison with the Et 3 N-free conditions (entries 4 and 5), probably due to not only a neutralization of the sec-ammonium moiety that disturbs the interaction between DB24C8 and axle component but also a dissociation of the dynamic covalent bond of boronate by humidity in the system.…”

Templated Synthesis of Interlocked Molecules

“…The free energy of activation was observed to increase upon reducing the size of the cavity of the macrocycle and/or enlarging the bulk of the stoppers. Rotaxanes have also been synthesized [146][147][148] by slippage using other well-known recognition motifs. For example [146], the interaction of secondary dialkylammonium ions with commercially available dibenzo [24]crown-8.…”

“…Rotaxanes have also been synthesized [146][147][148] by slippage using other well-known recognition motifs. For example [146], the interaction of secondary dialkylammonium ions with commercially available dibenzo [24]crown-8. In 1997, Vögtle [148] reported the synthesis of the first amide-type rotaxane using the slippage approach.…”

“…In fact an increase in temperature, solvent polarity or acidity can drastically affect [146] the stability of rotaxanes obtained by slippage. Thus, in the last decade, more and more attention has become focussed on dynamic covalent chemistry.…”

Development of [2]-Catenane with Orthogonal Binding Chloride Template

“…[1][2][3] More than two supramolecules can form molecular complex through selfassembly by coordination. 4 When the anion binding sites in each supramolecules form orthogonal complex, the binding sites provide three dimensional spaces.…”