Multivalency‐Directed Magic‐Ring [2](3)Catenane by Olefin Metathesis

Abstract

[a] Multivalency, [1] as a way to compensate for the weak monovalent interactions in nature, has attracted considerable interest in recent years.[2] Chemists tried to discover the physical basis of multivalency effects based on a thermodynamic model combined with computational studies and found that thermodynamics play a key role as far as multivalent interactions is concerned.[3] The construction of supermolecules by the bottom-up approach to mimic biomacromolecules and their assemblies is one of the main aims for supramolecular chemists.[4] Although multivalency provides a fascinating inspiration for chemists seeking to transfer concepts from the biological world into supramolecular chemistry, there are still very few examples of multivalency in the noncovalent synthesis of various elaborate supermolecules. [5] Mechanically interlocked molecules, [6] such as catenanes and rotaxanes, are not only aesthetically pleasing curiosities, but can function as the key components in future "intelligent" materials.[7] Although a vast number of syntheses of catenanes and rotaxanes have been reported, most of the strategies employ kinetically controlled covalent-bond formation as the final interlocking steps in which the product distribution relies on kinetic rather than thermodynamic control.[8] Therefore, chemists have exploited dynamic covalent chemistry (DCC) [9] as an alternative strategy that utilizes reversible reactions as the final interlocking step in which the product distribution relies on thermodynamic rather than kinetic control. Many reversible reactions, including the formation of imines, disulfides, and cyclic acetals, as well as olefin metatheses, have been employed as the final reaction steps to synthesize catenanes and rotaxanes. [10] Especially, the construction of magic-ring catenanes [5c] and magic-rod rotaxanes [11] by olefin metathesis has been recently reported. However, synthesis of more complex interlocked molecules by means of the DCC strategy is still a challenge.In recent years, we became interested in developing new supramolecular systems based on triptycene-derived synthetic hosts.[12] As a result, we reported a highly efficient approach to synthesize [2](3)catenanes by threefold metathesis reactions of a triptycene-based tris[2]pseudorotaxane. [13,14] Herein, we report formation of a novel multivalency-directed complex 1·2-3 H·PF 6 composed of the trisdialkylammonium strand ions 2-3 H·PF 6 and the triptycene-based homotritopic host 1, [13a] containing three dibenzo[24]crown-8 cavities, and the subsequent [2](3)catenane 4-3 H·3 PF 6 by the olefin metathesis reaction. Moreover, we also designed and synthesized a trisdialkylammonium macrocycle ion, 3-3 H·PF 6 , and found that it could form an interesting magicring [2](3)catenane with the homotritopic host 1 by reversible olefin metathesis (Scheme 1).Scheme 2 outlines the synthesis of the trisdialkylammonium strand ions 2-3 H·PF 6 . Condensation of the amine 10 with the aldehyde 9 gave the corresponding imine, which was reduced by...

Novel triptycene-derived hosts: synthesis and their applications in supramolecular chemistry

“…Interestingly, it was also found that the trisdialkylammonium macrocycle ions 27 could form a magic ring [2](3)catenane via two olefin metathesis steps. 27 These results show that the combination of multivalency and olefin metathesis provides a powerful tool for the synthesis of complex interlocked molecules. 28…”

Stepwise Motion in a Multivalent [2](3)Catenane

“…19 Its three dibenzo-24-crown-8 (DB24C8) rings are positioned in three orientations, which not only allow three dibenzylammonium guests to thread in, but also can accommodate a bent linear trisdialkylammonium strand to facilitate highly efficient synthesis of a [4]pseudocatenane. 20 To introduce more recognition stations into the guest component for the construction of functional catenanes, we proposed that a host with more free volume between the adjacent DB24C8 rings would better meet the requirement of the steric hindrance. Thus, a pyrazine-extended triptycene-derived tris-(crown ether) host eTC was designed.…”

Mechanically interlocked molecular handcuffs

“…Later work demonstrated it was also possible to produce the same (3)handcuff [2]catenane architecture by starting with an olenterminated tris(benzylammonium) strand. 79 Interestingly, if this strand was already conjoined as a macrocycle and later mixed with the tris(macrocyclic) host, a reversible ring-opening ring-closing metathesis reaction could be stimulated by the addition of Grubbs II catalyst, forming the triply catenated product in high yield. A chiral variation was also reported, 80 where the tris(macrocycle) was modied with (R)-1,1 0 -binaphthyl moieties.…”