Efficient production of [ n ]rotaxanes by using template-directed clipping reactions

Abstract

In this article, we report on the efficient synthesis of well defined, homogeneous [n]rotaxanes (n up to 11) by a template-directed thermodynamic clipping approach. By employing dynamic covalent chemistry in the form of reversible imine bond formation, [ dynamic covalent chemistry ͉ molecular recognition ͉ polyrotaxanes ͉ self-assembly ͉ template-directed synthesis M echanically interlocked and knotted compounds, such as rotaxanes (1-5), catenanes (6-10), suitanes (11, 12), trefoil knots (13-17), , and Solomon knots (21), represent challenging synthetic goals that have nevertheless been realized. These molecular compounds are usually synthesized by a template-directed approach (22) that depends on molecular recognition and self-assembly processes. Recently, their potential applications as molecular switches for nanoelectronics (23, 24) and molecular actuators for constructing artificial muscles (25), for fabricating smart surface materials (26), and for controlling the nanoscale release of molecules trapped in mesoporous silica (27)(28)(29) were demonstrated. Polyrotaxanes and well defined, homogeneous oligorotaxanes, in which the recognition sites on a dumbbell (an axle terminated by bulky stoppers) are encircled by large rings or macrocycles (wheels) by dint of molecular recognition, have become (30-36) one of the most intensively investigated subjects in mechanical chemistry. A general synthetic method for making rotaxanes, namely, the ''threading-followed-by-stoppering'' approach (Fig. 1, method A), involves (30-32) several macrocycles. First, the macrocycles are threaded onto oligomeric or polymeric axles carrying recognition sites at prescribed intervals along the axles to form pseudorotaxanes, then both ends of the axles are stoppered with bulky groups. Although this approach is relatively simple, it does not provide complete control over the number of threaded macrocycles, that is, the rings or beads are often not threaded onto all of the available recognition sites on the axles. Alternatively, a template-directed ''clipping'' approach (Fig. 1, method B), in which the macrocycles are formed from acyclic precursors in the presence of templating recognition sites on the dumbbells, has provided (33-36) a versatile means for the construction of some lower-order rotaxanes. Nonetheless, the efficient synthesis of well defined, homogeneous, higher-order polyrotaxanes continues to be a challenge to synthetic chemists.Recently, dynamic covalent chemistry (37-40), exemplified by reversible imine formation (41, 42), metal-ligand exchange (43), and olefin metathesis (44, 45), has been demonstrated to be an effective tool for the preparation of various exotic mechanically interlocked molecular compounds. It has been found that, in the presence of an appropriate template, one of the possible compounds in the dynamic library, after mixing the different components, can be amplified to give the thermodynamically most stable product. We have reported (see refs. 46-49) an example of such a template-directed synthesis of ...

Donor–Acceptor Oligorotaxanes Made to Order

“…Keywords: folding · noncovalent bonding interactions · oligomers · rotaxanes · template-directed syntheses While small molecule [2][3][4][5][6] donor-acceptor (DA) MIMs have had these footprints exposed and expressed, [8][9][10] the larger oligomeric [11][12][13] and polymeric [14] ones remain something of an enigma. The time is ripe to probe the nature of the noncovalent bonding interactions that dictate the secondary structures of DA-MIMs.…”

Dynamic Covalent Self‐Assembly Based on Oxime Condensation

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Oxime,w hose dynamic nature was reported to be switchable between ON/OFF by tuning the acidity,isemployed in anovel type of dynamic covalent approach that is amenable to use in water for self-assembly of purely organic molecules with complex topology.I ns trongly acidic conditions,t he dynamic nature of oxime is turned ON,allowing occurrence of error-checking and therefore acatenane and amacrocycle selfassembled in high yields.Inneutral conditions,oxime ceases to be dynamic,w hich helps to trap the self-assembled products even when the driving forces of their formation are removed. [2][3][4][5][6][7][8] Its reversible nature allows the systems to perform error-checking and self-correcting during searching for their thermodynamic minimum. [2][3][4][5][6][7][8] Its reversible nature allows the systems to perform error-checking and self-correcting during searching for their thermodynamic minimum.

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Synthesis of [5]Rotaxanes Containing Bi‐ and Tridentate Coordination Sites in the Axis

“…[94][95][96][97][98] The synthesis was carried out by following the classical CuAAC strategy but an important difference with previous cases should be stressed: in the present case, the stopper precursor is a semirotaxane (copper(I)- [2]semirotaxane 7 + ) and not a trivial bulky compound. This semirotaxane used as a stopper precursor is, itself, half-stoppered, making the final product a complete rotaxane.…”