 A synthetic transformation between mechanically-interlocked molecules is described. Specifically, a [2]catenane was found to partake in a dynamic ring-chain equilibration in the presence of an acyclic chain transfer agent with bulky chain ends to produce a [2]rotaxane. Dynamic ring-chain equilibration and chain transfer were enabled through catalytic olefin metathesis. In this study, conditions were sought to minimize competitive polymerization and to optimize the yield of the [2]rotaxane, based upon limiting [2]catenane. Various reaction conditions were screened; under optimal found conditions, the [2]rotaxane was isolated in 88% yield. This reaction is subject to thermodynamic control under conditions that favor dynamic olefin metathesis and, once operative, the equilibration is biased to favor [2]rotaxane under conditions that favor chain transfer. Mechanical entanglement of the spectator macrocycle was maintained over the course of the transformation, from [2]catenane to [2]rotaxane, despite acyclic reaction intermediates that lack bulky chain ends, via copper chelation of the spectator macrocycle. Demetalation of the isolated, copper-chelated [2]rotaxane provided the stable, metal-free, [2]rotaxane mechanical complex.

Synthesis of a [2]rotaxane via dynamic ring-chain equilibration

248th National Meeting (2014)

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