Rotaxane synthesis via a dynamic [2]catenane-ring-opening, axle-cleaving double cross metathesis

Abstract

Efficient routes to [2]rotaxanes are often compromised by formation of irrecoverable, non-interlocked byproducts. Herein, we report a thermodynamically steered, atom-economical strategy that couples a Cu(I)-templated, low-strain Sauvage-type [2]catenane with di-stoppered olefin via ring-opening double cross-metathesis (RO-DCM), implementing dynamic covalent chemistry to bias the system toward the most stable interlocked architecture. The transformation proceeds through ring opening of the metalated [2]catenane and its in situ “insertion” into the axle, engaging internal olefins on both partners. Optimization of metathesis parameters (Grubbs II, DCM, 40 °C) identified the stoichiometry of the di-stoppered olefin as the key lever; using ten equivalents furnished the metalated [2]rotaxane 6 in up to 88% isolated yield while suppressing mono-stoppered byproducts. Subsequent demetalation cleanly delivered [2]rotaxane 9. Analytical size-exclusion chromatography across the full component set provided diagnostic retention times, confirming product identity and the absence of catenane contamination. No dethreading of macrocycle 1 from 9 was detected under conventional heating in DCM or DMSO over 12–48 hours, underscoring kinetic persistence of the mechanical bond. Overall, this RO-DCM platform minimizes non-interlocked waste streams while providing a concise, high-yield entry to [2]rotaxanes from metathesis-addressable, copper-templated interlocks. Beyond the single-molecule level, the approach establishes a general ring-chain equilibration blueprint that should translate to sequence-defined, mechanically interlocked oligomers and polymers.