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

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Materials Science

Background:

• Synthesizing [2]rotaxanes efficiently is challenging due to byproduct formation.
• Existing methods often lack atom economy and generate non-interlocked waste.
• Dynamic covalent chemistry offers potential for controlled assembly of complex architectures.

Purpose of the Study:

• To develop a thermodynamically steered, atom-economical strategy for [2]rotaxane synthesis.
• To utilize ring-opening double cross-metathesis (RO-DCM) for constructing interlocked architectures.
• To minimize non-interlocked byproducts in [2]rotaxane formation.

Main Methods:

• Coupling a Cu(i)-templated [2]catenane with a di-stoppered olefin via RO-DCM.
• Employing dynamic covalent chemistry to favor the most stable interlocked product.
• Optimizing metathesis conditions, including catalyst (Grubbs II), solvent (DCM), temperature (40 °C), and stoichiometry.

Main Results:

• Achieved up to 88% isolated yield of the metalated [2]rotaxane using optimized RO-DCM conditions.
• Successfully suppressed mono-stoppered byproducts by controlling stoichiometry.
• Confirmed product identity and absence of contamination via analytical size-exclusion chromatography.
• Demonstrated kinetic persistence of the mechanical bond after demetalation.

Conclusions:

• The RO-DCM platform provides a concise, high-yield entry to [2]rotaxanes.
• This approach minimizes waste streams compared to traditional methods.
• The developed ring-chain equilibration blueprint is applicable to sequence-defined mechanically interlocked oligomers and polymers.