Two axles threaded using a single template site: active metal template macrobicyclic [3]rotaxanes.

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Materials Science

Background:

• Traditional rotaxane synthesis requires multiple template sites for interlocking components.
• Developing efficient methods for constructing complex rotaxanes is crucial for advanced molecular machinery.

Purpose of the Study:

• To present a novel one-pot synthesis of [3]rotaxanes utilizing a single metal template site.
• To demonstrate the formation of mechanical bonds within a bicyclic macrocycle through metal-templated covalent bond formation.

Main Methods:

• Employing a bicyclic molecule with a ligating portion that binds a transition metal ion.
• Utilizing the metal ion to template covalent bond formation (e.g., Cu(I)-catalyzed azide-alkyne cycloaddition) through macrocyclic cavities.
• Sequential or dual metal-catalyzed reactions to assemble axles with identical or different components.

Main Results:

• Achieved a one-pot synthesis of [3]rotaxanes with two identical axles in up to 86% yield using Cu(I) catalysis.
• Successfully synthesized [3]rotaxanes with two different axles by sequential Cu(I) catalysis or by employing dual metal catalysis (Pd(II) and Cu(I)).

Conclusions:

• A single metal template site can effectively direct the formation of multiple mechanical bonds in rotaxanes.
• This strategy offers a versatile and efficient approach to synthesizing complex [3]rotaxanes with tunable axle compositions.