Rotaxane synthesis exploiting the M(i)/M(iii) redox couple.

Area of Science:

• Supramolecular Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• Mechanically interlocked molecules (MIMs) are advanced molecular architectures with unique properties.
• Metal-based building blocks offer versatile platforms for constructing complex MIMs.
• Late transition metals like rhodium and iridium are key components in catalytic and material applications.

Purpose of the Study:

• To develop a novel synthetic route for late transition metal-containing [2]rotaxanes.
• To utilize rhodium(III) and iridium(III) complexes for the robust capture and retention of interlocked assemblies.
• To establish efficient and mild reaction conditions for the preparation of these metal-based rotaxanes.

Main Methods:

• Hydrogenation of rhodium(I) and iridium(I) precursors ([M(COD)(PPh3)2][BArF4]) to form metal complexes.
• Reaction of these metal complexes with a bipyridyl-terminated [2]pseudorotaxane.
• Detailed mechanistic studies including kinetic analysis of hydrogenation pathways.
• Spectroscopic characterization (NMR, Mass Spectrometry) and X-ray diffraction for structural elucidation.

Main Results:

• Successful preparation of late transition metal-containing [2]rotaxanes (1) using rhodium and iridium.
• Identification of disparate hydrogenation rates for rhodium and iridium precursors, explained by mechanistic studies.
• Development of optimized, mild reaction conditions (room temperature, 1 atm H2, ≤ 2 hours) for rotaxane synthesis.
• Solid-state structure of the iridium-based [2]rotaxane (1b) elucidated by X-ray diffraction.

Conclusions:

• Robust metal-based [2]rotaxanes can be synthesized by employing late transition metal complexes.
• Mechanistic understanding of hydrogenation pathways is crucial for optimizing synthetic strategies.
• The developed method provides a convenient and efficient route to novel metal-containing MIMs for advanced applications.