Olefin Metathesis in Confinement: Towards Covalent Organic Framework Scaffolds for Increased Macrocyclization...

Area of Science:

• Materials Science
• Organic Chemistry
• Catalysis

Background:

• Covalent organic frameworks (COFs) possess tunable structures and porosity.
• Their potential for spatially confined reactions remains largely unexplored.
• Heterogeneous catalysis using COFs is well-established.

Purpose of the Study:

• To utilize the porosity of COFs for spatially confined reactions.
• To develop a molecularly precise heterogeneous catalyst for olefin metathesis.
• To enhance macrocyclization selectivity in α,ω-diene ring-closing metathesis.

Main Methods:

• Synthesized a highly porous, crystalline, large-pore COF.
• Immobilized a Grubbs-Hoveyda-type catalyst onto the COF pore walls via silylation.
• Investigated α,ω-diene ring-closing metathesis reactions using the heterogeneous COF-catalyst.

Main Results:

• Achieved a molecularly precise heterogeneous olefin metathesis catalyst.
• Observed increased macro(mono)cyclization (MMC) selectivity (MMC:O=1.35) compared to homogeneous catalysis (MMC:O=0.90).
• Demonstrated a 51% increase in MMC selectivity due to COF pore confinement, showing substrate-size dependency.

Conclusions:

• Large-pore COFs can serve as effective catalytic supports for confined reactions.
• Pore confinement in COFs can significantly enhance reaction selectivity.
• This approach offers a pathway to precisely control catalytic outcomes through material design.