Well-defined silica-supported olefin metathesis catalysts

Area of Science:

• Organometallic Chemistry
• Catalysis
• Materials Science

Background:

• Ruthenium-based catalysts are crucial for olefin metathesis reactions.
• Immobilization of homogeneous catalysts onto solid supports enhances recyclability and simplifies product purification.
• N-heterocyclic carbene (NHC) ligands offer robust coordination to metal centers, improving catalyst stability and activity.

Purpose of the Study:

• To synthesize and characterize novel triethoxysilyl-functionalized NHC ligands.
• To prepare second-generation ruthenium olefin metathesis catalysts incorporating these ligands.
• To immobilize these ruthenium complexes onto silica gel and evaluate their performance as heterogeneous catalysts.

Main Methods:

• Synthesis of two triethoxysilyl-functionalized NHC ligands.
• Preparation of second-generation ruthenium-NHC complexes.
• Grafting of the ruthenium complexes onto silica gel.
• Evaluation of the heterogeneous catalysts in various olefin metathesis reactions.
• Analysis of catalyst recyclability and ruthenium leaching using ICP-MS (detection limit <5 ppb).

Main Results:

• Successful synthesis of the target NHC ligands and their corresponding ruthenium catalysts.
• The silica-supported ruthenium catalysts demonstrated high efficiency in multiple metathesis reactions.
• The heterogeneous catalysts were recycled over several reaction cycles without significant loss of activity.
• Ruthenium leaching into the reaction filtrate was below the detection limit (<5 ppb), indicating excellent retention.

Conclusions:

• Triethoxysilyl-functionalized NHC ligands enable the preparation of efficient, recyclable, silica-supported ruthenium metathesis catalysts.
• The immobilization strategy effectively prevents ruthenium contamination of the products.
• These solid-supported catalysts represent a promising advancement for sustainable and practical olefin metathesis.