Dinuclear Group 4 Metallocene Catalysts of the Type [(Cp₂M)₂(μ-Me)(μ-C₂R)]: Structure-Activity Relationships in...

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Zirconocene and titanocene complexes are key catalysts in olefin polymerization.
• Understanding dinuclear complex behavior is crucial for developing novel catalytic systems.
• Aluminum-free activators offer environmentally benign alternatives in catalysis.

Purpose of the Study:

• To synthesize and characterize novel heterodinuclear zirconocene/titanocene complexes.
• To investigate the catalytic activity of these complexes in ethylene polymerization using aluminum-free activators.
• To elucidate the mechanism of polymerization and the role of dinuclear active species.

Main Methods:

• Comproportion reaction for complex synthesis.
• Single-crystal X-ray analysis, NMR spectroscopy, and quantum chemical calculations for structural elucidation.
• Ethylene polymerization experiments using various aluminum-free activators ([Ph3C][B(C6F5)4], B(C6F5)3, SiHB system).

Main Results:

• Alkynyl group migration from Zr to Ti was confirmed structurally and computationally.
• Dinuclear complexes exhibited unique reactivity upon activation, leading to electron or methyl abstraction and cationic species formation.
• Linear polyethylenes with unsaturated groups predominantly on the Zr cationic center were produced.
• Silicon-terminated polyethylenes were obtained using the Ti cationic center with the SiHB system in dichloromethane.

Conclusions:

• The synthesized heterodinuclear zirconocene/titanocene complexes can be activated by aluminum-free activators to yield active species for ethylene polymerization.
• The dinuclear nature of the active species influences polymer properties, including end-group functionalization.
• Catalyst design involving heterodinuclear complexes offers pathways to control polymer microstructure.