Palladium-Catalyzed Dimerization of Vinyl Ethers: Mechanism, Catalyst Optimization, and Polymerization Applications

The electron-rich nature of vinyl ethers (CH 2 ═CHOR) enables their versatile reactivity patterns with transition metal catalysts. Furthermore, they are highly attractive monomers for the synthesis of many polymers and copolymers. However, it is challenging to incorporate these substrates in transition metal-catalyzed olefin polymerization due to various side reactions such as cationic polymerization and β-OR elimination. The Brookhart-type α-diimine palladium system can lead to the formation of branched (co)polymers with unique microstructures and potentially unique properties due to the characteristic chain-walking mechanism. Unfortunately, common vinyl ethers will induce cationic polymerization and catalyst decomposition for these catalysts. Within this context, the generation of ether-functionalized polyolefins with branched microstructures is attractive but remains a great challenge. In this study, we developed a system that combines palladium-catalyzed dimerization of vinyl ethers for the generation of β,γ-unsaturated acetals and palladium-catalyzed ethylene copolymerization with a dimerization product for the generation of polar functionalized branched polyolefins. The mechanism and catalyst optimization for the dimerization reaction were investigated in detail. This strategy combines catalytic organic synthesis and transition metal-mediated ethylene copolymerization to incorporate the abundant but challenging vinyl ether substrates into polyolefins. Importantly, the inserted acetal moiety can be readily converted to various functional groups through postpolymerization functionalization reactions, making this strategy even more versatile.