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

Abstract

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 metalcatalyzed olefin polymerization due to various side reactions such as cationic polymerization and β-OR elimination. The Brookharttype 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.

Influences of Ligand Backbone Substituents on Phosphinecarbonylpalladium and -nickel Catalysts for Ethylene Polymerization and Copolymerization with Polar Monomers

“…a c i s p r o h i b i t e d .catalysts and phosphinesulfonate Ni catalysts [14][15][16][17][18][19][20][21][22][24][25][26][27]37 Their catalytic performances are comparable with the previously reported phosphinesulfonate Pd catalysts and [P,PO]-type Ni and Pd catalysts.…”

Mechanistic Studies for Palladium Catalyzed Copolymerization of Ethylene with Vinyl Ethers

“…This process needs to overcome the free energy barrier of 28.3 (6.9 + 21.4) kcal/mol with the endergonic species 7 β _OEt by 9.4 (21.4 − 12) kcal/mol, thus suggesting the β -OEt elimination process is kinetically and thermodynamically unfavorable. The Pd-OEt active species hardly exists in this system, which is a different form of the α-diamine palladium system [ 51 ]. Further, ethylene insertions into the Pd−OEt bond of 7 β _OEt suffer from a very high energy barrier (27.5 kcal/mol), which is higher by 6.3 kcal/mol (=27.5 − 21.2 kcal/mol) for chain propagation, as shown in Figure 6 .…”

Influence of thiopheneyl‐based twisted backbone on the properties of α‐diimine nickel catalysts in ethylene polymerization

“…[20][21][22][23][24][25][26][27][28][29] In addition, the ligand sterics is also a superior approach to modulate the catalyst and polymer properties. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] In this regard, most of the researches have focused on building bulky amines for demandable ligand sterics with successful achievements but paid Daohong Liao and Shabnam Behzadi contributed equally to this work. much less attention to the backbone part of the α-diimine ligands.…”

“…[ 20–29 ] In addition, the ligand sterics is also a superior approach to modulate the catalyst and polymer properties. [ 30–44 ] In this regard, most of the researches have focused on building bulky amines for demandable ligand sterics with successful achievements but paid much less attention to the backbone part of the α‐diimine ligands. Ligand backbone also plays a crucial role to affect catalyst stability, activity, and polymer properties like molecular weight.…”