Highly Active and Thermally Robust Nickel Enolate Catalysts for the Synthesis of Ethylene‐Acrylate Copolymers

Abstract

The insertion copolymerization of polar olefins and ethylene remains a significant challenge in part due to catalysts' low activity and poor thermal stability. Herein we demonstrate a strategy toward addressing these obstacles through ligand design. Neutral nickel phosphine enolate catalysts with large phosphine substituents reaching the axial positions of Ni achieve activity of up to 7.7 × 10 3 kg mol À 1 h À 1 (efficiency > 35 × 10 3 g copolymer/g Ni) at 110 °C, notable for ethylene/acrylate copolymerization. NMR analysis of resulting copolymers reveals highly linear microstructures with main-chain ester functionality. Structureperformance studies indicate a strong correlation between axial steric hindrance and catalyst performance.

Switchable Synthesis of Ethylene/Acrylate Copolymers by a Dinickel Catalyst: Evidence for Chain Growth on Both Nickel Centers and Concepts of Cation Exchange Polymerization

“…In addition, a new olefinic species appears over time (Figure S27), which is similar to the internal olefin that was identified as a product of acrylate-induced β-H elimination. 107 This scenario is not observed with X-Ni 2 (Figure S17). Olefin generation, possibly by β-H elimination, being more facile with the NaBAr F 24 /X-Ni 2 mixture, is also S3 for the catalysis data).…”

“…76,107 A linear relationship was observed in the log plot of [X-Ni 2 ] over time. Assuming that tBA insertion into X-Ni 2 follows the same mechanism as a related mononuclear P,O−Ni complex (d[Ni]/dt = (k 1 *[tBA]/[py])*[Ni]),76 the rate constant k 1 , independent of pyridine and tBA concentrations, was determined (∼0.00033 min −1 , k obs-1 = k 1 *[tBA]/[py] = 0.00818 min −1 ).…”

Amine–Imine Nickel Catalysts with Pendant O-Donor Groups for Ethylene (Co)Polymerization

“…To improve the performance of nickel catalysts, some design strategies have been made beyond the simple steric/electronic modification. − An efficient method is the installation of a secondary interaction substituent by a proximally, flexibly, weakly coordinating ligand that interacts with the metal center to improve the copolymerization ability of the nickel catalyst . Brookhart-type palladium catalysts represent a major breakthrough in the copolymerization of ethylene with polar alkenes. − However, the nickel analogues showed less tolerance toward polar functionalities. , Chen et al developed the secondary interaction to introduce morpholine in α-diimine nickel complex (Figure V) which successfully copolymerized ethylene with polar monomers but produced low molecular weight copolymers .…”

“…40−43 An efficient method is the installation of a secondary interaction substituent by a proximally, flexibly, weakly coordinating ligand that interacts with the metal center to improve the copolymerization ability of the nickel catalyst. 44 Brookhart-type palladium catalysts represent a major breakthrough in the copolymerization of ethylene with polar alkenes. 45−47 However, the nickel analogues showed less tolerance toward polar functionalities.…”