Suppression of Chain Transfer and Promotion of Chain Propagation in Neutral Anilinotropone Nickel Polymerization Catalysis

Abstract

Both suppression of chain transfer and promotion of chain propagation are highly important but greatly challenging to enhance desirable turnover frequency (TOF) and molecular weight (MW) in olefin polymerization, which is one of the most important chemical reactions. A transition-metal catalyst is the most important key to controlling these fundamental steps. In this contribution, we report the neutral, single-component anilinotropone nickel catalyst Ni6 via an alternative synthetic pathway, which is the isomer of the milestone salicylaldiminato nickel catalyst Ni6-iso. Compared to the classic Ni6-iso, Ni6 produces polyethylenes with elevated TOF (five times), much higher MW (10 2 times), narrower molecular weight distribution (PDI = 1.05, living fashion at 40 °C), and lower branching density (substantially linear microstructure) in ethylene polymerization. In particular, in the copolymerization of ethylene with a polar comonomer, Ni6 concurrently gives 4.5 times higher TOF, 34 times higher MW, and 1.6 times higher comonomer incorporation relative to Ni6-iso. Mechanistic insights using density functional theory (DFT) calculation reveal both the suppression of chain transfer and promotion of chain propagation. This evidences the anilinotropone nickel catalyst as a promising candidate.

Enhancing Suppression of Chain Transfer via Catalyst Structural Evolution in Ethylene (Co)Polymerization

“…[ 1‐3 ] To this end, tremendous efforts have been devoted to designing novel ligands containing multiple sterically bulky substituents, as these bulky substituents have been found to facilitate the suppression of chain transfer. [ 4‐26 ] In the case of imine‐based late‐transition‐metal catalysts, the evolution of o ‐aryl substituents has endowed this type of catalysts with the capability to produce high molecular weight and even UHMWPE (ultra‐high molecular weight polyethylene) (Chart 1). Taking salicylaldimine Ni(II) system as an example, replacing the o ‐aryl ‐iso propyl moieties in the nickel complex with bulkier o ‐aryl‐dibenzhydryl or o ‐aryl‐dibenzosuberyl substituents provides gradually improved molecular weights of the resulting polyethylenes (Scheme 1).…”

Simple and Sterically Open Nickel Catalyst for Ultrahigh Molecular Weight Polyethylene Synthesis

“…To further emphasize the challenge of producing UHMWPEs at 1 bar, we further analyzed the sterically bulkier nickel derivatives ( Ni-1 – Ni-5 ) were further analyzed. These derivatives with bulkier N -aryl moieties only produce (ultra)­high-molecular-weight PEs at high ethylene pressures of 8–30 bar, ,− indicating that UHMWPEs are difficult to access at 1 bar, even using sterically bulky nickel catalysts. Even with notable early transition metal catalysts, such as the benchmark Ziegler–Natta catalysts, constrained geometry catalysts, Fujita catalysts, and metallocene catalysts, it is difficult to reach ultrahigh molecular weight levels ( M n > 4,000 kDa) at 1 bar. − …”

Advances on Controlled Chain Walking and Suppression of Chain Transfer in Catalytic Olefin Polymerization

“…86 Moreover, the modified nickel catalyst 25 has been synthesized to further improve the molecular weight of polyethylenes to 4.5 × 10 6 g mol −1 in polar solvents. 85 Besides salicylaldiminato nickel catalysts, other [N,O] nickel catalysts derived from enolatoimine (26), 93 anilinotropone ( 27), 94 and α-imino-ketone (28) 95 skeletons also exhibit superior performance on suppressing chain transfer to produce ultrahighmolecular-weight polyethylenes (M n = 10 6 g mol −1 ), among which the α-imino-ketone framework is very attractive due to the facile synthesis.…”