Suppression of Chain Transfer and Promotion of Chain Propagation in Neutral Anilinotropone Nickel Polymerization Catalysis
Kangkang Li, Hongliang Mu, Xiaohui Kang, Zhongbao Jian
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 (102 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.