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

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.