Insight into the Mechanism of Thermal Stability of α‑Diimine Nickel Complex in Catalyzing Ethylene Polymerization

The
union of experimental and computational methods can accelerate
the development of polymerization catalysts for industrial applications.
Herein, we report complementary experimental and computational studies
of the thermal stability of α-diimine nickel complexes by using
thermally stable Cat. 1 and a typical Brookhart catalyst
(B-Cat) as models. Experimentally, we found that many
more nickel atoms could be activated for Cat. 1 at elevated
temperature during the ethylene polymerization process compared to
those for B-Cat. Computationally, first-principle calculations
showed that the decomposition energies of Cat. 1 were
found to be higher than those of B-Cat, contributing
to the activation observed for Cat. 1. We found that
the presence of ethydene evidently affected the conformation of C1–N1–Ni–N2–C2
five-membered ring (where the nickel center is located) of Cat.
1, turning the envelope conformation (B-Cat) into
a half-chair conformation (Cat. 1). According to calculations,
the decomposition energy of the latter was 17.4 kJ/mol higher than
that of the former. These results provide information to elucidate
the mechanism of thermal stability of α-diimine nickel catalyst
and significantly advance the development of thermally stable α-diimine
nickel catalysts used in industry.