Axial Anagostic Interaction in α‑Diimine Nickel Catalysts: An Ultraefficient Occupation Strategy in Suppressing Associative Chain Transfers to Achieve UHMWPEs

Axial
anagostic bond Mt···H–C can occupy
the apical site of d8 square planar metal
complexes, which is highly desired, yet never explored, for olefin
polymerization because of its capability to suppress associative chain
transfer to access high molecular weight polyolefin products. In this
research, we present a method for how such axial anagostic interaction
Ni···H–C can be constructed into α-diimine
NiBr2 complexes, and more importantly, demonstrate its
pivotal role in improving the overall ethylene polymerization performance,
including (i) ultrahigh efficiency in suppressing associative chain
transfer to afford UHMWPEs with Mw up
to 724.2 × 104 g/mol, (ii) significantly impeded decomposition
of the cationic active species that brings in better storage stability,
and (iii) higher branched nature of the PE products that guarantee
a well-controlled living fashion for the whole polymerization process
even when Mw reaches ultrahigh levels.
With the aid of DFT calculations, the nature of such an anagostic
bond and its influence on each step of the polymerization process
are also elucidated.