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

Abstract

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 M_w 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 M_w 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.