# Design of Neutral Ni[N,N] Catalysts for High-Density Polyethylene Formation: Insights into Catalyst Deactivation

## TL;DR

Researchers designed new nickel catalysts for making high-density polyethylene and studied how these catalysts break down during polymerization.

## Contribution

The study introduces neutral Ni[N,N] catalysts and structurally characterizes their deactivation pathway via C–H activation for the first time.

## Key findings

- Neutral Ni[N,N] catalysts produced high-density polyethylene with melting points up to 140 °C.
- Catalyst deactivation via C–H activation was observed and structurally confirmed using NMR and X-ray diffraction.
- B(C6F5)3 was found essential for ethylene polymerization despite increased steric bulk.

## Abstract

Neutral Ni­[N,O] and cationic Ni­[N,N] complexes are two
prominent
classes of catalysts for the polymerization of ethylene. We report
the amalgamation of these motifs and describe the synthesis and catalytic
activity of two neutral Ni­[N,N] catalysts [Ni­(Ph)­(L)­(PPh3)], where L = 2-(arylamido)-5-methylcyclopent-2-en-1-arylimine (7) or 2-(arylamido)-cyclohex-2-en-1-arylimine (8); aryl is the ubiquitous 2,6-diisopropylphenyl group (Dipp). Despite
the increased steric bulk, ethylene polymerization was only achieved
using B­(C6F5)3 as an activator, forming
high-density polyethylene at 0 °C with T
m up to 140 °C, in contrast to the branched polymers characterized
by lower melting points that are more typically formed using nickel
catalysts. Surprisingly, both complexes undergo C–H activation
over days at room temperature, eliminating benzene and forming a cyclometalated
Ni­(II) complex that, for the first time, was characterized by multinuclear
NMR spectroscopy and single-crystal X-ray diffraction, structurally
characterizing this decomposition route for Ni ethylene polymerization
catalysts.