# Tunable bis(pyridinium amidate) ligands efficiently promote palladium-catalyzed ethylene polymerization

## TL;DR

This paper introduces new palladium complexes with tunable ligands that efficiently catalyze ethylene polymerization under mild conditions.

## Contribution

The study presents a novel class of bis(pyridinium amidate) ligands that enhance palladium-catalyzed ethylene polymerization efficiency.

## Key findings

- Sterically locked ligand structures significantly improved ethylene conversion and polymer production.
- Complex 4d produced 10.8 kg of polyethylene per mol of palladium at room temperature and 1 bar ethylene.
- Trimetallic Pd⋯K⋯Pd complexes formed during synthesis, revealing a dual role for NaBArF in the process.

## Abstract

A useful strategy for the co-polymerization of ethylene and functional olefins relies on palladium catalysts, as palladium typically shows in contrast to many other metals a high tolerance to a variety of functional groups. Here we have prepared a set of palladium complexes containing a N,N-bidentate coordinating bis(pyridinium amidate) (bisPYA) ligand. Ligand variation included either para- or an ortho-pyridinium amidate arrangement, with the pyridinium site either sterically flexible or locked through a dimethyl substitution ortho to the amidate. Activation of these complexes with NaBArF in the presence of ethylene indicated that sterically locked ligand structures promoted ethylene conversion and produced polymeric materials. In particular, complex 4d with an ortho-pyridinium amidate bisPYA ligand was active with a production of 10.8 kg polyethylene per mol palladium at room temperature and 1 bar ethylene. Synthesis of the complexes in the presence of K2CO3 or Ag2CO3 afforded adducts in which the K+ or Ag+ ion is bound by the two oxygens of the bisamidate core, thus leading to trimetallic Pd⋯K⋯Pd complexes. Such adduct formation indicates a dual role of NaBArF in halide abstraction and metal sequestration, thus rationalizing the need for 2.5 equivalent of NaBArF per palladium complex for effective polymerization.

Palladium complexes with symmetric N,N-bidentate bis(pyridinium amidate) ligands catalyze the olefin polymerization already at mild conditions, when the pyridinium site is ortho,ortho-dimethylated. The carbonyl groups engage in metal coordination.