Synthesis of Imine-Phenoxy Ligated Palladium Complexes for Norbornene Homopolymerization

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Metal complexes with tunable ligands are vital for controlling olefin polymerization.
• Ligand properties influence polymer molecular weight, crystallinity, and stereoregularity.

Purpose of the Study:

• To synthesize novel imine-phenoxy ligands and their corresponding palladium complexes.
• To investigate the catalytic activity of these complexes in norbornene polymerization.
• To correlate catalyst structure with polymer properties.

Main Methods:

• Single-step synthesis of imine-phenoxy ligands.
• Formation and characterization of mononuclear palladium complexes (Pd1-Pd4) using NMR, mass spectrometry, and X-ray diffraction.
• Polymerization of norbornene using Pd1-Pd4 catalysts.
• Analysis of polymer molecular weight via size-exclusion chromatography (SEC).

Main Results:

• Imine-phenoxy ligands and palladium complexes synthesized in high yields.
• X-ray analysis confirmed distorted square planar geometry around palladium.
• Pd1 catalyst, electronically deficient with high steric hindrance (%Vbur = 44.9), yielded the highest molecular weight poly(norbornene) (37.4 kDa).
• MMAO cocatalyst demonstrated superior performance, achieving high catalytic activity.

Conclusions:

• Electronically tuned imine-phenoxy ligands enable the synthesis of active palladium catalysts for norbornene polymerization.
• Catalyst structure, specifically electronic deficiency and steric bulk, significantly impacts polymer molecular weight.
• The developed catalytic system shows promise for producing high-molecular-weight poly(norbornene).