Ethylene tri-/tetramerization catalysts supported by diphosphinothiophene ligands

Area of Science:

• Organometallic Chemistry
• Catalysis
• Polymer Science

Background:

• Ethylene oligomerization is crucial for producing linear alpha-olefins.
• Chromium catalysts are widely studied for ethylene oligomerization.
• Ligand design is key to controlling catalyst activity and selectivity.

Purpose of the Study:

• To develop novel chromium catalysts supported by diphosphinothiophene ligands for ethylene tri- and tetramerization.
• To investigate the effect of ligand substitution on catalytic performance.
• To establish structure-activity relationships for these catalytic systems.

Main Methods:

• Synthesis of chromium catalysts with diphosphinothiophene ligands.
• Activation of catalysts using methylaluminoxane (MMAO-3A).
• Evaluation of catalytic activity and selectivity for ethylene oligomerization.
• Structural characterization of representative chromium complexes using single-crystal X-ray diffraction.

Main Results:

• Developed active Cr catalysts for ethylene tri-/tetramerization upon MMAO-3A activation.
• Identified a Cr precatalyst with a trimethylsilyl-substituted diphosphinothiophene ligand exhibiting high activity (686 kg (g Cr h^-1)^-1) and selectivity towards 1-hexene and 1-octene.
• Established a correlation between shorter C-C bond lengths in the ligand backbone, smaller ligand bite angles, and increased catalytic activity.

Conclusions:

• Diphosphinothiophene ligands enable highly active chromium-catalyzed ethylene oligomerization.
• Ligand backbone modifications, specifically C-C bond length, are critical for tuning catalytic performance.
• These findings provide a model for understanding ligand effects in chromium-catalyzed olefin transformations.