Chromium-based ethylene tetramerization with diphosphinoamines bearing pendent amine donors

• Diphosphinoamine ligands bearing pendent amine donors were synthesized.
• The ligands were subjected to Cr-catalyzed ethylene oligomerization.
• The new catalysts showed good selectivity and activity at elevated temperature.

Cr-catalyzed selective oligomerization of ethylene was carried out with diphosphinoamine ligands bearing pendent amine donors. Catalytic behavior of the Cr catalysts changed considerably, depending on the structural variation of ligands. The direct amine substitution on the nitrogen atom of backbone induced a conventional ethylene oligomerization with Schultz–Flory distribution. However, ethylene tetramerization was observed with other ligands having an ethylene or propylene linker between the two amines. Interestingly, the Cr catalysts having an ethylene linker and diisopropyl amine or having a propylene linker and diethyl amine groups showed a concurrent improvement of the selectivity for 1-hexene and 1-octene as well as the enhanced catalytic activity when the temperature increased from 30 ̊C to 60 ̊C. However, the Cr catalyst with diphosphinoamine ligand without a pendent amine donor showed that the trimerization of ethylene was increased at the expense of 1-octene selectivity with a significant loss of catalytic activity. Such a tendency was more evident at higher temperature and with chromium acetylacetonate as a precursor of the catalysts.

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