Heteroscorpionate bis-pyrazolyl ligands in Cr(III)-catalyzed ethylene oligomerization

•New Cr(III) catalysts supported by the bis-pyrazoyl ligands with a third heteroaryl group.•The Cr(III) catalysts for the selective ethylene trimerization and tetramerization.•Formation of An acetoxychromium(III) chloride from carboxyl-containing ligand through the HCl elimination.

We have investigated Cr(III) catalysts supported by the bis-pyrazoyl ligands containing a range of appendices from heteroaryl groups, such as quinolinyl, furanyl, and thiopheneyl, to hydroxy-containing groups such as carboxyl and hydroxyl. These catalysts, upon activation with MAO, are active for ethylene oligomerization. The Cr precatalyst supported by the bis-pyrazolyl ligand with thiopheneyl achieved a activity of 29.8 kg/(g Cr/h) with a total selectivity of 58.5% toward 1-hexene and 1-octene. The complexation reaction of carboxyl-containing ligand with Cr(THF)3Cl3 gave an acetoxychromium(III) chloride through the HCl elimination.

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