Selective ethylene tri-/tetramerization chromium catalysts based on binuclear PCCP ligands

Several novel binuclear PCCP ligands have been synthesized and characterized, and two PCCP scaffolds are connected using length adjustable alkyl linker. The results showed that the length of the linker and the electronic properties of the P-substituent in the binuclear PCCP ligands had remarkable influence on the catalytic activity and product selectivity. The longer linker inhibits catalytic activity, and the stronger the σ-donor ability of the P-substituent is beneficial for improving catalytic activity. The Cr complex bearing ligand 4, with shorter C4 linker and stronger the σ-donor ability of P-isopropyl substituents, exhibits excellent catalytic activity of 3856 kg·g-1·h-1 and 93.1 % combined (C6 + C8) product selectivity, with 53.0 % of the product being a C8 fraction. Furthermore, the Cr complexes bearing ligands 1–5 exhibit very low PE yield. Density functional theory (DFT) calculation shows that the tetramerization path of 4/Cr is favorable compared with the trimerization path in thermodynamics, which is highly consistent with the experimental results.