Highly Efficient Ethylene Tetramerization Using Cr Catalysts Constructed with Trifluoromethyl-Substituted -Aryl PNP Ligands.

Tetramerization of ethylene by chromium catalysts stabilized with functionalized -aryl phosphineamine ligands CH(-CF)N(PPh) (), CH(-CF)N(PPh) (), CH(-CF)N=PPh-PPh (), and CH(3,5-bis(CF))N(PPh) () was evaluated. The parameter optimization includes temperature, co-catalyst, and solvent. Upon activation with MMAO-3A, the new catalyst system especially with -functional PNP ligand () exhibited high 1-octene selectivity and productivity while giving minimum undesirable polyethylene and C olefin by-products. Using PhCl as a solvent at 75 °C led to a remarkable α-olefin (1-C + 1-C) selectivity (>90 wt %) at a reaction rate of 2000 kg·g ·h. Under identical conditions, analogous PNP ligands bearing -CH, -Et, and -Cl functional moieties at the meta position of the -phenyl ring displayed significantly lower reactivity. The catalyst with -functional ligand () exhibited lower activity and comparable selectivities, while the Cr/PPN (with ligand ) system gave no noticeable reactivity. The molecular structure of the precatalyst (-Cr), exhibiting a monomeric structural feature, was elucidated with the aid of single-crystal X-ray diffraction study.