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

[Image: see text] Tetramerization of ethylene by chromium catalysts stabilized with functionalized N-aryl phosphineamine ligands C(6)H(4)(m-CF(3))N(PPh(2))(2) (1), C(6)H(4)(p-CF(3))N(PPh(2))(2) (2), C(6)H(4)(o-CF(3))N=PPh(2)-PPh(2) (3), and C(6)H(3)(3,5-bis(CF(3)))N(PPh(2))(2) (4) was evaluated. The parameter optimization includes temperature, co-catalyst, and solvent. Upon activation with MMAO-3A, the new catalyst system especially with m-functional PNP ligand (1) exhibited high 1-octene selectivity and productivity while giving minimum undesirable polyethylene and C(10)(+) olefin by-products. Using PhCl as a solvent at 75 °C led to a remarkable α-olefin (1-C(6) + 1-C(8)) selectivity (>90 wt %) at a reaction rate of 2000 kg·g(Cr)(–1)·h(–1). Under identical conditions, analogous PNP ligands bearing −CH(3), −Et, and −Cl functional moieties at the meta position of the N-phenyl ring displayed significantly lower reactivity. The catalyst with p-functional ligand (2) exhibited lower activity and comparable selectivities, while the Cr/PPN (with ligand 3) system gave no noticeable reactivity. The molecular structure of the precatalyst (1-Cr), exhibiting a monomeric structural feature, was elucidated with the aid of single-crystal X-ray diffraction study.