Synthesis routes and molecular structure of the PNSiP ligand.

Silicon-bridged/N, P (PNSiP) ligand/Cr (III) catalyst system based on different fluorinated hydrocarbons as modifiers have been explored for ethylene selective tri-/tetramerization. Modifiers like 1H-Perfluorohexane (1H-PFH), Hexafluorobenzene (HFB), and Perfluorobiphenyl (PFB) have been proven to show a significant influence on ethylene oligomerization toward 1-hexene and 1-octene of the catalytic system. Among them, 1H-PFH showed the most significant promotion effect in improving activity from 0.95 × 10⁶ g·(mol Cr·h)⁻¹ to as much as 5.66 × 10⁶ g·(mol Cr·h)⁻¹ at high temperature 90°C. Through the analysis of nuclear magnetic resonance (NMR) spectroscopy and ultraviolet visible diffuse reflectance spectroscopy (UV–vis DRS) results, we concluded that 1H-PFH can react with an amount of trimethylaluminum (TMA) contained in the cocatalyst modified methylaluminoxane (MMAO) and the solubility of Cr (III) in solvent can be increased after adding 1H-PFH. Furthermore, the possible reaction routes of 1H-PFH with TMA and MMAO were proposed.