Unveiling -Alkyloxy/-Silyloxy-Substituted -Aryl PNP Ligands for Efficient Cr-Catalyzed Ethylene Tetramerization.

Novel -aryl-functionalized PNP ligands () bearing -alkyloxy/-silyloxy substituents were prepared and evaluated for chromium-catalyzed ethylene oligomerization using MMAO-3A as an activator. The selected Cr/PNP system under optimized condition exhibited high 1-octene-selective (up to 70 wt %) ethylene tetramerization at a remarkable rate (over 3000 kg gCr h). More importantly, the undesirable polyethylene selectivity was restricted to a minimum level of ∼1-2 wt % for pre-catalysts derived with ligands and . Employing chlorobenzene as a reaction medium yielded best productivity in conjunction to the total α-olefin (1-C + 1-C) selectivity (∼88 wt %). -aryl PNP ligands ( and ) incorporating -silyloxy substituents in the phenyl ring exhibited relatively poorer tetramerization performance while yielding higher PE fraction as compared to their -alkyloxy derivatives. A detailed molecular structure of the best-performing pre-catalyst -Cr was established by single-crystal X-ray diffraction analysis. The stability of /Cr-based catalyst system was investigated for a reaction time of up to 2 h under optimized condition.