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

Samir Barman; Nestor Garcia; E A Jaseer; Mohamed Elanany; Motaz Khawaji; Hassan Alasiri; Abdul Malik P Peedikakkal; Muhammad Naseem Akhtar; Rajesh Theravalappil

doi:10.1021/acsomega.3c03029

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

ACS Omega. 2023 Jul 14;8(29):26437-26443. doi: 10.1021/acsomega.3c03029. eCollection 2023 Jul 25.

Authors

Affiliations

¹ Center for Refining and Advanced Chemicals, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
² Fuels and Chemicals Division Aramco Research Center at KAUST, Thuwal 23955, Saudi Arabia.
³ Chemical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
⁴ Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
⁵ Interdisciplinary Research Center for Hydrogen and Energy Storage, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.

Abstract

Novel N-aryl-functionalized PNP ligands (1-4) bearing m-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^-1 h^-1). More importantly, the undesirable polyethylene selectivity was restricted to a minimum level of ∼1-2 wt % for pre-catalysts derived with ligands 1 and 2. Employing chlorobenzene as a reaction medium yielded best productivity in conjunction to the total α-olefin (1-C₆ + 1-C₈) selectivity (∼88 wt %). N-aryl PNP ligands (3 and 4) incorporating m-silyloxy substituents in the phenyl ring exhibited relatively poorer tetramerization performance while yielding higher PE fraction as compared to their m-alkyloxy derivatives. A detailed molecular structure of the best-performing pre-catalyst 1-Cr was established by single-crystal X-ray diffraction analysis. The stability of 1/Cr-based catalyst system was investigated for a reaction time of up to 2 h under optimized condition.