Chromium catalysts based on PNP(NR2)2 ligands for selective ethylene oligomerization

High active and selective 1–3 chromium catalysts based on the corresponding Ph 2 PN(cyclopentyl)P (NR 2 ) 2 ‐type L 1 – L 3 ligands ( L 1 : R = methyl, L 2 : R = ethyl, L 3 : R = isopropyl) have been explored for selective ethylene tri‐/tetramerization. We found that the ligand substituents and the experimental conditions considerably influenced the catalytic performance of 1–3 based catalysts. Combining a higher ethylene pressure can elevate the selectivity of 1‐octene (67.98%) of precatalyst 1 with high catalytic activity (9.3 × 10 6 g/[molCr h]). Furthermore, precatalysts 2–3 efficiently offer selective ethylene trimerization and afforded 97.76% 1‐hexene selectivity with 5.8 × 10 6 g/(molCr h) catalytic activity (in case precatalyst 3 ). A relatively low catalyst mass, high Al/Cr molar ratio, and high ethylene pressure display excellent catalytic activity and selectivity for ethylene oligomerization.