No abstract

No abstract

The corresponding Cr(III) catalysts (1-6) based on asymmetric (diphenylphosphino)benzene-type L 1 -L 6 ligands have been explored for ethylene selective trimerization. It is observed that the structure of the complexes has an obvious influence on their catalytic performance for ethylene selective oligomerization.All the 1-6 precatalysts may offer selective ethylene trimerization systems, and their catalytic performance is greatly influenced by the reaction conditions. The precatalyst 2, bearing diisopropylphosphanyl substituent, may exhibit the remarkably high catalytic activity of 9.83 Â 10 7 g/(molCrÁh) with 90.4% C 6 selectivity under suitable conditions. Single crystal X-ray analysis showed that the alkyl/alkylaminophosphanyl of the ligands may efficaciously tune the catalyst structure and thus influence the oligomerization activity and product selectivity.

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 Â 10 6 g/[molCr h]). Furthermore, precatalysts 2-3 efficiently offer selective ethylene trimerization and afforded 97.76% 1-hexene selectivity with 5.8 Â 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.

No abstract