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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.

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Nickel (II) complexes stabilized by PNP(NR2)2 (L1: R = Methyl, L2: R = ethyl, L3: R = isopropyl) ligands were synthesized and characterized. A narrow range of products was observed for catalytic systems containing nickel complexes and ethyl aluminum dichloride (EADC). All exhibit considerable activity in the ethylene dimerization to produce 1-butene. Precatalyst 1 is the most conducive for ethylene dimerization, producing 83.4% C4 (1-C4 36.8%) and 103.0 × 105 g/(molNi·h) in terms of its activity under the appropriate conditions. By adjusting the conditions of the catalytic system for precatalyst 2, high C4 selectivity (88.1%) with reasonable activity (76.9 × 1 05 g/(molNi·h)) can be obtained. The X-ray single-crystal analysis of complexes presents mononuclear bidentate coordination at the Ni center, and the relationship between certain bite angles may also imply catalytic performance.

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The in situ formation and activation of Cr(III) catalysts based on unsymmetrical PNP ligands yield efficient catalytic systems for selective ethylene tri-/tetramerization. The electronic nature (electron-withdrawing or electron-donating) and position (para or meta) of the substituents over the phenyl rings of the PNP, the nature of cocatalyst (DMAO/AlEt3 and MMAO-3A), and reaction conditions have been observed to have a marked impact on catalytic performance, particularly catalytic activity. Ligand L2, bearing 4-(trifluoromethyl)phenyl substituents, yielded 33.6 kg(product).g(Cr)−1·h−1 catalytic activity with 57.7% C8 selectivity under optimal conditions. Ligand L4, having para-tolyl substituents, yielded 43.3 kg(product).g(Cr)−1·h−1 with 59.0% C8 selectivity under optimum conditions. Changing the positions of both the electron-withdrawing and electron-donating substituents from para to meta over the phenyls of the PNP may lead to both catalytic systems exhibiting poor performance.