Synthesis Of Novel Series Of Short-chain Hyperbranched Nickel Complexes And Their Catalytic Performance Of Ethylene Oligomerization

Three series and five types of dendrimer-like nickel complexes were synthetized from corresponding 1.0-generation poly(amidoamine) dendrimer-like molecules(cyclohexylamine, ethylamine, 1-butylamine, 1-hexylamine and isopropylamine as core respectively), salicylaldehyde and nickel chloride hexahydrate via Schiff base condensation and one-pot synthesis of coordination reaction. The structure of three series of dendrimer and its corresponding nickel complexes were characterized by FT-IR, 1H-NMR and ESI-MS.Optimal reaction conditions of three series of dendrimer-like nickel complexes were evaluated in catalysis of ethylene oligomerization under methylaluminoxane as co-catalyst and toluene as solvent. The oligomerization results showed the best conditions of this catalytic system was 2μmol nickel complexes, Al/Ni ratio of 1000, 0.5MPa, 30 min and 25℃. Furthermore, under these catalysis conditions, three series of nickel complexes have reached best catalytic performance. A comparison of three series of nickel complexes showed that the catalyst of ethylamine as core with highest catalytic performance. Under these conditions, the catalytic activity was followed by 6.4×105g Olig(mol Ni·h)-1、5.9×105g Olig(mol Ni·h)-1、3.8×105g Olig(mol Ni·h)-1.Comparison of different effect of co-catalyst showed that ethylene oligomer products are mainly low carbon olefin under AlEt3 and MAO. Especially under the effect of AlEt3, more than 90% oligomer product was butene. Under the effect of EASC, ClAlEt2 and Cl2 AlEt, ethylene oligomerization was tandem with Friedel-Crafts alkylation reaction. Consequently,under these catalysis system the introduction of chloride ions should be avoided to keep high yield of ethylene oligomerization.The effects of different solvents such as toluene, cyclohexane and cyclohexane on catalytic performance of three series of nickel complexes were found that the distribution of oligomerization product was greatly influenced by the solvent. Under toluene solvent, the activity of ethylene oligomerize reaction was low. Under the catalytic system with aliphatic solvent, the activity of ethylene oligomerization was high but the oligomer product was mainly lower olefin.