Study On Catalytic Performance Of Novel Hyperbranched Transition Metal Complexes In The Oligomerization Of Ethylene

A series of hyperbranched transition metal complexes with the different length of bridging groups and the different center of catalytic activity were synthesized using hyperbranched molecules as bridging groups through functional modification of the end group amidocyanogen.The results of Fourier transform infrared spectroscopy(FT-IR),UV,1H nuclear magnetic resonance(1H-NMR)and Electrospray ionization mass spectrometry(ESI-MS)confirmed the structures of the synthetic hyperbranched ligands and its corresponding complexes were consistent with their theoretical design structures.On the basis of the systhesis and characterization,the catalytic properties of a series of hyperbranched salicylaldimine transition metal complexes for ethylene oligomerization were studied,and the effects of the polymeric system and polymeric conditions on the oligomerization activity and the product distribution were investigated in detail.The oligomerization results showed that all the hyperbranched salicylaldimine transition metal complexes showed moderate activities towards ethylene oligomerization using MAO as co-catalyst and toluene as solvent.The optimal reaction conditions of cobalt complex with octadecyl as core(Cat.3)were as follows: the molar ratio of Al/Co was 800,the reaction temperature was 25?,the reaction pressure was 0.5MPa and the reaction time was 30 min.The optimal reaction conditions of iron complex with octadecyl as core(Cat.6)were as follows: the molar ratio of Al/Fe was 500,the reaction temperature was 25?,the reaction pressure was 0.7MPa and the reaction time was 30 min.Under these conditions,the catalytic activities of Cat.3 and Cat.6 were followed by 1.85×105g/(mol Co·h)and 8.63×104g/(mol Fe·h),and the content of C8+ in oligoerization products were 55.38% and 21.58%,respectively.The effects of the hyperbranched molecules backbone and the kinds of metal center of complexes on the ethylene oligomerization were also studied.The results showed that the catalytic activity declined with increasing of the length of alkyl chain in the ligand backbone.The hyperbranched salicylaldimine transition metal complexes with 1-tetradecyl as core have the best catalytic performance.Compared to the iron analogue,the cobalt and nickel complexes exhibited higher catalytic activities.Among them,the cobalt complex had the best selectivity for C10+ oligomers.Based on the systematic study of catalytic performance of hyperbranched salicylaldiminetransition metal complexes for ethylene oligomerization,a series of hyperbranched PNP chromium complexes with hyperbranched molecules as bridging groups were synthesized,and the properties of catalytic ethylene oligomerization for these chromium complexes were investigated.Under MAO as co-catalyst and toluene as solvent,the optimal reaction conditions of chromium complex with 1-tetradecyl as core(Cat.7)were as follows: the molar ratio of Al/Cr was 500,the reaction temperature was 25?,the reaction pressure was 0.5MPa and the reaction time was 30 min.Under these conditions,the catalytic activity was followed by 1.54×105 g/(mol Cr·h),and the content of high carbon olefins was 49.40%.