Synthesis Of Asymmetric Imine Binuclear Titanium And Trinuclearnickel Complexes Andcatalytic Performances For Olefin Polymerization

Non-metallocene transition metal catalysts have attracted extensive attention due to the ease of synthesis,high overall yield,the ability to catalyze the copolymerization of olefin withα-olefin and polar monomers,and the ability to polymerize at low temperatures.In this work,several non-allocene asymmetric salicyladimine binuclear metal catalysts and trinuclear nickel catalysts were synthesized and used to catalyze ethylene homopolymerization and copolymerization of ethylene and other olefins.The majorfindingsare as follows:（1）Disalicylaldehyde imide ligand with asymmetric structure was synthesized from disalicylaldehyde compound 2 with methylene bridge,then direct coordination of these ligands with TiCl₄ was carried out to obtain the asymmetric salicylaldehyde imide binuclear titanium complex.The asymmetric binuclear titanium complexes were characterized by FTIR,¹H NMR,¹³C NMR,and elemental analysis.The asymmetric binuclear titanium complexes were used to catalyze ethylene homopolymerization.It was found that the complex with the methyl sulfide side arm（9a）had a maximum activity of 2.29×10⁶ gPE/mol Ti.h.atm under the activation of MMAO.The molecular weight of polyethylene catalyzed by 9a was higher than that of the corresponding mononuclear catalyst.Moreover,the molecular weight distribution of polyethylene catalyzed by these asymmetric binuclear titanium complexes was wider than that of the corresponding symmetric binuclear titanium catalysts.The metal centers at both ends of the asymmetric binuclear titanium catalyst are not the same,therefore may catalyze ethylene polymerization with wide molecular weight distribution.（2）The salicylaldehyde imide asymmetric binuclear titanium complexes 9a,9b and 9c were used to catalyze the copolymerization of ethylene with 1-hexene,norbornene,and polar monomers 9-decene-1-alcohol.It was found that these asymmetric complexes could effectively catalyze the copolymerization of ethylene with 1-hexene,norbornene and 9-decene-1-alcohol.The activity of ethylene copolymerization with 1-hexene or norbornene exceeded 10⁶ g/molTi.h.atm,and the activity of ethylene copolymerization with polar monomer 9-decene-1-alcohol was higher than 10⁵ g/molTi.h.atm.In addition,there were positive monomer effects in copolymerization.Under the same conditions,the insertion rate of norbornene in the copolymers was higher than that of the corresponding mononuclear catalysts 10a and10b,a resultdue to the bimetallic synergy between the two different metal centers.（3）Trinuclearα-diimide nickel complexes 18a,18b and 18c were synthesized and characterized by FTIR and elemental analysis.The complexes were used to catalyze ethylene homopolymerization under the activation of MAO.It was found that all of them could effectively catalyze ethylene homopolymerization,with the highest activity obtained by 18a,reaching 1.58×10⁶ g/mol Ni.h.Compared with the mononuclearα-diimine nickel catalyst 19,trinuclearα-diimine nickel catalyst18a-18c produced polymethylene with a higher average weight molecular weight,with that catalyzed by 18a reaching 31.50×10⁴ g/mol,nearly 2 times higher than that of mononuclear catalyst 19.The molecular weight distribution of polyethylene catalyzed by these trinuclear nickel catalysts was also appreciably wider than that produced by mononuclear compound 19.The molecular weight distribution for the asymmetric catalysts 18b and 18c were even wider,with that for 18c reaching 10.50.The results indicated that there were multiple active centers in the trinuclear complexes,and the asymmetric structure was favorable for the production of polymers with wider molecular weight distribution.