Synthesis And Property Of Silicon Phosphine Metal Complexes For Ethylene Oligomerization

Linear ?-olefin(LAO)is an important material for chemical production.It is widely used in surfactants,plasticizers,lubricants,oil additives and detergents.In the production process of LAO,ethylene oligomerization is a promising industrial production process,which can generate LAO with high activity and high selectivity.In ethylene oligomerization,the catalyst is the core technology of this process,so the development of new catalytic systems has always been a research hotspot in this field.The late transition metals nickel,cobalt and palladium and other metal complexes,as ethylene oligomerization catalysts,have good stability and advantages of single active center,so they have been widely concerned by academia and industry.Studies have shown that the structure of the ligand in the catalyst system and the type of metal are related to the selectivity of the product,and it has an important effect on the catalytic activity.Based on this,this paper synthesized a series of silicon phosphine ligands(L1-L6)by modifying the skeleton of silicon phosphine ligands,and synthesized a series of catalysts by changing the type of metal atoms.The effects of different reaction conditions on the oligomerization of ethylene catalyzed by metal complexes were also studied.In addition,the density functional theory(DFT)calculation method was also used to optimize and calculate the metal ring intermediate structure and relative Gibbs free energy spectrum of the Ni3 catalyst.The main research contents are as follows:(1)A series of silicon phosphine ligands(L1-L6)were synthesized,and the structure of the ligands(L1-L6)was characterized by NMR.Silicon phosphine ligands/nickel complexes(Ni1,Ni2,Ni3,Ni4),silicon phosphine ligand/cobalt complex(Co1,Co2,Co3,Co4)and silicon phosphine ligand/palladium complex(Pd1,Pd2,Pd3,Pd4)were synthesized,and there are characterized through mass spectrometry,elemental analysis and single crystal X-ray diffraction.The crystal structure analysis shows that the silicon phosphine ligand/metal complex is a twisted tetrahedral structure with metal as the center.(2)The silicon phosphine ligand/nickel complex(Ni1,Ni2,Ni3,Ni4)is used as a pre-catalyst,the monochlorodiethylaluminum(DEAC)is used as a co-catalyst,and methylcyclohexane is used as a solvent for ethylene oligomerization.Its main product is 1-butene.Under the same reaction conditions,the pre-catalyst Nil has the highest catalytic activity,which can reach 1.29×108 g/(molNi·h),the selectivity of 1-butene is 9.67%.The catalytic activity of pre-catalyst Ni3 is 2.29×107 g/(molNi·h),and the selectivity of 1-butene is 72.32%.In addition,the DFT calculation method was used to optimize and calculate the structure of the metal ring intermediate of the Ni3 pre-catalyst.At the same time,through the discussion of the Gibbs relative free energy spectrum of the catalyst intermediate and the comparison of the energy barrier,it was found that Ni3 pre-catalyst 1-butene had the highest selectivity.The theoretical analysis results are consistent with the experimental data.(3)Using silicon phosphine cobalt metal complex(Co1,Co2,Co3,Co4)as the precatalyst,DEAC and methylalumoxane(MAO)as co-catalyst and methylcyclohexane as solvent were researched for ethylene oligomerization.The main product is 1-butene.When the reaction time is 30 min,the ethylene pressure is 3 Mpa,the Al/Co molar ratio is 500,and the reaction temperature is 45?,the 1-butene selectivity of the pre-catalyst Co3 is as high as 91.72%.(4)The silicon phosphine ligand/palladium complex(Pdl,Pd2,Pd3,Pd4)was used as a precatalyst,MAO was used as a cocatalyst,and toluene was used as a solvent for ethylene oligomerization.When the Al/Pd molar ratio is 500,the reaction temperature is 45?,and the reaction time is 15min,the catalytic activity of the pre-catalyst Pd3 is as high as 2.29×105 g(molNi)-1·h-1.By comparing silicophosphine nickel/cobalt/palladium metal complexes,the results show that nickel metal complexes have the highest catalytic activity for ethylene dimerization,cobalt metal complexes have the highest selectivity of 1-butene,and palladium metal complexes has moderate catalytic activity and high selectivity for ethylene dimerization.