Zirconium Complex System Catalyst For Ethylene Polymerization

The one-pot oligo-cyclization of ethylene catalyzed by CpaZrCl2 with EAO (ethylaluminoxane) or Et3Al as cocatalyst is a newly founded reaction, and it has the latent application foreground. We have investigated the effects of the structures of pre-catalysts, the effect of cocatalyst and the addition of third-component (Et2Mg, EtMgBr) on the catalytic activity and selectivity to carbocyclic compounds. Base on the products of oligo-cyclization of ethylene and the reported mechanism about oligomerization and a,w-diene cyclization catalyzed by zirconocene complexes, a new mechanism for oligo-cyclization of ethylene is supposed.The oligomerization of ethylene catalyzed by metallocene complexes L12ZrCl2 (L1= Cp, Cp*, Ind) with Et3Al as cocatalyst (150℃, P(C2H4) = 1.4 MPa, Al/Zr = 100) gave 6-34% of cyclic oligomers, mainly exo-methylenecyclopentane, methylcyclopentane and a small amount of 1-methyl-1-ethylcyclopentane and vinylcyclohexane, along with open-chain alkenes. In contrast, the catalytic reactions by post-metallocene complexes L2ZrCl2 (L2 = salen, salphen) under identical conditions generated open-chain olefins exclusively. When Cp2TiCl2 was used in place of Cp2ZrCl2, the selectivity of 5-membered cyclic products was dropped dramatically.With Cp2ZrCl2/ Et3Al as catalyst for ethylene oligomerization, the addition of the third-component (Et2Mg) increases the catalytic activity and the selectivity of carbocyclic products apparently. Under the optimal condition (Cp2ZrCl2/Et3Al/Et2Mg = 1:100:10, 150℃, P(C2H4) = 1.4 MPa) the reaction afforded 51% of cyclic oligomers, among them five-membered cyclic compounds account for 44%. But with Cp2ZrCl2/EAO (Al/Zr=10:l) as catalyst for ethylene oligomerization, the addition of the t hird-component (Et2Mg) b enefits t he formation o f p olymers. When M AO was used as co-catalyst in an Al/Zr/Mg molar ratio of 10:1:2, polymers were obtained with an Mv value of 1.37×105 in an activity of 2.83×104 g polymer/mol(Zr).h. The addition of a small amount of Et2Mg to Cp2ZrCl2/EAO catalysts greatlypromoted the polymerization of ethylene in a low Al/Zr molar ratio.Three N2O2 ligands were synthesized. Two N4O4 eight-coordinated zirconium complexes were obtained by the reaction of ZrCl4 or Zr(NO2)4 with the prepared N2O2 ligands. Other two N2O2C12 six-coordinated zirconium complexes were also synthesized. IR, MS , 1H NMR spectra and X-Ray analysis were utilized for the determination of the structures of prepared zirconium complexes. At different reaction temperatures and various reaction periods, the catalytic performances in the ethylene oligomerization by N2O2C12 six-coordinated zirconium complexes with Et2AlCl as cocatalyst are tested.