Synthesis Of Heterobimetallic Cobalt And Nickel Complexes And Their Application As Catalysts For Ethylene Polymerization

Lignads PN5, PAN5 and MN5 which have the bis(imino)pyridine unit and theα-diimine unit were synthesized by condensation reaction between corresponding aldehyde compounds and ketone compounds catalyzed by para-toluenesulfonic acid. For preparation of the heterobinuclear cobalt and nickel complexes PN5CoNi, PAN5CoNi and MN5CoNi, CoCl2 was firstly selectively coordinated to the bis(imino)pyridine unit followed by coordination of NiBr2 to theα-diimine unit. The bis(imino)pyridine unit and theα-diimine unit are nonconjugated in PN5CoNi and PAN5CoNi. And the bis(imino)pyridine unit and theα-diimine unit are conjugated in MN5CoNi. The ligands and the complexes were characterized by various methods, such as ESI MS, elemental analysis, ICP and FT-IR etc.At first heterobinuclear catalyst PN5CoNi containing nonconjugated bis(imino)pyridine unit andα-diimine unit was used as catalyst for ethylene polymerization by using TEA(or TEA/ TEA/[PhMe2NH][B(C6F5)4](abbreviated as B)), TIBA, MMAO(or MMAO/B), AlEt2iBu(or AlEt2iBu/B) or AlEtiBu2(or AlEtiBu2/B) as cocatalyst. By deconvolution of molecular weight distribution (MWD) of produced PE with Flory distribution, the influence of the structure of the complexes, the interaction between the two metal centers and the structure of the cocatalysts on the performance of PN5CoNi in ethylene polymerization were studied. It has been found that:1) Compared with the binary complexes of equivalent corresponding mononuclear complexes (abbreviated as binary complexes), the ethylene polymerization activity of Co was similar, and the polymerization activity of Ni was quite different. When using TEA or TEA/[PhMe2NH][B(C6F5)4] (Al/Co(or Ni) ratio was 400) as cocatalyst, the Co site was well activated and the polymerization activity was high. The Ni site was then selectively deactivated and the polymerization activity was low. When using TEA/B(Al/Co(or Ni) ratio was 50) as cocatalyst, the Co site was not well activated. The polymerization activity of Ni site increased, which indicates it was selectively activated. Compared with TEA, when using MMAO or MMAO/B as cocatalyst, both of the activities of Co and Ni sites increased which indicate that MMAO can activate Co and Ni sites well.2) When using AlEt2iBu or AlEtiBu2 as cocatalyst by introducing iBu group to the alkyl aluminum, the Co site was deactivated and there was little influence on the Ni site. When using AlEt2iBu/B or AlEtiBu2/B as cocatalyst and the Al/(Co+Ni) ratio was low, the polymerization activity of Co site was low compared using TEA/B as cocatalyst, therefore the Ni site could be well activated.The influence of the structure of the catalyst PAN5CoNi which hasα-acenaphthenediimine unit and the cocatalyst on the performance of the ethylene polymerization was studied:When using TEA or TEA/B as cocatalyst, compared with the corresponding binary complex, the polymerization activity of Co site was similar, and the polymerization activity of Ni site was significantly low, which indicates the Ni site was selectively deactivated. When using AlEt2'Bu or AlEt'Bu2 as cocatalyst by introducing iBu group to the alkyl aluminum, the Co site was deactivated and there was little influence to the Ni site. When using AlEt2iBu/B or AlEtiBu2/B as cocatalyst and the Al/(Co+Ni) ratio was low, the polymerization activity of Co site was low compared using TEA/B as cocatalyst, then the Ni site was well activated.The influence of the structure of the heterobinuclear catalyst MN5CoNi, which contains conjugated bis(imino)pyridine unit and a-diimine unit and the structure of the cocatalysts on the performance of MN5CoNi in ethylene polymerization were also studied:Compared with binary complexes, the polymerization activity of cobalt or nickel sites was low. When using TEA as cocatalyst, the polymerization activity of Co or Ni sites was very low, which reveals that Co and Ni sites of MN5CoNi were deactivated. Compared with TEA, when using MMAO as cocatalyst, the polymerization activity increased and the amount of polyethylene produced by Ni site was higher than binary complexes. When using TEA/B as cocatalyst, both the polymerization activities of Co and Ni sites increased, but the amount of polyethylene produced by Ni site was lower than binary complexes, which indicates the Ni site was selectively deactivated.The influence of polymerization time on polymerization activity and MWD of polyethylene produced by MN5CoNi and binary complexes was investigated when using MMAO as cocatalyst. The process of activating Co and Ni sites in MN5CoNi was slow compared with binary complexes. But the Co and Ni sites were more stable than they in the binary complexes.There were only methyl branches in the PE produced by Ni sites of these three heterobinuclear complexes. And the branch degree of PE produced by Ni sites of heterobinuclear complexes was low compared with Ni sites in binary complexes, which indicates that the "chain walking" effect was suppressed when the ligand of the complex became larger.Compare PAN5CoNi with PN5CoNi containing nonjugated bis(imino)pyridine unit and a-diimine unit:The bis(imino)pyridine units are the same. When using TEA as cocatalyst, the activities of Co and Ni sites were high. By using TEA/B, AlEt2'Bu(or AlEt2'Bu/B) or AlEt'Bu2(or AlEt'Bu2/B) as cocatalyst, it is founded that when the polymerization activity of Co site in PN5CoNi was higher than that in PAN5CoNi, then the polymerization activity of Ni site in PN5CoNi was lower than that in PAN5CoNi. Vice versa. These results indicate that the Co and Ni sites deactivated each other.Compare MN5CoNi containing conjugated bis(imino)pyridine unit and the a-diimine unit with PN5CoNi and PAN5CoNi containing nonconjugated bis(imino)pyridine unit and the a-diimine unit:When using TEA as cocatalyst, the polymerization activities of Co and Ni sites in MN5CoNi were low. When using TEA/B as cocatalyst, the polymerization activity of Co site in MN5CoNi increased, while the polymerization activity of Ni site was still low. When using MMAO or MMAO/B as cocatalyst, the polymerization activities of Co and Ni sites in MN5CoNi were high. The MWs of PE produced by Co and Ni sites in MN5CoNi were low. These results above indicate that besides the structure of the catalyst, the structure of the cocatalysts also influenced the ethylene polymerization performance.The branches per 1000 carbon atoms of PE produced by Ni sites in PN5CoNi and PAN5CoNi were about 50, and the branches per 1000 carbon atoms of PE produced by Ni site in MN5CoNi were about 20～30. This is because the substituents of the ortho positionin in one phenyl group a-diimine unit were methyl, which is not favorable for "chain walking".