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Ethylene-bridged Indenyl-fluorenyl Metallocene Complexes for Efficient Preparation of Allyl-terminated Propylene Oligomers and Polymers via Selective β-Methyl Transfer

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Abstract

Four C1-symmetric ansa-metallocene complexes, C2H4(Ind)(2,7-tBu2-Flu)ZrCl2 (4), C2H4(3-Bn-Ind)(2,7-tBu2-Flu)ZrCl2 (5), C2H4(3-Bn-Ind)(3,6-tBu2-Flu)ZrCl2 (6), and C2H4(3-Bn-Ind)(2,7-tBu2-Flu)HfCl2 (7), were synthesized and characterized. The structures of complexes 4, 5, and 7 were further determined via X-ray diffraction studies. Upon activation with modified methylaluminoxane (MMAO) or AliBu3/[Ph3C][B(C6F5)4] (TIBA/TrB), most of these complexes showed high efficiency in catalyzing propylene oligomerization/polymerization to afford products dominantly with allyl terminals via selective β-methyl transfer (β-Me transfer). The introduction of 3-benzyl group on the indenyl ring of the complexes was found to be crucial in enabling highly selective β-Me transfer during the polymerization process, leading to selectivities up to 89% obtained by zirconocene complexes 5 and 6, and up to 91% obtained by hafnocene complex 7. Detailed chain-end analysis by 1H-NMR, 13C-NMR, and MALDI-TOF mass spectroscopy revealed that the allyl chain-ends of the polymeric products resulted from a selective β-Me transfer process after two successively primary insertions of the monomer. Further studies concerning the dependence of chain release selectivity as well as the molecular weight of products on monomer concentration suggested that both β-Me transfer (major) and β-hydrogen transfer (β-H transfer) (minor) mediated by 5/MMAO and 6/MMAO systems may mainly operate in a bimolecular pathway.

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Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (No. 21274041), the Key Project of Chinese Ministry of Education (No. 109064), and the Fundamental Research Funds for the Central Universities (No. WK1214048).

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  1. Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai, 200237, China

    Lei Zhang, Bin Zhang & Haiyan Ma

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  1. Lei Zhang
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Correspondence to Haiyan Ma.

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Ethylene-bridged Indenyl-fluorenyl Metallocene Complexes for Efficient Preparation of Allyl-terminated Propylene Oligomers and Polymers via Selective β-Methyl Transfer

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Zhang, L., Zhang, B. & Ma, H. Ethylene-bridged Indenyl-fluorenyl Metallocene Complexes for Efficient Preparation of Allyl-terminated Propylene Oligomers and Polymers via Selective β-Methyl Transfer. Chin J Polym Sci 37, 578–590 (2019). https://doi.org/10.1007/s10118-019-2224-1

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