摘要/Abstract

合成并表征了一系列新型亚乙基桥联多取代茚-芴锆、铪配合物ansa-C₂H₄-{2-Me-3-Bn-5，6-[1，3-（CH₂）₃]Ind}-（Flu） ZrCl₂（C1），ansa-C₂H₄-{2-Me-3-Bn-5，6-[1，3-（CH₂）₃]Ind}（2，7-^tBu₂-Flu） ZrCl₂（C2），ansa-C₂H₄-{2-Me-3-Bn-5，6-[1，3-（CH₂）₃]Ind}（3，6-^tBu₂-Flu） ZrCl₂（C3），ansa-C₂H₄-{2-Me-3-Bn-5，6-[1，3-（CH₂）₃]Ind}（Flu） HfCl₂（C4），并对典型配合物进行了X射线单晶衍射分析，确定了其空间结构.研究了该系列配合物在助催化剂作用下催化丙烯齐聚的行为，考察了催化剂结构及反应条件对齐聚反应的影响.配合物C1～C4与改性甲基铝氧烷（MMAO）或三异丁基铝/三苯甲基四（五氟苯基）硼酸盐（TIBA/TrB）组成的催化体系对丙烯齐聚表现出中等到高的催化活性.锆配合物C2和C3在40～100℃条件下普遍具有较高的β-甲基消除（β-Me消除）选择性（最高可达86%），实现了分子量M_n在400到4500 g·mol^－1范围内的烯丙基封端丙烯齐聚物的高效合成.铪催化剂体系C4/TIBA/TrB的β-Me消除选择性明显高于相应的锆催化剂体系，同时所得齐聚物的分子量更低.
关键词: 茂金属催化剂, 丙烯齐聚, 烯丙基端基, β-甲基消除
In metallocene-mediated propylene polymerization, β-methyl elimination (β-Me elimination) is considered as the key chain-release step for obtaining allyl-terminated products, which are highly preferred as macro(co)monomers or building blocks for preparing novel polymers. However, for most metallocene catalysts the transfer of a β-methyl is instinctively less favored due to its steric and electronic disadvantages. Up to date, very few cases have been found to be efficient for triggering selective β-methyl elimination. In this work, a series of novel ansa-metallocene complexes, ansa-C₂H₄-{2-Me-3-Bn- 5,6-[1,3-(CH₂)₃]Ind}(Flu)ZrCl₂ (C1), ansa-C₂H₄-{2-Me-3-Bn-5,6-[1,3-(CH₂)₃]Ind}(2,7-^tBu₂-Flu)ZrCl₂ (C2), ansa-C₂H₄-{2-Me-3-Bn-5,6-[1,3-(CH₂)₃]Ind}(3,6-^tBu₂-Flu)ZrCl₂ (C3) and ansa-C₂H₄-{2-Me-3-Bn-5,6-[1,3-(CH₂)₃]Ind}(Flu)HfCl₂ (C4), were synthesized via the reaction of the dilithium salts of the corresponding proligand with 1 equiv. of ZrCl₄ or HfCl₄ in Et₂O. All complexes were characterized by ¹H NMR, ¹³C NMR and elemental analysis. The molecular structures of complexes C1, C2, and C3 were further determined via X-ray diffraction method. In the solid state, these complexes adopted an indenyl-backward orientation with rotation angles (RA: the orientation of the indenyl ring with respect to the fluorenyl ring) ranging from －11.30° to －17.07°. Upon activation with modified methylaluminoxane (MMAO) or AlⁱBu₃/ [Ph₃C][B(C₆F₅)₄] (TIBA/TrB), all these complexes exhibited moderate to high activities for propylene oligomerization at 40～100 ℃, affording propylene oligomers with both allyl and vinylidene chain-ends, which arised from β-Me elimination and β-H eliminations respectively. The methyl group at the 2-position of the indenyl ring turned out to have negative effects on both catalytic activity and β-Me elimination selectivity. Zirconocene complex C1 polymerized propylene to give oligomers with 40%～52% allyl chain-ends. However, further modification of the fluorenyl moiety allowed a great improvement in β-Me elimination selectivity. At 40～100 ℃, zirconocene complexes C2 and C3 bearing a 2,7- or 3,6-di-tert-butyl- substituted fluorenyl moiety showed significantly higher β-Me elimination selectivities (C2, 81%～86%; C3, 68%～77%), affording propylene oligomers (M_n 400～4500 g·mol^－1) with allyl-dominant chain-ends. Moreover the substitution pattern of the fluorenyl moiety also substantially influenced the catalytic activities. The incorporation of an electron-donating 2,7-di-tert-butyl groups on the fluorenyl moiety led to notably increased catalytic activities of complex C2 at higher temper-
atures above 60 ℃, while complex C3 bearing a 3,6-di-tert-butyl-substituted fluorenyl moiety showed lowest activities among the zirconocene series due to its overcrowded coordination sites. Compared with its zirconocene analogue, the hafnocene complex C4 activated with TIBA/TrB proved to be even more selective toward β-Me elimination, and meanwhile gave products with much lower molecular weights. At 100 ℃, the hafnocene system mainly oligomerized propylene to dimers and trimers. Studies on the dependence of the product molecular weight and the chain-release selectivity on monomer concentration suggested that both β-Me and β-H elimination involved in these systems mainly operate in a bimolecular pathway.
Key words: metallocene catalyst, propylene oligomerization, allyl chain-end, β-methyl elimination


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