亚乙基桥联多取代茚-芴锆、铪配合物的合成、结构及催化丙烯选择性齐聚研究

Ethylene-Bridged Multi-Substituted Indenyl-Fluorenyl Zirconocene and Hafnocene Complexes:Synthesis,Structure and Catalytic Behavior for Propylene Selective Oligomerization

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Mn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.

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 aβ-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 selectiveβ-methyl elimination.In this work,a series of novel ansa-metallocene complexes,ansa-C2 H4-{2-Me-3-Bn-5,6-[1,3-(CH2)3]Ind}(Flu)ZrCl2(C1),ansa-C2 H4-{2-Me-3-Bn-5,6-[1,3-(CH2)3]Ind}(2,7-tBu2-Flu)ZrCl2(C2),ansa-C2 H4-{2-Me-3-Bn-5,6-[1,3-(CH2)3]Ind}(3,6-tBu2-Flu)ZrCl2(C3)and ansa-C2 H4-{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 Et2 O.All complexes were characterized by 1 H NMR,13 C 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/[Ph3 C][B(C6 F5)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 fromβ-Me elimination andβ-H eliminations respectively.The methyl group at the 2-position of the indenyl ring turned out to have negative effects on both catalytic activity andβ-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 inβ-Me elimination selectivity.At 40~100℃,zirconocene complexes C2 and C3 bearing a 2,7-or 3,6-di-tert-butylsubstituted fluorenyl moiety showed significantly higherβ-Me elimination selectivities(C2,81%~86%;C3,68%~77%),affording propylene oligomers(Mn 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 temperatures 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 towardβ-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 bothβ-Me andβ-H elimination involved in these systems mainly operate in a bimolecular pathway.