Synthesis of Ethylene-Bridged Bis(indenyl) Zirconium, Hafnium Complexes and Their Catalytic Behavior on Selective Propylene Oligomerization: the Effect of 3-Substituent on Indenyl Ring
Received date: 2023-05-30
Online published: 2023-08-30
Supported by
National Natural Science Foundation of China(21274041)
Oligomerization of propylene or other α-olefins is the main way to obtain various branched α-olefins, which are potential comonomers for the preparation of novel polymers with excellent properties or building blocks for manufacturing fine chemicals. Due to the different coordination-insertion and chain transfer modes involved in the oligomerization process of propylene, propylene oligomers with different structures were generally obtained, thus developing novel catalysts capable of catalyzing selective propylene oligomerization attracts great attention. In this work, a series of novel ethylene-bridged bis(indenyl) complexes meso-/rac-1~7 [ansa-C2H4-(3-R-4,7-Me2-C9H3)2MCl2: M=Zr, R=nBu (meso-/rac-1), iPr (meso-2), CH2Cy (meso-/rac-3), Bn (meso-/rac-4), CH2C6H4(4-CH3) (meso-/rac-5); M=Hf, R=CH2C6H4(4-CH3) (meso-/rac-7); ansa-C2H4-{2-Me-3-Bn-5,6-[1,3-(CH2)3]C9H2}2ZrCl2 (meso-6)] were synthesized via the reaction of the dilithium salts of the proligands with 1 equiv. of ZrCl4 or HfCl4 in Et2O, and in most of the cases, both the rac- and meso-isomers were separated in analytically pure forms via recrystallization. All complexes were characterized by nuclear magnetic resonances (1H NMR, 13C NMR) and elemental analysis (EA) methods. The molecular structures of typical complexes rac-1, meso-1, meso-2, meso-4, meso-5 and meso-6 were further determined by X-ray single crystal diffraction studies. The solid-state molecular structures of these complexes exhibit essentially similar geometrical parameters. The bond lengths between zirconium center and carbon atoms of the π-bonding five-membered ring of the indenyl unit vary slightly, suggesting a η5-coordination mode of the five-membered rings. In the presence of methylaluminoxane (MAO) as the cocatalyst, zirconium complexes meso-/rac-1~3 with an alkyl group on the 3-position of the indenyl ring catalyzed the oligomerization of propylene with high activities up to 9.73×106 g•mol-Zr－1•h－1, affording propylene oligomers with molecular weights of hundreds to thousands. Meanwhile, meso-/rac-1~3 exhibited low selectivities for β-Me elimination, with the highest allyl end group content being 41.3%. Zirconium and hafnium complexes meso-/rac-4~7 with a benzyl group or a substituted benzyl group on the 3-position of the indenyl ring were found to catalyze the dimerization of propylene in the presence of MAO, and mixtures including 1-pentene, 2-methyl-1-pentene, 4-methyl-1-pentene, 2,4-dimethyl-1-pentene were obtained. Temperature is the major factor affecting the activities of dimerization, and among them complex rac-4 showed the highest activity of 1.24×106 g•mol-Zr－1•h－1 at 80 ℃. The distribution of dimers is hardly affected by the reaction temperature or the Al/Zr molar ratio adopted. Among them, the hafnium complex rac-7 showed the highest β-Me elimination selectivity up to 60.1%.
Key words： metallocene; catalyst; propylene; oligomerization; dimerization
Bo Li , Haiyan Zhou , Haiyan Ma , Jiling Huang . Synthesis of Ethylene-Bridged Bis(indenyl) Zirconium, Hafnium Complexes and Their Catalytic Behavior on Selective Propylene Oligomerization: the Effect of 3-Substituent on Indenyl Ring[J]. Acta Chimica Sinica, 2023 , 81(10) : 1280 -1294 . DOI: 10.6023/A23050258
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