Ionic Liquid-Supported Bis-(salicylaldimine) Nickel Complexes: Robust and Recyclable Catalysts for Ethylene Oligomerizat
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Ionic Liquid-Supported Bis-(salicylaldimine) Nickel Complexes: Robust and Recyclable Catalysts for Ethylene Oligomerization in Biphasic Solvent System Ke-Ming Song Æ Hai-Yang Gao Æ Feng-Shou Liu Æ Jin Pan Æ Li-Hua Guo Æ Shao-Bo Zai Æ Qing Wu
Received: 22 March 2009 / Accepted: 7 April 2009 / Published online: 21 April 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Two new ionic liquid-supported bis-(salicylaldimine) Ni(II) complexes Ni[2-(O)C6H4CH=N(CH2)3(methylimidazole)Br]2 (1) and Ni[3, 5-tBu2-2-(O)C6H2CH= N(CH2)3(methylimidazole)Br]2 (2) have been synthesized and characterized. Ethylene oligomerizations were carried out with these two complexes in biphasic solvent systems consisting of chloroaluminate ionic liquid and n-heptane or toluene under mild reaction conditions. In the presence of diethylaluminum chloride, both complexes 1 and 2 are highly active for ethylene oligomerization. The olefinic products can be easily separated from the catalytic ionic liquid phase by simple decantation, and the nickel catalysts can be reused in successive ethylene oligomerization cycles. GC-MS analyzes showed that the obtained oligomers contained mainly C4, C6, and C8 olefins. Keywords Ethylene oligomerization Biphasic catalysis Nickel catalyst Ionic liquid
1 Introduction The ethylene oligomerization is one of the major industrial processes for the production of higher olefins. The obtained
K.-M. Song H.-Y. Gao (&) F.-S. Liu J. Pan L.-H. Guo S.-B. Zai Q. Wu DSAPM Lab, Institute of Polymer Science, School of Chemistry and Chemical Engineering, Sun Yat-Sen (Zhongshan) University, 510275 Guangzhou, China e-mail: [email protected] K.-M. Song Q. Wu (&) PCFM Lab, OFCM Institute, Sun Yat-Sen (Zhongshan) University, 510275 Guangzhou, China e-mail: [email protected]
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oligomers can be used as comonomers in polymerization, plasticizers and synthetic lubricants. [P, O] neutral catalysts currently used in industry for the Shell Higher Olefin Process (SHOP) [1, 2] were reported to be effective ethylene oligomerization catalysts. Besides, ethylene oligomerizations catalyzed by soluble transition metal complexes in homogeneous system have also been studied [3–6] and good results have been obtained in terms of activity and selectivity of higher olefins. However, in this homogeneous system, the separation of the catalyst from the reaction products has always been a problem. One of the most attractive proposed solutions for overcoming this drawback is to perform the oligomerization reaction in biphasic solvent system [7–10]. Ionic liquids (IL) (typically 1, 3-dialkylimidazolium organochloroaluminate) have been envisioned as solvents of nickel catalysts in olefin oligomerization reactions [11–13]. The good solubility of nickel complexes and poor solubility of olefin products in polar and non-coordinating ionic liquids enable the separation of the reaction products by simple decantation, allowing easy recycling of catalyst in the IL solution. Oligomerizations of ethylene [14–18], propylene [11, 13,
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