Nickel(II) Heterocyclic Carbene Complexes as Catalysts for Olefin Dimerization in an Imidazolium Chloroaluminate Ionic Liquid

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• 作者：David S. McGuinness ; Wolfgang Mueller ; Peter Wasserscheid ; Kingsley J. Cavell ; Brian W. Skelton ; Allan H. White ; and Ulli Englert
• 刊名：Organometallics
• 出版年：2002
• 出版时间：January 7, 2002
• 年：2002
• 卷：21
• 期：1
• 页码：175 - 181
• 全文大小：85K
• 年卷期：v.21,no.1(January 7, 2002)
• ISSN：1520-6041

文摘

Nickel(II) heterocyclic carbene complexes of the formula NiI₂(carbene)₂ (carbene =3-methyl-1-propylimidazolin-2-ylidene (1), 1-butyl-3-methylimidazolin-2-ylidene (2), 1-isopropyl-3-methylimidazolin-2-ylidene (3), 1,3-diisopropylimidazolin-2-ylidene (4)) have beenprepared and fully characterized by both spectroscopic methods and single-crystal X-raystructure analysis. All complexes have "square-planar" nickel environments, with the donoratoms pairwise trans, all obligate, except for one of the two independent molecular typesfound in 2, in which, with different substituents at the nitrogen atoms, the two rotamersare observed as independent molecules in the one crystal. Complexes 1-4 were tested ascatalysts for propene and 1-butene dimerization in both toluene and an imidazolium-chloroaluminate ionic liquid. While the complexes are inactive to sparingly active in toluene,highly active catalysts are produced in the ionic liquid. In all cases the complexes are moreactive toward 1-butene dimerization than is NiCl₂(PCy₃)₂ in the ionic liquid. The results areinterpreted in terms of catalyst stabilization by the imidazolium-based ionic liquid. In toluenethe complexes decompose rapidly via reductive elimination of imidazolium cations, while inthe ionic liquid no decomposition is observed. While reductive elimination of imidazolium ispossible in the ionic liquid, a rapid reoxidation via addition of the solvent imidazolium cationseems possible and may prevent the formation of Ni⁰ deposits associated with catalystdeactivation.