Oligomerization of Ethylene Catalyzed by Iron and Cobalt in Organoaluminate Dialkylimidazolium Ionic Liquids
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Oligomerization of Ethylene Catalyzed by Iron and Cobalt in Organoaluminate Dialkylimidazolium Ionic Liquids Daniel Thiele • Roberto Fernando de Souza
Received: 10 February 2010 / Accepted: 9 May 2010 / Published online: 28 May 2010 Ó Springer Science+Business Media, LLC 2010
Abstract Cationic iron and cobalt acetonitrile cationic complexes were prepared and used as catalyst precursors in catalytic ethylene oligomerization. The effects of temperature and the nature and effects of the co-catalysts were evaluated. The iron and cobalt catalysts are less active, giving turnover frequencies of 20,000 to 30,000 h-1 while the corresponding nickel analogs exhibit turnover frequencies of 215,000 h-1. The iron and cobalt catalysts were more selective for the synthesis of 1-butene, especially at lower temperatures, compared to the nickel catalyst. Keywords Ethylene Oligomerization Iron Cobalt Organoaluminate Ionic liquid
1 Introduction Recent developments in the use of coordination compounds as catalysts for the synthesis of linear a-olefins were made possible by the suitable development of ligands and the use of different metals. The advances achieved in this field allow access to catalysts that permit selective dimerization [1–3], trimerization [4], tetramerization [5], and even specific oligomerization [6] of ethylene. Although many types of oligomerization catalysts are known, the selective production of linear a-olefins, Electronic supplementary material The online version of this article (doi:10.1007/s10562-010-0371-7) contains supplementary material, which is available to authorized users. D. Thiele R. F. de Souza (&) Institute of Chemistry, UFRGS, Av. Bento Gonc¸alves, 9500, P.O. Box 15003, Porto Alegre CEP 91501-970, Brazil e-mail: [email protected]
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particularly those in the range of C6–C12, still present a great challenge. These systems pose several problems, including that of selectivity. The major difficulty is catalyst death due to deactivation during the separation of products from the catalyst. Some approaches have been developed to overcome this drawback. The most successful have been the chemical or physical immobilization of coordination compounds, allowing access to the advantages of heterogeneous catalysis, and the use of liquid–liquid biphasic catalysts, using ionic liquids as the immobilization phase for the transition metal catalysts. Oligomerization reactions in which ionic liquids act as the immobilization phase have been studied extensively for homogeneous nickel catalysts. Aspects such as the influence of ionic liquid acidity, due to the variety of compositions that can be obtained in chloroaluminate ionic liquids [7–9], additives [10, 11], variations in ionic liquids [12, 13] and reactor design [14, 15] have been considered. Several oligomerization catalysts were evaluated in ionic liquids, with different organic moieties [8, 12, 13, 16–22] and different counter-anions in cationic coordination compounds [23]. Many experiments have been performed to find appropriate conditions for
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