Alkylaluminum/Urea Hybrid Cocatalysts and Their Use in Iron-Catalyzed Oligomerization of Ethylene

Abstract

The bis(imino)pyridyl iron-based ethylene oligomerization catalysts have the advantages of mild reaction conditions, high activity and high selectivity to linear α-olefins. However, barriers, such as high polymer content in the product mixture and large methylaluminoxane (MAO) dosage, are still limitations for the development of these systems at the industrial scale. In this study, new cocatalysts are prepared by the reaction of alkylaluminums with urea and its derivatives, and successfully used to activate iron-based catalysts. It is found that the type and molar ratio of alkylaluminum and urea have significant influence on the performance of the cocatalysts. The activity of the preferred triisobutylaluminum/urea activated systems reaches more than 3.0 × 10⁸ g (mol-Fe)⁻¹ h⁻¹, and the polymer content can be controlled to be less than 2 wt.%. Notably, the catalytic system exhibits good high temperature stability, the activity can still reach 1.0 × 10⁸ g (mol-Fe)⁻¹ h⁻¹ even at 120 °C. Further ¹H NMR studies show that alkylaluminum can react with the NH moieties of urea, forming complex alkylaluminum clusters, even aluminoxane-like structures. This study offers a promising family of cocatalysts, making it possible to simultaneously improve their performance and reduce their cost.