No abstract

Since the discovery that bis(imino)pyridine ligands are able to confer high activities in ethylene oligomerization and polymerization to their iron complexes, considerable attention has been focused on catalyst design for these reactions and this research constitutes an ever-growing area in molecular catalysis. The tuning of the ligand structures and properties, and thus of catalysts, generally represents the basis for subsequent work contributing to process development and industrialization. Significant effort is therefore devoted to generate structural diversity in order to access the required catalyst stability and selectivity. This feature article outlines nitrogen-containing ligands that have been developed for the iron-catalyzed oligomerization of ethylene since the seminal discovery of the properties of bis(imino)pyridine ligands.

In a combined experimental and theoretical study the activation process of a single site ethylene oligomerization catalyst with aluminum based activators has been studied.The results put forward a plausible deactivation reaction path of the catalyst for trimethylaluminum, while for methylaluminoxane and a novel phenoxyaluminum-based activator the experimental catalyst's activity correlates with the energy barrier for the ethylene insertion. Graphical AbstractN N N Fe N N N Fe Al Al Cl TMA MAO or [PhOAlMe 2 ] 2 inactive catalyst oligomerization Cl Cl N N N Fe

L inear R-olefins (LAOs) are of considerable importance in the chemical and petrochemical industries. They represent an expanding market with a total demand of 4.2 million tons in 2006. The demand for LAO is growing faster in the C 4 ÀC 10 range than in the C 12 þ range. Light LAOs (C 4 ÀC 8 ) are mainly used as comonomers in the copolymerization of ethylene to produce high-density polyethylene and linear low-density polyethylene. Whereas several processes lead from short (C 4 ÀC 8 ) to full range (C 6

Multinuclear aluminum cocatalysts have been obtained by the reaction of various phenols, alcohols or diols with trimethylaluminum and were used in situ or as isolated, well-defined species, for the activation of an iron(ii) or an iron(iii) pre-catalyst for the oligomerization of ethylene. The best cocatalyst candidate involves 2,2'-biphenol () in a /AlMe3 ratio of 2/3.